15 research outputs found
Nonresonant effects in one- and two-photon transitions
We investigate nonresonant contributions to resonant Rayleigh scattering
cross sections of atoms. The problematic nonresonant contributions set a limit
to the accuracy to which atomic spectra determine energy levels. We discuss the
off-resonance effects in one-photon transitions. We also show that
off-resonance contributions for the 1S-2S two-photon transition in atomic
hydrogen are negligible at current and projected levels of experimental
accuracy. The possibility of a differential measurement for the detection of
off-resonance effects in one-photon transitions in atomic hydrogen is
discussed.Comment: 13 pages, LaTeX, 3 figures; submitted to Can. J. Phys. (Oct 2001);
discussion of one-photon transitions enhance
Analytical and numerical investigation of escape rate for a noise driven bath
We consider a system-reservoir model where the reservoir is modulated by an
external noise. Both the internal noise of the reservoir and the external noise
are stationary, Gaussian and are characterized by arbitrary decaying
correlation functions. Based on a relation between the dissipation of the
system and the response function of the reservoir driven by external noise we
numerically examine the model using a full bistable potential to show that one
can recover the turn-over features of the usual Kramers' dynamics when the
external noise modulates the reservoir rather than the system directly. We
derive the generalized Kramers' rate for this nonequilibrium open system. The
theoretical results are verified by numerical simulation.Comment: Revtex, 25 pages, 5 figures. To appear in Phys. Rev.
Self-consistent Green's function method for nuclei and nuclear matter
Recent results obtained by applying the method of self-consistent Green's
functions to nuclei and nuclear matter are reviewed. Particular attention is
given to the description of experimental data obtained from the (e,e'p) and
(e,e'2N) reactions that determine one and two-nucleon removal probabilities in
nuclei since the corresponding amplitudes are directly related to the imaginary
parts of the single-particle and two-particle propagators. For this reason and
the fact that these amplitudes can now be calculated with the inclusion of all
the relevant physical processes, it is useful to explore the efficacy of the
method of self-consistent Green's functions in describing these experimental
data. Results for both finite nuclei and nuclear matter are discussed with
particular emphasis on clarifying the role of short-range correlations in
determining various experimental quantities. The important role of long-range
correlations in determining the structure of low-energy correlations is also
documented. For a complete understanding of nuclear phenomena it is therefore
essential to include both types of physical correlations. We demonstrate that
recent experimental results for these reactions combined with the reported
theoretical calculations yield a very clear understanding of the properties of
{\em all} protons in the nucleus. We propose that this knowledge of the
properties of constituent fermions in a correlated many-body system is a unique
feature of nuclear physics.Comment: 110 pages, accepted for publication on Prog. Part. Nucl. Phy
Trace metal distribution in sediments of the Pearl River Estuary and the surrounding coastal area, South China
Information dynamics of a particle in a magnetic field
We discuss the time evolution of information entropy (S) of a harmonic oscillator driven by thermal noise in the presence of a magnetic field. Our analysis is based on the Fokker-Planck description of the stochastic process. It shows that the relaxation time of a given non equilibrium state increases with increase of strength of the applied magnetic field. It further increases if the thermal noise becomes colored.
The dependence of the time derivative of the entropy, its upper bound and related quantity on the strength of magnetic field, damping, noise correlation time and temperature is studied in detail