1,313 research outputs found
Crossover Behavior in Burst Avalanches of Fiber Bundles: Signature of Imminent Failure
Bundles of many fibers, with statistically distributed thresholds for
breakdown of individual fibers and where the load carried by a bursting fiber
is equally distributed among the surviving members, are considered. During the
breakdown process, avalanches consisting of simultaneous rupture of several
fibers occur, with a distribution D(Delta) of the magnitude Delta of such
avalanches. We show that there is, for certain threshold distributions, a
crossover behavior of D(Delta) between two power laws D(Delta) proportional to
Delta^(-xi), with xi=3/2 or xi=5/2. The latter is known to be the generic
behavior, and we give the condition for which the D(Delta) proportional to
Delta^(-3/2) behavior is seen. This crossover is a signal of imminent
catastrophic failure in the fiber bundle. We find the same crossover behavior
in the fuse model.Comment: 4 pages, 4 figure
Discrete Fracture Model with Anisotropic Load Sharing
A two-dimensional fracture model where the interaction among elements is
modeled by an anisotropic stress-transfer function is presented. The influence
of anisotropy on the macroscopic properties of the samples is clarified, by
interpolating between several limiting cases of load sharing. Furthermore, the
critical stress and the distribution of failure avalanches are obtained
numerically for different values of the anisotropy parameter and as a
function of the interaction exponent . From numerical results, one can
certainly conclude that the anisotropy does not change the crossover point
in 2D. Hence, in the limit of infinite system size, the crossover
value between local and global load sharing is the same as the one
obtained in the isotropic case. In the case of finite systems, however, for
, the global load sharing behavior is approached very slowly
Phase transition in the modified fiber bundle model
We extend the standard fiber bundle model (FBM) with the local load sharing
in such a way that the conservation of the total load is relaxed when an
isolated fiber is broken. In this modified FBM in one dimension (1D), it is
revealed that the model exhibits a well-defined phase transition at a finite
nonzero value of the load, which is in contrast to the standard 1D FBM. The
modified FBM defined in the Watts-Strogatz network is also investigated, and
found is the existences of two distinct transitions: one discontinuous and the
other continuous. The effects of the long-range shortcuts are also discussed.Comment: 7 pages, to appear in Europhys. Let
Long Distance, Unconditional Teleportation of Atomic States Via Complete Bell State Measurements
This paper proposes a scheme for creating and storing quantum entanglement
over long distances. Optical cavities that store this long-distance
entanglement in atoms could then function as nodes of a quantum network, in
which quantum information is teleported from cavity to cavity. The
teleportation can be carried out unconditionally via measurements of all four
Bell states, using a method of sequential elimination.Comment: 13 pages, 4 figure
Optical control and entanglement of atomic Schroedinger fields
We develop a fully quantized model of a Bose-Einstein condensate driven by a
far off-resonant pump laser which interacts with a single mode of an optical
ring cavity. In the linear regime, the cavity mode exhibits spontaneous
exponential gain correlated with the appearance of two atomic field side-modes.
These side-modes and the cavity field are generated in a highly entangled
state, characterized by thermal intensity fluctuations in the individual modes,
but with two-mode correlation functions which violate certain classical
inequalities. By injecting an initial coherent field into the optical cavity
one can significantly decrease the intensity fluctuations at the expense of
reducing the correlations, thus allowing for optical control over the quantum
statistical properties of matter waves.Comment: 4 page
Oldest known pantherine skull and evolution of the tiger
The tiger is one of the most iconic extant animals, and its origin and evolution have been intensely debated. Fossils attributable to extant pantherine species-lineages are less than 2 MYA and the earliest tiger fossils are from the Calabrian, Lower Pleistocene. Molecular studies predict a much younger age for the divergence of modern tiger subspecies at <100 KYA, although their cranial morphology is readily distinguishable, indicating that early Pleistocene tigers would likely have differed markedly anatomically from extant tigers. Such inferences are hampered by the fact that well-known fossil tiger material is middle to late Pleistocene in age. Here we describe a new species of pantherine cat from Longdan, Gansu Province, China, Panthera zdanskyi sp. nov. With an estimated age of 2.55–2.16 MYA it represents the oldest complete skull of a pantherine cat hitherto found. Although smaller, it appears morphologically to be surprisingly similar to modern tigers considering its age. Morphological, morphometric, and cladistic analyses are congruent in confirming its very close affinity to the tiger, and it may be regarded as the most primitive species of the tiger lineage, demonstrating the first unequivocal presence of a modern pantherine species-lineage in the basal stage of the Pleistocene (Gelasian; traditionally considered to be Late Pliocene). This find supports a north-central Chinese origin of the tiger lineage, and demonstrates that various parts of the cranium, mandible, and dentition evolved at different rates. An increase in size and a reduction in the relative size of parts of the dentition appear to have been prominent features of tiger evolution, whereas the distinctive cranial morphology of modern tigers was established very early in their evolutionary history. The evolutionary trend of increasing size in the tiger lineage is likely coupled to the evolution of its primary prey species
