Showing papers by "University of Stuttgart published in 1975"
TL;DR: In this article, a tutorial approach to cooperative phenomena in systems far from thermal equilibrium and in non-physical systems is presented, with particular emphasis on the question of how order and self-organization may arise.
Abstract: This article consists of two parts. The first part presents a tutorial approach to cooperative phenomena in systems far from thermal equilibrium and in nonphysical systems. Particular emphasis is placed on the question of how order and self-organization may arise. The following example is treated among others: the ordered phase of the laser giving rise to both coherently oscillating atomic dipole moments and coherent light emission. A complete analogy of the laser light distribution function to that of the Ginzburg-Landau theory of superconductivity is found mathematically which allows us to interpret the laser threshold as a quasi-second-order phase transition with soft modes, critical slowing down, etc. Similar phenomena, again closely resembling phase transitions, are found in tunnel diodes and in the nonlinear wave interaction which occurs, for example, in nonlinear optics. Remarkable analogies between the instability of the laser and those in hydro-dynamics are elaborated. While these phenomena show pronounced analogies to phase transitions in thermal equilibrium, there are further classes of instabilities and new phases which rather resemble hard excitations known in electrical engineering. Chemical oscillations are particularly important examples. In addition, the first part of this article contains the example of the cooperative behavior of neuron networks and shows the applicability of simple physical concepts, e.g., the Ising model, to the problem of the dynamics of social groups. All these above-mentioned examples demonstrate clearly that rather complex phenomena brought about by the cooperation of many subsystems can be understood and described by a few simple concepts. One of the main concepts is the order parameter; another is the adiabatic elimination of the variables of the subsystems, which is based upon a hierarchy of time constants present in most systems. The second part of this article gives a systematic account of the mathematical tools which allow us to deal with fluctuations. It contains the master equation, the Fokker-Planck equation, the generalized Fokker-Planck equation, and the Langevin equations, and gives several general methods for deriving the stationary and, in certain cases, the nonstationary solutions of master equations and the Fokker-Planck equations. Such general classes comprise those in which detailed balance is present or in which the coupling to the reservoirs is weak. In the quantum mechanical domain, the density matrix and the projection formalism for its reduction are presented. Finally, it is shown how the principle of quantum-classical correspondence allows us to translate quantum statistical problems completely into the classical domain.
815 citations
TL;DR: In this paper, finite element incremental formulations for non-linear static and dynamic analysis are reviewed and derived starting from continuum mechanics principles, and a consistent summary, comparison, and evaluation of the formulations which have been implemented in the search for the most effective procedure.
Abstract: SUMMARY Starting from continuum mechanics principles, finite element incremental formulations for non-linear static and dynamic analysis are reviewed and derived. The aim in this paper is a consistent summary, comparison, and evaluation of the formulations which have been implemented in the search for the most effective procedure. The general formulations include large displacements, large strains and material non-linearities. For specific static and dynamic analyses in this paper, elastic, hyperelastic (rubber-like) and hypoelastic elastic-plastic materials are considered. The numerical solution of the continuum mechanics equations is achieved using isoparametric finite element discretization. The specific matrices which need be calculated in the formulations are presented and discussed. To demonstrate the applicability and the important differences in the formulations, the solution of static and dynamic problems involving large displacements and large strains are presented.
789 citations
TL;DR: A relationship that exists between some queuing networks and electrical networks, with customers and throughput being analogous to electrical charge and electrical current, respectively is determined.
Abstract: We consider a queuing network with M exponential service stations and with N customers. We study the behavior of a subsystem σ, which has a single node as input and a single node as output, when th...
328 citations
162 citations
TL;DR: In this paper, the effect of additional diffusion on luminescence quenching was studied based on a pair probability method for the statistics of resonance energy transfer and simple approximate formulae for luminescent quench were derived and compared with results previously given in the literature.
151 citations
TL;DR: In this article, the coercive force is calculated for a rigid and a one- or two-dimensionalally vaulted Bloch wall on the basis of a statistical theory, and it is shown that the validity of the various pinning models developed previously depends on the defect density, the interaction force, and the area and flexibility of the domain wall.
