3,664 research outputs found
Euler hydrodynamics of one-dimensional attractive particle systems
We consider attractive irreducible conservative particle systems on
, without necessarily nearest-neighbor jumps or explicit invariant
measures. We prove that for such systems, the hydrodynamic limit under Euler
time scaling exists and is given by the entropy solution to some scalar
conservation law with Lipschitz-continuous flux. Our approach is a
generalization of Bahadoran et al. [Stochastic Process. Appl. 99 (2002) 1--30],
from which we relax the assumption that the process has explicit invariant
measures.Comment: Published at http://dx.doi.org/10.1214/009117906000000115 in the
Annals of Probability (http://www.imstat.org/aop/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Structure and Strength of Dislocation Junctions: An Atomic Level Analysis
The quasicontinuum method is used to simulate three-dimensional
Lomer-Cottrell junctions both in the absence and in the presence of an applied
stress. The simulations show that this type of junction is destroyed by an
unzipping mechanism in which the dislocations that form the junction are
gradually pulled apart along the junction segment. The calculated critical
stress needed for breaking the junction is comparable to that predicted by line
tension models. The simulations also demonstrate a strong influence of the
initial dislocation line directions on the breaking mechanism, an effect that
is neglected in the macroscopic treatment of the hardening effect of junctions.Comment: 4 pages, 3 figure
Mesoscopic Analysis of Structure and Strength of Dislocation Junctions in FCC Metals
We develop a finite element based dislocation dynamics model to simulate the
structure and strength of dislocation junctions in FCC crystals. The model is
based on anisotropic elasticity theory supplemented by the explicit inclusion
of the separation of perfect dislocations into partial dislocations bounding a
stacking fault. We demonstrate that the model reproduces in precise detail the
structure of the Lomer-Cottrell lock already obtained from atomistic
simulations. In light of this success, we also examine the strength of
junctions culminating in a stress-strength diagram which is the locus of points
in stress space corresponding to dissolution of the junction.Comment: 9 Pages + 4 Figure
Current Fluctuations of the One Dimensional Symmetric Simple Exclusion Process with Step Initial Condition
For the symmetric simple exclusion process on an infinite line, we calculate
exactly the fluctuations of the integrated current during time
through the origin when, in the initial condition, the sites are occupied with
density on the negative axis and with density on the positive
axis. All the cumulants of grow like . In the range where , the decay of the distribution of is
non-Gaussian. Our results are obtained using the Bethe ansatz and several
identities recently derived by Tracy and Widom for exclusion processes on the
infinite line.Comment: 2 figure
Mutations in the Fatty Acid 2-Hydroxylase Gene Are Associated with Leukodystrophy with Spastic Paraparesis and Dystonia
Myelination is a complex, developmentally regulated process whereby myelin proteins and lipids are coordinately expressed by myelinating glial cells. Homozygosity mapping in nine patients with childhood onset spasticity, dystonia, cognitive dysfunction, and periventricular white matter disease revealed inactivating mutations in the FA2H gene. FA2H encodes the enzyme fatty acid 2-hydroxylase that catalyzes the 2-hydroxylation of myelin galactolipids, galactosylceramide, and its sulfated form, sulfatide. To our knowledge, this is the first identified deficiency of a lipid component of myelin and the clinical phenotype underscores the importance of the 2-hydroxylation of galactolipids for myelin maturation. In patients with autosomal-recessive unclassified leukodystrophy or complex spastic paraparesis, sequence analysis of the FA2H gene is warranted
Silicon carbide absorption features: dust formation in the outflows of extreme carbon stars
Infrared carbon stars without visible counterparts are generally known as
extreme carbon stars. We have selected a subset of these stars with absorption
features in the 10-13 m range, which has been tentatively attributed to
silicon carbide (SiC). We add three new objects meeting these criterion to the
seven previously known, bringing our total sample to ten sources. We also
present the result of radiative transfer modeling for these stars, comparing
these results to those of previous studies. In order to constrain model
parameters, we use published mass-loss rates, expansion velocities and
theoretical dust condensation models to determine the dust condensation
temperature. These show that the inner dust temperatures of the dust shells for
these sources are significantly higher than previously assumed. This also
implies that the dominant dust species should be graphite instead of amorphous
carbon. In combination with the higher condensation temperature we show that
this results in a much higher acceleration of the dust grains than would be
expected from previous work. Our model results suggest that the very optically
thick stage of evolution does not coincide with the timescales for the
superwind, but rather, that this is a very short-lived phase. Additionally, we
compare model and observational parameters in an attempt to find any
correlations. Finally, we show that the spectrum of one source, IRAS
175343030, strongly implies that the 10-13 m feature is due to a solid
state rather than a molecular species.Comment: 13 Figure
Measurement of the forward-backward asymmetries for charm- and bottom-quark pair productions at =58GeV with electron tagging
We have measured, with electron tagging, the forward-backward asymmetries of
charm- and bottom-quark pair productions at =58.01GeV, based on
23,783 hadronic events selected from a data sample of 197pb taken with
the TOPAZ detector at TRISTAN. The measured forward-backward asymmetries are
and , which are consistent with the standard model
predictions.Comment: 19 pages, Latex format (article), 5 figures included. to be published
in Phys. Lett.
Open and Hidden Charm Production in 920 GeV Proton-Nucleus Collisions
The HERA-B collaboration has studied the production of charmonium and open
charm states in collisions of 920 GeV protons with wire targets of different
materials. The acceptance of the HERA-B spectrometer covers negative values of
xF up to xF=-0.3 and a broad range in transverse momentum from 0.0 to 4.8
GeV/c. The studies presented in this paper include J/psi differential
distributions and the suppression of J/psi production in nuclear media.
Furthermore, production cross sections and cross section ratios for open charm
mesons are discussed.Comment: 5 pages, 9 figures, to be published in the proceedings of the 6th
International Conference on Hyperons, Charm & Beauty Hadrons (BEACH04),
Chicago, IL, June 27 - July 3, 200
Search for the Flavor-Changing Neutral Current Decay with the HERA-B Detector
We report on a search for the flavor-changing neutral current decay using events recorded with a dimuon trigger in
interactions of 920 GeV protons with nuclei by the HERA-B experiment. We find
no evidence for such decays and set a 90% confidence level upper limit on the
branching fraction .Comment: 17 pages, 4 figures (of which 1 double), paper to be submitted to
Physics Letters
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