271,908 research outputs found
Magneto-optical evidence of the percolation nature of the metal-insulator transition in the 2D electron system
We compare the results of the transport and time-resolved
magneto-luminescence measurements in disordered 2D electron systems in
GaAs-AlGaAs heterostructures in the extreme quantum limit, in particular, in
the vicinity of the metal-insulator transition (MIT). At filling factors , the optical signal has two components: the single-rate exponentially
decaying part attributed to a uniform liquid and a power-law long-living tail
specific to a microscopically inhomogeneous state of electrons. We interprete
this result as a separation of the 2D electron system into a liquid and
localized phases, especially because the MIT occurs strikingly close to those
filling factors where the liquid occupies of the sample area (the
percollation threshold condition in two-component media).Comment: 5 pages RevTex + 4 fig., to appear in PRB, Rapid Com
Large N dynamics in QED in a magnetic field
The expression for the dynamical mass of fermions in QED in a magnetic field
is obtained for a large number of the fermion flavor N in the framework of 1/N
expansion. The existence of a threshold value N_{thr}, dividing the theories
with essentially different dynamics, is established. For the number of flavors
N << N_{thr}, the dynamical mass is very sensitive to the value of the coupling
constant \alpha_b, related to the magnetic scale \mu = |eB|. For N of order
N_{thr} or larger, a dynamics similar to that in the Nambu-Jona-Lasinio model
with cutoff of order |eB| and the dimensional coupling constant G \sim
1/(N|eB|) takes place. In this case, the value of the dynamical mass is
essentially \alpha_b independent (the dynamics with an infrared stable fixed
point). The value of N_{thr} separates a weak coupling dynamics (with
\tilde{\alpha}_b \equiv N\alpha_b << 1) from a strong coupling one (with
\tilde{\alpha}_b \gtrsim 1) and is of order 1/\alpha_b.Comment: 4 pages, REVTe
Stability properties of the collective stationary motion of self-propelling particles with conservative kinematic constraints
In our previous papers we proposed a continuum model for the dynamics of the
systems of self-propelling particles with conservative kinematic constraints on
the velocities. We have determined a class of stationary solutions of this
hydrodynamic model and have shown that two types of stationary flow, linear and
radially symmetric (vortical) flow, are possible. In this paper we consider the
stability properties of these stationary flows. We show, using a linear
stability analysis, that the linear solutions are neutrally stable with respect
to the imposed velocity and density perturbations. A similar analysis of the
stability of the vortical solution is found to be not conclusive.Comment: 13 pages, 3 figure
Effective Action and Conformal Phase Transition in Three-Dimensional QED
The effective action for local composite operators in is considered.
The effective potential is calculated in leading order in ( is the
number of fermion flavors) and used to describe the features of the phase
transition at , . It is shown that this
continuous phase transition satisfies the criteria of the conformal phase
transition, considered recently in the literature. In particular, there is an
abrupt change of the spectrum of light excitations at the critical point,
although the phase transition is continuous, and the structure of the equation
for the divergence of the dilatation current is essentially different in the
symmetric and nonsymmetric phases. The connection of this dynamics with the
dynamics in is briefly discussed.Comment: 17 pages, RevTex file, no figures. The discussion of the effective
action is extende
Non-equilibrium excitation of methanol in Galactic molecular clouds: multi-transitional observations at 2 mm
We observed 14 methanol transitions near lambda=2 mm in Galactic star-forming
regions. Broad, quasi-thermal J(0)-J(-1)E methanol lines near 157 GHz were
detected toward 73 sources. Together with the 6(-1)-5(0)E and 5(-2)-6(-1)E
lines at 133 GHz and the 7(1)-7(0)E line at 165 GHz, they were used to study
the methanol excitation. In the majority of the observed objects, the Class I
6(-1)-5(0)E transition is inverted, and the Class II 5(-2)-6(-1)E and
6(0)-6(-1)E transitions are overcooled. This is exactly as predicted by models
of low gain Class I masers. The absence of the inversion of Class II
transitions 5(-2)-6(-1)E and 6(0)-6(-1)E means that quasi-thermal methanol
emission in all objects arises in areas without a strong radiation field, which
is required for the inversion.Comment: 23 pages paper (uses aasms4.sty), 12 pages tables (uses apjpt4.sty),
10 Jpeg figures, submitted to the ApJ
Detection of an intergalactic meteor particle with the 6-m telescope
On July 28, 2006 the 6-m telescope of the Special Astrophysical Observatory
of the Russian Academy of Sciences recorded the spectrum of a faint meteor. We
confidently identify the lines of FeI and MgI, OI, NI and molecular-nitrogen
N_2 bands. The entry velocity of the meteor body into the Earth's atmosphere
estimated from radial velocity is equal to 300 km/s. The body was several tens
of a millimeter in size, like chondrules in carbon chondrites. The radiant of
the meteor trajectory coincides with the sky position of the apex of the motion
of the Solar system toward the centroid of the Local Group of galaxies.
