Showing papers by "University of Stuttgart published in 1978"
TL;DR: In this paper, a new definition of rotations is introduced, called semitangential rotations, which leads to a reformulation of the theory of Ziegler [1,2] which is clearly consistent and correct.
189 citations
TL;DR: In this paper, the authors derived an exact time-convolutionless masterequation for the probability with a colored random force and showed the mathematical equivalence of the formally different approaches of a Langevin description and a mastererquation description.
Abstract: For the statistical behavior of macrovariables described in terms of Langevin equations with a in general colored random force we deduce useful formulas which simplify the calculation of correlation functions. Utilizing these results and the stochastic properties of the random force we derive an exact time-convolutionless masterequation for the probability hereby showing the mathematical equivalence of the formally different approaches of a Langevin description and a masterequation description. We study in detail the class of time-instantaneous Langevin equations and the important class of retarded (Mori-type) Langevin equations with both, Gaussian and general colored random forces. Using the generalization of the nonlinear Langevin equation for continuous Markov processes with white Gaussian noise and white generalized Poisson noise we show that the resulting masterequation can be recast in the Kramers-Moyal form. Interpreting this Langevin equation in the Stratonovitch sense we deduce the fluctuation induced drift (spurious drift) which can be divided up into two parts, the well known part induced by white Gaussian noise and the one induced by white generalized Poisson noise.
168 citations
TL;DR: In this paper, it is shown that correlation effects can be adequately treated using the local spin density approximation using the computational effort of very small compared to CI calculations, and the method is applied to correlation energies and ionization potentials of the atoms Li to Ar and binding energies of the diatomic hydrides LiH to HCl.
Abstract: It is shown that dynamical correlation effects can be adequately treated using the local spin-density approximation. The computational effort is very small compared to CI calculations. The method is applied to correlation energies and ionization potentials of the atoms Li to Ar and binding energies of the diatomic hydrides LiH to HCl.
127 citations
TL;DR: In this paper, a recursion formula is established which gives the relevant upper (+) and lower (-) bounds for the tensor Ceff of effective elastic moduli of the overall grade n material.
Abstract: Using elasticity as an illustration a recursion formula is established which gives the relevant upper (+) and lower (-) bounds C(+or-n), (n=2,3,4... infinity ) for the tensor Ceff of effective elastic moduli of the overall grade n material. It follows from this formula that for n to infinity both C(+n) and C(-n) converge towards the well known self-consistent tensor Csc which therefore represents a material which, in a statistical sense, is perfectly homogeneous, isotropic and disordered. All these results also have implications for other material properties and for disordered structures other than polycrystals. Since the self-consistent approach is isomorphic to the coherent potential approximation, some of the conclusions should also be relevant for other areas of solid state physics.
126 citations
TL;DR: A software package OLIOPT was developed for the on-line optimization of the steady-state behaviour of slow dynamic processes in a relatively short time period and is suited for industrial processes with one or more variable inputs.
121 citations
TL;DR: In this article, it is shown that a broad variety of slow chemisorption steps can serve as buffer with the restriction that the buffer step should not, or at least only slightly, contribute to the surface reaction.
89 citations
TL;DR: In this paper, a far-infrared polarimeter is combined with a Veron-type interferometer to yield the line integrals in a plasma simultaneously along the same probing beam.
88 citations
TL;DR: In this article, a better interpretation of different performances of distinct systems is possible and conclusions can be drawn to optimize material selection and operating conditions for specific applications, by means of typical examples.
85 citations
79 citations
TL;DR: In this article, the ground-state energy of the electron-hole plasma in GaAs, InP, and GaSb is determined using several spectroscopic techniques, and the experimental data can be explained assuming that at least for temperatures higher than 7 K the density of the plasma is determined by the Mott density rather than by the equilibrium liquid density.
