Models for Metal Hydride Particle Shape, Packing, and Heat Transfer

A multiphysics modeling approach for heat conduction in metal hydride powders is presented, including particle shape distribution, size distribution, granular packing structure, and effective thermal conductivity. A statistical geometric model is presented that replicates features of particle size and shape distributions observed experimentally that result from cyclic hydride decreptitation. The quasi-static dense packing of a sample set of these particles is simulated via energy-based structural optimization methods. These particles jam (i.e., solidify) at a density (solid volume fraction) of 0.665+/-0.015 - higher than prior experimental estimates. Effective thermal conductivity of the jammed system is simulated and found to follow the behavior predicted by granular effective medium theory. Finally, a theory is presented that links the properties of bi-porous cohesive powders to the present systems based on recent experimental observations of jammed packings of fine powder. This theory produces quantitative experimental agreement with metal hydride powders of various compositions.Comment: 12 pages, 12 figures, 2 table

Challenges to providing HIV prevention education to youth with disabilities in South Africa

Purpose: In South Africa, little is known how HIV prevention education is implemented in schools for learners with disabilities. This article reports on findings from a study exploring the extent to which HIV education is reached to people with disabilities in South Africa, and the challenges faced by educators providing HIV prevention education to learners with disabilities. Method: A survey questionnaire completed by 34 schools for learners with special education needs in the Western Cape province of South Africa. Additional complimentary data were collected through interviews with a total of 21 members of staff at schools for learners with disabilities. Results: Respondents recognise the importance of providing HIV prevention education for people with disabilities. Staff reports some challenges in providing HIV prevention education: barriers to communication; discomfort about issues of sexuality and disability; disagreements among staff about what is appropriate content for sexual health education; and fears of promoting sexual activity. Conclusions: There is a need for HIV prevention education to be specifically customized to the needs of the specific population. A general programme, which is included as part of a general curriculum and generally tailored to “mainstream” schools, would need to be adapted according to specific needs and disabling barriers faced

Magnetic flux jumps in textured Bi2Sr2CaCu2O(8+d)

Magnetic flux jumps in textured Bi2Sr2CaCu2O(8+d) have been studied by means of magnetization measurements in the temperature range between 1.95 K and Tc, in an external magnetic field up to 9 T. Flux jumps were found in the temperature range 1.95 K - 6 K, with the external magnetic field parallel to the c axis of the investigated sample. The effect of sample history on magnetic flux jumping was studied and it was found to be well accounted for by the available theoretical models. The magnetic field sweep rate strongly influences the flux jumping and this effect was interpreted in terms of the influence of both flux creep and the thermal environment of the sample. Strong flux creep was found in the temperature and magnetic field range where flux jumps occur suggesting a relationship between the two. The heat exchange conditions between the sample and the experimental environment also influence the flux jumping behavior. Both these effects stabilize the sample against flux instabilities, and this stabilizing effect increases with decreasing magnetic field sweep rate. Demagnetizing effects are also shown to have a significant influence on flux jumping.Comment: 10 pages, 6 figures, RevTeX4, submitted to Phys. Rev.

Wolbachia and DNA barcoding insects: patterns, potential and problems

Wolbachia is a genus of bacterial endosymbionts that impacts the breeding systems of their hosts. Wolbachia can confuse the patterns of mitochondrial variation, including DNA barcodes, because it influences the pathways through which mitochondria are inherited. We examined the extent to which these endosymbionts are detected in routine DNA barcoding, assessed their impact upon the insect sequence divergence and identification accuracy, and considered the variation present in Wolbachia COI. Using both standard PCR assays (Wolbachia surface coding protein – wsp), and bacterial COI fragments we found evidence of Wolbachia in insect total genomic extracts created for DNA barcoding library construction. When >2 million insect COI trace files were examined on the Barcode of Life Datasystem (BOLD) Wolbachia COI was present in 0.16% of the cases. It is possible to generate Wolbachia COI using standard insect primers; however, that amplicon was never confused with the COI of the host. Wolbachia alleles recovered were predominantly Supergroup A and were broadly distributed geographically and phylogenetically. We conclude that the presence of the Wolbachia DNA in total genomic extracts made from insects is unlikely to compromise the accuracy of the DNA barcode library; in fact, the ability to query this DNA library (the database and the extracts) for endosymbionts is one of the ancillary benefits of such a large scale endeavor – for which we provide several examples. It is our conclusion that regular assays for Wolbachia presence and type can, and should, be adopted by large scale insect barcoding initiatives. While COI is one of the five multi-locus sequence typing (MLST) genes used for categorizing Wolbachia, there is limited overlap with the eukaryotic DNA barcode region

Personal information and regulatory requirements for direct marketing: A South African insurance industry experiment

