6,545 research outputs found
Preservation of equilibrium in orthograde and inverted body positions
The mechanism for regulation of the vertical pose with retention of equilibrium in the inverted body position was investigated
Mixed Quantum/Classical Approach for Description of Molecular Collisions in Astrophysical Environments
An efficient and accurate mixed quantum/classical theory approach for computational treatment of inelastic scattering is extended to describe collision of an atom with a general asymmetric-top rotor polyatomic molecule. Quantum mechanics, employed to describe transitions between the internal states of the molecule, and classical mechanics, employed for description of scattering of the atom, are used in a self-consistent manner. Such calculations for rotational excitation of HCOOCH3 in collisions with He produce accurate results at scattering energies above 15 cm–1, although resonances near threshold, below 5 cm–1, cannot be reproduced. Importantly, the method remains computationally affordable at high scattering energies (here up to 1000 cm–1), which enables calculations for larger molecules and at higher collision energies than was possible previously with the standard full-quantum approach. Theoretical prediction of inelastic cross sections for a number of complex organic molecules observed in space becomes feasible using this new computational tool
On the preservation of equilibrium in the orthograde and inverted positions of the body
The mechanism which regulates the vertical posture when maintaining equilibrium in an inverted position of the body is discussed
Detection of quantum light in the presence of noise
Detection of quantum light in the presence of dark counts and background
radiation noise is considered. The corresponding positive operator-valued
measure is obtained and photocounts statistics of quantum light in the presence
of noise is studied.Comment: 4 pages, 1 figure; misprints correcte
Symmetric Exclusion Process with a Localized Source
We investigate the growth of the total number of particles in a symmetric
exclusion process driven by a localized source. The average total number of
particles entering an initially empty system grows with time as t^{1/2} in one
dimension, t/log(t) in two dimensions, and linearly in higher dimensions. In
one and two dimensions, the leading asymptotic behaviors for the average total
number of particles are independent on the intensity of the source. We also
discuss fluctuations of the total number of particles and determine the
asymptotic growth of the variance in one dimension.Comment: 7 pages; small corrections, references added, final versio
A consistent model for \pi N transition distribution amplitudes and backward pion electroproduction
The extension of the concept of generalized parton distributions leads to the
introduction of baryon to meson transition distribution amplitudes (TDAs),
non-diagonal matrix elements of the nonlocal three quark operator between a
nucleon and a meson state. We present a general framework for modelling nucleon
to pion () TDAs. Our main tool is the spectral representation for \pi N
TDAs in terms of quadruple distributions. We propose a factorized Ansatz for
quadruple distributions with input from the soft-pion theorem for \pi N TDAs.
The spectral representation is complemented with a D-term like contribution
from the nucleon exchange in the cross channel. We then study backward pion
electroproduction in the QCD collinear factorization approach in which the
non-perturbative part of the amplitude involves \pi N TDAs. Within our two
component model for \pi N TDAs we update previous leading-twist estimates of
the unpolarized cross section. Finally, we compute the transverse target single
spin asymmetry as a function of skewness. We find it to be sizable in the
valence region and sensitive to the phenomenological input of our \pi N TDA
model.Comment: 39 pages, 9 figure
Coherently photo-induced ferromagnetism in diluted magnetic semiconductors
Ferromagnetism is predicted in undoped diluted magnetic semiconductors
illuminated by intense sub-bandgap laser radiation . The mechanism for
photo-induced ferromagnetism is coherence between conduction and valence bands
induced by the light which leads to an optical exchange interaction. The
ferromagnetic critical temperature T_C depends both on the properties of the
material and on the frequency and intensity of the laser and could be above 1
K.Comment: 11 pages, 2 figures, preprint styl
Long Range Bond-Bond Correlations in Dense Polymer Solutions
The scaling of the bond-bond correlation function along linear polymer
chains is investigated with respect to the curvilinear distance, , along the
flexible chain and the monomer density, , via Monte Carlo and molecular
dynamics simulations. % Surprisingly, the correlations in dense three
dimensional solutions are found to decay with a power law with and the exponential behavior commonly assumed is
clearly ruled out for long chains. % In semidilute solutions, the density
dependent scaling of with
( being Flory's exponent) is set by the
number of monomers contained in an excluded volume blob of size
. % Our computational findings compare well with simple scaling arguments
and perturbation calculation. The power-law behavior is due to
self-interactions of chains on distances caused by the connectivity
of chains and the incompressibility of the melt. %Comment: 4 pages, 4 figure
The Gribov parameter and the dimension two gluon condensate in Euclidean Yang-Mills theories in the Landau gauge
The local composite operator A^2 is added to the Zwanziger action, which
implements the restriction to the Gribov region in Euclidean Yang-Mills
theories in the Landau gauge. We prove the renormalizability of this action to
all orders of perturbation theory. This allows to study the dimension two gluon
condensate by the local composite operator formalism when the restriction
is taken into account. The effective action is evaluated at one-loop order in
the MSbar scheme. We obtain explicit values for the Gribov parameter and for
the mass parameter due to , but the expansion parameter turns out to be
rather large. Furthermore, an optimization of the perturbative expansion in
order to reduce the dependence on the renormalization scheme is performed. The
properties of the vacuum energy, with or without , are investigated. It is
shown that in the original Gribov-Zwanziger formulation (without ), the
vacuum energy is always positive at 1-loop order, independently from the
renormalization scheme and scale. With , we are unable to come to a
definite conclusion at the order considered. In the MSbar scheme, we still find
a positive vacuum energy, again with a relatively large expansion parameter,
but there are renormalization schemes in which the vacuum energy is negative,
albeit the dependence on the scheme itself appears to be strong. We recover the
well known consequences of the restriction, and this in the presence of :
an infrared suppression of the gluon propagator and an enhancement of the ghost
propagator. This behaviour is in qualitative agreement with the results
obtained from the studies of the Schwinger-Dyson equations and from lattice
simulations.Comment: 42 pages, 10 .eps figures. v2: Version accepted for publication in
Phys.Rev.D. Added references. Technical details have been collected in two
appendice
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