Showing papers by "University of Stuttgart published in 1983"

Canonical form observer design for non-linear time-variable systems

Abstract: An observer of canonical (phase-variable) form for non-linear time-variable systems is introduced. The development of this non-linear time-variable form requires regularity of the non-linear time-variable- observability matrix of the system. From the relationships derived during the development, it follows that a non-linear time-variable observer can be dimensioned by an eigenvalue assignment with respect to the canonical state coordinates if a linearization of system non-linearities about the reconstructed state trajectories is permissible. This is an assumption similar to that of the extended Kalman filter based on a linearization about the current estimate.

A Comparative Performance Evaluation of 27 Nonlinear Programming Codes

Abstract: The numerical performance of 27 computer programs, which are all designed to solve the general constrained nonlinear optimization problem, is to be evaluated. In contrast to Schittkowski [34], where besides of one exception, the same codes are compared on randomly generated test problems, the test examples are now given by the 115 hand-selected and real life problems published in Hock and Schittkowski [19]. The different type of the test examples requires the development of a special evaluation system based on priority theory. Detailed numerical results are presented allowing a quantitative comparison of the performance criteria efficiency and reliability.

ACYL- AND ALKYLIDENEPHOSPHINES. XXI.1 Acylphosphines and Their Derivatives with Phosphorus Atoms of Coordination Number 3, 2, and 1

Abstract: The following article summarizes our work on acylphosphines and acylphosphides as well as on alkylidene- and alkylidynephosphines, most of which were thought only thirty years ago not to exist under ordinary conditions.

Synopsis and Introduction

Abstract: The human brain is probably the most complex system we know. From a global point of view it is organized in localizable functional units such as the visual cortex, the speech center, etc. Its individual components, the neurons, can be made visible by stains. According to present days estimates there are 1010 – 1011 neurons in the brain. An individual neuron may have several hundred or more dendrites as input lines transmitting signals from other neurons. Depending on the specific classification scheme used, there are a dozen to several dozens of different types of neurons. There is increasing evidence that in the visual cortex and possibly other parts of the brain neurons are organized within functional subunits in the form of columns whose boundaries are to some extent flexible. These few remarks make it clear how complex the structure of the brain may be.

The effect of tensile stresses on the magnetic properties of Co58Fe5Ni10Si11B16 amorphous alloys

Abstract: For the amorphous alloy of nominal composition Co53Fe5Ni10Si11B16 magnetic properties such as the anisotropy energy, the initial susceptibility, the coercive field, and the remanent magnetization are investigated at room temperatue as functins of an applied tensile stress. From an analysis of the magnetization process in the presence of applied and internal stresses the mean value of the compressive internal stresses and the saturation magnetostriction constant are determined. In der amorphen Legierung Co58Fe5Ni10Si11B16 wird der Einflus von auseren Zugspannungen auf magnetische Kenngrosen, wie Anisotropieenergie, Anfangssuszeptibilitat, Koerzitivfeldstarke und Remanenz untersucht. Aus der Analyse der Magnetisierungsvorgange unter Einflus von inneren und auseren Spannungen konnen der Mittelwert der Druckspannungne sowie die Magnetostriktionskonstante bestimmt werden.

Zufall und Notwendigkeit

Abstract: Wir verfolgen einen Ball, der von einem Fusballspieler uber den Rasen gedribbelt wird. Seine Geschwindigkeit υ wird sich aus zwei Grunden andern. Einmal wird das Gras durch die Reibung die Geschwindigkeit des Balles kontinuierlich reduzieren, andererseits wird der Fusballspieler durch zufallige Stose die Geschwindigkeit des Balls erhohen. Die Bewegungsgleichung fur den Fusball wird durch das Newtonsche Gesetz prazise beschrieben: Masse × Beschleunigung = Kraft, d.h. $$m\, \cdot \,\dot \upsilon \, = \,F.$$ (6.1)

Ionization of the Direct-Gap Exciton in Photoexcited Germanium

Abstract: The excitonic absorption at the direct gap in Ge is measured as a function of the density and temperature of excitations at the indirect gap. The spectra are analyzed by means of a many-body theory which is valid for arbitrary free-carrier densities. The critical densities for the ionization are determined for temperatures from 8.5 to 60 K and compared with other predictions.

