Uma sonda de calor transiente controlada por computador para medir fluxo de fluido em meios porosos.

Uma sonda de calor transiente controlada por computador foi desenvolvida para medir fluxo em meios porosos. O sistema e operado automaticamente com o auxilio de uma placa de computador e basicamente composto de um sensor do tipo sonda-termistor, uma fonte de corrente eletrica constante de dois niveis, um conversor de sinal analogicos para digital, um transistor de efeito de campo e um conjunto de amplificadores operacionais. A sonda e alternadamente comutada entre dois modulos de operacao, alta e baixa potencia. Um programa foi desenvolvido para solicitar ao usuario os tempos para controlar o termistor e permitir os registros de identificacao do local, data, horario e dados para posicoes especificas da memoria. Os principios, a concepcao, a montagem e o funcionamento de toda a instrumentacao sao descritos. O sistema foi testado e avaliado em dois diferentes meios porosos. Resultados indicaram que o termistor aquecido e capaz de detectar o fluxo de fluido uma vez que sua resposta termica transiente foi afetada pela taxa de fluxo local

Thermoelectric transport of perfectly conducting channels in two- and three-dimensional topological insulators

Topological insulators have gapless edge/surface states with novel transport properties. Among these, there are two classes of perfectly conducting channels which are free from backscattering: the edge states of two-dimensional topological insulators and the one-dimensional states localized on dislocations of certain three-dimensional topological insulators. We show how these novel states affect thermoelectric properties of the systems and discuss possibilities to improve the thermoelectric figure of merit using these materials with perfectly conducting channels.Comment: 10 pages, 6 figures, proceedings for The 19th International Conference on the Application of High Magnetic Fields in Semiconductor Physics and Nanotechnology (HMF-19

Addressing legal and policy barriers to male circumcision for adolescent boys in South Africa

With millions of adolescents becoming infected with HIV globally, it is essential that barriers to much-needed interventions are reduced for at-risk adolescents. In this article we review the legal and policy framework in South Africa for adolescent access to male circumcision. We are of the view that the framework does confer protection for adolescent boys while enabling access to male circumcision; however, we identify ambiguities and tensions that exist between the Children’s Act, regulations and national guidelines. We recommend reform to further enable access by this vulnerable group to this prevention modality

Glass-Like Heat Conduction in High-Mobility Crystalline Semiconductors

The thermal conductivity of polycrystalline semiconductors with type-I clathrate hydrate crystal structure is reported. Ge clathrates (doped with Sr and/or Eu) exhibit lattice thermal conductivities typical of amorphous materials. Remarkably, this behavior occurs in spite of the well-defined crystalline structure and relatively high electron mobility ($\sim 100 cm^2/Vs$). The dynamics of dopant ions and their interaction with the polyhedral cages of the structure are a likely source of the strong phonon scattering.Comment: 4 pages, 3 postscript figures, to be published, Phys. Rev. Let

One step forward, two steps back – requiring ministerial approval for all ‘non-therapeutic\' health research involving minors

The new National Health Act has clarified that children may take part in ‘non-therapeutic\' research (NTR) and the age at which they may provide independent consent to such research, viz. at legal majority. However, the Act will require consent from the Minister of Health for all research classed as NTR and involving minors regardless of the level of risk. This requirement is overly broad. It will require that low-risk research without direct benefits, which might be adequately reviewed by an accredited research ethics committee (REC), must also be reviewed by the Minister. As it currently stands this requirement serves no plausible ethical purpose, will cause delays and discourage essential research on the needs of children, and may inspire researchers and RECs alike to ‘foil the system\'. We argue that in the long term there should be comprehensive law reform for child research. However, in the short term, amendments should be made to the Act to narrow the scope of this provision. The amendment should require ministerial consent for research that is currently not approvable by an REC in terms of national ethical guidelines, namely, research that does not hold out direct benefit but presents more than a minor increase over minimal risk. If our law reform recommendations are rejected, we favour the delegation of this task to RECs because, if they receive appropriate training, they should be competent to conduct it. We accept the disadvantages, namely that the same body will review protocols twice from slightly different perspectives and that certain categories of research will remain unapprovable.South African Medical Journal Vol. 97 (2) 2007: pp.200-202

