General Relativistic Simulations of Jet Formation in a Rapidly Rotating Black Hole Magnetosphere

To investigate the formation mechanism of relativistic jets in active galactic nuclei and micro-quasars, we have developed a new general relativistic magnetohydrodynamic code in Kerr geometry. Here we report on the first numerical simulation of jet formation in a rapidly-rotating (a=0.95) Kerr black hole magnetosphere. We study cases in which the Keplerian accretion disk is both co-rotating and counter-rotating with respect to the black hole rotation. In the co-rotating disk case, our results are almost the same as those in Schwarzschild black hole cases: a gas pressure-driven jet is formed by a shock in the disk, and a weaker magnetically-driven jet is also generated outside the gas pressure-driven jet. On the other hand, in the counter-rotating disk case, a new powerful magnetically-driven jet is formed inside the gas pressure-driven jet. The newly found magnetically-driven jet in the latter case is accelerated by a strong magnetic field created by frame dragging in the ergosphere. Through this process, the magnetic field extracts the energy of the black hole rotation.Comment: Co-rotating and counter-rotating disks; 8 pages; submitted to ApJ letter

Magnetized Accretion Inside the Marginally Stable Orbit around a Black Hole

Qualitative arguments are presented to demonstrate that the energy density of magnetic fields in matter accreting onto a black hole inside the marginally stable orbit is automatically comparable to the rest-mass energy density of the accretion flow. Several consequences follow: magnetic effects must be dynamically significant, but cannot be so strong as to dominate; outward energy transport in Alfven waves may alter the effective efficiency of energy liberation; and vertical magnetic stresses in this region may contribute to "coronal" activity.Comment: to appear in Ap. J. Letter

HARM: A Numerical Scheme for General Relativistic Magnetohydrodynamics

We describe a conservative, shock-capturing scheme for evolving the equations of general relativistic magnetohydrodynamics. The fluxes are calculated using the Harten, Lax, and van Leer scheme. A variant of constrained transport, proposed earlier by T\'oth, is used to maintain a divergence free magnetic field. Only the covariant form of the metric in a coordinate basis is required to specify the geometry. We describe code performance on a full suite of test problems in both special and general relativity. On smooth flows we show that it converges at second order. We conclude by showing some results from the evolution of a magnetized torus near a rotating black hole.Comment: 38 pages, 18 figures, submitted to Ap

Numerical 3+1 general relativistic magnetohydrodynamics: a local characteristic approach

We present a general procedure to solve numerically the general relativistic magnetohydrodynamics (GRMHD) equations within the framework of the 3+1 formalism. The work reported here extends our previous investigation in general relativistic hydrodynamics (Banyuls et al. 1997) where magnetic fields were not considered. The GRMHD equations are written in conservative form to exploit their hyperbolic character in the solution procedure. All theoretical ingredients necessary to build up high-resolution shock-capturing schemes based on the solution of local Riemann problems (i.e. Godunov-type schemes) are described. In particular, we use a renormalized set of regular eigenvectors of the flux Jacobians of the relativistic magnetohydrodynamics equations. In addition, the paper describes a procedure based on the equivalence principle of general relativity that allows the use of Riemann solvers designed for special relativistic magnetohydrodynamics in GRMHD. Our formulation and numerical methodology are assessed by performing various test simulations recently considered by different authors. These include magnetized shock tubes, spherical accretion onto a Schwarzschild black hole, equatorial accretion onto a Kerr black hole, and magnetized thick accretion disks around a black hole prone to the magnetorotational instability.Comment: 18 pages, 8 figures, submitted to Ap

Magnetohydrodynamics in full general relativity: Formulation and tests

A new implementation for magnetohydrodynamics (MHD) simulations in full general relativity (involving dynamical spacetimes) is presented. In our implementation, Einstein's evolution equations are evolved by a BSSN formalism, MHD equations by a high-resolution central scheme, and induction equation by a constraint transport method. We perform numerical simulations for standard test problems in relativistic MHD, including special relativistic magnetized shocks, general relativistic magnetized Bondi flow in stationary spacetime, and a longterm evolution for self-gravitating system composed of a neutron star and a magnetized disk in full general relativity. In the final test, we illustrate that our implementation can follow winding-up of the magnetic field lines of magnetized and differentially rotating accretion disks around a compact object until saturation, after which magnetically driven wind and angular momentum transport inside the disk turn on.Comment: 28 pages, to be published in Phys. Rev.

