Scattering of a Long Cosmic String by a Rotating Black Hole

The scattering of a straight, infinitely long string by a rotating black hole is considered. We assume that a string is moving with velocity v and that initially the string is parallel to the axis of rotation of the black hole. We demonstrate that as a result of scattering, the string is displaced in the direction perpendicular to the velocity by an amount kappa(v,b), where b is the impact parameter. The late-time solution is represented by a kink and anti-kink, propagating in opposite directions at the speed of light, and leaving behind them the string in a new ``phase''. We present the results of the numerical study of the string scattering and their comparison with the weak-field approximation, valid where the impact parameter is large, b/M >> 1, and also with the scattering by a non-rotating black hole which was studied in earlier works.Comment: 27 pages, 14 figures, to be published in Classical and Quantum Gravit

Opening the doors of learning: Increasing access to music degrees

This article is contextualized for Music and is a response to the CHE (2013) Report that proposes a flexible curriculum structure for undergraduate degrees in South Africa, to address student under preparedness. Research states that music graduates need well developed identities in music, as well as generic, transferable skills to ensure lifelong employment and that a bachelor of music degree is best suited for this. However, in the South African context, the bachelor of music degree qualification is not accessible to the majority of prospective students as they are under prepared to study music at tertiary level. Only a minority of learners receive quality music education at school, while the majority of learners, including those from low socio-economic communities, do not receive formal music education. Under preparedness to study music, has traditionally been addressed through certificates and diploma qualifications in music. A discussion, and interpretation of the literature, has led to the researcher to develop an alternate framework to both improve student access to music degrees and manage under preparedness. The proposed approach advocates that music departments at universities adopt the framework of the national certificate vocation as an alternative to certificates and diplomas. The alternative curriculum structure for music, would be a more cost effective way to address under preparedness, improve academic success and lead to high skill levels. The study is situated in a constructivist, interpretive worldview, with a qualitative research design. Purposive sampling in the form of the choice of literature for the theoretical framework was adopted. While this theoretical study is contextualized for music, it is applicable to other fields

Medical recipients of the Victoria cross during the Anglo-Boer war, 1899 -1902

No Abstrac

The use of the road to health card in monitoring child health

Objectives: The Road to Health Chart (RTHC) provides a simple, cheap, practical and convenient method of monitoring child health. The RTHC could assist with vaccine compliance and early identification of growth faltering, to improve general health. The purpose of the study was to assess whether the RTHCs were adequately completed and interpreted at primary, secondary and tertiary care levels in South Africa. Methods: The study was carried out at a primary, secondary and tertiary care centre. A questionnaire was administered to 100 subjects from each; seeking demographic information, whether the RTHC was brought along, and if not why it was not brought. Results: Most children were brought by their mothers. The RTHC was not brought to 48% of the consultations; of those, about 72% thought that bringing the RTHC along was not necessary. Health workers seldom asked to see the RTHC at the primary and secondary care settings, but 50% of them did so at Ga-Rankuwa Hospital (p = 0,002). In only 8 cases overall were the children below the 3rd percentile of weight-for-age. Approximately 20% had incomplete immunisations. Conclusions: Many parents believe that the RTHC is only required for Well-baby-clinic visits, not for consultations. The RTHC is not often asked for at consultations; the fact that this is more often done at the tertiary care centre may be that much of the service is supplied by paediatricians-in-training. Health workers should ask to see the RTHC, in order for mothers to understand the importance of the information. The study showed that the RTHC is not used to its full potential. South African Family Practice Vol. 49 (1) 2007: pp. 1

Books

Neurobiology Neurobiology: 2 ed. Ed. by Gordon M. Shepherd. Pp. xiv + 689. Illustrared. R74,50. Oxford: Oxford Universiry Press. 1988.Medical physiology Textbook of Medical Physiology. Ed. by A. C. Guyton. Pp. xli + 1014. Illustrated. Kent: Harcourt, Brace, Jovanovich. 1991.Bilingual heart and stress booklets The Healthy HeartlDie Gesonde Hart. Ed. by G. Jackson. Coping with Stress/Oorwin Stres. Ed. by T. Trauer. pp. 77. Illustrated. RI9,95. Cape Town: Tafelberg. 1990

Application of the Cubed-Sphere Grid to Tilted Black-Hole Accretion Disks

In recent work we presented the first results of global general relativistic magnetohydrodynamic (GRMHD) simulations of tilted (or misaligned) accretion disks around rotating black holes. The simulated tilted disks showed dramatic differences from comparable untilted disks, such as asymmetrical accretion onto the hole through opposing "plunging streams" and global precession of the disk powered by a torque provided by the black hole. However, those simulations used a traditional spherical-polar grid that was purposefully underresolved along the pole, which prevented us from assessing the behavior of any jets that may have been associated with the tilted disks. To address this shortcoming we have added a block-structured "cubed-sphere" grid option to the Cosmos++ GRMHD code, which will allow us to simultaneously resolve the disk and polar regions. Here we present our implementation of this grid and the results of a small suite of validation tests intended to demonstrate that the new grid performs as expected. The most important test in this work is a comparison of identical tilted disks, one evolved using our spherical-polar grid and the other with the cubed-sphere grid. We also demonstrate an interesting dependence of the early-time evolution of our disks on their orientation with respect to the grid alignment. This dependence arises from the differing treatment of current sheets within the disks, especially whether they are aligned with symmetry planes of the grid or not.Comment: 15 pages, 11 figures, submitted to Ap