Quad Trees, a Datastructure for Discrete Vector Optimization Problems

Abstract: The datastructure “quad tree” is used to identify efficent solutions of discrete vector optimization problems. This datastructure is very well suited to support several types of searches among the set of efficient solutions. Computational experiences with the construction of the set of efficient solutions of some randomly generated test problems are reported.

Complex time path integrals beyond the stationary phase approximation: decay of metastable states and quantum statistical metastability

Abstract: The complex-time path-integral expression for $\mathrm{Tr}{(E\ensuremath{-}H)}^{\ensuremath{-}1}$ is reexamined and applied to barrier-penetration effects in quantum mechanics and field theory. Shortcomings of the conventional method for low-lying states are analyzed and resolved. This is achieved by an appropriate treatment of quasisymmetry modes occurring in the path integral and by computing certain contributions to the Fourier transform of the path integral without a stationary-phase approximation. We obtain agreement with the results of the instanton method for the ground state. For growing quantum numbers our results smoothly approach those of the standard WKB approximation. We also consider a scalar field theory with a false vacuum and compute the decay rates ${\ensuremath{\Gamma}}_{n}$ of $n$-meson states built thereon. Final emphasis is placed on the quantum-statistical metastability of a grand canonical ensemble of these mesons at temperature ${\ensuremath{\beta}}^{\ensuremath{-}1}$.

Amplified spontaneous emission (ASE) in laser oscillators and amplifiers

Abstract: Dye-laser oscillators and amplifiers are studied theoretically with inclusion of amplified spontaneous emission (ASE). Assuming pencil-like geometry in both cases, laser signal intensity and ASE intensity are described with appropriate photon-transport equations. In particular, there exist different boundary conditions fox both fluxes in the laser cavity case due to the different feedback behavior of an optical resonator for laser modes and ASE modes. The interaction of laser output and ASE intensity is discussed in detail, including laser output optimization without and with ASE effects. For single- and double-pass amplifiers closed-form solutions for gain saturation due to input signal and ASE flux axe also given. More complicated gain functions, such as inclusion of reabsorption in dye lasers, are also treated in some detail.

Involvement of dopaminergic neurotransmission in the control of goal-directed movements

Abstract: Changes produced in dopamine (DA) activity, by administration of the DA-antagonists metoclopramide (10 mg/kg IM) and tiapride (16 mg/kg IM) and of the DA agonists apomorphine (0.5 and 1 mg/kg IM) and bromocriptine (8 mg/kg orally), specifically modified predatory behavior in the ferret. Sulpiride (40 mg/kg IP and 90 mg/kg IM) did not change the behavior. The number of bites necessary to kill the prey was reduced by metoclopramide and tiapride. The number of bites after the death of the prey was not changed. The latency from the first bite to the death of the prey was shortened. Apomorphine and bromocriptine increased the number of bites. The DA receptor blockers haloperidol, chlorpromazine, and clozapine had similar effects to metoclopramide and tiapride, and the DA agonist L-dopa had similar effects to apomorphine and bromocriptine. The pattern of results indicated that, considering the two major DA receptor types, D-2 receptors or D-2 in combination with D-1 but not D-1 receptors alone were involved in the control of goal-directed movements. The results also provided some evidence that blockade of these DA receptors caused a narrowing of the range of exhibited behavioral responses. Stimulation of the DA receptors had opposite effects.

A New CSMA-CD Protocol for Local Area Networks with Dynamic Priorities and Low Collision Probability

Abstract: This paper reports on the implementation of a local area network (LAN) operating under a new CSMA-CD protocol with dynamic priorities (CSMA-CD-DP). User terminals, host computers, and other servers are connected to a common broad-band channel through N network access stations in a clustered manner. This concept reduces the number of network access stations and enhances the utilization of hardware and software resources greatly. A new protocol has been developed which organizes the decentralized operation of the distributed network access stations and which allows for a number of specific features. In the idle state the channel is operated in the contention mode. After the beginning of a transmission, the channel is operated in a reservation mode. Channel arbitration after a completed transmission is resolved by staggered delays; at any time, each station owns a distinct transmission delay which is changed after every successful transmission by broadcasted acknowledgments. This protocol strictly limits the possibility of collisions and approaches the effectiveness of token and polling protocols with increasing load. Through specific allocations of transmission delays, static priorities or dynamic overload control can be realized easily. The performance of the CSMA-CD-DP protocol has been modeled and analyzed analytically as well as by simulation. Results for normal load and overload reveal high throughput and low transfer times which are basic for a wide range of applications in LAN's.

