3,259 research outputs found
Ultra-discrete Optimal Velocity Model: a Cellular-Automaton Model for Traffic Flow and Linear Instability of High-Flux Traffic
In this paper, we propose the ultra-discrete optimal velocity model, a
cellular-automaton model for traffic flow, by applying the ultra-discrete
method for the optimal velocity model. The optimal velocity model, defined by a
differential equation, is one of the most important models; in particular, it
successfully reproduces the instability of high-flux traffic. It is often
pointed out that there is a close relation between the optimal velocity model
and the mKdV equation, a soliton equation. Meanwhile, the ultra-discrete method
enables one to reduce soliton equations to cellular automata which inherit the
solitonic nature, such as an infinite number of conservation laws, and soliton
solutions. We find that the theory of soliton equations is available for
generic differential equations, and the simulation results reveal that the
model obtained reproduces both absolutely unstable and convectively unstable
flows as well as the optimal velocity model.Comment: 9 pages, 6 figure
Exact solution and asymptotic behaviour of the asymmetric simple exclusion process on a ring
In this paper, we study an exact solution of the asymmetric simple exclusion
process on a periodic lattice of finite sites with two typical updates, i.e.,
random and parallel. Then, we find that the explicit formulas for the partition
function and the average velocity are expressed by the Gauss hypergeometric
function. In order to obtain these results, we effectively exploit the
recursion formula for the partition function for the zero-range process. The
zero-range process corresponds to the asymmetric simple exclusion process if
one chooses the relevant hop rates of particles, and the recursion gives the
partition function, in principle, for any finite system size. Moreover, we
reveal the asymptotic behaviour of the average velocity in the thermodynamic
limit, expanding the formula as a series in system size.Comment: 10 page
A Canonical Approach to the Quantization of the Damped Harmonic Oscillator
We provide a new canonical approach for studying the quantum mechanical
damped harmonic oscillator based on the doubling of degrees of freedom
approach. Explicit expressions for Lagrangians of the elementary modes of the
problem, characterising both forward and backward time propagations are given.
A Hamiltonian analysis, showing the equivalence with the Lagrangian approach,
is also done. Based on this Hamiltonian analysis, the quantization of the model
is discussed.Comment: Revtex, 6 pages, considerably expanded with modified title and refs.;
To appear in J.Phys.
Self-magnetic compensation and Exchange Bias in ferromagnetic Samarium systems
For Sm(3+) ions in a vast majority of metallic systems, the following
interesting scenario has been conjured up for long, namely, a magnetic lattice
of tiny self (spin-orbital) compensated 4f-moments exchange coupled (and phase
reversed) to the polarization in the conduction band. We report here the
identification of a self-compensation behavior in a variety of ferromagnetic Sm
intermetallics via the fingerprint of a shift in the magnetic hysteresis (M-H)
loop from the origin. Such an attribute, designated as exchange bias in the
context of ferromagnetic/antiferromagnetic multilayers, accords these compounds
a potential for niche applications in spintronics. We also present results on
magnetic compensation behavior on small Gd doping (2.5 atomic percent) in one
of the Sm ferromagnets (viz. SmCu(4)Pd). The doped system responds like a
pseudo-ferrimagnet and it displays a characteristic left-shifted linear M-H
plot for an antiferromagnet.Comment: 7 pages and 7 figure
Hamiltonian formalism in Friedmann cosmology and its quantization
We propose a Hamiltonian formalism for a generalized
Friedmann-Roberson-Walker cosmology model in the presence of both a variable
equation of state (EOS) parameter and a variable cosmological constant
, where is the scale factor. This Hamiltonian system containing
1 degree of freedom and without constraint, gives Friedmann equations as the
equation of motion, which describes a mechanical system with a variable mass
object moving in a potential field. After an appropriate transformation of the
scale factor, this system can be further simplified to an object with constant
mass moving in an effective potential field. In this framework, the
cold dark matter model as the current standard model of cosmology corresponds
to a harmonic oscillator. We further generalize this formalism to take into
account the bulk viscosity and other cases. The Hamiltonian can be quantized
straightforwardly, but this is different from the approach of the