The processing of personal information by companies should be in line with ethical and regulatory requirements. Whilst respecting the right to privacy, personal information can be used to create value in the economy as well as on an individual level by tailoring and targeting services. However, personal information should not be processed under false pretences for the purposes of direct marketing. Data protection regulations, such as the Protection of Personal Information Act (PoPI) 2013, regulate the processing of personal information. Accordingly, companies domiciled in South Africa have to comply with the conditions of PoPI and must process personal information in line with the agreed purpose. PoPI will have an impact on direct marketing and certain conditions will apply to protect individuals’ personal information, as well as how and by whom it is used. This research sets out to investigate whether companies in the insurance industry are complying with the direct marketing conditions of PoPI pertaining to opt in and opt out preferences as well as a few other aspects. An experiment was conducted in South Africa whereby two new cellphone numbers and six new e-mail addresses were deposited in the economy by requesting online insurance quotes from twenty different insurance companies. For half of the online insurance quotes the researchers elected to opt in for direct marketing and for the other half to opt out. Any communication received on the cellphone numbers or e-mail addresses was recorded and analysed to establish if the preferences expressed were being complied with. The results indicate that data was shared and possibly leaked; this finding was based on the number of contacts received from companies that were not part of the sample. It was found that opt out preferences for direct marketing were not honoured by some companies. Other aspects, such as the availability of the option to opt in or opt out for direct marketing when depositing personal information on websites, secure processing of personal information and the use of privacy disclaimers, were also found to be lacking in some instances. This indicates that the insurance industry in South Africa might not yet be fully compliant with the requirements for direct marking, as required by PoPI and the Consumer Protection Act (CPA). The results of the research can be used to improve direct marketing interactions with consumers, helping to ensure not only compliance with PoPI, but also the maintenance of a trusting relationship by respecting privacy.College of Engineering, Science and Technolog

Electric charge quantization and the muon anomalous magnetic moment

We investigate some proposals to solve the electric charge quantization puzzle, which simultaneously explain the recent measured deviation on the muon anomalous magnetic moment. For this we assess extensions of the Electro-Weak Standard Model spanning modifications on the scalar sector only. It is interesting to verify that one can have modest extensions which easily account for the solution for both problems.Comment: 20 pages, 1 figures, needs macro axodraw.st

Lepton Flavor Non-Conservation

In the present work we review the most prominent lepton flavor violating processes (\mu \ra e\gamma, \mu \ra 3e, $(\mu , e)$ conversion, $M-\bar M$ oscillations etc), in the context of unified gauge theories. Many currently fashionable extensions of the standard model are considered, such as: {\it i)} extensions of the fermion sector (right-handed neutrino); {\it ii)} minimal extensions involving additional Higgs scalars (more than one isodoublets, singly and doubly charged isosinglets, isotriplets with doubly charged members etc.); {\it iii)} supersymmetric or superstring inspired unified models emphasizing the implications of the renormalization group equations in the leptonic sector. Special attention is given to the experimentaly most interesting $(\mu - e)$ conversion in the presence of nuclei. The relevant nuclear aspects of the amplitudes are discussed in a number of fashionable nuclear models. The main features of the relevant experiments are also discussed, and detailed predictions of the above models are compared to the present experimental limits.Comment: (IOA-300/93, review article, 83p, 6 epsf figures , available upon request from [email protected])

X-Ray Spectroscopy of Stars

(abridged) Non-degenerate stars of essentially all spectral classes are soft X-ray sources. Low-mass stars on the cooler part of the main sequence and their pre-main sequence predecessors define the dominant stellar population in the galaxy by number. Their X-ray spectra are reminiscent, in the broadest sense, of X-ray spectra from the solar corona. X-ray emission from cool stars is indeed ascribed to magnetically trapped hot gas analogous to the solar coronal plasma. Coronal structure, its thermal stratification and geometric extent can be interpreted based on various spectral diagnostics. New features have been identified in pre-main sequence stars; some of these may be related to accretion shocks on the stellar surface, fluorescence on circumstellar disks due to X-ray irradiation, or shock heating in stellar outflows. Massive, hot stars clearly dominate the interaction with the galactic interstellar medium: they are the main sources of ionizing radiation, mechanical energy and chemical enrichment in galaxies. High-energy emission permits to probe some of the most important processes at work in these stars, and put constraints on their most peculiar feature: the stellar wind. Here, we review recent advances in our understanding of cool and hot stars through the study of X-ray spectra, in particular high-resolution spectra now available from XMM-Newton and Chandra. We address issues related to coronal structure, flares, the composition of coronal plasma, X-ray production in accretion streams and outflows, X-rays from single OB-type stars, massive binaries, magnetic hot objects and evolved WR stars.Comment: accepted for Astron. Astrophys. Rev., 98 journal pages, 30 figures (partly multiple); some corrections made after proof stag