107 citations
TL;DR: A recursive method for efficient computational analysis of a wide class of queuing problems is presented and interarrival and service times are described by multidimensional Markovian processes while arrival and service rates are allowed to be state dependent.
Abstract: A recursive method for efficient computational analysis of a wide class of queuing problems is presented. Interarrival and service times are described by multidimensional Markovian processes while arrival and service rates are allowed to be state dependent.
103 citations
TL;DR: In this article, the electron and hole trap levels in the band gap of doped molecular crystals may be described by a simple polarization model taking into account the shift of electron and holes levels (positive and negative ionic states) of the free dopant molecule during its incorporation into a polarizable crystal-continuum.
Abstract: It is discussed under which conditions electron and hole trap levels in the band gap of doped molecular crystals may be described by a simple polarization model taking into account the shift of electron and hole levels (positive and negative ionic states) of the free dopant molecule during its incorporation into a polarizable crystal-continuum. Measurements are presented for anthracene doped with tetracene (T), acridine (Ac), and phenazine (Ph). The trap levels obtained are: E = 0.42 eV; E = 0.12 to 0.17 eV (depending on the orientation); E = 0 eV; E = 0.21 eV, E = 0 eV; E = 0.54 eV for holes (p) and electrons (n), respectively.
78 citations
TL;DR: In this paper, the authors proposed a linearization of the Ginzburg-Landau equations with fluctuating forces and obtained the stationary distribution function as solution of the Fokker-Planck equation.
Abstract: The recently found close analogies between the continuous mode laser, the Benard instability, and chemical instabilities with respect to their phase transition-like behaviour are shown to have a common root. We start from equations of motion containing fluctuations. We first assume external parameters permitting only stable solutions and linearize the equations, which define a set of modes. When the external parameters are changed the modes getting unstable are taken as order parameters. Since their relaxation time tends to infinity the damped modes can be eliminated adiabatically leaving us with a set of nonlinear coupled order parameter equations resembling the time dependent Ginzburg-Landau equations with fluctuating forces. In two and three dimensions additional terms occur which allow for e.g. hexagonal spatial structures. We also treat the hard mode instability and obtain the stationary distribution function as solution of the Fokker-Planck equation. Our procedure has immediate applications to the Taylor instability, to various chemical reaction models, to the parametric oscillator in nonlinear optics and to some biological models. Furthermore, it allows us to treat analytically the onset of laser pulses, higher instabilities in the Benard and Taylor problems and chemical oscillations including fluctuations.
76 citations
TL;DR: In this article, the magnetic susceptibility of the β-phase CoGa has been correlated with the defect structure of this phase, and the effective local magnetic moment per TAS -atom was found to be (5.02±0.06)μ B.
75 citations
TL;DR: In this article, it was shown that the existence of a metastable state in which positrons in metals are self-trapped by strong interaction with the lattice gives rise to an anomalous temperature dependence in positron annihilation properties.
Abstract: It is shown that the existence of a metastable state in which positrons in metals are “self-trapped” by strong interaction with the lattice gives rise to an anomalous temperature dependence in positron annihilation properties. The “intermediate” temperature variation of the shape of the annihilation photon line discovered by MacKenzieet al. is well accounted for by this mechanism; alternative interpretations in terms of thermal expansion effects may be refuted. This result calls for considerable revision of some of the published monovacancy formation energies obtained from positron annihilation measurements. Approximate criteria for the existence and the metastability of a selftrapped state of positively charged particles in metals are given. It is found that metastable self-trapping may occur for positrons; hydrogen isotopes and positive muons should be self-trapped in configurations that are always stable relative to the Bloch-wave states of these particles.
TL;DR: In this paper, the authors present angegebenen rund 50 Formfaktoren Grundlage einer Vielzahl von geometrischen Anordnungen, denen skalare potentialfelder zugrundeliegen.
TL;DR: In this article, a quantitative study of the proton transfer reactions which follow the dissociation of the 8-hydroxypyrene-1,3,6-trisulphonic acid ion ROH by flash photolysis in aqueous solution is presented.
