42,775 research outputs found
A Review on Ab Initio Approaches for Multielectron Dynamics
In parallel with the evolution of femtosecond and attosecond laser as well as
free-electron laser technology, a variety of theoretical methods have been
developed to describe the behavior of atoms, molecules, clusters, and solids
under the action of those laser pulses. Here we review major ab initio
wave-function-based numerical approaches to simulate multielectron dynamics in
atoms and molecules driven by intense long-wavelength and/or ultrashort
short-wavelength laser pulses. Direct solution of the time-dependent
Schr\"odinger equation (TDSE), though its applicability is limited to He, , and Li, can provide an exact description and has been greatly
contributing to the understanding of dynamical electron-electron correlation.
Multiconfiguration self-consistent-field (MCSCF) approach offers a flexible
framework from which a variety of methods can be derived to treat both atoms
and molecules, with possibility to systematically control the accuracy. The
equations of motion of configuration interaction coefficients and molecular
orbitals for general MCSCF ansatz have recently been derived. Time-dependent
extension of the -matrix theory, originally develop for electron-atom
collision, can realistically and accurately describe laser-driven complex
multielectron atoms.Comment: 17 pages, 9 figure
Step Bunching with Alternation of Structural Parameters
By taking account of the alternation of structural parameters, we study
bunching of impermeable steps induced by drift of adatoms on a vicinal face of
Si(001). With the alternation of diffusion coefficient, the step bunching
occurs irrespective of the direction of the drift if the step distance is
large. Like the bunching of permeable steps, the type of large terraces is
determined by the drift direction. With step-down drift, step bunches grows
faster than those with step-up drift. The ratio of the growth rates is larger
than the ratio of the diffusion coefficients. Evaporation of adatoms, which
does not cause the step bunching, decreases the difference. If only the
alternation of kinetic coefficient is taken into account, the step bunching
occurs with step-down drift. In an early stage, the initial fluctuation of the
step distance determines the type of large terraces, but in a late stage, the
type of large terraces is opposite to the case of alternating diffusion
coefficient.Comment: 8pages, 16 figure
The Multicomponent KP Hierarchy: Differential Fay Identities and Lax Equations
In this article, we show that four sets of differential Fay identities of an
-component KP hierarchy derived from the bilinear relation satisfied by the
tau function of the hierarchy are sufficient to derive the auxiliary linear
equations for the wave functions. From this, we derive the Lax representation
for the -component KP hierarchy, which are equations satisfied by some
pseudodifferential operators with matrix coefficients. Besides the Lax
equations with respect to the time variables proposed in \cite{2}, we also
obtain a set of equations relating different charge sectors, which can be
considered as a generalization of the modified KP hierarchy proposed in
\cite{3}.Comment: 19 page
Cosmic Sculpture: A new way to visualise the Cosmic Microwave Background
3D printing presents an attractive alternative to visual representation of
physical datasets such as astronomical images that can be used for research,
outreach or teaching purposes, and is especially relevant to people with a
visual disability. We here report the use of 3D printing technology to produce
a representation of the all-sky Cosmic Microwave Background (CMB) intensity
anisotropy maps produced by the Planck mission. The success of this work in
representing key features of the CMB is discussed as is the potential of this
approach for representing other astrophysical data sets. 3D printing such
datasets represents a highly complementary approach to the usual 2D projections
used in teaching and outreach work, and can also form the basis of
undergraduate projects. The CAD files used to produce the models discussed in
this paper are made available.Comment: Accepted for publication in the European Journal of Physic
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