SYNTHESIS AND CHARACTERIZATION OF CdO THIN FILMS BY SUCCESSIVE IONIC LAYER ADSORPTION REACTION (SILAR) METHOD USING TWO DIFFERENT COMPLEXING AGENTS

CHAPTER ONE

         1.1 General Introduction

The sun releases an estimated 1017 Joules of energy, which it delivers to earth in one second [1]. Earth’s ultimate recoverable resource of crude oil, estimated at 3 trillion barrels, contains 1.7×1022 joules of energy, which the sun supplies to earth in 1.5 days [1]. The amount of energy humans use annually, about 4.6×1020 Joules, is delivered to earth by the sun in one hour [2]. The enormous power that the sun continuously delivers to earth is 1.2×105 terawatts (TW), dwarfs every other energy source [2], renewable or non renewable. It dramatically exceeds the rate at which human civilization produces and uses energy, currently about 13TW [3]. The impressive supply of solar energy is complemented by its versatility. Sunlight can be converted into electricity by exciting electrons in a solar cell. It can yield chemical fuel via natural photosynthesis in green plants or artificial photosynthesis in human-engineered system’s [4] Concentrated or unconcentrated sunlight can produce heat for direct use or further conversion to electricity. Despite the abundance and versatility of solar energy, we use very little of it to directly power human activities. Solar electricity accounts for a minuscule 0.015% of world electricity production, and solar heat for 0.3% of global heating of space and water [5]. Biomass produced by natural photosynthesis is by far the largest use of solar energy; its combustion or gasification accounts for about 11% of human energy need [6].              However, more than two-third of that is gathered unsustainably, that is, with no replacement plan and burned in small, inefficient stores where combustion is and the resulting pollutants are uncontrolled.

Between 80% and 85% of world energy comes from fossil fuels, a product of ancient biomass stored beneath earth’s surface for up to 200 million years [7]. Fossil fuel resources are of finite extent and are distributed unevenly beneath earth’s surface. When fossil fuels are converted into useful energy through combustion they produce green house gases and other harmful environmental pollutants. In contrast, solar photons are inexhaustible and unrestricted by geographical boundaries. Their direct use for energy production does not threaten heat or climate. The solar resources, magnitude, wide availability, versatility and benign effect on the environment and climate make it an appealing energy source. It is anticipated that by the year 2030 the world demand for electricity will double and the demands for fuel and heat will increase by 60% [7]. The utilization gap between solar energy’s potential and our use of it can be overcome by raising the efficiency of the conversion processes.

The use of photovoltaic (PV) modules for electricity generation has come under intensive research in recent times, with a view to increasing the efficiency and reducing investment capital [8]. Generating significant fraction of future energy requirement from PVs is a major challenge to solar energy physicists [9], particularly because present PV production is almost insignificant relative to fossil fuel-based generation [10].

        1.2   Purpose of the Study

The purpose of the study is to:

  • deposit cadmium oxide (CdO) thin film on glass substrate using the Successive Ionic                               Layer Adsorption and Reaction techniques (SILAR), for two complexing agents,NH3 and NaOH.
  • characterize the deposited CdO films using the UV/VIS/NIR spectroscopy.
  • investigate the effects of the number of cycles on the band gaps of the deposited CdO thin film.
  • study the variation between the optical conductivity and the band gap energy of the film.
  • determine the relationship between the dielectric function of the material and the band gap energy and number of cycles.
  • investigate the effect of complexing agents on deposition of CdO films.
  • to study the structural properties of the deposited films.

         1.3 Scope of the Study

This research work is limited to the growth and characterization of CdO thin films grown on glass substrate using SILAR technique. The deposition of CdO will be carried out using ammonia (NH3) and sodium hydroxide (NaOH) as  complexing agents.

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SUZAKU SPECTRAL OBSERVATION

Introduction

  • Eclipsing Binary Stars

Eclipsing binary stars are just one of the several types of variable stars. These stars appear as a single point of light to an observer, but based on its brightness variation and spectroscopic observations we can say certainly that the single point of light is actually two stars in close orbit around one another. The variations in light intensity from eclipsing binary stars are caused by one star passing in front of the other relative to an observer. An eclipsing binary star is a binary star in which the orbit plane of the two stars lies so nearly in the line of sight of the observer that the components undergo mutual eclipses. Algol and Ex Hya are the best-known example of an eclipsing binary[1]

Eclipsing binaries are variable stars, not because the light of the individual components vary but because of the eclipses. The light curve of an eclipsing binary is characterized by periods of practically constant light, with periodic drops in intensity. If one of the stars is larger than the other, one will be obscured by a total eclipse while the other will be obscured by an annular eclipse. The period of the orbit of an eclipsing binary may be determined from a study of the light curve, and the relative sizes of the individual stars can be determined in terms of the radius of the orbit by observing how quickly the brightness changes as the disc of the near star slides over the disc of the distant star[2].

  • Cataclysmic variables (CVs)

These are binary star systems that have a white dwarf and a normal star companion. The white dwarf is often referred to as the “primary” star, and the normal star as the “companion” or the “secondary” star. The companion star, a star that is “normal,” like our Sun, loses material onto the white dwarf via accretion. The white dwarf is a dense compact object whose magnetic field is stronger at the poles; hence matter from the secondary companion is channeled to the magnetic poles during the accretion process. There are probably more than a million of these cataclysmic variables in the galaxy, but only few have been studied in X-rays so far (Warner 1995). Depending on the physical size of the white dwarf’s magnetosphere, the transferred material can either interact directly with the magnetosphere, e.g. in Polars, or result in the formation of an accretion disc, e.g. in intermediate polars. The accretion disc can be thought of as a machine, facilitating the extraction of angular momentum from the material, allowing it to accrete onto the white dwarf where gravitational potential energy of the gas is released as heat and radiation results in interesting observational properties of these systems (outbursts and brightening). Based on the observational properties of these systems, cataclysmic variables can be grouped into several categories e.g. classical novae, dwarf novae, recurrent novae, nova-like variables and Magnetic Cataclysmic Variables (mCVs) (Warner 1995).

  • Formation of Cataclysmic Variables

Stars are born from gravitationally collapsing molecular and interstellar dust clouds. The collapse is induced through instability in the cloud which could be due to shock waves from a nearby supernova. A star develops when the core of the contracting protostar reaches a temperature that is enough for the ignition of nuclear fusion reactions. Less massive clouds require high densities to collapse while more massive clouds require lower densities to collapse thus more massive clouds collapse first (Kippenhahn & Weigert, 1990). As the density of the gas cloud increases, small parts of the cloud would collapse independently. Ultimately the cloud would fragment into many parts forming a whole cluster of stars. Stars therefore form in clusters finding themselves gravitationally bound in binaries, triplets, pairs of binaries or similar combinations. Stars destined to become CVs begin as binaries separated by a few hundred solar radii, orbiting each other approximately every ten years (Hellier 2001). One of the stars must be less than a solar mass and the other more massive. The more massive star evolves more rapidly, since the greater weight on its core ensures a higher pressure and temperature, and therefore a more vigorous nuclear burning rate. The more massive star eventually expands and becomes a red giant (Hellier 2001); hence overflowing its Roche lobe, and transfer its outer layers to the less massive companion. The more massive star is closer to the centre-of-mass (CM) of the binary, and material transferred to the less massive companion star therefore moves further from the CM. This results in increase of angular momentum of the material being transferred. Conserving the overall binary angular momentum will result in a decrease in the binary separation if the mass transfer is conservative (Frank  et al. 1992). This dynamical mass transfer to the companion star will have dramatic consequences that will sculpture the further evolution of this system. This influx of material cannot be assimilated by the companion star, and the material overfills both Roche lobes forming a cloud surrounding the two stars. This is the “common envelope” phase in which the pre-cataclysmic variable is effectively orbiting within a massive red giant. The drag on the stars as they orbit drain their orbital energy causing them to spiral inwards, reducing their separation from about one hundred solar radii to about one solar radius in approximately one thousand years (Hellier 2001). The new-naked binary is either a cataclysmic binary, or if the separation is still too large for mass transfer, a detached binary is formed (Hellier 2001).

  • Accretion Disc formation

Material transferred from the secondary star falls onto the magnetized rotating white dwarf due to gravitation, the spiralling-in process entails a loss of angular momentum by the magnetized rotating white dwarf, being transferred outwards by internal torques (Frank et al. 1992). The ring thus spreads out into a thin disc which continues spreading until the inner edge meets the compact star; or in the case of a magnetized primary, the radius where the disc ram pressure balances the magnetospheric pressure. This defines the so called magnetospheric radius of the white dwarf. The interaction of the disc with the primary star may lead to a spin-up or spin-down torque that affects the rotating compact star (Wang 1987). Angular momentum flowing outwards through the disc enables the inward flow of material thereby releasing energy. At the outer edge of the disc tidal interactions with the secondary star soak up the angular momentum and return it to the orbit of the secondary; limiting the outward spread of the disc, (Hellier 2001). This is replenished by mass transfer from the secondary star. Material will continue to flow inwards towards the white dwarf ( Frank et al. 1992) if: (i) Material in the disc loses angular momentum. (ii) The primary star rotates slowly enough allowing inflow of material instead of expelling it centrifugally. When a disc has been formed, the stream of material from the secondary star hits the edge of the disc, forming a “bright spot”. At this spot, the stream of material falling radially, encounters material moving across its path in a circular orbit. Not much is understood about the turbulent encounter, however, computer simulations suggest that the dense core of the stream punches a hole in the disc and is gradually assimilated into the circular flow, (Hellier 2001).

  • Magnetic Cataclysmic Variables (mCVs)

In mCVs, the white dwarf usually has a substantial magnetic field that can either intercept the mass flow from the secondary from reaching down to the surface of the white dwarf, preventing the formation of an accretion disc, or disrupting the disc if present. The magnetospheric field also facilitates the mass inflow onto the surface of the compact white dwarf, a process called magnetic accretion[3]. These magnetic CVs can be subdivided into AM Her stars or polars in which the white dwarf rotation is phase locked to the orbital motion of the binary companion and the DQ Her stars or intermediate polars in which the rotation period of the white dwarf is shorter than the orbital period, (Rosen et al. 1988).

  • Polars (also AM Herculis Star).

AM Her type systems are distinct from other CVs in that they completely lack an accretion disk. In polar systems, the magnetic field of the white dwarf is too strong for an accretion disk to form. The strong magnetic field of the white dwarf has the following important implications: (i) Polars are synchronously rotating systems (Prot = Porb), with orbital periods lying between ~ 81 and 222 minutes (Chanmugam & Ray 1984). The phase locked interaction is caused by the strong magnetic interaction between the white dwarf and the low mass secondary star. (ii) The formation of the disc is prevented (i.e. diskless accretion) because of its strong magnetic field (Chanmugam & Ray 1984).

[1] http://www.physics.sfasu.edu/astro/ebstar.

[2] http://en.wikipedia.org/wiki/Microsoft_PowerPoint.

[3] http://imagine.gsfc.nasa.gov/docs/science

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SEVEN-FACTOR CENTRAL COMPOSITE DESIGN ROBUST TO A PAIR OF MISSING OBSERVATIONS

                           ABSTRACT

In this work, the seven-factor central composite design  is studied in respect of a pair of missing values using the minimax loss criterion. It was observed empirically that seven-factor central composite design with , , , and    is robust at  and variance robust at . We also observed that the loss effect of missing a pair of factorial points is a decreasing function of  increasing , while the loss effect of a pair of axial points is a decreasing and increasing function of increasing . The loss effect of missing a factorial and axial points has no specific direction of increase or decrease on increasing  values.

CHAPTER ONE

 INTRODUCTION

1.1     Background of the Study

Response Surface Methodology (RSM) is defined by Montgomery (2005, Chapter 11) as a collection of Mathematical and Statistical techniques useful for the modeling and analysis of problems in which a response of interest is influenced by several variables and the objective is to optimize this response.  Onukogu (1997, Chapter.1) and Carley et al. (2004) posit that RSM is extensively applied in situations where several input variables potentially influence some performance measure or quality characteristic of the process. The input variables are sometimes called independent or predictor variables and are subject to the control of the experimenter, while the performance measure or quality characteristic is called response. Bradley (2007) stated the objectives of studying RSM to include:

  • understanding the topography of the response surface (local maximum, local minimum, ridge lines); and

(ii)     finding the region where the optimal response occurs.

The goal is to move rapidly and efficiently along a path to get a maximum or a minimum response so that the response is optimized: see also Montgomery (2005, Chapter 11) and Lenth (2009).

The major goal of any experimental design is to adjust the experimental conditions so that maximal information is gained from experiment. In accordance with the preceding assertion, Lenth (2009) explained that RSM comprises a body of methods for exploring for optimum operating conditions through experimental methods. Adding that, it involves doing several experiments and using the results of one experiment to provide direction for what to do next.

The development of RSM was originated by Box and Wilson (1951) and has since become an efficient tool of modern statistics, which is used to study the relationship between one or more responses and a number of quantitative treatment factors. Wang et al. (2009) has demonstrated the application of RSM in the production of caffeic acid from tobacco waste. Response surface methodology has found its applications in the area of chemical and food industries, biological, biomedical and biopharmaceutical fields  and Agricultural Science, see Mead and Pike (1975), Ahmad and Gilmour (2010). Many other recent applications of RSM in the field of scientific experimentation may be found in: Balkin and Lin (2000), Montgomery (2005, Chapter 11) and Bradley (2007).

In many applications of Response Surface Methodology, good estimation of the derivatives of the response function may be as important or perhaps more important than estimation of mean response. Certainly, the computation of a stationary point in a second-order analysis or the use of gradient techniques for example, steepest ascent or ridge analysis depends heavily on the partial derivation of the estimated response function with respect to the design variables. Since designs that attain certain properties in  (estimated response) do not enjoy the same properties for the estimated derivatives (slope), it is important for the user to consider experimental designs that are constructed with the derivatives in mind: see Victorbabu (2009).

1.2   Response Surface

Given a response of interest, , and a vector of independent factors, , that influence , the relationship between  and  can be written as follows:

1.2.1

where  represent random error which is assumed to be normally distributed with mean zero and variance . Since the true response surface function  is usually unknown, a response surface of  is created to approximate . Predicted values are then obtained using

The most widely used response surface approximating functions are simple low-order polynomials.  If little curvature appears to exist, the first-order polynomial given in equation (1.2.2) can be employed. If significant curvature exists, the second-order polynomial in equation (1.2.3) including all the two-factor interactions can be used.

The parameters of the polynomials in Equations (1.2.2) and (1.2.3) are usually determined using a least squares regression analysis to fit these response surface approximations to existing data. These approximations are normally used for prediction within Response Surface Methodology: see Simpson et al. (1997).

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RELATIONSHIP BETWEEN RAINFALL PATTERN IN NORTH CENTRAL AND SOUTHERN NIGERIA AND SOME TROPICAL CLIMATE SYSTEMS

ABSTRACT

Monthly rainfall data from meteorological stations in Nigeria are analyzed from 1951 to 1992, in relation to some Tropical climate systems: Tropical South Atlantic (TSA) sea surface temperature index, North Atlantic Ocean (NAO) atmospheric index, Tropical North Atlantic (TNA) sea surface temperature index, Central Indian Precipitation (CIP) index and Outgoing Longwave Radiation Anomaly (OLRA). The analysis also includes August break (Monsoon break intensity (MBI) ) and annual rainfall anomaly index (RAI). The analyses show that the rainfall anomalies although sometimes intense do not have predictable patterns. The teleconnection between CIP and total rainfall in Nigeria suggests that the rainfall patterns in Nigeria is likely to be modulated by the Tropical Easterly Jet (TEJ) connecting rainfall pattern in Central India to that in Nigeria. The August break is observed to be highly variable and does not show a clear pattern of variability. Its variablility may be connected with multiple forcings from ocean and mesoscale circulations.

CHAPTER ONE

GENERAL INTRODUCTION

1.1       Introduction

Nigeria has witnessed series of episodes of climate extremes which have continued to pose serious threats to lives and properties. Floods and drought conditions across the country have had far reaching and devastating effect on her economy and food security. Nigeria depends largely on the vagaries of weather, especially rainfall for its rain fed agriculture. The monsoon over West Africa is a seasonal prevailing wind blowing from the South Atlantic Ocean. Monsoon systems affect more than one-third of world’s population in numerous and varied ways, from agricultural irrigation to catastrophic disasters on an enormous spatial scale, such as flood or drought (Maher and Hu, 2006). The activity of this wind system has also been closely linked to Hydro power plants, infrastructural development, flood control dams, desert encroachment and visibility. Studies have linked the climate of Nigeria to various global systems such as; Intertropical Convergence Zone (ITCZ) (Chineke et al.,2010, Akinsanola and Ogunjobi, 2014), El Nino Southern Oscillation (Okeke et al.,2006, Olaniran, 2002) and West African Monsoon (Adeyemi et al.,2001, Chineke et al.,2010,). Other vagaries include Sea Surface Temperature (SST) which affects rainfall patterns in the Sahel (Thorncroft and Hodges, 2001). How these global and regional climate drivers interact and affect climate change is still not known. The ITCZ is the zone of contact between the Tropical Continental (CT) air mass and the Tropical Maritime air mass (MT) and sweeps across West Africa once every year. This region of contact between the two air masses at the surface is therefore a zone of moisture discontinuity and is also known as the Zone of Intertropical Discontinuity (ITD). The ITCZ is both a zonal and global phenomenon (Clement et al., 2009). It is responsible for the rainy season in the tropics. Understanding, interpreting and exploring the dynamics of weather and climate extremes is still an active area of research today (Nnamchi et al., 2015).

1.2       Climate of Nigeria.

Nigeria (Latitude 4o-13oN and Longitude 2o-14oE) is located in the tropics and borders the Gulf of Guinea between Benin on the West and Cameroon on the East. It has an area of 923,765 square km. The country’s land mass extends from the Gulf of Guinea in the South to its boundary with Niger and Chad republics in the North. (Thorncroft et al., 2001).

