565 research outputs found
Failure Probabilities and Tough-Brittle Crossover of Heterogeneous Materials with Continuous Disorder
The failure probabilities or the strength distributions of heterogeneous 1D
systems with continuous local strength distribution and local load sharing have
been studied using a simple, exact, recursive method. The fracture behavior
depends on the local bond-strength distribution, the system size, and the
applied stress, and crossovers occur as system size or stress changes. In the
brittle region, systems with continuous disorders have a failure probability of
the modified-Gumbel form, similar to that for systems with percolation
disorder. The modified-Gumbel form is of special significance in weak-stress
situations. This new recursive method has also been generalized to calculate
exactly the failure probabilities under various boundary conditions, thereby
illustrating the important effect of surfaces in the fracture process.Comment: 9 pages, revtex, 7 figure
Self-Attracting Walk on Lattices
We have studied a model of self-attracting walk proposed by Sapozhnikov using
Monte Carlo method. The mean square displacement
and the mean number of visited sites are calculated for
one-, two- and three-dimensional lattice. In one dimension, the walk shows
diffusive behaviour with . However, in two and three dimension, we
observed a non-universal behaviour, i.e., the exponent varies
continuously with the strength of the attracting interaction.Comment: 6 pages, latex, 6 postscript figures, Submitted J.Phys.
Swelling-collapse transition of self-attracting walks
We study the structural properties of self-attracting walks in d dimensions
using scaling arguments and Monte Carlo simulations. We find evidence for a
transition analogous to the \Theta transition of polymers. Above a critical
attractive interaction u_c, the walk collapses and the exponents \nu and k,
characterising the scaling with time t of the mean square end-to-end distance
~ t^{2 \nu} and the average number of visited sites ~ t^k, are
universal and given by \nu=1/(d+1) and k=d/(d+1). Below u_c, the walk swells
and the exponents are as with no interaction, i.e. \nu=1/2 for all d, k=1/2 for
d=1 and k=1 for d >= 2. At u_c, the exponents are found to be in a different
universality class.Comment: 6 pages, 5 postscript figure
Scaling of interfaces in brittle fracture and perfect plasticity
The roughness properties of two-dimensional fracture surfaces as created by
the slow failure of random fuse networks are considered and compared to yield
surfaces of perfect plasticity with similar disorder. By studying systems up to
a linear size L=350 it is found that in the cases studied the fracture surfaces
exhibit self-affine scaling with a roughness exponent close to 2/3, which is
asymptotically exactly true for plasticity though finite-size effects are
evident for both. The overlap of yield or minimum energy and fracture surfaces
with exactly the same disorder configuration is shown to be a decreasing
function of the system size and to be of a rather large magnitude for all cases
studied. The typical ``overlap cluster'' length between pairs of such
interfaces converges to a constant with increasing.Comment: Accepted for publication in Phys. Rev.