Observations of faint sporadic meteors with FAVOR TV CCD camera confirmed the
radiant at a higher than 96% confidence level. We conclude that this meteor
particle is likely to be of extragalactic origin. The following important
questions remain open: (1) How metal-rich dust particles came to be in the
extragalactic space? (2) Why are the sizes of extragalactic particles larger by
two orders of magnitude (and their masses greater by six orders of magnitude)
than common interstellar dust grains in our Galaxy? (3) If extragalactic dust
surrounds galaxies in the form of dust (or gas-and-dust) aureoles, can such
formations now be observed using other observational techniques (IR
observations aboard Spitzer satellite, etc.)? (4) If inhomogeneous
extragalactic dust medium with the parameters mentioned above actually exists,
does it show up in the form of irregularities on the cosmic microwave
background (WMAP etc.)?Comment: 9 pages, 6 EPS figure
Time-Dependent Invariants and Green's Functions in the Probability Representation of Quantum Mechanics
In the probability representation of quantum mechanics, quantum states are
represented by a classical probability distribution, the marginal distribution
function (MDF), whose time dependence is governed by a classical evolution
equation. We find and explicitly solve, for a wide class of Hamiltonians, new
equations for the Green's function of such an equation, the so-called classical
propagator. We elucidate the connection of the classical propagator to the
quantum propagator for the density matrix and to the Green's function of the
Schr\"odinger equation. Within the new description of quantum mechanics we give
a definition of coherence solely in terms of properties of the MDF and we test
the new definition recovering well known results. As an application, the forced
parametric oscillator is considered . Its classical and quantum propagator are
found, together with the MDF for coherent and Fock states.Comment: 29 pages, RevTex, 6 eps-figures, to appear on Phys. Rev.
Self-Similar Bootstrap of Divergent Series
A method is developed for calculating effective sums of divergent series.
This approach is a variant of the self-similar approximation theory. The
novelty here is in using an algebraic transformation with a power providing the
maximal stability of the self-similar renormalization procedure. The latter is
to be repeated as many times as it is necessary in order to convert into closed
self-similar expressions all sums from the series considered. This multiple and
complete renormalization is called self-similar bootstrap. The method is
illustrated by several examples from statistical physics.Comment: 1 file, 22 pages, RevTe
Entanglement production with multimode Bose-Einstein condensates in optical lattices
Deep optical lattices are considered, in each site of which there are many
Bose-condensed atoms. By the resonant modulation of trapping potentials it is
possible to transfer a macroscopic portion of atoms to the collective nonlinear
states corresponding to topological coherent modes. Entanglement can be
generated between these modes. By varying the resonant modulating field it is
possible to effectively regulate entanglement production in this multimode
multitrap system of Bose condensates.Comment: Latex file, 16 pages, 7 figure
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