Fracture precursors in disordered systems
A two-dimensional lattice model with bond disorder is used to investigate the
fracture behaviour under stress-controlled conditions. Although the cumulative
energy of precursors does not diverge at the critical point, its derivative
with respect to the control parameter (reduced stress) exhibits a singular
behaviour. Our results are nevertheless compatible with previous experimental
findings, if one restricts the comparison to the (limited) range accessible in
the experiment. A power-law avalanche distribution is also found with an
exponent close to the experimental values.Comment: 4 pages, 5 figures. Submitted to Europhysics Letter
Hydrodynamic dispersion within porous biofilms
Many microorganisms live within surface-associated consortia, termed biofilms, that can form intricate porous structures interspersed with a network of fluid channels. In such systems, transport phenomena, including flow and advection, regulate various aspects of cell behavior by controlling nutrient supply, evacuation of waste products, and permeation of antimicrobial agents. This study presents multiscale analysis of solute transport in these porous biofilms. We start our analysis with a channel-scale description of mass transport and use the method of volume averaging to derive a set of homogenized equations at the biofilm-scale in the case where the width of the channels is significantly smaller than the thickness of the biofilm. We show that solute transport may be described via two coupled partial differential equations or telegrapher's equations for the averaged concentrations. These models are particularly relevant for chemicals, such as some antimicrobial agents, that penetrate cell clusters very slowly. In most cases, especially for nutrients, solute penetration is faster, and transport can be described via an advection-dispersion equation. In this simpler case, the effective diffusion is characterized by a second-order tensor whose components depend on (1) the topology of the channels' network; (2) the solute's diffusion coefficients in the fluid and the cell clusters; (3) hydrodynamic dispersion effects; and (4) an additional dispersion term intrinsic to the two-phase configuration. Although solute transport in biofilms is commonly thought to be diffusion dominated, this analysis shows that hydrodynamic dispersion effects may significantly contribute to transport
Resonantly enhanced nonlinear optics in semiconductor quantum wells: An application to sensitive infrared detection
A novel class of coherent nonlinear optical phenomena, involving induced
transparency in quantum wells, is considered in the context of a particular
application to sensitive long-wavelength infrared detection. It is shown that
the strongest decoherence mechanisms can be suppressed or mitigated, resulting
in substantial enhancement of nonlinear optical effects in semiconductor
quantum wells.Comment: 4 pages, 3 figures, replaced with revised versio
Discrete Symmetry and Stability in Hamiltonian Dynamics
In this tutorial we address the existence and stability of periodic and
quasiperiodic orbits in N degree of freedom Hamiltonian systems and their
connection with discrete symmetries. Of primary importance in our study are the
nonlinear normal modes (NNMs), i.e periodic solutions which represent
continuations of the system's linear normal modes in the nonlinear regime. We
examine the existence of such solutions and discuss different methods for
constructing them and studying their stability under fixed and periodic
boundary conditions. In the periodic case, we employ group theoretical concepts
to identify a special type of NNMs called one-dimensional "bushes". We describe
how to use linear combinations such NNMs to construct s(>1)-dimensional bushes
of quasiperiodic orbits, for a wide variety of Hamiltonian systems and exploit
the symmetries of the linearized equations to simplify the study of their
destabilization. Applying this theory to the Fermi Pasta Ulam (FPU) chain, we
review a number of interesting results, which have appeared in the recent
literature. We then turn to an analytical and numerical construction of
quasiperiodic orbits, which does not depend on the symmetries or boundary
conditions. We demonstrate that the well-known "paradox" of FPU recurrences may
be explained in terms of the exponential localization of the energies Eq of
NNM's excited at the low part of the frequency spectrum, i.e. q=1,2,3,....
Thus, we show that the stability of these low-dimensional manifolds called
q-tori is related to the persistence or FPU recurrences at low energies.
Finally, we discuss a novel approach to the stability of orbits of conservative
systems, the GALIk, k=2,...,2N, by means of which one can determine accurately
and efficiently the destabilization of q-tori, leading to the breakdown of
recurrences and the equipartition of energy, at high values of the total energy
E.Comment: 50 pages, 13 figure
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