Showing papers by "University of Stuttgart published in 1993"

Ab initio energy-adjusted pseudopotentials for elements of groups 13-17

Abstract: Quasi-relativistic energy-adjusted ab initio pseudopotentials for the elements of groups 13–17 up to atomic number 53 (I) are presented together with corresponding energy-optimized valence basis sets. Test calculations for atomic excitation and ionization energies show the reliability of the derived pseudopotentials and basis sets.

A combination of quasirelativistic pseudopotential and ligand field calculations for lanthanoid compounds

Abstract: Improved energy-adjusted quasirelativistic pseudopotentials for lanthanoid atoms with fixed valency are presented and tested in molecular calculations for CeO, CeF, EuO, GdO, YbO, and YbF. The pseudopotential calculations treat the lanthanoid 4f shell as part of the core and yield accurate estimates for average bond lengths, vibrational frequencies and dissociation energies of all states belonging to a superconfiguration. Information for each individual state of the considered superconfiguration may be obtained from subsequent ligand field model calculations. The results of this combined pseudo-potential and ligand field approach (PPLFT) are compared to more accurate calculations with ab initio pseudopotentials that include the lanthanoid 4f orbitals explicitly in the valence shell and to available experimental data.

Stochastic resonance without external periodic force.

Abstract: A model of a two-dimensional autonomous system subject to external noise is investigated. Without noise the system has a stable limit cycle in a certain region of control parameter. Various noise-induced effects have been found numerically, such as a noise-induced frequency shift in the presence of the deterministic limit cycle, and noise-induced coherent oscillations in the absence of the deterministic limit cycle. An interesting result is that the stochastic resonance phenomenon appears in a system without an external signal and when the asymptotic state of the deterministic system is stationary.

Temporal interpretation, discourse relations and commonsense entailment

Abstract: This paper presents a formal account of how to determine the discourse relations between propositions introduced in a text, and the relations between the events they describe. The distinct natural interpretations of texts with similar syntax are explained in terms of defeasible rules. These characterise the effects of causal knowledge and knowledge of language use on interpretation. Patterns of defeasible entailment that are supported by the logic in which the theory is expressed are shown to underly temporal interpretation.

Box Splines

Abstract: This chapter provides a brief introduction to box and half-box splines with particular focus on triangular splines and surface design. A particular example of box splines are the B-splines with equidistant knots. In general, box splines consist of regularly arranged polynomial pieces and they have a useful geometric interpretation. Namely they can be viewed as density functions of the shadows of higher dimensional boxes and half-boxes. Of particular interest for Geometric Design are box spline surfaces that consist of triangular polynomial pieces. These box spline surfaces have planar domains, but it is quite simple to construct arbitrary two-dimensional surfaces, i.e., manifolds, with these box splines.

Accuracy of energy-adjusted quasirelativistic ab initio pseudopotentials

Abstract: The results of valence-only self-consistent field calculations on Hg n+ (n = 0, 1, 2) and HgH n+ (n = 0, 1) using nonrelativistic and quasirelativistic energy-adjusted ab initio pseudopotentials for Hg are compared with corresponding all-electron values from nonrelativistic (Hartree-Fock) and relativistic (Dirac-Fock) atomic as well as from nonrelativistic (Hartree-Fock) and quasirelativistic (Hartree-Fock with no-pair Hamiltonian) molecular calculations. The accuracy of the energy-adjusted ab initio pseudopotential scheme, e.g., the reproduction of the major relativistic effects, is demonstrated both for the atom and the molecule. Correlation effects are included in the quasirelativistic pseudopotential studies by means of large-scale configuration interaction calculations. The quasirelativistic pseudopotential results obtained in the intermediate coupling scheme are in excellent agreement with available experimental data.