Nigeria has the following climate zones:

(i)         The Tropical monsoon climate which is found in the southern part of the country. This climate is influenced by the monsoons originating from the South Atlantic Ocean, which is brought into the country by the (Maritime Tropical) air mass. The Tropical monsoon climate has a very small temperature range. For example Warri town in the southern part of Nigeria, records a maximum of 28oC for its hottest month while its lowest temperature is 26oC in its coldest month (Houghton et al.,1995). The southern part of Nigeria experiences heavy and abundant rainfall. The annual rainfall recorded in this region is very high, usually above the 2,000 mm rainfall totals expected for tropical rainforest climates worldwide. Over 4,000 mm of rainfall is recorded in the coastal region of Nigeria around the Niger delta area. The southern region experiences two  rainfall peaks, usually in the months of June and September.

(ii)        Tropical Savannah Climate is extensive in area and covers most of Western Nigeria to Central Nigeria beginning from the Tropical rainforest climate boundary in Southern Nigeria to the Central part of Nigeria, where, it exerts enormous influence on the region. The tropical savannah climate exhibits a well-marked rainy season with a single peak known as the summer maximum due to its location from the coast (Olaniran 2002).

(iii)       The Sahel Climate or Tropical dry Climate is the predominant climate type in the far northern part of Nigeria. Annual rainfall totals are lower compared to the southern and north central part of Nigeria. Rainy season in the northern part of Nigeria lasts for only three to four  months (June-September). The rest of the year is hot and dry with temperatures climbing as high as 40oC (Adeyemi et al., 2001).

(iv)       Alpine Climate or highland climate or mountain climate, are found on highlands regions in Nigeria. Highlands with the alpine climate in Nigeria, are well over 1,520 metres above sea level. Due to their location in the tropics, their elevation is high enough to reach the temperate climate line in the tropics thereby giving the highlands, mountains and the plateau regions standing above this height, a cool mountain climate.

Temperatures throughout Nigeria are generally high; diurnal variations are most pronounced than seasonal ones. Highest temperatures occur during the dry season; rains moderate afternoon highs during the wet season. Average highs and lows for Lagos are 31oC and 23oC in January and 28oC and 23oC in June (Akinsanola and Ogunjobi, 2014). In the north, temperatures can reach as high as 44oC before the onset of the rains or drop as low as 6oC during intrusion of cool air.

Nigeria has four observed seasons which are:

A long rainy season which starts in March and lasts to the end of July, with a peak period in June over most parts of southern Nigeria.

A short dry season is in August and lasts for 3-4 weeks. This is due to the ITCZ moving to the north during the summer solstice.

A short rainy season follows the brief dry period in August and lasts from early September to mid-October as the ITCZ moves south again, with a peak period at the end of September. The rains are not usually as heavy as those in the long rainy season.

A long dry season starts from late October and lasts to early March with peak dry conditions between early December and late February. Vegetation growth is generally hampered, grasses dry and leaves fall from deciduous trees due to reduced moisture.

Many global and continental systems are linked to the climate of Nigeria. They include Tropical Easterly Jet (TEJ) (Olaniran, 2010), El Nino Southern Oscillation (Okeke et al.,2006), North Tropical Atlantic Sea Surface Temperature (Cook et al.,1998).

1.3       Tropical Easterly Jet (TEJ)

The TEJ is part of the Indian summer monsoon system and it extends from India over Africa in the Northern Hemisphere summer months, generally at a height of around 12-15 km (Thorn croft et al, 2001). The west-east axis of the TEJ is located between 4-10oN. On the southern side of the axis, conditions are conducive to the ascent of air and consequently rainfall occurrence whilst the northern side is marked by subsidence. (Yanjun et al., 2008). This can produce wet conditions from the middle belt to the south and dry conditions over the extreme north.

1.4       Tropical North Atlantic Index (TNA)

The Tropical North Atlantic Index is Anomaly of the average of the monthly Sea Surface Temperature SST from 5.5N-23.5N and 15W-57.5W. The TNA is also part of the major source of moisture for the monsoon system of Nigeria.(Farmer and Wigley,1985).

According to Palmer (1986), warming of the tropical Atlantic ocean reduces the meridional gradient of sea surface temperature (SST) south of the ITZC and this  results in a weakening of the Hadley meridional circulation (i.e. the pattern of circulation of the atmosphere over the tropics). The weakened circulation reduces the intensity of the southwest monsoon flow into West and Central Africa and consequently rainfall over southern Nigeria. (Olaniran 2002)

1.5       El Nino Southern Oscillations and Other Teleconnections

Teleconnection studies are on-going to establish linkage between Nigerian rainfall and continental climate system (Nnamchi et al.,2015). El Nino is the term used to describe the excessive warming of the upper ocean in the tropical eastern Pacific lasting up to a year or even more. The cooling phase of El Nino is called La Nina. Changes in the El Nino events are related to changes in the Pacific Circulation. These changes have been reported to have a drastic impact on the ITCZ status and this could be a global effect reaching Nigeria (Clement et al.,2009).

1.6       Outgoing Long Wave Radiation.

From most literature studied so far, it is obvious that not much work has been done with regards to the effect of outgoing long wave radiation (OLR) on rainfall pattern in Nigeria. The OLR have long been observed by satellites as proxies in detecting deep convection over the tropics. (Sukumaran and Stordal, 2013). The OLR might provide physical insight into the study of rainfall variability in Nigeria (Okeke et al., 2006).

1.7       What is Rainfall Anomaly?

Rainfall anomaly is the deviation of the annual rainfall from the normal or expected mean annual rainfall of a place (Olaniran, 2002). The deviation gives rise to departures from the mean annual rainfall either above it or below the mark. The departures could be deficit or surplus depending on the mean. The departures are referred to as anomalies. A persistent departure from the normal e.g. above mean rainfall index of the same sign constitutes a climatic fluctuation. (Farmer and Wigley, 1985).These climatic fluctuations are indices of climate change impacts.

1.8       Purpose of Study

The purpose of this work is to

  1. To measure the intensity of the monsoon break and to determine the association of the monsoon break with the rainfall anomalies and the climate indices.
  2. investigate the relationship between rainfall anomaly (including monsoon breaks) and other climate systems purported to drive the rainfall pattern in Nigeria.

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PREDICTION OF ARRIVAL TIME OF CORONAL MASS EJECTIONS USING THE ONSET OF GEOMAGNETIC STORM

Abstract

Predicting the arrival time of Coronal Mass Ejections (CMEs) with a lower value of average error between the predicted and the observed transit time is very crucial in space weather forecast. We proposed a modified Empirical Coronal Mass Ejection Arrival (ECA) model to predict the arrival time of twenty eight (28) CMEs from the sun to the earth. We tested the modified model by using data obtained from coronagraph observations of Large Angle Spectrometric coronagraph on aboard the Solar and Heliospheric Observatory (SOHO/LASCO) CME catalogue from the period of 1998-2012. To ascertain the accuracy of our model, we employed the three Empirical Coronal Mass Ejection arrival (ECA) models of Gopalswamy to our data points. The average error obtained between the CMEs transit time and models predicted  transit time with their  fractional errors were 4.27 hours and 0.10 for the modified model; 10.41hours and 0.23 for the VG2002 model; 12.3hours and 0.29 for G2001 model; 14.46 hours and  0.34 for the G2000 model. Other analyses revealed that Solar wind speed and solar activity cycle have significant influence on CMEs transit time.  Solar wind speed and CMEs speed at 1AU have been observed to have contributed to the magnitude of geomagnetic storm. Our modified model has proved to be effective in prediction of arrival time of CMEs. This least average error obtained between CMEs transit time and the model’s predicted transit time and the fractional error was much lower than all the existing models. It is our recommendation that future work be carried out employing our modified model with a view to confirming its accuracy.

CHAPTER ONE

INTRODUCTION

  • General Introduction

Coronal mass ejections (CMEs) are massive burst of solar materials (clouds of plasma and magnetic fields) that shoot off the Sun’s surface and released into space. Over a distance of a few solar radii, CMEs may accelerate up to a speed of 300  and subsequently propagate through the solar wind away from the Sun (Mostl et al., 2014 ;Yashiro et al., 2001)

CMEs are known to be the major cause of severe geomagnetic disturbances which is often referred to as space weather (Zhang et al., 2001; Cheng et al., 2014; Cyr et al; 2000; Tripathi et al., 2005). There are several space weather phenomena which tend to be associated with or are caused by geomagnetic storm. These include: Solar Energetic Particles (SEP) events (hazardous to Humans), Geomagnetically Induced Currents (GIC) which cause damages to satellites and electricity grid, ionospheric disturbances which may lead to radio and radar scintillation, disruption of navigation by magnetic compass and aurora displays at much lower latitudes than normal (Baker and John 2008).

Researchers have been able to continuously monitor the Sun using both full disk images and coronagraphs. With the launch of the solar and heliospheric observatory (SOHO), studies of the evolution of CMEs have been carried out which primarily focused on observations by the Large Angle and Spectrometric Coronagraph (LASCO) on board SOHO. Studies were also devoted to the in situ identification of CMEs near the Earth by Advanced Composition Explorer (ACE) that samples particles from the Sun as they stream toward the planet Earth. The Solar Dynamic Observatory (SDO) focuses on solar atmosphere. Other information and the properties of CMEs come from signatures of CMEs in time series of plasma and magnetic field measurement (in situ) in the interplanetary medium especially at 1AU (AU is the astronomical unit of measurement of sun-earth distance) where they are usually referred to as interplanetary CMEs (ICMEs). Combining observations at 1AU with those of the Sun, then permits a close link between solar events and its interplanetary manifestations.

Most of the studies carried out to predict the arrival time of CMEs from the Sun to the Earth have been with a lot of assumptions regarding the geometry and evolution of CMEs in the Inter Planetary (IP) medium. Many works have been done by many researchers in this regard in predicting the arrival time of CMEs to 1AU using different models. Predicting the arrival time of CMEs with a minimal error has been a major issue in the field of Heliophysics, because the average error between the observed transit time and predicted transit time obtained in all the result of the models so far are still very large. There is need for a lower value between the predicted and observed transit time.

Predicting the arrival time of CMEs with minimal average error will help serve as a practical way of getting advanced warning of solar disturbances heading towards the earth, save billions of currency that would have been used to repair or replace damaged satellites and power grids, identify communication problems, help high altitude flight management and make provisions for renewable energy sources to protect the Earth against a black out.

1.2 The Earth’s Atmosphere.

The Atmosphere of the Earth is a layer of gases surrounding the planet Earth that is retained by Earth’s gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect) and reducing temperature extremes between day and night (the diurnal temperature variation).

The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. Although air content and atmospheric pressure vary at different layers, air suitable for the survival of terrestrial plants and animals is found in the Earth’s troposphere.

1.2.1 The Thermal structure of the Earth’s Atmosphere.

In general, air pressure and density decrease with altitude in the atmosphere. The general pattern of the temperature/altitude profile is constant and recognizable through means such as balloon soundings. The temperature behavior provides a useful metric to distinguish between atmospheric layers.

The Earth’s atmosphere is stratified into five main layers, namely; the troposphere, stratosphere, mesosphere, thermosphere and Exosphere.

The troposphere is the lowest layer of the Earth’s atmosphere. It extends from the Earth’s surface to an average height of about 12km, although this altitude actually varies from about 9km at the poles to 17km at the equator. The temperature in the troposphere decreases as altitude increases, dropping from about 17oC to -52oC (Subbiondo, 2004). This is because it is mostly heated through energy transfer from the surface. Thus, the lowest part of the troposphere is typically the warmest section of the troposphere. This promotes vertical mixing the troposphere is denser than all its overlying atmospheric layers because a larger atmospheric weight sits on top of the troposphere and causes it to be most severely compressed. It is primarily composed of Nitrogen (78%) and Oxygen (21%) with only small concentrations of other trace gases. Nearly all atmospheric water vapor or moisture is found in the troposphere, so it is the layer where most conventional aviation activity takes place.

The stratosphere is the second –lowest layer of the Earth’s atmosphere. It is bounded by the stratopause. The stratosphere contains the ozone layer. In this layer, the temperature rises with increasing altitude. The rise in temperature is caused by the absorption of ultraviolet radiation (UV) radiation from the Sun by the ozone layer which restricts turbulence and mixing. The troposphere is bounded above by the tropopause, a boundary marked by stable temperature. The stratospheric temperature profile creates very stable atmospheric conditions so that the stratosphere lacks the weather-producing air turbulence that is so prevalent in the troposphere.

The mesosphere is the third highest layer of the Earth’s atmosphere, occupying the region above the stratosphere and below the thermosphere. It extends from the stratosphere an attitude of about 50km to the menopause at 80-85km above the sea level. Temperature drops in increasing attitude to the mesopause; it is the coldest region on Earth. According to State and Gardner (2010), the average temperature of the mesopause is around 85oC (-120oF or 190K).The mesosphere is also the layer where most meteors burn up upon atmospheric entrance. It is too high above the Earth to be accessible by jet-powered aircraft and too low to support satellites and orbital or sub-orbital spacecraft. It is mainly accessed by rocket-powered aircraft and unmanned sounding rockets.

The Thermosphere is the second-highest layer of Earth’s atmosphere, it extends from the mesopause (which separates it from the mesosphere) at an altitude of about 80km up to the thermopause at an altitude range of 500-l,000km.The lower part of the thermosphere from 80km to 550km above the Earth’s surface contains the atmosphere. In this region temperature increases with altitude. This is due to the extremely low density of its molecules. The temperature of this layer can rise as high as l,727°C (Subbiondo,2004).The air is rarefied that an individual molecule travels an average of 1 kilometer between collisions with other molecules.

The exosphere is the outermost layer of the Earth’s atmosphere. It extends from the exobase, which is located at the top of the thermosphere at an altitude of about 700km above sea level to about 10,000km. The exosphere merges with the emptiness of outer space, where there is no atmosphere. The layer is mainly composed of extremely low densities of hydrogen, helium and several heavier molecules including nitrogen, oxygen and carbon dioxide closer to the exobase. The atoms and molecules are so far apart that they can travel hundreds of kilometers without colliding with one another. Since the exosphere no longer behaves like a gas, the particles constantly escape into space. The free moving particles follow ballistic trajectories and may migrate in and out the magnetosphere or the solar wind.

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INVESTIGATION OF EFFECTS OF CME ON IONOSPHERIC TEC OVER NSUKKA

CHAPTER ONE: INTRODUCTION

1.1 General Introduction

Modern society depends heavily on a variety of technologies that are susceptible to the extremes of space weather — severe disturbances of the upper atmosphere and of the near-Earth space environment that are driven by the magnetic activity of the Sun. for instance, strong electrical currents driven in the Earth’s surface during auroral events can disrupt and damage modern electric power grids and may contribute to the corrosion of oil and gas pipelines. Changes in the ionosphere during geomagnetic storms driven by magnetic activity of the Sun interfere with high-frequency radio communications and GPS navigation. During polar cap absorption events caused by solar protons, radio communications can be severely compromised for commercial airliners on transpolar crossing routes. Exposure of spacecrafts to energetic particles during solar energetic particle events and radiation belt enhancements can cause temporary operational anomalies, damage critical electronics, degrade solar arrays, and blind optical systems such as imagers and star trackers used on commercial and government satellites. Space explorers must be constantly aware of the current space weather and be prepared to handle the most extreme conditions that might be encountered.

Thus, this work aims at making valuable contribution to space weather monitoring since much of the dynamics of storm-time ionosphere originates in the equatorial region.

1.2 The Earth’s Atmosphere

The Earth’s atmosphere is stratified into layers based on temperature variation as shown in Fig.1.1. The stratification in increasing order of altitude from sea surface are; the troposphere (0 – 18 Km), Stratosphere (18 – 90 Km), Mesosphere (90 -350 Km), thermosphere (350 – 1000km). The Ionosphere is overlapped by both mesosphere and thermosphere.

Each layer is characterized by different density of atmospheric constituents and experience different weather phenomenon. Due to its apparent proximity to the Sun, the ionosphere is specifically characterized by ionized particles and thus is greatly influenced by space weather.

1.3 The Ionosphere

The ionosphere has several layers created at different altitudes and made up of different densities of ionization. Each layer has its own properties, and the existence and number of layers change daily under the influence of the Sun. During the day, the ionosphere is heavily ionized by the Sun. During the night hours the cosmic rays dominate because there is no ionization caused by the Sun, which has set below the horizon. Thus there is a daily cycle associated with the ionizations.

In addition to the daily fluctuations, activity on the Sun can cause dramatic sudden changes to the ionosphere. The Sun can unexpectedly erupt with a solar flare (Okeke and Soon, 2004), which is a violent explosion in the Sun’s atmosphere caused by huge magnetic activity. These sudden flares produce large amounts of X-rays and EUV energy that travel to the Earth and other planets at the speed of light.

The Sun spews out a constant stream of X-ray and extreme ultraviolet (EUV) radiation. This energy, along with that from cosmic rays, affects the Earth’s ionosphere. When solar energy in the form of solar wind blows across the ionosphere, electrons are precipitated from neutral molecules, resulting in ionization.  These free electrons in the ionosphere strongly influence propagation of radio signals.

As illustrated in Fig. 1.2, radio frequencies of very long wavelength and otherwise very low frequency (VLF) reflect off these free electrons in the ionosphere thus, allowing radio communication over the horizon and around the curved Earth. The strength of the received radio signal changes according to how much ionization has occurred and from which level of the ionosphere the VLF wave has reflected.

