145 research outputs found
Transmission Phase of an Isolated Coulomb-Blockade Resonance
In two recent papers, O. Entin-Wohlman et al. studied the question: ``Which
physical information is carried by the transmission phase through a quantum
dot?'' In the present paper, this question is answered for an islolated
Coulomb-blockade resonance and within a theoretical model which is more closely
patterned after the geometry of the actual experiment by Schuster et al. than
is the model of O. Entin-Wohlman et al. We conclude that whenever the number of
leads coupled to the Aharanov-Bohm interferometer is larger than two, and the
total number of channels is sufficiently large, the transmission phase does
reflect the Breit-Wigner behavior of the resonance phase shift.Comment: 6 pages and one figur
Towards an Explanation of the Mesoscopic Double-Slit Experiment: a new model for charging of a Quantum Dot
For a quantum dot (QD) in the intermediate regime between integrable and
fully chaotic, the widths of single-particle levels naturally differ by orders
of magnitude. In particular, the width of one strongly coupled level may be
larger than the spacing between other, very narrow, levels. In this case many
consecutive Coulomb blockade peaks are due to occupation of the same broad
level. Between the peaks the electron jumps from this level to one of the
narrow levels and the transmission through the dot at the next resonance
essentially repeats that at the previous one. This offers a natural explanation
to the recently observed behavior of the transmission phase in an
interferometer with a QD.Comment: 4 pages, 2 figures, Journal versio
Spin Effects and Transport in Quantum Dots with overlapping Resonances
The role of spin is investigated in the transport through a quantum dot with
two overlapping resonances (one having a width larger than the level separation
and the other very narrow, cf. Silvestrov and Imry, Phys. Rev. Lett. {\bf 85},
2565 (2000)). For a series of consecutive charging resonances, one electron
from the leads populates one and the same broad level in the dot. Moreover,
there is the tendency to occupy the same level also by the second electron
within the same resonance. This second electron is taken from the narrow levels
in the dot. The narrow levels are populated (and broad level is depopulated)
via sharp rearrangements of the electronic configuration in the Coulomb
blockade valleys. Possible experimental manifestations of this scenario are
considered. Among these there are sharp features in the valleys and in the
Mixed Valence regime and an unusual Kondo effect.Comment: 7 pages, 3 figures, just a published versio
Quantum universal detectors
We address the problem of estimating the expectation value of an
arbitrary operator O via a universal measuring apparatus that is independent of
O, and for which the expectation values for different operators are obtained by
changing only the data-processing. The ``universal detector'' performs a joint
measurement on the system and on a suitably prepared ancilla. We characterize
such universal detectors, and show how they can be obtained either via Bell
measurements or via local measurements and classical communication between
system and ancilla.Comment: 4 pages, no figure
Kinetic energy density functionals from the Airy gas, with an application to the atomization kinetic energies of molecules
We construct and study several semilocal density functional approximations
for the positive Kohn-Sham kinetic energy density. These functionals fit the
kinetic energy density of the Airy gas and they can be accurate for integrated
kinetic energies of atoms, molecules, jellium clusters and jellium surfaces. We
find that these functionals are the most accurate ones for atomization kinetic
energies of molecules and for fragmentation of jellium clusters. We also report
that local and semilocal kinetic energy functionals can show "binding" when the
density of a spin unrestricted Kohn-Sham calculation is used.Comment: 7 pages, 7 figure
Effect of vibratory stimulation of foot support areas in rats on the functional state of leg muscles and the content of N2A titin isoforms in gravity relief
In this work, we studied the effect of vibratory stimulation of the foot support zones on the functional state of the leg muscles and the content of N2A titin isoforms in rats under simulated microgravity (suspension model). The results of this study showed that vibratory stimulation of the support zones of the rat foot in a gravity discharge may reduce the drop in the amplitude of leg muscle motor response and undesirable reduction of the titin content. © 2014 Pleiades Publishing, Inc
Scattering phases in quantum dots: an analysis based on lattice models
The properties of scattering phases in quantum dots are analyzed with the
help of lattice models. We first derive the expressions relating the different
