Quasilinear Drift Of Cosmic Rays In Weak Turbulent Electromagnetic Fields

A general quasilinear transport parameter for particle drift in arbitrary turbulence geometry is presented. The new drift coefficient is solely characterized by a nonresonant term and is evaluated for slab and two-dimensional turbulence geometry. The calculations presented here demonstrate that fluctuating electric fields are a key quantity for understanding quasilinear particle drift in slab geometry. It is shown that particle drift does not exist in unpolarized and purely magnetic slab fluctuations. This is in stark contrast to previous models, which are restricted to slab geometry and the field line random walk limit. The evaluation of the general transport parameter for two-dimensional turbulence geometry, presented here for the first time for dynamical magnetic turbulence, results in a drift coefficient valid for a magnetic power spectrum and turbulence decay rate varying arbitrarily in wavenumber. For a two-component, slab/two-dimensional turbulence model, numerical calculations are presented. The new quasilinear drift, induced by the magnetic perturbations, is compared with a standard drift expression related to the curvature and gradient of an unperturbed heliospheric background magnetic field. The considerations presented here offer a solid ground and natural explanation for the hitherto puzzling observation that drift models often describe observations much better when drift effects are reduced.Comment: 23 pages, 6 figures, accepted for publication in Ap

Population genomics of Cercospora beticola

Fungal plant pathogens pose a serious threat to global food safety and security, and can result in significant yield loss. Fungal plant pathogens have evolved with their hosts during the history of crop domestication. While some fungal phytopathogens of modern crops have maintained the ability to infect the wild relatives of these crops, many have evolved host-specificity due to the evolutionary arms race. Co-evolution between plants and their pathogens spans many generations. Therefore, we have employed the pathosystem of the fungal pathogen Cercospora beticola and its hosts Beta vulgaris ssp. (domesticated beet) and B. maritima (sea beet). This pathosystem is exceptional as sugar beet has a relatively short domestication history of ~300 years, compared to several thousand year history of other modern crops. Investigating the effect crop domestication has on fungal evolution in such a short time frame may provide insight into the early processes underlying the evolution of host-specificity. The availability of whole genome sequencing data for entire populations of fungal plant pathogens has enabled detailed analyses of genomic variation within and among field populations. Using population genomic data, we are able to detect population structure of a phytopathogenic fungus, identify regions that are highly differentiated between isolates, and predict the evolutionary trajectory of disease epidemics. The primary focus of this thesis was to describe the population genomics of the fungus Cercospora beticola, and determine the influence of host domestication on recent evolution and population structure of the fungus. Chapter 1 addressed the challenge of assembling and analysing population genomic data of species with structural variation, as is the case for many pathogenic fungi. We compared and contrasted two variant calling methods used in population genomics. We show that the commonly used method of variant calling, reference mapping-based approaches, as well as more recently adapted multiple genome alignment-based methods perform equally well at high sequencing depths in species with variable amounts of repetitive content. However, we also found that reference mapping-based approaches are reliable at average and high sequencing depths, regardless of repetitive content. In Chapter 2, we analyse the population genetic structure of C. beticola with the aim of comparing the genetic variation in populations of domesticated and wild beet species. Specifically, we make use of population genomics tools to elucidate whether C. beticola isolates from wild and domesticated hosts show strong signals of host specialisation. Sugar beet is comparatively novel crop, and provides insight into the early specialisation processes pathogens of domesticated plants. We collected isolates from wild and domesticated beet from Europe and North America and show that there are not clear populations of C. beticola isolates that infect wild or domesticated beet. We show that C. beticola isolates are likely a global population, with substantial admixture between individuals from all hosts and locations. While there is admixture between individuals from all locations, isolates from sea beet in the UK showed more differentiation from the isolates from other locations suggesting some barriers to gene flow and distinct population histories of the sea beet isolates. We investigated regions where the isolates from the UK are different from isolates from mainland Europe and North America, and showed that there are likely phenotypic differences between isolates from Croatian sea beet and the English sea beet isolates. We illustrate a region where the isolates from Croatia contained a premature stop codon in a gene involved in the production of an aflatoxin in high frequency, while it was present at a low frequency the isolates from English sea beet. Thus, we show that while C. beticola may not show strong signatures of host specialisation yet, there are some differences between isolates from different locations indicating the potential for future population divergence. In Chapter 3, we compare and contrast C. beticola to four other Cercospora species to elucidate differences and similarities in genome content and synteny within the genus. We show that C. beticola has a higher number of genes encoding proteins that are involved host-pathogen interaction. We also note that the other Cercospora species that has a broad host range included in this, C. cf. flagellaris, has a similar repertoire of genes. We also show that these two species share substantial synteny. We postulate that they most recent common ancestor of these two species likely had a plastic genome that underwent several translocation events. Taken together, we show that the Cercospora genus is shaped by its interactions with its environment and the various hosts. We show that C. beticola has not yet shown strong association with either host or location

