13,058 research outputs found
Empirical Emission Functions for LPM Suppression of Photon Emission from Quark-Gluon Plasma
The LPM suppression of photon emission rates from the quark gluon plasma have
been studied at different physical conditions of the plasma given by
temperature and chemical potentials.The integral equation for the transverse
vector function (f(p_t)) consisting of multiple scattering effects is solved
for the parameter set {p,k,kappa,T}, for bremsstrahlung and AWS processes. The
peak positions of these distributions depend only on the dynamical variable
x=(T/kappa)|1/p-1/(p+k)|. Integration over these distributions multiplied by
x^2 factor also depends on this variable x,leading to a unique global emission
function g(x) for all parameters. Empirical fits to this dimensionless emission
function, g(x), are obtained. The photon emission rate calculations with LPM
suppression effects reduce to one dimensional integrals involving folding over
the empirical g(x) function with appropriate distribution functions and the
kinematic factors. Using this approach, the suppression factors for both
bremsstrahlung and AWS have been estimated for various chemical potentials and
compared with the variational method
Relativistic Theory of Hydrodynamic Fluctuations with Applications to Heavy Ion Collisions
We develop the relativistic theory of hydrodynamic fluctuations for
application to high energy heavy ion collisions. In particular, we investigate
their effect on the expanding boost-invariant (Bjorken) solution of the
hydrodynamic equations. We discover that correlations over a long rapidity
range are induced by the propagation of the sound modes. Due to the expansion,
the dispersion law for these modes is non-linear and attenuated even in the
limit of zero viscosity. As a result, there is a non-dissipative wake behind
the sound front which is generated by any instantaneous point-like fluctuation.
We evaluate the two-particle correlators using the initial conditions and
hydrodynamic parameters relevant for heavy-ion collisions at RHIC and LHC. In
principle these correlators can be used to obtain information about the
viscosities because the magnitudes of the fluctuations are directly
proportional to them.Comment: 39 pages, 6 figures; references adde
Slow light in moving media
We review the theory of light propagation in moving media with extremely low
group velocity. We intend to clarify the most elementary features of
monochromatic slow light in a moving medium and, whenever possible, to give an
instructive simplified picture
Formation and Equilibrium Properties of Living Polymer Brushes
Polydisperse brushes obtained by reversible radical chain polymerization
reaction onto a solid substrate with surface-attached initiators, are studied
by means of an off-lattice Monte Carlo algorithm of living polymers (LP).
Various properties of such brushes, like the average chain length and the
conformational orientation of the polymers, or the force exerted by the brush
on the opposite container wall, reveal power-law dependence on the relevant
parameters. The observed molecular weight distribution (MWD) of the grafted LP
decays much more slowly than the corresponding LP bulk system due to the
gradient of the monomer density within the dense pseudo-brush which favors
longer chains. Both MWD and the density profiles of grafted polymers and chain
ends are well fitted by effective power laws whereby the different exponents
turn out to be mutually self-consistent for a pseudo-brush in the
strong-stretching regime.Comment: 33 pages, 11 figues, J.Chem. Phys. accepted Oct. 199
Controlling quasiparticle excitations in a trapped Bose-Einstein condensate
We describe an approach to quantum control of the quasiparticle excitations
in a trapped Bose-Einstein condensate based on adiabatic and diabatic changes
in the trap anisotropy. We describe our approach in the context of Landau-Zener
transition at the avoided crossings in the quasiparticle excitation spectrum.
We show that there can be population oscillation between different modes at the
specific aspect ratios of the trapping potential at which the mode energies are
almost degenerate. These effects may have implications in the expansion of an
excited condensate as well as the dynamics of a moving condensate in an atomic
wave guide with a varying width
Phase effects in neutrino conversions during a supernova shock wave
Neutrinos escaping from a core collapse supernova a few seconds after bounce
pass through the shock wave, where they may encounter one or more resonances
corresponding to . The neutrino mass eigenstates in
matter may stay coherent between these multiple resonances, giving rise to
oscillations in the survival probabilities of neutrino species. We provide an
analytical approximation to these inevitable phase effects, that relates the
density profile of the shock wave to the oscillation pattern. The phase effects
are present only if the multiple resonances encountered by neutrinos are
semi-adiabatic, which typically happens for 10^{-5} \lsim \sin^2 \theta_{13}
\lsim 10^{-3}. The observability of these oscillations is severely limited by
the inability of the detectors to reconstruct the neutrino energy faithfully.
For typical shock wave profiles, the detection of these phase effects seems
rather unlikely. However, if the effects are indeed identified in the \nuebar
spectra, they would establish inverted hierarchy and a nonzero value of
.Comment: 10 pages, 9 eps figures. Major changes made. Final version to be
published in PR
A growth walk model for estimating the canonical partition function of Interacting Self Avoiding Walk
We have explained in detail why the canonical partition function of
Interacting Self Avoiding Walk (ISAW), is exactly equivalent to the
configurational average of the weights associated with growth walks, such as
the Interacting Growth Walk (IGW), if the average is taken over the entire
genealogical tree of the walk. In this context, we have shown that it is not
always possible to factor the the density of states out of the canonical
partition function if the local growth rule is temperature-dependent. We have
presented Monte Carlo results for IGWs on a diamond lattice in order to
demonstrate that the actual set of IGW configurations available for study is
temperature-dependent even though the weighted averages lead to the expected
thermodynamic behavior of Interacting Self Avoiding Walk (ISAW).Comment: Revised version consisting of 12 pages (RevTeX manuscript, plus three
.eps figure files); A few sentences in the second paragraph on Page 4 are
rewritten so as to make the definition of the genealogical tree, , clearer. Also, the second equality of Eq.(1) on Page 4, and its
corresponding statement below have been remove
Fermi-liquid effects in the gapless state of marginally thin superconducting films
We present low temperature tunneling density-of-states measurements in Al
films in high parallel magnetic fields. The thickness range of the films, t=6-9
nm, was chosen so that the orbital and Zeeman contributions to their parallel
critical fields were comparable. In this quasi-spin paramagnetically limited
configuration, the field produces a significant suppression of the gap, and at
high fields the gapless state is reached. By comparing measured and calculated
tunneling spectra we are able to extract the value of the antisymmetric
Fermi-liquid parameter G^0 and thereby deduce the quasiparticle density
dependence of the effective parameter G^0_{eff} across the gapless state.Comment: 6 pages, 4 figure
Technology as an economic catalyst in rural and depressed places in Massachusetts
This paper uses case studies, including two cities (Lynn and New Bedford), a sub-city district (Roxbury) and two towns in rural Franklin County (Greenfield and Orange), to examine the role of technology as a potential economic catalyst in rural and depressed places in Massachusetts. Though the five target areas vary in size, density, geographic area, demographic characteristics and economic resources, each exhibits chronic patterns of economic distress related to the decline of manufacturing, construction and other key industries
Studying freeze-out and hadronization in the Landau hydrodynamical model
We study the rapidity spectra in ultra-relativistic heavy ion collisions in
the framework of the Landau hydrodynamical model. We find that thermal smearing
effects improve the agreement with experimental results on pion rapidity
spectra. We describe a simple model of the hadronization and discuss its
consequences regarding the pion multiplicity and the increasing entropy
condition.Comment: 7 pages, 3 figure
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