1,921 research outputs found
Energy bursts in fiber bundle models of composite materials
As a model of composite materials, a bundle of many fibers with
stochastically distributed breaking thresholds for the individual fibers is
considered. The bundle is loaded until complete failure to capture the failure
scenario of composite materials under external load. The fibers are assumed to
share the load equally, and to obey Hookean elasticity right up to the breaking
point. We determine the distribution of bursts in which an amount of energy
is released. The energy distribution follows asymptotically a universal power
law , for any statistical distribution of fiber strengths. A similar
power law dependence is found in some experimental acoustic emission studies of
loaded composite materials.Comment: 5 pages, 4 fig
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 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
Failure avalanches in fiber bundles for discrete load increase
The statistics of burst avalanche sizes during failure processes in a
fiber bundle follows a power law, , for large avalanches.
The exponent depends upon how the avalanches are provoked. While it is
known that when the load on the bundle is increased in a continuous manner, the
exponent takes the value , we show that when the external load is
increased in discrete and not too small steps, the exponent value is
relevant. Our analytic treatment applies to bundles with a general probability
distribution of the breakdown thresholds for the individual fibers. The
pre-asymptotic size distribution of avalanches is also considered.Comment: 4 pages 2 figure
On the cohomology of Young modules for the symmetric group
The main result of this paper is an application of the topology of the space
to obtain results for the cohomology of the symmetric group on
letters, , with `twisted' coefficients in various choices of Young
modules and to show that these computations reduce to certain natural questions
in representation theory. The authors extend classical methods for analyzing
the homology of certain spaces with mod- coefficients to describe the
homology \HH_{\bullet}(\Sigma_d, V^{\otimes d}) as a module for the general
linear group over an algebraically closed field of characteristic
. As a direct application, these results provide a method of reducing the
computation of (where
, are Young modules) to a representation theoretic
problem involving the determination of tensor products and decomposition
numbers. In particular, in characteristic two, for many , a complete
determination of \Hs Y^\lambda) can be found. This is the first nontrivial
class of symmetric group modules where a complete description of the cohomology
in all degrees can be given. For arbitrary the authors determine
\HH^i(\Sigma_d,Y^\lambda) for . An interesting phenomenon is
uncovered--namely a stability result reminiscent of generic cohomology for
algebraic groups. For each the cohomology \HH^i(\Sigma_{p^ad},
Y^{p^a\lambda}) stabilizes as increases. The methods in this paper are
also powerful enough to determine, for any and , precisely when
\HH^{\bullet}(\sd,Y^\lambda)=0. Such modules with vanishing cohomology are of
great interest in representation theory because their support varieties
constitute the representation theoretic nucleus.Comment: Substantially revised, original stability conjecture proven for all
primes. To appear, Advances in Mathematic
Optical quenching and recovery of photoconductivity in single-crystal diamond
We study the photocurrent induced by pulsed-light illumination (pulse
duration is several nanoseconds) of single-crystal diamond containing nitrogen
impurities. Application of additional continuous-wave light of the same
wavelength quenches pulsed photocurrent. Characterization of the optically
quenched photocurrent and its recovery is important for the development of
diamond based electronics and sensing
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