Abstract: The ground-state energy of the electron-hole plasma in GaAs, InP, and GaSb is determined using several spectroscopic techniques. Comparison with calculated values shows that the data can be understood within the many-body theory for a high-density plasma in semiconductors; however, the experimental values for the ground-state energy are lower than predicted from the theory. Although these results imply that binding of the electron-hole plasma should be possible, the existence of a liquid in GaAs could not be proven. The experimental data can be explained assuming that at least for temperatures higher than 7 K the density of the plasma is determined by the Mott density rather than by the equilibrium liquid density.
77 citations
TL;DR: In this paper, the authors discuss the question of the construction of a linear semigroup for the time evolution of the single-event probabilities of general non-Markov processes and show that such a semigroup may not exist for all finite times.
Abstract: We discuss the question of the construction of a linear semigroup for the time evolution of the single-event probabilities of general non-Markov processes. It is shown that such a linear semigroup may not exist for all finite times. The consequences are sketched for the description of equilibrium and nonequilibrium systems. Further, the relationship with nonstationary Markov processes is investigated, and some confusion in recent works is cleared up using the example of free Brownian motion.
TL;DR: In this article, it was shown that screw-type chaos is possible in the Zhabotinskii reaction with a simple Bonhoeffer-van der Pol circuit, which can be run as both an astable and a monostable "flip-flop".
Abstract: THE Belousov–Zhabotinskii reaction is a chemical Bonhoeffer–van der Pol circuit, that is, a relaxation oscillator that can be run as both an astable and a monostable ‘flip-flop’1–3. Apparently the reaction also belongs to the slightly more complicated class of‘universal circuits’4 as introduced by Khaikin5–6. Oscillators of this type not only show ‘smooth’ and ‘relaxation type’ oscillations5–6, but also ‘chaotic’ oscillations4. As evidenced by the simplest equation of this type7, both ‘spiral type’ and ‘screw type’ chaos20 are possible in such systems. We present here preliminary evidence for the occurrence of screw-type chaos in the Zhabotinskii reaction.
TL;DR: The atomic jump processes involved in the vacancy mechanisms of self-diffusion in metals are reviewed with particular attention to disvacancies in this paper, where the most important measurements which are helpful to separate mono- and divacancy contributions are discussed.
TL;DR: Preliminary crystal structure analyses for isomorphous n-propanol and p-iodo-phenol complexes with β-cyclodextrin (β-CD) are reported which are felt to provide interesting models for another aspect of biological chemistry, that of diffusion through a lipid bilayer membrane.
Abstract: CYCLODEXTRINS have received considerable attention as models for biological macromolecules. Much of this interest has been stimulated by their suitability for serving as relatively low molecular weight models for enzymes which catalyse various hydrolytic reactions1. Like enzymes, they form a complex with the substrate prior to the rate determining step of the reaction catalysed. We report here preliminary crystal structure analyses for isomorphous n-propanol and p-iodo-phenol complexes with β-cyclodextrin (β-CD) which we feel may provide interesting models for another aspect of biological chemistry, that of diffusion through a lipid bilayer membrane.
TL;DR: It is postulated that although ABA is involved in the regulation of tuberization, it is the balance between ‘promoting’ hormones such as ABA and ‘inhibiting’ hormone such as gibberellic acid which is the controlling factor.
Abstract: Potato plants (Solanum tuberosum L.) were grown under constant climatic conditions in water culture with continuous and discontinuous nitrogen supply. The effect of N nutrition on tuberization and abscicic acid (ABA) content in various parts of the plants was investigated. With the exception of the stolons, interrupting the N supply caused an increase in the ABA content. After renewed N supply the ABA content dropped within 3 days to the original level. With continuous N supply the ABA content varied only to a limited extent. The ABA content of the stolons was not affected by the mode of N nutrition and remained at an almost constant level despite the fact that exogenous ABA was translocated within the stolon acropetally and accumulated in the tip. After tuberization the ABA content of the stolons and tubers rose considerably. The increase in ABA content in roots. exudate, and shoot after N withdrawal was accompanied by the initiation of tuberization in ‘physiologically old’ plants but not in “physiologically young’ plants of the same age. It is postulated that although ABA is involved in the regulation of tuberization, it is the balance between ‘promoting’ hormones such as ABA and ‘inhibiting’ hormones such as gibberellic acid which is the controlling factor.
