22,074 research outputs found
Generalized Emission Functions for Photon Emission from Quark-Gluon Plasma
The Landau-Pomeranchuk-Migdal effects on photon emission from the quark gluon
plasma have been studied as a function of photon mass, at a fixed temperature
of the plasma. The integral equations for the transverse vector function () and the longitudinal function () consisting of multiple scattering effects are solved by the
self consistent iterations method and also by the variational method for the
variable set \{\}, considering the bremsstrahlung and the processes. We define four new dynamical scaling variables,
,,, for bremsstrahlung and {\bf aws} processes and
analyse the transverse and longitudinal components as a function of
\{\}. We generalize the concept of photon emission function and we
define four new emission functions for massive photon emission represented by
, , , . These have been constructed using the exact
numerical solutions of the integral equations. These four emission functions
have been parameterized by suitable simple empirical fits. In terms of these
empirical emission functions, the virtual photon emission from quark gluon
plasma reduces to one dimensional integrals that involve folding over the
empirical functions with appropriate quark distribution
functions and the kinematic factors. Using this empirical emission functions,
we calculated the imaginary part of the photon polarization tensor as a
function of photon mass and energy.Comment: In nuclear physics journals and arxiv listings, my name used to
appear as S.V.S. Sastry. Hereafter, my name will appear as, S.V.
Suryanarayan
The bound on viscosity and the generalized second law of thermodynamics
We describe a new paradox for ideal fluids. It arises in the accretion of an
\textit{ideal} fluid onto a black hole, where, under suitable boundary
conditions, the flow can violate the generalized second law of thermodynamics.
The paradox indicates that there is in fact a lower bound to the correlation
length of any \textit{real} fluid, the value of which is determined by the
thermodynamic properties of that fluid. We observe that the universal bound on
entropy, itself suggested by the generalized second law, puts a lower bound on
the correlation length of any fluid in terms of its specific entropy. With the
help of a new, efficient estimate for the viscosity of liquids, we argue that
this also means that viscosity is bounded from below in a way reminiscent of
the conjectured Kovtun-Son-Starinets lower bound on the ratio of viscosity to
entropy density. We conclude that much light may be shed on the
Kovtun-Son-Starinets bound by suitable arguments based on the generalized
second law.Comment: 11 pages, 1 figure, published versio
Evaluation of specific heat for superfluid helium between 0 - 2.1 K based on nonlinear theory
The specific heat of liquid helium was calculated theoretically in the Landau
theory. The results deviate from experimental data in the temperature region of
1.3 - 2.1 K. Many theorists subsequently improved the results of the Landau
theory by applying temperature dependence of the elementary excitation energy.
As well known, many-body system has a total energy of Galilean covariant form.
Therefore, the total energy of liquid helium has a nonlinear form for the
number distribution function. The function form can be determined using the
excitation energy at zero temperature and the latent heat per helium atom at
zero temperature. The nonlinear form produces new temperature dependence for
the excitation energy from Bose condensate. We evaluate the specific heat using
iteration method. The calculation results of the second iteration show good
agreement with the experimental data in the temperature region of 0 - 2.1 K,
where we have only used the elementary excitation energy at 1.1 K.Comment: 6 pages, 3 figures, submitted to Journal of Physics: Conference
Serie
Relativistic viscoelastic fluid mechanics
A detailed study is carried out for the relativistic theory of
viscoelasticity which was recently constructed on the basis of Onsager's linear
nonequilibrium thermodynamics. After rederiving the theory using a local
argument with the entropy current, we show that this theory universally reduces
to the standard relativistic Navier-Stokes fluid mechanics in the long time
limit. Since effects of elasticity are taken into account, the dynamics at
short time scales is modified from that given by the Navier-Stokes equations,
so that acausal problems intrinsic to relativistic Navier-Stokes fluids are
significantly remedied. We in particular show that the wave equations for the
propagation of disturbance around a hydrostatic equilibrium in Minkowski
spacetime become symmetric hyperbolic for some range of parameters, so that the
model is free of acausality problems. This observation suggests that the
relativistic viscoelastic model with such parameters can be regarded as a
causal completion of relativistic Navier-Stokes fluid mechanics. By adjusting
parameters to various values, this theory can treat a wide variety of materials
including elastic materials, Maxwell materials, Kelvin-Voigt materials, and (a
nonlinearly generalized version of) simplified Israel-Stewart fluids, and thus
we expect the theory to be the most universal description of single-component
relativistic continuum materials. We also show that the presence of strains and
the corresponding change in temperature are naturally unified through the
Tolman law in a generally covariant description of continuum mechanics.Comment: 52pages, 11figures; v2: minor corrections; v3: minor corrections, to
appear in Physical Review E; v4: minor change
The secular practice of a spiritual technique:mindfulness-based interventions and spirituality
Mindfulness meditation (MM) is an ancient Buddhist spiritual practice that has been secularised into popular and effective therapeutic interventions. This is the first empirical study to investigate the spiritual and secular context of mindfulness-based interventions through the prism of Common Factors theory, specifically focusing on the work of Frank (1973) and the concept of a healing ‘myth’ or story.