Towards a generalized computational fluid dynamics technique for all Mach numbers

Currently there exists no single unified approach for efficiently and accurately solving computational fluid dynamics (CFD) problems across the Mach number regime, from truly low speed incompressible flows to hypersonic speeds. There are several CFD codes that have evolved into sophisticated prediction tools with a wide variety of features including multiblock capabilities, generalized chemistry and thermodynamics models among other features. However, as these codes evolve, the demand placed on the end user also increases simply because of the myriad of features that are incorporated into these codes. In order for a user to be able to solve a wide range of problems, several codes may be needed requiring the user to be familiar with the intricacies of each code and their rather complicated input files. Moreover, the cost of training users and maintaining several codes becomes prohibitive. The objective of the current work is to extend the compressible, characteristic-based, thermochemical nonequilibrium Navier-Stokes code GASP to very low speed flows and simultaneously improve convergence at all speeds. Before this work began, the practical speed range of GASP was Mach numbers on the order of 0.1 and higher. In addition, a number of new techniques have been developed for more accurate physical and numerical modeling. The primary focus has been on the development of optimal preconditioning techniques for the Euler and the Navier-Stokes equations with general finite-rate chemistry models and both equilibrium and nonequilibrium thermodynamics models. We began with the work of Van Leer, Lee, and Roe for inviscid, one-dimensional perfect gases and extended their approach to include three-dimensional reacting flows. The basic steps required to accomplish this task were a transformation to stream-aligned coordinates, the formulation of the preconditioning matrix, incorporation into both explicit and implicit temporal integration schemes, and modification of the numerical flux formulae. In addition, we improved the convergence rate of the implicit time integration schemes in GASP through the use of inner iteration strategies and the use of the GMRES (General Minimized Resisual) which belongs to the class of algorithms referred to as Krylov subspace iteration. Finally, we significantly improved the practical utility of GASP through the addition of mesh sequencing, a technique in which computations begin on a coarse grid and get interpolated onto successively finer grids. The fluid dynamic problems of interest to the propulsion community involve complex flow physics spanning different velocity regimes and possibly involving chemical reactions. This class of problems results in widely disparate time scales causing numerical stiffness. Even in the absence of chemical reactions, eigenvalue stiffness manifests itself at transonic and very low speed flows which can be quantified by the large condition number of the system and evidenced by slow convergence rates. This results in the need for thorough numerical analysis and subsequent implementation of sophisticated numerical techniques for these difficult yet practical problems. As a result of this work, we have been able to extend the range of applicability of compressible codes to very low speed inviscid flows (M = .001) and reacting flows

Paedophiles in the community: inter-agency conflict, news leaks and the local press

This article explores the leaking of confidential information about secret Home Office plans to house convicted paedophiles within a local community (albeit inside a prison). It argues that a politics of paedophilia has emerged in which inter-agency consensus on the issue of ‘what to do’ with high-profile sex offenders has broken down. Accordingly, the article situates newspaper ‘outing’ of paedophiles in the community in relation to vigilante journalism and leaked information from official agencies. The article then presents research findings from a case study of news events set in train following a whistle-blowing reaction by Prison Officers’ Association officials to Home Office plans. Drawing from a corpus of 10 interviews with journalists and key protagonists in the story, the article discusses both the dynamics of whistle blowing about paedophiles and also what happens after the whistle has blown

Resonant States in the Electronic Structure of the High Performance Thermoelectrics AgPbmSbTe_{m}SbTe_{2+m}$ ; The Role of Ag-Sb Microstructures

Ab initio electronic structure calculations based on gradient corrected density functional theory were performed on a class of novel quaternary compounds AgPb$_{m}SbTe$_{2+m}$, which were found to be excellent high temperature thermoelctrics with large figure of merit ZT ~2.2 at 800K. We find that resonant states appear near the top of the valence and bottom of the conduction bands of bulk PbTe when Ag and Sb replace Pb. These states can be understood in terms of modified Te-Ag(Sb) bonds. Electronic structure near the gap depends sensitively on the microstructural arrangements of Ag-Sb atoms, suggesting that large ZT values may originate from the nature of these ordering arrangements.Comment: Accepted in Physical Review Letter