Showing papers by "University of Stuttgart published in 1986"

NLPQL: A fortran subroutine solving constrained nonlinear programming problems

Abstract: NLPQL is a FORTRAN implementation of a sequential quadratic programming method for solving nonlinearly constrained optimization problems with differentiable objective and constraint functions. At each iteration, the search direction is the solution of a quadratic programming subproblem. This paper discusses the organization of NLPQL, including the formulation of the subproblem and the information that must be provided by a user. A summary is given of the performance of different algorithmic options of NLPQL on a collection of test problems (115 hand-selected or application problems, 320 randomly generated problems). The performance of NLPQL is compared with that of some other available codes.

A stochastic theory of phase transitions in human hand movement

Abstract: The order parameter equation for the relative phase of correlated hand movements, derived in a previous paper by Haken et al. (1985), is extended to a time-dependent stochastic differential equation. Its solutions are determined close to stationary points and for the transition region. Remarkably good agreement between this theory and recent experiments done by Kelso and Scholz (1985) is found, and new predictions are offered.

Consistent linearization for path following methods in nonlinear FE analysis

Abstract: This paper is focussed on path following methods which are derived from consistent linearizations. The linearization procedure leads to some well-known constraint equations—like the constant arc length in the load-displacement space—and to different formulations than those given in the literature. A full Newton scheme for the unknown quantities (displacements and load parameter) can be formulated. A comparison of the derived algorithms with other path following methods is included to show advantages and limits of the methods. Using the linearization technique together with scaling a family of path following methods is introduced. Here, the scaling bypasses physical inconsistencies associated with mixed quantities like displacements and rotations in the global vector of the unknowns. Several possible scaling procedures are derived from a unified formulation. A discussion of these methods by means of numerical examples shows that up to now the choice of the scaling procedure is problem-dependent. If the arc-length methods are combined with a modified Newton method, an enhancement of the algorithms is achieved by line search techniques. Here, a simple but efficient line search was implemented and compared with a numerical relaxation technique. Both methods improve the convergence rate considerably.

Min-max heaps and generalized priority queues

Abstract: A simple implementation of double-ended priority queues is presented The proposed structure, called a min-max heap, can be built in linear time; in contrast to conventional heaps, it allows both FindMin and FindMax to be performed in constant time; Insert, DeleteMin, and DeleteMax operations can be performed in logarithmic timeMin-max heaps can be generalized to support other similar order-statistics operations efficiently (eg, constant time FindMedian and logarithmic time DeleteMedian); furthermore, the notion of min-max ordering can be extended to other heap-ordered structures, such as leftist trees

Intrastriatal injection of DL-2-amino-5-phosphonovaleric acid (AP-5) induces sniffing stereotypy that is antagonized by haloperidol and clozapine.

Abstract: DL-2-amino-5-phosphonovaleric acid (AP-5), which blocks glutamatergic transmission at the NMDA-preferring receptor, was injected into the antero-dorsal striatum of rats. AP-5-induced behavioural changes were assessed i) using a stereotypy rating scale and ii) using an experimental chamber designed to quantify sniffing. In both behavioural situations it was shown that AP-5 (10 micrograms/0.5 microliter) induced continuous intensive sniffing similar to that induced by small doses of systemically administered amphetamine or apomorphine. However, oral stereotypies were not induced by AP-5. Systemically injected clozapine (5 and 10 mg/kg SC) as well as haloperidol (0.1 mg/kg IP) antagonized AP-5-induced sniffing. These results show that besides dopamine receptors, NMDA receptors are involved in the control of sniffing. In behavioural terms, the effect of glutamate mediated by the NMDA receptor in the striatum is opposite to that of dopamine.

Diffusion of gold in dislocation-free or highly dislocated silicon measured by the spreading-resistance technique

Abstract: The diffusion of Au in dislocation-free or plastically deformed Si (1011 to 1013 dislocations/m2) was measured with the aid of the spreading-resistance technique. The Au profiles produced indislocation-free Si slices by in-diffusion from both surfaces possess nonerfc-type U shapes as predicted by the so-called kick-out diffusion model. This model is used to calculate the contribution of self-interstitials to the (uncorrelated) Si self-diffusion coefficient,D =0.064×exp(−4.80 eV/kT)m2 s−1, from the present and previous data on the diffusivity and solubility of Au in Si in the temperature range 1073–1473 K. Inhighly dislocated Si the diffusion of Au is considerably faster than in dislocation-free Si. From the erfc-type penetration profiles found in this case, effective Au diffusion coefficients were deduced and combined with data on the solubility of Au in Si. ThusC D i=0.0064 ×exp(−3.93 eV/kT)m2 s−1 was obtained in the temperature range 1180–1427 K, whereC andD i are the solubility and diffusivity of interstitial Au in Si.

