549 research outputs found
Interdependence of ICD Rates in Paired Quantum Dots on Geometry
Using state of the art antisymmetrized multiconfiguration time dependent Hartree MCTDH electron dynamics calculations we study the interdependence of the intermolecular Coulombic decay ICD process on the geometric parameters of a doubly charged paired quantum dot PQD model system in the framework of the effective mass approximation EMA . We find that ICD displays a maximum rate for a certain geometry of the electron emitting quantum dot, which is simultaneously dependent on both the distance between the quantum dots as well as the photon absorbing quantum dot s geometry. The rate maximum is shown to be caused by the competing effects of polarization of electron density and Coulomb repulsion. The ICD rate maximized PQD geometry in GaAs QDs yields a decay time of 102.39 ps. It is given by two vertically aligned cylindrical QDs with radii of 14.42 nm separated by 86.62 nm. The photon absorbing QD then has a height of 46.59 nm and the electron emitting QD a height of 16.33 n
Relativistic Quark Spin Coupling Effects in the Nucleon Electromagnetic Form Factors
We investigate the effect of different forms of relativistic spin coupling of
constituent quarks in the nucleon electromagnetic form factors. The
four-dimensional integrations in the two-loop Feynman diagram are reduced to
the null-plane, such that the light-front wave function is introduced in the
computation of the form factors. The neutron charge form factor is very
sensitive to different choices of spin coupling schemes, once its magnetic
moment is fitted to the experimental value. The scalar coupling between two
quarks is preferred by the neutron data, when a reasonable fit of the proton
magnetic momentum is found.Comment: 13 pages, needs axodraw.ps and axodraw.sty for diagrams of Fig.
Relativistic Quark Spin Coupling Effects in the Correlations Between Nucleon Electroweak Properties
We investigate the effect of different relativistic spin couplings of
constituent quarks on nucleon electroweak properties. Within each quark spin
coupling scheme the correlations between static electroweak observables are
found to be independent of the particular shape of the momentum part of the
nucleon light-front wave function. The neutron charge form factor is very
sensitive to different choices of spin coupling schemes once the magnetic
moment is fitted to the experimental value. However, it is found rather
insensitive to the details of the momentum part of the three-quark wave
function model.Comment: 23 pages, 13 figures, requires axodraw.sty 1 figure corrected, 1
refs. added, some changes in tex
Independence of , Poincare Invariance and the Non-Conservation of Helicity
A relativistic constituent quark model is found to reproduce the recent data
regarding the ratio of proton form factors, . We show that
imposing Poincare invariance leads to substantial violation of the helicity
conservation rule, as well as an analytic result that the ratio
for intermediate values of .Comment: 13 pages, 7 figures, to be submitted to Phys. Rev. C typos corrected,
references added, 1 new figure to show very high Q^2 behavio
Mean-atom-trajectory model for the velocity autocorrelation function of monatomic liquids
We present a model for the motion of an average atom in a liquid or
supercooled liquid state and apply it to calculations of the velocity
autocorrelation function and diffusion coefficient . The model
trajectory consists of oscillations at a distribution of frequencies
characteristic of the normal modes of a single potential valley, interspersed
with position- and velocity-conserving transits to similar adjacent valleys.
The resulting predictions for and agree remarkably well with MD
simulations of Na at up to almost three times its melting temperature. Two
independent processes in the model relax velocity autocorrelations: (a)
dephasing due to the presence of many frequency components, which operates at
all temperatures but which produces no diffusion, and (b) the transit process,
which increases with increasing temperature and which produces diffusion.
Because the model provides a single-atom trajectory in real space and time,
including transits, it may be used to calculate all single-atom correlation
functions.Comment: LaTeX, 8 figs. This is an updated version of cond-mat/0002057 and
cond-mat/0002058 combined Minor changes made to coincide with published
versio
The effect of bacterial lipopolysaccharide on gastric emptying in rats suffering from moderate renal insufficiency
The non-random walk of stock prices: The long-term correlation between signs and sizes
We investigate the random walk of prices by developing a simple model
relating the properties of the signs and absolute values of individual price
changes to the diffusion rate (volatility) of prices at longer time scales. We
show that this benchmark model is unable to reproduce the diffusion properties
of real prices. Specifically, we find that for one hour intervals this model
consistently over-predicts the volatility of real price series by about 70%,
and that this effect becomes stronger as the length of the intervals increases.
By selectively shuffling some components of the data while preserving others we
are able to show that this discrepancy is caused by a subtle but long-range
non-contemporaneous correlation between the signs and sizes of individual
returns. We conjecture that this is related to the long-memory of transaction
signs and the need to enforce market efficiency.Comment: 9 pages, 5 figures, StatPhys2
Inactivated Parapoxvirus ovis induces a transient increase in the expression of proinflammatory, Th1-related, and autoregulatory cytokines in mice
Active Brownian Particles. From Individual to Collective Stochastic Dynamics
We review theoretical models of individual motility as well as collective
dynamics and pattern formation of active particles. We focus on simple models
of active dynamics with a particular emphasis on nonlinear and stochastic
dynamics of such self-propelled entities in the framework of statistical
mechanics. Examples of such active units in complex physico-chemical and
biological systems are chemically powered nano-rods, localized patterns in
reaction-diffusion system, motile cells or macroscopic animals. Based on the
description of individual motion of point-like active particles by stochastic
differential equations, we discuss different velocity-dependent friction
functions, the impact of various types of fluctuations and calculate
characteristic observables such as stationary velocity distributions or
diffusion coefficients. Finally, we consider not only the free and confined
individual active dynamics but also different types of interaction between
active particles. The resulting collective dynamical behavior of large
assemblies and aggregates of active units is discussed and an overview over
some recent results on spatiotemporal pattern formation in such systems is
given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte
Carbono do solo e atributos de fertilidade em resposta à calagem superficial em plantio direto
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