510 research outputs found
Gaussian Belief with dynamic data and in dynamic network
In this paper we analyse Belief Propagation over a Gaussian model in a
dynamic environment. Recently, this has been proposed as a method to average
local measurement values by a distributed protocol ("Consensus Propagation",
Moallemi & Van Roy, 2006), where the average is available for read-out at every
single node. In the case that the underlying network is constant but the values
to be averaged fluctuate ("dynamic data"), convergence and accuracy are
determined by the spectral properties of an associated Ruelle-Perron-Frobenius
operator. For Gaussian models on Erdos-Renyi graphs, numerical computation
points to a spectral gap remaining in the large-size limit, implying
exceptionally good scalability. In a model where the underlying network also
fluctuates ("dynamic network"), averaging is more effective than in the dynamic
data case. Altogether, this implies very good performance of these methods in
very large systems, and opens a new field of statistical physics of large (and
dynamic) information systems.Comment: 5 pages, 7 figure
Quasiparticle relaxation rate and shear viscosity of superfluid 3He-A_1 at low temperatures
Quasiparticle relaxation rate,, and the shear viscosity tensor
of the A_1-phase of superfluid 3He are calculated at low temperatures and
melting pressure, by using Boltzmann equation approach in momentum space. The
collision integral is written in terms of inscattering and outscattering
collision integrals. The interaction between normal and Bogoliubov
quasiparticles is considered in calculating transition probabilities in the
binary, decay and coalescence processes. We obtain that both
and are proportional to
>. The shear viscosities , and are
proportional to . The constant of proportionality of the shear
viscosity tensor is in nearly good agreement with the experimental results of
Roobol et al., and our exact theoretical calculation.Comment: 8 pages, some typos were correcte
Cardiovascular collapse caused by carbon dioxide insufflation during one-lung anaesthesia for thoracoscopic dorsal sympathectomy
Publisher's copy made available with the permission of the publisherCarbon dioxide insufflation into the pleural space during one-lung anaesthesia for thoracoscopic surgery is used in some centres to improve surgical access, even though this practice has been associated with well-described cardiovascular compromise. The present report is of a 35-year-old woman undergoing thoracoscopic left dorsal sympathectomy for hyperhidrosis. During one-lung anaesthesia the insufflation of carbon dioxide into the non-ventilated hemithorax for approximately 60 seconds, using a pressure-limited gas inflow, was accompanied by profound bradycardia and hypotension that resolved promptly with the release of the gas. Possible mechanisms for the cardiovascular collapse are discussed, and the role of carbon dioxide insufflation as a means of expediting lung collapse for procedures performed using single-lung ventilation is questioned.RJD Harris, G Benveniste, J Pfitznerhttp://www.aaic.net.au/Article.asp?D=200119
Shear viscosity of the A_1-phase of superfluid 3He
The scattering processes between the quasiparticles in spin- up superfluid
with the quasiparticles in spin-down normal fluid are added to the other
relevant scattering processes in the Boltzmann collision terms. The Boltzmann
equation has been solved exactly for temperatures just below T_c_1. The shear
viscosity component of the A_1- phase drops as C_1(1-T/T_c_1)^(1/2). The
numerical factor C_1 is in fairly good agreement with the experiments
Effects of radiative heat transfer on the structure of turbulent supersonic channel flow
International audienceThe interaction between turbulence in a minimal supersonic channel and radiative heat transfer is studied using large-eddy simulation. The working fluid is pure water vapour with temperature-dependent specific heats and molecular transport coefficients. Its line spectra properties are represented with a statistical narrow-band correlated-k model. A grey gas model is also tested. The parallel no-slip channel walls are treated as black surfaces concerning thermal radiation and are kept at a constant temperature of 1000 K. Simulations have been performed for different optical thicknesses (based on the Planck mean absorption coefficient) and different Mach numbers. Results for the mean flow variables, Reynolds stresses and certain terms of their transport equations indicate that thermal radiation effects counteract compressibility (Mach number) effects. An analysis of the total energy balance reveals the importance of radiative heat transfer, compared to the turbulent and mean molecular heat transport
Universal behavior of Ferromagnet at Quantum Critical Point
The heavy-fermion metal can be tuned from ferromagnetism
at to non-magnetic state at some critical concentration . The
non-Fermi liquid behavior (NFL) at is recognized by power low
dependence of the specific heat given by the electronic contribution,
magnetic susceptibility and volume expansion coefficient
at low temperatures: . We
also demonstrate that the behavior of normalized effective mass
observed in at agrees with that of
observed in paramagnetic and conclude that these alloys
exhibit the universal NFL thermodynamic behavior at their quantum critical
points. We show that the NFL behavior of can be accounted
for within frameworks of quasiparticle picture and fermion condensation quantum
phase transition, while this alloy exhibits a universal thermodynamic NFL
behavior which is independent of the characteristic features of the given alloy
such as its lattice structure, magnetic ground state, dimension etc.Comment: 5 pages, 3 figure
On peak phenomena for non-commutative
A non-commutative extension of Amar and Lederer's peak set result is given.
