3,768 research outputs found
Correlations and the relativistic structure of the nucleon self-energy
A key point of Dirac Brueckner Hartree Fock calculations for nuclear matter
is to decompose the self energy of the nucleons into Lorentz scalar and vector
components. A new method is introduced for this decomposition. It is based on
the dependence of the single-particle energy on the small component in the
Dirac spinors used to calculate the matrix elements of the underlying NN
interaction. The resulting Dirac components of the self-energy depend on the
momentum of the nucleons. At densities around and below the nuclear matter
saturation density this momentum dependence is dominated by the non-locality of
the Brueckner G matrix. At higher densities these correlation effects are
suppressed and the momentum dependence due to the Fock exchange terms is
getting more important. Differences between symmetric nuclear matter and
neutron matter are discussed. Various versions of the Bonn potential are
considered.Comment: 18 pages LaTeX, including 6 figure
Towards a Robuster Interpretive Parsing
The input data to grammar learning algorithms often consist of overt forms that do not contain full structural descriptions. This lack of information may contribute to the failure of learning. Past work on Optimality Theory introduced Robust Interpretive Parsing (RIP) as a partial solution to this problem. We generalize RIP and suggest replacing the winner candidate with a weighted mean violation of the potential winner candidates. A Boltzmann distribution is introduced on the winner set, and the distributionâs parameter is gradually decreased. Finally, we show that GRIP, the Generalized Robust Interpretive Parsing Algorithm significantly improves the learning success rate in a model with standard constraints for metrical stress assignment
Statistical analysis of the velocity and scalar fields in reacting turbulent wall-jets
The concept of local isotropy in a chemically reacting turbulent wall-jet
flow is addressed using direct numerical simulation (DNS) data. Different DNS
databases with isothermal and exothermic reactions are examined. The chemical
reaction and heat release effects on the turbulent velocity, passive scalar and
reactive species fields are studied using their probability density functions
(PDF) and higher order moments for velocities and scalar fields, as well as
their gradients. With the aid of the anisotropy invariant maps for the Reynolds
stress tensor the heat release effects on the anisotropy level at different
wall-normal locations are evaluated and found to be most accentuated in the
near-wall region. It is observed that the small-scale anisotropies are
persistent both in the near-wall region and inside the jet flame. Two
exothermic cases with different Damkohler number are examined and the
comparison revealed that the Damkohler number effects are most dominant in the
near-wall region, where the wall cooling effects are influential. In addition,
with the aid of PDFs conditioned on the mixture fraction, the significance of
the reactive scalar characteristics in the reaction zone is illustrated. We
argue that the combined effects of strong intermittency and strong persistency
of anisotropy at the small scales in the entire domain can affect mixing and
ultimately the combustion characteristics of the reacting flow
Study of relativistic bound state wave functions in quasielastic (e,e'p) reactions
The unpolarized response functions of the quasielastic reaction are calculated for three different types of relativistic
bound state wave functions. The wave functions are obtained from relativistic
Hartree, relativistic Hartree-Fock and density dependent relativistic Hartree
calculations that reproduce the experimental charge radius of O. The
sensitivity of the unpolarized response functions to the single particle
structure of the different models is investigated in the relativistic plane
wave impulse approximation. Redistributions of the momentum dependence in the
longitudinal and transverse response function can be related to the binding
energy of the single particle states. The interference responses and
reveal a strong sensitivity to the small component of the relativistic
bound state wave function.Comment: 18 pages REVTEX, 5 figures include
Relativistic Structure of the Nucleon Self-Energy in Asymmetric Nuclei
The Dirac structure of the nucleon self-energy in asymmetric nuclear matter
cannot reliably be deduced from the momentum dependence of the single-particle
energies. It is demonstrated that such attempts yield an isospin dependence
with even a wrong sign. Relativistic studies of finite nuclei have been based
on such studies of asymmetric nuclear matter. The effects of these isospin
components on the results for finite nuclei are investigated.Comment: 9 pages, Latex 4 figures include
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