400 research outputs found
Equilibration and freeze-out in an exploding system
We use a simple gas model to study non-equilibrium aspects of the
multiparticle dynamics relevant to heavy ion collisions. By performing
numerical simulations for various initial conditions we identify several
characteristic features of the fast dynamics occurring in implosion-explosion
like processes.Comment: 4 pages, submitted to PR
Entropy puzzle in small exploding systems
We use a simple hard-core gas model to study the dynamics of small exploding
systems. The system is initially prepared in a thermalized state in a spherical
container and then allowed to expand freely into the vacuum. We follow the
expansion dynamics by recording the coordinates and velocities of all particles
until their last collision points (freeze-out). We have found that the entropy
per particle calculated for the ensemble of freeze-out points is very close to
the initial value. This is in apparent contradiction with the Joule experiment
in which the entropy grows when the gas expands irreversibly into a larger
volume.Comment: 10 pages, 4 figures, accepted June 17 2003 for publication in Physics
Letters
The Advanced Composition Explorer Shock Database and Application to Particle Acceleration Theory
The theory of particle acceleration via diffusive shock acceleration (DSA) has been studied in depth by Gosling et al. (1981), van Nes et al. (1984), Mason (2000), Desai et al. (2003), Zank et al. (2006), among many others. Recently, Parker and Zank (2012, 2014) and Parker et al. (2014) using the Advanced Composition Explorer (ACE) shock database at 1 AU explored two questions: does the upstream distribution alone have enough particles to account for the accelerated downstream distribution and can the slope of the downstream accelerated spectrum be explained using DSA? As was shown in this research, diffusive shock acceleration can account for a large population of the shocks. However, Parker and Zank (2012, 2014) and Parker et al. (2014) used a subset of the larger ACE database. Recently, work has successfully been completed that allows for the entire ACE database to be considered in a larger statistical analysis. We explain DSA as it applies to single and multiple shocks and the shock criteria used in this statistical analysis. We calculate the expected injection energy via diffusive shock acceleration given upstream parameters defined from the ACE Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM) data to construct the theoretical upstream distribution. We show the comparison of shock strength derived from diffusive shock acceleration theory to observations in the 50 keV to 5 MeV range from an instrument on ACE. Parameters such as shock velocity, shock obliquity, particle number, and time between shocks are considered. This study is further divided into single and multiple shock categories, with an additional emphasis on forward-forward multiple shock pairs. Finally with regard to forwardforward shock pairs, results comparing injection energies of the first shock, second shock, and second shock with previous energetic population will be given
The Advanced Composition Explorer Shock Database and Application to Particle Acceleration Theory
The theory of particle acceleration via diffusive shock acceleration (DSA) has been studied in depth by Gosling et al. (1981), van Nes et al. (1984), Mason (2000), Desai et al. (2003), Zank et al. (2006), among many others. Recently, Parker and Zank (2012, 2014) and Parker et al. (2014) using the Advanced Composition Explorer (ACE) shock database at 1 AU explored two questions: does the upstream distribution alone have enough particles to account for the accelerated downstream distribution and can the slope of the downstream accelerated spectrum be explained using DSA? As was shown in this research, diffusive shock acceleration can account for a large population of the shocks. However, Parker and Zank (2012, 2014) and Parker et al. (2014) used a subset of the larger ACE database. Recently, work has successfully been completed that allows for the entire ACE database to be considered in a larger statistical analysis. We explain DSA as it applies to single and multiple shocks and the shock criteria used in this statistical analysis. We calculate the expected injection energy via diffusive shock acceleration given upstream parameters defined from the ACE Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM) data to construct the theoretical upstream distribution. We show the comparison of shock strength derived from diffusive shock acceleration theory to observations in the 50 keV to 5 MeV range from an instrument on ACE. Parameters such as shock velocity, shock obliquity, particle number, and time between shocks are considered. This study is further divided into single and multiple shock categories, with an additional emphasis on forward-forward multiple shock pairs. Finally with regard to forward-forward shock pairs, results comparing injection energies of the first shock, second shock, and second shock with previous energetic population will be given
Does the quark-gluon plasma contain stable hadronic bubbles?
