Particle precipitation involves the injection of energetic particles into the ionosphere which could increase the ionisation and conductivity of the upper atmosphere. The goal of this study was to examine the ionospheric response and changes due to particle precipitation in the region over South Africa, using a combination of groundbased and satellite instruments. Particle precipitation events were identified from satellite particle flux measurements of the Defence Meteorological Satellite Program (DMSP). Comprehensive studies were done on the events of 5 April, 2000 and 7 October, 2000. Analysis of the data from the satellite instruments indicates that no particle precipitation was observed over the South African region during these events and that it is unlikely to occur during other such events. To validate the data, methods and tools used in this study, precipitation in the South Atlantic anomaly (SAA) region is used. Satellite ion density measurements revealed that strong density enhancements occurred over the SAA region at satellite altitudes during the precipitation events, but this did not occur in the South African region. The measurements also revealed how the ionisation enhancements in the SAA region correlated with geomagnetic and solar activities. Particle precipitation and convective electric fields are two major magnetospheric energy sources to the upper atmosphere in the auroral and the SAA regions. These increase dramatically during geomagnetic storms and can disturb thermospheric circulation in the atmosphere and alter the rates of production and recombination of the ionised species. Ionosonde observations at Grahamstown, South Africa (33.30S, 26.50E), provided the data to build a picture of the response of the ionosphere over the South African region to particle precipitation during the precipitation events. This analysis showed that, within the confines of the available data, no direct connections between particle precipitation events and disturbances in the ionosphere over this region were revealed.

From Introduction: The minimum in the scalar magnitude of the geographic total field, which lies off the coast of Brazil, allows the mirror points of trapped particles to dip low into the atmosphere over the South Atlantic Ocean, resulting in two regions of maximum intensity of preciptated particles in that region, one from the inner belt and one from the outer. High charged particle fluxes have been observed at low altitudes over these regions by satellites Sputnik 5 and 6 (Ginsburg et al, 1961) and Discoverer 31 (Seward and Kornblum, 1963) amongst others. The more southerly of these two regions acts as a sink for electrons from the outer radiation belt and will be referred to in what follows as the Southern Radiation Anomaly. Gladhill and van Rooyen (1963) predicted that the energy deposited in the upper atmosphere by these charged particles would be sufficient to give rise to enhanced geophysical effects such as auroral emission, X-rays and ionization and heating of the upper atmosphere in this region. Although some of these effects have been correlated with precipitated electrons, no definite relation had until now been established between ionospheric effects and precipitated particles. The aim of this thesis was to investigate such a relationship and the results were extremely successful. It will be shown conclusively in what follows, that the precipitation of electrons can account for the ionospheric disturbances defined by a disturbance criterion at all stations around L=4. Part I describes the exploration of the radiation belts and the magnetosphere with rockets and satellites. The resulting theoretical models based on the observations are discussed. A brief review is given of the work that has been done to date to derive equations for the loss and replenishment of particles in the belts. Because of the complexity of these and the number of doubtful factors involved, a simple model of injection of electrons into the outer belt is devised, giving average values of trapped and precipitated electron fluxes at any point around L=4. In Part II, this model is employed together with the disturbance criterion of Gledhill and Torr (1965) to examine the relationship between ionospheric disturbances and electron fluxes. Also the energy range of the precipitated particles is examined.

As early as 1896, around the time of the discovery of the electron by J.J. Thompson, Birkeland was led to propose that aurorae were caused by fast moving electrons or similarly charged particles emitted by the sun and 'sucked in towards' the auroral zones by the geomagnetic field. He later supported this idea by firing electrons at a dipole field surrounding a sphere covered with a fluorescent coating. Extensive ground based observations of auroral features eventually led, in 1950, to the initial direct evidence of the fact that auroral emissions are due to energetic charged particles, consisting partly of protons, entering the earth's atmosphere (Meinel, 1951). However, it was only in 1952 and 1953 that the first measurements of what was later interpreted as bremsstrahlung X- rays from precipitating electrons were made at auroral latitudes. (Meredith et aI, 1955) During the IGY, 1957 - 1958, a number of rockets were fired through and near, visible aurorae and large fluxes of low energy electrons were detected ... Intro., p. 1.

