497 research outputs found
Ionization of Rydberg atoms in a low frequency field: modelling by maps of transition to chaotic behavior
We investigate a microwave ionization of highly excited atom in a low
frequency field and show that such a process may be studied on the bases of map
for the electron energy change during the period of the electron motion between
two subsequent passages at aphelion. Simple approximate criterion results to
the threshold field for transition to chaotic behavior very close to the
numerical results. We show that transition from adiabatic to chaotic ionization
mechanism takes place when the field frequency to the electron's Kepler
frequency ration approximately equals 0.1.Comment: 5 pages, LaTEX, 37Kb, 2 figures (compressed and uuencoded PostScript)
included in text. To be published in Chaos: The interplay between
stochastics, classics and quanta, Ed. by P. Garbaczewski, et al. Lecture
notes in Physics, 1995
Kinks in the Presence of Rapidly Varying Perturbations
Dynamics of sine-Gordon kinks in the presence of rapidly varying periodic
perturbations of different physical origins is described analytically and
numerically. The analytical approach is based on asymptotic expansions, and it
allows to derive, in a rigorous way, an effective nonlinear equation for the
slowly varying field component in any order of the asymptotic procedure as
expansions in the small parameter , being the frequency
of the rapidly varying ac driving force. Three physically important examples of
such a dynamics, {\em i.e.}, kinks driven by a direct or parametric ac force,
and kinks on rotating and oscillating background, are analysed in detail. It is
shown that in the main order of the asymptotic procedure the effective equation
for the slowly varying field component is {\em a renormalized sine-Gordon
equation} in the case of the direct driving force or rotating (but phase-locked
to an external ac force) background, and it is {\em the double sine-Gordon
equation} for the parametric driving force. The properties of the kinks
described by the renormalized nonlinear equations are analysed, and it is
demonstrated analytically and numerically which kinds of physical phenomena may
be expected in dealing with the renormalized, rather than the unrenormalized,
nonlinear dynamics. In particular, we predict several qualitatively new effects
which include, {\em e.g.}, the perturbation-inducedComment: New copy of the paper of the above title to replace the previous one,
lost in the midst of the bulletin board. RevTeX 3.
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Recovery and use of fission product noble metals
Noble metals in fission products are of strategic value. Market prices for noble metals are rising more rapidly than recovery costs. A promising concept has been developed for recovery of noble metals from fission product waste. Although the assessment was made only for the three noble metal fission products (Rh, Pd, Ru), there are other fission products and actinides which have potential value. (DLC
Three-Body Halos. II. from Two- to Three-Body Asymptotics
The large distance behavior of weakly bound three-body systems is
investigated. The Schr\"{o}dinger equation and the Faddeev equations are
reformulated by an expansion in eigenfunctions of the angular part of a
corresponding operator. The resulting coupled set of effective radial equations
are then derived. Both two- and three-body asymptotic behavior are possible and
their relative importance is studied for systems where subsystems may be bound.
The system of two nucleons outside a core is studied numerically in detail and
the character of possible halo structure is pointed out and investigated.Comment: 16 pages, compressed and uuencoded PosrScript file, IFA-94/3
From Greenland to Canada in Ten Days: Tracks of Bowhead Whales, Balaena mysticetus, across Baffin Bay
Five bowhead whales (Balaena mysticetus) were instrumented with satellite transmitters in northwestern Disko Bay, West Greenland, in May 2001. Best results were obtained when tags were deployed with a pole rather than a pneumatic gun. At least three of the tagged whales remained in the northwestern part of the bay for one to two weeks after tagging. A male and a female whale moved from Disko Bay to northern Canada. They left Disko Bay 11 days apart and took different routes across Baffin Bay to the southern part of the North Water polynya, just east of the entrance to Lancaster Sound. The whales crossed the central part of Baffin Bay relatively rapidly (travel time of 9-10 days, 3.1 and 4.5 km/h). Dive behaviour of one whale was monitored and showed changes in dive depths, dive rates, and surfacing times in different localities, indicating behavioural changes probably related to feeding. The whales were presumably feeding in both Disko Bay in May and in the southern part of the North Water (southeast of Bylot Island) in June. This study confirms whalers' observations that bowhead whales move between West Greenland and the east coast of Baffin Island.En mai 2001, cinq baleines boréales (Balaena mysticetus) ont été équipées d'émetteurs spatiaux dans le nord-ouest de la baie de Disko (Groenland occidental). Les meilleurs résultats ont été obtenus lorsque les marqueurs ont été apposés avec une perche plutôt qu'avec un fusil à air comprimé. Au moins trois des baleines marquées sont restées