2,607 research outputs found
Extreme Mass Ratio Binary: Radiation reaction and gravitational waveform
For a successful detection of gravitational waves by LISA, it is essential to
construct theoretical waveforms in a reliable manner. We discuss gravitational
waves from an extreme mass ratio binary system which is expected to be a
promising target of the LISA project.
The extreme mass ratio binary is a binary system of a supermassive black hole
and a stellar mass compact object. As the supermassive black hole dominates the
gravitational field of the system, we suppose that the system might be well
approximated by a metric perturbation of a Kerr black hole. We discuss a recent
theoretical progress in calculating the waveforms from such a system.Comment: Classical and Quantum Gravity 22 (2005) S375-S379, Proceedings for
5th International LISA Symposiu
From the self-force problem to the Radiation reaction formula
We review a recent theoretical progress in the so-called self-force problem
of a general relativistic two-body system. Although a two-body system in
Newtonian gravity is a very simple problem, some fundamental issues are
involved in relativistic gravity. Besides, because of recent projects for
gravitational wave detection, it comes to be possible to see those phenomena
directly via gravitational waves, and the self-force problem becomes one of
urgent and highly-motivated problems in general relativity. Roughly speaking,
there are two approaches to investigate this problem; the so-called
post-Newtonian approximation, and a black hole perturbation.
In this paper, we review a theoretical progress in the self-force problem
using a black hole perturbation. Although the self-force problem seems to be
just a problem to calculate a self-force, we discuss that the real problem is
to define a gauge invariant concept of a motion in a gauge dependent metric
perturbation.Comment: a special issue for Classical and Quantum Gravity, a review article
of Capra Ranch Meeting
An Exploratory Study of Nucleon-Nucleon Scattering Lengths in Lattice QCD
An exploratory study is made of the nucleon-nucleon -wave scattering
lengths in quenched lattice QCD with the Wilson quark action. The - and
- scattering lengths are also calculated for comparison. The
calculations are made with heavy quarks corresponding to . The results show that the - system has an attractive force in
both spin-singlet and triplet channels, with their scattering lengths
significantly larger than those for the - and - cases, a
trend which is qualitatively consistent with the experiment. Problems toward a
more realistic calculation for light quarks are discussed.Comment: 9 pages. Latex file. Figures are also included as ps file
Gauge Problem in the Gravitational Self-Force II. First Post Newtonian Force under Regge-Wheeler Gauge
We discuss the gravitational self-force on a particle in a black hole
space-time. For a point particle, the full (bare) self-force diverges. It is
known that the metric perturbation induced by a particle can be divided into
two parts, the direct part (or the S part) and the tail part (or the R part),
in the harmonic gauge, and the regularized self-force is derived from the R
part which is regular and satisfies the source-free perturbed Einstein
equations. In this paper, we consider a gauge transformation from the harmonic
gauge to the Regge-Wheeler gauge in which the full metric perturbation can be
calculated, and present a method to derive the regularized self-force for a
particle in circular orbit around a Schwarzschild black hole in the
Regge-Wheeler gauge. As a first application of this method, we then calculate
the self-force to first post-Newtonian order. We find the correction to the
total mass of the system due to the presence of the particle is correctly
reproduced in the force at the Newtonian order.Comment: Revtex4, 43 pages, no figure. Version to be published in PR
Improved tunneling magnetoresistance at low temperature in manganite junctions grown by molecular beam epitaxy
We report resistance versus magnetic field measurements for a
La0.65Sr0.35MnO3/SrTiO3/La0.65Sr0.35MnO3 tunnel junction grown by
molecular-beam epitaxy, that show a large field window of extremely high
tunneling magnetoresistance (TMR) at low temperature. Scanning the in-plane
applied field orientation through 360^/circ, the TMR shows 4-fold symmetry,
i.e. biaxial anisotropy, aligned with the crystalline axes but not the junction
geometrical long axis. The TMR reaches ~ 1900% at 4K, corresponding to an
interfacial spin polarization of > 95% assuming identical interfaces. These
results show that uniaxial anisotropy is not necessary for large TMR, and lay
the groundwork for future improvements in TMR in manganite junctions.Comment: 6 pages, 7 figures; accepted in Applied Physics Letter
Predicting tire/pavement noise impact reduction using numerical simulation and experimental data for open graded asphalt mixture
The environmental impact of noise from roads and highways traffic is relevant in urban and rural areas. The use of open-graded asphalt pavements reduces significantly the noise, entrapping the acoustic waves inside the porous structure of the material. In this paper we propose a simulation approach in order to predict the acoustic properties of the asphalt mixture from geometrical and topological indicators. In detail we have generated, using a Random Sequential Adsorption model, synthetic samples starting from the same grading and bitumen contents of real samples manufactured in laboratory. We have measured the acoustic adsorption coefficient of the real samples and we have investigated the correlation between this coefficient and some numerical indicators extracted from the simulated samples. Dimension and content of voids seem to be the most significant indicators for predicting acoustic properties of HMA. These correlations, that seem to be very promising, are useful in order to optimize the design of HMA in the perspective of minimizing noise impact
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Reduced brain mammillary body volumes and memory deficits in adolescents who have undergone the Fontan procedure.
