447 research outputs found
Micromechanics and homogenization techniques for analyzing the continuum damage of rock salt
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Models for predicting damage evolution in metal matrix composites subjected to cyclic loading
A thermomechanical analysis of a continuous fiber metal matrix composite (MMC) subjected to cyclic loading is performed herein. The analysis includes the effects of processing induced residual thermal stresses, matrix inelasticity, and interface cracking. Due to these complexities, the analysis is performed computationally using the finite element method. Matrix inelasticity is modelled with a rate dependent viscoplasticity model. Interface fracture is modelled by the use of a nonlinear interface constitutive model. The problem formulation is summarized, and results are given for a four-ply unidirectional SCS-6/{beta}21S titanium composite under high temperature isothermal mechanical fatigue. Results indicate rate dependent viscoplasticity can be a significant mechanism for dissipating the energy available for damage propagation, thus contributing to improved ductility of the composite. Results also indicate that the model may be useful for inclusion in life prediction methodologies for MMC`s
Differential geometry construction of anomalies and topological invariants in various dimensions
In the model of extended non-Abelian tensor gauge fields we have found new
metric-independent densities: the exact (2n+3)-forms and their secondary
characteristics, the (2n+2)-forms as well as the exact 6n-forms and the
corresponding secondary (6n-1)-forms. These forms are the analogs of the
Pontryagin densities: the exact 2n-forms and Chern-Simons secondary
characteristics, the (2n-1)-forms. The (2n+3)- and 6n-forms are gauge invariant
densities, while the (2n+2)- and (6n-1)-forms transform non-trivially under
gauge transformations, that we compare with the corresponding transformations
of the Chern-Simons secondary characteristics. This construction allows to
identify new potential gauge anomalies in various dimensions.Comment: 27 pages, references added, matches published versio
Relic Gravitational Waves and Their Detection
The range of expected amplitudes and spectral slopes of relic (squeezed)
gravitational waves, predicted by theory and partially supported by
observations, is within the reach of sensitive gravity-wave detectors. In the
most favorable case, the detection of relic gravitational waves can be achieved
by the cross-correlation of outputs of the initial laser interferometers in
LIGO, VIRGO, GEO600. In the more realistic case, the sensitivity of advanced
ground-based and space-based laser interferometers will be needed. The specific
statistical signature of relic gravitational waves, associated with the
phenomenon of squeezing, is a potential reserve for further improvement of the
signal to noise ratio.Comment: 25 pages, 9 figures included, revtex. Based on a talk given at
"Gyros, Clocks, and Interferometers: Testing General Relativity in Space"
(Germany, August 99
SU(N) Evolution of a Frustrated Spin Ladder
Recent studies indicate that the weakly coupled spin-1/2 Heisenberg
antiferromagnet with next nearest neighbor frustration supports massive spinons
when suitably tuned. The straightforward SU(N) generalization of the low energy
ladder Hamiltonian yields two independent SU(N) Thirring models with N-1
multiplets of massive ``spinon'' excitations. We study the evolution of the
complete set of low-energy dynamical structure factors using form factors.
Those corresponding to the smooth (staggered) magnetizations are qualitatively
different (the same) in the N=2 and N>2 cases. The absence of single-particle
peaks preserves the notion of spinons stabilized by frustration. In contrast to
the ladder, we note that the N=infinity limit of the four chain magnet is not a
trivial free theory.Comment: 10 pages, RevTex, 5 figures; SU(N) approach clarifie
Nonmonotonic dependence of the absolute entropy on temperature in supercooled Stillinger-Weber silicon
Using a recently developed thermodynamic integration method, we compute the
precise values of the excess Gibbs free energy (G^e) of the high density liquid
(HDL) phase with respect to the crystalline phase at different temperatures (T)
in the supercooled region of the Stillinger-Weber (SW) silicon [F. H.