TL;DR: An abstract data model is introduced which is suited to express the semantics of schemas respectively data instances and a logical data definition language and logical data language are proposed which allow to specify the kind of information which may be stored in the data base and which ensures the correctness and consistency of this information.
TL;DR: In this article, the effect of atomic disorder and precipitations on the magnetic field and phase boundaries of permanent magnet particles was studied and the properties of extremely narrow domain walls were discussed.
TL;DR: In this article, it was shown that rate multiplicity can be caused by competing chemisorption of A and B upon the same active sites of the catalyst, if at least one of the reaction steps is of second order.
TL;DR: In this article, the authors investigated the catalytic fading of some yellow azo dyes in the presence of blue, violet or red anthraquinonoid dyes and showed that this phenomenon occurs only in presence of oxygen and is suppressed by adding typical singlet oxygen quenchers.
Abstract: The catalytic fading of some yellow azo dyes in the presence of blue, violet or red anthraquinonoid dyes has been investigated. It can be shown that this phenomenon occurs only in the presence of oxygen and is suppressed by adding typical singlet oxygen quenchers. On substituting singlet oxygen producers like methylene blue for the anthraquinonoid dyes, the catalytic fading still takes place, indicating that a photo-oxygenation reaction according to the type II mechanism is responsible. By carrying out competitive photooxidation experiments in ethylcellulose films, relative rate constants for the reaction with singlet oxygen in a rigid material were determined.
TL;DR: In this article, a linear stability analysis of the Gierer-Meinhardt model is performed to determine the critical parameters where the homogeneous distribution of activator and inhibitor concentrations becomes unstable.
Abstract: We first perform a linear stability analysis of the Gierer-Meinhardt model to determine the critical parameters where the homogeneous distribution of activator and inhibitor concentrations becomes unstable. There are two kinds of instabilities, namely, one leading to spatial patterns and another one leading to temporal oscillations. Focussing our attention on spatial pattern formation we solve the corresponding nonlinear equations by means of our previously introduced method of generalized Ginzburg-Landau equations. We explicitly consider the two-dimensional case and find both rolls and hexagon-like structures. The impact of different boundary conditions on the resulting patterns is also discussed. The occurrence of the new patterns has all the features of nonequilibrium phase transitions.
TL;DR: In this paper, an assessment of the incremental solution methods for the analysis of inelastic rate problems is presented, in which the possibilities of the initial load method are explored to improve the accuracy and stability of the traditional explicit operators by higher-order time expansions and implicit weighting schemes.
01 Jun 1978
TL;DR: In this paper, a simple relation is derived between the presolar nebula's temperature and the upper limit to the mass of the planetesimals, based on available observational evidence on the solid particles in interplanetary and interstellar space and of theoretical considerations on the relationship between them and on the sedimentation process.
Abstract: If we assume that the cometary nuclei originated by the gravitational instability of a dust layer, which formed in the equatorial plane of the outer parts of the presolar nebula (PSN) during a period of approximate equilibrium between gravity, centrifugal force, and the pressure gradient, a simple relation is derived between the PSN's temperature and the upper limit to the mass of the planetesimals. It contains, besides the density of the cometary nucleiρp, only the fraction (by mass) of the condensable elements in the PSN, which became part of the dust particle disc, which, on the basis of available observational evidence on the solid particles in interplanetary and interstellar space and of theoretical considerations on the relationship between them and on the sedimentation process, is found to be of the order of ≳~10%; this estimate will require still further justification. Assuming a temperature in the range 15–20 K, an equatorial diameter of the PSN of 0.1 pc andρp ≈ few 0.1 g/cm3, upper limits for the planetesimal's mass of ≈ 1018g and for their radius of ≈ 10 km are obtained (on the basis of conservation of circulation, of mass and of angular momentum in the differentially rotating disc), in fair agreement with observation. With the dispersion of those parts of the PSN — of an assumed original mass of 2–3M⊙ —, which did not become part of the Sun or the planets, by the young Sun's activity, the planetesimals must have lost a large part of their gravitational binding energy and their orbits must have become so large (semimajor axis several 104 A.U. or more, if not negative), that stellar perturbations produced the distribution in configurational and in velocity space now observed.
