15,027 research outputs found
Spinodal decomposition: An alternate mechanism of phase conversion
The scenario of homogeneous nucleation is investigated for a first order
quark-hadron phase transition in a rapidly expanding background of quark gluon
plasma. It is found that significant supercooling is possible before
hadronization begins. This study also suggests that spinodal decomposition
competes with nucleation and may provide an alternative mechanism for phase
conversion.Comment: LaTeX, 4 pages with 3 Postscript figures. Talk given at International
Conference on Physics and Astrophysics of Quark Gluon Plasma (ICPAQGP 2001),
Nov. 26-30, 2001, Jaipur, Indi
Simulation study of the filamentation of counter-streaming beams of the electrons and positrons in plasmas
The filamentation instability driven by two spatially uniform and
counter-streaming beams of charged particles in plasmas is modelled by a
particle-in-cell (PIC) simulation. Each beam consists of the electrons and
positrons. The four species are equally dense and they have the same
temperature. The one-dimensional simulation direction is orthogonal to the beam
velocity vector. The magnetic field grows spontaneously and rearranges the
particles in space, such that the distributions of the electrons of one beam
and the positrons of the second beam match. The simulation demonstrates that as
a result no electrostatic field is generated by the magnetic field through its
magnetic pressure gradient prior to its saturation. This electrostatic field
would be repulsive at the centres of the filaments and limit the maximum charge
and current density. The filaments of electrons and positrons in this
simulation reach higher charge and current densities than in one with no
positrons. The oscillations of the magnetic field strength induced by the
magnetically trapped particles result in an oscillatory magnetic pressure
gradient force. The latter interplays with the statistical fluctuations in the
particle density and it probably enforces a charge separation, by which
electrostatic waves grow after the filamentation instability has saturated.Comment: 13 pages, 8 figure
Random Matrices with Correlated Elements: A Model for Disorder with Interactions
The complicated interactions in presence of disorder lead to a correlated
randomization of states. The Hamiltonian as a result behaves like a
multi-parametric random matrix with correlated elements. We show that the
eigenvalue correlations of these matrices can be described by the single
parametric Brownian ensembles. The analogy helps us to reveal many important
features of the level-statistics in interacting systems e.g. a critical point
behavior different from that of non-interacting systems, the possibility of
extended states even in one dimension and a universal formulation of level
correlations.Comment: 19 Pages, No Figures, Major Changes to Explain the Mathematical
Detail
Gauge transformation through an accelerated frame of reference
The Schr\"{o}dinger equation of a charged particle in a uniform electric
field can be specified in either a time-independent or a time-dependent gauge.
The wave-function solutions in these two gauges are related by a phase-factor
reflecting the gauge symmetry of the problem. In this article we show that the
effect of such a gauge transformation connecting the two wave-functions can be
mimicked by the effect of two successive extended Galilean transformations
connecting the two wave-function. An extended Galilean transformation connects
two reference frames out of which one is accelerating with respect to the
other.Comment: 7 Pages, Latex fil
Metal-insulator transitions in tetrahedral semiconductors under lattice change
Although most insulators are expected to undergo insulator to metal
transition on lattice compression, tetrahedral semiconductors Si, GaAs and InSb
can become metallic on compression as well as by expansion. We focus on the
transition by expansion which is rather peculiar; in all cases the direct gap
at point closes on expansion and thereafter a zero-gap state persists
over a wide range of lattice constant. The solids become metallic at an
expansion of 13 % to 15 % when an electron fermi surface around L-point and a
hole fermi surface at -point develop. We provide an understanding of
this behavior in terms of arguments based on symmetry and simple tight-binding
considerations. We also report results on the critical behavior of conductivity
in the metal phase and the static dielectric constant in the insulating phase
and find common behaviour. We consider the possibility of excitonic phases and
distortions which might intervene between insulating and metallic phases.Comment: 12 pages, 8 figure
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