The polynomial-time hierarchy and sparse oracles

Abstract: Questions about the polynomial-time hierarchy are studied. In particular, the questions, “Does the polynomial-time hierarchy collapse?” and “Is the union of the hierarchy equal to PSPACE?” are considered, along with others comparing the union of the hierarchy with certain probabilistic classes. In each case it is shown that the answer is “yes” if and only if for every sparse set S, the answer is “yes” when the classes are relativized to S if and only if there exists a sparse set S such that the answer is “yes” when the classes are relativized to S. Thus, in each case the question is answered if it is answered for any arbitrary sparse oracle set.Long and Selman first proved that the polynomial-time hierarchy collapses if and only if for every sparse set S, the hierarchy relative to S collapses. This result is re-proved here by a different technique.

Design of dies for the extrusion of sheets and annular parisons: The distribution problem

Abstract: A systematic design of the classical “coat hanger” die is proposed and tested experimentally. The objectives of the design are 1. distribution of the polymer over the width of the die before it reaches the final lip section for thickness adjustment, 2. invariance of distribution to flow rate, 3. invariance to changes in polymer viscosity, and 4. uniform average residence time. The die design is based on a flow model which assumes power-law viscosity, steady shear flow In each cross-section, uniform temperature, and separation of the flows into a manifold component and a component in a slit section of uniform height. The design corrects for an oversimplification of the pressure gradient that was applied in previous studies; and it differs from previous designs by suggesting a rectangular cross-section for the manifold. Applications to side-fed dies for extrusion blow molding and to a sheet extrusion die achieved uniform distribution and did not require any additional flow corrections (such as choker bars or flexible lips). With the new design, the lip region of the die can freely be used for thickness control, fine tuning, or further shaping of the extrudate.

High power mode conversion for linearly polarized HE11 hybrid mode output

Abstract: Efficient plasma heating by ECR-wave irradiation requires axisymmetric, narrow, pencil-like millimetre wave beams with well-defined polarization. The linearly polarized gaussian-like HE11, mode satisfies these conditions best. This quasi-optical hybrid mode can be generated from TE0n gyrotron mode compositions by the two multi-step mode conversion processes: (1) ΣTE0n to TE01 to TE11 to HE11 or (2) ΣTE0n to TE01 to TM11 to HE11. The first scheme has the advantage that the converters can all be made without bends, allowing an arbitrary choice and fast change of the polarization plane. The second scheme does not exhibit this advantage, but it is more suitable at very high frequencies (e.g. 140GHz) because efficient TE01-to-TM11 transducers can be made considerably shorter than serpentine TE01-to-TE11 mode converters. This paper presents computations on mode converter systems of the first type at 70GHz and of both types at 140GHz (ID = 27 · 8 mm for 200kW transmission lines). The structure of wall perturbati...

Microwave Penetration and Attenuation in Desert Soil: A Field Experiment with the Shuttle Imaging Radar

Abstract: Receivers buried in the Nevada desert were used with the Shuttle Imaging Radar to measure microwave attenuation as a function of soil moisture in situ. Results agree closely with laboratory measureements of attenuation and suggest that penetration of tens of centimeters in desert soils is common for L-band (1.2-GHz) radar.

The phoshate mineral associations of the Tsaobismund pegmatite, Namibia

Abstract: A detailed mineralogical investigation using the classical methods of identification by X-ray diffraction and by optical properties in thin sections, has revealed thirty one phosphate minerals occurring in the Tsaobismund pegmatite. This investigation is complemented by wet chemical and, mainly, electron microprobe analyses performed on the phosphates known to be typomorphic or considered to be relevant to the hydrothermal alteration. Additionally, microprobe analyses are also given for garnet, gahnite, and ferrocolumbite associated with the phosphates. On the basis of their chemical composition, particularly in terms of their Fe, Mn, and Mg contents, three types of triphylites are distinguished. Triphylite 1 only occurs as a primary phase, triphylite 2 shows exsolution lamellae of sarcopside, and triphylite 3 is partly replaced by a fluorophosphate of the triplite-zwieselite series. These minerals constitute three generations of the parent phases, which were progressively transformed by metasomatic processes, hydrothermal alteration, and by weathering, to give finally three types of complex associations. The Li(Fe,Mn)PO4 minerals appear to be more sensitive to such transformations than those of the (Fe,Mn)2PO4F series. Four main stages of hydrothermal alteration processes have been recognized in the Tsaobismund pegmatite: (i) the Mason-Quensel sequence results from a progressive oxidation of Fe and Mn, and a concomitant Li-leaching of triphylite yielding ferrisicklerite and heterosite, successively; (ii) the metasomatic exchange of Na for Li produces alluaudite; in the present case, the formation of hagendorfite from triphylite 2 is considered to be earlier than the generation of alluaudite-Na□ occurring in the three associations; (iii) the hydration phase mainly transforms the parent Li(Fe,Mn)PO4 phase into grey hureaulite, associated with barbosalite and tavorite; (iv) the formation of fluorapatite, not particularly widespread, replaces alluaudite-Na□, as well as zwieselite s.l. The following crystallization sequence of the initially formed phosphate minerals is proposed: triphylite 1 → triphylite 2 + sarcopside (associated with garnet) → triphylite 3 + zwieselite s.l. The most prominent feature of this succession is the increase in the Mg and Zn contents in the composition of the phosphates, as well as the decrease in their Li contents. The variations of the Fe/Mn ratios in this sequence are discussed. The succession triphylite-zwieselite within weakly differentiated and Li-poor pegmatites is of general significance.