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INTERPRETATION OF AEROMAGNETIC DATA OF IDAH AREA NORTH CENTRAL NIGERIA

                                    CHAPTER ONE

                                     INTRODUCTION

1.1 Introduction

Geomagnetism is the branch of geophysics that studies earth’s magnetic field. The science of geomagnetism developed slowly. The earliest writings about compass navigation are credited to the Chinese and dated to 250 years B.C. When Gilbert published the first textbook on geomagnetism in 1600, he concluded that the earth itself behaved as a great magnet. In the early nineteenth century, Gauss (1848) introduced improved magnetic field observation techniques and the spherical harmonic method for geomagnetic field analysis. Not until 1940 did the comprehensive textbook of Chapman and Bartels bring us into the modern age of geomagnetism (Campbell, 2003).

Magnetic surveying investigates the subsurface based on variations in the earth’s magnetic field that result from the magnetic properties of the underlying rocks.  Mostly, the earth’s magnetic field is generated in the fluid outer core of the earth by self exciting dynamo process. Electrical current flowing is the slowly moving molten iron generates the magnetic field which is generally referred to as the main field as observed on the earth’s surface.

Airborne geophysical surveying is a process of measuring the variation of several key physical or geochemical parameters of the earth. The most important parameters measured are conductivity, magnetic susceptibility, rock density, radioactive element concentration, and reflectance spectra. Any change in the earth’s near surface that causes a measurable change in these parameters presents a potential application for airborne geophysics. The systems used to measure these parameters are electromagnetic, gamma-ray spectrometry, magnetic, and gravity. Airborne geophysics has always been at the forefront of technological developments and innovation. Modern exploration systems can measure minute changes in the geophysical properties of the earth with high sensitivity instruments and survey platforms. Exploration projects utilise GPS navigation and timing, laser and radar altimeters, satellite communications and innovative data processing techniques.

An aeromagnetic survey is a common type of geophysical survey carried out using a magnetometer on board or towed behind an aircraft. The principle is similar to a magnetic survey carried out with a hand-held magnetometer, but allows much larger areas of the earth’s surface to be covered quickly for regional reconnaissance. The aircraft typically flies in a grid like pattern with height and line spacing determining the resolution of the data (and cost of the survey per unit area) (Olasehinde, 2009).

Airborne geophysical surveys are applicable in oil and mineral exploration, engineering projects, geothermal mapping, land management; they are excellent tools for mapping exposed bedrock, geological structures (such as basements, faults, dikes, sills, kimberlites), sub-surface conductors, paleochannels, mineral deposits and salinity.

1.2 Solid earth structure

The interior structure of the earth is layered in spherical shells, like an onion as shown in fig1.1. These layers can be defined by either their chemical or their rheological properties. The earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. Scientific understanding of earth’s internal structure is based on observations of topography and bathymetry, observations of rock in outcrop, samples brought to the surface from greater depths by volcanic activity, analysis of the seismic waves that pass through earth, measurements of the gravity field of earth, and experiments with crystalline solids at pressures and temperatures characteristic of earth’s deep interior.The structure of earth can be defined in two ways: by mechanical properties such as rheSology, or chemically. Mechanically, it can be divided into lithosphere, asthenosphere, mesospheric mantle, outer core, and the inner core.

The interior of earth is divided into five important layers. Chemically, the earth can be divided into the crust, upper mantle, lower mantle, outer core, and inner core.

The layering of earth has been inferred indirectly using the time of travel of refracted and reflected seismic waves created by earthquakes. The outer core does not allow shear waves to pass through it, while the speed of travel (seismic velocity) is different in other layers. The changes in seismic velocity between different layers causes refraction according to Snell’s law, like light bending as it passes through a prism. Likewise, reflections are caused by change in acoustic impedance and are similar to light reflecting from a mirror (Lowie, 1997).

1.3 The geomagnetic field

Earth’s magnetic field (also known as the geomagnetic field) is the magnetic field that extends from the earth’s inner core to where it meets the solar wind, a stream of energetic particles emanating from the sun.  It is approximately the field of a magnetic dipole tilted at an angle of 11 degrees with respect to the rotational axis—as if there were a bar magnet placed at that angle at the centre of the Earth. However, unlike the field of a bar magnet, earth’s field changes over time because it is generated by the motion of molten iron alloys in the earth’s outer core (the geodynamo).

Near the surface of the earth, its magnetic field can be closely approximated by the field of a magnetic dipole positioned at the centre of the earth and tilted at an angle of about 10° with respect to the rotational axis of the earth. The dipole is roughly equivalent to a powerful barmagnet, with its south pole pointing towards the geomagnetic north pole .  This may seem surprising, but the north pole of a magnet is so defined because, if allowed to rotate freely, it points roughly northward (in the geographic sense). Since the north pole of a magnet attracts the south poles of other magnets and repels the north poles, it must be attracted to the south pole of earth’s magnet. The dipolar field accounts for 80–90% of the field in most locations (Merrill et al., 1996).

The earth’s field is not constant at any point on its surface but undergoes variations of different periods. From the stand point of applied geophysics, the most important are the diurnal variations and magnetic storm. Their disturbing effect must be suitably eliminated from magnetic survey observations (Parasnis, 1986).

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INFLUENCE OF ZONAL WIND AND GEOMAGNETIC STORM ON OZONE VARIATION IN NIGERIA

CHAPTER ONE

1.1       BACKGROUND OF THE STUDY

Ozone depletion and geomagnetic storm are among the most severe phenomena that disturb the world today. When there is ozone depletion, harmful ultraviolet (UV) radiations from the sun penetrates into the earth and affect human health and ecosystem in general. Ozone depletion and geomagnetic storm generally contribute to climate change. Some research works have suggested that geomagnetic storm is always associated with ozone variation in the mid-latitude. Until now, no scientific work has been carried out to ascertain this fact. Also, researchers have hitherto considered the zonal wind to be weak at the tropics (where Nigeria is located) hence, dynamical processes around the low and mid-latitude have not been adequately considered.

As a secondary pollutant, ozone is not emitted directly but is generated in the atmosphere through a complex series of chemical reactions initiated by absorption of solar energy (Seinfeld and Pandis, 1998 J.H. Seinfeld and P.J. Pandis, Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, John Wiley, New York (1998).Seinfeld and Pandis, 1998). The atmospheric wind influences the time of occurrence of the daytime ozone maximum. Increase in air temperature as a result of intense solar radiation causes an increase in the variation of total ozone. This is because ozone in the stratosphere is created and destroyed primarily by ultraviolet (UV) radiation from the sun. That is; ozone is formed when oxygen molecules absorb UV radiation and split apart into two oxygen atoms (O), which combine with other oxygen molecules (O2), to form ozone molecules (O3). Ozone is also broken apart as it absorbs UV radiation. In this way, UV helps sustain the natural balance of ozone in the stratosphere, while ozone in turn absorbs UV, protecting life on earth from these harmful radiations.

The solar chromospheric activity in the ultraviolet region is of great importance to our understanding of both the physical properties of the sun as a star, and of the solar influence on the earth’s stratospheric chemistry.  Okeke (2012) noted that how sun’s magnetic field connects with the geomagnetic field determines how solar activity affects the earth. The interaction between the solar plasma and the earth’s magnetic field causes a number of current systems to develop in the magnetosphere during a magnetic storm. In other words, compression of the magnetosphere by plasma causes development of magnetopause current and ring current systems which are the main current systems responsible for a typical magnetic storm recorded at mid- and low-latitudes. When the solar activity is high both solar UV radiation and ozone concentrations are high.

The atmospheric activities that cause ozone variations are photochemical processes and dynamical processes. The former refers to the production and destruction of ozone and it is driven by solar ultraviolet (UV) photochemistry in the upper stratosphere. The later refers to how ozone is transported from one location to another by winds and large scale circulation patterns in the atmosphere. Atmospheric angular momentum (AAM) is a fundamental circulation index used in representing and measuring the dynamic state of the whole circulation of the atmosphere and climate (Peixoto and Oort, 1992; Abaraca del Rio et al., 2000; 2003). It has been observed that much of the historic development of modern meteorology is connected with the study of how atmospheric momentum is maintained locally or transported from one region to another and how it is exchanging momentum with the oceans and solid earth (Peixoto and Oort, 1992). The main contributions to the axial AAM components are the global zonal winds in the troposphere and stratosphere. AAM is highly correlated with changes in length of day (LOD), a measure of the earth’s rotation rate (Eubanks, 1993).

Nigeria, being in the tropics and where not much research work in the depletion of ozone and consequences of zonal winds, solar activity phenomenon together with geomagnetic storms on the ozone variation has been investigated, it becomes crucial that this study be carried out in Nigeria. Hence, in our study, an attempt will be made to study the effect of this interaction; zonal winds, solar activity and magnetic storm influence over six stations namely; Sokoto (13.030N 05.270E), Maiduguri (12.000N 13.330E), Abuja (09.080N 07.050E), Ikeja (06.420N 03.450E), Port-Harcourt (04.850N 07.02oE) and Enugu (06.430N 07.480E), in the tropics – Nigeria (West Africa) as a case study; this was selected according to the six (6) geo-political zones in Nigeria to ensure even distribution. Isikwue (2009) suggested that effects of geomagnetic storms on ozone in the tropical latitudes be carried out, since Mitra (1947) noted that increase in the ozone values in the middle atmosphere was always associated with geomagnetic storms. Since then, no research work has been carried out to investigate the extent or validity of Mitra’s finding; it is on this note and on existing controversies and inconsistencies that this work becomes very necessary.

1.2       THE EARTH’S ATMOSPHERE

The atmosphere that is very essential for all life forms on earth is a mixture of many gases. The three major components of ordinary air near the surface are nitrogen (76.9%) and oxygen (20.7%) with the next largest component being water vapor (1.4%). Many gases in the atmosphere are capable of chemical reactions. Some of those present in trace amounts may form combinations that are commonly considered to be pollutants. These and other potentially harmful gases are monitored in many urban areas by State Health departments or by Environmental Protection Agency, these include nitrogen oxides, sulfur dioxide, carbon monoxide, methane, ozone, and ammonia (Eagleman, 1980). The atmosphere protects life on earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.

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INFLUENCE OF SOLAR AND GEOMAGNETIC ACTIVITIES ON CLIMATE CHANGE IN NIGERIA

ABSTRACT

This study investigates the influence of solar activity and geomagnetic activity on climate change over Nigeria, in order to ascertain their impact on the observed climate change in the country. Data of sunspot number and geomagnetic aa index were obtained from World Data Center and National Centers for Environmental Information. The data spanned from 1950 – 2012 and 1950 – 2010 respectively. Pressure corrected hourly cosmic rays data were obtained from Thule Neutron Monitor Station (76.5o N, 68.5o W, 26.0 m) with the geomagnetic cut-off rigidity of 1.0 GV and Haleakala Neutron Monitor Station (20.71o N, 156.17o W, 3052 m) with the geomagnetic cut-off rigidity of 13.3 GV. The data span for 56 years (1957 – 2012) and 16 years (1991 – 2006) respectively. Monthly mean global cloud cover data for high, middle, and low clouds were obtained from the International Satellite Cloud Climatology Project (ISCCP)-D2 datasets, for a period of 27 years (1983 – 2009). Monthly mean daily rainfall, minimum and maximum temperature data for 20 synoptic stations in Nigeria were obtained from Nigeria Meteorological (NIMET) Agency. The data span for 63 years (1950 – 2012). Descriptive, bivariate and spectral analyses, as well as Mann-Kendall trend test were employed in analyzing the data. These analyses were executed using Microsoft Excel, XLSTAT, MATLAB, and SPSS. The standardized decadal rainfall and temperature anomalies from 1950 – 2010, using 1981 – 2010 as the based period were presented using ArcGIS software. Results reveal that sunspot number varies in opposite direction with galactic cosmic rays (GCRs) based on the 11-year solar cycle. This was also observed in the variations of aa index with GCRs. From the correlation analysis, sunspot number and aa index were strongly but negatively correlated with cosmic rays with correlation coefficients of -0.843 and -0.686 respectively. This indicates that solar and geomagnetic activities modulate cosmic rays penetrating into the Earth’s atmosphere. The variations of GCRs with cloud cover show that cosmic rays have good correlation with low cloud cover from 1983 – 1995, in contrast to high and middle cloud cover as observed by other researchers. On the other hand, in the recent quiet period of solar cycles, cosmic rays have good correlation with high and middle cloud covers in contrast to low cloud cover. This contradicts the previous findings by some authors. The variations of cloud covers with rainfall and temperature show that changes in cloud covers are associated with changes in rainfall and temperature. The air temperature was observed to increase in the period under study which could be associated with global warming. Similarly, rainfall was also observed to be on the increase. This was confirmed from the results obtained using Mann-Kendall trend test. These are evidence of climate change. The proposed GCR – cloud hypothesis was yet to be established in this study, hence, the connection between solar and geomagnetic activities with climatic parameters is yet to be fully confirmed. However, results of the spectral analysis reveal that Schwabe, Hale and Gleissberg cycles, as well as some atmospheric phenomena (such as quasi-biennial oscillation), were detected in geomagnetic, solar activity and climatic parameters in Nigeria. This implies that signature of solar and geomagnetic activities effect exists on rainfall and temperature, which could be linked to the observed climate change in Nigeria. Hence, we suggest that apart from anthropogenic activities, solar and geomagnetic activity, as well as atmospheric phenomena might play important role in climate change observed in Nigeria.

CHAPTER ONE

INTRODUCTION

1.1       Background of the Study

It is a clear fact that the Earth’s climate has changed in the past, still changing at present and is expected to change in the future. Information from tree rings, ice layer, marine deposits, e.t.c. as documented in historical as well as in geological records have shown that the Earth’s climate is constantly changing. In addition to natural climate changes, the risk of human influence on climate has recently been seriously considered by the Intergovernmental Panel on Climate Change (IPCC). The reasons for these changes, however, have always been the subject of discussions and are still not well understood.

It is obvious that the effect of this changes is manifested more strongly now than ever before. The effects of climate changes (such as loss of sea ice, accelerated sea level rise, global temperature rise, extreme events, oceans rise, e.t.c) that scientists had predicted in the past, that could result from global climate change is more severe now (National Academy of Sciences and Royal Society, 2014).

Climate change is affected by many factors: the influence of continental drift, variations in solar intensity, volcanism, the impact of meteors and comets, changes in the Earth’s orbital parameters, ice acculations and depletion, variations in oceans circulations and chemistry, changes in terrestrial and aquatic life, and changes in atmospheric composition and circulation.

The effects of natural factors such as geomagnetic activity, volcanic activities, e.t.c. and primarily of the solar activity and the associated variation of solar radiation and fluxes of galactic cosmic rays (GCRs), as well as the effect of the geomagnetic dipole variations on the climate processes, are important for understanding the physical causes of modern climate changes (Dergachev et al., 2004).

Studies have shown that solar variability has played a crucial role in the past climate changes. Sunspot numbers have been generally used as a reliable parameter to measure solar activity (Tiwari et al., 2011). Controversy, however, remains over what levels of solar variability are required to generate significant climate change and what mechanisms are involved (Laut, 2011).

The Earth’s magnetic field varies over many time scales leading to irregular variations known as geomagnetic activity or storms. This is due to extreme events, such as coronal mass ejections from the Sun.  Recent studies have shown that past climate changes may have been connected with variations in the Earth’s magnetic field elements at various time scales (Dergachev et al., 2012).

The IPCC (2013), reported that human impact has been the dominant cause of observed climate change. Since changes in climate have significant implications for present lives, for future generations and for ecosystems on which humanity depends, it continues to be a subject of an active study area and public debate.

1.2       The Earth’s atmosphere

The Earth’s atmosphere is a layer of gases surrounding the planet Earth. It has a mass of about 5.15 x 1018 kg, three-quarters of which is within about 11 km of the surface (Lutgens and Tarbuck, 1998). The atmosphere has no definite upper limit, however; it becomes thinner and thinner with increasing altitude, eventually merging with empty space, which surrounds all the planets. The study of the Earth’s atmosphere and its processes is called atmospheric science (aerology).

The major components of air are nitrogen, oxygen, and argon. These constitute the major gases in the atmosphere. Water vapour, dust particles, ozone, and other trace gases are also present in a small percentage. They can have significant effects on weather and climate.

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GEOPHYSICAL INVESTIGATION OF ABAKALIKI AREA USING AEROMAGNETIC METHOD

ABSTRACT

Aeromagnetic data over Abakaliki area of the lower Benue trough of Nigeria was interpreted qualitatively and quantitatively using Oasis montaj software (version: 6.4.2 H.J).The interpretation unveiled basic intrusive bodies like dyke, lacolyte and batholyte in the study area. It also showed fault zone which trends North East to south western (NE-SW) part of the study area.

Quantitative interpretation of the area was carried out by source parameter imaging and forward and inverse modeling. Source parameter imaging unveiled predominance of deep seated bodies in the south western part of the area, while shallow bodies are predominant in the south eastern part of the study area. Depth obtained by source parameter imaging ranged from 99.50m to 5930.78m.  Forward and inverse modeling was carried out using potent Q software which is an extension of the Oasis montaj software used in the work. The magnetic anomalies over the area were modeled by bodies in the form of sphere and ellipsoid by varying the total magnetic intensity parameters such as susceptibility, inclination, declination, depth of burial and by varying the length, width and height of the bodies used in the model. The radius of the spherical bodies are 1457m, 17704m and 4883m for models A, B and D representing Obubra, Abakaliki and Ameka respectively. Lengths of the ellipsoids are 6099m and 5341m.Width of the ellipsoids are 411m and 2203m while Heights of the ellipsoids are 6017m and 275m (for models C and E representing Enyigba and Ameri respectively).  Depth obtained by forward and inverse modeling ranged from 477m to 6366m. Depth obtained for model A (Obubra) is 546m with susceptibility of 0.0180SI (signifying limestone).  Height obtained for model B (Abakaliki) is 50m (likely the out crop near college of Agricultural sciences-CAS EBSU) with susceptibility of -0.0017SI (signifying calcite). Depth obtained for model C (Enyigba) is 956m with susceptibility of -0.0134SI (signifying Rock salt). Depth obtained for model D (Ameka) is 6366m with susceptibility of -0.009SI (signifying Quartz). Depth obtained for model E (Ameri) is 477m with susceptibility of -0.006SI (signifying Calcite). These values correlate with some of the works done in the study area. The presence of out crop, intrusive and minerals like calcite, pyrite, rock salt and limestone were delineated in the area.

