Showing papers by "University of Stuttgart published in 1990"

Energy-adjustedab initio pseudopotentials for the second and third row transition elements

Abstract: Nonrelativistic and quasirelativisticab initio pseudopotentials substituting the M(Z−28)+-core orbitals of the second row transition elements and the M(Z−60)+-core orbitals of the third row transition elements, respectively, and optimized (8s7p6d)/[6s5p3d]-GTO valence basis sets for use in molecular calculations have been generated. Additionally, corresponding spin-orbit operators have also been derived. Atomic excitation and ionization energies from numerical HF as well as from SCF pseudopotential calculations using the derived basis sets differ in most cases by less than 0.1 eV from corresponding numerical all-electron results. Spin-orbit splittings for lowlying states are in reasonable agreement with corresponding all-electron Dirac-Fock (DF) results.

Rapid kinetics of second messenger formation in olfactory transduction

Abstract: OLFACTORY transduction is thought to be mediated by a membrane-bound receptor protein initiating a multistep reaction cascade which ultimately leads to a depolarizing generator current1,2. There is considerable evidence for the involvement of adenylate cyclase in vertebrate olfactory transduction3–6, and some data indicate that phospholipase C may have a central role in insect olfaction7. However, one must show that odorants not only stimulate enzyme activity but also induce changes in concentrations of relevant second messengers. One important criterion for a candidate second messenger of chemo-electrical transduction is that its formation must precede the onset of the odorant-induced membrane permeability changes which proceed on a subsecond time-scale8. Here we report an odorant-induced, transient accumulation of cyclic AMP in isolated olfactory cilia from rats, and the generation of inositol trisphosphate in antennal preparations from insects, both of which show subsecond time courses that are sufficiently rapid to mediate the odorant-regulated permeability of olfactory receptor cells.

Rapid activation of alternative second messenger pathways in olfactory cilia from rats by different odorants.

Abstract: The molecular mechanisms mediating the chemo-electrical signal transduction in olfactory receptor cells are still elusive. In this study odor induced formation of second messengers in rat olfactory cilia was monitored in a subsecond time range using a rapid kinetic device. Application of micromolar concentration of citralva induced a rapid, transient elevation of the cyclic adenosine monophosphate level, whereas the concentration of inositol trisphosphate was not affected. In contrast, pyrazine caused a rise in the concentration of inositol trisphosphate, not affecting the level of cyclic adenosine monophosphate. Analysis of the kinetic parameter for the odorant induced reaction indicated that apparently two systems are operating simultaneously. The activating effects of odorants appear to be mediated via different G-proteins. Thus, at least two different second messenger pathways appear to be involved in olfactory signal transduction.

Nonlocal microplane model for fracture, damage, and size effect in structures

Abstract: A generalized microplane model, which was previously developed to describe tensile cracking and nonlinear triaxial response of brittleplastic materials in compression and shear, is implemented in a

Non-parallel stability of a flat-plate boundary layer using the complete Navier-Stokes equations

Abstract: Non-parallel effects which are due to the growing boundary layer are investigated by direct numerical integration of the complete Navier-Stokes equations for incompressible flows The problem formulation is spatial, ie disturbances may grow or decay in the downstream direction as in the physical experiments In the past various non-parallel theories were published that differ considerably from each other in both approach and interpretation of the results In this paper a detailed comparison of the Navier-Stokes calculation with the various non-parallel theories is provided It is shown, that the good agreement of some of the theories with experiments is fortuitous and that the difference between experiments and theories concerning the branch I neutral location cannot be explained by non-parallel effects

Detuned lasers and the complex Lorenz equations: Subcritical and supercritical Hopf bifurcations