TL;DR: In this paper, the shape and monochromatic properties of the TEA-CO 2 hybrid laser were analyzed with reference to numerical solutions of simplified rate equations and the mechanism of single-frequency operation of the hybrid laser was discussed.
Abstract: The mechanism of a new method of obtaining high-power single-frequency pulses from a TEA-CO 2 laser is discussed. Measurements of the shape and monochromaticity of pulses from the hybrid laser which has both a TEA and a low-pressure gain section inside one resonator are presented. The mechanism of single-frequency operation of the hybrid laser is discussed with reference to numerical solutions of simplified rate equations. The low-pressure section provides gain only over a narrow range of frequencies so that a mode lying in that bandwidth builds up faster than neighboring modes to give a single-frequency pulse resembling in overall shape the normal TEA laser pulse. If the system is already lasing when the TEA discharge begins, the single-mode radiation already present rapidly grows to give a single-frequency pulse lacking a gain-switched peak.
TL;DR: In this article, a radial arrangement of orthogonal reflecting planes which are formed by the sides of the crystalline cones and purine layers surrounding them is proposed for superposition ray path in the eye of crayfish.
Abstract: Histological and optical observations in the eye of crayfish lead to a new hypothesis of the superposition ray path in this eye. Rays from an object point entering through different facets are superimposed not by refracting systems as in other superposition eyes but by a radial arrangement of orthogonal reflecting planes which are formed by the sides of the crystalline cones and purine layers surrounding them.
TL;DR: In this paper, the authors reported on measurements of the 7Li nuclear spin relaxation time in solid lithium as a function of temperature (−170°C≦T≦+180°C) and Larmor frequency (450kHz≦v Li≦31.5 MHz).
Abstract: We report on measurements of the7Li nuclear spin relaxation timeT 1 in solid lithium as a function of temperature (−170°C≦T≦+180°C) and Larmor frequency (450kHz≦v Li≦31.5 MHz). Using a relaxation model developed by Wolf and Cavelius and combining it with Seeger's diffusion formalism, the diffusion parameters for mono-and divacancy migration were evaluated by a least squares fit to the newly obtainedT 1 data as well as to previousT 1ϱ measurements. The result for the self-diffusion coefficientD SD is given byD SD=D 10·exp(−Q 1/RT)·[1+D 21·exp(−Q 21/RT)], withD 10=0.038 cm2s−1,Q 1=12.0 kcal mol−1,D 21=250,Q 21=4 kcal mol−1 andR=1.985·10−3 kcal mol−1 degree−1. Due to the flexibility of Seeger's formula, which contrasts with the standard Arrhenius interpretation of diffusion, discrepancies between earlier high- and low-frequency NMR investigations were eliminated. Furthermore, an excellent agreement with available results from tracer experiments was achieved by taking into account the theoretical predictions of the isotope effect and the vacancy correlation factor.
TL;DR: In this article, the basic idea is brought to a logical conclusion by the direct construction of the factorised form of the elemental and overall stiffness matrices from their natural stiffness roots, denoted as the natural factor formulation.
TL;DR: The nucleation field of Co 17 Sm 2 -platelets which are precipitated in a Co 5 Sm-matrix has been determined for finite and infinite extensions of the platelet.
TL;DR: The concept underlying this progress report is that the electronic destabilization of systems having eight π-electrons should be especially pronounced in the case of six-membered rings for steric and electronic reasons.
Abstract: The terms “aromatic” and “antiaromatic” have attracted widespread interest in recent years. After all the discussion about the meaning of words, one fact remains: the energy content of planar systems displaying cyclic electron delocalization depends upon the number of, and the orbital interactions between, the participating electrons. The concept underlying this progress report is that the electronic destabilization of systems having eight π-electrons should be especially pronounced in the case of six-membered rings for steric and electronic reasons. Such systems are found primarily in anionic, but also in neutral, heterocycles containing hetero ring members which possess electron pairs capable of delocalizing into the π-system. The production and reactivity of such systems are investigated and their biological significance discussed.
