199,335 research outputs found
Non-Fermi-Liquid Behavior from the Fermi-Liquid Approach
Non-Fermi liquid behavior of strongly correlated Fermi systems is derived
within the Landau approach. We attribute this behavior to a phase transition
associated with a rearrangement of the Landau state that leads to flattening of
a portion of the single-particle spectrum in the vicinity
of the Fermi surface. We demonstrate that the quasiparticle subsystem
responsible for the flat spectrum possesses the same thermodynamic properties
as a gas of localized spins. Theoretical results compare favorably with
available experimental data. While departing radically from prevalent views on
the origin of non-Fermi-liquid behavior, the theory advanced here is
nevertheless a conservative one of in continuing to operate within the general
framework of Landau theory.Comment: 8 pages, 4 figures, corrected list of author
Decays with Corrections in Factorization
It is commonly believed that a careful investigation of the subleading terms
is crucial for a better understanding of the factorization in charmless B
decays. In this work the penguin-dominated decays are discussed
systematically, including the subleading corrections in due to soft and
hard gluons, besides the annihilation contributions. Soft-gluon effects for all
the relevant 4-quark effective operators are calculated within the framework of
the light-cone QCD sum rules (LCSR). Our observation is that such soft and hard
corrections are less important than the annihilation effects, enhancing only
the branching ratios by a few percent; the resultant increase in the branching
ratios due to the overall effects is between about
of the QCD factorization results with the corrections, as
the weak phase ranges from to .
Impacts of the involved uncertainties are discussed in some details.Comment: 22 pages,6 figure
Fluctuations in mixtures of lamellar- and nonlamellar-forming lipids
We consider the role of nonlamellar-forming lipids in biological membranes by
examining fluctuations, within the random phase approximation, of a model
mixture of two lipids, one of which forms lamellar phases while the other forms
inverted hexagonal phases. To determine the extent to which nonlamellar-forming
lipids facilitiate the formation of nonlamellar structures in lipid mixtures,
we examine the fluctuation modes and various correlation functions in the
lamellar phase of the mixture. To highlight the role fluctuations can play, we
focus on the lamellar phase near its limit of stability. Our results indicate
that in the initial stages of the transition, undulations appear in the
lamellae occupied by the tails, and that the nonlamellar-forming lipid
dominates these undulations. The lamellae occupied by the head groups pinch off
to make the tubes of the hexagonal phase. Examination of different correlations
and susceptibilities makes quantitative the dominant role of the
nonlamellar-forming lipids.Comment: 7 figures (better but larger in byte figures are available upon
resuest), submitte
Phase Diagram for Magnon Condensate in Yttrium Iron Garnet Film
Recently, magnons, which are quasiparticles describing the collective motion
of spins, were found to undergo Bose-Einstein condensation (BEC) at room
temperature in films of Yttrium Iron Garnet (YIG). Unlike other quasiparticle
BEC systems, this system has a spectrum with two degenerate minima, which makes
it possible for the system to have two condensates in momentum space. Recent
Brillouin Light scattering studies for a microwave-pumped YIG film of thickness
d=5 m and field H=1 kOe find a low-contrast interference pattern at the
characteristic wavevector of the magnon energy minimum. In this report, we
show that this modulation pattern can be quantitatively explained as due to
non-symmetric but coherent Bose-Einstein condensation of magnons into the two
energy minima. Our theory predicts a transition from a high-contrast symmetric
phase to a low-contrast non-symmetric phase on varying the and , and a
new type of collective oscillations.Comment: 6 figures. Accepted by Nature Scientific Report
Energy-efficient data acquisition for accurate signal estimation in wireless sensor networks
Long-term monitoring of an environment is a fundamental requirement for most wireless sensor networks. Owing to the fact that the sensor nodes have limited energy budget, prolonging their lifetime is essential in order to permit long-term monitoring. Furthermore, many applications require sensor nodes to obtain an accurate estimation of a point-source signal (for example, an animal call or seismic activity). Commonly, multiple sensor nodes simultaneously sample and then cooperate to estimate the event signal. The selection of cooperation nodes is important to reduce the estimation error while conserving the network’s energy. In this paper, we present a novel method for sensor data acquisition and signal estimation, which considers estimation accuracy, energy conservation, and energy balance. The method, using a concept of ‘virtual clusters,’ forms groups of sensor nodes with the same spatial and temporal properties. Two algorithms are used to provide functionality. The ‘distributed formation’ algorithm automatically forms and classifies the virtual clusters. The ‘round robin sample scheme’ schedules the virtual clusters to sample the event signals in turn. The estimation error and the energy consumption of the method, when used with a generalized sensing model, are evaluated through analysis and simulation. The results show that this method can achieve an improved signal estimation while reducing and balancing energy consumption
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