EAS‐elements for two‐dimensional, three‐dimensional, plate and shell structures and their equivalence to HR‐elements

Abstract: The enhanced assumed strain (EAS) method, recently proposed by Simo and Rifai13, is used to develop new four-node membrane, plate and shell elements and eight-node solid elements. The equivalence of certain EAS-elements with Hellinger-Reissner (HR) elements is discussed. For instance, the seven-parameter element EAS-7 with 2 × 2 integration is identical to the HR-element of Pian and Sumihara2. Eight-node solid elements which are free of volumetric locking and four-node shell elements which have an improved membrane and bending behaviour, compared to the Bathe-Dvorkin shell element7, are introduced. Numerical tests for linear elastic problems show an improved performance of the EAS-elements.

Cloning and expression of odorant receptors

Abstract: Myriads of odorous molecules that vary widely in structure are nevertheless readily detected and discriminated by the sense of smell, but how this is achieved by the olfactory system has been a long-standing puzzle. Several different models have been proposed, and previous observations indicate that the recognition sites for odorous molecules could be G-protein-coupled receptor proteins, an idea supported by the discovery of a new gene family that probably encodes a diversity of odorant receptors. Here we report the identification of new members of the gene family encoding putative odorant receptors and demonstrate that they are indeed transcribed in olfactory receptor neurons. Furthermore, the receptor-encoding complementary DNA is expressed in non-neuronal surrogate cells, which generate second messenger responses upon stimulation with appropriate odorants, indicating that the receptors recognize odorants and couple to G proteins of the host cells.

Microbial crusts of the late jurassic: Composition, palaeoecological significance and importance in reef construction

Abstract: Upper Jurassic reefs contain variable amounts of calcareous microbial crusts. In examples from Portugal, Spain and southern Germany they occur within coral biostromes and bioherms, mixed coral-siliceous sponge reefs, siliceous sponge meadows and mudmounds, and build up thrombolities with or without additional reef metazoans. The crusts are of paramount importance for the establishment and development of positive buildups. Commonly, reef growth starts with crusts which develop from a narrow base and rapidly expand laterally by rising above the sea floor. Reef associations with little or no microbial crust normally did not develop distinct relief.

Use of 5-cyano-2,3-ditolyl tetrazolium chloride for quantifying planktonic and sessile respiring bacteria in drinking water.

Abstract: Direct microscopic quantification of respiring (i.e., viable) bacteria was performed for drinking water samples and biofilms grown on different opaque substrata. Water samples or biofilms developed in flowing drinking water were incubated with the vital redox dye 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and R2A medium. One hour of incubation with 0.5 mM CTC was sufficient to obtain intracellular reduction of CTC to the insoluble fluorescent formazan (CTF) product, which was indicative of cellular respiratory (i.e., electron transport) activity. This result was obtained with both planktonic and biofilm-associated cells. Planktonic bacteria were captured on 0.2-microns-pore-size polycarbonate membrane filters and examined by epifluorescence microscopy. Respiring cells containing CTF deposits were readily detected and quantified as red-fluorescing objects on a dark background. The number of CTC-reducing bacteria was consistently greater than the number of aerobic CFU determined on R2A medium. Approximately 1 to 10% of the total planktonic population (determined by counterstaining with 4,6-diamidino-2-phenylindole) were respirometrically active. The proportion of respiring bacteria in biofilms composed of drinking water microflora was greater, ranging from about 5 to 35%, depending on the substratum. Respiring cells were distributed more or less evenly in biofilms, as demonstrated by counterstaining with 4,6-diamidino-2-phenylindole. The amount of CTF deposited in single cells of Pseudomonas putida that formed monospecies biofilms was quantified by digital image analysis and used to indicate cumulative respiratory activity. These data indicated significant cell-to-cell variation in respiratory activity and reduced electron transport following a brief period of nutrient starvation.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of two mutated vacuolar proteins reveals a degradation pathway in the endoplasmic reticulum or a related compartment of yeast.