TL;DR: A distributed parameter filter was used to estimate the transient temperature profile in an aluminum slab subject to heating and cooling, producing good state estimates even with only one thermocouple measurement and with rather high measurement noise.
TL;DR: In this article, the phosphorus azides P(N3)3 (I), PO(N 3)3(II), and P3)5 (III) are prepared by reaction of the corresponding PCl-compounds and sodium azide.
Abstract: Die Phosphorazide P(N3)3 (I), PO(N3)3 (II), und P(N3)5 (III) lassen sich durch Umsetzung der entsprechenden PCl-Verbindungen und Natriumazid darstellen. III zerfallt in Losung leicht in I und Stickstoff. Die Schwingungsspektren werden diskutiert. III ist kovalent aufgebaut und besitzt D3h-Symmetrie.
Phosphorus Azides and their Vibrational Spectra
The phosphorus azides P(N3)3 (I), PO(N3)3 (II), and P(N3)5 (III) are prepared by reaction of the corresponding PCl-compounds and sodium azide. III decomposes in solution to I and nitrogen. The vibrational spectra are assigned and discussed. III is covalent and has D3h symmetry.
TL;DR: In this paper, a Fortschrittsbericht liegt der Gedanke zugrunde, das die elektronische Destabilisierung von Systemen with acht π-Elektronen bei sechs-gliedrigen Ringen aus sterischen und electronischen Grunden besonders ausgepragt sein sollte.
Abstract: Die Begriffe „aromatisch” und „antiaromatisch” haben in den letzten Jahren ein breites Interesse gefunden. Unabhangig von der haufig gefuhrten Diskussion um Worte bleibt als Tatbestand: Der Energieinhalt ist bei planaren Systemen mit cyclischer Elektronendelokalisation von der Zahl und von der Orbitalwechselwirkung der beteiligten Elektronen abhangig. Diesem Fortschrittsbericht liegt der Gedanke zugrunde, das die elektronische Destabilisierung von Systemen mit acht π-Elektronen bei sechsgliedrigen Ringen aus sterischen und elektronischen Grunden besonders ausgepragt sein sollte. Dabei kommen vor allem anionische, aber auch neutrale Heterocyclen mit Heteroringgliedern, welche in das π-System delokalisierbare Elektronenpaare besitzen, in Betracht. Die Erzeugung und Reaktivitat solcher Systeme wird untersucht und ihre biologische Bedeutung diskutiert.
TL;DR: In this article, the authors present a fully nonlinear stochastic theory of chemical reactions closely below, at and above instability points, using the Prigogine-Lefever-Nicolis model of two interacting kinds of molecules.
Abstract: We present a fully nonlinear stochastic theory of chemical reactions closely below, at and above instability points. As explicit example we treat the Prigogine-Lefever-Nicolis model of two interacting kinds of molecules, generalizing it to two and three dimensions, to a mode continuum, and taking into account fluctuations. Adopting a description by means of birth and death processes we establish the master-equation, and proceed to the Fokker-Planck equation. This is transformed to new coordinates connected with unstable and stable modes. After adiabatic elimination of the stable modes, we obtain a functional Fokker-Planck equation for a continuous set of “unstable” modes. This final equation can now be treated by standard methods. In one dimension our results reveal striking analogies to the Ginzburg-Landau theory of superconductivity, to the continuous mode laser and to small-band excitations at hydrodynamical instabilities, while in three dimensions, in thin layers a hexagonal structure similar to Benard cells occurs.
TL;DR: In this article, a hot transition in the action spectrum and microscopic electron mobilities were observed in single crystals of the zone-refined charge-transfer complex anthracene-pyromellitic-dianhydride.
TL;DR: The structure of the grafted polymer can be described as mutually-penetrating, ellipsoidally-deformed random coils fixed to the silica surface.
