2,602 research outputs found
Occupation numbers in Self Consistent RPA
A method is proposed which allows to calculate within the SCRPA theory the
occupation numbers via the single particle Green function. This scheme complies
with the Hugenholtz van Hove theorem. In an application to the Lipkin model it
is found that this prescription gives consistently better results than two
other commonly used approximations: lowest order boson expansion and the number
operator method.Comment: 25 pages, 10 figures, submitted to Nucl. Phys.
Control system maintains selected liquid level
Single-sensor control system maintains liquid hydrogen at a preselected desired level within a tank, regardless of boiloff. It calibrates output in percentage. Thus, when the fuel is at the desired level, the system output will indicate 100 percent regardless of what percent of tank capacity the fuel has reached
The Linear Sigma-Model in the 1/N-Expansion via Dynamical Boson Mappings and Applications to -Scattering
We present a non-perturbative method for the study of the O(N+1)-version of
the linear sigma-model. Using boson-mapping techniques, in close analogy to
those well-known for fermionic systems, we obtain a systematic 1/N-expansion
for the Hamiltonian which is symmetry-conserving order by order. The leading
order for the Hamiltonian is evaluated explicitly and we apply the method to
-scattering, in deriving the T-matrix to leading order.Comment: 28 pages, Latex, (with minor corrections to some misprints in the
appendix of the old version
Two-particle spatial correlations in superfluid nuclei
We discuss the effect of pairing on two-neutron space correlations in
deformed nuclei. The spatial correlations are described by the pairing tensor
in coordinate space calculated in the HFB approach. The calculations are done
using the D1S Gogny force. We show that the pairing tensor has a rather small
extension in the relative coordinate, a feature observed earlier in spherical
nuclei. It is pointed out that in deformed nuclei the coherence length
corresponding to the pairing tensor has a pattern similar to what we have found
previously in spherical nuclei, i.e., it is maximal in the interior of the
nucleus and then it is decreasing rather fast in the surface region where it
reaches a minimal value of about 2 fm. This minimal value of the coherence
length in the surface is essentially determined by the finite size properties
of single-particle states in the vicinity of the chemical potential and has
little to do with enhanced pairing correlations in the nuclear surface. It is
shown that in nuclei the coherence length is not a good indicator of the
intensity of pairing correlations. This feature is contrasted with the
situation in infinite matter.Comment: 14 pages, 17 figures, submitted to PR
Fermion Condensation and Non Fermi Liquid Behavior in a Model with Long Range Forces
The phenomenon of the so called Fermion condensation, a phase transition
analogous to Bose condensation but for Fermions, postulated in the past to
occur in systems with strong momentum dependent forces, is reanalysed in a
model with infinite range interactions. The strongly non Fermi Liquid behavior
of this system is demonstrated analytically at and at in the
superconducting and normal phases. The validity of the quasiparticle picture is
investigated and seems to hold true for temperatures less than the
characteristic temperature of the Fermion condensation.Comment: 22 LaTeX pages, 6 figures can be obtained from [email protected]
- …