Abstract: The fate of a mutant form of each of the two yeast vacuolar enzymes proteinase yscA (PrA) and carboxypeptidase yscY (CPY) has been investigated. Both mutant proteins are rapidly degraded after entering the secretory pathway. Mutant PrA is deleted in 37 amino acids spanning the processing site region of the PrA pro-peptide. The mutant enzyme shows no activity towards maturation of itself or other vacuolar hydrolases, a function of wild-type PrA. Mutant CPY carries an Arg instead of a Gly residue in a highly conserved region, two positions distant from the active-site Ser. In contrast to wild-type CPY, the mutant form was quickly degraded by trypsin in vitro, indicating an altered structure. Using antisera specific for alpha-1-->6 and alpha-1-->3 outer-chain mannose linkages, no Golgi-specific carbohydrate modification could be detected on either mutant protein. Subcellular fractionation studies located both mutant enzymes in the endoplasmic reticulum. Degradation kinetics of both proteins show the same characteristics, indicating similar degradation pathways. The degradation process was shown to be independent of a functional sec18 gene product and takes place before Golgi-specific carbohydrate modifications occur. The proteasome, the major proteolytic activity of the cytoplasm, is not involved in this degradation event. All degradation characteristics of the two mutant proteins are consistent with a degradation process within the endoplasmic reticulum ('ER degradation').

Quantized periodic orbits in large antidot arrays.

Abstract: The resistivity {\it rho} $_{{\it xx}}$ measured in large antidot arrays as a function of an applied perpendicular magnetic field {\it B} displays distinct quantum oscillations at very low temperatures. These oscillations characteristically differ from conventional Shubnikov-de Haas oscillations which are periodic in 1/{\it B}. A crossover to {\it B } periodic oscillations at low {\it B} discloses the influence of the imposed potential. Applying semiclassical periodic orbit theory to the nonintegrable (chaotic) electron motion in the antidot lattice we attribute these phenomena to the quantization of few fundamental periodic orbits.

Anaerobic transformation of 2,4,6-trinitrotoluene (TNT).

Abstract: A sulfate-reducing bacterium using trinitrotoluene (TNT) as the sole nitrogen source was isolated with pyruvate and sulfate as the energy sources. The organism was able to reduce TNT to triaminotoluene (TAT) in growing cultures and cell suspensions and to further transform TAT to still unknown products. Pyruvate, H2, or carbon monoxide served as the electron donors for the reduction of TNT. The limiting step in TNT conversion to TAT was the reduction of 2,4-diamino-6-nitrotoluene (2,4-DANT) to triaminotoluene. The reduction proceeded via 2,4-diamino-6-hydroxylaminotoluene (DAHAT) as an intermediate. The intermediary formation of DAHAT was only observed in the presence of carbon monoxide or hydroxylamine, respectively. The reduction of DAHAT to triaminotoluene was inhibited by both CO and NH2OH. The inhibitors as well as DANT and DAHAT significantly inhibited sulfide formation from sulfite. The data were taken as evidence for the involvement of dissimilatory sulfite reductase in the reduction of DANT and/or DAHAT to triaminotoluene. Hydrogenase purified from Clostridium pasteurianum and carbon monoxide dehydrogenase partially purified from Clostridium thermoaceticum also catalyzed the reduction of DANT in the presence of methyl viologen or ferredoxin, however, as the main reduction product DAHAT rather than triaminotoluene was formed. The findings could explain the function of CO as an electron donor for the DANT reduction (to DAHAT) and the concomitant inhibitory effect of CO on triaminotoluene formation (from DAHAT) by the inhibition of sulfite reductase.(ABSTRACT TRUNCATED AT 250 WORDS)

The scope of indefinites

Abstract: This paper claims that indefinite descriptions, singular and plural, have different scope properties than genuine quantifiers. This claim is based on their distinct behavior in island constructions: while indefinites in islands can have intermediate (and maximal) scope readings, quantifiers cannot. Further, the simplest in situ interpretation strategy for indefinites results in incorrect truth conditions for intermediate (and maximal) scope readings. I introduce a mechanism which “auto-matically” preserves the restriction on free variables corresponding to indefinites, in a way which allows the restriction to be carried up in the course of semantic interpretation and to be used at the level where the variable is quantified. This mechanism is a realization of the “indefinites-as-free-variables” proposal of Lewis, Kamp, and Heim, but emphasizes the role of the restriction. I then show that distributive readings of plural indefinites also display island-escaping behavior and argue for an independent, island-insensitive distribution mechanism.