Abstract: Durch eine radikalische Polymerisationsreaktion wird Polystyrol kovalent an die Oberflache von Siliciumdioxid gebunden. Die Pfropfreaktion wird ausgelost durch kovalent an der SiO2-Oberflache gebundene Phenylradikale, die durch thermischen Zerfall von Phenyl-diazo-thioathergruppen entstehen. Die Menge des aufgepfropften Polymeren ist abhangig von den Reaktionsparametern Zeit, Temperatur und Konzentration an Monomerem und an initiierenden Diazogruppen. Die Pfropfpolymerisation verlauft in heterogener Phase nach dem fur radikalische Polymerisationen bekannten Zeitgesetz in 1. Ordnung bezuglich Monomerkonzentration und ist beendet, wenn initiierende Radikale infolge von Rekombinationen oder sterischer Hinderung an der SiO2-Oberflache die Polymerisation nicht mehr auslosen konnen.
Der kovalente Charakter der Bindung zwischen Polymerem und Siliciumdioxid wird IR-spektroskopisch und durch Adsorptions-Desorptions-Versuche nachgewiesen. Die durch die radikalische Polyreaktion an der Oberflache gebundene Menge an Polymerem ist um eine bis zwei Grosenordnungen groser als die irreversibel adsorptiv gebundene. Die Struktur der gebundenen Makromolekule kann als solche sich zum Teil durchdringender, elliptoidisch verformter Knauel beschrieben werden.
Polystyrene is covalently bound to the surface of amorphous silica by a radical graft polymerization, which is initiated by phenyl radicals generated by thermal decomposition of covalently bound phenyl-diazo thioether groups. The amount of grafted polymer depends on reaction time, temperature, and concentration of the monomer and the initiating diazo groups. The kinetics of the polymerization reaction obeys a first order in relation to the monomer concentration, up to a conversion of about 70 to 80%. The graft reaction is terminated when initiating radicals are no more available as a result of recombination reactions or sterical hindrance on the silica surface.
The covalent nature of the bond between the macromolecules and the silica surface is shown by means of IR-spectroscopy and by adsorption and desorption experiments. Ten to one hundred times as much polymer can be covalently bound to the silica surface by the radical graft reaction than can be irreversibly adsorbed. The structure of the grafted polymer can be described as mutually-penetrating, ellipsoidally-deformed random coils fixed to the silica surface.
TL;DR: In this paper, a discussion of the most effective methods for the detection and prevention of errors is presented, using a classification of the errors according to various attributes, conclusions can be drawn concerning the possible causes of these errors.
Abstract: Program errors detected during internal testing of the operating system DOS/VS form the basis for an investigation of error distributions in system programs. Using a classification of the errors according to various attributes, conclusions can be drawn concerning the possible causes of these errors. The information thus obtained is applied in a discussion of the most effective methods for the detection and prevention of errors.
TL;DR: In this paper, a comparison of electronic and Mossbauer spectra with the limiting S N 1 rates of ligand loss in aqueous solution for complexes Fe(CN) 5 L ∩- where L is H 2 O, NH 3, pyridine, pyrazine carboxylate, N-methylpyrazinium, dimethyl and tetramethylenesulfoxide is presented.
TL;DR: Water metabolism of llamas and goats under conditions of ad libitum feeding (control) and under restricted food and water intake was measured using tritiated water and under condition of reduced water intake goats reduced food intake more than llamas.
TL;DR: The content of gangliosideand glycoprotein-bound NeuNAc is measured in different areas of the chicken brain during development and the gangLioside pattern is determined.
Abstract: THE CONCENTRATION of N-acetylneuraminic acid (NeuNAc) was found to increase throughout development in the prenatal chicken brain (GRAY & IRWIN, 1973; SCHENGRUND & ROSENBERG, 1971) and the rat brain (HOLIAN et al., 1971; SUZUKI, 1965). In addition the ganglioside patterns of the rat and human brain (SUZUKI, 1965; VANLER et al., 1971) and the embryonic chicken brain (SCHENGRUND & ROSENBERG, 1971) were found to change during development. Corresponding data for the chicken brain, at the time immediately around the hatching and post-hatching stages are however still lacking. We therefore measured the content of gangliosideand glycoprotein-bound NeuNAc in different areas of the chicken brain during development and also determined the ganglioside pattern.