2,277 research outputs found
Energy-transfer rate in a double-quantum-well system due to Coulomb coupling
We study the energy-transfer rate for electrons in a double-quantum-well
structure, where the layers are coupled through screened Coulomb interactions.
The energy-transfer rate between the layers (similar to the Coulomb drag effect
in which the momentum transfer rate is considered) is calculated as functions
of electron densities, interlayer spacing, the temperature difference of the
2DEGs, and the electron drift velocity in the drive layer. We employ the full
wave vector and frequency dependent random-phase approximation at finite
temperature to describe the effective interlayer Coulomb interaction. We find
that the collective modes (plasmons) of the system play a dominant role in the
energy transfer rates. The contribution of optical phonons to the transfer
rates through the phonon mediated Coulomb coupling mechanism has also been
considered.Comment: LaTex, 5 pages, 4 figures, uses grafik.sty (included
Chiral single-wall gold nanotubes
Based on first-principles calculations we show that gold atoms can form both
free-standing and tip-suspended chiral single-wall nanotubes composed of
helical atomic strands. Free-standing, infinite (5,5) tube is found to be
energetically the most favorable. While energetically less favorable, the
experimentally observed (5,3) tube stretching between two tips corresponds to a
local minimum in the string tension. Similarly, the (4,3) tube is predicted as
a favorable structure yet to be observed experimentally. Analysis of band
structure, charge density, and quantum ballistic conductance suggests that the
current on these wires is less chiral than expected, and there is no direct
correlation between the numbers of conduction channels and helical strands.Comment: Figures provided in eps forma
Thermodynamics of Delta resonances
The thermodynamic potential of a system of pions and nucleons is computed
including the piN interactions in the P33 channel. A consistent treatment of
the width of the resonance in this channel, the Delta(1232) resonance, is
explored in detail. In the low-density limit we recover the leading term of the
virial expansion for the thermodynamic potential. An instructive diagrammatic
interpretation of the contributions to the total baryon number is presented.
Furthermore, we examine within a fireball model the consequences for the pion
spectra in heavy-ion collisions at intermediate energies, including the effect
of collective flow. A consistent treatment of the Delta width leads to a
substantial enhancement of the pion yield at low momenta.Comment: 12 pages, 3 Postscript figures, LaTeX, elsart, epsfig, minor changes,
references added, to be published in Physics Letters
Test of the isotropy of the speed of light using a continuously rotating optical resonator
We report on a test of Lorentz invariance performed by comparing the
resonance frequencies of one stationary optical resonator and one continuously
rotating on a precision air bearing turntable. Special attention is paid to the
control of rotation induced systematic effects. Within the photon sector of the
Standard Model Extension, we obtain improved limits on combinations of 8
parameters at a level of a few parts in . For the previously least
well known parameter we find . Within the Robertson-Mansouri-Sexl test theory, our measurement
restricts the isotropy violation parameter to
, corresponding to an eightfold improvement with
respect to previous non-rotating measurements.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let
Ab-initio electron transport calculations of carbon based string structures
First-principles calculations show that monatomic strings of carbon have high
cohesive energy and axial strength, and exhibit stability even at high
temperatures. Due to their flexibility and reactivity, carbon chains are
suitable for structural and chemical functionalizations; they form also stable
ring, helix, grid and network structures. Analysis of electronic conductance of
various infinite, finite and doped string structures reveal fundamental and
technologically interesting features. Changes in doping and geometry give rise
to dramatic variations in conductance. In even-numbered linear chains strain
induces substantial decrease of conductance. The double covalent bonding of
carbon atoms underlies their unusual chemical, mechanical and transport
properties.Comment: 4 pages, 4 figure
Dynamics of Phononic Dissipation at the Atomic Scale: Dependence on Internal Degrees of Freedom
Dynamics of dissipation of a local phonon distribution to the substrate is a
key issue in friction between sliding surfaces as well as in boundary
lubrication. We consider a model system consisting of an excited nano-particle
which is weakly coupled with a substrate. Using three different methods we
solve the dynamics of energy dissipation for different types of coupling
between the nano-particle and the substrate, where different types of
dimensionality and phonon densities of states were also considered for the
substrate. In this paper, we present our analysis of transient properties of
energy dissipation via phonon discharge in the microscopic level towards the
substrate. Our theoretical analysis can be extended to treat realistic
lubricant molecules or asperities, and also substrates with more complex
densities of states. We found that the decay rate of the nano-particle phonons
increases as the square of the interaction constant in the harmonic
approximation.Comment: 10 pages, 6 figures, submitted to Phys. Rev.
Covariant transport approach for strongly interacting partonic systems
The dynamics of partons, hadrons and strings in relativistic nucleus-nucleus
collisions is analyzed within the novel Parton-Hadron-String Dynamics (PHSD)
transport approach, which is based on a dynamical quasiparticle model for
partons (DQPM) matched to reproduce recent lattice-QCD results - including the
partonic equation of state - in thermodynamic equilibrium. Scalar- and
vector-interaction densities are extracted from the DQPM as well as effective
scalar- and vector-mean fields for the partons. The transition from partonic to
hadronic degrees of freedom is described by covariant transition rates for the
fusion of quark-antiquark pairs or three quarks (antiquarks), respectively,
obeying flavor current-conservation, color neutrality as well as
energy-momentum conservation. Since the dynamical quarks and antiquarks become
very massive close to the phase transition, the formed resonant 'pre-hadronic'
color-dipole states ( or ) are of high invariant mass, too, and
sequentially decay to the groundstate meson and baryon octets increasing the
total entropy. When applying the PHSD approach to Pb+Pb colllisions at 158
AGeV we find a significant effect of the partonic phase on the
production of multi-strange antibaryons due to a slightly enhanced
pair production from massive time-like gluon decay and a larger formation of
antibaryons in the hadronization process.Comment: 12 pages, 6 figures, to be published in the Proceedings of the 26th
Winter Workshop on `Nuclear Dynamics', Ochto Rios, Jamaica, 2-9 January,
2010
Jamming coverage in competitive random sequential adsorption of binary mixture
We propose a generalized car parking problem where cars of two different
sizes are sequentially parked on a line with a given probability . The free
parameter interpolates between the classical car parking problem of only
one car size and the competitive random sequential adsorption (CRSA) of a
binary mixture. We give an exact solution to the CRSA rate equations and find
that the final coverage, the jamming limit, of the line is always larger for a
binary mixture than for the uni-sized case. The analytical results are in good
agreement with our direct numerical simulations of the problem.Comment: 4 pages 2-column RevTeX, Four figures, (there was an error in the
previous version. We replaced it (including figures) with corrected and
improved version that lead to new results and conclusions
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