778 research outputs found
Low temperature electron transfer in strongly condensed phase
Electron transfer coupled to a collective vibronic degree of freedom is
studied in strongly condensed phase and at lower temperatures where quantum
fluctuations are essential. Based on an exact representation of the reduced
density matrix of the electronic+reaction coordinate compound in terms of path
integrals, recent findings on the overdamped limit in quantum dissipative
systems are employed. This allows to give for the first time a consistent
generalization of the well-known Zusman equations to the quantum domain.
Detailed conditions for the range of validity are specified. Using the Wigner
transform these results are also extended to the quantum dynamics in full phase
space. As an important application electronic transfer rates are derived that
comprise adiabatic and nonadiabatic processes in the low temperature regime
including nuclear tunneling. Accurate agreement with precise quantum Monte
Carlo data is observed.Comment: 16 pages, 6 figures, revised version with minor change
Electron Transfer in Donor-Acceptor Systems: Many-Particle Effects and Influence of Electronic Correlations
We investigate electron transfer processes in donor-acceptor systems with a
coupling of the electronic degrees of freedom to a common bosonic bath. The
model allows to study many-particle effects and the influence of the local
Coulomb interaction U between electrons on donor and acceptor sites. Using the
non-perturbative numerical renormalization group approach we find distinct
differences between the electron transfer characteristics in the single- and
two-particle subspaces. We calculate the critical electron-boson coupling
alpha_c as a function of and show results for density-density correlation
functions in the whole parameter space. The possibility of many-particle
(bipolaronic) and Coulomb-assisted transfer is discussed.Comment: 4 pages, 4 figure
Quantum Brownian Motion With Large Friction
Quantum Brownian motion in the strong friction limit is studied based on the
exact path integral formulation of dissipative systems. In this limit the
time-nonlocal reduced dynamics can be cast into an effective equation of
motion, the quantum Smoluchowski equation. For strongly condensed phase
environments it plays a similar role as master equations in the weak coupling
range. Applications for chemical, mesoscopic, and soft matter systems are
discussed and reveal the substantial role of quantum fluctuations.Comment: 11 pages, 6 figures, to appear in: Chaos: "100 years of Brownian
motion
Inhibition of neurite outgrowth in differentiating mouse N2a neuroblastoma cells by phenyl saligenin phosphate: Effects on MAP kinase (ERK 1/2) activation, neurofilament heavy chain phosphorylation and neuropathy target esterase activity
Sub-lethal concentrations of the organophosphate phenyl saligenin phosphate (PSP) inhibited the outgrowth of axon-like processes in differentiating mouse N2a neuroblastoma cells (IC50 2.5 μM). A transient rise in the phosphorylation state of neurofilament heavy chain (NFH) was detected on Western blots of cell extracts treated with 2.5 μM PSP for 4 h compared to untreated controls, as determined by a relative increase in reactivity with monoclonal antibody Ta51 (anti-phosphorylated NFH) compared to N52 (anti-total NFH). However, cross-reactivity of PSP-treated cell extracts was lower than that of untreated controls after 24 h exposure, as indicated by decreased reactivity with both antibodies. Indirect immunofluorescence analysis with these antibodies revealed the appearance of neurofilament aggregates in the cell bodies of treated cells and reduced axonal staining compared to controls. By contrast, there was no significant change in reactivity with anti-a tubulin antibody B512 at either time point. The activation state of the MAP kinase ERK 1/2 increased significantly after PSP treatment compared to controls, particularly at 4 h, as indicated by increased reactivity with monoclonal antibody E-4 (anti-phosphorylated MAP kinase) but not with polyclonal antibody K-23 (anti-total MAP kinase). The observed early changes were concomitant with almost complete inhibition of the activity of neuropathy target esterase (NTE), one of the proposed early molecular targets in organophosphate-induced delayed neuropathy (OPIDN)
Time-dependent quantum transport: A practical scheme using density functional theory
We present a computationally tractable scheme of time-dependent transport
phenomena within open-boundary time-dependent density-functional-theory. Within
