439 research outputs found
Multiphonon anharmonic decay of a quantum mode
A nonperturbative theory of multiphonon anharmonic transitions between energy
levels of a local mode is presented. It is shown that the rate of transitions
rearranges near the critical level number : at smaller the process
slows down, while at larger it accelerates in time, causing a jump-like
loss of energy followed by the generation of phonon bursts. Depending on
parameters, phonons are emitted in pairs, triplets etc.Comment: submitted to Europhys.Let
Driving defect modes of Bose-Einstein condensates in optical lattices
We present an approximate analytical theory and direct numerical computation
of defect modes of a Bose-Einstein condensate loaded in an optical lattice and
subject to an additional localized (defect) potential. Some of the modes are
found to be remarkably stable and can be driven along the lattice by means of a
defect moving following a step-like function defined by the period of Josephson
oscillations and the macroscopic stability of the atoms.Comment: 4 pages, 5 figure
Elastic pp-scattering at \sqrt s=7 TeV with the genuine Orear regime and the dip
The unitarity condition unambigously requires the Orear region to appear in
between the diffraction cone at low transferred momenta and hard parton
scattering regime at high transferred momenta in hadron elastic scattering. It
originates from rescattering of the diffraction cone processes. It is shown
that such region has been observed in the differential cross section of the
elastic pp-scattering at \sqrt s=7 TeV. The Orear region is described by
exponential decrease with the scattering angle and imposed on it damped
oscillations. They explain the steepening at the end of the diffraction cone as
well as the dip and the subsequent maximum observed in TOTEM data. The failure
of several models to describe the data in this region can be understood as
improper account of the unitarity condition. It is shown that the real part of
the amplitude can be as large as the imaginary part in this region. The overlap
function is calculated and shown to be small outside the diffraction peak. Its
negative sign there indicates the important role of phases in the amplitudes of
inelastic processes.Comment: 5 pages, 2 figures, revtex
Defect modes of a Bose-Einstein condensate in an optical lattice with a localized impurity
We study defect modes of a Bose-Einstein condensate in an optical lattice
with a localized defect within the framework of the one-dimensional
Gross-Pitaevskii equation. It is shown that for a significant range of
parameters the defect modes can be accurately described by an expansion over
Wannier functions, whose envelope is governed by the coupled nonlinear
Schr\"{o}dinger equation with a delta-impurity. The stability of the defect
modes is verified by direct numerical simulations of the underlying
Gross-Pitaevskii equation with a periodic plus defect potentials. We also
discuss possibilities of driving defect modes through the lattice and suggest
ideas for their experimental generation.Comment: 14 pages, 9 Figures, 1 Tabl
Extraordinary magnetoresistance in graphite: experimental evidence for the time-reversal symmetry breaking
The ordinary magnetoresistance (MR) of doped semiconductors is positive and
quadratic in a low magnetic field, B, as it should be in the framework of the
Boltzmann kinetic theory or in the conventional hopping regime. We observe an
unusual highly-anisotropic in-plane MR in graphite, which is neither quadratic
nor always positive. In a certain current direction MR is negative and linear
in B in fields below a few tens of mT with a crossover to a positive MR at
higher fields, while in a perpendicular current direction we observe a giant
super-linear and positive MR. These extraordinary MRs are respectively
explained by a hopping magneto-conductance via non-zero angular momentum
orbitals, and by the magneto-conductance of inhomogeneous media. The linear
orbital NMR is a unique signature of the broken time-reversal symmetry (TRS) in
graphite. While some local paramagnetic centers could be responsible for the
broken TRS, the observed large diamagnetism suggests a more intriguing
mechanism of this breaking, involving superconducting clusters with
unconventional (chiral) order parameters and spontaneously generated
normal-state current loops in graphite.Comment: 4 pages, 5 figure
Feasibility study on the design of a probe for rectal cancer detection
Rectal examination techniques are considered in terms of detection capability, patient acceptance, and cost reduction. A review of existing clinical techniques are considered in terms of detection capability, patient acceptance, and cost reduction. A review of existing clinical techniques and of relevant aerospace technology included evaluation of the applicability of visual, thermal, ultrasound, and radioisotope modalities of examination. The desired improvements can be obtained by redesigning the proctosigmoidoscope to have reduced size, additional visibility, and the capability of readily providing a color photograph of the entire rectosigmoid mucosa in a single composite view
Quantum description for a chiral condensate disoriented in a certain direction in isospace
We derive a quantum state of the disoriented chiral condensate dynamically,
considering small quantum fluctuations around a classical chiral condensate
disoriented in a certain direction in isospace. The obtained
nonisosinglet quantum state has the characteristic features; (i) it has the
form of the squeezed state, (ii) the state contains not only the component of
pion quanta in the direction but also the component in the
perpendicular direction to and (iii) the low momentum pions in the
state violate the isospin symmetry. With the quantum state, we calculate the
probability of the neutral fraction depending on the time and the pion's
momentum, and find that the probability has an unfamiliar form. For the low
momentum pions, the parametric resonance mechanism works with the result that
the probability of the neutral fraction becomes the well known form
approximately and that the charge fluctuation is small.Comment: 19 page
Field-induced interaction of a pseudoscalar particle with photon in a magnetized plasma
The effective interaction of a pseudoscalar particle with photon in plasma
with the presence of a constant uniform magnetic field is investigated. It is
shown that under some physical conditions the effective coupling between
pseudoscalar particle and photon does not depend on medium parameters and
particles momentum. The probability of the familon decay into photon pair in a
strongly magnetized degenerate ultrarelativistic plasma is calculated.Comment: 10 pages, 2 figures. To be published in Modern Physics Letters
Hall helps Ohm: some corrections to negative-U centers approach to transport properties of YBaCuO and LaSrCuO
For broad oxygen and strontium doping ranges, temperature dependences
(T-dependences) of the normal state resistivity \rho(T) of YBa_2Cu_3O_x (YBCO)
and La_(2-x)Sr_xCuO_4 (LSCO) are calculated and compared to experiments. Holes
transport was taken in the \tau-approximation, where \tau(T,\epsilon) is due to
acoustic phonons. Besides, T-dependence of the chemical potential \mu(T) and
effective carrier mass m* ~10-100 free electron masses, obtained by negative-U
centers modelling the T-dependence of the Hall coefficient, were used to
calculate \rho(T). In addition, it is demonstrated that anisotropy of the
cuprates does not affect the calculated T-variation of neither Hall coefficient
nor \rho, but only rescale their magnitudes by factors depending on
combinations of m_ab and m_c.Comment: 4th International Conference Fundamental Problems of High-Temperature
Superconductivity, Moscow-Zvenigorod (October 3-7, 2011) Submitted to J.
Supercond. Nov. Magn.: after revision. Extension for Supercond. Sci. Technol.
24 075026 (2011), DOI: 10.1088/0953-2048/24/7/075026 Contains: 2 pages, 3
figure
Chiral Fluid Dynamics and Collapse of Vacuum Bubbles
We study the expansion dynamics of a quark-antiquark plasma droplet from an
initial state with restored chiral symmetry. The calculations are made within
the linear model scaled with an additional scalar field representing
the gluon condensate. We solve numerically the classical equations of motion
for the meson fields coupled to the fluid-dynamical equations for the plasma.
Strong space-time oscillations of the meson fields are observed in the course
of the chiral transition. A new phenomenon, the formation and collapse of
vacuum bubbles, is also predicted. The particle production due to the
bremsstrahlung of the meson fields is estimated.Comment: 12 pages Revtex,5 figures, Figures modified, minor changes in text.
To be published in Phys. Rev. Let
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