143,568 research outputs found
Multi-frequency imaging of perfectly conducting cracks via boundary measurements
Imaging of perfectly conducting crack(s) in a 2-D homogeneous medium using
boundary data is studied. Based on the singular structure of the Multi-Static
Response (MSR) matrix whose elements are normalized by an adequate test
function at several frequencies, an imaging functional is introduced and
analyzed. A non-iterative imaging procedure is proposed. Numerical experiments
from noisy synthetic data show that acceptable images of single and multiple
cracks are obtained.Comment: 4 pages, 3 figure
Transition rates for a S \ge 1 model coupled to a phonon bath
We investigate transition rates between different spin configurations for spins weakly coupled to a -dimensional phonon bath. This study is
motivated by understanding observed magnetization relaxation as a function of
temperature in diverse magnetic systems such as arrays of magnetic
nanoparticles and magnetic molecules. We assume that the magnetization of the
spin system relaxes through consecutive emission or absorption of a single
phonon. From a weak, linear spin-phonon coupling Hamiltonian, we derive
transition rates that would be used to examine dynamic properties of the system
in kinetic Monte Carlo simulations. Although the derived phonon-assisted
transition rates satisfy detailed balance, in the case of two and three
dimensional phonon baths, transitions between degenerate states are not
allowed. Thus, if there are no alternative paths along which the spin system
can relax, the relaxation time diverges. Otherwise, the system finds other
paths, which leads to an increase in the relaxation time and energy barrier.
However, when higher-order phonon processes are included in the transition
rates, it is found that the system can reach the states which were inaccessible
due to the forbidden transitions. As a result, the system recovers some of the
dynamic properties obtained using the Glauber transition rate.Comment: 8 figures. Submitted to PR
NASTRAN distribution through COSMIC
The NASTRAN program package is one of the most important in terms of size and use in the COSMIC inventory at the University of Georgia. A brief history of the COSMIC facility as it relates to the NASTRAN program package is presented, followed by a discussion of the NASTRAN disseminations. COSMIC, which is the acronym for the Computer Software Management and Information Center, is operated by the University of Georgia's Computer Center under contract to NASA. The purpose of COSMIC is to make available to the public the computer software and documentation developed as part of the NASA program. It is, perhaps, best described as a clearinghouse for the NASA-sponsored computer software, although the functions specified under the contract go much further than simply duplicating the programs and documentation for distribution. A sizeable portion of the workscope involves screening the programs to insure that they are free of syntax errors, that all necessary subroutines are present, and that the documentation includes sufficiently detailed instructions to allow purchasers to install and operate the program or system
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