2,147 research outputs found
Self-consistent Approach to Off-Shell Transport
The properties of two forms of the gradient expanded Kadanoff--Baym
equations, i.e. the Kadanoff--Baym and Botermans-Malfliet forms, suitable to
describe the transport dynamics of particles and resonances with broad spectral
widths, are discussed in context of conservation laws, the definition of a
kinetic entropy and the possibility of numerical realization. Recent results on
exact conservations of charge and energy-momentum within Kadanoff-Baym form of
quantum kinetics based on local coupling schemes are extended to two cases
relevant in many applications. These concern the interaction via a finite range
potential, and, relevant in nuclear and hadron physics, e.g. for the
pion--nucleon interaction, the case of derivative coupling.Comment: 35 pages, submitted to issue of Phys. Atom. Nucl. dedicated to S.T.
Belyaev on the occasion of his 80th birthday. Few references are adde
Random inelasticity and velocity fluctuations in a driven granular gas
We analyze the deviations from Maxwell-Boltzmann statistics found in recent
experiments studying velocity distributions in two-dimensional granular gases
driven into a non-equilibrium stationary state by a strong vertical vibration.
We show that in its simplest version, the ``stochastic thermostat'' model of
heated inelastic hard spheres, contrary to what has been hitherto stated, is
incompatible with the experimental data, although predicting a reminiscent high
velocity stretched exponential behavior with an exponent 3/2. The experimental
observations lead to refine a recently proposed random restitution coefficient
model. Very good agreement is then found with experimental velocity
distributions within this framework, which appears self-consistent and further
provides relevant probes to investigate the universality of the velocity
statistics.Comment: 5 pages, 5 eps figure
Electron-Ion Recombination Rate Coefficients and Photoionization Cross Sections for Astrophysically Abundant Elements. VII. Relativistic calculations for O VI and O VII for UV and X-ray modeling
Aimed at ionization balance and spectral analysis of UV and X-ray sources, we
present self-consistent sets of photoionization cross sections, recombination
cross sections, and rate coefficients for Li-like O VI and He-like O VII.
Relativistic fine structure is considered through the Breit-Pauli R-matrix
(BPRM) method in the close coupling approximation, implementing the unified
treatment for total electron-ion recombination subsuming both radiative and
di-electronic recombination processes. Self-consistency is ensured by using an
identical wavefunction expansion for the inverse processes of photoionization
and photo-recombination. Radiation damping of resonances, important for H-like
and He-like core ions, is included. Compared to previous LS coupling results
without radiative decay of low-n (<= 10) resonances, the presents results show
significant reduction in O VI recombination rates at high temperatures. In
addition to the total rates, level-specific photoionization cross sections and
recombination rates are presented for all fine structure levels n (lSLJ) up to
n <= 10, to enable accurate computation of recombination-cascade matrices and
spectral formation of prominent UV and X-ray lines such as the 1032,1038 A
doublet of O VI, and the `triplet' forbidden, intercombination, and resonance
X-ray lines of O VII at 22.1, 21.8, and 21.6 \ang respectively. Altogether,
atomic parameters for 98 levels of O VI and 116 fine structure levels of O VII
are theoretically computed. These data should provide a reasonably complete set
of photoionization and recombination rates in collisional or radiative
equilibrium.Comment: 33 pages, 8 figures, submitted to ApJ
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