Effects of electron correlations on energy bands of semiconductors: A projection-technique treatment

A recently developed method based on projection techniques is applied to the computation of electron correlations in excited states of semiconductors. In particular it is shown that the method is able to reproduce the results previously obtained by applying the variational Local Ansatz. The advantages of the present approach are its conceptual simplicity and that it can be applied not only to weakly but also to strongly correlated electronic systems.Dedicated to Professor W. Brenig on the occasion of his 60th birthday     

Die Szintillationslichtausbeute energiereicher Deuteronen und α-Teilchen in organischen Kristallen

The light output of anthracene and terphenyl bombarded with deuterons from 8 to 25.3 MeV and with α-particles from 20 to 49.5 MeV has been measured as a function of energy. Both anthracene and terphenyl gave for low energies a nonlinear response tending towards linearity above 18 MeV for deuterons and 35 MeV for α-particles. The dependence of the light output upon the impact direction of the incident particles has been found not to be disappearing even at highest energies, but in contrast there appear new fine structures. Furtheron the specific light outputdS/dxvs specific energy lossdE/dx has been investigated in direct measurements on thin crystals. The quantitydS/dx depends on the impact direction even atdE/dx=35 keV/mg cm^?2.     

Surface magnetization near the critical temperature and the temperature dependence of magnetic-electron scattering from NiO

The temperature dependence of low energy electrons scattered by the exchange interaction in antiferromagnetic NiO is obtained over the temperature range T_N?T?295 K. By doping the N₁O crystal with (less than 0.1 %) Li, the conductivity was increased sufficiently to obtain data at lower temperatures than previously reported.     

On the use of chemical potentials in the condensation of a pure vapour

The thermodynamic relations valid for the condensation of a pure vapour at constant temperature have been derived using appropriate chemical potentials. The results are discussed for an imperfect gas and curvature dependent surface tension of the liquid.     

The algebra of holonomic equations

Summary. In this article algorithmic methods are presented that have essentially been introduced into computer algebra systems like Maple, Mathematica or REDUCE within the last decade. The main ideas are due to Stanley and Zeilberger. Some of them had already been discovered in the last century by Beke, but because of their complexity the underlying algorithms have fallen into oblivion. We give a survey of these techniques, show how they can be used to identify transcendental functions, and present implementations of these algorithms in computer algebra systems. Received: 21.2.1996 / Accepted: 22.1.1997