50,910 research outputs found
Dynamic model for failures in biological systems
A dynamic model for failures in biological organisms is proposed and studied
both analytically and numerically. Each cell in the organism becomes dead under
sufficiently strong stress, and is then allowed to be healed with some
probability. It is found that unlike the case of no healing, the organism in
general does not completely break down even in the presence of noise. Revealed
is the characteristic time evolution that the system tends to resist the stress
longer than the system without healing, followed by sudden breakdown with some
fraction of cells surviving. When the noise is weak, the critical stress beyond
which the system breaks down increases rapidly as the healing parameter is
raised from zero, indicative of the importance of healing in biological
systems.Comment: To appear in Europhys. Let
Affine maps of density matrices
For quantum systems described by finite matrices, linear and affine maps of
matrices are shown to provide equivalent descriptions of evolution of density
matrices for a subsystem caused by unitary Hamiltonian evolution in a larger
system; an affine map can be replaced by a linear map, and a linear map can be
replaced by an affine map. There may be significant advantage in using an
affine map. The linear map is generally not completely positive, but the linear
part of an equivalent affine map can be chosen to be completely positive and
related in the simplest possible way to the unitary Hamiltonian evolution in
the larger system.Comment: 4 pages, title changed, sentence added, reference update
Dynamic model of fiber bundles
A realistic continuous-time dynamics for fiber bundles is introduced and
studied both analytically and numerically. The equation of motion reproduces
known stationary-state results in the deterministic limit while the system
under non-vanishing stress always breaks down in the presence of noise.
Revealed in particular is the characteristic time evolution that the system
tends to resist the stress for considerable time, followed by sudden complete
rupture. The critical stress beyond which the complete rupture emerges is also
obtained
Testing a new luminosity/redshift indicator for -ray bursts
We have tested a relative spectral lag (RSL) method suggested earlier as a
luminosity/redshift (or distance) estimator, using the generalized method by
Schaefer & Collazzi. We find the derivations from the luminosity/redshift-RSL
(L/R-RSL) relation are comparable with the corresponding observations. Applying
the luminosity-RSL relation to two different GRB samples, we find that there
exist no violators from the generalized test, namely the Nakar & Piran test and
Li test. We also find that about 36 per cent of Schaefer's sample are outliers
for the L/R-RSL relation within 1 confidence level, but no violators at
3 level within the current precision of L/R-RSL relation. An analysis
of several potential outliers for other luminosity relations shows they can
match the L/R-RSL relation well within an acceptable uncertainty. All the
coincident results seem to suggest that this relation could be a potential tool
for cosmological study.Comment: 7 pages, 6 figures and 1 table; Comments are welcom
Ghosts and Tachyons in the Fifth Dimension
We present several solutions for the five dimensional gravity models in the
presence of bulk ghosts and tachyons to argue that these "troublesome" fields
can be a useful model-building tool. The ghost-like signature of the kinetic
term for a bulk scalar creates a minimum in the scale factor, removing the
necessity for a negative tension brane in models with the compactified fifth
dimension. It is shown that the model with the positive tension branes and a
ghost field in the bulk leads to the radion stabilization. The bulk scalar with
the variable sign kinetic term can be used to model both positive and negative
tension branes of a finite width in the compact dimension. Finally, we present
several ghost and tachyon field configurations in the bulk that lead to the
localization of gravity in four dimensions, including one solution with the
Gaussian profile for the metric, g_{\mu\nu}(y)=\eta_{\mu\nu}\exp{-\alpha y^2},
which leads to a stronger localization of gravity than the Randall-Sundrum
model.Comment: New references adde
Putative spin liquid in the triangle-based iridate BaIrTiO
We report on thermodynamic, magnetization, and muon spin relaxation
measurements of the strong spin-orbit coupled iridate BaIrTiO,
which constitutes a new frustration motif made up a mixture of edge- and
corner-sharing triangles. In spite of strong antiferromagnetic exchange
interaction of the order of 100~K, we find no hint for long-range magnetic
order down to 23 mK. The magnetic specific heat data unveil the -linear and
-squared dependences at low temperatures below 1~K. At the respective
temperatures, the zero-field muon spin relaxation features a persistent spin
dynamics, indicative of unconventional low-energy excitations. A comparison to
the isostructural compound BaRuTiO suggests that a concerted
interplay of compass-like magnetic interactions and frustrated geometry
promotes a dynamically fluctuating state in a triangle-based iridate.Comment: Physical Review B accepte
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