                                                    CHAPTER ONE

INTRODUCTION

The study of geophysics has helped man to access hidden treasures in the sub-surface of the earth. These treasures usually appear as anomalies which could be accessed by different geophysical survey methods such as magnetic method, gravitational method, seismic method, electromagnetic method etc.

In geophysical exploration during the last decade, potential field methods have a renewed interest in the search for solid minerals and hydrocarbons.  In  the  gravity  and  magnetic method data processing, the first and the most crucial step is the removal of the effect of deep-seated  structures  from  the  observed  Bouguer  gravity  or  from  the  observed  total magnetic  fields,  in  order  to  enhance  the  signatures  of  shallow  bodies  (Ndougsa  et  al., 2007). These shallow bodies are associated in solid mining exploration firstly to precious metals  (gold,  diamond)  which  have  a  different  density  with  the  surroundings  (gravity exploration) and secondly to substances such as magnetite, hematite, which have contain an iron ore deposit (magnetic exploration) (Ndougsa et al., 2012).

Magnetic survey investigates the subsurface based on variation in the earth’s magnetic field that results from the magnetic properties of the underlying rocks. Magnetic survey can be carried out on land, sea and in air. However, magnetic survey is in principle similar to gravity survey. Aeromagnetic survey aids in indicating major basement surface structures which reveal encouraging exploration areas that could be studied in broader detail using seismic geophysical survey method. The earth’s magnetic field acts on the magnetic minerals in the crust, inducing a secondary field which reflects the distribution of the minerals. The main magnetic field induces a field which varies slowly from one place to another while the crustal field which is the portion of the magnetic field associated with the magnetism induced by the earth’s main magnetic field varies more rapidly (Reford, 1962).

The traditional role of aeromagnetic studies over continental areas is to establish geologic and tectonic frame works and to explore for minerals. The magnetic method is a relatively inexpensive method of learning about geologic hazards such as seismically active faults, shallow magma chambers and volcanic centers. Induced magnetic method may be the only way to study hazardous structures in places where they are concealed beneath young deposits, water and vegetation. Aeromagnetic data have long been used by the petroleum industry to map structures and to enhance depth to magnetic basement (Steenland, 1965).

The use of computers in the 1960s for processing and interpreting geophysical data has application in estimation of depth to basement and mapping of basement structures. It has been demonstrated in literature and other forms that high resolution aeromagnetic data provide valuable data that solves problems in petroleum exploration.

 

Aeromagnetic survey has application also in mapping of potential ground water resources in the arid and semi-arid areas of the world. The fact that most sedimentary rocks and surface cover formations like water are effectively nonmagnetic implies that the observed anomalies are attributable to the underlying igneous and metamorphic rocks.

Aeromagnetic survey is the oldest potential field method used for hydrocarbon exploration. The aim of the aeromagnetic survey is to detect minerals or rocks that have unusual magnetic properties by causing anomalies in the intensity of the earth’s magnetic field. Aeromagnetic survey is the exploration method of the earth’s magnetic field intensity with magnetometers installed in airplanes or helicopters. The process is to operate the magnetometer continuously along equally spaced parallel flight lines covering the survey area. The principle of the geophysical survey is similar to a magnetic survey carried out with a hand held magnetometer but it allows much larger areas of the earth’s surface to be quickly covered. The aircraft flies in a grid –like pattern with height and line spacing determining the resolution of the data. As the aircraft flies, the magnetometer records tiny variation in the intensity of the ambient magnetic field due to the temporal effects of the constantly varying solar wind and spatial variations in the earth’s magnetic field. The spatial variation of the earth’s field is due to the regional magnetic field and the local effect of magnetic minerals in the earth’s crust. Subtraction of the solar and regional effects reveals the spatial distribution and relative abundance of magnetic minerals.

Aeromagnetic survey covers much larger areas of the earth’s surface quickly for regional reconnaissance than hand-held magnetometer.

The increasing demand for metals of all kinds and the use of petroleum products have led to the development of many geophysical techniques of ever increasing sensitivity for detection and mapping of unseen deposits and structures (Telford et al, 1990).

1.2    Background to the study

Magnetic method is the primary tool in the search for minerals. It is used in many areas such as locating intra-sedimentary faults, defining subtle lithological contacts, mapping salt domes in weakly magnetic sediments. These applications have increased the methods utility in all areas of exploration especially in the search for minerals, oil and gas, geothermal resources, natural hazards assessment, mapping impact structures, underground water survey, engineering and environmental studies. Aeromagnetic methods traditionally are used to Map crystalline basement, igneous rocks at depth and for mapping faults that offset Basin fills and for delineating buried igneous bodies in the near surface (Grauch, 2001).

Aeromagnetic data represents variations in the strength of the Earth’s magnetic field that are produced by changes in magnetization of the crust. Magnetization of rocks is determined by the quantity of magnetic minerals (commonly titanomagnetites) and by the strength and direction of remanent magnetization carried by those magnetic minerals. The quantity of magnetic minerals is measured as magnetic susceptibility and produces an induced magnetization. The remanent magnetization is based on the permanent alignment of magnetic domains within the rock and is measured using paleomagnetic methods (Butler, 1992).

Aeromagnetic surveys respond to the total magnetization of rocks, which is the vector sum of the induced and remanent magnetizations. Igneous and crystalline metamorphic rocks commonly have high total magnetizations compared with other rock types, whereas sedimentary rocks and poorly consolidated sediments have much lower magnetizations (Reynolds et.al, 1990; Hudson et.al, 1999).

The aeromagnetic geophysical method plays a distinguished role in terms of rapid rate coverage of geophysical survey area. The main purpose of aeromagnetic geophysical survey is to detect minerals or rocks that have unusual magnetic properties which reveal themselves by causing anomalies in the intensity of the earth’s magnetic field (USGS, 1997).

Aeromagnetic   data was once presented as contour plots but it is more commonly expressed as colour and shaded computer generated Pseudo-topographic images where in the apparent hills, ridges and valleys are referred to as aeromagnetic anomalies. The Aeromagnetic survey is applied in mapping these anomalies in the earth’s magnetic field and it is subsequently correlated with the underground geological structures.

1.3 Geology of the study area

Abakaliki lies in the lower Benue Trough. It is located between latitudes 6o35N to 6o45 N and longitudes 8o42 E to 8o47 E, with average elevation of 117m. The Lower Benue trough is believed to have been formed during the formation of the Benue Trough. A series of tectonic activities characterize the formation of block faulting. This occurred during the separation of the South American Continent (Olade, 1975, Nwachukwu, 1972 and White man, 1982).

The separation of the continents led to an aborted rift (Aulacogen) which was later filled with transgressive and regressive sedimentary deposits.  Aside Abakaliki anticlinorium towards the Anambra basin, the Afikpocyncline is also part of the Lower Benue Trough. The sequence of events that led to the formation of the Benue Trough and its component units are well documented (Burke et al, 1971, Benkhelil, 1982, Nwachukwu, 1972, Olade, 1975, Ofoegbu, 1985, Ojoh, 1992).

The Lower Benue Trough underlain by thick sedimentary sequences deposited in the cretaceous and the Precambrian basement complex is essentially made up of granitic and magnetic rocks which are predominant in the eastern part of the study area (Ofoegbu and Onuoha, 1990).

The development of Abakaliki anticlinorium was adversely affected by the folding episode which occurred during the santonian, hence, the Predominantly compressional nature of the fold that occurred during the period was revealed by their asymmetry and reversed faults.

The sediments that occur in the Abakaliki anticlinorium belong to Four (4) geologic formations (Fig 1.1). These include: Asu-river group (Albian), Awgu shale (caniacian),Nkporo shale  and Ezeaku shale(Turonian).

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GALACTIC COSMIC RAY VARIABILITY IN THE HIGH AND MID LATITUDES DURING SOLAR CYCLES 22 AND 23

ABSTRACT

Galactic cosmic rays are modulated in the hliosphere primarily due to the global merged interaction regions with intense magnetic field which leads to a decrease in the galactic cosmic rays throughout the heliosphere.  Using long term averages of solar wind (SW) component parameters in addition to cosmic ray count rates of two high latitude Neutron monitor stations (Apatity and Thule) and two mid latitude stations (Newark and Tbilisi) with different rigidity cut-offs, we analyzed the effect of these SW components on the counts rates under different interplanetary magnetic field (IMF) disturbance levels. From first order partial correlation, we found that the total interplanetary magnetic field (Total B) was the most dominant modulating parameter especially during quiet conditions and the solar wind dynamic pressure (SWDP) was more effective during disturbed conditions. The influence of the more subtle parameters like solar wind speed (SWS), Z component of IMF (Bz) and solar wind density were masked by these dominant parameters vis IMF (Total B) and SWDP. Also, cosmic ray count rates on these stations studied showed similar annual variation trend, with station of lowest cut-off rigidity having highest amplitude and vice versa, confirming cut-off rigidity as another important modulating factor.                                               

CHAPTER ONE

1.1       COSMIC RAYS

The cosmic rays (CRs) are energetic charged subatomic particles originating from the outer space with lifetime of the order 106 years or longer, incident at the top of the terrestrial atmosphere and produce showers of particles on interaction with the atmosphere which penetrate and impact the earth’s atmosphere and sometimes  reach the earth’s surface. Apart from particles associated with solar flare, cosmic Rays come from outside the solar system. The incoming charged particles are modulated by the solar wind, the expanding magnetized plasma generated by the sun, which decelerate and partially excludes the lower energy cosmic rays from the inner solar system. CRs are mostly pieces of atoms: protons, electrons, and atomic nuclei which have had all of the surrounding electrons stripped during their high-speed (almost the speed of light) passage through the space.

The need to study cosmic rays and their interaction with earth is driven by the understanding that CRs are the major source of ion production in the lower atmosphere (troposphere and stratosphere), therefore, the electrical properties of the atmosphere such as atmospheric electric current, lightening production and thunder cloud formation e.t.c., can be affected by cosmic rays (Ermakov and Komozokov, 1992). It also damages micro-electronics and life outside the protection of the atmosphere and Geomagnetic field. CRs have sufficient energy to alter the state of element in electronic integrated circuit, causing transient errors to occur, such as corrupted data in electronic memory devices or incorrect performance of central processing unit (CPU). It ionizes the nitrogen and oxygen molecules in the atmosphere which leads to a number of chemical reaction; and is responsible for the continuous production of a number of unstable isotopes in the atmosphere of the earth, such as carbon 14 (14C).

n + 14N  à P + 14C                                                                                                1

Cosmic Rays are one of the most important barriers standing against interplanetary travel and pose threat to electronics placed aboard outgoing probe.  Magnetic shielding for spacecraft have to be considered in order to minimize damages to electronics and human by cosmic rays ( Nancy, 2005).

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FABRICATION AND CHARACTERIZATION OF PHOTOELECTROCHEMICAL SOLAR CELLS USING CHEMICALLY SYNTHESIZED ZINC OXIDE THIN FILMS

 

ABSTRACT

Mesoporous nanostructures of zinc oxide (ZnO) were successfully synthesized by chemical bath deposition (CBD) technique and used to fabricate photoelectrochemical (PEC) solar cells. The synthesis proceeded in an alkaline bath of an aqueous solution of 0.1 M Zn(NO3)2.6H2O at a bath temperature of 353 K and pH of 11.5 on microscope glass slide and stainless steel slide substrates. The ZnO was doped with Al and Cu at varying concentrations from 1-5 at. %. As-deposited films were annealed at 673 K for 2 h.  The synthesized ZnO thin films had thickness in the range of 2.03-10.43 µm. Crystal structure studies revealed that all the ZnO thin films were polycrystalline with hexagonal wurtzite structure and preferential growth in the 002 crystal plane. Crystallite sizes in the range of 8-29 nm were obtained along the 002 crystal plane and the crystallinity of the doped samples was strongly affected by the concentrations of the dopants. Surface morphological studies indicated that the synthesized ZnO thin films had nanoflakes, nanodendrites and nanorods morphologies which confirmed the effects of surfactant, dopants and annealing on ZnO. Optical studies revealed that all the films had low absorbance in the visible region of the solar spectrum with transmittance ranging from 42-90 %.  Energy band gaps of the undoped and doped ZnO were found to decrease from 3.03 eV to 2.70 eV. All the measured optical properties of the ZnO thin films showed strong dependence on the concentration of the dopants. Surface wettability studies confirmed that all the synthesized ZnO thin films were porous (hydrophilic), giving water contact angles in the range of 0o to 71.3o. For the first time in literature, this synthesized ZnO thin films were further sensitized with Indigofera arrecta plant dye and also Rhodamine 6G to develop/fabricate dye-sensitized solar cells (DSSCs).  The fabricated PEC solar cells produced short circuit current (ISC) of 12.34 μA/cm2 and open circuit voltage (VOC) of 388 V for unsensitized undoped ZnO electrode giving power conversion efficiencies (η) of 0.003 and fill factor (FF) of 0.43. Unsensitized aluminum doped zinc oxide (AZO) electrode yielded ISC in the range of 21 μA/cm2 to 29 μA/cm2, VOC in the range of 333 mV to 641 mV, η in the range 0.0037 % to 0.01 % and FF in the range of 0.34 to 0.43. While unsensitized copper doped zinc oxide (CZO) electrodes produced ISC in the range of 16 μA/cm2 to 98 μA/cm2 and VOC in the rage of 774 mV to 796 mV, giving η in the range of 0.0009 % to 0.062 % and FF in the range of 0.06 to 0.63. Further upon dye-sensitization of the ZnO electrodes with Rhodamine 6G and Indigofera arrecta plant dye respectively, the PEC solar cells of undoped ZnO produced ISC of 0.24 mA/cm2 and VOC of 360mV for Rhodamine 6G and ISC of 0.29 mA/cm2 and VOC of 595 mV for Indigofera arrecta plant dye.  These produced η of 0.11 % and FF of 0.45 for Rhodamine 6G and η of 0.16 % and FF of 0.44 for Indigofera arrecta plant dye. AZO electrodes produced ISC in the ranges of 0.3 mA/cm2 to 0.4 mA/cm2 and VOC in the ranges 376 mV to 515 mV using Rhodamine 6G and ISC in the range of 0.84 mA/cm2 to 1.35 mA/cm2 and VOC in the range of 596 mV to 664 mV for Indigofera arrecta plant dye. These yielded η in the range of 0.16 % to 0.22 % and FF in the range of 0.40 to 0.49 for Rhodamine 6G and η in the range of 0.29 % to 0.51 % and FF in the range of 0.42 to 0.47 using Indigofera arrecta plant dye. On the other hand, CZO electrodes produced ISC in the range of 0.49 mA/cm2 to 0.97 mA/cm2 and VOC in the range of 355 mV to 473 mV for Rhodamine 6G and ISC in the range of 0.91 mA/cm2 to 6.8 mA/cm2 and VOC in the range of 656 mV to 914 mV using Indigofera arrecta plant dye.  These yielded η in the range of 0.18 % to 0.39 % and FF in the range of 0.39 to 0.46 using Rhodamine 6G and η in the range of 0.40 % to 4.16 % and FF in the range of 0.42 to 0.54 for Indigofera arrecta plant dye. The η of 4.16 % obtained in this work using Indigofera arrecta plant dye is the highest ever obtained using natural dyes from plants as found in the available literature.  Electrochemical impedance spectra of all the PEC solar cells shows impedance variations that agrees with the ISC and VOC results for all the cells as stated above.

ACKNOWLEDGEMENT.

When a man undertakes a journey, he has the good will of both God and men. When he returns, he brings with him great thankfulness for the grace and mercy of God and for the good wishes of men. My journey could not have been easily gotten this far if God had not granted it. I have indeed enjoyed special favours from God during the whole period of this work and so I glorify His name.

There are men who are akin to God in affairs of man. Their blessing, advice, assistance and challenging personalities are a source of strength, a sense of direction and dedication to duty and opens up a world of insatiable aspiration for us. Their lives provide us with the inspirational model in the process of struggling for self-actualization.

I am particularly grateful to my supervisors, Professor R.U. Osuji and Dr. F.I. Ezema for their relentless efforts, their great concern for the success of this research work, their tolerating patience and their commitment to academic excellence. They have gone extra miles from supervisor-student relationship to ensure excellence in the work. I owe a lot of appreciation to Professor C.D. Lokhande, coordinator of Thin film Laboratory, Department of Physics, Shivaji University, Klohapur, India and the entire students of the Department for their immense contributions to the success of this work. Professor C.D. Lokhande offered me his laboratory, materials and guidance for the experimental part of this work; above all, their overwhelming hospitality kept me comfortable during my stay in Kolhapur, India.

I am especially indebted to my wife, Mrs. Catherine Tyona and my children, Master Joshua Keghtor, Ms. Happiness Nguvan, Ms. Joy Mimi and Master Caleb Tavershima Tyona and also my Cousin, Ms. Msuur Nyiter. They have endured patiently all the hardships that besiege the family as a result of this work: my consistent absence and financial short fall amongst many others. My gratitude goes to the entire family of Late Evangelist Tyona Kange: Mr. Samuel Kange, Mr. Terkimbi Tyona just to mention few, for their persistent prayer, moral support and otherwise throughout the course of this work.

I would not forget the good relationship I enjoyed with the staff and postgraduate students of the Department of Physics and Astronomy, University of Nigeria, Nsukka. I really appreciate my friends who helped in the course of this work: Mr. James Ezema, Dr. S.B. Jambure, Dr. Ravindra Bulakhe and Dr. Nana Shinde just to mention few.

