35,360 research outputs found
Stability of the pentaquark in a naive string model
The pentaquark is studied in a simple model of confinement where the quarks
and the antiquark are linked by flux tubes of minimal cumulated length, and the
Coulomb-like interaction, the spin-dependent terms and the antisymmetrization
constraints are neglected.. The ground-state is found to be stable against
spontaneous dissociation into a meson and a baryon, both in the case of five
equal-mass constituents and for a static quark or antiquark surrounded by four
equal masses.Comment: 8 pages, 2 figures, minor corrections, references added, to appear in
Phys. Rev.
Approach to equilibrium for the phonon Boltzmann equation
We study the asymptotics of solutions of the Boltzmann equation describing
the kinetic limit of a lattice of classical interacting anharmonic oscillators.
We prove that, if the initial condition is a small perturbation of an
equilibrium state, and vanishes at infinity, the dynamics tends diffusively to
equilibrium. The solution is the sum of a local equilibrium state, associated
to conserved quantities that diffuse to zero, and fast variables that are
slaved to the slow ones. This slaving implies the Fourier law, which relates
the induced currents to the gradients of the conserved quantities.Comment: 23 page
Entropy and Correlations in Lattice Gas Automata without Detailed Balance
We consider lattice gas automata where the lack of semi-detailed balance
results from node occupation redistribution ruled by distant configurations;
such models with nonlocal interactions are interesting because they exhibit
non-ideal gas properties and can undergo phase transitions. For this class of
automata, mean-field theory provides a correct evaluation of properties such as
compressibility and viscosity (away from the phase transition), despite the
fact that no H-theorem strictly holds. We introduce the notion of locality -
necessary to define quantities accessible to measurements - by treating the
coupling between nonlocal bits as a perturbation. Then if we define
operationally ``local'' states of the automaton - whether the system is in a
homogeneous or in an inhomogeneous state - we can compute an estimator of the
entropy and measure the local channel occupation correlations. These
considerations are applied to a simple model with nonlocal interactions.Comment: 13 pages, LaTeX, 5 PostScript figures, uses psfig. Submitted to Int.
J. Mod. Phys.
A formula for the First Eigenvalue of the Dirac Operator on Compact Spin Symmetric Spaces
Let be a simply connected spin compact inner irreducible symmetric
space, endowed with the metric induced by the Killing form of sign-changed.
We give a formula for the square of the first eigenvalue of the Dirac operator
in terms of a root system of . As an example of application, we give the
list of the first eigenvalues for the spin compact irreducible symmetric spaces
endowed with a quaternion-K\"{a}hler structure
Determination of the reaction plane in ultrarelativistic nuclear collisions
In the particles produced in a nuclear collision undergo collective flow, the
reaction plane can in principle be determined through a global event analysis.
We show here that collective flow can be identified by evaluating the reaction
plane independently in two separate rapidity intervals, and studying the
correlation between the two results. We give an analytical expression for the
correlation function between the two planes as a function of their relative
angle. We also discuss how this correlation function is related to the
anisotropy of the transverse momentum distribution. Email contact:
[email protected]: Saclay-T93/026 Email: [email protected]
Femtosecond Self-Reconfiguration of Laser-Induced Plasma Patterns in Dielectrics
Laser-induced modification of transparent solids by intense femtosecond laser
pulses allows fast integration of nanophotonic and nanofluidic devices with
controlled optical properties. So far, the local and dynamic nature of the
interactions between plasma and light needed to correctly explain nanograting
fabrication on dielectric surfaces has been missing in the theoretical models.
With our numerical approach, we show that a self-consistent dynamic treatment
of the plasma formation and its interaction with light triggers an ultrafast
reconfiguration of the periodic plasma patterns on a field-cycle time scale.
Within this framework, a simple stability analysis of the local interactions
explains how the laser-induced plasma patterns change their orientation with
respect to the incident light polarization, when a certain energy density
threshold is reached. Moreover, the reconfigured sub-wavelength plasma
structures grow into the bulk of the sample and agree with the experimental
findings of self-organized volume nanogratings. Mode coupling of the incident
and transversally scattered light with the periodic plasma structures is
sufficient to initiate the growth and the self-organization of the
characteristic pattern with a periodicity of a half-wavelength in the medium.Comment: 8 pages, 7 figure
Relativistic analysis of the LISA long range optical links
The joint ESA/NASA LISA mission consists in three spacecraft on heliocentric
orbits, flying in a triangular formation of 5 Mkm each side, linked by infrared
optical beams. The aim of the mission is to detect gravitational waves in a low
frequency band. For properly processing the science data, the propagation
delays between spacecraft must be accurately known. We thus analyse the
propagation of light between spacecraft in order to systematically derive the
relativistic effects due to the static curvature of the Schwarzschild spacetime
in which the spacecraft are orbiting with time-varying light-distances. In
particular, our analysis allows to evaluate rigorously the Sagnac effect, and
the gravitational (Einstein) redshift.Comment: 6 figures; accepted for publication in PR
Discovery of the Orbit of the Transient X ray Pulsar SAX J2103.5+4545
Using X-ray data from the Rossi X-Ray Timing Explorer (RXTE), we carried out
pulse timing analysis of the transient X-ray pulsar SAX J2103.5+4545. An
outburst was detected by All Sky Monitor (ASM) October 25 1999 and reached a
peak X-ray brightness of 27 mCrab October 28. Between November 19 and December
27, the RXTE/PCA carried out pointed observations which provided us with pulse
arrival times. These yield an eccentric orbit (e= 0.4 \pm 0.2) with an orbital
period of 12.68 \pm 0.25 days and light travel time across the projected
semimajor axis of 72 \pm 6 sec. The pulse period was measured to be 358.62171
\pm 0.00088 s and the spin-up rate (2.50 \pm 0.15) \times 10^{-13} Hz s^{-1}.
The ASM data for the February to September 1997 outburst in which BeppoSAX
discovered SAX J2103.5+4545 (Hulleman, in't Zand and Heise 1998) are modulated
at time scales close to the orbital period. Folded light curves of the 1997 ASM
data and the 1999 PCA data are similar and show that the intensity increases at
periastron passages.Comment: To appear in The Astrophysical Journal (Letters
Global General Relativistic Magnetohydrodynamic Simulations of Accretion Tori
This paper presents an initial survey of the properties of accretion flows in
the Kerr metric from three-dimensional, general relativistic
magnetohydrodynamic simulations of accretion tori. We consider three fiducial
models of tori around rotating, both prograde and retrograde, and nonrotating
black holes; these three fiducial models are also contrasted with axisymmetric
simulations and a pseudo-Newtonian simulation with equivalent initial
conditions to delineate the limitations of these approximations.Comment: Submitted to ApJ. 30 pages, 21 figures. Animations and
high-resolution version of figures available at
http://www.astro.virginia.edu/~jd5
A study to ascertain what effect the study of homophones has on spelling achievement
Thesis (Ed.M.)--Boston Universit
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