this approach all the response properties of a system are determined from the
time-propagation of the set of ``occupied'' Kohn-Sham orbitals under the
influence of the external bias. This central idea is combined with an
open-boundary description of the geometry of the system that is divided into
three regions: left/right leads and the device region (``real simulation
region''). We have derived a general scheme to extract the set of initial
states in the device region that will be propagated in time with proper
transparent boundary-condition at the device/lead interface. This is possible
due to a new modified Crank-Nicholson algorithm that allows an efficient
time-propagation of open quantum systems. We illustrate the method in
one-dimensional model systems as a first step towards a full first-principles
implementation. In particular we show how a stationary current develops in the
system independent of the transient-current history upon application of the
bias. The present work is ideally suited to study ac transport and
photon-induced charge-injection. Although the implementation has been done
assuming clamped ions, we discuss how it can be extended to include dissipation
due to electron-phonon coupling through the combined simulation of the
electron-ion dynamics as well as electron-electron correlations.Comment: 14 pages, 9 figures, one of which consist of two separate file
Quantum transport through a DNA wire in a dissipative environment
Electronic transport through DNA wires in the presence of a strong
dissipative environment is investigated. We show that new bath-induced
electronic states are formed within the bandgap. These states show up in the
linear conductance spectrum as a temperature dependent background and lead to a
crossover from tunneling to thermal activated behavior with increasing
temperature. Depending on the strength of the electron-bath coupling, the
conductance at the Fermi level can show a weak exponential or even an algebraic
length dependence. Our results suggest a new environmental-induced transport
mechanism. This might be relevant for the understanding of molecular conduction
experiments in liquid solution, like those recently performed on poly(GC)
oligomers in a water buffer (B. Xu et al., Nano Lett 4, 1105 (2004)).Comment: 5 pages, 3 figure
Fluctuation-Facilitated Charge Migration along DNA
We propose a model Hamiltonian for charge transfer along the DNA double helix
with temperature driven fluctuations in the base pair positions acting as the
rate limiting factor for charge transfer between neighboring base pairs. We
compare the predictions of the model with the recent work of J.K. Barton and
A.H. Zewail (Proc.Natl.Acad.Sci.USA, {\bf 96}, 6014 (1999)) on the unusual
two-stage charge transfer of DNA.Comment: 4 pages, 2 figure
Density of Superfluid Helium Droplets
The classical integral cross sections of large superfluid 4He_N droplets and
the number of atoms in the droplets (N=10^3-10^4) have been measured in
molecular beam scattering experiments. These measurements are found to be in
good agreement with the cross sections predicted from density functional
calculations of the radial density distributions with a 10-90 % surface
thickness of 5.7\AA. By using a simple model for the density profile of the
droplets a thickness of about 6-8\AA is extracted directly from the data.Comment: 27 pages, REVTeX, 5 postscript figure
Expansion of nanoplasmas and laser-driven nuclear fusion in single exploding clusters
The expansion of laser-irradiated clusters or nanodroplets depends strongly
on the amount of energy delivered to the electrons and can be controlled by
using appropriately shaped laser pulses. In this paper, a self-consistent
kinetic model is used to analyze the transition from quasineutral,
hydrodinamic-like expansion regimes to the Coulomb explosion (CE) regime when
increasing the ratio between the thermal energy of the electrons and the
electrostatic energy stored in the cluster. It is shown that a suitable
double-pump irradiation scheme can produce hybrid expansion regimes, wherein a
slow hydrodynamic expansion is followed by a fast CE, leading to ion overtaking
and producing multiple ion flows expanding with different velocities. This can
be exploited to obtain intracluster fusion reactions in both homonuclear
deuterium clusters and heteronuclear deuterium-tritium clusters, as also proved
by three-dimensional molecular-dynamics simulations.Comment: 9 pages, 3 figures, to appear in Plasma Physics and Controlled Fusio
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