You have all made this journey a bearable one. God bless you all.

CHAPTER ONE

INTRODUCTION AND THEORETICAL BACKGROUND

1.1.        NANOMATERIALS

1.1.1.     General Introduction to Nanomaterials

Although nanotechnology is a relatively recent development in scientific research, the development of its central concepts happened over a longer period of time. The emergence of nanotechnology in the 1980s was caused by the convergence of experimental advances such as in the invention of the scanning tunneling microscope (STM) in 1981 by Gerd Binnig and Heinrich Rohrer at IBM Zurich Research Laboratory, for which they received the Nobel Prize in Physics in 1986. Harry Kroto, Richard Smalley, and Robert Curl, discovered fullerenes in 1985, who together won the 1996 Nobel Prize in Chemistry (Cembrero et al. 2004).

Around the same time, K. Eric Drexler developed and popularized the concept of nanotechnology and founded the field of molecular nanotechnology. In 1979, Drexler encountered Richard Feynman’s 1959 talk, “There’s Plenty of Room at the Bottom”. The term “nanotechnology”, originally coined by Norio Taniguchi in 1974, was unknowingly appropriated by Drexler in his 1986 book, “Engines of Creation: The Coming Era of Nanotechnology”, which proposed the idea of a nanoscale “assembler” which would be able to build a copy of itself and of other items of arbitrary complexity. He also first published the term “grey goo” to describe what might happen if a hypothetical self-replicating molecular nanotechnology went out of control. Drexler’s vision of nanotechnology is often called “Molecular Nanotechnology” (MNT) or “molecular manufacturing,” and Drexler at one point proposed the term “zettatech” which never became popular (The Institute of Nanotechnology, 2006; Allhoff et al. 2010).

In the early 2000s, the field was subject to growing public awareness and controversy, with prominent debates about both its potential implications, exemplified by the Royal Society’s report on nanotechnology, as well as the feasibility of the applications envisioned by advocates of molecular nanotechnology, which culminated in the public debate between Eric Drexler and Richard Smalley in 2001 and 2003 (Wang et al. 2006). Governments moved to promote and fund research into nanotechnology with programs such as the National Nanotechnology Initiative.

The early 200s also saw the beginnings of commercial applications of nnotechnology, although these were limited to bulk applications of nanomaterials, such as the Silver Nano platform for using silver nanoparticles as an antibacterial agent, nanoparticle-based transparent sunscreens, and carbon nanotubes for stain-resistant textiles (The Institute of Nanotechnology, 2006; Porter et al. 2007).

Nanotechnology is the engineering of functional systems at the molecular scale. This covers both current work and concepts that are more advanced. In its original sense, nanotechnology refers to the projected ability to construct items from the bottom up, using techniques and tools being developed today to make complete, high performance products (Singh et al. 2004; Kostoff et al. 2007).

One nanometer (nm) is one billionth, or 10−9 of a meter. By comparison, typical carbon-carbon bond lengths, or the spacing between these atoms in a molecule, are in the range 0.12–0.15 nm, and a DNA double-helix has a diameter around 2 nm. On the other hand, the smallest cellular life-forms, the bacteria of the genus Mycoplasma, are around 200 nm in length. By convention, nanotechnology is taken as the scale range from 1 to 100 nm following the definition used by the National Nanotechnology Initiative in the US. The lower limit is set by the size of atoms (hydrogen has the smallest atoms, which are approximately a quarter of a nm diameter) since nanotechnology must build its devices from atoms and molecules. The upper limit is more or less arbitrary but is around the size that phenomena not observed in larger structures start to become apparent and can be made use of in the nano device. These new phenomena make nanotechnology distinct from devices which are merely miniaturised versions of an equivalent macroscopic device such as integrated circuits; such devices are on a larger scale and come under the description of microtechnology (Singh et al. 2004; Konenkamp et al. 2002).

Two main approaches are used in nanotechnology, “bottom-up” and “top-down”. In the bottom-up approach, materials and devices are built from molecular components which assemble themselves chemically by principles of molecular recognition. In the top-down approach, nano-objects are constructed from larger entities without atomic-level control (Wang et al. 2006; Porter et al 2007).

Areas of Physics such as nanoelectronics, nanomechanics, nanophotonics and nanoionics have evolved during the last few decades to provide a basic scientific foundation of nanotechnology. A number of physical phenomena become pronounced as the size of the system decreases. These include statistical mechanical effects, as well as quantum mechanical effects, for example the “quantum size effect” where the electronic properties of solids are altered with great reductions in particle size (Cavalcanti et al. 2007). This effect does not come into play by going from macro to micro dimensions. However, quantum effects become dominant when the nanometer size range is reached, typically at distances of 100 nanometers or less, the so called quantum realm. Additionally, a number of physical (mechanical, electrical, optical, etc.) properties change when compared to macroscopic systems. One example is the increase in surface area to volume ratio altering mechanical, thermal and catalytic properties of materials. Diffusion and reactions at nanoscale, nanostructured materials and nanodevices with fast ion transport are generally referred to as nanoionics. Mechanical properties of nanosystems are of interest in the nanomechanics research. The catalytic activity of nanomaterials also opens potential risks in their interaction with biomaterials (Singh et al. 2004; Cavalcanti et al. 2007).

Materials reduced to the nanoscale can show different properties compared to what they exhibit on a macroscale, enabling unique applications. For instance, opaque substances become transparent, example copper; stable materials turn combustible, example aluminum; insoluble materials become soluble, example gold. A material such as gold, which is chemically inert at normal scales, can serve as a potent chemical catalyst at nanoscales. Much of the fascination with nanotechnology stems from these quantum and surface phenomena that matter exhibits at the nanoscale (Cenbrero et al. 2004). Modern synthetic chemistry has reached the point where it is possible to prepare small molecules to almost any structure. These methods are used today to manufacture a wide variety of useful chemicals such as pharmaceuticals or commercial polymers. This ability raises the question of extending this kind of control to the next-larger level, seeking methods to assemble these single molecules into supramolecular assemblies consisting of many molecules arranged in a well defined manner Wang et al. 2006). Nanotechnology is one of the frontier areas of science due to its versatile application in various fields. Nanomaterials find applications in fields such as miniaturization in electronics, catalysis, optics, biological and in the solar energy sector. In addition, nanomaterials yield the next generation computer chips, better insulation materials, tougher and harder nanomaterials cutting tools, elimination of pollutants, high energy batteries, efficient solar cells, high power magnets, high-sensitivity sensors, automobiles with greater fuel efficiency, aerospace components with enhanced performance (Guo et al. 2010).

 

1.1.2.     Why Nanomaterials?

Materials reduced to the nanoscale can show different properties compared to what they exhibit on a macroscale, enabling unique applications (Allhoff et al. 2010). Two principal factors are responsible for such significant difference in properties of nanoscale materials from other materials: increased relative surface area and quantum effects. These factors can affect or enhance reactivity, strength and electrical characteristics (Allhoff et al. 2010).

Increase in surface area to volume ratio:

Materials at nanoscale has relatively larger surface area when compared to the same volume (or mass) of the material produced in a large form. Consider a sphere of radius r, the surface area and volume of the sphere are given by Eq. (1.1) and (1.2) below:

(1.1)

(1.2)

The ratio of the surface area to the volume will yield

(1.3)

Eq. (1.3) indicates an increase in surface to volume ratio with decrease in size of material. Thus, when there is a decrease in radius of a sphere, its surface area to volume area ratio increases (Allhoff et al. 2010; Singh et al. 2004).

Quantum confinement effect:

Contemporary literature on ultradisperse semiconductor distinguishes between the effects arising as a result of increase in surface area and the degree of surface imperfection with decrease in the size of the crystals. Quantum size effects due to radical change in the electronic state of the semiconductor (Fig. 1.1) crystals less than a certain “critical” size, determined in turn by the extent to which the electron-hole pair photogenerated in the semiconductor is delocalized (Allhoff et al. 2010; Singh et al. 2004). These effects also differ in the range of sizes in which they appear. Size effects are observed in semiconductor crystals measuring 10 – 100 nm, whereas quantum size effects are usually characteristic of nanocrystallites measuring less than 10 nm. In the literature, semiconductor nanoparticles in which quantum size effect of one type or another appear, are often called quantum size particles or quantum points in order to

Fig. 1.1. Dependence of quantum-sized semiconductor’s band gap on particle size (Wang, 2004).

emphasize their special electronic structure (Allhoff et al. 2010; Singh et al. 2004). It is necessary to mention the tentative nature of the size in so far as the exact “critical” size after which the appearance of quantum size effects can be expected is largely determined by the chemical nature of the semiconductor and can vary from 0.5 (CuCl) to 46 (PbSe) or more nanometers.

From the positions of quantum mechanics, the “critical” size (the threshold for the appearance of quantum size effects) corresponds to the De Broglie wavelength of the free electron. During the analysis of the interband absorption of the semiconductor nanoparticle, the Bohr radius of the exciton (aB), which can be calculated from the electrophysical constants of the bulk semiconductor, can be used as such a criterion. The data that have accumulated on size effects in semiconductor nanoparticles make it possible to examine them according to the nature of the effect on the properties of the nanocrystals. Restriction of the free motion of the exciton in the bulk of the nanocrystal leads to an increase of its energy   in relation to the volume (bulk) semiconductor  (Guo et al. 2010) The increase in the energy of the exciton as a result of the quantum size effect  can be calculated in the approximation of the effective masses, which is based on assumptions about the parabolic nature of the permitted energy band close to their edges and the invariability of the effective masses of the electron of the conduction band  and the hole of the valence band  in the transition from the bulk to the ultradisperse semiconductors. The approximation gives the following expression for ∆E (Guo et al. 2010):

(1.4)

where ћ is the Plank’s constant,   and   are the effective masses of electron and hole respectively, R is the atomic radius and   is the Rydberg energy.

In the above Eq. (1.4), the first term, which depends on R2, corresponds to the increase in the energy of the exciton as a result of its spatial restriction in the potential box-the semiconductor nanocrystal. The second term determines the energy of coulombic interaction of the electron and the hole in the composition of the exciton and increases with decrease in the size of the nanoparticles. The value of   in the third term is called the Rydberg energy of the exciton and takes account of the correlation between the motion of the electron and the hole. As seen, the last two terms of the above Eq. (1.4) lead to a decrease in the energy of the exciton, which is restricted in the volume of the particle (Guo et al. 2010).

 

1.2.        ZINC OXIDE (ZnO)

1.2.1.     Introduction to Zinc Oxide (ZnO)

There are three one-dimensional (1 D) nanostrauctures that are most actively studied in nanotechnology, these include: carbon nanotubes, Silicon nanowires and ZnO nanowires/nanorods. ZnO is a key technological material. The lack of a centre of symmetry in the wurtzite structure, combined with large electromechanical coupling, results in strong piezoelectric and pyroelectric properties and the consequent use of ZnO in mechanical actuators and piezoelectric sensors. In addition, ZnO is a wide band-gap (3.37 eV) compound semiconductor that is suitable for short wavelength optoelectronic applications. The high exciton binding energy (60meV) in ZnO crystal can ensure efficient excitonic emission at room temperature. Also, room temperature ultraviolet (UV) luminescence has been reported in disordered nanoparticles and thin films. ZnO is transparent to visible light and can be made highly conductive by doping (Wang, 2004).

ZnO is a versatile functional material that has a diverse group of growth morphologies, such as nanocombs, nanorings, nanohelixes/nanosprings, nanobelts, nanowires and nanocages. Its nanostructures have a wide range of high technology applications such as surface acoustic wave filters, photonic crystals, photodetectors, light emitting diodes, photodiodes, gas sensors, optical modulator waveguide, solar cells and varistors (Wang, 2004).

Different nanostructures of ZnO have been reported (Fig. 1.2). ZnO films have also been synthesised by several techniques such as molecular beam epitaxy, RF magnetron sputtering, chemical vapour deposition, physical vapour deposition, spray pyrolysis, electrodedeposition, aqueous chemical method, chemical bath deposition (CBD), successive ionic layer adsorption and reaction (SILAR) and sol-gel spin coating. However, the last three methods present several advantages such as: inexpensive, easy procedure, possibility of large-scale deposition, low temperature growth and direct control over the film morphology (Zhiyong and Jia, 2005; Ezema and Osuji, 2007; Ezugwu et al. 2007).

CBD and SILAR greatly facilitate to grow 1D ZnO nanostructures by the thermal decomposition of hexamethylenetetramine (HMTA) and zinc acetate. A seed layer of ZnO nanoparticle grown on the substrate is used to initiate the growth of the nanostructure on the substrate. HMTA is a highly water soluble, non-ionic tetradentate cylic tertiary amine. Thermal degradation of HMTA releases hydroxyl ions which react with Zn2+ ions to form ZnO as follows:

(CH2)6N4 + 6H2O  6HCHO + 4NH3

 

 

One of the most attracting applications of ZnO is in dye-sensitized solar cells (DSSCs), offering an inexpensive production and relatively high energy conversion efficiency (Choi et al. 2011). Porous titanium dioxide (TiO2) was known to be the commonly used semiconductor anodes with ruthenium complexes as the mostly used sensitizer. However, it is difficult to grow TiO2 anisotropically to obtain hierarchical and ordered structures (Park and Kim, 2008). ZnO has several advantages over TiO2: it can be easily grown into a large number of nanostructures, it exhibits higher electron mobility than TiO2 (200 cm2 V-1s-1 for ZnO as against 155 cm2V-1s-1 for TiO2). Debye Huckel screening length in ZnO is about 4 nm for a carrier concentration of 1018 cm-3 and is very stable against photo corrosion; it has high excitonic stability and it is an

 

Fig 1.2. Different nanostructures of ZnO: (a) nanorings (b) nanobelts (c) nanocombs (d) nanowires (e) nanohelixes (f) nanorods (g) nanoparticles (h) nanoflowers (i) nanotubes (Wang, 2004; Zhiyong and Jia, 2005).

 

environmental friendly material (Zhiyong and Jia, 2005; Choi et al.2011; Suzuki et al. 2006; Kong et al. 2004). These properties make ZnO more desirable in DSSCs application. In the growth process of ZnO nanostructures for DSSCs, it is important to use organic surfactants (structure directing agents) in the CBD and SILAR methods due to their direct effect on morphological and structural properties which consequently affect the performance of dye-sensitized solar cells. The surfactant molecules bind to the different ZnO surfaces and affect crystal growth (Ezema and Osuji, 2007; Ezugwu et al. 2007).

1.2.2.     Why ZnO Nanostructures?

The discovery of carbon nanotubes rapidly stimulated interest in 1D materials with various morphologies such as wires, rods, ring, belts etc, due to their great potential or fundamental studies of the effects of morphology, dimensionality and size on their physical and chemical properties (Zhiyong and Jia, 2005). 1D nanostructures such as nanowires and nanorods are ideal systems for investigating the dependence of the electrical and mechanical properties on size and dimensionality. They are expected to play an important role as both interconnect and functional components in the fabrication of nanoscale electronic and optoelectronic devices. Many unique and fascinating properties have already been proposed or demonstrated for this class of materials, such as superior mechanical toughness, higher luminescence efficiency, enhancement of thermoelectric figure of merit and a lower lasing threshold (Zhiyong and Jia, 2005; Choi et al. 2011).

In the old generations of photoelectrochemeical (PEC) solar cells, photoelectrodes were made from bulky semiconductor materials such as Si, GaAs or CdS. However, these kinds of photoelectrodes when exposed to light they undergo photocorrosion that results in poor stability of the PEC solar cell. The use of sensitized wide bandgap semiconductors such as TiO2, or ZnO resulted in high chemical stability of the cell due to their resistance to photocorrosion (Kostoff et al. 2007; Khalil, 2011). The problem with bulky single or poly-crystalline wide bandgap is the low light to current conversion efficiency mainly due to inadequate adsorption of sensitizer because of limited surface area of the electrode. One approach to enhance light-harvesting efficiency (LHE) and hence the light to current conversion efficiency is to increase surface area (the roughness factor) of the sensitized photoelectrode. Due to the remarkable changes in mechanical, electrical, magnetic, optical and chemical properties of nanostructured materials compared to its phase in bulk structures, it received considerable attention (Wang et al. 2006). Moreover, because the area occupied by one dye molecule is much larger than its optical cross section for light capture, the absorption of light by a monolayer of dye is insubstantial. It has been confirmed that high photovoltaic efficiency cannot be achieved with the use of a flat layer of semiconductor or wide bandgap semiconductor oxide surface but rather by use of nanostructured layer of very high roughness factor (surface area). Therefore, bulky layer of ZnO were replaced with nanoporous ZnO layer as a photoelectrode (Khalil, 2011).

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EVALUATION OF RADIOPROTECTIVE EFFECT OF GONGRONEMA LATIFOLIO LEAF EXTRACT ON WHOLE-BODY IRRADIATED WISTAR ALBINO RATS

ABSTRACT

The purpose of the study was to evaluate the radioprotective effects of Gongronema latifolio (GL) leaf extract on a whole-body irradiated wistar albino rats. A prospective experimental and cross-sectional design was adopted for this study and it included a control group and experimental group. Part of the control group (normal control NC) was not irradiated neither was it administered with GL extract but the other part (experimental control EC) was only exposed to graded radiation doses (GRDs). In the experimental group, the pre-treatment group (PRT) received GL extract orally before being exposed to GRDs while post-treatment group were exposed to GRDs before receiving GL extract orally.

Phytochemical analysis of GL extract was done to re-determine the bioactive constituents of the extract. Physical changes were observed and recorded in all the groups using weight loss as an index. The blood samples of the animal groups were collected before and after irradiation (IR) for following analysis namely liver function test (LFT) {which includes-Alkaline phosphase (ALP), Alanine amino-transferase (ALT), Aspatate amino-transferase (AST)}, and antioxidant enzymes tests like Malondialdehyde (MDA), Glutathione (GSH), Catalase (CAT) and Superoxide dismutase (SOD)}.

