15,918 research outputs found
Long-Time Behavior of Velocity Autocorrelation Function for Interacting Particles in a Two-Dimensional Disordered System
The long-time behavior of the velocity autocorrelation function (VACF) is
investigated by the molecular dynamics simulation of a two-dimensional system
which has both a many-body interaction and a random potential. With
strengthening the random potential by increasing the density of impurities, a
crossover behavior of the VACF is observed from a positive tail, which is
proportional to t^{-1}, to a negative tail, proportional to -t^{-2}. The latter
tail exists even when the density of particles is the same order as the density
of impurities. The behavior of the VACF in a nonequilibrium steady state is
also studied. In the linear response regime the behavior is similar to that in
the equilibrium state, whereas it changes drastically in the nonlinear response
regime.Comment: 12 pages, 5 figure
Crustal structure beneath the Trondelag Platform and adjacent areas of the Mid-Norwegian margin, as derived from wide-angle seismic and potential field data
The outer mid-Norwegian margin is characterized by strong breakup magmatism and has been extensively surveyed. The crustal structure of the inner continental shelf, however, is less studied, and its relation to the onshore geology, Caledonian structuring, and breakup magmatism remains unclear. Two Ocean Bottom Seismometer profiles were acquired across the Trøndelag Platform in 2003, as part of the Euromargins program. Additional-land stations recorded the marine shots. The P-wave data were modeled by ray-tracing, supported by gravity modeling. Older multi-channel seismic data allowed for interpretation of stratigraphy down to the top of the Triassic. Crystalline basement velocity is ~6 km s-1 onshore. Top basement is difficult to identify offshore, as velocities (5.3-5.7 km s-1) intermediate between typical crystalline crust and Mesozoic sedimentary strata appear 50-80 km from the coast. This layer thickens towards the Klakk-Ytreholmen Fault Complex and predates Permian and later structur-ing.
The velocities indicate sedimentary rocks, most likely Devonian. Onshore late- to post-Caledonian detachments have been proposed to extend offshore, based on the magnetic anomaly pattern. We do not find the expected correlation between upper basement velocity structure and detachments.
However, there is a distinct, dome-shaped lower-crustal body with a velocity of 6.6-7.0 km s-1. This is thickest under the Froan Basin, and the broad magnetic anomaly used to delineate the detachments correlates with this. The proposed offshore continuation of the detachments thus
appears- unreliable. While we find indications of high density and velocity (~7.2 km s-1) lower crust under the Rås Basin, similar to the proposed igneous underplating of the outer margin, this is poorly constrained near the end of our profiles. The gravity field indicates that this body may be continuous from the pre-breakup basement structures of the Utgard High to the Frøya High, suggesting that it could be an island arc or oceanic terrane-accreted during the Caledonian orogeny. Thus, we find no clear evidence of early Cenozoic igneous underplating of the inner part of the shelf
Velocity Tails for Inelastic Maxwell Models
We study the velocity distribution function for inelastic Maxwell models,
characterized by a Boltzmann equation with constant collision rate, independent
of the energy of the colliding particles. By means of a nonlinear analysis of
the Boltzmann equation, we find that the velocity distribution function decays
algebraically for large velocities, with exponents that are analytically
calculated.Comment: 4 pages, 2 figure
Patterns and Long Range Correlations in Idealized Granular Flows
An initially homogeneous freely evolving fluid of inelastic hard spheres
develops inhomogeneities in the flow field (vortices) and in the density field
(clusters), driven by unstable fluctuations. Their spatial correlations, as
measured in molecular dynamics simulations, exhibit long range correlations;
the mean vortex diameter grows as the square root of time; there occur
transitions to macroscopic shearing states, etc.
The Cahn--Hilliard theory of spinodal decomposition offers a qualitative
understanding and quantitative estimates of the observed phenomena. When
intrinsic length scales are of the order of the system size, effects of
physical boundaries and periodic boundaries (finite size effects in
simulations) are important.Comment: 13 pages with 7 postscript figures, LaTeX (uses psfig). Submitted to
International Journal of Modern Physics
Quantum information processing using strongly-dipolar coupled nuclear spins
Dipolar coupled homonuclear spins present challenging, yet useful systems for
quantum information processing. In such systems, eigenbasis of the system
Hamiltonian is the appropriate computational basis and coherent control can be
achieved by specially designed strongly modulating pulses. In this letter we
describe the first experimental implementation of the quantum algorithm for
numerical gradient estimation on the eigenbasis of a four spin system.Comment: 5 pages, 5 figures, Accepted in PR
Quantum Magnetic Properties in Perovskite with Anderson Localized Artificial Spin-1/2
Quantum magnetic properties in a geometrically frustrated lattice of spin-1/2
magnet, such as quantum spin liquid or solid and the associated spin
fractionalization, are considered key in developing a new phase of matter. The
feasibility of observing the quantum magnetic properties, usually found in
geometrically frustrated lattice of spin-1/2 magnet, in a perovskite material
with controlled disorder is demonstrated. It is found that the controlled
chemical disorder, due to the chemical substitution of Ru ions by Co-ions, in a
simple perovskite CaRuO3 creates a random prototype configuration of artificial
spin-1/2 that forms dimer pairs between the nearest and further away ions. The
localization of the Co impurity in the Ru matrix is analyzed using the Anderson
localization formulation. The dimers of artificial spin-1/2, due to the
localization of Co impurities, exhibit singlet-to-triplet excitation at low
temperature without any ordered spin correlation. The localized gapped
excitation evolves into a gapless quasi-continuum as dimer pairs break and
create freely fluctuating fractionalized spins at high temperature. Together,
these properties hint at a new quantum magnetic state with strong resemblance
to the resonance valence bond system.Comment: 8 pages, 6 figure
Velocity fluctuations in a one dimensional Inelastic Maxwell model
We consider the velocity fluctuations of a system of particles described by
the Inelastic Maxwell Model. The present work extends the methods, previously
employed to obtain the one-particle velocity distribution function, to the
study of the two particle correlations. Results regarding both the homogeneous
cooling process and the steady state driven regime are presented. In particular
we obtain the form of the pair correlation function in the scaling region of
the homogeneous cooling process and show that some of its moments diverge. This
fact has repercussions on the behavior of the energy fluctuations of the model.Comment: 16 pages, 1 figure, to be published on Journal of Statistical
Mechanics: Theory and Experiment
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