TL;DR: In this article, the authors analyzed the band-to-band luminescence lineshape of the electron-hole plasma emission in GaAs and showed that hole-phonon interaction gives an important contribution to the cooling of the carrier system.
Abstract: The band-to-band luminescence lineshape of the electron—hole plasma emission in GaAs is analyzed as a function of the excess energy of the photocreated electrons and holes. This yields experimental data for the dependence of the effective carrier temperature of the electron—hole plasma on the excess excitation energy for high electron and hole densities. Carrier temperatures as low as 5 K can be obtained in the case of resonant excitation. A discussion of these data in terms of the possible energy dissipation processes shows that hole—phonon interaction gives an important contribution to the cooling of the carrier system.
Die Linienform der Band—Band-Lumineszenz der Elektron—Loch-Plasmaemission in GaAs wird als Funktion der uberschussigen Energie der photoangeregten Elektronen und Locher analysiert. Dies ergibt experimentelle Werte fur die Abhangigkeit der effektiven Ladungstragertemperatur des Elektron—Loch-Plasmas von der Anregungsenergie fur hohe Elektronen- und Locherdichten. Ladungstragertemperaturen bis herab zu 5 K konnen im Fall von Resonanzanregung erhalten werden. Eine Diskussion dieser Werte mit den moglichen Energiedissipationsprozessen zeigt, das die Locher—Phononen-Wechselwirkung einen wesentlichen Beitrag zur Abkuhlung des Ladungstragersystems liefert.
TL;DR: Time-dependent fluorescence processes can be investigated using a phase fluorometer with variable frequency using the high cutoff frequency of 500 MHz leads to a time-resolving power of about 1 ps.
Abstract: Time‐dependent fluorescence processes can be investigated using a phase fluorometer with variable frequency. The high cutoff frequency of 500 MHz leads to a time‐resolving power of about 1 ps.
TL;DR: In this paper, Faraday rotation measurements using a ferrite modulation technique were performed on one channel of the 337 μm-interferometer on TFR, which is intended as a preparatory step towards poloidal-field determination on the basis of the Faraday effect in a multi-channel configuration.
Abstract: Faraday rotation measurements using a ferrite modulation technique were performed on one channel of the 337 μm-interferometer on TFR. The experiment is intended as a preparatory step towards poloidal-field determination on the basis of the Faraday effect in a multi-channel configuration. The technical feasibility of precise Faraday rotation measurements under machine conditions is demonstrated. The measured rotation is unambiguously due to the poloidal magnetic field and agrees fairly with what can be estimated.
TL;DR: In this paper, the structural composition of hard and brown coal tar pitches and coal extracts is analyzed by 13C n.m. spectroscopy on the basis of the chemical-shift data for selected model compounds.
TL;DR: In this paper, the resonance interaction between different NR2 substituents and the arylic π-system in mono-, 1, 3-bis-and 1,3, 5-tris(dialkylamino)benzenes was derived for the relative donor strength of the pyrrolidino, dimethylamino, piperidino and morpholino group.
TL;DR: In this article, an incremental total Lagrangian formulation is presented which allows the calculation of arbitrarily large displacements and rotations, and the derivation of the tangential stiffness as well as some remarks concerning its efficient programming are given.
TL;DR: In this article, the radical yields and rate constants in the quenching reaction of thionine triplet with the complete series of monohaiogen substituted ardlincs as electron donors were determined by flash spectroscopy.
TL;DR: Dimethylpropynylmetal compounds of Al, Ga and In are formed in 40-60% yield by the reaction of NaC�CCH3 with (CH3)2MIIIHal (MIII Al, GA, In; Hal Cl, Br) as mentioned in this paper.