The result of the phytochemical analysis revealed the presence of the following bioactive agents- alkaloids (3.11mg/g), tannins (2.43mg/g), flavonoids (1.31mg/g), phenols (1.10mg/g) and saponin (0.8mg/g). Body weight of the rats exposed to 6Gy in EC (51g) significantly (p<0.05) decreased when compared to NC (115g) and PRT (70g) but not significantly (p>0.05) different from PST (60g) group. ALP mean levels recorded in rats exposed to 4Gy increased (p<0.05) significantly in EC (74iU/L) when compared to PRT (37iU/L), PST (43iU/L) and NC (39iU/L) group on day 8 after IR. ALT mean level for rats exposed to 4Gy elevated (p<0.05) significantly in EC (50iU/L) relatively to PRT (31.67iU/L), PST (38.67iU/L) and NC (37iU/L) on day 8 after IR. MDA activity levels for rats exposed to 6Gy significantly (p<0.05) increased in EC (70%) relatively to PRT (35%), PST (59%) and NC (36%) on day 8 after IR. For rats exposed to 2Gy, GSH % activities decreased (p<0.05) significantly in EC (26%) when compared to PRT (59%) and NC (69%) on day 8 after IR. For rats exposed to 4Gy, CAT % activities significantly (p<0.05) decreased in EC (31%), PRT (49%) and PST (44%) relatively to NC (79%) on day 8 after IR. For rats exposed to 2Gy, SOD % activities decreased significantly in EC (29.33%), PRT (50.67%) and PST (40.67) when compared to NC (75%) on day 8 after IR.

Consequently, the result obtained suggested that GL extract emeroliates oxidative stress induced by ionizing radiation, thus affirming its radioprotective potentials. The result also demonstrated that the extract was more effective in PRT group relatively to PST group

CHAPTER ONE

INTRODUCTION

1.1 Background of the study

With the discovery of x-rays in 1895 and radioactivity in 1896, the biologic effects were also observed shortly after. Within the first six months of its use in treating patients, several cases of erythema, dermatitis and alopecia were already reported among x-ray operators and their patients. The first report of a skin cancer ascribed to x-rays was reported in 1902,  followed eight years later by experimental confirmation, Bushberget al., (2002).

Radiation medicine is one of the major sources of ionizing radiation due to its numerous applications in the hospital. Other sources of radiation exposure include radon in houses, contamination from weaponstesting sites, nuclear accidents and cosmic rays.Today, ionizing radiation is not only employed in treatment of diseases and industry but also in developing new varieties of high-yielding crops and enhancing storage period of food materials. Radiotherapy is one of the common sources of ionizing radiation and more so one of the most common modality used for treating human cancer. About 80% of cancer patients need radiotherapy at some time or the other either for curative or palliative purpose, Cherupally et al., (2001). It is essentially used in the treatment of a number of malignancies, but frequently its use is limited due to its adverse effects on normal tissue.

The effects of radiation on human cells/tissue can be divided into somatic and genetic effects. Somatic effects are harms exposed individual suffer during their life time such as radiation induced cancers, opacification of the eye etc, while genetic effects are radiation induced mutation to an individual genes and DNA that can contribute to the birth defective descendants Podgorsak, (2005). Somatic effects of radiation exposure can be classified as either stochastic or non-stochastic. A stochastic effect is the effect in which the probability of the effect, rather than its severity, increases with dose. Radiation-induced cancer and genetic effects are stochastic in nature. Stochastic effect is believed not to have a dose threshold. In non-stochastic effect, there is a threshold dose below which the effect is not seen. Cataract, erythema, fibrosis and hematopoietic damage are some of the non-stochastic effects that can result from large radiation exposure.

Radiation interactions that produce biologic changes are classified as either direct or indirect action. The change takes place by direct action if biologic macromolecules such as deoxyribonucleic acid (DNA), ribonucleic acid (RNA) or proteins become ionized or excited by an ionizing particle or photon passing through them or near them.The DNA damages caused per Gray are about 1000 single strand breaks (SSB), 40 double strand breaks and 950 base depurination. Roughly 4.4 x 107 single strand breaks, 1.4 x 107 double strand breaks and 1.1 x 107base lesion per year occur per mammalian cell, Fleck, et al,.(1999). Indirect effects are the result of radiation interactions within the medium (e.g. cytoplasm or water) which creates highly reactive free radicals chemical that in turn interact with the target molecule, Bushberget al., 2002). Because 70% to 85% of the mass of living system is composed of water, the vast majority of radiation-induced damage from medical irradiation is mediated through indirect action on water molecules. Exposure of biological tissues to ionizing radiation immediately leads to ionization and excitation of their constituent atoms. The molecules where the atoms reside then dissociate, resulting in so called free radicals, Mayles et al., (2007). This free radicals are reactive oxygen species such as hyoxyl radical (OH), superoxide radicals ( ), singlet oxygen and peroxyl radicals (ROO) in irradiated tissue that incite several pathophysiological changes in the body, Maurya, et al., (2011).

Free radicals can diffuse in the cell, producing damage at locations remote from their origin. They may inactive cellular mechanisms directly or via damage to genetic material (DNA and RNA), and they are believed to be the primary cause of biologic damage from low linear energy transfer (LET) radiation, Bushberg et al., (2002). It is estimated that two-thirds of DNA damage is caused indirectly by scavengeable radicals (Root and Okada, 1972), as reported in lobachevsky, et al., (n.d).Generally ionizing radiation causes either excitation or ionization or both to atoms and molecules which lead to the following conditions.

  • Generation of free radicals as mentioned earlier.
  • Breaking of chemical bonds.
  • Formation of new chemical bonds and cross-linkage between macromolecules.
  • Damage to biomolecules (e.g. DNA, RNA, Lipids, Proteins) which controls or regulates vital cell processes.

The detrimental consequences of irradiation (IR) of cells and tissues can be encountered in cancer radiation therapy. Apart from normal tissue damage, another issue associated with cancer radiotherapy is the potential for emergency of secondary radiation-induced cancers, affecting more than 1% of patients (Hall, 2006).Severally protective mechanisms have been adopted in radiotherapy to reduce oxidative stress in patients and it includes;

  • Physical protection (E.g. Conformal radiotherapy, intensity modulated radiotherapy IMRT etc).
  • Biological protection (E.g. hyperfractionation and Ultrafractionation).

Attempts have also been made to protect personnel working inradiation medicine departments, radiopharmaceutical centers, nuclear power operations, aviations, uranium miners and other sources of ionizing radiation through the provision of the following; personal dosimeter, shielding devices, radiation detection equipment and other safety procedures, policies etc so as to ensure safety of patient, occupational staff and the general public. But the truth is thationizing radiation and radioactive substances are natural and permanent features of theenvironment,and thus the risks associatedwith radiation exposure can only be restricted and cannot be eliminated entirely.

Consequently, attempt to mitigate radiation toxicity in normal cells/tissues and in a whole organism are of significant clinical importance and an area of active research, considering the fact that ionizing radiation is on increase in numerous aspect of human life. There isexigency to develop and improve on another protective mechanism aside from the ones mention earlier that can mitigatenormal tissues from toxic effects of radiation.It has also been considered realizable that radiation therapy for cancer patients could be enhanced by the use of radioprotectors to protect normal tissues from unwanted radiation exposure.

Radioprotectors are compounds that are designed either to mitigate or prevent the damage caused by radiation in normal tissue. These compounds are often antioxidants and must be present before or at the time of radiation for effectiveness. It has also been found in the studies that chemical agents given after radiation exposure may assist in DNA repair activities, reduce inflammation and persistent radiation-induced oxidative stress and facilitate death pathways (apoptosis) of damaged cells, Kumud et al.,(2014). Other agents, termed mitigators, may be used to minimize toxicity even after radiation has been delivered, Deborah et al., (2010).

A number of compounds have been evaluated under the anti-irradiation drug development program, in 1948 for the first time, Patt et al., reported that cysteine is an effective radioprotector and showed that it can protect mice from harmful effects of total body x-ray irradiation when administered before radiation exposure. Badr et al., (1999) in their study suggested  that melatonin administration confers protection against damage inflicted by radiation when given prior to exposure to irradiation and not after, and supports the contention that melatonin radioprotection is achieved by its ability as a scavenger for free radicals generated by ionizing radiation. The radioprotective effect of abana, following a total body irradiation was studied by Baliga et al., (2004). Their result indicates that the radioprotective activity of abana may be due to free radical scavenging and increase GSH levelin the irradiated mice.

Several chemical compounds have been synthesized and tested for their radioprotective ability (Sweeney, 1979). The major disadvantage of some these compounds has been their high toxicity at the optimum protective dose (Sweeney,1979), which forestall their effective use in man.

Gongronema latifolium (GL) is an edible plant, less toxic, relatively cheap and available, thus, it is considered a possible radioprotective material. This study therefore aims at providing information on the radioprotective effects of GL on wistar albino rats whose whole-bodies were exposed to different doses of radiation.

  • Objectives of the study
  • This research investigates the possible radioprotective effect of Gongronema latifolio(GL) extract on a whole-body irradiated wistar rats through the following specific objectives.
  1. Tore-determine the phytochemical constituent of GL extract, so as to find out the bioactive constituents of the leaves.
  2. To observe any physical changes following graded doses of radiation to wistar albino rats.
  3. To determine any radioprotective effects of GL by measuring changes in liver enzymes following exposure to graded radiation doses (GRDs).
  4. To determine lipid oxidative degradation using malondialdehyde (MDA) as an index for radiation damage in un-irradiated and radiated animal groups.
  5. To determine the scavenging of free electron activity in all the animal groups following exposure to graded radiation doses by measuring the antioxidant enzymes.
  6. To compare the radioprotective effects of GL extract in both pre-treated animals and post-treated animals exposed to radiation.

1.3 Justification of the study

So far it is only few com­pounds that are radio­protectors registered forhuman use that has shown good radioprotective effects.However, they have significant shortcomings including relatively high toxicity and unfavorable routes of administration, which negatively affect their application and efficacy,(Lirenet al., (2010).

  • This very study will be a contribution in the search for new cost effective and relatively less toxic radioprotectors.
  • This study will provide information on whether latifolio can serve as prophylactic agent, mitigator or therapeutic agents, in whole-body irradiated rats.
  • Results obtained in this study will also contribute significantly to the growing search for radioprotectors.

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EFFECT OF MAGNETIC FIELD ON THE THERMAL CONDUCTIVITY OF SINGLE CRYSTAL OF YBa2Cu3O7-

ABSTRACT

This research investigated the effect of magnetic field on the thermal conductivity of high temperature type II superconductors. The result suggested that the thermal conductivity of high temperature type II superconductor YBa2Cu3O7- decreases as the applied magnetic field increases at a given temperature. We also found out that the superconducting energy gap of YBa2Cu3O7- decreases in response to increasing temperature and applied magnetic field. At a critical temperature of about 100K, we noted a sharp decrease in the energy gap of the substance. This implies that, the superconducting energy gap decreases in response to increase in temperature until at a critical temperature of about 100K,the material transits to normal state, thus resulting to increase in superconducting energy gap again. Our finding also revealed that specific heat of YBa2Cu3O7- is proportional to electron density.

CHAPTER ONE

General Introduction

  • Introduction and Discovery of Superconductivity

             The phenomenon of superconductivity was first observed by Kamerlingh Onnes in Leiden in 1911[1], three years after he liquefied helium gas. He then measured the electrical resistivity of metals such as gold, platinium and mercury. He found that the electrical resistivity of mercury vanished almost completely below 4.2K. The phenomenon by which a material loses all its electrical resistivity below a certain temperature is called superconductivity [2]. The temperature at which this occurs is known as the critical or transition temperature and it is normally denoted by Tc. At temperatures below the critical temperature, the superconducting electrons are ordered and therefore, do not carry heat. Thus, the ordered nature of superconducting electrons reduce the thermal conductivity of superconductors since there is no exchange of heat energy due to non- interactive nature of the super- conducting electrons with the lattice [3].

Superconductivity occurs in many metallic elements of the periodic alloys, and inter-metallic compounds at either low or high temperature. The search for new superconductors is an ongoing process by material scientists with superconducting transition temperature (Tc) above 30K in a mixture of lanthanum and barium-copper oxide [4] La2-x­BaxCuOx . High temperature superconductors, otherwise known as high-Tc superconductors were first discovered by Bednorz and Müller in 1986 [4].  Attempts to substitute yittrium (Y) for lanthanum (La) resulted in a polyphase mixture containing a new superconductor with Tc ≈ 90K [5]. Several other copper oxide superconductors were discovered, some with   Tc  above  120K [6]. Magnesium dibromide MgB2 was found to be superconducting with Tc of 39K. [7]

Anderson identified three essential features of the new superconductors [8]. First the materials are quasi–two dimension (2D); the key structural units seem to be the presence of CuO2 plane and the interplane coupling is very weak. Second, high–Tc superconductivity is created by doping a “Mott” insulator. A Mott insulator is a material in which the conductivity vanishes as temperature tends to zero, even though band theory would predict it to be metallic [9]. Third, Anderson proposed that the combination of proximity to a Mott insulating phase and low dimensionality would cause the doped material to exhibit fundamentally new behaviour, not explicable in terms of conventional metal physics.

Generally, superconductors can be categorised into type I and type II superconductors. In type I superconductors, the transition from superconducting state to normal state in the presence of applied magnetic field is very sharp while in type II superconductors, the transition from super-conducting state to normal state in the presence of applied magnetic field takes place after going through a mixed state region. Table 1.1 gives the transition temperature (  Tc  ) and the year of the discovery of some novel superconductors.

 

Table 1.1 High Temperature Superconductors, Tc and Year of Discovery     

Superconductors Tc(K) Year of Discovery        Reference
(La0.9Ba0.3)2CuO4- at 1Gpa 52     1986                                 [4]
YBa2Cu3O7- 95     1986                                [4]
Bi2Sr2Ca2Cu3O10 108     1988                                [10]
Tl2Ba2Ca2Cu3O10 127     1988                                [11]
HgBa2 Ca2 Cu3 O8+ 133     1993                                [12]
Hg Ba2 Ca2 Cu3 O8+ at 25Gpa 155     1993                                [13]
MgB2 39     2001                                [14,15]
LaO1-xFxFeAs 26     2008                                [16]
SmFeAs 55     2008                                [16,17]

 

Most of the cuprate superconductors were derived from YBa2Cu3O7- by replacing yittrium with either bismuth (Bi), thalium (Tl )or mercury (Hg) or barium (Ba) with lead (Pb), for example. It is therefore necessary to examine the crystal structure of YBa2Cu3O7-in some detail.

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EFFECT OF INTERSTELLAR MEDIUM ON RADIO PULSAR SPIN-DOWN PROPERTIES

ABSTRACT

A statistical analysis of a large sample of 668 radio pulsars was undertaken in other to investigate the possible dependence of interstellar medium (ISM) parameters [dispersion measure (DM) and rotation measure (RM)] on pulsar spin-down parameters [rotation period ( ) and spin-down rate ( )]. The existence of such relationship will have a far reaching implication on the theories of pulsar birth and evolution. A simple descriptive analysis of the data reveals that the sample is quite heterogeneous, consisting of normal and recycled millisecond pulsars. Specifically, the published values of , , DM and RM for objects in the sample were found to vary over a wide range: ~ 0.002 – 9 s, 3 × 10-21 – 2 × 10-11 ss-1, 2 – 1100 cm-3pc and -3000 – 2400 radm-2, respectively, with the corresponding mean values of ~ 0.69 ± 0.02 s, (9.94 ± 0.05) × 10-14 ss-1, 181 ± 7 cm-3pc and 157 ± 10 radm-2. Scatter plots of DM and RM (irrespective of sign) against  reveal large amplitude (~ 3 orders of magnitude) scatter in the ISM parameters superimposed on a striking trend in which pulsars with large values of  (young pulsars), on average, are characterized by large DM and |RM| values. A simple regression analysis of the DM/|RM| –  data yields a moderate correlation (with correlation coefficient r ~ 0.5). A simple interpretation of the moderate DM/|RM| ‒   relationship is that objects with large  (corresponding to young pulsars) are, on average, located in a region of ISM with high electron density content (in this case, the galactic plane). On the other hand, smaller values of , DM and |RM| correspond to relatively older pulsars located in regions farther away from the galactic plane (with low electron density content). The DM/|RM| ‒   correlation increased significantly (with correlation coefficient r ~ 0.95), when mean values of the parameters were employed in the analysis. The observed large scatter in the ISM data highlights the complex nature of the electron content distribution in the ISM and the large dispersion in both the magnitude and direction of pulsar space velocities. Similar analysis did show any appreciable dependence of both DM and RM on the pulsar rotation period. Our analysis also reaffirms the existence of a strong correlation (r ~ 0.7) between the DM and RM parameters, which are used to characterize the ISM.

CHAPTER ONE 

INTRODUCTION 

1.1 What are Pulsars?

            A pulsar is a highly magnetized, rapidly rotating neutron star that emits beams of broad band electromagnetic radiation. This radiation can only be observed when the beam of emission sweeps across the earth, much the way a lighthouse can be seen when the light is pointed in the direction of an observer. The events leading to the formation of a pulsar begin when the core of a massive (> 10 ) star is collapsed into a neutron star during a supernova explosion, where  is the mass of the sun which is ~ 2  1030 kg. The neutron star retains most of the angular momentum and only a tiny fraction of the size of its progenitor star. The sharp reduction in the stellar moment of inertia results in significant amplification of the rotation speed of neutron stars. Beams of radiation are emitted along the magnetic axis of the pulsar as it spins about the rotation axis of the neutron star. The magnetic axis of the pulsar determines the direction of the electromagnetic beam, with the magnetic axis not necessarily aligned with its rotation axis. This misalignment causes the beam to be modulated by the rotation of the neutron star. The beam originates from the rotational kinetic energy of the neutron star, which generates an electric field from the movement of the very strong magnetic field, resulting in the acceleration of protons and electrons on the star surface and the creation of an electromagnetic beam emanating from the poles of the magnetic field.