The hypotheses predicted that a philosophically integrated role-induction to MM, would be more effective at improving credibility and expectations, state mindfulness and affect outcomes compared to philosophically narrower spiritual or secular presentations.
Participants were randomly allocated to a role-induction group (integrated / spiritual / secular) and all received the same MM-intervention. Additionally, congruency effects between participants’ dispositional spirituality / secularity and induction group were tested. 165 participants (82 % female, mean age 25 years, SD=11.15) completed the online study. While all groups showed improvements on measures of credibility and expectations, state mindfulness and negative affect across timepoints, contrary to hypotheses the integrated induction group did not improve more than the secular or spiritual groups, nor were strong congruency effects found.
Results are discussed in the context of a possible primary ‘myth’ of MM that overrides secondary divisions between secularity / spirituality; the ‘myth’ of finding peace in a frantic world
Properties of new unflavored mesons below 2.4 GeV
The global features of spectrum of highly excited light nonstrange mesons can
be well understood within both chiral symmetry restoration scenario combined
with the relation and within nonrelativistic description based on
the relation . The predictions of these two alternative
classifications for missing states are different and only future experiments
can distinguish between the two. We elaborate and compare systematically the
predictions of both schemes, which may serve as a suggestion for future
experiments devoted to the search for missing states.Comment: 5 pages, to appear in Phys. Rev. C XX, 005200 (2007
Spin Response and Neutrino Emissivity of Dense Neutron Matter
We study the spin response of cold dense neutron matter in the limit of zero
momentum transfer, and show that the frequency dependence of the
long-wavelength spin response is well constrained by sum-rules and the
asymptotic behavior of the two-particle response at high frequency. The
sum-rules are calculated using Auxiliary Field Diffusion Monte Carlo technique
and the high frequency two-particle response is calculated for several
nucleon-nucleon potentials. At nuclear saturation density, the sum-rules
suggest that the strength of the spin response peaks at 40--60
MeV, decays rapidly for 100 MeV, and has a sizable strength below
40 MeV. This strength at relatively low energy may lead to enhanced neutrino
production rates in dense neutron-rich matter at temperatures of relevance to
core-collapse supernova.Comment: 11 pages, 4 figures. Minor change. Published versio
Accurate momentum transfer cross section for the attractive Yukawa potential
Accurate expression for the momentum transfer cross section for the
attractive Yukawa potential is proposed. This simple analytic expression agrees
with the numerical results better than to within in the regime
relevant for ion-particle collisions in complex (dusty) plasmas.Comment: to be published in Physics of Plasma
Numbers of donors and acceptors from transport measurements in graphene
A method is suggested to separately determine the surface density of
positively and negatively charged impurities that limit the mobility in a
graphene monolayer. The method is based on the exact result for the transport
cross-section, according to which the massless carriers are scattered more
strongly when they are attracted to a charged impurity than when they are
repelled from it.Comment: 3 pages, 1 figur
A theory of MHD instability of an inhomogeneous plasma jet
A problem of the instability of an inhomogeneous axisymmetric plasma jet in a
parallel magnetic field is solved. The jet boundary becomes, under certain
conditions, unstable relative to magnetosonic oscillations (Kelvin-Helmholtz
instability) in the presence of a shear flow at the jet boundary. Because of
its internal inhomogeneity the plasma jet has resonance surfaces, where
conversion takes place between various modes of plasma MHD oscillations.
Propagating in inhomogeneous plasma, fast magnetosonic waves drive the Alfven
and slow magnetosonic oscillations, tightly localized across the magnetic
shells, on the resonance surfaces. MHD oscillation energy is absorbed in the
neighbourhood of these resonance surfaces. The resonance surfaces disappear for
the eigen-modes of slow magnetosonic waves propagating in the jet waveguide.
The stability of the plasma MHD flow is determined by competition between the
mechanisms of shear flow instability on the boundary and wave energy
dissipation because of resonant MHD-mode coupling. The problem is solved
analytically, in the WKB approximation, for the plasma jet with a boundary in
the form of a tangential discontinuity over the radial coordinate. The
Kelvin-Helmholtz instability develops if plasma flow velocity in the jet
exceeds the maximum Alfven speed at the boundary. The stability of the plasma
jet with a smooth boundary layer is investigated numerically for the basic
modes of MHD oscillations, to which the WKB approximation is inapplicable. A
new "global" unstable mode of MHD oscillations has been discovered which,
unlike the Kelvin-Helmholtz instability, exists for any, however weak, plasma
flow velocities
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