Abstract: By a suitable variable transformation we show that detuned lasers can be described by complex Lorenz equations and establish a close analogy between detuned lasers and baroclinic instability. The analogy enables us to get all analytical and exact results for the second threshold of the detuned single-mode lasers. In order to discriminate sub- from supercritical Hopf bifurcations, we use a combined approach of elimination procedure and normal form techniques to make a systematic calculation of the criterion for both of the systems. The influence of the parameter variations on the nature of the bifurcation is discussed in detail. For detuned lasers it is shown that, if we restrict ourselves to the case of b\ensuremath{\le}1 (b=${\ensuremath{\gamma}}_{\mathrm{?}}$/${\ensuremath{\gamma}}_{\mathrm{\ensuremath{\perp}}}$, i.e., the ratio of the longitudinal to the transversal relaxation constant of the atoms) and not-too-small k (=\ensuremath{\kappa}/${\ensuremath{\gamma}}_{\mathrm{\ensuremath{\perp}}}$, with \ensuremath{\kappa} denoting the cavity relaxation constant) and \ensuremath{\Delta}, for given b and \ensuremath{\Delta} (\ensuremath{\Delta} and k or k and b), there exists a ${\mathit{k}}_{\mathit{c}}$ (${\mathit{b}}_{\mathit{c}}$ or ${\mathrm{\ensuremath{\Delta}}}_{\mathit{c}}$) such that the Hopf bifurcation is subcritical if k${\mathit{k}}_{\mathit{c}}$ (bg${\mathit{b}}_{\mathit{c}}$ or \ensuremath{\Delta}${\mathrm{\ensuremath{\Delta}}}_{\mathit{c}}$) and supercritical if kg${\mathit{k}}_{\mathit{c}}$ (b${\mathit{b}}_{\mathit{c}}$ or \ensuremath{\Delta}g${\mathrm{\ensuremath{\Delta}}}_{\mathit{c}}$). Numerical investigations show that period-doubling bifurcations to chaos exist not only for the subcritical but also for the supercritical case.

Comparative performance study of space priority mechanisms for ATM networks

Abstract: Priorities for buffer access, also called space priorities, are discussed in connection with the asynchronous transfer mode (ATM), which is widely accepted as the basis for the future broadband ISDN. The introduction of priorities enables the ATM layer to adapt the quality of the cell transfer to the quality of service requirements of the specific broadband ISDN services in order to improve the utilization of the network resources. A description is given of different space priority mechanisms and their performance evaluation. A comparative performance study of these concepts is given, indicating the good performance characteristics of a simple buffering scheme called partial buffer sharing. >

A hypersingular boundary integral method for two-dimensional screen and crack problems

Abstract: We analyze hypersingular integral equations on a curved open smooth arc in R 2 that model either curved cracks in an elastic medium or the scattering of acoustic and elastic waves at a hard screen. By using the Mellin transformation we obtain sharp regularity results for the solution of these equations in Sobolev spaces in the form of singular expansions. In particular we show that the expansions do not contain logarithmic singularities

Different types of dienelactone hydrolase in 4-fluorobenzoate-utilizing bacteria.

Abstract: Of various benzoate-utilizing bacteria tested, Alcaligenes eutrophus 335, A. eutrophus H16, A. eutrophus JMP222, A. eutrophus JMP134, Alcaligenes strain A7, and Pseudomonas cepacia were able to grow with 4-fluorobenzoate as the sole source of carbon and energy. P. cepacia also utilizes 3-fluorobenzoate. Except for A. eutrophus JMP134, which is known to grow with 2,4-dichlorophenoxyacetate and 3-chlorobenzoate (R. H. Don and J. M. Pemberton, J. Bacteriol. 145:681-686, 1981), the strains were unable to grow at the expense of these compounds or 4-chlorobenzoate. Assays of cell extracts revealed that all strains express dienelactone hydrolase and maleylacetate reductase activities in addition to enzymes of the catechol branch of the 3-oxoadipate pathway when growing with 4-fluorobenzoate. Induction of dienelactone hydrolase and maleylacetate reductase apparently is not necessarily connected to synthesis of catechol 1,2-dioxygenase type II and chloromuconate cycloisomerase activities, which are indispensable for the degradation of chlorocatechols. Substrate specificities of the dienelactone hydrolases provisionally differentiate among three types of this activity. (i) Extracts of A. eutrophus 335, A. eutrophus H16, A. eutrophus JMP222, and Alcaligenes strain A7 convert trans-4-carboxymethylenebut-2-en-4-olide (trans-dienelactone) much faster than the cis-isomer (type I). (ii) The enzyme present in P. cepacia shows the opposite preference for the isomeric substrates (type II). (iii) Cell extracts of A. eutrophus JMP134, as well as purified dienelactone hydrolase from Pseudomonas strain B13 (E. Schmidt and H.-J. Knackmuss, Biochem. J. 192:339-347, 1980), hydrolyze both dienelactones at rates that are of the same order of magnitude (type III). This classification implies that A. eutrophus JMP134 possesses at least two different dienelactone hydrolases, one of type III encoded by the plasmid pJP4 and one of type I, which is also present in the cured strain JMP222.

