94 research outputs found
Landauer Theory, Inelastic Scattering and Electron Transport in Molecular Wires
In this paper we address the topic of inelastic electron scattering in
mesoscopic quantum transport. For systems where only elastic scattering is
present, Landauer theory provides an adequate description of transport that
relates the electronic current to single-particle transmission and reflection
probabilities. A formalism proposed recently by Bonca and Trugman facilitates
the calculation of the one-electron transmission and reflection probabilities
for inelastic processes in mesoscopic conductors connected to one-dimensional
ideal leads. Building on their work, we have developed a self-consistent
procedure for the evaluation of the non-equilibrium electron distributions in
ideal leads connecting such mesoscopic conductors to electron reservoirs at
finite temperatures and voltages. We evaluate the net electronic current
flowing through the mesoscopic device by utilizing these non-equilibrium
distributions. Our approach is a generalization of Landauer theory that takes
account of the Pauli exclusion principle for the various competing elastic and
inelastic processes while satisfying the requirement of particle conservation.
As an application we examine the influence of elastic and inelastic scattering
on conduction through a two site molecular wire with longitudinal phonons using
the Su-Schrieffer-Heeger model of electron-phonon coupling.Comment: 25 pages, 8 figure
Temperature Dependence of Electric and Magnetic Gluon Condensates
The contribution of Lorentz non-scalar operators to finite temperature
correlation functions is discussed. Using the local duality approach for the
one-pion matrix element of a product of two vector currents, the temperature
dependence of the average gluonic stress tensor is estimated in the chiral
limit to be . At a
normalization point GeV we obtain . Together with the
known temperature dependence of the Lorentz scalar gluon condensate we are able
to infer and separately
in the low-temperature hadronic phase.Comment: 11 pages, TPI-MINN-92/37-
Biologische bestrijding van Duponchelia : bestrijding van Duponchelia fovealis met bodempredatoren en biologische middelen, met aandacht voor invloeden van gewas, teeltsubstraat en toedieningstechniek
De vlinder Duponchelia fovealis is een opkomend plaagorganisme dat zich in de jaren negentig heeft gevestigd in de Nederlandse kassen. Schade wordt vooral ondervonden in potplanten door vraat van rupsen aan plantendelen. Deze rupsen leven over het algemeen goed verscholen bij de plantvoet, waardoor een bestrijding met insecticiden in dichte gewassen onvoldoende effectief kan zijn. Een alternatief voor insecticiden kan inzet van bodempredatoren zijn. Rupsen en eieren van Duponchelia worden mogelijk wel bereikt met deze rovers, die actief zoeken naar prooien. Het doel van dit onderzoek was het ontwikkelen van een biologisch bestrijdingssysteem, waarmee populaties van Duponchelia tot een acceptabel niveau kunnen worden onderdrukt. In dit onderzoek is daarom gekeken naar de effecten van nieuwe bodempredatoren en de invloed van gewas en substraat op deze bodempredatoren en op Duponchelia zelf. De effecten van een aantal biologische en chemische middelen op Duponchelia zijn onder kasomstandigheden bepaald, waarbij eveneens is gekeken naar combinaties van behandelingen. Tenslotte werd aandacht gegeven aan het belang van spuitfrequentie en toedieningstechniek op de effectiviteit van een verspuitbaar middel
Quantum mechanics with a time-dependent random unitary Hamiltonian: A perturbative study of the nonlinear Keldysh sigma-model
We analyze the perturbative series of the Keldysh-type sigma-model proposed
recently for describing the quantum mechanics with time-dependent Hamiltonians
from the unitary Wigner-Dyson random-matrix ensemble. We observe that vertices
of orders higher than four cancel, which allows us to reduce the calculation of
the energy-diffusion constant to that in a special kind of the matrix \phi^4
model. We further verify that the perturbative four-loop correction to the
energy-diffusion constant in the high-velocity limit cancels, in agreement with
the conjecture of one of the authors.Comment: 27 pages, 15 figures; typos corrected, one reference adde
Low-energy photon-photon collisions to two loops revisited
In view of ongoing experimental activities to determine the pion
polarizabilities, we have started to recalculate the available two-loop
expressions in the framework of chiral perturbation theory, because they have
never been checked before. We make use of the chiral Lagrangian at order p^6
now available, and of improved techniques to evaluate the two-loop diagrams.
Here, we present the result for the neutral pions. The cross section for the
reaction gamma+gamma->pi0+pi0 agrees with the earlier calculation within a
fraction of a percent. We present analytic results for the dipole and
quadrupole polarizabilities, and compare the latter with a recent evaluation
from data on gamma+gamma->pi0+pi0.Comment: 28 pages, 7-eps figures, 1 tabl
Het effect van chemische gewasbeschermingsmiddelen op biologische bestrijders - Deel 1: Laboratoriumtoetsen met roofmijten en roofwantsen; Deel 2: Veldtoetsen met de roofwants Orius laevigatus
Effect of screening of the electron-phonon interaction on the temperature of Bose-Einstein condensation of intersite bipolarons
Here we consider an interacting electron-phonon system within the framework
of extended Holstein-Hubbard model at strong enough electron-phonon interaction
limit in which (bi)polarons are the essential quasiparticles of the system. It
is assumed that the electron-phonon interaction is screened and its potential
has Yukawa-type analytical form. An effect of screening of the electron-phonon
interaction on the temperature of Bose-Einstein condensation of the intersite
bipolarons is studied for the first time. It is revealed that the temperature
of Bose-Einstein condensation of intersite bipolarons is higher in the system
with the more screened electron-phonon interaction.Comment: 6 pages, 4 figure
Polarons with a twist
We consider a polaron model where molecular \emph{rotations} are important.
Here, the usual hopping between neighboring sites is affected directly by the
electron-phonon interaction via a {\em twist-dependent} hopping amplitude. This
model may be of relevance for electronic transport in complex molecules and
polymers with torsional degrees of freedom, such as DNA, as well as in
molecular electronics experiments where molecular twist motion is significant.
We use a tight-binding representation and find that very different polaronic
properties are already exhibited by a two-site model -- these are due to the
nonlinearity of the restoring force of the twist excitations, and of the
electron-phonon interaction in the model. In the adiabatic regime, where
electrons move in a {\em low}-frequency field of twisting-phonons, the
effective splitting of the energy levels increases with coupling strength. The
bandwidth in a long chain shows a power-law suppression with coupling, unlike
the typical exponential dependence due to linear phonons.Comment: revtex4 source and one eps figur
Universal corrections to the Fermi-liquid theory
We show that the singularities in the dynamical bosonic response functions of
a generic 2D Fermi liquid give rise to universal, non-analytic corrections to
the Fermi-liquid theory. These corrections yield a term in the specific
heat, terms in the effective mass and the uniform spin susceptibility
, and term in . The existence of these
terms has been the subject of recent controversy, which is resolved in this
paper. We present exact expressions for all non-analytic terms to second order
in a generic interaction and show that only U(0) and matter.Comment: references added, a typo correcte
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