We calculate the thermodynamic potential of bubbles of hadrons embedded in
quark-gluon plasma, and of droplets of quark-gluon plasma embedded in hadron
phase. This is a generalization of our previous results to the case of non-zero
chemical potentials. As in the zero chemical potential case, we find that a
quark-gluon plasma in thermodynamic equilibrium may contain stable bubbles of
hadrons of radius fm. The calculations are performed within the
MIT Bag model, using an improved multiple reflection expansion. The results are
of relevance for neutron star phenomenology and for ultrarelativistic heavy ion
collisions.Comment: 12 pages including 8 figures. To appear in Phys. Rev.
Chiral phase properties of finite size quark droplets in the Nambu--Jona-Lasinio model
Chiral phase properties of finite size hadronic systems are investigated
within the Nambu--Jona-Lasinio model. Finite size effects are taken into
account by making use of the multiple reflection expansion. We find that, for
droplets with relatively small baryon numbers, chiral symmetry restoration is
enhanced by the finite size effects. However the radius of the stable droplet
does not change much, as compared to that without the multiple reflection
expansion.Comment: RevTex4, 9 pages, 6 figures, to be published in Phys. Rev.
Reducing multi-photon rates in pulsed down-conversion by temporal multiplexing
We present a simple technique to reduce the emission rate of higher-order
photon events from pulsed spontaneous parametric down-conversion. The technique
uses extra-cavity control over a mode locked ultrafast laser to simultaneously
increase repetition rate and reduce the energy of each pulse from the pump
beam. We apply our scheme to a photonic quantum gate, showing improvements in
the non-classical interference visibility for 2-photon and 4-photon
experiments, and in the quantum-gate fidelity and entangled state production in
the 2-photon case.Comment: 8 pages, 6 figure
Spin chirality induced by the Dzyaloshinskii-Moriya interaction and the polarized neutron scattering
We discuss the influence of the Dzyaloshinskii-Moriya (DM) interaction in the
Heizenberg spin chain model for the observables in the polarized neutron
scattering experiments. We show that different choices of the parameters of DM
interaction may leave the spectrum of the problem unchanged, while the
observable spin-spin correlation functions may differ qualitatively.
Particularly, for the uniform DM interaction one has the incommensurate
fluctuations and polarization-dependent neutron scattering in the paramagnetic
phase. We sketch the possible generalization of our treatment to higher
dimensions.Comment: 4 pages, REVTEX, no figures, references added, to appear in PR
Microstructure and velocity of field-driven Ising interfaces moving under a soft stochastic dynamic
We present theoretical and dynamic Monte Carlo simulation results for the
mobility and microscopic structure of 1+1-dimensional Ising interfaces moving
far from equilibrium in an applied field under a single-spin-flip ``soft''
stochastic dynamic. The soft dynamic is characterized by the property that the
effects of changes in field energy and interaction energy factorize in the
transition rate, in contrast to the nonfactorizing nature of the traditional
Glauber and Metropolis rates (``hard'' dynamics). This work extends our
previous studies of the Ising model with a hard dynamic and the unrestricted
SOS model with soft and hard dynamics. [P.A. Rikvold and M. Kolesik, J. Stat.
Phys. 100, 377 (2000); J. Phys. A 35, L117 (2002); Phys. Rev. E 66, 066116
(2002).] The Ising model with soft dynamics is found to have closely similar
properties to the SOS model with the same dynamic. In particular, the local
interface width does not diverge with increasing field, as it does for hard
dynamics. The skewness of the interface at nonzero field is very weak and has
the opposite sign of that obtained with hard dynamics.Comment: 19 pages LaTex with 7 imbedded figure
Temperature Dependence of Facet Ridges in Crystal Surfaces
The equilibrium crystal shape of a body-centered solid-on-solid (BCSOS) model
on a honeycomb lattice is studied numerically. We focus on the facet ridge
endpoints (FRE). These points are equivalent to one dimensional KPZ-type growth
in the exactly soluble square lattice BCSOS model. In our more general context
the transfer matrix is not stochastic at the FRE points, and a more complex
structure develops. We observe ridge lines sticking into the rough phase where
thesurface orientation jumps inside the rounded part of the crystal. Moreover,
the rough-to-faceted edges become first-order with a jump in surface
orientation, between the FRE point and Pokrovsky-Talapov (PT) type critical
endpoints. The latter display anisotropic scaling with exponent instead
of familiar PT value .Comment: 12 pages, 19 figure
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