Electrochemical Reduction of Carbon Dioxide on Conductive Metallic Oxides

Abstract: Faradaic efficiencies and current‐voltage characteristics for the reduction of on various conductive oxide mixtures (, , , , ) were determined. Product analysis was performed by gas chromatography. Electrodes composed of and show high current efficiencies for methanol production when polarized near the equilibrium potential of hydrogen evolution in solutions of saturated with . It can be concluded from the Tafel slopes that the first electron transfer is the rate‐limiting step in the reduction of on the investigated oxides in acidic media.

Composition Factors from the Group Ring and Artin's Theorem on Orders of Simple Groups

Abstract: The integral group ring of a finite group determines the isomorphism type of the chief factors of the group. Two proofs are given, one of which applies Cameron's and Teague's generalisation of Artin's theorem on the orders of finite simple groups to the orders of characteristically simple groups. The generalisation states that a direct power of a finite simple group is determined by its order with the same two types of exception which Artin found. Its proof, given here in detail, adapts and makes explicit certain functions of a natural number variable which Artin used implicitly. These functions contribute to the argument through a series of tables which supply their values for the orders of finite simple groups.

Strategies for Solving the Vertical Datum Problem Using Terrestrial and Satellite Geodetic Data

Abstract: The classical procedure of establishing precise height networks is based upon geodetic levelling, potentially including gravity information along the levelling lines. Since levelling is a relative operation some vertical datum must be fixed in order to determine “absolute” heights of benchmarks. In most cases the vertical datum of a height network has been defined by assigning zero height to the long-term mean value of local sea level observed at a fundamental tide gauge station. The vertical datum of largely extended height networks has often been fixed by employing several tide gauge stations situated along the coastline. In any case the definition of datum of classical vertical networks is connected with the concept of local mean sea level; the equipotential surface of the earth’s gravity field passing through the fundamental tide gauge mark is the reference surface of heights derived from levelling.

Biological effects of shock-waves

Abstract: Extracorporeal shock wave lithotripsy has become established worldwide as the method of choice for the treatment of nephrolithiasis and ureterolithiasis over the last 10 years. Although initial studies showed no damaging effects of the shock waves on organs and tissues, numerous recent reports have presented evidence for severe acute effects and chronic complications after shock wave treatment. The pathophysiological effects on kidneys and the histopathological effects on organs or tissues in man and animal, and also the effects on cells in culture and tumors are sumarized. Suspended and immobilized cell cultures were used to characterize and quantify the efficacy of shock wave. Extended applications of shock waves and possible modifications to shock wave generators are discussed.

Elliptic genera, involutions, and homogeneous spin manifolds

Abstract: We study the normalized elliptic genera Φ(X)=ϕ(X)/e k/2 for 4k-dimensional homogeneous spin manifolds X and show that they are constant as modular functions. The basic tool is a reduction formula relating Φ(X) to that of the self-intersection of the fixed point set of an involution γ on X. When Φ(X) is a constant it equals the signature of X. We derive a general formula for sign(G/H), G⊃H compact Lie groups, and determine its value in some cases by making use of the theory of involutions in compact Lie groups.

Thermal vacancies and positron-lifetime measurements in Fe 76.3 Al 23.7

Abstract: The formation of thermal vacancies in the intermetallic compound ${\mathrm{Fe}}_{76.3}$${\mathrm{Al}}_{23.7}$ was investigated between 20 and 1060 \ifmmode^\circ\else\textdegree\fi{}C by positron-lifetime measurements. The positron lifetime ${\mathrm{\ensuremath{\tau}}}_{\mathit{f}}$=112 ps at 20 \ifmmode^\circ\else\textdegree\fi{}C indicates that no structural vacancies can be detected. The increase of the mean positron lifetime \ensuremath{\tau}\ifmmode\bar\else\textasciimacron\fi{} due to thermal vacancy formation starts at relatively low temperatures (${\mathit{T}}_{3}$=475 \ifmmode^\circ\else\textdegree\fi{}C). The fit of a simple two-state trapping model to the temperature variation of \ensuremath{\tau}\ifmmode\bar\else\textasciimacron\fi{} yields an effective vacancy formation enthalpy ${\mathit{H}}^{\mathit{F}}$=1.18\ifmmode\pm\else\textpm\fi{}0.04 eV, which suggests a thermal vacancy concentration at the melting temperature of several atomic percent which is much higher than in pure metals and similar to that found in some intermetallic compounds with a B2 structure. From a comparison with self-diffusion results, a vacancy migration enthalpy of ${\mathit{H}}^{\mathit{M}}$=1.4--1.6 eV is deduced. The phase transitions in the present alloy are discussed in terms of vacancy formation and migration.