dans la partie nord-ouest de la baie pendant une à deux semaines après le marquage. Deux individus, un mâle et une femelle, se sont déplacés de la baie de Disko au nord du Canada. Ils ont quitté la baie à 11 jours d'écart et ont emprunté des trajets différents pour traverser la baie de Baffin et rejoindre la partie méridionale de la polynie de l'Eau du Nord, située juste à l'est de l'entrée du détroit de Lancaster. Les baleines ont traversé la partie centrale de la baie de Baffin assez vite (en 9 et 10 jours, soit 3,1 et 4,5 km/h). On a suivi le comportement de plongée d'une baleine, qui a montré des changements dans la profondeur des plongées, leur fréquence et le temps en surface à divers endroits, révélant des modifications du comportement probablement associées au nourrissage. On suppose que les baleines s'alimentaient dans la baie de Disko en mai aussi bien que dans la partie méridionale de l'Eau du Nord (au sud-est de l'île Bylot) en juin. Cette étude confirme les observations des baleiniers à l'effet que les baleines boréales se déplacent entre l'ouest du Groenland et la côte est de l'île de Baffin
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Separation of catalyst from Fischer-Tropsch slurry
This paper describes a process for the separation of catalysts used in Fischer-Tropsch synthesis. The separation is accomplished by extraction in which the organic compounds in the wax are dissolved and carried away from the insoluble inorganic catalyst particles that are primarily inorganic. The purified catalyst can be upgraded by various methods
Long-Range Correlations in Closed Shell Nuclei
The effects of correlations on the bulk properties of nuclei are investigated
in large model spaces including up to 21 single-particle orbits. The evaluation
of the single-particle Green function is made feasible by means of the BAGEL
approximation. The spectral function for single-nucleon pick-up and removal is
investigated for the nuclei and . Special attention is paid
to the effects produced by correlations on the calculated ground state
properties of closed shell nuclei. It is observed that correlations beyond the
Brueckner Hartree Fock approximation tend to improve the results obtained using
realistic nucleon nucleon interactions.Comment: 23 pages 4 figures not included, Report Tu-93-081
Critical Currents and Vortex States at Fractional Matching Fields in Superconductors with Periodic Pinning
We study vortex states and dynamics in 2D superconductors with periodic
pinning at fractional sub-matching fields using numerical simulations. For
square pinning arrays we show that ordered states form at 1/1, 1/2, and 1/4
filling fractions while only partially ordered states form at other filling
fractions, such as 1/3 and 1/5, in agreement with recent imaging experiments.
For triangular pinning arrays we observe matching effects at filling fractions
of 1/1, 6/7, 2/3, 1/3, 1/4, 1/6, and 1/7. For both square and triangular
pinning arrays we also find that, for certian sub-matching fillings, vortex
configurations depend on pinning strength. For weak pinning, ordering in which
a portion of the vortices are positioned between pinning sites can occur.
Depinning of the vortices at the matching fields, where the vortices are
ordered, is elastic while at the incommensurate fields the motion is plastic.
At the incommensurate fields, as the applied driving force is increased, there
can be a transition to elastic flow where the vortices move along the pinning
sites in 1D channels and a reordering transition to a triangular or distorted
triangular lattice. We also discuss the current-voltage curves and how they
relate to the vortex ordering at commensurate and incommensurate fields.Comment: 14 figure
Correlated N-boson systems for arbitrary scattering length
We investigate systems of identical bosons with the focus on two-body
correlations and attractive finite-range potentials. We use a hyperspherical
adiabatic method and apply a Faddeev type of decomposition of the wave
function. We discuss the structure of a condensate as function of particle
number and scattering length. We establish universal scaling relations for the
critical effective radial potentials for distances where the average distance
between particle pairs is larger than the interaction range. The correlations
in the wave function restore the large distance mean-field behaviour with the
correct two-body interaction. We discuss various processes limiting the
stability of condensates. With correlations we confirm that macroscopic
tunneling dominates when the trap length is about half of the particle number
times the scattering length.Comment: 15 pages (RevTeX4), 11 figures (LaTeX), submitted to Phys. Rev. A.
Second version includes an explicit comparison to N=3, a restructured
manuscript, and updated figure
Large-space shell-model calculations for light nuclei
An effective two-body interaction is constructed from a new Reid-like
potential for a large no-core space consisting of six major shells and is used
to generate the shell-model properties for light nuclei from =2 to 6. (For
practical reasons, the model space is partially truncated for =6.) Binding
energies and other physical observables are calculated and compare favorably
with experiment.Comment: prepared using LaTex, 21 manuscript pages, no figure
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