Structure of pressinoic acid: the cyclic moiety of vasopressin.

Abstract: Arginine vasopressin consists of a 20-membered, disulfide-linked macrocyclic ring system called pressinoic acid to which is attached a COOH-terminal tripeptide. The molecular conformation of pressinoic acid has been determined from single crystal x-ray diffraction data. The 20-membered macrocyclic ring, stabilized by two intramolecular hydrogen bonds, has a type I beta-bend centered on Gln4 and Asn5 and a highly distorted type II' bend centered on Phe3 and Gln4. In vasopressin the Asn5 side chain extends away from the macrocyclic ring system and hydrogen bonds to the terminal tripeptide, but in pressinoic acid the Asn5 side chain lies over the molecule and forms a strong hydrogen bond to the nitrogen of Tyr2. The absence of pressor activity in pressinoic acid may be a result of both the loss of the COOH-terminal tripeptide and the incorrect orientation of the Asn5 side chain. Whether this class of hormones has pressor or oxytocic activity is determined by the orientation of the Tyr2 side chain, that is, whether it is extended away from or over the ring system, respectively. In pressinoic acid, the Tyr2 side chain is in the expected "pressor conformation," that is, extended away from the ring system, and is stabilized through a hydrophobic interaction with the Phe3 side chain. Thus, the conformation of the pressinoic acid molecule partly explains the activity of vasopressin-like hormones.

An application of correlation energy density functionals to atoms and molecules

Abstract: Four density functionals — including that recently introduced by Perdew ((1986) Phys Rev B33: 8822)—are tested for first-row atoms, hydrides and dimers. Calculated contributions of the correlation energy to the ionization potentials and electron affinities of atoms and to the dissociation energies of molecules are compared with “empirical” values which were reevaluated for this purpose. An improvement over Hartree-Fock is found in all cases if the self-interaction or the gradient correction are included in the density functional, although there is a rather large variation in the accuracy of the predictions.

Effect of powder particle morphology on the sintering behaviour of polymers

Abstract: The sintering behaviour of several amorphous and semicrystalline polymeric powders was studied. The coalescence of particles of polystyrene, PMMA and polyethylene of various molecular weights was photographically followed. The coalescence of the amorphous materials was found to depend on the common parameters affecting sintering including particle size and polymer viscosity. However, unexpectedly fast sintering was observed for the crystalline polyethylenes. The dominating factor in their coalescence, unaccounted for by the Frankel expression, is the internal particle morphology which increases the total particle surface energy. The polyethylene particles were actually found to be aggregates of small nodules, less than 1μm in diameter, interconnected by a very fine fibrillar network. It is concluded that some semicrystalline high viscosity polymers, known to be unprocessable by common methods, do sinter due to their highly developed internal particle morphology.

Ultrastructural localization of calcium in the CNS of vertebrates.

Abstract: The ultrastructural localization of calcium in synaptic areas of the CNS of fish was investigated. Prefixation with phosphate-buffered glutaraldehyde followed by post-fixation with osmium/potassium-bichromate was used to precipitate and visualize endogenous calcium without the addition of external calcium. The presence of calcium in the electron-dense precipitates produced using this method was demonstrated by electron spectroscopic imaging using a Zeiss EM-902 transmission electron microscope, and in various control experiments using the calcium chelator EGTA. In the optic tectum of fish, electron dense precipitates containing calcium were found not only in intracellular compartments, e.g. the smooth endoplasmic reticulum, mitochondria and synaptic vesicles, but also at extracellular locations, particularly in synaptic clefts. In the extracellular sites, only chelat complexes of ionic calcium were found. This would seem to be in agreement with electrophysiological and biochemical data reported in earlier studies. Thus, using the present method, it should be possible to obtain further ultrastructural information concerning the mechanisms of synaptic transmission.