GRMHD prediction of coronal variability in accreting black holes

On the basis of data from an energy-conserving 3D general relativistic MHD simulation, we predict the statistical character of variability in the coronal luminosity from accreting black holes. When the inner boundary of the corona is defined to be the electron scattering photosphere, its location depends only on the mass accretion rate in Eddington units (\dot{M}). Nearly independent of viewing angle and \dot{M}, the power spectrum over the range of frequencies from approximately the orbital frequency at the innermost stable circular orbit (ISCO) to ~100 times lower is well approximated by a power-law with index -2, crudely consistent with the observed power spectra of hard X-ray fluctuations in AGN and the hard states of Galactic binary black holes. The underlying physical driver for variability in the light curve is variations in the accretion rate caused by the chaotic character of MHD turbulence, but the power spectrum of the coronal light output is significantly steeper. Part of this contrast is due to the fact that the mass accretion rate can be significantly modulated by radial epicyclic motions that do not result in dissipation, and therefore do not drive luminosity fluctuations. The other part of this contrast is due to the inward decrease of the characteristic inflow time, which leads to decreasing radial coherence length with increasing fluctuation frequency.Comment: Accepted for publication in ApJ, 35 pages, 11 figures (8 color and 3 greyscale), AASTEX. High-resolution versions can be found at the following links: [PS] http://www.pha.jhu.edu/~scn/papers/grmhd_var.ps [PDF] http://www.pha.jhu.edu/~scn/papers/grmhd_var.pd

Rethinking the discovery function of proof within the context of proofs and refutations

Proof and proving are important components of school mathematics and have multiple functions in mathematical practice. Among these functions of proof, this paper focuses on the discovery function that refers to invention of a new statement or conjecture by reflecting on or utilizing a constructed proof. Based on two cases in which eighth and ninth graders engaged in proofs and refutations, we demonstrate that facing a counterexample of a primitive statement can become a starting point of students’ activity for discovery, and that a proof of the primitive statement can function as a useful tool for inventing a new conjecture that holds for the counterexample. An implication for developing tasks by which students can experience this discovery function is mentioned.ArticleInternational Journal of Mathematical Education in Science and Technology. 45(7):1053-1067 (2014)journal articl

A Human Torque Teno Virus Encodes a MicroRNA That Inhibits Interferon Signaling

Rodney P. Kincaid, James M. Burke, Jennifer C. Cox, Christopher S. Sullivan, The University of Texas at Austin, Molecular Genetics and Microbiology, Austin, Texas, United States of AmericaEthel-Michele de Villiers, Division for the Characterization of Tumorviruses, Deutsches Krebsforschungszentrum, Heidelberg, GermanyTorque teno viruses (TTVs) are a group of viruses with small, circular DNA genomes. Members of this family are thought to ubiquitously infect humans, although causal disease associations are currently lacking. At present, there is no understanding of how infection with this diverse group of viruses is so prevalent. Using a combined computational and synthetic approach, we predict and identify miRNA-coding regions in diverse human TTVs and provide evidence for TTV miRNA production in vivo. The TTV miRNAs are transcribed by RNA polymerase II, processed by Drosha and Dicer, and are active in RISC. A TTV mutant defective for miRNA production replicates as well as wild type virus genome; demonstrating that the TTV miRNA is dispensable for genome replication in a cell culture model. We demonstrate that a recombinant TTV genome is capable of expressing an exogenous miRNA, indicating the potential utility of TTV as a small RNA vector. Gene expression profiling of host cells identifies N-myc (and STAT) interactor (NMI) as a target of a TTV miRNA. NMI transcripts are directly regulated through a binding site in the 3′UTR. SiRNA knockdown of NMI contributes to a decreased response to interferon signaling. Consistent with this, we show that a TTV miRNA mediates a decreased response to IFN and increased cellular proliferation in the presence of IFN. Thus, we add Annelloviridae to the growing list of virus families that encode miRNAs, and suggest that miRNA-mediated immune evasion can contribute to the pervasiveness associated with some of these viruses.This work was supported by grants RO1AI077746 from the National Institutes of Health, RP110098 from the Cancer Prevention and Research Institute of Texas, a Burroughs Wellcome Investigators in Pathogenesis Award to CSS, a UT Austin Powers Graduate Fellowship to RPK, a UT Austin Institute for Cellular and Molecular Biology fellowship, and the DKFZ for EMdV. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Molecular BiosciencesMicrobiologyEmail: [email protected]