Methodik und Ergebnisse von Tracerexperimenten über katalytische Reaktionen von Kohlenwasserstoffen

Tracermethoden können wichtige Beiträge zur Aufklärung katalytischer Kohlenwasserstoffreaktionen liefern. In dieser Arbeit werden einige Ergebnisse mehrjähriger Untersuchungen mit ¹⁴C-markierten Verbindungen zusammenfassend dargestellt. Es wird speziell auf Benzenbildungsreaktionen bei der Leichtbenzin-Reformierung und auf Reaktionsmechanismen bei der Isomerísierung von C₈-Aromaten eingegangen.     

Jamming and crystallization in athermal polymer packings

Dense packings of chains of hard spheres possess characteristic features that do not have a counterpart in corresponding packings of monomeric spheres especially near the maximally random jammed (MRJ) state. From the modelling perspective the additional requirement that spheres keep their connectivity while maximizing the occupied volume fraction imposes severe constraints on generation algorithms of dense chain configurations. The extremely sluggish dynamics imposed by the uncrossability of chains precludes the use of deterministic or stochastic dynamics to generate all but dilute polymer packings. As a viable alternative, especially tailored chain-connectivity-altering Monte Carlo (MC) algorithms have been developed that bypass this kinetic hindrance and have actually been able to produce packings of hard-sphere chains in a volume fraction range spanning from infinite dilution up to the MRJ state. Such very dense athermal polymer packings share a number of structural features with packings of monomeric hard spheres, but also display unique characteristics due to the constraints imposed by connectivity. We give an overview of the most relevant results of our recent modeling work on packings of freely-jointed chains of tangent hard spheres about the MRJ state, local structure, chain dimensions and their scaling with density, topological constraints in the form of entanglements and knots, contact network at jamming, and entropically driven crystallization.     

Inclusive ϱ0,K *±(892) andf production in\bar p p Interactions at 12 GeV/c

Inclusive production of ?⁰,K ^*±(892), andf is studied in \(\bar p\) p interactions at 12 GeV/c. The inclusive cross sections for ?⁰,K ^*±(892), andf are found to be 6.7±0.3 mb, 1.0±0.2 mb, and 1.4±0.3 mb, respectively. The differential cross sections are presented as a function of c.m. rapidity, Feynmanx and square of the transverse momentump _T ² . Comparison with the correspondingpp data shows some interesting differences which can be attributed to the \(\bar p\) p annihilation. The results are compared with the predictions of the quark fusion model.     

Ferromagnetic Resonance of FeNi/Cu/FeNi Thin Film on Coplanar Waveguide with Operating Frequency of 1 to 20 GHz

Russian Physics Journal - The paper presents the calculation results of the coplanar waveguide geometry using the method of conformal mapping and computerized simulation with COMSOL Multiphysics...     

On static and radiative space-times

The conformal constraint equations on space-like hypersurfaces are discussed near points which represent either time-like or spatial infinity for an asymptotically flat solution of Einstein's vacuum field equations. In the case of time-like infinity a certain radiativity condition, is derived which must be satisfied by the data at that point. The case of space-like infinity is analysed in detail for static space-times with non-vanishing mass. It is shown that the conformal structure implied here on a slice of constant Killing time, which extends analytically through infinity, satisfies at spatial infinity the radiativity condition. Thus to any static solution exists a certain radiative solution which has a smooth structure at past null infinity and is regular at past time-like infinity. A characterization of these solutions by their free data is given and non-symmetry properties are discussed.     

Exciton-related optical nonlinearities in semiconductors and semiconductor microcrystallites

We report on large optical nonlinearities due to specific many-body effects in high-density electron-hole pair systems. On bulk CdS we study the effect of free-carrier screening on the absorption and refraction in the vicinity of the band-gap at room temperature. Steady-state saturable absorption at mW-power levels and four-wave mixing with first-order efficiencies as large as 2% of the incoming light are demonstrated on a 1m slab. On CuBr microcrystallites embedded in glass we investigate the changes of the exciton absorption caused by many-exciton effects both at cryo and room temperature. In contrast to bulk semiconductors, we observe a blue shift of the exciton peak at resonant optical excitation. In addition, strong saturation of absorption with very large contrast shows up. We find Lorentzian saturation intensities in the 100 kW/cm² range.     

Valence state and magnetic interactions in magnetically ordered Eu(Pd1−x Au x )2Si2

X-ray diffraction,¹⁵¹Eu Mössbauer effect (ME) and magnetic susceptibility measurements have been performed to investigate the valence behavior and the magnetic interactions of the Eu ions in the intermetallic series Eu(Pd_1–x Au _x )₂Si₂ (0x1) as a Forx>0.4 all experimental techniques are in agreement with each other and suggest a divalent 4f ⁷ ground state of the Eu ion. Belowx=0.4 the different methods lead to different results: while the lattice parameters and the ME isomer shift suggest an instable behavior of the valence the magnetic susceptibility proves a pure divalent 4f ⁷ ground state. These differences can be explained by assuming a partial extension of the 4f-shell radius such that the localized character of the 4f-electrons is preserved.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday     

Non-linear axisymmetric vibration of orthotropic thin circular plates on elastic foundations

This study deals with the large amplitude axisymmetric free vibrations of cylindrically orthotropic thin circular plates resting on elastic foundations. Geometric non-linearity due to moderately large deflections has been included. Movable and immovable simply supported plates and immovable clamped plates resting on Winkler, Pasternak and non-linear Winkler foundations have been considered. The von Kármán type governing equations have been employed. Harmonic vibrations are assumed and the time t is eliminated by the Kantorovich averaging method. An orthogonal point collocation method is used for spatial discretization. Numerical results are presented for the linear natural frequency of the first axisymmetric mode and for the ratio of the non-linear period to the linear period of natural vibration. The effects of foundation parameters, the orthotropic parameter and the edge conditions on the non-linear vibration behaviour have been investigated.     

Emission of neutrino pairs by an electron in an ultrastrong magnetic field

The transitions of relativistic electrons in a magnetic field with the emission of an antineutrino-neutrino pair are considered. Probabilities are obtained for electron transitions to the ground state and weakly excited states. It is shown that in the case of an ultrastrong magnetic field (HH_o=m²c³/e=4.41·10¹³ G) such transitions made a considerable contribution to the total probability of the process.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 110–114, March, 1978.In conclusion, the authors express their profound gratitude to A. A. Sokolov for his attention to our work.