Stillinger and T. A. Weber, Phys. Rev. B. 32, 5262 (1985)]. Based on the slope
of G^e with respect to T, we find that the absolute entropy of the HDL phase
increases as its enthalpy changes from the equilibrium value at T \ge 1065 K to
the value corresponding to a non-equilibrium state at 1060 K. We find that the
volume distribution in the equilibrium HDL phases become progressively broader
as the temperature is reduced to 1060 K, exhibiting van-der-Waals (VDW) loop in
the pressure-volume curves. Our results provides insight into the thermodynamic
cause of the transition from the HDL phase to the low density phases in SW
silicon, observed in earlier studies near 1060 K at zero pressure.Comment: This version is accepted for publication in Journal of Statistical
Physics (11 figures, 1 table
Bcc He as a Coherent Quantum Solid
In this work we investigate implications of the quantum nature of bcc %
He. We show that it is a unique solid phase with both a lattice structure and
an Off-Diagonal Long Range Order of coherently oscillating local electric
dipole moments. These dipoles arise from the local motion of the atoms in the
crystal potential well, and oscillate in synchrony to reduce the dipolar
interaction energy. The dipolar ground-state is therefore found to be a
coherent state with a well defined global phase and a three-component complex
order parameter. The condensation energy of the dipoles in the bcc phase
stabilizes it over the hcp phase at finite temperatures. We further show that
there can be fermionic excitations of this ground-state and predict that they
form an optical-like branch in the (110) direction. A comparison with
'super-solid' models is also discussed.Comment: 12 pages, 8 figure
On the gravitational, dilatonic and axionic radiative damping of cosmic strings
We study the radiation reaction on cosmic strings due to the emission of
dilatonic, gravitational and axionic waves. After verifying the (on average)
conservative nature of the time-symmetric self-interactions, we concentrate on
the finite radiation damping force associated with the half-retarded minus
half-advanced ``reactive'' fields. We revisit a recent proposal of using a
``local back reaction approximation'' for the reactive fields. Using
dimensional continuation as convenient technical tool, we find, contrary to
previous claims, that this proposal leads to antidamping in the case of the
axionic field, and to zero (integrated) damping in the case of the
gravitational field. One gets normal positive damping only in the case of the
dilatonic field. We propose to use a suitably modified version of the local
dilatonic radiation reaction as a substitute for the exact (non-local)
gravitational radiation reaction. The incorporation of such a local
approximation to gravitational radiation reaction should allow one to complete,
in a computationally non-intensive way, string network simulations and to give
better estimates of the amount and spectrum of gravitational radiation emitted
by a cosmologically evolving network of massive strings.Comment: 48 pages, RevTex, epsfig, 1 figure; clarification of the domain of
validity of the perturbative derivation of the string equations of motion,
and of their renormalizabilit
Hydrodynamics of Spatially Ordered Superfluids
We derive the hydrodynamic equations for the supersolid and superhexatic
phases of a neutral two-dimensional Bose fluid. We find, assuming that the
normal part of the fluid is clamped to an underlying substrate, that both
phases can sustain third-sound modes and that in the supersolid phase there are
additional modes due to the superfluid motion of point defects (vacancies and
interstitials).Comment: 24 pages of ReVTeX and 7 uuencoded figures. Submitted for publication
in Phys. Rev.
Generalized Spectral Signatures of Electron Fractionalization in Quasi-One and -Two Dimensional Molybdenum Bronzes and Superconducting Cuprates
We establish the quasi-one-dimensional Li purple bronze as a photoemission
paradigm of Luttinger liquid behavior. We also show that generalized signatures
of electron fractionalization are present in the angle resolved photoemission
spectra for quasi-two-dimensional purple bronzes and certain cuprates. An
important component of our analysis for the quasi-two-dimensional systems is
the proposal of a ``melted holon'' scenario for the k-independent background
that accompanies but does not interact with the peaks that disperse to define
the Fermi surface.Comment: 7 pages, 8 figure
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