734 research outputs found
A simple parameter-free one-center model potential for an effective one-electron description of molecular hydrogen
For the description of an H2 molecule an effective one-electron model
potential is proposed which is fully determined by the exact ionization
potential of the H2 molecule. In order to test the model potential and examine
its properties it is employed to determine excitation energies, transition
moments, and oscillator strengths in a range of the internuclear distances, 0.8
< R < 2.5 a.u. In addition, it is used as a description of an H2 target in
calculations of the cross sections for photoionization and for partial
excitation in collisions with singly-charged ions. The comparison of the
results obtained with the model potential with literature data for H2 molecules
yields a good agreement and encourages therefore an extended usage of the
potential in various other applications or in order to consider the importance
of two-electron and anisotropy effects.Comment: 8 pages, 6 figure
Symmetry of the Atomic Electron Density in Hartree, Hartree-Fock, and Density Functional Theory
The density of an atom in a state of well-defined angular momentum has a
specific finite spherical harmonic content, without and with interactions.
Approximate single-particle schemes, such as the Hartree, Hartree-Fock, and
Local Density Approximations, generally violate this feature. We analyze, by
means of perturbation theory, the degree of this violation and show that it is
small. The correct symmetry of the density can be assured by a
constrained-search formulation without significantly altering the calculated
energies. We compare our procedure to the (different) common practice of
spherically averaging the self-consistent potential. Kohn-Sham density
functional theory with the exact exchange-correlation potential has the correct
finite spherical harmonic content in its density; but the corresponding exact
single particle potential and wavefunctions contain an infinite number of
spherical harmonics.Comment: 11 pages, 6 figures. Expanded discussion of spherical harmonic
expansion of Hartree density. Some typos corrected, references adde
Angular versus radial correlation effects on momentum distributions of light two-electron ions
We investigate different correlation mechanisms for two-electron systems and
compare their respective effects on various electron distributions. The
simplicity of the wave functions used allows for the derivation of closed-form
analytical expressions for all electron distributions. Among other features, it
is shown that angular and radial correlation mechanisms have opposite effects
on Compton profiles at small momenta.Comment: 22 pages, 5 figures, 3 tabl
Quantum calculations of Coulomb reorientation for sub-barrier fusion
Classical mechanics and Time Dependent Hartree-Fock (TDHF) calculations of
heavy ions collisions are performed to study the rotation of a deformed nucleus
in the Coulomb field of its partner. This reorientation is shown to be
independent on charges and relative energy of the partners. It only depends
upon the deformations and inertias. TDHF calculations predict an increase by
30% of the induced rotation due to quantum effects while the nuclear
contribution seems negligible. This reorientation modifies strongly the fusion
cross-section around the barrier for light deformed nuclei on heavy collision
partners. For such nuclei a hindrance of the sub-barrier fusion is predicted.Comment: accepted for publication in Physical Review Lette
Studies on ram acrosin. Activation of proacrosin accompanying the isolation of acrosin from spermatozoa, and purification of the enzyme by affinity chromatography
A Multi-Configuration Mixing Approach with Symmetry-Projected Complex Hartree-Fock-Bogoliubov Determinants
A multi-configuration mixing approach built on essentially complex,
symmetry-projected Hartree-Fock-Bogoliubov (HFB) mean fields is introduced. The
mean fields are obtained by variation after projection. The configuration space
consists out of the symmetry-projected HFB vacuum and the symmetry-projected
two-quasiparticle excitations for even, and the symmetry-projected
one-quasiparticle excitations for odd A systems. The underlying complex HFB
transformations are assumed to be time-reversal invariant and axially
symmetric. The model allows nuclear structure calculations in large model
spaces with arbitrary two-body interactions. The approach has been applied to
Ne and Ne. Good agreement with the exact shell model results and
considerable improvement with respect to older calculations, in which only real
HFB transformations were admitted, is obtained.Comment: 30 pages LaTeX file, 4 Postscript figure
Berry phases for the nonlocal Gross-Pitaevskii equation with a quadratic potential
A countable set of asymptotic space -- localized solutions is constructed by
the complex germ method in the adiabatic approximation for the nonstationary
Gross -- Pitaevskii equation with nonlocal nonlinearity and a quadratic
potential. The asymptotic parameter is 1/T, where is the adiabatic
evolution time.
A generalization of the Berry phase of the linear Schr\"odinger equation is
formulated for the Gross-Pitaevskii equation. For the solutions constructed,
the Berry phases are found in explicit form.Comment: 13 pages, no figure
A new purple sulfur bacterium from saline littoral sediments, Thiorhodotvibrio winogradskyi gen. nov. and sp. nov.
Two strains of a new purple sulfur bacterium were isolated in pure culture from the littoral sediment of a saline lake (Mahoney Lake, Canada) and a marine microbial mat from the North Sea island of Mellum, respectively. Single cells were vibrioid-to spirilloid-shaped and motile by means of single polar flagella. Intracellular photosynthetic membranes were of the vesicular type. As photosynthetic pigments, bacteriochlorophyll a and the carotenoids lycopene, rhodopin, anhydrorhodovibrin, rhodovibrin and spirilloxanthin were present.
Hydrogen sulfide and elemental sulfur were used under anoxic conditions for phototrophic growth. In addition one strain (06511) used thiosulfate. Carbon dioxide, acetate and pyruvate were utilized by both strains as carbon sources. Depending on the strain propionate, succinate, fumarate, malate, tartrate, malonate, glycerol or peptone may additionally serve as carbon sources in the light. Optimum growth rates were obtained at pH 7.2, 33 °C, 50 mol m-2 s-1 intensity of daylight fluorescent tubes and a salinity of 2.2–3.2% NaCl. During growth on sulfide, up to ten small sulfur globules were formed inside the cells. The strains grew microaerophilic in the dark and exhibited high specific respiration rates. No vitamins were required for growth. The DNA base composition was 61.0–62.4 mol% G+C.
The newly isolated bacterium belongs to the family chromatiaceae and is described as a member of a new genus and species, Thiorhodovibrio winogradskyi gen. nov. and sp. nov. with the type strain SSP1, DSM No. 6702
Quantum versus classical statistical dynamics of an ultracold Bose gas
We investigate the conditions under which quantum fluctuations are relevant
for the quantitative interpretation of experiments with ultracold Bose gases.
This requires to go beyond the description in terms of the Gross-Pitaevskii and
Hartree-Fock-Bogoliubov mean-field theories, which can be obtained as classical
(statistical) field-theory approximations of the quantum many-body problem. We
employ functional-integral techniques based on the two-particle irreducible
(2PI) effective action. The role of quantum fluctuations is studied within the
nonperturbative 2PI 1/N expansion to next-to-leading order. At this accuracy
level memory-integrals enter the dynamic equations, which differ for quantum
and classical statistical descriptions. This can be used to obtain a
'classicality' condition for the many-body dynamics. We exemplify this
condition by studying the nonequilibrium evolution of a 1D Bose gas of sodium
atoms, and discuss some distinctive properties of quantum versus classical
statistical dynamics.Comment: 19 pages, 10 figure
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