Computer Integrated Manufacturing And Engineering

Abstract: 1. The Manufacturing System. 2. CIM Models and Concepts. 3. Analysis Tools for Manufacturing. 4. Flexible Manufacturing and Assembly Equipment. 5. Control Structures for Manufacturing Systems in the CAM Area. 6. Communication Nets and Protocol Standards. 7. CAD: Its Role in Manufacturing. 8. Process Planning and Manufacturing Scheduling. 9. Robotics. 11. City Assurance. 12. References and Further Reading. Index.

ZnO/CdS/Cu(In,Ga)Se/sub 2/ thin film solar cells with improved performance

Abstract: This paper reports results from experiments concerning the growth of CuInSe/sub 2/ films on different substrate materials, uncoated, and coated with molybdenum. Specifically the effect on the structure, i.e. preferred orientation, of the polycrystalline films is investigated. It is found that soda-lime float glass results in the most oriented films and also that the highest solar cell conversion efficiency is obtained with devices made from such films. In another set of experiments the effect of various deposition conditions for the ZnO window layer is studied. It is found that optimum performance is not strongly dependent on the deposition process. The highly doped part of the window, ZnO:Al, has been replaced with ITO on some devices and a comparison is made. Finally, ZnO/CdS/CuInSe/sub 2/ and ZnO/CdS/Cu(In,Ga)Se/sub 2/ thin film devices exhibiting active area conversion efficiencies of 15.4% and 16.9%, respectively, are demonstrated. >

A beta-adrenergic receptor kinase-like enzyme is involved in olfactory signal termination.

Abstract: We have previously shown that second-messenger-dependent kinases (cAMP-dependent kinase, protein kinase C) in the olfactory system are essential in terminating second-messenger signaling in response to odorants. We now document that subtype 2 of the beta-adrenergic receptor kinase (beta ARK) is also involved in this process. By using subtype-specific antibodies to beta ARK-1 and beta ARK-2, we show that beta ARK-2 is preferentially expressed in the olfactory epithelium in contrast to findings in most other tissues. Heparin, an inhibitor of beta ARK, as well as anti-beta ARK-2 antibodies, (i) completely prevents the rapid decline of second-messenger signals (desensitization) that follows odorant stimulation and (ii) strongly inhibits odorant-induced phosphorylation of olfactory ciliary proteins. In contrast, beta ARK-1 antibodies are without effect. Inhibitors of protein kinase A and protein kinase C also block odorant-induced desensitization and phosphorylation. These data suggest that a sequential interplay of second-messenger-dependent and receptor-specific kinases is functionally involved in olfactory desensitization.

TR60 and TR80 tumor necrosis factor (TNF)-receptors can independently mediate cytolysis.

Abstract: The human rhabdomyosarcoma cell line KYM-1 coexpresses high numbers of both tumor necrosis factor-alpha (TNF) receptors, TR60 and TR80, and is highly sensitive to TNF-induced cytotoxicity. We show here that each receptor type can mediate cytotoxicity on its own on selective stimulation. This was achieved using receptor specific antibodies, able to compete with ligand binding to the respective receptor molecules. Thus, the TR60-specific monoclonal antibody H398 was strongly agonistic, i.e., cytotoxic, in the presence of a secondary cross-linking immunoglobulin. Selective stimulation of TR80 by antibody-mediated receptor crosslinking also induced strong cytotoxicity in KYM-1 cells. Interestingly, when both receptor subsets were stimulated in parallel by limited receptor cross-linking, additive cytolytic effects were observed. In each case the respective Fab fragments showed no agonistic activity. When the natural ligand TNF was used to induce cytolysis, blocking studies with receptor specific Fab fragments indicated that the main cytotoxic effect of TNF is mediated via TR60, although these receptors represent only about 8% of the total TNF receptor number.