863 research outputs found
Relativistic Kinetics of Phonon Gas in Superfluids
The relativistic kinetic theory of the phonon gas in superfluids is
developed. The technique of the derivation of macroscopic balance equations
from microscopic equations of motion for individual particles is applied to an
ensemble of quasi-particles. The necessary expressions are constructed in terms
of a Hamilton function of a (quasi-)particle. A phonon contribution into
superfluid dynamic parameters is obtained from energy-momentum balance
equations for the phonon gas together with the conservation law for superfluids
as a whole. Relations between dynamic flows being in agreement with results of
relativistic hydrodynamic consideration are found. Based on the kinetic
approach a problem of relativistic variation of the speed of sound under phonon
influence at low temperature is solved.Comment: 23 pages, Revtex fil
Studying conformally flat spacetimes with an elastic stress energy tensor using 1+3 formalism
Conformally flat spacetimes with an elastic stress energy tensor given by a
diagonal trace-free anisotropic pressure tensor are investigated using 1+3
formalism. We show how the null tetrad Ricci components are related to the
pressure components and energy density. The 1+3 Bianchi and Jacobi identities
and Einstein field equations are written for this particular case. In general
the commutators must be considered since they supply potentially new
information on higher order derivatives of the 1+3 quantities. We solve the
system for the non rotating case which consist of ODEs of a spatial coordinate
Insulated skin temperature as a measure of core body temperature for individuals wearing CBRN protective clothing
This study assessed the validity of insulated skin temperature (Tis) to predict rectal temperature (Tre) for use as a non-invasive measurement of thermal strain to reduce the risk of heat illness for emergency service personnel. Volunteers from the Police, Fire and Rescue, and Ambulance Services performed rolerelated tasks in hot (30 ◦C) and neutral (18 ◦C) conditions, wearing service specific personal protective equipment. Insulated skin temperature and micro climate temperature (Tmc) predicted Tre with an adjusted r2 = 0.87 and standard error of the estimate (SEE) of 0.19 ◦C. A bootstrap validation of the equation resulted in an adjusted r2 = 0.85 and SEE = 0.20 ◦C. Taking into account the 0.20 ◦C error, the prediction of Tre resulted in a sensitivity and specificity of 100% and 91%, respectively. Insulated skin temperature and Tmc can be used in a model to predict Tre in emergency service personnel wearing CBRN protective clothing with an SEE of 0.2 ◦C. However, the model is only valid for Tis over 36.5 ◦C, above which thermal stability is reached between the core and the skin
Magnetic Anisotropy in the Molecular Complex V15
We apply degenerate perturbation theory to investigate the effects of
magnetic anisotropy in the magnetic molecule V15. Magnetic anisotropy is
introduced via Dzyaloshinskii-Moriya (DM) interaction in the full Hilbert space
of the system. Our model provides an explanation for the rounding of
transitions in the magnetization as a function of applied field at low
temperature, from which an estimate for the DM interaction is found. We find
that the calculated energy differences of the lowest energy states are
consistent with the available data. Our model also offers a novel explanation
for the hysteretic nature of the time-dependent magnetization data.Comment: Final versio
The effect of twisted magnetic field on the resonant absorption of MHD waves in coronal loops
The standing quasi modes in a cylindrical incompressible flux tube with
magnetic twist that undergoes a radial density structuring is considered in
ideal magnetohydrodynamics (MHD). The radial structuring is assumed to be a
linearly varying density profile. Using the relevant connection formulae, the
dispersion relation for the MHD waves is derived and solved numerically to
obtain both the frequencies and damping rates of the fundamental and
first-overtone modes of both the kink (m=1) and fluting (m=2,3) waves. It was
found that a magnetic twist will increase the frequencies, damping rates and
the ratio of the oscillation frequency to the damping rate of these modes. The
period ratio P_1/P_2 of the fundamental and its first-overtone surface waves
for kink (m=1) and fluting (m=2,3) modes is lower than 2 (the value for an
untwisted loop) in the presence of twisted magnetic field. For the kink modes,
particularly, the magnetic twists B_{\phi}/B_z=0.0065 and 0.0255 can achieve
deviations from 2 of the same order of magnitude as in the observations.
Furthermore, for the fundamental kink body waves, the frequency bandwidth
increases with increasing the magnetic twist.Comment: 18 pages, 9 figure
About Bianchi I with VSL
In this paper we study how to attack, through different techniques, a perfect
fluid Bianchi I model with variable G,c and Lambda, but taking into account the
effects of a -variable into the curvature tensor. We study the model under
the assumption,div(T)=0. These tactics are: Lie groups method (LM), imposing a
particular symmetry, self-similarity (SS), matter collineations (MC) and
kinematical self-similarity (KSS). We compare both tactics since they are quite
similar (symmetry principles). We arrive to the conclusion that the LM is too
restrictive and brings us to get only the flat FRW solution. The SS, MC and KSS
approaches bring us to obtain all the quantities depending on \int c(t)dt.
Therefore, in order to study their behavior we impose some physical
restrictions like for example the condition q<0 (accelerating universe). In
this way we find that is a growing time function and Lambda is a decreasing
time function whose sing depends on the equation of state, w, while the
exponents of the scale factor must satisfy the conditions
and
, i.e. for all equation of state relaxing in this way the
Kasner conditions. The behavior of depends on two parameters, the equation
of state and a parameter that controls the behavior of
therefore may be growing or decreasing.We also show that through
the Lie method, there is no difference between to study the field equations
under the assumption of a var affecting to the curvature tensor which the
other one where it is not considered such effects.Nevertheless, it is essential
to consider such effects in the cases studied under the SS, MC, and KSS
hypotheses.Comment: 29 pages, Revtex4, Accepted for publication in Astrophysics & Space
Scienc
Observing Direct CP Violation in Untagged B-Meson Decays
Direct CP violation can exist in untagged B-meson decays to self-conjugate,
three-particle final states; it would be realized as a population asymmetry in
the untagged decay rate across the mirror line of the Dalitz plot of the
three-body decay. We explore the numerical size of this direct CP-violating
effect in a variety of B-meson decays to three pseudoscalar mesons; we show
that the resulting asymmetry is comparable to the partial rate asymmetry in the
analogous tagged decays, making the search for direct CP violation in the
untagged decay rate, for which greater statistics accrue, advantageous.Comment: 31 pages, REVTeX4, 1 eps figure, references added, typos corrected,
version to appear in PR
Topological Defects and CMB anisotropies : Are the predictions reliable ?
We consider a network of topological defects which can partly decay into
neutrinos, photons, baryons, or Cold Dark Matter. We find that the degree-scale
amplitude of the cosmic microwave background (CMB) anisotropies as well as the
shape of the matter power spectrum can be considerably modified when such a
decay is taken into account. We conclude that present predictions concerning
structure formation by defects might be unreliable.Comment: 14 pages, accepted for publication in PR
Knowledge-based energy functions for computational studies of proteins
This chapter discusses theoretical framework and methods for developing
knowledge-based potential functions essential for protein structure prediction,
protein-protein interaction, and protein sequence design. We discuss in some
details about the Miyazawa-Jernigan contact statistical potential,
distance-dependent statistical potentials, as well as geometric statistical
potentials. We also describe a geometric model for developing both linear and
non-linear potential functions by optimization. Applications of knowledge-based
potential functions in protein-decoy discrimination, in protein-protein
interactions, and in protein design are then described. Several issues of
knowledge-based potential functions are finally discussed.Comment: 57 pages, 6 figures. To be published in a book by Springe
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