Self-pulsing at stimulated scattering processes

Periodic pulsations of the output intensity at stimulated scattering processes are shown to occur in the presence of a feedback of the scattered wave, produced by partial reflection at the edges of the scattering medium. The scaling of the oscillation period is given for both forward and back scattering.     

Validity of approximative treatments of Δ-isobar degrees of freedom

A perturbative approach to Δ-isobar components of the three-nucleon ground-state wave function is developed. It is based on the transition potential connecting nucleon-nucleon partial waves and partial waves with isobars. The perturbative results with single Δ-isobar excitation are compared to those of an exact coupled-channel calculation and turn out to be in satisfactory agreement for many Δ-effects. Within the perturbative method the role of the ρ-exchange in the transition potential and the importance of double Δ-excitations in the three-nucleon ground state are discussed. Effective nuclear operators such as three-nucleon forces and exchange currents, when simulating Δ-propagation in static approximation, are found to grossly overestimate Δ-effects.     

Zeitliche Entwicklung des Reflexionskoeffizienten einer Plasmaschicht bei starker elektromagnetischer Einstrahlung

We have calculated numerically the temporal evolution of the nonlinear reflection coefficient R of an overdense plasma layer by solving the system of partial differential equations consisting of the wave equation for the slowly varying amplitude of the electric field and the hydrodynamic equations for the ion motion, including a ponderomotive force term. In dependence of the (normalized) amplitude of the incident wave u_A two regimes exist: Below a critical amplitude u_A^* ? 1 the reflection coefficient is approximately independent on the amplitude u_A and temporally constant. In the opposite case u_A>u_A^*, on the other hand, ‖R‖² decreases slowly with time down to a minimum value and after that it increases rapidly to the initial value. We think, that our results are important to interpret the anomalous reflectivity observed in some experiments when strong electromagnetic waves are incident on an overdense plasma.     

Untersuchung der Strukturen und Eigenschaften der Nitride in Eisenlegierungen durch Isolierung

Zusammenfassung In Fortsetzung früherer Untersuchungen wurden die für das Vorkommen und die Untersuchung der Siliciumnitride wichtigen Eigenschaften, wie Löslichkeit im festen Eisen bei verschiedenen Temperaturen, Habitus. Struktur und optische Eigenschaften bestimmt.Durch elektrolytische Isolierung wurden aus nitrierten Eisenlegierungen weiterhin Nitride des Chroms, Vanadiums, Titans, Niobs, Tantals, Zirkons, Aluminiums und Bors gewonnen und ihre Strukturen und Formen bestimmt. Da das Verhalten dieser Nitride gegenüber Säuren von besonderer Bedeutung für die Bestimmung des Stickstoffs in Stahl- und Eisenlegierungen ist, wurden die Löslichkeiten der isolierten Nitride in Säuren untersucht.

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Summary Following previous investigations, a determination was made of properties which are essential for the presence and examination of silicon nitrides, such as solubility in solid iron at different temperatures, behaviour, structure, and optical characteristics.Nitrides of chromium, vanadium, titanium, niobium, tantalum, aluminium, and boron were extracted from nitrided iron alloys by means of electrolytic isolation, and their structures and shapes were determined. As the behavior of these nitrides in acids is very important for the determination of nitrogen in steel and iron alloys, the solubility of isolated nitrides in acids was investigated.

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Der Deutschen Forschungsgemeinschaft sei auch an dieser Stelle für die Unterstützung der Arbeit besonders gedankt.     

Rechenautomat 704 IBM

Ohne Zusammenfassung     

Regularity of multivariate vector subdivision schemes

In this paper we discuss methods for investigating the convergence of multivariate vector subdivision schemes and the regularity of the associated limit functions. Specifically, we consider difference vector subdivision schemes whose restricted contractivity determines the convergence of the original scheme and describes the connection between the regularity of the limit functions of the difference subdivision scheme and the original subdivision scheme.