3,320 research outputs found
Environment effects on the electric conductivity of the DNA
We present a theoretical analysis of the environment effects on charge
transport in double-stranded synthetic poly(G)-poly(C) DNA molecules attached
to two ideal leads. Coupling of the DNA to the environment results in two
effects: (i) localization of carrier functions due to the static disorder and
(ii) phonon-induced scattering of the carrier between these localized states,
resulting in hopping conductivity. A nonlinear Pauli master equation for
populations of localized states is used to describe the hopping transport and
calculate the electric current as a function of the applied bias. We
demonstrate that, although the electronic gap in the density of states shrinks
as the disorder increases, the voltage gap in the characteristics becomes
wider. Simple physical explanation of this effect is provided.Comment: 8 pages, 2 figures, to appear in J. Phys.: Condens. Matte
Photon recoil momentum in a Bose-Einstein condensate of a dilute gas
We develop a "minimal" microscopic model to describe a
two-pulse-Ramsay-interferometer-based scheme of measurement of the photon
recoil momentum in a Bose-Einstein condensate of a dilute gas [Campbell et al.,
Phys. Rev. Lett. 94, 170403 (2005)]. We exploit the truncated coupled
Maxwell-Schroedinger equations to elaborate the problem. Our approach provides
a theoretical tool to reproduce essential features of the experimental results.
Additionally, we enable to calculate the quantum-mechanical mean value of the
recoil momentum and its statistical distribution that provides a detailed
information about the recoil event.Comment: 6 pages, 4 figure
On the Exponential Decay of the n-point Correlation Functions and the Analyticity of the Pressure
The goal of this paper is to provide estimates leading to a direct proof of
the exponential decay of the n-point correlation functions for certain
unbounded models of Kac type. The methods are based on estimating higher order
derivatives of the solution of the Witten Laplacian equation on one forms
associated with the hamiltonian of the system. We also provide a formula for
the Taylor coefficients of the pressure that is suitable for a direct proof the
analyticity
Nonlinear resonance reflection from and transmission through a dense glassy system built up of oriented linear Frenkel chains: two-level models
A theoretical study of the resonance optical response of assemblies of
oriented short (as compared to an optical wavelength) linear Frenkel chains is
carried out using a two-level model. We show that both transmittivity and
reflectivity of the film may behave in a bistable fashion and analyze how the
effects found depend on the film thickness and on the inhomogeneous width of
the exciton optical transition.Comment: 26 pages, 9 figure
Statistics of low-energy levels of a one-dimensional weakly localized Frenkel exciton: A numerical study
Numerical study of the one-dimensional Frenkel Hamiltonian with on-site
randomness is carried out. We focus on the statistics of the energy levels near
the lower exciton band edge, i. e. those determining optical response. We found
that the distribution of the energy spacing between the states that are well
localized at the same segment is characterized by non-zero mean, i.e. these
states undergo repulsion. This repulsion results in a local discrete energy
structure of a localized Frenkel exciton. On the contrary, the energy spacing
distribution for weakly overlapping local ground states (the states with no
nodes within their localization segments) that are localized at different
segments has zero mean and shows almost no repulsion. The typical width of the
latter distribution is of the same order as the typical spacing in the local
discrete energy structure, so that this local structure is hidden; it does not
reveal itself neither in the density of states nor in the linear absorption
spectra. However, this structure affects the two-exciton transitions involving
the states of the same segment and can be observed by the pump-probe
spectroscopy. We analyze also the disorder degree scaling of the first and
second momenta of the distributions.Comment: 10 pages, 6 figure
Localization properties of a one-dimensional tight-binding model with non-random long-range inter-site interactions
We perform both analytical and numerical studies of the one-dimensional
tight-binding Hamiltonian with stochastic uncorrelated on-site energies and
non-fluctuating long-range hopping integrals . It was argued recently [A.
Rodriguez at al., J. Phys. A: Math. Gen. 33, L161 (2000)] that this model
reveals a localization-delocalization transition with respect to the disorder
magnitude provided . The transition occurs at one of the band edges (the upper
one for and the lower one for). The states at the other band edge are always
localized, which hints on the existence of a single mobility edge. We analyze
the mobility edge and show that, although the number of delocalized states
tends to infinity, they form a set of null measure in the thermodynamic limit,
i.e. the mobility edge tends to the band edge. The critical magnitude of
disorder for the band edge states is computed versus the interaction exponent
by making use of the conjecture on the universality of the normalized
participation number distribution at transition.Comment: 7 pages, 6 postscript figures, uses revtex
Pauli-Villars Regularization in nonperturbative Hamiltonian approach on the Light Front
The advantage of Pauli-Villars regularization in quantum field theory
quantized on the light front is explained. Simple examples of scalar
field theory and Yukawa-type model are used. We give also an
example of nonperturbative calculation in the theory with Pauli-Villars fields,
using for that a model of anharmonic oscillator modified by inclusion of ghost
variables playing the role similar to Pauli-Villars fields.Comment: LaTeX, 10 pages, 2 figures. Article will be published in AIP
Conference Proceedings, the final publication will be available at
http://scitation.aip.org/content/aip/proceeding/aipc
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