1,506 research outputs found
MTRAC - A computer program for analysis of circuits including magnetic cores. Volume 2 - Input data and program listing
Input data cards program listing for MTRA
Testing the labour theory of value: An exchange
Exchange on open letters on the methodologies for testing price value correlations
Dynamic treatment of vibrational energy relaxation in a heterogeneous and fluctuating environment
A computational approach to describe the energy relaxation of a
high-frequency vibrational mode in a fluctuating heterogeneous environment is
outlined. Extending previous work [H. Fujisaki, Y. Zhang, and J.E. Straub, J.
Chem. Phys. {\bf 124}, 144910 (2006)], second-order time-dependent perturbation
theory is employed which includes the fluctuations of the parameters in the
Hamiltonian within the vibrational adiabatic approximation. This means that the
time-dependent vibrational frequencies along an MD trajectory are obtained via
a partial geometry optimization of the solute with fixed solvent and a
subsequent normal mode calculation. Adopting the amide I mode of
N-methylacetamide in heavy water as a test problem, it is shown that the
inclusion of dynamic fluctuations may significantly change the vibrational
energy relaxation. In particular, it is found that relaxation occurs in two
phases, because for short times ( 200 fs) the spectral density
appears continuous due to the frequency-time uncertainty relation, while at
longer times the discrete nature of the bath becomes apparent. Considering the
excellent agreement between theory and experiment, it is speculated if this
behavior can explain the experimentally obtained biphasic relaxation the amide
I mode of N-methylacetamide.Comment: 24 pages, 7 figures, submitted to J. Chem. Phy
MTRAC - A computer program for analysis of circuits including magnetic cores. Volume 1 - Computation, program, and application Final report
Method of computation, organization, and applications of Modified transient analysis by compute
Coherent charge transport through molecular wires: influence of strong Coulomb repulsion
We derive a master equation for the electron transport through molecular
wires in the limit of strong Coulomb repulsion. This approach is applied to two
typical situations: First, we study transport through an open conduction
channel for which we find that the current exhibits an ohmic-like behaviour.
Second, we explore the transport properties of a bridged molecular wire, where
the current decays exponentially as a function of the wire length. For both
situations, we discuss the differences to the case of non-interacting
electrons.Comment: 15 pages, 4 figures, elsart style, accepted at Chem Phy
Vibrational inelastic scattering effects in molecular electronics
We describe how to treat the interaction of travelling electrons with
localised vibrational modes in nanojunctions. We present a multichannel
scattering technique which can be applied to calculate the transport properties
for realistic systems, and show how it is related to other methods that are
useful in particular cases. We apply our technique to describe recent
experiments on the conductance through molecular junctions.Comment: LaTeX, 12 pages, 3 figure
Molecular Wires Acting as Coherent Quantum Ratchets
The effect of laser fields on the electron transport through a molecular wire
being weakly coupled to two leads is investigated. The molecular wire acts as a
coherent quantum ratchet if the molecule is composed of periodically arranged,
asymmetric chemical groups. This setup presents a quantum rectifier with a
finite dc-response in the absence of a static bias. The nonlinear current is
evaluated in closed form within the Floquet basis of the isolated, driven wire.
The current response reveals multiple current reversals together with a
nonlinear dependence (reflecting avoided quasi-energy crossings) on both, the
amplitude and the frequency of the laser field. The current saturates for long
wires at a nonzero value, while it may change sign upon decreasing its length.Comment: 4 pages, 4 figures, RevTeX
Theory and simulations of squeeze-out dynamics in boundary lubrication
The dynamics of expulsion of the last liquidlike monolayer of molecules confined between two surfaces (measured recently for the first time [J. Chem. Phys. 114, 1831 (2001)]) has been analyzed by solving the two-dimensional Navier-Stokes equation combined with kinetic Monte Carlo simulations. Instabilities in the boundary line of the expelled film produce a rough boundary for all length scales above a critical value. The squeeze-out of liquid is shown to result from the 2D-pressure gradient in the lubrication film in the contact area. The Monte Carlo simulations agrees well with experiments, reproducing most qualitative and quantitative features. In particular it shows the formation of small islands, which (in the absence of pinning mechanism) drift slowly to the periphery of the contact area. We calculate the drift velocity analytically as a function of the distance of the island to the periphery of the contact area. Experiments indicate that some kind of pinning mechanism prevails, trapping fluid pockets for very long times. When including such pinning areas in the simulations, three distinct squeeze phases and time scales were observed: (1) initial fast squeeze of most of the fluid; (2) slower squeeze of unpinned fluid pockets; (3) long term pinning of fluid pockets. We also show that a distribution of small pinning areas may produce a synergistic effect, slowing down the second phase of the squeeze, compared to a small number of big pinning areas. The paper presents a new stochastic numerical approach to problems of moving boundaries which naturally accounts for thermal fluctuations and their effect in unstable dynamics. (C) 2001 American Institute of Physics
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