scattering phases and the dot Green functions. We analyze in detail the Friedel
sum rule and discuss the deviation of the phase of the transmission amplitude
from the Friedel phase at the zeroes of the transmission. The occurrence of
such zeroes is related to the parity of the isolated dot levels. A statistical
analysis of the isolated dot wave-functions reveals the absence of significant
correlations in the parity for large disorder and the appearance, for weak
disorder, of certain dot states which are strongly coupled to the leads. It is
shown that large differences in the coupling to the leads give rise to an
anomalous charging of the dot levels. A mechanism for the phase lapse observed
experimentally based on this property is discussed and illustrated with model
calculations.Comment: 18 pages, 9 figures. to appear in Physical Review
Effect of vibrostimulation of foot and supporting afferentation on functional state of shin muscles in rats during hindlimb unloading
© 2014, Pleiades Publishing, Inc. The goal of this work was to study the influence of daily 3-hr vibrostimulation of the supporting zones of the foot and 3-hr of usual locomotion on the functional state of the soleus, gastrocnemius, and tibial anterior muscles in rats after 7 and 14 days of hindlimb unloading. After 7 days of unloading the soleus weight decreased, while the weight of gastrocnemius and tibial anterior remained unchanged. After 14 days of hindlimb unloading a weight reduction was observed in all studied muscles. Vibrostimulation of the foot and supporting afferentation prevented the loss of weight in gastrocnemius and tibial anterior during the first week of unloading and reduced the negative effect of hindlimb unloading in 14 days. Our results demonstrate that the amplitude of the M-response after 7 days of hindlimb unloading was decreased predominantly in soleus as compared to gastrocnemius and tibial anterior. By the 14 day we observed restoration of the amplitude of the M-response in gastrocnemius and tibial anterior, and the increased amplitude of the M-response in soleus. Different techniques for foot stimulation in rats during hindlimb unloading demonstrated the positive effect in regard to M-response restoration — the amplitude of the M-response was increased in all studied muscles. Thus, our results demonstrate that foot vibrostimulation or supporting afferentation can completely prevent atrophy caused by hindlimb unloading in gastrocnemius and tibial anterior and decrease atrophy in soleus in rats
Laplacian-level density functionals for the kinetic energy density and exchange-correlation energy
We construct a Laplacian-level meta-generalized gradient approximation
(meta-GGA) for the non-interacting (Kohn-Sham orbital) positive kinetic energy
density of an electronic ground state of density . This meta-GGA is
designed to recover the fourth-order gradient expansion in the
appropiate slowly-varying limit and the von Weizs\"{a}cker expression
in the rapidly-varying limit. It is constrained to
satisfy the rigorous lower bound .
Our meta-GGA is typically a strong improvement over the gradient expansion of
for atoms, spherical jellium clusters, jellium surfaces, the Airy gas,
Hooke's atom, one-electron Gaussian density, quasi-two dimensional electron
gas, and nonuniformly-scaled hydrogen atom. We also construct a Laplacian-level
meta-GGA for exchange and correlation by employing our approximate in
the Tao, Perdew, Staroverov and Scuseria (TPSS) meta-GGA density functional.
The Laplacian-level TPSS gives almost the same exchange-correlation enhancement
factors and energies as the full TPSS, suggesting that and
carry about the same information beyond that carried by and . Our
kinetic energy density integrates to an orbital-free kinetic energy functional
that is about as accurate as the fourth-order gradient expansion for many real
densities (with noticeable improvement in molecular atomization energies), but
considerably more accurate for rapidly-varying ones.Comment: 9 pages, 16 figure
Changes in the functional state of spinal-cord cell structures under gravitational unloading
© 2016, Pleiades Publishing, Inc.The functional properties of the spinal-cord structures of experimental rats under a 7-day gravitational unloading were assessed using the method of transcranial magnetic stimulation. Hypogravity was modeled by hanging the animals by their tails in an antiorthostatic position. The gastrocnemius muscle potentials evoked by magnetic stimulation of the efferent structures of the spinal cord were registered. We found that gravitational unloading causes significant changes in motor-potential parameters and the central motor transmission time. We propose that the cause of the revealed transformations is afferent inflow limitation, first of all the motor type, as well as adaptation of the central nervous system to new conditions of motor activity
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