Circuit tutor : a computer-aided learning package for electrical engineering

The development of Circuit Tutor, the subject of this dissertation, resulted from a conviction that computers can further enrich the Electronic Engineering curriculum. After an investigation into the different roles of the computer in education the use of modelling and simulation was selected as an effective Computer Aided Learning method. It was realised that the development of any non-trivial simulation program is however not an easy task. The programmer must not only model the circuit behaviour, but also write the man-machine interface (MMI). The main goal of Circuit Tutor was to provide a ready-made simulation environment which makes effective use of the graphics capabilities of the microcomputer for the simulation of a whole class of electrical circuit simulations. To facilitate rapid prototyping the installer is provided with: (1) a man-machine interface which provides the user with a graph, 3 meters, a circuit diagram of the circuit, a menu facility, windows to view circuit parameters and outputs: (2) a program scheduler; (3) a library of maths functions, including Gauss-Jordan elimination of complex matrices; and (4) Circuit Draw: a utility to draw a circuit diagram. Particular emphasis was placed on the design of the user's interface. It has been possible to restrict the effort to link in a new circuit model to 3 modifications to the man-machine interface (MMI) part of the program. Present software and MMI design were investigated. Circuit Tutor and Circuit Draw were developed using modular software design techniques. A modular design chart similar to that proposed by Wiener (1984) was found to be useful during the design stages of both Circuit Tutor and Circuit Draw. Available computer languages for the IBM PC were evaluated and Turbo Pascal selected, as it offered most of the features necessary for the implementation of a modern, modular software design. Four circuits were implemented to serve as examples. The documentation was structured in a manner appropriate to a software project: Part 1 gives an introduction to computers in education and provides the rationale for the use of simulation. A brief overview of Circuit Tutor and Circuit Draw is presented. Part 2 contains the User's Reference Manual for Circuit Tutor and the Circuit Draw Utility. Part 3 contains the Designer's Reference Manual for Circuit Tutor and the Circuit Draw Utility

Die effek van die intraveneuse infusie van hipertensien-II-Peptiden op die miokardiale metabolisme en die kardiopulmonale hemodinamika van honde

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On the anomalous component

The so-called anomalous cosmic ray component, which occurs at energies of about 10 MeV/nucleon and consists only of He, N, O, and Ne, has been a subject of interest for more than a decade. The origin of this component is generally considered to be interstellar neutral gas that is ionized and accelerated in the solar wind. The mechanism and the location for the acceleration, however, remains an unsolved problem. A model is used which includes the effects of gradient and curvature drifts and considers the implications of observed spatial gradients of the anomalous component for the location of the acceleration region. It is concluded that if drifts are important the acceleration region cannot lie at the solar poles. It is also concluded that there is no single region for the acceleration which can account for both the observed intensities and gradients in models which include drift effects

Perceptions of registered nurses in four state health insititutions on continuing formal education

This study investigated registered nurses in four selected state health institutions’ perceptions with regard to continuing formal education. The relevance of continuing formal education is being emphasised globally by the increasing quest for quality assurance and quality management systems within an ethos of continuous improvement. According to Tlholoe (2006:5), it is important to be committed to continual learning, as people’s knowledge become less relevant because skills gained early in a career are insufficient to avoid costly mistakes made through ignorance. Continuing formal education in nursing is a key element to the maintenance of quality in health care delivery. The study described: • registered nurses’ views on continuing formal education • registered nurses’ perceived barriers to continuing formal education A quantitative descriptive survey design was chosen using a questionnaire for data collection. The sample consisted of 40 registered nurses working at four state health institutions in the Western Cape Province, South Africa. Convenience sampling was selected to include registered nurses who were on duty on the days during which the researcher visited the health institutions to distribute the questionnaires. The questionnaire contained mainly closed-ended and a few open-ended questions. Content validity of the instrument was ensured by doing a thorough literature review before construction of items and a pretest. Reliability was established by the pretest and providing the same information to all respondents before completion of the questionnaires. The ethical considerations of informed consent, anonymity and confidentiality were adhered to and consent to conduct the study was obtained from relevant authorities. Descriptive statistics, based on calculations using the Microsoft (MS) Excel (for Windows 2000) programme, were used to summarise and describe the research results. The research results indicated that most registered nurses perceive continuing formal education as beneficial to their personal and professional growth and that it could lead towards improving the quality of patient/client care, but barriers exist which prevent or deter them from undertaking continuing formal education programmes. The main structural barriers included lack of funding and lack of coherent staff development planning and physical barriers including job and family responsibilities.Department of HE and Training approved lis

Sovereign Credit Risk in a Hidden Markov Regime - Switching Framework. Part 2

This research applies a discrete-time Markov-modulated model to default probability estimation and adapts it to Merton\u2019s contingent claims approach, backing the hypothesis that a regime-switching framework which allows for structural shifts can substantially improve the underestimation of default probabilities associated with the Merton structural model. The modeling apparatus is applied to sovereign risk proving that the methodology can be tractably extended to a contingent claims approach, and is investigated as a followup paper to an extensive methodology found in the previous edition of the Capco Journal of Financial Transformation (37) [Potgieter and Fusai (2013)]. CDS quotes are used to calibrate the regime switching model and are then used to estimate sovereign assets in both developed and emerging markets