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The single-particle spectral functions in asymmetric nuclear matter are computed using the ladder approximation within the theory of finite temperature Green's functions. The internal energy and the momentum distributions of protons and neutrons are studied as a function of the density and the asymmetry of the system. The proton states are more strongly depleted when the asymmetry increases while the occupation of the neutron states is enhanced as compared to the symmetric case. The self-consistent Green's function approach leads to slightly smaller energies as compared to the Brueckner Hartree Fock approach. This effect increases with density and thereby modifies the saturation density and leads to smaller symmetry energies., Comment: 7 pages, 7 figures

The nuclear spectral function at high missing energies and momenta has been determined from a self-consistent calculation of the Green's function in nuclear matter using realistic nucleon-nucleon interactions. The results are compared with recent experimental data derived from ($e,e'p$) reactions on $^{12}C$. A rather good agreement is obtained if the Green's functions are calculated in a non-perturbative way., Comment: 10 pages, 3 figures

The nucleon spectral function in nuclear matter fulfills an energy weighted sum rule. Comparing two different realistic potential, these sum rules are studied for Green's functions that are derived self-consistently within the $T$ matrix approximation at finite temperature., Comment: 7 pages, 4 figures

The properties of symmetric nuclear matter are investigated within the Green's functions approach. We have implemented an iterative procedure allowing for a self-consistent evaluation of the single-particle and two-particle propagators. The in-medium scattering equation is solved for a realistic (non-separable) nucleon-nucleon interaction including both particle-particle and hole-hole propagation. The corresponding two-particle propagator is constructed explicitely from the single-particle spectral functions. Results are obtained for finite temperatures and an extrapolation to T=0 is presented., Comment: 11 pages 5 figures

Effects of spin polarization on the structure of symmetric nuclear matter and pure neutron matter are investigated. We show that the spin polarization induces a deformation of the Fermi spheres for nucleons with spin parallel and opposite to the polarization axes. This feature can be related to the structure of the one pion exchange contribution to a realistic nucleon-nucleon interaction. While the anisotropies in the momentum distribution lower the energy of the system by small amount, the associated variations of the single particle energies with the angle between the polarization axis and the particle momentum are significant., Comment: 5 pages, 1 figure

The structure of nucleon self-energy in nuclear matter is evaluated for various realistic models of the nucleon-nucleon (NN) interaction. Starting from the Brueckner-Hartree-Fock approximation without the usual angle-average approximation, the effects of hole-hole contributions and a self-consistent treatment within the framework of the Green function approach are investigated. Special attention is paid to the predictions for the spectral function originating from various models of the NN interaction which all yield an accurate fit for the NN phase shifts., Comment: 26 pages, 12 figures

The influence of $\Delta$ isobar components on the ground state properties of nuclear systems is investigated for nuclear matter as well as finite nuclei. Many-body wave functions, including isobar configurations, and binding energies are evaluated employing the framework of the coupled-cluster theory. It is demonstrated that the effect of isobar configurations depends in a rather sensitive way on the model used for the baryon-baryon interaction. As examples for realistic baryon-baryon interactions with explicit inclusion of isobar channels we use the local ($V28$) and non-local meson exchange potentials (Bonn$_{2000}$) but also a model recently developed by the Salamanca group, which is based on a quark picture. The differences obtained for the nuclear observables are related to the treatment of the interaction, the $\pi$-exchange contributions in particular, at high momentum transfers., Comment: 12 pages, including 5 figures

$\Delta$ isobar components in the nuclear many-body wave function are investigated for the deuteron, light nuclei (${}^{16}O$) and infinite nuclear matter within the framework of the coupled-cluster theory. The predictions derived for various realistic models of the baryon-baryon interaction are compared to each other. These include local ($V28$) and non-local meson exchange potentials (Bonn$_{2000}$) but also a model recently derived by the Salamanca group accounting for quark degrees of freedom. The characteristic differences which are obtained for the $N\Delta$ and $\Delta\Delta$ correlation functions are related to the approximation made in deriving the matrix elements for the baryon-baryon interaction., Comment: 15 pages, 6 figures incl

The use of the systems approach in educational inquiry is not new, and the models of input/output, input/process/product, and cybernetic systems have been widely used. The general systems model is an extension of all these, adding the dimension of environmental influence on the system as well as system influence on the environment. However, if the theory model is changed, traditional statistical procedures may no longer be applicable and other mehtods should be used. The Set, Information, Graph, and General System Model (SIGGS) is a further extension of general systems in that set theory, information theory, and digraph theory are used as models to extend general systems theory. This paper further discusses the application of the SIGGS model and information statistics to the Indiana Behavior Management Systems (IBMS), an observation system concerned with teacher management of off task, deviant learner behavior, which was used in an evaluation of Programmed Reentry (of mildly handicapped children) Into Mainstream Education (Project PRIME). (BW)

Observer disagreement is important insofar as it limits the reliabilities of observational records. This discussion evolves around methods and conditions under which observer agreement can be measured as to minimize such an occurrence. Observers should be trained to nearly perfect agreement with a criterion or expert coder on unambiguous examples of behavioral categories before actual data collection. Disagreement on ambiguities may help reflect a more accurate representation of the real world. In addition to criterion-related agreement, it is suggested that intraobserver agreement be obtained by showing a video tape twice to all observers in which conditions parallel those encountered in the field. While criterion-related and intraobserver agreement measures have been recommended for both before and during a study, they should not be used as evidence of observer agreement in the actual classroom, but rather to assist an investigator in documenting adequacy of observational skills. After a study is finished, reliabilities of observational data and coefficients of stability and observer agreement should be calculated by using intraclass correlation coefficients. (Author/RC)