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

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

A novel topology of high-speed SRM for high-performance traction applications

A novel topology of high-speed Switched Reluctance Machine (SRM) for high-performance traction applications is presented in this article. The target application, a Hybrid Electric Vehicle (HEV) in the sport segment poses very demanding specifications on the power and torque density of the electric traction machine. After evaluating multiple alternatives, the topology proposed is a 2-phase axial flux machine featuring both segmented twin rotors and a segmented stator core. Electromagnetic, thermal and mechanical models of the proposed topology are developed and subsequently integrated in an overall optimisation algorithm in order to find the optimal geometry for the application. Special focus is laid on the thermal management of the machine, due to the tough thermal conditions resulting from the high frequency, high current and highly saturated operation. Some experimental results are also included in order to validate the modelling and simulation results

A rapid and low-cost DNA extraction method for isolating Escherichia coli DNA from animal stools

The price of commercial DNA extraction methods makes the routine use of polymerase chain reaction amplification (PCR) based methods rather costly for scientists in developing countries. A guanidium thiocayante-based DNA extraction method was investigated in this study for the isolation of Escherichia coli (E. coli) DNA from goat, chicken, pig, cow and human stool samples. Two versions of the lysis buffer, with and without _-casein, were tested to alleviate PCR inhibition associated with DNA isolated from stool samples. Results obtained show that, this method using the lysis buffer containing _-casein, produces PCR ready DNA at a fraction of the cost of commercial DNA extraction kits & copy; 2011 Academic Journals

The role of the school in inculcating citizenship values in South Africa: theoretical and international comparative perspectives

In view of the serious moral decay in South African society, this article reports on our research regarding the role of the school in the inculcation of citizenship values (as part of the brief of South African education). We regard a set of citizenship values consonant with a democratic dispensation to be a core component of a moral order essential for South Africa. Using a combination of interpretive-constructivist and comparative approaches, we examine and evaluate the experiences of other post-conflict societies in using education to inculcate citizenship values. We conclude that schools can be successful with respect to the inculcation of citizenship values, provided that the curriculum itself does not discriminate against any group or category of people. Desegregation can only be beneficial in the absence of negative depiction (including criminalisation) or the unequal treatment of any particular societal grouping. Our research suggests that active citizenship education is needed in schools. For this reason, we contend that teacher education has to form an integral part of a moral revival project. Lastly, we highlight the importance of finding democratically agreed-upon ways to continually engage with parents, legal caregivers and other stakeholders and role-players before and during the execution of any such project

Cutting EdgE 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’s 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 follow-up 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

Survival of children in Cape Town known to be vertically infected with HIV-1

Objective. To determine the survival patterns of children in Cape Town known to be vertically infected with HIV.Design. Retrospective record review of children diagnosed with symptomatic HIV infection during the period 1 December 1990 - 31 May 1995.Setting. Hospitals in the Cape Town metropolitan area.Patients. 193 children were known to be vertically HIV infected. HIV diagnosis was based on the following criteria: two positive HIV enzyme-linked immunosorbent assays (ELlSAs) in children older than 15 months and a positive ELlSA together with a positive polymerase chain reaction (PCR) in younger children. The mothers of the children were known to be HIV-positive. On the basis of the presenting clinical findings children were assigned to a disease severity category (A, B or C) according to the Centers for Disease Control and Prevention (CDC)'s 1994 revised classification system for HIV infection in children.Outcome measures. Survival was analysed according to the Kaplan-Meier method. Survival time was defined as the length of time between clinical diagnosis of HIV and death or last contact with the health services. Mortality risk in relation to specific variables at diagnosis such as age and clinical manifestations was determined by calculation of odds ratios (ORs) with 95% confidence intervals (Cls).Results. The median age at diagnosis was 5 months; 72% of children were aged less than 1 year at diagnosis. According to the CDC clinical classification, 47 (24%) fell into category A, 111 (58%) into category Band 35 (18%) into category C. Of the 193 patients 85 (44%) were alive at the time of review, 65 (34%) had died and 43 (22%) were lost to folloW-Up. Risk of death was significantly associated with age less than 6 months (OR 4.7, Cl 2.1 - 10.3) and severe disease, Le. CDC category C (OR 2.7; Cl 1.1 - 6.9) at time of diagnosis. The median survival for all the children from time of diagnosis was 32 months. Infants diagnosed before 6 months of age had significantly shorter median survival (10 months) compared with 36 months for those diagnosed at 7 - 12 months of age. For the children over the age of 12 months the cumulative proportion surviving at 48 months was 78%. Children with severe disease (category C) had a median survival of 21 months, significantly lower than that in category B (32 months). For the children in category A the cumulative proportion surviving at 48 months was 66%.Conclusion. The median survival of children with HIV was 32 months from time of diagnosis, and survival was influenced by age and disease severity