631 research outputs found
Calculation of Scattering by the Distorted Wave Born Approximation
An approximate scattering theory that utilizes the exact solutions for spherical defects is being developed. A defect of arbitrary shape can be represented by a sphere S and a remainder volume Ī“v. By treating Ī“v as a perturbation, one obtains an approximate solution that contains non-trivial frequency dependence and phase information. The approach is expected to be useful for studying defects with small but significant deviations (such as sharp edges) from spherical shape
Crack Identification and Characterization in the Rayleigh Limit
We discuss apparent characteristic features of Rayleigh scattering of elastic waves from cracks. Interpreting these features, we propose a procedure that in some experimental situations may be useful to distinguish generally-shaped cracks from volume defects. For elliptically-shaped cracks, we propose additional procedures that in principle allow the unique specification of crack size, shape and orientation; however, we suggest that in practice only the crack plane orientation and a lower bound on the crack length is measurable. We also comment upon the inversion procedure of Kahn and Rice
Combining chromosomal arm status and significantly aberrant genomic locations reveals new cancer subtypes
Many types of tumors exhibit chromosomal losses or gains, as well as local
amplifications and deletions. Within any given tumor type, sample specific
amplifications and deletionsare also observed. Typically, a region that is
aberrant in more tumors,or whose copy number change is stronger, would be
considered as a more promising candidate to be biologically relevant to cancer.
We sought for an intuitive method to define such aberrations and prioritize
them. We define V, the volume associated with an aberration, as the product of
three factors: a. fraction of patients with the aberration, b. the aberrations
length and c. its amplitude. Our algorithm compares the values of V derived
from real data to a null distribution obtained by permutations, and yields the
statistical significance, p value, of the measured value of V. We detected
genetic locations that were significantly aberrant and combined them with
chromosomal arm status to create a succint fingerprint of the tumor genome.
This genomic fingerprint is used to visualize the tumors, highlighting events
that are co ocurring or mutually exclusive. We allpy the method on three
different public array CGH datasets of Medulloblastoma and Neuroblastoma, and
demonstrate its ability to detect chromosomal regions that were known to be
altered in the tested cancer types, as well as to suggest new genomic locations
to be tested. We identified a potential new subtype of Medulloblastoma, which
is analogous to Neuroblastoma type 1.Comment: 34 pages, 3 figures; to appear in Cancer Informatic
Dynamical Inequality in Growth Models
A recent exponent inequality is applied to a number of dynamical growth
models. Many of the known exponents for models such as the Kardar-Parisi-Zhang
(KPZ) equation are shown to be consistent with the inequality. In some cases,
such as the Molecular Beam Equation, the situation is more interesting, where
the exponents saturate the inequality. As the acid test for the relative
strength of four popular approximation schemes we apply the inequality to the
exponents obtained for two Non Local KPZ systems. We find that all methods but
one, the Self Consistent Expansion, violate the inequality in some regions of
parameter space. To further demonstrate the usefulness of the inequality, we
apply it to a specific model, which belongs to a family of models in which the
inequality becomes an equality. We thus show that the inequality can easily
yield results, which otherwise have to rely either on approximations or general
beliefs.Comment: 6 pages, 4 figure
Elastic Wave Scattering by General Shaped Defects: the Distorted Wave Born Approximation
An approximate theory for scattering of elastic wave by general shaped defects has been developed. A defect of arbitrary shape can be represented by a sphere S and a remainder volume R. Using the exact solution for a sphere and treating R as a perturbation, the solution corresponding to the Distorted Wave Born Approximation is obtained. This solution contains non-trivial frequency dependence and phase information. Preliminary comparisons with experiments will be presented
Predicted signatures of p-wave superfluid phases and Majorana zero modes of fermionic atoms in RF absorption
We study the superfluid phases of quasi-2D atomic Fermi gases interacting via
a p-wave Feshbach resonance. We calculate the absorption spectra of these
phases under a hyperfine transition, for both non-rotating and rotating
superfluids. We show that one can identify the different phases of the p-wave
superfluid from the absorption spectrum. The absorption spectrum shows clear
signatures of the existence of Majorana zero modes at the cores of vortices of
the weakly-pairing phase
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Efficiency in the Optimum Supply of Public Goods
Lau, Sheshinski, and Stiglitz discuss efficiency in the optimum supply of public goods
Dynamic stability of crack fronts: Out-of-plane corrugations
The dynamics and stability of brittle cracks are not yet fully understood.
Here we use the Willis-Movchan 3D linear perturbation formalism [J. Mech. Phys.
Solids {\bf 45}, 591 (1997)] to study the out-of-plane stability of planar
crack fronts in the framework of linear elastic fracture mechanics. We discuss
a minimal scenario in which linearly unstable crack front corrugations might
emerge above a critical front propagation speed. We calculate this speed as a
function of Poisson's ratio and show that corrugations propagate along the
crack front at nearly the Rayleigh wave-speed. Finally, we hypothesize about a
possible relation between such corrugations and the long-standing problem of
crack branching.Comment: 5 pages, 2 figures + supplementary informatio
Distributed CSMA with pairwise coding
We consider distributed strategies for joint routing, scheduling, and network coding to maximize throughput in wireless networks. Network coding allows for an increase in network throughput under certain routing conditions. We previously developed a centralized control policy to jointly optimize for routing and scheduling combined with a simple network coding strategy using max-weight scheduling (MWS) [9]. In this work we focus on pairwise network coding and develop a distributed carrier sense multiple access (CSMA) policy that supports all arrival rates allowed by the network subject to the pairwise coding constraint. We extend our scheme to optimize for packet overhearing to increase the number of beneficial coding opportunities. Simulation results show that the CSMA strategy yields the same throughput as the optimal centralized policy of [9], but at the cost of increased delay. Moreover, overhearing provides up to an additional 25% increase in throughput on random topologies.United States. Dept. of Defense. Assistant Secretary of Defense for Research & EngineeringUnited States. Air Force (Air Force Contract FA8721-05-C-0002
Optimal routing and scheduling for a simple network coding scheme
We consider jointly optimal routing, scheduling, and network coding strategies to maximize throughput in wireless networks. While routing and scheduling techniques for wireless networks have been studied for decades, network coding is a relatively new technique that allows for an increase in throughput under certain topological and routing conditions. In this work we introduce k-tuple coding, a generalization of pairwise coding with next-hop decodability, and fully characterize the region of arrival rates for which the network queues can be stabilized under this coding strategy. We propose a dynamic control policy for routing, scheduling, and k-tuple coding, and prove that our policy is throughput optimal subject to the k-tuple coding constraint. We provide analytical bounds on the coding gain of our policy, and present numerical results to support our analytical findings. We show that most of the gains are achieved with pairwise coding, and that the coding gain is greater under 2-hop than 1-hop interference. Simulations show that under 2-hop interference our policy yields median throughput gains of 31% beyond optimal scheduling and routing on random topologies with 16 nodes.National Science Foundation (U.S.) (grant CNS-0915988)United States. Office of Naval Research (grant N00014-12-1-0064)United States. Office of Naval Research. Multidisciplinary University Research Initiative (grant number W911NF-08-1-0238)United States. Air ForceUnited States. Dept. of Defense (Contract No. FA8721-05-C-0002
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