1,889 research outputs found
Equivalence of Darmois-Israel and Distributional-Methods for Thin Shells in General Relativity
A distributional method to solve the Einstein's field equations for thin
shells is formulated. The familiar field equations and jump conditions of
Darmois-Israel formalism are derived. A carefull analysis of the Bianchi
identities shows that, for cases under consideration, they make sense as
distributions and lead to jump conditions of Darmois-Israel formalism.Comment: 17 pages Latex, no figures, to be published in Journ. Math. Phy
Tests of relativity using a microwave resonator
The frequencies of a cryogenic sapphire oscillator and a hydrogen maser are
compared to set new constraints on a possible violation of Lorentz invariance.
We determine the variation of the oscillator frequency as a function of its
orientation (Michelson-Morley test) and of its velocity (Kennedy-Thorndike
test) with respect to a preferred frame candidate. We constrain the
corresponding parameters of the Mansouri and Sexl test theory to and which is equivalent to the best previous result for the
former and represents a 30 fold improvement for the latter.Comment: 8 pages, 2 figures, submitted to Physical Review Letters (October 3,
2002
E-Learning for Teachers and Trainers : Innovative Practices, Skills and Competences
Reproduction is authorised provided the source is acknowledged.Final Published versio
A New Limit on Signals of Lorentz Violation in Electrodynamics
We describe the results of an experiment to test for spacetime anisotropy
terms that might exist from Lorentz violations. The apparatus consists of a
pair of cylindrical superconducting cavity-stabilized oscillators operating in
the TM_{010} mode with one axis east-west and the other vertical. Spatial
anisotropy is detected by monitoring the beat frequency at the sidereal rate
and its first harmonic. We see no anisotropy to a part in 10^{13}. This puts a
comparable bound on four linear combinations of parameters in the general
Standard Model extension, and a weaker bound of <4 x 10^{-9} on three others.Comment: 4 pages, 3 figures, 2 table
Fracture analysis of concrete gravity dam under earthquake induced loads
In this paper, seismic fracture behavior of the concrete gravity dam using finite element (2D) theory has been studied. Bazant model which is non-linear fracture mechanics criteria as a measure of growth and smeared crack was chosen to develop profiles of the crack. Behavior of stress - strain curves of concrete as a simplified two-line, dam and reservoir system using the formulation of the Euler - Lagrange was chosen. According to the above models, Koyna concrete gravity dam were investigated by the 1967 earthquake record. The results provide profiles of growth and expansion first with the effects of reservoir and second without it. Comparison of the obtained results shows good agreement with the works of the other researchers
Limits on the Time Evolution of Space Dimensions from Newton's Constant
Limits are imposed upon the possible rate of change of extra spatial
dimensions in a decrumpling model Universe with time variable spatial
dimensions (TVSD) by considering the time variation of (1+3)-dimensional
Newton's constant. Previous studies on the time variation of (1+3)-dimensional
Newton's constant in TVSD theory had not been included the effects of the
volume of the extra dimensions and the effects of the surface area of the unit
sphere in D-space dimensions. Our main result is that the absolute value of the
present rate of change of spatial dimensions to be less than about
10^{-14}yr^{-1}. Our results would appear to provide a prima facie case for
ruling the TVSD model out. We show that based on observational bounds on the
present-day variation of Newton's constant, one would have to conclude that the
spatial dimension of the Universe when the Universe was at the Planck scale to
be less than or equal to 3.09. If the dimension of space when the Universe was
at the Planck scale is constrained to be fractional and very close to 3, then
the whole edifice of TVSD model loses credibility.Comment: 22 pages, accepted for publication in Int.J.Mod.Phys.
The Association Between Borna Disease Virus and Chronic Fatigue Syndrome: A Systematic Review and Meta-Analysis
Context: Several studies have controversial results regarding the association between Borna disease virus (BDV) and chronic fatigue syndrome (CFS). The present systematic review and meta-analysis investigated the association between CFS and BDV. Evidence Acquisition: The present study was conducted based on the PRISMA guidelines for systematic review and meta-analysis studies. To avoid bias, all procedures of the study were performed by two researchers independently. A comprehensive search was performed using online databases, including PubMed, Scopus, Embase, PsycINFO, science Direct, Cochrane Library, web of science, and Google scholar using the MeSH keywords until December 12th, 2016. Heterogeneity among studies was evaluated using Cochran's Q test I-2 Index. Finally, the random effect model was used for combined Odds Ratio (OR) using Review Manger software version 5.3.5. Results: Among 9 eligible studies comprising 610 cases and 2176 controls, the total OR for association between BDV and CFS was estimated to be 10.41 (95 confidence interval CI: 4.24 - 25.55, P < 0.0001). For subgroup analysis by the diagnostic methods (ELISA, RT-PCR, and Western blot), OR was 2.47 (95% CI: 0.77 - 7.96, P=0.13), 12.20 (95% CI: 1.66 - 89.57, P=0.01), and 28.36 (95% CI: 3.76- 213.85, P=0.001), respectively (test for subgroup differences: P=0.08; I-2=59.5). Subgroup analysis for BDV and CFS association by antigens and antibodies had an OR of 12.20 (1.66, 89.57) and 8.20 (3.32, 20.22), respectively (test for subgroup differences: P=0.72; I-2=0). Conclusions: This study supports the association between BDV and CFS and shows the role of viral agents in etiology of CFS. Therefore, viral agents may play a role in the etiology of neuropsychiatric disorders
Radiation from the LTB black hole
Does a dynamical black hole embedded in a cosmological FRW background emit
Hawking radiation where a globally defined event horizon does not exist? What
are the differences to the Schwarzschild black hole? What about the first law
of black hole mechanics? We face these questions using the LTB cosmological
black hole model recently published. Using the Hamilton-Jacobi and radial null
geodesic-methods suitable for dynamical cases, we show that it is the apparent
horizon which contributes to the Hawking radiation and not the event horizon.
The Hawking temperature is calculated using the two different methods giving
the same result. The first law of LTB black hole dynamics and the thermal
character of the radiation is also dealt with.Comment: 9 pages, revised version, Europhysics Letter 2012 97 2900
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