BackgroundAdolescents with single ventricle heart disease (SVHD) who have undergone the Fontan procedure show cognitive/memory deficits. Mammillary bodies are key brain sites that regulate memory; however, their integrity in SVHD is unclear. We evaluated mammillary body (MB) volumes and their associations with cognitive/memory scores in SVHD and controls.MethodsBrain MRI data were collected from 63 adolescents (25 SVHD; 38 controls) using a 3.0-Tesla MRI scanner. Cognition and memory were assessed using Montreal Cognitive Assessment (MoCA) and Wide Range Assessment of Memory and Learning 2. MB volumes were calculated and compared between groups (ANCOVA, covariates: age, sex, and total brain volume [TBV]). Partial correlations and linear regression were performed to examine associations between volumes and cognitive scores (covariates: age, sex, and TBV).ResultsSVHD group showed significantly lower MoCA and WRAML2 scores over controls. MB volumes were significantly reduced in SVHD over controls. After controlling for age, sex, and TBV, MB volumes correlated with MoCA and delayed memory recall scores in SVHD and controls.ConclusionAdolescents with SVHD show reduced MB volumes associated with cognitive/memory deficits. Potential mechanisms of volume losses may include developmental and/or hypoxic/ischemic-induced processes. Providers should screen for cognitive deficits and explore possible interventions to improve memory
El concepto jurisprudencial de empresa en Chile. Analisis y confrontacion de su contenido en el Derecho Comercial y en Materia Laboral
72 p.El objetivo de esta Memoria de Prueba, es analizar el concepto de empresa manejado por los tribunales superiores de justicia de nuestro país, en el ámbito del Derecho Comercial, durante los últimos seis años, con la finalidad de confrontarlo con la noción jurisprudencial de empresa en el terreno laboral, determinando sus similitudes, diferencias y eventuales implicancias. El método de investigación, consistió en un análisis deductivo de las sentencias recopiladas, discriminando y
clasificando los contenidos preponderantes que se le otorgan a la palabra empresa, para luego contrastarlas con lo dispuesto en materia laboral. Existen distintos conceptos jurisprudenciales de empresa entre las disciplinas jurídicas estudiadas. La jurisprudencia comercial, en general, no discute el concepto de empresa, inclinándose por diversas teorías que ha elaborado la doctrina comercial. Por otro lado, la jurisprudencia laboral dispone otras formas de entender la empresa, mas amplias y orientadas por principios fácticos que pretenden resguardar los
derechos laborales
Axiomatic approach to radiation reaction of scalar point particles in curved spacetime
Several different methods have recently been proposed for calculating the
motion of a point particle coupled to a linearized gravitational field on a
curved background. These proposals are motivated by the hope that the point
particle system will accurately model certain astrophysical systems which are
promising candidates for observation by the new generation of gravitational
wave detectors. Because of its mathematical simplicity, the analogous system
consisting of a point particle coupled to a scalar field provides a useful
context in which to investigate these proposed methods. In this paper, we
generalize the axiomatic approach of Quinn and Wald in order to produce a
general expression for the self force on a point particle coupled to a scalar
field following an arbitrary trajectory on a curved background. Our equation
includes the leading order effects of the particle's own fields, commonly
referred to as ``self force'' or ``radiation reaction'' effects. We then
explore the equations of motion which follow from this expression in the
absence of non-scalar forces.Comment: 17 pages, 1 figur
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