94,808 research outputs found
Stress intensity factors in two bonded elastic layers containing cracks perpendicular to and on the interface. Part 1: Analysis
The basic crack problem which is essential for the study of subcritical crack propagation and fracture of layered structural materials is considered. Because of the apparent analytical difficulties, the problem is idealized as one of plane strain or plane stress. An additional simplifying assumption is made by restricting the formulation of the problem to crack geometries and loading conditions which have a plane of symmetry perpendicular to the interface. The general problem is formulated in terms of a coupled system of four integral equations. For each relevant crack configuration of practical interest, the singular behavior of the solution near and at the ends and points of intersection of the cracks is investigated and the related characteristic equations are obtained. The edge crack terminating at and crossing the interface, the T-shaped crack consisting of a broken layer and a delamination crack, the cross-shaped crack which consists of a delamination crack intersecting a crack which is perpendicular to the interface, and a delamination crack initiating from a stress-free boundary of the bonded layers are some of the practical crack geometries considered
Gaussian Effective Potential and the Coleman's normal-ordering Prescription : the Functional Integral Formalism
For a class of system, the potential of whose Bosonic Hamiltonian has a
Fourier representation in the sense of tempered distributions, we calculate the
Gaussian effective potential within the framework of functional integral
formalism. We show that the Coleman's normal-ordering prescription can be
formally generalized to the functional integral formalism.Comment: 6 pages, revtex; With derivation details and an example added. To
appear in J. Phys.
Absorption by Extremal D3-branes
The absorption in the extremal D3-brane background is studied for a class of
massless fields whose linear perturbations leave the ten-dimensional background
metric unperturbed, as well as the minimally-coupled massive scalar. We find
that various fields have the same absorption probability as that of the
dilaton-axion system, which is given exactly via the Mathieu equation. We
analyze the features of the absorption cross-sections in terms of effective
Schr\"odinger potentials, conjecture a general form of the dual effective
potentials, and provide explicit numerical results for the whole energy range.
As expected, all partial-wave absorption probabilities tend to zero (one) at
low (large) energies, and exhibit an oscillatory pattern as a function of
energy. The equivalence of absorption probabilities for various modes has
implications for the correlation functions on the field, including subleading
contributions on the field-theory side. In particular, certain half-integer and
integer spin fields have identical absorption probabilities, thus providing
evidence that the corresponding operator pairs on the field theory side belong
to the same supermultiplets.Comment: Latex, 9 figures and 17 page
Thermalized Displaced Squeezed Thermal States
In the coordinate representation of thermofield dynamics, we investigate the
thermalized displaced squeezed thermal state which involves two temperatures
successively. We give the wavefunction and the matrix element of the density
operator at any time, and accordingly calculate some quantities related to the
position, momentum and particle number operator, special cases of which are
consistent with the results in the literature. The two temperatures have
diffenent correlations with the squeeze and coherence components. Moreover,
different from the properties of the position and momentum, the average value
and variance of the particle number operator as well as the second-order
correlation function are time-independent.Comment: 7 pages, no figures, Revtex fil
Gamma-ray bursts: postburst evolution of fireballs
The postburst evolution of fireballs that produce -ray bursts is
studied, assuming the expansion of fireballs to be adiabatic and relativistic.
Numerical results as well as an approximate analytic solution for the evolution
are presented. Due to adoption of a new relation among , and
(see the text), our results differ markedly from the previous studies.
Synchrotron radiation from the shocked interstellar medium is attentively
calculated, using a convenient set of equations. The observed X-ray flux of GRB
afterglows can be reproduced easily. Although the optical afterglows seem much
more complicated, our results can still present a rather satisfactory approach
to observations. It is also found that the expansion will no longer be highly
relativistic about 4 days after the main GRB. We thus suggest that the
marginally relativistic phase of the expansion should be investigated so as to
check the afterglows observed a week or more later.Comment: 17 pages, 4 figures, MNRAS in pres
The (1+1)-dimensional Massive sine-Gordon Field Theory and the Gaussian Wave-functional Approach
The ground, one- and two-particle states of the (1+1)-dimensional massive
sine-Gordon field theory are investigated within the framework of the Gaussian
wave-functional approach. We demonstrate that for a certain region of the
model-parameter space, the vacuum of the field system is asymmetrical.
Furthermore, it is shown that two-particle bound state can exist upon the
asymmetric vacuum for a part of the aforementioned region. Besides, for the
bosonic equivalent to the massive Schwinger model, the masses of the one boson
and two-boson bound states agree with the recent second-order results of a
fermion-mass perturbation calculation when the fermion mass is small.Comment: Latex, 11 pages, 8 figures (EPS files
Accurate determination of the Gaussian transition in spin-1 chains with single-ion anisotropy
The Gaussian transition in the spin-one Heisenberg chain with single-ion
anisotropy is extremely difficult to treat, both analytically and numerically.
We introduce an improved DMRG procedure with strict error control, which we use
to access very large systems. By considering the bulk entropy, we determine the
Gaussian transition point to 4-digit accuracy, , resolving a long-standing debate in quantum magnetism. With
this value, we obtain high-precision data for the critical behavior of
quantities including the ground-state energy, gap, and transverse string-order
parameter, and for the critical exponent, . Applying our
improved technique at highlights essential differences in
critical behavior along the Gaussian transition line.Comment: 4 pages and 4 figure
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