The rotation period ( ) of most pulsars are known to increase at constant rates as the pulsars convert their rotational kinetic energy into electromagnetic radiation and particle wind according to the spin-down law (e.g. Manchester and Taylor, 1977):

(1.1)

where  is the braking index,  is the pulsar spin-down rate and  is usually assumed to be a constant. When a pulsar’s spin period slows down sufficiently, the radio pulsar mechanism is believed to turn off (the so-called “death line”). This turn-off seems to take place after about 10 – 100 million years, which means that of all the neutron stars in the 13.6 billion years age of the universe, around 99% no longer pulsate (Young et al., 1999). There are currently over 2000 known radio pulsars and their rotation periods are in the range of about 1.5 ms and 8.5 s (Seiradakis and Wielebinski, 2004; Manchester et al., 2005).

1.2 History of Discovery of Radio Pulsars

            The discovery of pulsars by Professor Anthony Hewish and Jocelyn Bell Burnell in 1967 is one of the most important and dramatic advances in the history of radio astronomy (Hewish et al., 1968). The story began in 1965 when Hewish started the construction of an 82 MHz (3.7 m wavelength) array of 2048  dipoles for scintillation studies of compact radio quasars. The dipoles were set horizontally several wavelengths above the ground in regular rows covering an area of 20,000 square metres. Graduate students at Cambridge University helped in the construction of the radio antenna. One of them, Jocelyn Bell from Ireland, was responsible for the network of thousands of cables (transmission lines) between the antenna and receiver. The array was physically fixed but by introducing appropriate phasing with different cable lengths, the beam could be shifted in declination. The earth’s rotation provided scanning in right ascension. Hewish had designed the antenna to investigate the compact quasar radio sources by their scintillation as produced by the irregular structure of the interplanetary medium.

In early measurements by Hey et al. (1946), fluctuations were observed in the radio emission from Cygnus A, which are due to inhomogeneities in the earth’s ionosphere. Hewish (1955) and Vitkevitch (1955) noted that the outer solar corona scattered radio waves, increasing the apparent diameter of radio sources. Both coronal scattering and ionospheric-induced fluctuations are similar scintillation phenomena but only differ in scale. Beginning in 1962, Hewish, Scott and Wills (1964) noted rapid fluctuations (with periods of a few seconds) in the intensity of a number of radio sources, notably 3C48, 3C119, 3C138 and 3C147, as measured at 178 MHz. Two of these sources were already known to possess very small angular diameters. It was concluded that the fluctuations were a scintillation effect produced by the interplanetary medium and is most severe for sources of angular diameter < 1 arcsec and at wavelengths of more than 1 m. The effect was found to become stronger with decreasing angular distance to the sun and the fluctuation rate faster with increasing wavelength. The belief that this scintillation effect could provide a convenient technique for estimating the angular diameter of radio sources in the range < 1 arcsec motivated the new antenna array by Hewish and his co-workers.

The plan was to survey most of the sky north of declination -080 once a week, keeping this region under constant surveillance. By July, 1967 construction of the array was completed and observations were begun with output recorded at short time constant with a pen-on-paper chart. Jocelyn Bell was given the responsibility of analyzing the 100 s of meters of chart paper flowing from the recorder each week in order to note times and declinations of chart deflections having a rapid fluctuation or scintillation. In October, 1967, she noted some unusual deflections lasting a minute or two which she could not readily identify as either a scintillating quasar or as interference from a terrestrial source, e.g. a gasoline engine ignition. Recalling that she had seen something like it several weeks earlier, she searched back through the records and found that it had appeared several times before and at the same declination and right ascension. This suggested that it was of celestial and not terrestrial origin, but curiously, the signals appeared conspicuously near midnight when interplanetary scintillation drops to a very low value.

Systematic investigation of these signals began in November, 1967. High speed recordings showed that they consisted of a series of pulses of about  second duration with a repetition period of 1.337 s which was maintained with astonishing precision. The thought that the signal might be the beacon of an extraterrestrial civilization was entertained at one point, but lack of Doppler variation in the pulse rate from planetary motion around a star and the discovery of three more pulsing signals elsewhere in the sky seemed to rule out this possibility. Announcement of the discovering of these pulsating  objects or pulsars appeared in the February 24, 1968 issue of “Nature” with a tentative explanation offered that the sources were oscillating white dwarf or neutron stars (Hewish et al., 1968). The discovery of pulsars with periods less than  second and a spin-down rate led to the identification of pulsars as rotating neutron stars.

This serendipitous discovery of pulsars was entirely unexpected but so was Karl Guthe Jansky’s discovery of radio emission from our galaxy that marked the beginning of radio astronomy, as well as Arno Penzias and Robert Wilson’s discovering of 3 K sky background. It is remarkable that in all the three cases (pulsars, galactic radio emission and 3 K), the design of the instrument and the circumstances of its use were almost ideally suited for the discovery. Many astronomers around the world joined in further observations and studies of the pulsar and in searching for new ones, generating a vast literature on pulsars.

1.3 Classification of Pulsars

              There are three generic classes of pulsars, based on the possible energy source which powers their emissions.

  • Rotation-powered pulsars are powered by the rotational kinetic energy of the underlying neutron stars. The Electromagnetic radiation emitted can be across a large portion of the electromagnetic (EM) spectrum, generally from the x-ray region down to the radio region. Typically the radiation is seen in the radio region of the EM spectrum. As such, rotation-powered pulsars are referred to as radio pulsars. There are mainly two groups or types of rotation-powered pulsars which include the normal and the millisecond radio pulsars. The normal radio pulsars are mostly isolated, fast spinning neutron stars. More than 1000 members of this class have been discovered and they all have rotation periods in the range of ~ 0.03 to 8.5 s. The characteristic age of normal radio pulsars is of the order of 108 yr while their surface magnetic field is about 1012 G (Seiradakis and Wielebinski, 2004). More than 90 percent of the known normal radio pulsars have period derivative 10-17 ss-1, however objects with ~ 10-19 ss-1 also exist. Normal radio pulsars are generally expected to spin down steadily with time. However, the normal radio pulsars residing in the globular clusters (Manchester et al., 1985; Wolszczan et al., 2000) are known to be spinning up instead, presumably owing to the gravitational interaction between the pulsars and the other densely packed stars in the cluster. When these interactions result in acceleration in excess of the pulsar spin-down rate, there is a net acceleration which corresponds to spin-up of the pulsar.

Radio pulsars whose spin periods are less than 25 ms (e.g. Kaspi, 1997), and which, according to the standard evolutionary model (e.g. Bhattacharya and van den Heuvel, 1991) acquired these fast spin rates after an episode of “spin-up”, probably through mass and angular momentum accretion from a low mass binary companion are referred to as millisecond pulsars. The fastest millisecond pulsar found to date has a period of 1.56 ms (Backer et al., 1982). The origin of millisecond pulsars is still unknown. The leading theory is that they begin life as longer period pulsars but are spun up or recycled through accretion (Bhattacharya, 1996; Lyne and Smith, 1998). For this reason, millisecond pulsars are sometimes called recycled pulsars. About 40 members of this class have been observed and a significant percentage of them are in binary systems with main sequence stars (Kaspi et al., 1994), or degenerate stars – white dwarfs (Lyne and Smith, 1990) or neutron stars (Taylor and Weisberg, 1982; Nice et al., 1996). The characteristic age of millisecond pulsars is slightly above 109 yr (Seiradakis and Wielebinski, 2004). Millisecond pulsars are characterized by very small spin-down rates, < 10-17 ss-1 and relatively weak surface magnetic field,  ~ 108 – 109 G. The low surface magnetic field has been associated with the accretion processes, in which the field is believed to be appreciably buried in the accreted material. However there is, as yet, no physical mechanism which plausibly explains how the magnetic field of a neutron star could significantly decay (Bhattacharya and Srinivasan, 1995).

  • X-ray pulsars are powered by energy released during mass accretion from the binary companion and are generally classified into two: High-Mass and Low-Mass X-ray Pulsars. In High-Mass X-ray Binaries (HMXBs), the mass of the companion is greater than 10 solar masses (e.g. Joss and Rappaport, 1984). Examples of HMXBs are LMC X-4, Cen X-3 and SMC X-1. Their rotation periods range from 0.069 to 835 s, while the orbital periods have been found to lie between 0.2 and 187 days. HMXBs are characterized by high surface magnetic fields of ~ 1012 G (Lyne and Smith, 1998). A subclass of X-ray pulsars, in which the mass of the companion is usually less than 1 solar mass, is known as the Low-Mass X-ray Binaries (LMXBs). These objects are more difficult to study owing to the fact that only little light, if any, can be observed directly from the companion star. Orbital periods are generally less than 1 day. X-ray binaries are characterized by rapid decrease in the rotation periods (that is they spun-up with time). This observation suggests that the torque responsible for the spin-up, the accretion torque, could be orders of magnitude greater than the magnetic braking torque (Lyne and Smith, 1998).
  • Magnetars are presumably powered by the decay of hyper-strong fields, whose decay timescale is of order ~ 103 – 104 years (Thompson and Duncan, 1996). They are highly magnetized neutron stars in fact much more than conventional neutron stars by a factor of up to 100 or more, with magnetic fields in the order of 1014 Magnetars are capable of emitting bursts of both x-rays and gamma rays through the decay of their very strong magnetic field. The very strong magnetic field of a magnetar is thought to be inherited when the neutron star is first created during a supernova explosion (Duncan, 1998). These magnetars could manifest as soft gamma repeaters (SGR) where x-ray stars sporadically emit bright, short (0.1 s) repeating flashes of low-energy gamma rays and anomalous x-ray pulsars (AXPs) which are slowly rotating pulsars with periods of 6 – 12 seconds (Karttunen et al., 2006). The Fermi space Telescope has uncovered a subclass of rotation-powered pulsars that emits only gamma rays (Atkinson, 2008). There have been only about one hundred gamma-ray pulsars identified out of about over 2000 known pulsars (Atkinson, 2008). Although all the three classes of objects are neutron stars, their observable behaviour and the underlying physics are significantly different.

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COSMIC RAYS VARIABILITY IN THE MID AND HIGH LATITUDES DURING SOLAR QUIET DAYS

ABSTRACT

We have studied the variability of Cosmic rays flux during solar quiet days at mid and high latitudes. By using the five (5) quietest days for each month, the monthly mean diurnal variation of cosmic ray anisotropy have been derived for the period 1981-2007, which covers part of cycles 21, 22 and 23.  These quiet days are days during which the sun is relatively magnetically quiet, leading to less anisotropic behavior in the diurnal flux of cosmic rays measured on the earth’s surface. Four stations (Rome, Oulu, Inuvik and Thule) were used in this study to understand the important features of the high latitude and mid-latitude diurnal wave, and how solar and geomagnetic activity may be influencing the wave characteristics. Cosmic ray wave characteristics were obtained by discrete Fourier transform (DFT).  The mean, diurnal amplitude, phase and dispersion for each month’s diurnal wave were calculated and profiled. There was clear indication that the terrestrial effect on the variability of the monthly mean was more associated with geomagnetic activity rather than rigidity of the cosmic rays.  Correlation of the time series of these wave characteristics with solar and geomagnetic activity index showed better association with solar activity.

CHAPTER ONE

1.1     INTRODUCTION

Cosmic rays are high-energy charged particles originating mainly from the outer space. They travel at nearly the speed of light and strike the earth from all directions. Most cosmic rays are nuclei of atoms ranging from the lightest to the heaviest elements in the periodic table. Cosmic rays also include high energy electrons, positrons and other subatomic particles. There are broadly three types of cosmic rays; solar cosmic rays (SCRs), galactic cosmic rays (GCRs) and anomalous cosmic rays (ACRs). SCRs originate from the sun and have energy within the range (kilo-electron volt) KeV < 10 to 100 MeV (Mega-electron volt) occasionally reaching 1GeV (Giga-electron volt). GCRs originate from supernovae explosions. They have energy within the range 100MeV < E < 10GeV. ACRs originate from neutral interstellar atoms that have been ionized by solar UV radiation after entering the heliosphere. They have energies of 107 – 108 eV. Cosmic rays attract great interest due to the damage they inflict on electronics and life outside the protection of an atmosphere and a magnetic field, they also provide important channels for astrophysical information.

1.2       DISCOVERY AND EARLY RESEARCH

Cosmic rays were discovered in 1912 by Victor Hess when he found that an electroscope discharged more rapidly as he ascended in a balloon. He attributed this to a source of radiation entering the atmosphere from above and in 1936 was awarded a noble prize in physics for his discovery. For some time it was believed that the radiation was electromagnetic in nature (hence the name cosmic “ray”) and some textbooks still incorrectly include cosmic rays as part of the electromagnetic spectrum. However, during the 1930’s it was found that cosmic rays must be electrically charged because they are affected by the earth’s magnetic field.

From the 1930s to the 1950s before man-made particle accelerators reached very high energies, cosmic rays served as source of particles for high energy physics investigations which led to the discovery of subatomic particles that included the positron and muon. Some of these applications have continued ever with the dawn of space age. The main focus of cosmic ray research has been directed towards astrophysical investigations of where cosmic rays originate, how they get accelerated to such high velocities, what role they play in the dynamics of the galaxy and what their composition tells us about matter from outside the solar system. To measure cosmic rays count rate before they have been slowed down and broken up by the atmosphere, research is carried out by instruments mounted on spacecraft and high altitude balloons, using particle detectors similar to those used in nuclear and high energy physics experiments.

1.3       COSMIC RAY COMPOSITION

Cosmic rays include essentially all of the elements in the periodic table; about 89% of the nuclei are hydrogen (protons), 10% helium and about 1% other heavier elements. The common heavier elements (such as carbon, oxygen, magnesium, silicon and iron) are present in similar relative abundances as in the solar system but there are important differences in elemental and isotopic composition that provide information on the origin and history of galactic cosmic rays. For example, there is a significant overabundance of the rare elements Li, Be and B produced when heavier cosmic rays such as carbon, nitrogen and oxygen disintegrate into lighter nuclei during collisions with the interstellar gas. The isotope 22Ne is also overabundant, showing that the nucleosynthesis of cosmic rays and solar system material differ.

1.4       COSMIC RAYS IN THE SOLAR SYSTEM

Just as cosmic rays are deflected by the magnetic field in interstellar space, they are also affected by the interplanetary magnetic field embedded in the solar wind (the plasma of ions and electrons blowing from the solar corona at about 400km/sec) and therefore have difficulty reaching the inner solar system. Spacecrafts (e.g. voyager 1 and 2) venturing out towards the boundary of the solar system has found that the intensity of galactic cosmic rays increases with distance from the sun. As solar activity varies over the 11-year solar cycle the intensity of cosmic rays at Earth also varies in anti-correlation with the sunspot number.

The sun is also a sporadic source of cosmic ray nuclei and electrons that are accelerated by shock waves traveling through the corona as solar flares thereby releasing magnetic energy; during such occurrences, the intensity of energetic particles in space can increase by a factor of 102 to 106. Such solar particle events are much more frequent during the active phase of the solar cycle. The maximum energy reached in solar particle events is typically 10 to 100MeV, occasionally reaching 1GeV (approximately once a year) to 10GeV (approximately once a decade). Solar energetic particles can be used to measure the elemental and isotopic composition of the sun, thereby complementing spectroscopic studies of solar material.

1.5       COSMIC RAYS ON EARTH

When high energy cosmic rays undergo collisions with atoms of the upper atmosphere, they produce a cascade of “secondary” particles that shower down through the atmosphere to the earth’s surface. Secondary cosmic rays include pions (which quickly decay to produce muons, neutrinos and gamma rays), as well as electrons and positrons produced by muon decay and gamma ray interaction with atmospheric atoms. The number of particles reaching the Earth’s surface is directly related to the energy of the cosmic ray that strikes the upper atmosphere as low energy cosmic rays are blocked off by the atmosphere. Cosmic rays with energies beyond 1014eV are studied with large “air shower” arrays of detectors distributed over many square kilometres that sample the particles produced. The frequency of air showers ranges from about 100 per m2 for a year with energies > 1015eV to only about 1 per km2 for a century with energies beyond 1020eV.

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COMPARATIVE ANALYSIS OF CALCULATED AND MEASURED ENTRANCE SKIN DOSE OFCOMMON RADIOGRAPHIC PROCEDURES IN BENUE STATE TEACHING HOSPITAL MAKURDI BENUE STATE

CHAPTER ONE

INTRODUCTION

  • Background of the Study

Life on earth has developed with ever present background radiation. It is not a new thing invented by the wit of man; radiation has always been there (Hall, 2012). Radiation is a fact of life. It is all around us all the time, hence, we live in a naturally radioactive world. Radiation could be defined as the energy that travels through space or matter in form of electromagnetic waves or photons or streams of radioactive particles (IAEA, 2005; Bushberg et al., 2002). Radiation can either be non-ionizing or ionizing, depending on its ability to ionize matter. Non-ionizing radiation does not produce ionization or ions in the medium through which it passes. It has enough energy to move atoms in a molecule around or cause them to vibrate, but not enough to remove them. Examples of non-ionizing radiation include visible ray, infrared rays among others. Ionizing radiation is a kind of radiation that is capable of transferring energy to the atoms of the material which it interacts with, changing their physical state and leaving them electrically charged or ionized. Ionizing radiation is categorized by the nature of the particles or electromagnetic waves creating the ionizing effect. Ionizing radiation has different ionization mechanisms, and may be grouped as directly or indirectly ionizing. Directly ionizing are those that carry a charge and can, therefore, interact directly with atomic electrons through coulomb forces (IAEA, 2005; Bushberg et al., 2002). Examples of directly ionizing particles are alpha particles, beta particles, electrons, protons and heavy ions. Indirectly ionizing are those that are electrically neutral and do not interact with atomic electrons through coulomb fores. Indirectly ionizing radiation (photons or neutrons) deposits energy in the medium through a two-step process:

  • First, a charged particle is released in the medium (photons release electrons or positrons, neutrons release protons or heavier ions)
  • Second, the released charged particles deposit energy in the medium through direct Coulomb interactions with orbital electrons of the atoms in the medium. Examples of indirectly ionization particles are X- rays and rays and neutrons (WHO, 2014; IAEA, 2005).

