4,927 research outputs found
Simulation of granular jet: Is granular flow really a "perfect fluid?"
We perform three-dimensional simulations of a granular jet impact for both
frictional and frictionless grains. Small shear stress observed in the
experiment[X. Cheng et al., Phys. Rev. Lett. 99, 188001 (2007) ] is reproduced
through our simulation. However, the fluid state after the impact is far from a
perfect fluid, and thus, similarity between granular jets and quark gluon
plasma is superficial, because the observed viscosity is finite and its value
is consistent with the prediction of the kinetic theory.Comment: 8 pages 11 figures(9 figures: text, 2 figures: supplementary
material) 2 tables. To be published in Phys. Rev.
An attempt to find precursors in the ULF geomagnetic data by means of flicker noise spectroscopy
International audienceThe flicker noise spectroscopy which is a new phenomenological method for the retrieval of information contained in chaotic time signals, is based on the analysis of recognizable irregularities (pulse, jumps, and discontinuities of derivatives of various order). This method is applied to the ULF (ultra-low-frequency) data observed at Guam in 1992?1994, in order to study the temporal nonlinear behavior of the lithospheric activity prior to the large 1993 Guam earthquake (8 August 1993). We have found that the lithosphere must have exhibited the step-like discontinuous behaviors in the lithosphere 101, 78, 54, 31 and 8 days before the main shock. This kind of nonlinear temporal behavior can be tracked by means of our flicker noise spectroscopy
Giant tunnel magnetoresistance and high annealing stability in CoFeB/MgO/CoFeB magnetic tunnel junctions with synthetic pinned layer
We investigated the relationship between tunnel magnetoresistance (TMR) ratio
and the crystallization of CoFeB layers through annealing in magnetic tunnel
junctions (MTJs) with MgO barriers that had CoFe/Ru/CoFeB synthetic ferrimagnet
pinned layers with varying Ru spacer thickness (tRu). The TMR ratio increased
with increasing annealing temperature (Ta) and tRu, reaching 361% at Ta = 425C,
whereas the TMR ratio of the MTJs with pinned layers without Ru spacers
decreased at Ta over 325C. Ruthenium spacers play an important role in forming
an (001)-oriented bcc CoFeB pinned layer, resulting in a high TMR ratio through
annealing at high temperatures.Comment: 10 pages, 5 figures, submitted to Applied Physics Letter
Runaway Merging of Black Holes: Analytical Constraint on the Timescale
Following the discovery of a black hole (BH) with a mass of 10^3-10^6 M(sun)
in a starburst galaxy M82, we study formation of such a BH via successive
merging of stellar-mass BHs within a star cluster. The merging has a runaway
characteristic. This is because massive BHs sink into the cluster core and have
a high number density, and because the merging probability is higher for more
massive BHs. We use the Smoluchowski equation to study analytically the
evolution of the BH mass distribution. Under favorable conditions, which are
expected for some star clusters in starburst galaxies, the timescale of the
runaway merging is at most of order 10^7 yr. This is short enough to account
for the presence of a BH heavier than 10^3 M(sun) in an ongoing starburst
region.Comment: 10 pages, no figures, to appear in The Astrophysical Journal
(Letters
Correlation between X-ray flux and rotational acceleration in Vela X-1
The results of a search for correlations between X-ray flux and angular acceleration for the accreting binary pulsar Vela X-1 are presented. Results are based on data obtained with the Hakucho satellite during the interval 1982 to 1984. In undertaking this correlation analysis, it was necessary to modify the usual statistical method to deal with conditions imposed by generally unavoidable satellite observing constraints, most notably a mismatch in sampling between the two variables. The results are suggestive of a correlation between flux and the absolute value of the angular acceleration, at a significance level of 96 percent. The implications of the methods and results for future observations and analysis are discussed
Collision of One-Dimensional Nonlinear Chains
We investigate one-dimensional collisions of unharmonic chains and a rigid
wall. We find that the coefficient of restitution (COR) is strongly dependent
on the velocity of colliding chains and has a minimum value at a certain
velocity. The relationship between COR and collision velocity is derived for
low-velocity collisions using perturbation methods. We found that the velocity
dependence is characterized by the exponent of the lowest unharmonic term of
interparticle potential energy
Pion pole contribution to hadronic light-by-light scattering and muon anomalous magnetic moment
We derive an analytic result for the pion pole contribution to the
light-by-light scattering correction to the anomalous magnetic moment of the
muon, . Using the vector meson dominance model (VMD) for
the pion transition form factor, we obtain .Comment: 4 pages, revte
Electroweak Hadronic Contributions to the muon g-2
We reanalyze the two-loop electroweak hadronic contributions to the muon g-2
that may be enhanced by large logarithms. The present evaluation is improved
over those already existing in the literature by the implementation of the
current algebra Ward identities and the inclusion of the correct short-distance
QCD behaviour of the relevant hadronic Green's function.Comment: 29 pages, 6 figures, LaTeX. Typos fixe
Heat conduction induced by non-Gaussian athermal fluctuations
We study the properties of heat conduction induced by non-Gaussian noises
from athermal environments. We find that new terms should be added to the
conventional Fourier law and the fluctuation theorem for the heat current,
where its average and fluctuation are determined not only by the noise
intensities but also by the non-Gaussian nature of the noises. Our results
explicitly show the absence of the zeroth law of thermodynamics in athermal
systems.Comment: 15 pages, 4 figures, PRE in pres
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