Understanding the changes occurring in the mechanical properties during martensite tempering is essential in the development of new industrial grades. The aim of this research was to develop new ultra-high strength steels via nanoprecipitation control, which requires an understanding of the processing-microstructure-property relationship in medium carbon (0.5-0.6 wt.%) steels throughout tempering. Much of the work has been centred in understanding the role of silicon at the precipitation level and in the recovery of martensite. By using an existing spring steel grade, the effect of interrupted ageing (IA) in tempered martensite has been studied. In IA, an intermediate step between quenching and tempering is introduced, where quenched martensite is left to rest at room temperature for a defined period of time. By allowing carbon segregation into dislocation cores, the incorporation of IA resulted in a more stable microstructure and hardness improvement. The effect of silicon in the epsilon to cementite carbide transition has also been studied. The classical nucleation theory was applied in order to model cementite formation under paraequilibrium conditions, thus incorporating silicon during nucleation. Characterisation using high energy X-rays showed the inhibiting effect of silicon in the overall cementite precipitation. The second effect of silicon was observed in the martensite recovery. A series of experiments were carried out in order to capture the various microstructural changes taking place during tempering: precipitation, grain size and dislocation density evolution. It was observed that the addition of silicon reduces the rate of martensite recovery, owing to the reduced cross-slip in the ferrite lattice. A plasticity model based on irreversible thermodynamics and EBSD characterisation was applied to identify the effective grain size. The results from these two techniques require further research. Nevertheless, based on the post-failure analysis by TEM, it appears that at relatively early tempering stages, even low angle lath boundaries can contribute to strengthening, where piled-up dislocations have been observed at lath boundaries.

An innovative approach for the removal of heavy metal ions such as Pb2+ and Cd2+ from aqueous solution was evaluated. It was established that alkaline filtration, which is in essence the combination of alkaline precipitation and membrane filtration, could drastically increase both the efficiency and completeness of Pb2+ or Cd2+ ions removal, producing water whose metal concentration satisfying drinking water standard from a simulation wastewater containing 5 ppm or more Pb2+ or Cd2+ ions. Filtration with three different membranes, including microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) membranes, were studied at three different pH levels, i.e., 7.0, 8.5, and 10, in terms of metal ion rejection, flux, and permeate pH and at varied dissolved inorganic carbon (DIC) concentration. Increasing the pH of the feed in the tested range would lead to the decrease of metal ion concentration in permeate while flux was in general unaffected. When the feed pH was 10, the Pb2+ concentration in permeate was below 10 ppb regardless of the DIC concentration and membrane for filtration. The effects of DIC concentration were significant but complex. It was found that MF, UF, NF could all effectively reject Pb2+ ions at pH 8.5 and pH 10 although only NF was charged. A hypothesis was proposed to explain the mechanism of alkaline filtration based on experimental data.

Hydrological changes in catchments world over have affected regional climate and pose serious challenge to future water resource management. The Ganges drainage basin (GDB) is one such region which has undergone rapid transformation in land and water use, more specifically in the latter half of 20th century. GDB has a population of more than half a billion people and is spread across India, China (Tibet), Nepal and Bangladesh. Further, hydrological investigations accounting land and water use changes in GDB are rare. This study is an attempt to resolve hydrological changes in the Ganges basin using the fundamental water balance, focusing particularly on water use changes through irrigation. Between the period 1951-1959 and 1991- 2000, precipitation (P) in the Ganges basin has reduced by 11.25 % while evapotranspiration (ET) has only reduced by 3.61 %. In addition, the ET/P has increased from 0.483 to 0.525 during the same period suggesting a larger partitioning of P towards ET. This suggests greater utilization of P to release water vapor in the atmosphere and thus causing a reduced water flow downstream. With water availability at the fulcrum of future concern for regional and national water security, these findings should encourage policy makers to account for hydrological changes in the GDB in planning sustainable water use.

