461 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
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
An evaluation of the relative efficacy of an open airway, an oxygen reservoir and continuous positive airway pressure 5 cmH2O on the non-ventilated lung
Publisher's copy made available with the permission of the publisher © Australian Society of AnaesthetistsThe aim of this study, during one-lung ventilation, was to evaluate if oxygenation could be improved by use of a simple oxygen reservoir or application of 5 cmH2O continuous positive airway pressure (CPAP) to the non-ventilated lung compared with an open airway. Twenty-three patients with lung malignancy, undergoing thoracotomy requiring at least 60 minutes of one-lung ventilation before lung lobe excision, were studied. After routine induction and establishment of one-lung ventilation, the three treatments were applied in turn to the same patient in a sequence selected randomly. The first treatment was repeated as a fourth treatment and these results of the repeated treatment averaged to minimize the effect of slow changes. Arterial oxygenation was measured by an arterial blood gas 15 minutes after the application of each treatment. Twenty patients completed the study. Mean PaO2 (in mmHg) was 210.3 (SD 105.5) in the 'OPEN' treatment, 186.0 (SD 109.2) in the 'RESERVOIR' treatment, and 240.5 (SD 116.0) in the 'CPAP' treatment. This overall difference was not quite significant (P=0.058, paired ANOVA), but comparison of the pairs showed that there was a significant better oxygenation only with the CPAP compared to the reservoir treatments (t=2.52, P=0.021). While the effect on the surgical field was not apparent in most patients, in one patient surgery was impeded during CPAP. Our results show that the use of a reservoir does not give oxygenation better than an open tube, and is less effective than the use of CPAP 5 cmH2O on the non-ventilated lung during one-lung ventilation.J. Slimani, W. J. Russell, C. Jurisevichttp://www.aaic.net.au/Article.asp?D=200404
Figure rotation of dark halos in CDM simulations
We investigate the figure rotation of dark matter halos identified in Lambda
CDM simulations. We find that when strict criteria are used to select suitable
halos for study, 5 of the 222 halos identified in our z=0 simulation output
undergo coherent figure rotation over a 5h^{-1}Gyr period. We discuss the
effects of varying the selection criteria and find that pattern speeds for a
much larger fraction of the halos can be measured when the criteria are
relaxed. Pattern speeds measured over a 1h^{-1}Gyr period follow a log-normal
distribution, centred at Omega_p = 0.25h rad/Gyr with a maximum value of 0.94h
rad/Gyr. Over a 5h^{-1}Gyr period, the average pattern speed of a halo is about
0.1h rad/Gyr and the largest pattern speed found is 0.24h rad/Gyr. Less than
half of the selected halos showed alignment between their figure rotation axis
and minor axis, the exact fraction being somewhat dependent on how one defines
a halo. While the pattern speeds observed are lower than those generally
thought capable of causing spiral structure, we note that coherent figure
rotation is found over very long periods and argue that further simulations
would be required before strong conclusions about spiral structure in all
galaxies could be drawn. We find no correlation between halo properties such as
total mass and the pattern speed.Comment: accepted to MNRAS, 8 page
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
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 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
Behavior of Fermi Systems Approaching Fermion Condensation Quantum Phase Transition from Disordered Phase
The behavior of Fermi systems which approach the fermion condensation quantum
phase transition (FCQPT) from the disordered phase is considered. We show that
the quasiparticle effective mass diverges as
where is the system density and is the critical point at which
FCQPT occurs. Such a behavior is of general form and takes place in both three
dimensional (3D) systems and two dimensional (2D) ones. Since the effective
mass is finite, the system exhibits the Landau Fermi liquid behavior. At
, the behavior can be viewed as a highly correlated
one, because the effective mass is large and strongly depends on the density.
In case of electronic systems the Wiedemann-Franz law is held and
Kadowaki-Woods ratio is preserved. Beyond the region ,
the effective mass is approximately constant and the system becomes
conventional Landau Fermi liquid.Comment: 9 pages, revtex, no figure
Nodes of the Gap Function and Anomalies in Thermodynamic Properties of Superfluid He
Departures of thermodynamic properties of three-dimensional superfluid He
from the predictions of BCS theory are analyzed. Attention is focused on
deviations of the ratios and
from their BCS values, where is the pairing gap at zero
temperature, is the critical temperature, and and are the
superfluid and normal specific heats. We attribute these deviations to the
momentum dependence of the gap function , which becomes well
pronounced when this function has a pair of nodes lying on either side of the
Fermi surface. We demonstrate that such a situation arises if the P-wave
pairing interaction , evaluated at the Fermi surface, has a sign
opposite to that anticipated in BCS theory. Taking account of the momentum
structure of the gap function, we derive a closed relation between the two
ratios that contains no adjustable parameters and agrees with the experimental
data. Some important features of the effective pairing interaction are inferred
from the analysis.Comment: 17 pages, 4 figure
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