As its simple applications it is shown that any non-commutative
-algebra has unique predual,and moreover some
restriction in some of the results of Blecher and Labuschagne are removed,
making them hold in full generality.Comment: final version (the presentation of some part is revised and one
reference added
Second wind of the Dulong-Petit Law at a quantum critical point
Renewed interest in 3He physics has been stimulated by experimental
observation of non-Fermi-liquid behavior of dense 3He films at low
temperatures. Abnormal behavior of the specific heat C(T) of two-dimensional
liquid 3He is demonstrated in the occurrence of a T-independent term in C(T).
To uncover the origin of this phenomenon, we have considered the group velocity
of transverse zero sound propagating in a strongly correlated Fermi liquid. For
the first time, it is shown that if two-dimensional liquid 3He is located in
the vicinity of the quantum critical point associated with a divergent
quasiparticle effective mass, the group velocity depends strongly on
temperature and vanishes as T is lowered toward zero. The predicted vigorous
dependence of the group velocity can be detected in experimental measurements
on liquid 3He films. We have demonstrated that the contribution to the specific
heat coming from the boson part of the free energy due to the transverse
zero-sound mode follows the Dulong-Petit Law. In the case of two-dimensional
liquid 3He, the specific heat becomes independent of temperature at some
characteristic temperature of a few mK.Comment: 5 pages, 1 figur
Universal Behavior of Heavy-Fermion Metals Near a Quantum Critical Point
The behavior of the electronic system of heavy fermion metals is considered.
We show that there exist at least two main types of the behavior when the
system is nearby a quantum critical point which can be identified as the
fermion condensation quantum phase transition (FCQPT). We show that the first
type is represented by the behavior of a highly correlated Fermi-liquid, while
the second type is depicted by the behavior of a strongly correlated
Fermi-liquid. If the system approaches FCQPT from the disordered phase, it can
be viewed as a highly correlated Fermi-liquid which at low temperatures
exhibits the behavior of Landau Fermi liquid (LFL). At higher temperatures ,
it demonstrates the non-Fermi liquid (NFL) behavior which can be converted into
the LFL behavior by the application of magnetic fields . If the system has
undergone FCQPT, it can be considered as a strongly correlated Fermi-liquid
which demonstrates the NFL behavior even at low temperatures. It can be turned
into LFL by applying magnetic fields . We show that the effective mass
diverges at the very point that the N\'eel temperature goes to zero. The
phase diagrams of both liquids are studied. We demonstrate that these
phase diagrams have a strong impact on the main properties of heavy-fermion
metals such as the magnetoresistance, resistivity, specific heat,
magnetization, volume thermal expansion, etc.Comment: Revtex, 11 pages, revised and accepted by JETP Let
Energy scales and the non-Fermi liquid behavior in YbRh2Si2
Multiple energy scales are detected in measurements of the thermodynamic and
transport properties in heavy fermion metals. We demonstrate that the
experimental data on the energy scales can be well described by the scaling
behavior of the effective mass at the fermion condensation quantum phase
transition, and show that the dependence of the effective mass on temperature
and applied magnetic fields gives rise to the non-Fermi liquid behavior. Our
analysis is placed in the context of recent salient experimental results. Our
calculations of the non-Fermi liquid behavior, of the scales and thermodynamic
and transport properties are in good agreement with the heat capacity,
magnetization, longitudinal magnetoresistance and magnetic entropy obtained in
remarkable measurements on the heavy fermion metal YbRh2Si2.Comment: 8 pages, 8 figure
- …