There are basically two sources of radiation: Natural and man-made or artificial radiation. Natural radiation is that which is natural and inevitably present in our environment. Humans are continuously irradiated by internal and external sources. Internal sources include the radionuclides that enter the body through food, water and air. External sources include space or cosmic radiation and terrestrial radiation.

Cosmic radiation consists of fast moving particles that exist in space and originate from a variety of sources, including the sun and other cosmic events in the universe. Cosmic rays are mostly protons but can be other particles or wave energy (CNR, 2012).

Terrestrial radiations emanate from naturally occurring radioactive elements present in varying amounts in all types of water, soils, air, rocks, food and in human body itself (Yussuf et al., 2012; Bushberg et al., 2002). Whatever its origin, radiation is ubiquitous in the environment (HPS, 2010).

Exposure to man-made radiation can also be from medical treatments and activities involving radioactive materials. The following are the most common sources of man-made radiation: medical sources, industrial sources, nuclear fuel cycle and industrial sources (CNR, 2012). However, medical radiation exposure such as diagnostic X-rays, nuclear medicine and radiation therapy constitute the largest man-made source of exposure to ionizing radiation to which humans are subjected (Sharifat and Olarinoye, 2009; Ng et al., 1998). The  average  dose  to  the  population  from  medical  exposure  is  estimated  to  be  about  0.2-2  mSv  per  year  in industrialized countries (UNSCEAR, 2000). Diagnostic X-rays used in hospitals for emergency cases and for routine physical examination are good examples of man-made radiation.

 

Diagnostic radiology is a rapidly developing branch of modern medicine. It has over the past few decades evolved into a highly sophisticated diagnostic tool; improving the imaging of human internal anatomy and detection of lesions which were previously impossible to detect. (Chougule and Hussain, 1993).  Despite its contribution to diagnosis, diagnostic radiology is burdened with the concern of the safety of patients and radiology staff. This is because the procedures of diagnostic radiology utilize X-ray which is ionizing in nature and it transmits a certain amount of risk to the patient and staff despite its usefulness. The harmful biological effects of X-ray have long been established (Lampinnen, 2000). It was estimated that diagnostic radiology and nuclear medicine contributed 96% to the collective effective dose from manmade sources in the U.K (NRPB, 1993). Similar estimate showed that this contribution was 88% in the U.S.A (NCRP, 1987).

 

The study of biological effects of X-rays on living tissues started soon after its serendipitous discovery by Wilhelm Roentgen in 1895. To reduce the untoward biological effects associated with X-ray and the dose delivered to patients during medical intervention, the dose has to be kept as low as possible while at the same time trying to obtain optimum image for accurate diagnosis (ICRP, 2005).

 

In view of the significant benefits from properly conducted medical exposures, the principal concern in radiological protection is therefore, the reduction of examinations that are either unlikely to be helpful to patient or involve high doses in order to meet specified clinical objectives. In order to achieve this, there is a need to optimize X-ray equipment and radiological techniques Patient dose measurement is an integral part of this optimization procedure (NRPB, 1990; Faulkner et al., 1999). Such optimization procedure will reveal X-ray facilities with high doses after which possible dose reduction measures may be specified. Dose measurement is also necessary so as to establish dose constraints, determine risk to patient and to justify the examination (Faulkner et al., 1999).

 

At the moment, researchers have shifted their interest in protecting both the patient and staff from harmful effect of radiation to improving the technology of the procedures and constant dose monitoring (Muhohora and Nyanda, 2001). Though, it was once thought that use of digital systems in diagnostic radiology would reduce radiation doses, studies so far conducted suggested otherwise. There is a tendency towards increased radiation doses with use of digital systems. The reasons cited include the fact that overexposure can go undetected, unlike with conventional film-screen combination, where the image turns dark indicating overexposure (Ng and Rehani, 2006). A case of overexposure was reported in some centers which used digital systems, there was an average of 68 exposures per examination in upper gastrointestinal fluoroscopic examinations compared with sixteen (16) exposures with conventional systems. (Axelsson et al., 2000). Also, Reiner et al. (2000), reported that in several United States hospitals the number of examinations per inpatient increased by 82% after transition to digital systems and the number of examinations per outpatient visit increased by 21% while the number of examinations per visit nationally decreased by only 19%. The implication of these statistics is increased radiation risk to both the patient and staff.

 

From the foregoing it is evident that transition to better technology has improved the diagnostic quality of the images and added more radiation risk, albeit minimally. Thus, medical physicists and radiation workers are left with the option of continually monitoring radiation doses delivered to patients with a view to keeping them reasonably low .One of the methods used for monitoring patient dose is the determination of Entrance Skin Dose (ESD) as proposed by the national protocol for patient dose measurement in diagnostics radiology (NRPB, 1992).

 

Radiation dose to patients represents an estimate of the likelihood of patients to develop stochastic radiation effects. Thus, the greater the dose absorbed, the greater the chances of stochastic effect, and may even reach a level that can elicit some non-stochastic effects. In view of this, the objective of radiation protection is to keep the probability of developing stochastic radiation effects to a minimum. This is achieved by constant dose monitoring to ensure that doses delivered per examination are within safe limits, but dosimetry is rarely routinely carried out in our radiology departments because of lack of equipment and personnel. Patients dose have always been measured using thermo-luminescence dosimeter (TLD) or ionization chamber. These two dosimeters though accurate, are relatively expensive, time consuming, a cumbersome and may intervene with patient exposure (Hanan, 2007).

 

Thermo-luminescent dosimeters (TLDs) have the advantage of being physically small, enabling them to be stuck directly and obstructively to the patient’s skin with little interference in patient’s mobility or comfort. They fully measure the radiation backscatter from the patient and do not obstruct useful diagnostic information. However TLD technique requires prolonged annealing and reading process. Furthermore, the use of TLD technique requires special equipment and thorough calibration facilities which may not be available in most X-ray departments (NRPB, 1992).

 

Ionization chambers are bulky and require connecting cables. They are usually difficult to attach in sufficiently close contact to the patient skin to ensure complete measurement of the backscatter radiation, severely restrict patient mobility and cast interfering shadows on radiographs. They are consequently not recommended for direct measurement of entrance skin dose on patients (NRPB, 1992).

 

A much easier and cost effective method of dose assessment can be done using calculation methods (Hanan, 2007). The method utilizing calculation by different formulae represents a viable option but the accuracy of these formulae has not been verified empirically. An empirical study which is the main scope of this research is therefore needed to establish the most accurate formulae to use in centers that lack equipment and personnel for dosimetry using various dosimeters.

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ANALYSIS OF GLITCH ACTIVITY IN ROTATING NEUTRON STARS

ABSTRACT

A total of 660 discrete jumps in the rotation frequency ( ) and the spin-down rate ( ) of about 140 pulsars were studied. Out of the 660 discrete jumps, 394 were classical glitches (the so-called macroglitches) and 266 were microglitches. The objects are grouped into normal radio pulsars, anomalous x-ray pulsars and recycled millisecond pulsars. A bimodal distribution was observed in many of the pulsar glitch parameters, namely the discrete absolute fractional jumps in the rotation frequency ( ), the entire absolute discrete jumps in the spin down rate (|Δ |), cumulative of the absolute jumps in the rotation frequency ( ), cumulative of the absolute fractional jumps in rotation frequency ) for macroglitches may suggest that  glitch events may be triggered by  dual glitch mechanism. The distribution of the entire absolute discrete fractional jumps in the rotation frequency (| |)  cumulative of the absolute jumps in the rotation frequency ( ) and the cumulative of the absolute jumps in spin down rate (∑|Δ |) of microglitches equally suggests that a glitch event is triggered by one mechanism. It was observed that some of the macroglitches have magnitudes in  (rotation frequency) which overlapped with the microglitches completely which suggest that some of the rotational jumps that was characterized as macroglitches by previous authors should have been recorded as microglitches since their glitch magnitude   . The distribution of the glitches over the spin down parameters shows that pulsars with characteristic age 3  4, rotational frequency of    0.9, spin down rate ) and surface magnetic field strength of 12  13 on logarithmic scales exhibit the highest frequency of macroglitches while those within the characteristic age 5  6 , rotational frequency of    0.4 , spin down rate of    and surface magnetic field strength of 11  12 on logarithmic scales exhibit the highest frequency of microglitches. From the regression analysis, it was observed that there was a strong positive linear relationship between ( )  (∑|Δ |)for the macroglitches and microglitches data when analysed separately and jointly. There was no correlation between  ( )    data for both samples. On the otherhand, there was a strong  (    | | correlation for the macroglitches and microglitches data when analysed separately and jointly.

 

CHAPTER ONE

GENERAL INTRODUCTION

1.0 An Overview of Rotating Neutron Stars

A neutron star is the core remnant of a supernova event, a violent explosion that marks the death of a massive (  to  , where  is mass of the sun) star. A typical neutron star is believed to be spherical in structure with a radius of about 12 km (Kaspi et al.,1994) and a mass of about 1.2  to 2.1  (Kramer et al., 2006). Neutron stars rotate and can emit broad band beams of electromagnetic radiations that are detected as pulsars. Pulsars are rapidly rotating highly magnetized neutron stars (Lorimer & Kramer, 2005). The beams of radiation are emitted along the magnetic axis of the pulsar as it spins about the rotation axis. The emitted radiations can be observed when the beam of emission sweeps across the earth much the same way a lighthouse can be seen when it is pointed in the direction of an observer (Lorimer et al., 2005). These pulsed emissions have been detected and studied over the whole electromagnetic spectrum ranging from the high energy gamma rays to the low energy radio waves (Lyne & Graham-Smith, 1998). Pulsars are well known for their stable rotation which allows them to be used as cosmic clocks. According to the data in Australia Telescope National Facility catalogue of pulsars, over 2500 pulsars have being discovered (Manchester et al. 2005).

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A STUDY ON THE EFFECT OF SOLAR ACTIVITY ON OZONE VARIATION IN LAGOS NIGERIA

CHAPTER ONE

  • INTRODUCTION

The earth’s climate is a dynamic system undergoing continuous change on seasonal, annual, decadal and longer timescales. Scientific evidence suggests that a complex interplay of natural and human-related forces may explain such climate variability and change. Some consequences of this variability are natural hazards such as earthquakes, volcanoes, landslides, floods, wildfires, extreme weather, coastal hazards, space weather plus major pollution events. Better preparation for any impacts due to climate variability and change requires better understanding of its causes and effects. Improved global observation is a fundamental need for filling knowledge gaps in climate science. Furthermore, a better understanding of greenhouse gas effects will greatly facilitate decision-making related to sustainable development of terrestrial, oceanic and atmospheric resources.

 

1.2            THE EARTH’S ATMOSPHERE

The earth’s atmosphere is a layer of gases surrounding the planet earth that is retained by earth’s gravity. It is the life giving blanket of the earth. It protects life on earth by absorbing ultra violet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night.

1.2.1          Composition

Dry air contains approximately (by volume) 78% nitrogen, 20.95% oxygen, 0.93% argon, 0.03% carbon dioxide, 1% water vapor and small amount of other gases.

1.2.2         Structure of the Atmosphere

The primary indices for stratifying the earth’s atmosphere are the variation in pressure, density, temperature and composition. Hence considering the thermal variation in the atmosphere, the earth’s atmosphere is structured into four layers, which are the: troposphere, stratosphere, mesosphere and thermosphere.

Troposphere: It extends from the surface of the earth to between 7Km at the poles and 17Km at the equator. It contains approximately 80% of the mass of the atmosphere. The tropopause is the boundary between the troposphere and the stratosphere. It is in the troposphere that life exists. It is characterized by a decrease in temperature with altitude, intense convectional heat current and turbulent motions. This temperature pattern in the troposphere stems from absorption of the energy from the sun by earth’s surface and its remittance upward as infrared heat waves.

 

Stratosphere: The stratosphere extends from the tropopause to about 51Km up the atmosphere. Temperature increase with height and this hinders turbulent motions. The stratopause is the boundary between the stratosphere and the mesosphere.  Because temperature rises with height in the stratosphere, the condition of warmer air above colder air exists. Such a condition is convectively stable. Vertical motions are therefore suppressed, leading to vertical stratification of the air masses it contains; hence the name stratosphere. This increase in temperature with height—the definition of an inversion–acts as a global cap on the weather. Convective motions  are limited to the height of the tropopause. Air parcels rising up from the surface through the troposphere hit the tropopause and flatten out almost as if it were a rigid lid

Mesosphere: The mesosphere extends from the stratopause to 80-85Km up the atmosphere. Temperature decreases with height in the mesosphere. The mesopause is the boundary between the mesosphere and the thermosphere and is noted to be the coldest region in the atmosphere.

Thermosphere: The thermosphere extends from the mesopause to about 350-800Km up the atmosphere. Temperature increases with height from the mesopause up to the thermopause in the thermosphere and after then remains constant.

 

Other layers within these four thermally stratified layers include:

The Ozone layer: It is contained within the stratosphere, precisely from about 15 to 30Km altitude.

The Ionosphere: It is the part of the atmosphere that is ionised by solar radiation and stretches from 50 to 1000Km.

 

1.3       OZONE LAYER    

The ozone layer is a belt of naturally occurring ozone gas that is found from 15 to 30 Kilometers above Earth and serves as a shield from the harmful ultraviolet radiation emitted by the sun. Ozone is a highly reactive molecule that contains three oxygen atoms. It is constantly being formed and broken down in the high atmosphere, 6.2 to31 miles (10 to 50 kilometers) above Earth, in the region called the stratosphere.

The ozone layer of the atmosphere protects life on Earth by absorbing harmful ultraviolet radiation from the Sun. If all the ultraviolet radiation given off by the sun were allowed to reach the surface of Earth, most of the life on Earth’s surface would probably be destroyed. Short wavelengths of ultraviolet radiation, such as UV-A and B are damaging to the cell structure of living organisms. Fortunately, the ozone layer absorbs almost all of the short wavelength ultraviolet radiation and much of the long wavelength ultraviolet radiation given off by the sun.

 

1.3.1   OZONE VARIATION

The interplay of ozone photochemistry and ozone transport processes gives rise to ozone variation at different latitudes and altitude. Generally, atmospheric variations could be classified into four time-scales namely: short-term, seasonal, interannual, and long term.

Short-Term Variability

Short-term variability refers to day-to-day and week-to-week variations. For example, the effects of the passage of a weather system are classified as short-term variability. A global map of ozone for a given day looks very much like a weather map with high and low ozone amounts corresponding to weather systems, though in the reverse (anti correlated) sense to high and low pressure systems. The map for the next day will show movement of both these weather systems and the ozone amounts. They are several types of short- term variability that affect ozone photochemical process rates in the stratosphere (especially the upper stratosphere). These include diurnal variations, variations in solar ultraviolet radiation, temperature driven fluctuations, and particle precipitation events that originate from electromagnetic storms on the Sun.

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ASSESSMENT OF OCCUPATIONAL EXPOSURE AND RADIATION PROTECTION IN SOME SELECTED WELL-LOGGING AND INDUSTRIAL RADIOGRAPHY FACILITIES IN NIGERIA

ASSESSMENT OF OCCUPATIONAL EXPOSURE AND RADIATION PROTECTION IN SOME SELECTED WELL-LOGGING AND INDUSTRIAL RADIOGRAPHY FACILITIES IN NIGERIA

 

CHAPTER ONE

INTRODUCTION

1.1        Background to the Study

Nigeria has, for a very longtime, engaged in the peaceful application of nuclear technology. The use of ionizing radiation, because of its unique properties, has considerably increased over the years in oil and gas industry.

Due to the adverse health effect when people are over-exposed to ionizing radiation, radiation is feared by many, worldwide, and Nigerians are no exception. This concern is even much higher with inhabitants living at close proximity to nuclear establishments and other facilities using ionizing radiation sources. What most people do not realize is that radiation is present everywhere, in everything in the environment and even in the bodies (Oyeyinka et al, 2012). There is cosmic radiation made up of protons, alpha particles and heavy nuclei bombarding the earth from space which, upon interaction with the atmosphere results into large assortment of secondary particles, including pie (π) and mu (µ) mesons, electromagnetic photons, neutrons, protons and electrons contributing high radiation dose burden to man even at sea level (Maduemezia et al, 2008).

Other natural radiation includes the terrestrial gamma rays from land, sea and walls of houses we live. Humans are also internally exposed from radiation emitted by radionuclides absorbed into the body through the consumed food (Oyeyinka et al, 2012). Examples of such radionuclides are potassium-40, heavy elements and carbon-14. Therefore, living isolated from radiation is almost impossible in the modern world as humans and animals are subjected to both natural and artificial radiation in the environment, due to increase in living standard (Zakari et al, 2009). There is no need for fear of radiation but there is the need to understand its properties, make use of it and reduce the exposure to dose levels which the society judged as acceptable, with minimum associated risk. As long as the contribution from the artificial radionuclides does not push the annual dose equivalent level beyond 1mSv for the public and 20mSv averaged over five years for classified workers, then there is no need to fear radiation (NNRA, 2003).

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ASSESSMENT OF OCCUPATIONAL EXPOSURE AND RADIATION PROTECTION IN SOME SELECTED WELL-LOGGING AND INDUSTRIAL RADIOGRAPHY FACILITIES IN NIGERIA