182 research outputs found
Diffusion and solubility of oxygen in silver
The diffusion and solubility of oxygen in Ag in the temperature range between 412 and 862 C was determined. The following interpolation formula was found for the solubility: L = 8.19.1/100.exp(-11 860/RT)Mol O2/g.At.Ag.at 1/.5. The process obeys the Sieverts square root law within the limits of error. The dissolution of oxygen in Ag may be accompanied by the dissociation of the oxygen molecules into atoms. The tests on Ag-foils reveal that below a temperature of about 500 C a higher solubility is simulated by the adsorption of oxygen. The diffusion coefficient of oxygen in silver obeys the following equation: D = 2.72.1/100.exp(-11 000/RT)sq cm/s. The relatively low activation energy of 11 kcal/g.At suggests that the diffusion of oxygen takes places over interstitial sites
A quasi classical approach to fully differential ionization cross sections
A classical approximation to time dependent quantum mechanical scattering in
the M\o{}ller formalism is presented. Numerically, our approach is similar to a
standard Classical-Trajectory-Monte-Carlo calculation. Conceptually, however,
our formulation allows one to release the restriction to stationary initial
distributions. This is achieved by a classical forward-backward propagation
technique. As a first application and for comparison with experiment we present
fully differential cross sections for electron impact ionization of atomic
hydrogen in the Erhardt geometry.Comment: 6 pages, 2 figure
Hurst's Rescaled Range Statistical Analysis for Pseudorandom Number Generators used in Physical Simulations
The rescaled range statistical analysis (R/S) is proposed as a new method to
detect correlations in pseudorandom number generators used in Monte Carlo
simulations. In an extensive test it is demonstrated that the RS analysis
provides a very sensitive method to reveal hidden long run and short run
correlations. Several widely used and also some recently proposed pseudorandom
number generators are subjected to this test. In many generators correlations
are detected and quantified.Comment: 12 pages, 12 figures, 6 tables. Replaces previous version to correct
citation [19
A semi-classical over-barrier model for charge exchange between highly charged ions and one-optical electron atoms
Absolute total cross sections for electron capture between slow, highly
charged ions and alkali targets have been recently measured. It is found that
these cross sections follow a scaling law with the projectile charge which is
different from the one previously proposed basing on a classical over-barrier
model (OBM) and verified using rare gases and molecules as targets. In this
paper we develop a "semi-classical" (i.e. including some quantal features) OBM
attempting to recover experimental results. The method is then applied to
ion-hydrogen collisions and compared with the result of a sophisticated
quantum-mechanical calculation. In the former case the accordance is very good,
while in the latter one no so satisfactory results are found. A qualitative
explanation for the discrepancies is attempted.Comment: RevTeX, uses epsf; 6 pages text + 3 EPS figures Journal of Physics B
(scehduled March 2000). This revision corrects fig.
Quasiclassical double photoionization from the 2^{1,3}S excited states of helium including shakeoff
We account for the different symmetries of the 2^{1,3}S helium excited states
in a quasiclassical description of the knockout mechanism augmented by a
quantum shakeoff contribution. We are thus able to formulate the separate
contribution of the knockout and shakeoff mechanisms for double photoionization
for any excess energy from the 2^{1,3}S states. Photoionization ratios and
singly differential cross sections calculated for the 2^{1,3}S excited states
of helium are found to be in very good agreement with recent theoretical
results.Comment: 9 pages, 5 figure
Ion Collisions in Very Strong Electric Fields
A Classical Trajectory Monte Carlo (CTMC) simulation has been made of
processes of charge exchange and ionization between an hydrogen atom and fully
stripped ions embedded in very strong static electric fields (
V/m), which are thought to exist in cosmic and laser--produced plasmas.
Calculations show that the presence of the field affects absolute values of the
cross sections, enhancing ionization and reducing charge exchange. Moreover,
the overall effect depends upon the relative orientation between the field and
the nuclear motion. Other features of a null-field situation, such as scaling
laws, are revisited.Comment: Latex, 13 pages, 11 figures (available upon request), to be published
in Journal of Physics
A quasi classical approach to electron impact ionization
A quasi classical approximation to quantum mechanical scattering in the
Moeller formalism is developed. While keeping the numerical advantage of a
standard Classical--Trajectory--Monte--Carlo calculation, our approach is no
longer restricted to use stationary initial distributions. This allows one to
improve the results by using better suited initial phase space distributions
than the microcanonical one and to gain insight into the collision mechanism by
studying the influence of different initial distributions on the cross section.
A comprehensive account of results for single, double and triple differential
cross sections for atomic hydrogen will be given, in comparison with experiment
and other theories.Comment: 21 pages, 10 figures, submitted to J Phys
Electron impact double ionization of helium from classical trajectory calculations
With a recently proposed quasiclassical ansatz [Geyer and Rost, J. Phys. B 35
(2002) 1479] it is possible to perform classical trajectory ionization
calculations on many electron targets. The autoionization of the target is
prevented by a M\o{}ller type backward--forward propagation scheme and allows
to consider all interactions between all particles without additional
stabilization. The application of the quasiclassical ansatz for helium targets
is explained and total and partially differential cross sections for electron
impact double ionization are calculated. In the high energy regime the
classical description fails to describe the dominant TS1 process, which leads
to big deviations, whereas for low energies the total cross section is
reproduced well. Differential cross sections calculated at 250 eV await their
experimental confirmation.Comment: LaTeX, 22 pages, 10 figures, submitted to J. Phys.
Fractional jumps: complete characterisation and an explicit infinite family
In this paper we provide a complete characterisation of transitive fractional
jumps by showing that they can only arise from transitive projective
automorphisms. Furthermore, we prove that such construction is feasible for
arbitrarily large dimension by exhibiting an infinite class of projectively
primitive polynomials whose companion matrix can be used to define a full orbit
sequence over an affine space
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