709 research outputs found
A rejection-free Monte Carlo method for the hard-disk system
We construct a rejection-free Monte Carlo method for the hard-disk system.
Rejection-free Monte Carlo methods preserve the time-evolution behavior of the
standard Monte Carlo method, and this relationship is confirmed for our method
by observing nonequilibrium relaxation of a bond-orientational order parameter.
The rejection-free method gives a greater computational efficiency than the
standard method at high densities. The rejection free method is implemented in
a shrewd manner using optimization methods to calculate a rejection probability
and to update the system. This method should allow an efficient study of the
dynamics of two-dimensional solids at high density.Comment: 8 pages, 9 figures. This paper has been combined into the
cond-mat/0508652, and published in Phys. Rev.
Recent advances in the theory of nuclear forces
After a brief historical review, we present recent progress in our
understanding of nuclear forces in terms of chiral effective field theory.Comment: 6 pages, 2 figures; talk at International Symposium on Correlations
Dynamics in Nuclei, University of Tokyo, Japan, 31 January-4 February, 200
Non-linear rheology of layered systems - a phase model approach
We study non-linear rheology of a simple theoretical model developed to mimic
layered systems such as lamellar structures under shear. In the present work we
study a 2-dimensional version of the model which exhibits a Kosterlitz-Thouless
transition in equilibrium at a critical temperature Tc. While the system
behaves as Newtonain fluid at high temperatures T > Tc, it exhibits shear
thinning at low temperatures T < Tc. The non-linear rheology in the present
model is understood as due to motions of edge dislocations and resembles the
non-linear transport phenomena in superconductors by vortex motions.Comment: 10 pages, 5 figures, contribution to the conference proceeding of
International Conference on Science of Friction, Irago Aichi, Japan Sept 9-13
200
Micro-structure of damage in thermally activated fracture of Lennard-Jones systems
We investigate the effect of thermal fluctuations on the critical stress and
the micro-structure of damage preceding macroscopic fracture of Lennard-Jones
solids under a constant external load. Based on molecular dynamics simulations
of notched specimens at finite temperature, we show that the crystalline
structure gets distorted ahead of the crack in the secondary creep regime. The
damage profile characterizing the spatial distribution of lattice distortions
is well described by an exponential form. The characteristic length of the
exponential form provides the scale of damage which is found to be an
increasing function of the temperature: At low temperature damage is strongly
localized to the crack tip, while at high temperature damage extends to a
broader range leading to more efficient relaxation of overloads. As a
consequence, the stress intensity factor decreases with increasing temperature.
The final macroscopic failure of the system occurs suddenly which is initiated
by the creation of vacancies and voids. The creep strength exhibits the inverse
square root scaling with the notch size corrected by the extension of the
process zone.Comment: 6 pages, 8 figure
Dissipation Enhanced Asymmetric Transport in Quantum Ratchets
Quantum mechanical motion of a particle in a periodic asymmetric potential is
studied theoretically at zero temperature. It is shown based on semi-classical
approximation that the tunneling probability from one local minimum to the next
becomes asymmetric in the presence of weak oscillating field, even though there
is no macroscopic field gradient in average. Dissipation enhances this
asymmetry, and leads to a steady unidirectional current, resulting in a quantum
ratchet system.Comment: 12 pages, 2 Figures, submitted to J. Phys. Soc. Jp
Standing waves in the Lorentz-covariant world
When Einstein formulated his special relativity, he developed his dynamics
for point particles. Of course, many valiant efforts have been made to extend
his relativity to rigid bodies, but this subject is forgotten in history. This
is largely because of the emergence of quantum mechanics with wave-particle
duality. Instead of Lorentz-boosting rigid bodies, we now boost waves and have
to deal with Lorentz transformations of waves. We now have some understanding
of plane waves or running waves in the covariant picture, but we do not yet
have a clear picture of standing waves. In this report, we show that there is
one set of standing waves which can be Lorentz-transformed while being
consistent with all physical principle of quantum mechanics and relativity. It
is possible to construct a representation of the Poincar\'e group using
harmonic oscillator wave functions satisfying space-time boundary conditions.
This set of wave functions is capable of explaining the quantum bound state for
both slow and fast hadrons. In particular it can explain the quark model for
hadrons at rest, and Feynman's parton model hadrons moving with a speed close
to that of light.Comment: LaTex 20 pages, presented at the 2004 meeting of the International
Association of Relativistic Dynamincs, to be published in the proceeding
A Simplified Cellular Automaton Model for City Traffic
We systematically investigate the effect of blockage sites in a cellular
automaton model for traffic flow. Different scheduling schemes for the blockage
sites are considered. None of them returns a linear relationship between the
fraction of ``green'' time and the throughput. We use this information for a
fast implementation of traffic in Dallas.Comment: 12 pages, 18 figures. submitted to Phys Rev
Fluctuating work in coherent quantum systems: proposals and limitations
One of the most important goals in quantum thermodynamics is to demonstrate
advantages of thermodynamic protocols over their classical counterparts. For
that, it is necessary to (i) develop theoretical tools and experimental set-ups
to deal with quantum coherence in thermodynamic contexts, and to (ii) elucidate
which properties are genuinely quantum in a thermodynamic process. In this
short review, we discuss proposals to define and measure work fluctuations that
allow to capture quantum interference phenomena. We also discuss fundamental
limitations arising due to measurement back-action, as well as connections
between work distributions and quantum contextuality. We hope the different
results summarised here motivate further research on the role of quantum
phenomena in thermodynamics.Comment: As a chapter of: F. Binder, L. A. Correa, C. Gogolin, J. Anders, and
G. Adesso (eds.), "Thermodynamics in the quantum regime - Recent Progress and
Outlook", (Springer International Publishing). Second version: Misspell in
the title correcte
Accurate Charge-Dependent Nucleon-Nucleon Potential at Fourth Order of Chiral Perturbation Theory
We present the first nucleon-nucleon potential at
next-to-next-to-next-to-leading order (fourth order) of chiral perturbation
theory. Charge-dependence is included up to next-to-leading order of the
isospin-violation scheme. The accuracy for the reproduction of the NN data
below 290 MeV lab. energy is comparable to the one of phenomenological
high-precision potentials. Since NN potentials of order three and less are
known to be deficient in quantitative terms, the present work shows that the
fourth order is necessary and sufficient for a reliable NN potential derived
from chiral effective Lagrangians. The new potential provides a promising
starting point for exact few-body calculations and microscopic nuclear
structure theory (including chiral many-body forces derived on the same
footing).Comment: 4 pages Revtex including one figur
Rectification of Fluctuations in an Underdamped Ratchet
We investigate analytically the motion of underdamped particles subject to a
deterministic periodic potential and a periodic temperature. Despite the fact
that an underamped particle experiences the temperature oscillation many times
in its escape out of a well and in its motion along the potential, a net
directed current linear in the friction constant is found. If both the
potential and the temperature modulation are sinusoidal with a phase lag
, this current is proportional to .Comment: 4 pages REVTEX, 2 figures include
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