What Can Research on Teacher Thinking Contribute to Teacher Preparation? A Second Opinion:

Abstract: Recent reviews suggest that research can only provide teacher educators with food for thought, observational methods, and rationales for current practice. Although each of those contributions is valuable, research on teaching and teacher education can provide even more. It is inappropriate to turn research results into teaching prescriptions and teacher-testing systems, but research knowledge still can, and should, play a substantive, constructive role in teacher education.

Reconstitution of CF0F1 into liposomes using a new reconstitution procedure.

Abstract: The H+-ATPase (ATP synthase) from chloroplasts was isolated, purified and reconstituted into phosphatidylcholine/phosphatidic-acid liposomes. Liposomes prepared by reverse-phase evaporation were treated with various amounts of Triton X-100 and protein incorporation was studied at each step of the solubilization process. After detergent removal by SM2-Biobeads, the activities of the resulting proteoliposomes were measured indicating that the most efficient reconstitution was obtained by insertion of the protein into preformed, detergent-saturated liposomes. The conditions for the reconstitution were optimized with regard to ATP synthesis driven by an artificially generated ΔpH/ΔΨ. An important benefit of the new reconstituted CF0F1 liposomes is the finding that the rate of ATP synthesis remains constant up to 10 s, indicating a low basal membrane permeability.

Purification and characterization of dichloromuconate cycloisomerase from Alcaligenes eutrophus JMP 134.

Abstract: Dichloromuconate cycloisomerase from Alcaligenes eutrophus JMP 134 was purified to homogeneity. The enzyme has an Mr of about 270,000 as determined by gel filtration and consists of six to eight subunits of identical Mr 40,000 as determined by SDS/PAGE. Mn2+ ions as well as thiol groups are required for activity. A high Km value of about 4 mM for cis,cis-muconate explains the reported low activity with this compound. Relatively high Km values were also calculated for monochloro-substituted cis,cis-muconates (300-500 microM), in contrast with the low Km value of 20 microM for 2,4-dichloro-cis,cis-muconate. The catalytic constant of the pure enzyme was 3820 min-1 when measured with 2,4-dichloro-cis,cis-muconate.

Modified Green Functions in the Theory of Heterogeneous and/or Anisotropic Linearly Elastic Media

Abstract: The concept of the modified Green function, defined as certain second derivatives of the conventional tensor Green function, has been proved useful in solving elastic (and other) problems in the media of complicated constitution, such as heterogeneous or anisotropic continua. Emphasis is laid on infinite media. Contrary to the conventional approach, situations with finite stress and strain in the infinite regions are also investigated. Depending on the conditions four modified Green functions appear. These are limits of the four (modified) Green functions of finite bodies that grow beyond bounds. Certain properties of these functions are illustrated of the two basic boundary value problems of potential theory, assuming that the growing bodies are spheres. It is shown that the concept of modified Green functions is particularly useful in the elasticity theory of random media.

An evaluation of some systematic error sources affecting terrestrial gravity anomalies

Abstract: Terrestrial free-air gravity anomalies form a most essential data source in the framework of gravity field determination. Gravity anomalies depend on the datums of the gravity, vertical, and horizontal networks as well as on the definition of a normal gravity field; thus gravity anomaly data are affected in a systematic way by inconsistencies of the local datums with respect to a global datum, by the use of a simplified free-air reduction procedure and of different kinds of height system. These systematic errors in free-air gravity anomaly data cause systematic effects in gravity field related quantities like e.g. absolute and relative geoidal heights or height anomalies calculated from gravity anomaly data.

The differential geometry of elementary point and line defects in Bravais crystals

Abstract: Since line defects (dislocations) and point defects (vacancies, self-interstitials, point stacking faults) in Bravais crystals can mutually convert, only theories which comprise these two sorts of defects can be closed in the sense of general field theory. Since the pioneering work of Kondo and of Bilby, Bullough, and Smith it is clear that differential geometry is the appropriate mathematical tool to formulate a field theory of defects in ordered structures. This is done here on the example of the Bravais crystal, where the above-mentioned defects are the only elementary point and line defects. It is shown that point defects can be described by a step-counting procedure which makes it possible to include also point stacking faults as elementary point defects. The results comprise two equations with the appropriate interpretation of the mathematical symbols. The point defects are step-counting defects and are essentially described by a metric tensorg, which supplements the torsion∑ responsible for the dislocations. The proposed theory is meant to form a framework for defect phenomena, in a similar way that Maxwell's theory is a framework for the electromagnetic world.