Random manifolds in non-linear resistor networks: Applications to varistors and superconductors
We show that current localization in polycrystalline varistors occurs on
paths which are, usually, in the universality class of the directed polymer in
a random medium. We also show that in ceramic superconductors, voltage
localizes on a surface which maps to an Ising domain wall. The emergence of
these manifolds is explained and their structure is illustrated using direct
solution of non-linear resistor networks
The location of Airy-0, the Mars prime meridian reference, from stereo photogrammetric processing of THEMIS IR imaging and digital elevation data
The small crater Airy-0 was selected from Mariner 9 images to be the reference for the Mars prime meridian. Initial analyses in the year 2000 tied Viking Orbiter and Mars Orbiter Camera images of Airy-0 to the evolving Mars Orbiter Laser Altimeter global digital terrain model to update the location of Airy-0. Based upon this tie and radiometric tracking of landers/rovers from Earth, new expressions for the Mars spin axis direction, spin rate, and prime meridian epoch value were produced to define the orientation of the Martian surface in inertial space over time. Since the Mars Global Surveyor mission and Mars Orbiter Laser Altimeter global digital terrain model were completed some time ago, a more exhaustive study has been performed to determine the accuracy of the Airy-0 location and orientation of Mars at the standard epoch. Thermal Emission Imaging System (THEMIS) IR image cubes of the Airy and Gale crater regions were tied to the global terrain grid using precision stereo photogrammetric image processing techniques. The Airy-0 location was determined to be about 0.001° east of its predicted location using the currently defined International Astronomical Union (IAU) prime meridian location. Information on this new location and how it was derived will be provided to the NASA Mars Exploration Program Geodesy and Cartography Working Group for their assessment. This NASA group will make a recommendation to the IAU Working Group on Cartographic Coordinates and Rotational Elements to update the expression for the Mars spin axis direction, spin rate, and prime meridian location
Optomagnetic composite medium with conducting nanoelements
A new type of metal-dielectric composites has been proposed that is
characterised by a resonance-like behaviour of the effective permeability in
the infrared and visible spectral ranges. This material can be referred to as
optomagnetic medium. The analytical formalism developed is based on solving the
scattering problem for considered inclusions with impedance boundary condition,
which yields the current and charge distributions within the inclusions. The
presence of the effective magnetic permeability and its resonant properties
lead to novel optical effects and open new possible applications.Comment: 48 pages, 13 figures. accepted to Phys. Rev. B; to appear vol. 66,
200
Order to disorder transition in the XY-like quantum magnet Cs2CoCl4 induced by noncommuting applied fields
We explore the effects of noncommuting applied fields on the ground-state
ordering of the quasi-one-dimensional spin-1/2 XY-like antiferromagnet Cs2CoCl4
using single-crystal neutron diffraction. In zero field interchain couplings
cause long-range order below T_N=217(5) mK with chains ordered
antiferromagnetically along their length and moments confined to the (b,c)
plane. Magnetic fields applied at an angle to the XY planes are found to
initially stabilize the order by promoting a spin-flop phase with an increased
perpendicular antiferromagnetic moment. In higher fields the antiferromagnetic
order becomes unstable and a transition occurs to a phase with no long-range
order in the (b,c) plane, proposed to be a spin liquid phase that arises when
the quantum fluctuations induced by the noncommuting field become strong enough
to overcome ordering tendencies. Magnetization measurements confirm that
saturation occurs at much higher fields and that the proposed spin-liquid state
exists in the region 2.10 < H_SL < 2.52 T || a. The observed phase diagram is
discussed in terms of known results on XY-like chains in coexisting
longitudinal and transverse fields.Comment: revtex, 14 figures, 2 tables, to appear in Phys. Rev.
Stressed backbone and elasticity of random central-force systems
We use a new algorithm to find the stress-carrying backbone of ``generic''
site-diluted triangular lattices of up to 10^6 sites. Generic lattices can be
made by randomly displacing the sites of a regular lattice. The percolation
threshold is Pc=0.6975 +/- 0.0003, the correlation length exponent \nu =1.16
+/- 0.03 and the fractal dimension of the backbone Db=1.78 +/- 0.02. The number
of ``critical bonds'' (if you remove them rigidity is lost) on the backbone
scales as L^{x}, with x=0.85 +/- 0.05. The Young's modulus is also calculated.Comment: 5 pages, 5 figures, uses epsfi
Temporally disordered Ising models
We present a study of the influence of different types of disorder on systems
in the Ising universality class by employing both a dynamical field theory
approach and extensive Monte Carlo simulations. We reproduce some well known
results for the case of quenched disorder (random temperature and random
field), and analyze the effect of four different types of time-dependent
disorder scarcely studied so far in the literature. Some of them are of obvious
experimental and theoretical relevance (as for example, globally fluctuating
temperatures or random fields). All the predictions coming from our field
theoretical analysis are fully confirmed by extensive simulations in two and
three dimensions, and novel qualitatively different, non-Ising transitions are
reported. Possible experimental setups designed to explore the described
phenomenologies are also briefly discussed.Comment: Submitted to Phys. Rev. E. Rapid Comm. 4 page
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