3,238 research outputs found
Schwarzschild Tests of the Wahlquist-Estabrook-Buchman-Bardeen Tetrad Formulation for Numerical Relativity
A first order symmetric hyperbolic tetrad formulation of the Einstein
equations developed by Estabrook and Wahlquist and put into a form suitable for
numerical relativity by Buchman and Bardeen (the WEBB formulation) is adapted
to explicit spherical symmetry and tested for accuracy and stability in the
evolution of spherically symmetric black holes (the Schwarzschild geometry).
The lapse and shift which specify the evolution of the coordinates relative to
the tetrad congruence are reset at frequent time intervals to keep the
constant-time hypersurfaces nearly orthogonal to the tetrad congruence and the
spatial coordinate satisfying a kind of minimal rate of strain condition. By
arranging through initial conditions that the constant-time hypersurfaces are
asymptotically hyperbolic, we simplify the boundary value problem and improve
stability of the evolution. Results are obtained for both tetrad gauges
(``Nester'' and ``Lorentz'') of the WEBB formalism using finite difference
numerical methods. We are able to obtain stable unconstrained evolution with
the Nester gauge for certain initial conditions, but not with the Lorentz
gauge.Comment: (accepted by Phys. Rev. D) minor changes; typos correcte
Thermodynamic Properties of Spherically-Symmetric, Uniformly-Accelerated Reference Frames
We aim to study the thermodynamic properties of the spherically symmetric
reference frames with uniform acceleration, including the spherically symmetric
generalization of Rindler reference frame and the new kind of uniformly
accelerated reference frame. We find that, unlike the general studies about the
horizon thermodynamics, one cannot obtain the laws of thermodynamics for their
horizons in the usual approaches, despite that one can formally define an area
entropy (Bekenstein-Hawking entropy). In fact, the common horizon for a set of
uniformly accelerated observers is not always exist, even though the
Hawking-Unruh temperature is still well-defined. This result indicates that the
Hawking-Unruh temperature is only a kinematic effect, to gain the laws of
thermodynamics for the horizon, one needs the help of dynamics. Our result is
in accordance with those from the various studies about the acoustic black
holes.Comment: 8 page
The effect of geometry on charge confinement in three dimensions
We show that, in contrast to the flat case, the Maxwell theory is not
confining in the background of the three dimensional BTZ black-hole (covering
space). We also study the effect of the curvature on screening behavior of
Maxwell-Chern-Simons model in this space-time.Comment: 8 pages. To be published in Europhysics Letter
Unimolecular Reactions Following Indoor and Outdoor Limonene Ozonolysis
Limonene is one of the monoterpenes with the largest biogenic emissions and is also widely used as an additive in cleaning products, leading to significant indoor emissions. Studies have found that the formation of secondary organic aerosols (SOAs) from limonene oxidation has important implications for indoor air quality. Although ozonolysis is considered the major limonene oxidation pathway under most indoor conditions, little is known about the mechanisms for SOA formation from limonene ozonolysis. Here, we calculate the rate coefficients of the possible unimolecular reactions of the first-generation peroxy radicals formed by limonene ozonolysis using a high-level multiconformer transition state theory approach. We find that all of the peroxy radicals formed initially in the ozonolysis of limonene react unimolecularly with rates that are competitive both indoors and outdoors, except under highly polluted conditions. Differences in reactivity between the peroxy radicals from ozonolysis and those formed by OH, NO₃, and Cl oxidation are discussed. Finally, we sketch possible oxidation mechanisms for the different peroxy radicals under both indoor and pristine atmospheric conditions and in more polluted environments. In environments with low concentrations of HO₂ and NO, efficient autoxidation will lead to the formation of highly oxygenated organic compounds and thus likely aid in the growth of SOA
Consistent Gravitationally-Coupled Spin-2 Field Theory
Inspired by the translational gauge structure of teleparallel gravity, the
theory for a fundamental massless spin-2 field is constructed. Accordingly,
instead of being represented by a symmetric second-rank tensor, the fundamental
spin-2 field is assumed to be represented by a spacetime (world) vector field
assuming values in the Lie algebra of the translation group. The flat-space
theory naturally emerges in the Fierz formalism and is found to be equivalent
to the usual metric-based theory. However, the gravitationally coupled theory,