Wheeler-DeWitt equation in quantum cosmology.Comment: 7 pages, no figure; v2: matches the version accepted by PR
High Precision CTE-Measurement of SiC-100 for Cryogenic Space-Telescopes
We present the results of high precision measurements of the thermal
expansion of the sintered SiC, SiC-100, intended for use in cryogenic
space-telescopes, in which minimization of thermal deformation of the mirror is
critical and precise information of the thermal expansion is needed for the
telescope design. The temperature range of the measurements extends from room
temperature down to 10 K. Three samples, #1, #2, and #3 were
manufactured from blocks of SiC produced in different lots. The thermal
expansion of the samples was measured with a cryogenic dilatometer, consisting
of a laser interferometer, a cryostat, and a mechanical cooler. The typical
thermal expansion curve is presented using the 8th order polynomial of the
temperature. For the three samples, the coefficients of thermal expansion
(CTE), \bar{\alpha}_{#1}, \bar{\alpha}_{#2}, and \bar{\alpha}_{#3} were
derived for temperatures between 293 K and 10 K. The average and the dispersion
(1 rms) of these three CTEs are 0.816 and 0.002 (/K),
respectively. No significant difference was detected in the CTE of the three
samples from the different lots. Neither inhomogeneity nor anisotropy of the
CTE was observed. Based on the obtained CTE dispersion, we performed an
finite-element-method (FEM) analysis of the thermal deformation of a 3.5 m
diameter cryogenic mirror made of six SiC-100 segments. It was shown that the
present CTE measurement has a sufficient accuracy well enough for the design of
the 3.5 m cryogenic infrared telescope mission, the Space Infrared telescope
for Cosmology and Astrophysics (SPICA).Comment: in press, PASP. 21 pages, 4 figure
Caldirola-Kanai Oscillator in Classical Formulation of Quantum Mechanics
The quadrature distribution for the quantum damped oscillator is introduced
in the framework of the formulation of quantum mechanics based on the
tomography scheme. The probability distribution for the coherent and Fock
states of the damped oscillator is expressed explicitly in terms of Gaussian
and Hermite polynomials, correspondingly.Comment: LaTeX, 5 pages, 1 Postscript figure, Contribution to the VIII
International Conference on Symmetry Methods in Physics, Dubna 1997, to be
published in the Proceedings of the Conferenc
Mesoscopic circuits with charge discreteness:quantum transmission lines
We propose a quantum Hamiltonian for a transmission line with charge
discreteness. The periodic line is composed of an inductance and a capacitance
per cell. In every cell the charge operator satisfies a nonlinear equation of
motion because of the discreteness of the charge. In the basis of one-energy
per site, the spectrum can be calculated explicitly. We consider briefly the
incorporation of electrical resistance in the line.Comment: 11 pages. 0 figures. Will be published in Phys.Rev.
Level-of-Detail Triangle Strips for Deforming Meshes
Applications such as video games or movies often contain deforming
meshes. The most-commonly used representation of these types of meshes consists in dense polygonal models. Such a large amount of
geometry can be efficiently managed by applying level-of-detail techniques
and specific solutions have been developed in this field. However,
these solutions do not offer a high performance in real-time applications.
We thus introduce a multiresolution scheme for deforming meshes.
It enables us to obtain different approximations over all the frames of
an animation. Moreover, we provide an efficient connectivity coding by means of triangle strips as well as a flexible framework adapted to the GPU pipeline. Our approach enables real-time performance and, at the same time, provides accurate approximations
Unitary relations in time-dependent harmonic oscillators
For a harmonic oscillator with time-dependent (positive) mass and frequency,
an unitary operator is shown to transform the quantum states of the system to
those of a harmonic oscillator system of unit mass and time-dependent
frequency, as well as operators. For a driven harmonic oscillator, it is also
shown that, there are unitary transformations which give the driven system from
the system of same mass and frequency without driving force. The transformation
for a driven oscillator depends on the solution of classical equation of motion
of the driven system. These transformations, thus, give a simple way of finding
exact wave functions of a driven harmonic oscillator system, provided the
quantum states of the corresponding system of unit mass are given.Comment: Submitted to J. Phys.
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