Do the colors of your letters depend on your language? Language-dependent and universal influences on grapheme-color synesthesia in seven languages

Grapheme-color synesthetes experience graphemes as having a consistent color (e.g., “N is turquoise”). Synesthetes’ specific associations (which letter is which color) are often influenced by linguistic properties such as phonetic similarity, color terms (“Y is yellow”), and semantic associations (“D is for dog and dogs are brown”). However, most studies of synesthesia use only English-speaking synesthetes. Here, we measure the effect of color terms, semantic associations, and non-linguistic shape-color associations on synesthetic associations in Dutch, English, Greek, Japanese, Korean, Russian, and Spanish. The effect size of linguistic influences (color terms, semantic associations) differed significantly between languages. In contrast, the effect size of nonlinguistic influences (shape-color associations), which we predicted to be universal, indeed did not differ between languages. We conclude that language matters (outcomes are influenced by the synesthete’s language) and that synesthesia offers an exceptional opportunity to study influences on letter representations in different languages.Depto. de Psicobiología y Metodología en Ciencias del ComportamientoFac. de PsicologíaTRUEpu

ZnS Ultrathin interfacial layers for optimizing carrier management in Sb2S3-based photovoltaics

Antimony chalcogenides represent a family of materials of low toxicity and relative abundance, with a high potential for future sustainable solar energy conversion technology. However, solar cells based on antimony chalcogenides present open-circuit voltage losses that limit their efficiencies. These losses are attributed to several recombination mechanisms, with interfacial recombination being considered as one of the dominant processes. In this work, we exploit atomic layer deposition (ALD) to grow a series of ultrathin ZnS interfacial layers at the TiO2/Sb2S3 interface to mitigate interfacial recombination and to increase the carrier lifetime. ALD allows for very accurate control over the ZnS interlayer thickness on the ångström scale (0-1.5 nm) and to deposit highly pure Sb2S3. Our systematic study of the photovoltaic and optoelectronic properties of these devices by impedance spectroscopy and transient absorption concludes that the optimum ZnS interlayer thickness of 1.0 nm achieves the best balance between the beneficial effect of an increased recombination resistance at the interface and the deleterious barrier behavior of the wide-bandgap semiconductor ZnS. This optimization allows us to reach an overall power conversion efficiency of 5.09% in planar configuration

Three-Dimensional Hydrodynamic Simulations of Accretion Tori in Kerr Spacetimes

This paper presents results of three-dimensional simulations of global hydrodynamic instabilities in black hole tori, extending earlier work by Hawley to Kerr spacetimes. This study probes a three-dimensional parameter space of torus angular momentum, torus size, and black hole angular momentum. We have observed the growth of the Papaloizou-Pringle instability for a range of torus configurations and the resultant formation of m=1 planets. We have also observed the quenching of this instability in the presence of early accretion flows; however, in one simulation both early accretion and planet formation occurred. Though most of the conclusions reached in Hawley's earlier work on Schwarzschild black holes carry over to Kerr spacetime, the presence of frame dragging in the Kerr geometry adds an element of complexity to the simulations; we have seen especially clear examples of this phenomenon in the accretion flows that arise from retrograde tori.Comment: Accepted for publication in ApJ. 23 pages, 11 figures, animations available at http://www.astro.virginia.edu/~jd5v/h91redux/h91redux.htm

Aplicação da biônica no desenvolvimento de produtos: uma sinergia entre o design de calçados e os novos materiais

Este trabalho tem como objetivo verificar a potencialidade das resinas poliuretanas (PU) com a adição de cargas de celulolignina a 10, 20, 30, 40 e 50% na aplicação em solados de calçados e averiguar sua capacidade de moldagem da forma, geometrias e texturas com o uso das ferramentas da Biônica. O PU é utilizado na área calçadista devido à alta resistência a abrasão, flexão e rasgo, flexibilidade, elasticidade, conforto, fácil moldagem de formas e baixa densidade. Os compósitos com uso de fibra natural tem sido um atrativo pela redução do custo do produto, conceito de sustentabilidade e passíveis de reciclabilidade, alta resistência e propriedades específicas superiores aos componentes isolados. Por meio da Biônica realizam-se analogias que relacionam formas, funções e comportamentos dos meios naturais, solucionando problemas existentes ou geram-se possibilidades inovadoras no produto. Na metodologia foi realizado um estudo exploratório de planejamento das misturas da resina PU com variações de celulose e lignina em 10, 20, 30, 40, 50% de carga. Foi feita a Microscopia Eletrônica de Varredura (MEV) utilizando um aparelho tipo VP 1450 LMEDEMAR- EEL-USP. Utilizou-se como ferramenta de desenvolvimento de texturas a Biônica no Laboratório de Texturas, Materiais e Modelagem - FATEA. Os resultados preliminares obtidos pelo MEV foram: a partir de 30% lignina apresenta mudanças na morfologia, que contribui na fragilização estrutural, já mistura com a celulose a partir de 40% em sua composição proporciona alterações significativas em sua forma estrutural (morfologia da partícula) rompendo, ocasionando o aumento da dureza e a perda a maleabilidade e ductilidade. A reprodução da forma desenvolvida por meio da Biônica é plenamente reproduzível ao material