The relationship between leaf physiognomy and precipitation has been explored worldwide in regions under different climate conditions. Unlike the linear relationship established between the percentage of woody dicot species with entire margins and mean annual temperature, precipitation has been reported to correlate to different leaf physiognomic characters depending on the region where the correlation is studied. To investigate if precipitation can be calculated from leaf physiognomic characters on the basis of regional sample sites, data from 50 mesic to humid forests in China were analyzed in this study. With data from Chinese forests, the leaf-area analysis based on linear regression between natural logarithms of leaf size and mean annual precipitation (MAP) shows no significant correlation. Both single and multiple linear regression analyses fail to confirm the correlation between leaf physiognomy and precipitation, which may result from the similarity of modern spatial distribution of temperature and precipitation in China. Our results show that, due to variations in climatic conditions among sampling regions, leaf physiognomic characters that correlate to precipitation are not consistent worldwide, and applications of models without considering regional constraints could mislead our understanding of palaeoclimate. Therefore, when choosing a leaf physiognomic model for palaeoclimate reconstructions, it is important to determine if the leaf physiognomy of the palaeoflora lies within the leaf physiognomic spectrum of the model used.

The relationship between leaf physiognomy and precipitation has been explored worldwide in regions under different climate conditions. Unlike the linear relationship established between the percentage of woody dicot species with entire margins and mean annual temperature, precipitation has been reported to correlate to different leaf physiognomic characters depending on the region where the correlation is studied. To investigate if precipitation can be calculated from leaf physiognomic characters on the basis of regional sample sites, data from 50 mesic to humid forests in China were analyzed in this study. With data from Chinese forests, the leaf-area analysis based on linear regression between natural logarithms of leaf size and mean annual precipitation (MAP) shows no significant correlation. Both single and multiple linear regression analyses fail to confirm the correlation between leaf physiognomy and precipitation, which may result from the similarity of modern spatial distribution of temperature and precipitation in China. Our results show that, due to variations in climatic conditions among sampling regions, leaf physiognomic characters that correlate to precipitation are not consistent worldwide, and applications of models without considering regional constraints could mislead our understanding of palaeoclimate. Therefore, when choosing a leaf physiognomic model for palaeoclimate reconstructions, it is important to determine if the leaf physiognomy of the palaeoflora lies within the leaf physiognomic spectrum of the model used.

The Texas High Plains produces the most substantial amount of cotton in Texas. The region is a semi-arid area with limited precipitation, and it is, therefore, susceptible to climate change. Cotton production in the Texas High Plains is mostly dependent on irrigation to increase yield. The overall goal of this research was to study the interrelationships between climate change and cotton yield using correlation analysis and also to study how climate has changed in the region using trend analysis. A three-decade data (1987-2017) was analyzed to establish the relationship between climate change and cotton and also to determine how climate has changed in the area over the last 30 years. The research used precipitation and temperature data to assess climate change.The results of this research showed that annual mean temperature has lesser impacts on cotton yield, and the correlation between annual precipitation and cotton yield is insignificant. It also found out that high rates of temperature at the boll opening stage of cotton growth results in decreased cotton yield and that at the boll development and boll opening stages, precipitation is needed. Again, the research indicated that, on average, there had been a significant increase in temperature, but precipitation trends are insignificant. About 60% of cotton acreage in the area is irrigated. Therefore the research also found out that increasing trends of cotton yield may contribute to the decline of groundwater in the area.

This study was designed to understand the possible impact of carbon dioxide on different reservoir rocks in south-central Mississippi. Eight samples, including six from the Heidelberg field (Mississippi), were exposed to carbon dioxide under simulated subsurface conditions of elevated temperature and pressure and then analyzed using thin section petrography, scanning electron microscopy, X-ray diffraction, and focused ion beam-SEM. Three of the eight samples showed dissolution in calcite and corrosion in smectite. SEM and EDS analysis of treated sample 5 (Se-5/shaly-sandtsone) and sample 8 (S-8/dolomitic-limestone) revealed newly precipitated lath- and fibrous-like crystals composed of sulfur (S), oxygen (O), and calcium (Ca), thus interpreted as gypsum. Three-dimensional analysis using FIB of dolomitic limestone samples (Smackover Formation) revealed that gypsum crystals fill fracture porosity. This study significantly contributes to the understanding of carbon dioxide impact on reservoir rock and promotes better management of natural gas resources.