with gravitation itself described by teleparallel gravity, is shown not to
present the consistency problems of the spin-2 theory constructed on the basis
of general relativity.Comment: 16 pages, no figures. V2: Presentation changes, including addition of
a new sub-section, aiming at clarifying the text; version accepted for
publication in Class. Quantum Grav
Huygens' Principle for the Klein-Gordon equation in the de Sitter spacetime
In this article we prove that the Klein-Gordon equation in the de Sitter
spacetime obeys the Huygens' principle only if the physical mass of the
scalar field and the dimension of the spatial variable are tied by
the equation . Moreover, we define the incomplete Huygens'
principle, which is the Huygens' principle restricted to the vanishing second
initial datum, and then reveal that the massless scalar field in the de Sitter
spacetime obeys the incomplete Huygens' principle and does not obey the
Huygens' principle, for the dimensions , only. Thus, in the de Sitter
spacetime the existence of two different scalar fields (in fact, with m=0 and
), which obey incomplete Huygens' principle, is equivalent to
the condition (in fact, the spatial dimension of the physical world). For
these two values of the mass are the endpoints of the so-called in
quantum field theory the Higuchi bound. The value of the
physical mass allows us also to obtain complete asymptotic expansion of the
solution for the large time. Keywords: Huygens' Principle; Klein-Gordon
Equation; de Sitter spacetime; Higuchi Boun
Stereoselectivity in Atmospheric Autoxidation
We show that the diastereomers of hydroxy peroxy radicals formed from OH and O_2 addition to C2 and C3, respectively, of crotonaldehyde (CH_3CHCHCHO) undergo gas-phase unimolecular aldehydic hydrogen shift (H-shift) chemistry with rate coefficients that differ by an order of magnitude. The stereospecificity observed here for crotonaldehyde is general and will lead to a significant diastereomeric-specific chemistry in the atmosphere. This enhancement of specific stereoisomers by stereoselective gas-phase reactions could have widespread implications given the ubiquity of chirality in nature. The H-shift rate coefficients calculated using multiconformer transition state theory (MC-TST) agree with those determined experimentally using stereoisomer-specific gas-chromatography chemical ionization mass spectroscopy (GC–CIMS) measurements
Audition in vampire bats, Desmodus rotundus
1. Within the tonotopic organization of the inferior colliculus two frequency ranges are well represented: a frequency range within that of the echolocation signals from 50 to 100 kHz, and a frequency band below that of the echolocation sounds, from 10 to 35 kHz. The frequency range between these two bands, from about 40 to 50 kHz is distinctly underrepresented (Fig. 3B).
2. Units with BFs in the lower frequency range (10–25 kHz) were most sensitive with thresholds of -5 to -11 dB SPL, and units with BFs within the frequency range of the echolocation signals had minimal thresholds around 0 dB SPL (Fig. 1).
3. In the medial part of the rostral inferior colliculus units were encountered which preferentially or exclusively responded to noise stimuli. — Seven neurons were found which were only excited by human breathing noises and not by pure tones, frequency modulated signals or various noise bands. These neurons were considered as a subspeciality of the larger sample of noise-sensitive neurons. — The maximal auditory sensitivity in the frequency range below that of echolocation, and the conspicuous existence of noise and breathing-noise sensitive units in the inferior colliculus are discussed in context with the foraging behavior of vampire bats
Centers of Mass and Rotational Kinematics for the Relativistic N-Body Problem in the Rest-Frame Instant Form
In the Wigner-covariant rest-frame instant form of dynamics it is possible to
develop a relativistic kinematics for the N-body problem. The Wigner
hyperplanes define the intrinsic rest frame and realize the separation of the
center-of-mass. Three notions of {\it external} relativistic center of mass can
be defined only in terms of the {\it external} Poincar\'e group realization.
Inside the Wigner hyperplane, an {\it internal} unfaithful realization of the
Poincar\'e group is defined. The three concepts of {\it internal} center of
mass weakly {\it coincide} and are eliminated by the rest-frame conditions. An
adapted canonical basis of relative variables is found. The invariant mass is
the Hamiltonian for the relative motions. In this framework we can introduce
the same {\it dynamical body frames}, {\it orientation-shape} variables, {\it
spin frame} and {\it canonical spin bases} for the rotational kinematics
developed for the non-relativistic N-body problem.Comment: 78 pages, revtex fil
- …