Diffusion and solubility of gold in silicon

Abstract: By means of neutron activation analysis and mechanical sectioning, diffusion and solubility of gold in silicon were investigated from 1371 K to 1073 K and from 1573 K to 1073 K, respectively. The results confirm that in Si, Au diffuses via the so-called kick-out mechanism and that, at least above 1320 K, self-diffusion takes place via an interstitialcy mechanism. Within the framework of the kick-out model from the Au diffusion and solubility data the interstitialcy contribution DSDI to the self-diffusion coefficient between 1371 K and 1073 K was calculated. In this indirect manner DSDI ≈ 2×10-20 cm2s-1 at 1073 K was found. Such a low value could not have been measured by any of the available direct techniques.

Fluctuations in reversible chemical reactions

Abstract: The paper proposes a new approach to describe fluctuations of reversible chemical reactions in closed systems. The deterministic rate laws are cast into the form of nonlinear Onsager type closed laws. By means of nonlinear transport theory a Fokker-Planck equation describing the stochastic process of concentration fluctuations is obtained. It is shown that the stochastic formulation reduces to the correct deterministic rate laws in the thermodynamic limit V → ∞ with the concentrations kept fixed. Concrete examples of reactions in ideal mixtures are given and the results of the presented approach are compared with those of the usual approach by means of a birth and death type master equation. It is shown that both approaches lead to the same stationary probability and exhibit the same natural boundaries reflecting the fact of a restricted state space. The proposed Fokker-Planck equation is different from the Fokker-Planck equation obtained from the master equation by truncating its Kramers-Moyal expansion. However, the two equations are shown to have identical Fokker-Planck coefficients in the vicinity of the deterministic equilibrium state. Compared with the usual master equation approach the proposed stochastic modeling of chemical reactions has the advantage of allowing for a straightforward extension to reactions in non-ideal mixtures.

Phylogenetical aspects of brain gangliosides in vertebrates

Abstract: The concentration and composition of brain gangliosides in 78 vertebrate species belonging to the classes of Agnathes, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves and Mammalia were investigated. 1. An increase in the concentration of gangliosides takes place with anagenetic progress of nervous organization during phylogeny which is accompanied by a simultaneous decrease in the content of neuronal sialo-glycoproteins. This tendency can be observed in the main classes from cartilaginous fishes to mammals and also in smaller taxonomic units such as Elasmobranchia, Salmoniformes, Gadiformes, Percoidea, Notothenoidea, Rodentia. This indicates that gangliosides were more frequently selected than sialo-glycoproteins during vertebrate evolution. 2. Over a phylogenetic series the complexity of brain ganglioside composition is strikingly reduced. Among cold-blooded vertebrates a large number of complex and highly sialylated ganglioside fractions is present in the CNS, whereas in the warm-blooded birds and mammals only few fractions constitute the brain pattern, and these have less polarity. 3. The anagenetic change in the complexity of the brain ganglioside character is correlated to changes in the use of the three biosynthesis pathways of gangliosides (‘b’-pathway in Agnatha, ‘b’ and ‘c’ in cartilaginous and lower bony fishes, ‘a, b, c’ in ancient sturgeons and lungfish, ‘c’ in higher evolved bony fish, ‘b’, ‘c’ in amphibians, ‘b’ and ‘a’ in reptiles and birds and mainly the ‘a’-pathway in highly evolved mammals). 4. The data support the hypothesis that the great variations in concentration and composition of vertebrate brain gangliosides are not only dependent on the phylogenetic level of nervous organisation, but that they may also originate from the state of thermal adaptation. By these variations, vertebrates may be to maintain optimum rates of neuronal transmission while being adapted to different temperature habitats.