Showing papers by "University of Stuttgart published in 1991"

A New Look at Electron Localization

Abstract: two-particle density for electrons of parallel spin, a function of two electrons’ coordinates (x, y , z and x’, y‘ , z‘) which gives the joint probability of finding one electron at position x , y , z and another electron of the same spin at position x’, y’ , z‘. The analysis showed that electrons of parallel spin restrict themselves to separate regions of space, and hence follows the notion of localized electron pairs. A well-known application of these concepts are the Gillespie and Nyholm

Ab initio pseudopotentials for Hg through Rn

Abstract: Quasirelativistic and nonrelativistic energy adjusted ab initio pseudopotentials for the elements Hg through Rn are presented together with corresponding optimized valence basis sets. Core-valence correlation is accounted for by semiempirical polarization potentials. Corrections to the point charge repulsion in the core-nucleus interaction for subsequent molecular calculations are also provided. The reliability of the pseudopotential method is demonstrated in atomic test calculations for electron affinities, excitation and ionization energies as well as spin-orbit splittings by comparison with nonrelativistic, quasirelativistic and relativistic all-electron data. Results obtained by means of two quasirelativistic configuration interaction schemes that include spin-orbit coupling are compared with experimental data.

Proteinase yscE, the yeast proteasome/multicatalytic-multifunctional proteinase: mutants unravel its function in stress induced proteolysis and uncover its necessity for cell survival.

Abstract: Proteinase yscE is the yeast equivalent of the proteasome, a multicatalytic-multifunctional proteinase found in higher eukaryotic cells. We have isolated three mutants affecting the proteolytic activity of proteinase yscE. The mutants show a specific reduction in the activity of the complex against peptide substrates with hydrophobic amino acids at the cleavage site and define two complementation groups, PRE1 and PRE2. The PRE1 gene was cloned and shown to be essential. The deduced amino acid sequence encoded by the PRE1 gene reveals weak, but significant similarities to proteasome subunits of other organisms. Two-dimensional gel electrophoresis identified the yeast proteasome to be composed of 14 different subunits. Comparison of these 14 subunits with the translation product obtained from PRE1 mRNA synthesized in vitro demonstrated that PRE1 encodes the 22.6 kd subunit (numbered 11) of the yeast proteasome. Diploids homozygous for pre1-1 are defective in sporulation. Strains carrying the pre1-1 mutation show enhanced sensitivity to stresses such as incorporation of the amino acid analogue canavanine into proteins or a combination of poor growth medium and elevated temperature. Under these stress conditions pre1-1 mutant cells exhibit decreased protein degradation and accumulate ubiquitin-protein conjugates.

A mathematical model for the behavior of pedestrians

Abstract: The movement of pedestrians is supposed to show certain regularities which can be best described by an “algorithm” for individual behavior and is easily simulated on computers. This behavior is assumed to be determined by an intended velocity, by several attractive and repulsive effects, and by fluctuations. The movement of pedestrians is dependent on decisions, which have the purpose of optimizing their behavior and can be explicitly modeled. Some interesting applications of the model to real situations are given, especially to formation of groups, behavior in queues, avoidance of collisions, and selection processes among behavioral alternatives.

Extension of the phosphorus depletion zone in VA-mycorrhizal white clover in a calcareous soil

Abstract: To examine the influence of vesicular-arbuscular (VA) mycorrhizal fungi on phosphorus (P) depletion in the rhizosphere, mycorrhizal and non-mycorrhizal white clover (Trifolium repens L.) were grown for seven weeks in a sterilized calcareous soil in pots with three compartments, a central one for root growth and two outer ones for hyphae growth. Compartmentation was accomplished by a 30-μm nylon net. The root compartment received a uniform level of P (50 mg kg−1 soil) in combination with low or high levels of P (50 or 150 mg kg−1 soil) in the hyphal compartments. Plants were inoculated withGlomus mosseae (Nicol. & Gerd.) Gerd. & Trappe or remained uninfected.

Mineralization of the sulfonated azo dye Mordant Yellow 3 by a 6-aminonaphthalene-2-sulfonate-degrading bacterial consortium.

Abstract: Under anaerobic conditions the sulfonated azo dye Mordant Yellow 3 was reduced by the biomass of a bacterial consortium grown aerobically with 6-aminonaphthalene-2-sulfonic acid. Stoichiometric amounts of the aromatic amines 6-aminonaphthalene-2-sulfonate and 5-aminosalicylate were generated and excreted into the medium. After re-aeration of the culture, these amines were mineralized by different members of the bacterial culture. Thus, total degradation of a sulfonated azo dye was achieved by using an alternating anaerobic-aerobic treatment. The ability of the mixed bacterial culture to reduce the azo dye was correlated with the presence of strain BN6, which possessed the ability to oxidize various naphthalenesulfonic acids. It is suggested that strain BN6 has a transport system for naphthalenesulfonic acids which also catalyzes uptake of sulfonated azo dyes. These dyes are then gratuitously reduced in the cytoplasm by unspecific reductases.

Actions of imidacloprid and a related nitromethylene on cholinergic receptors of an identified insect motor neurone

Abstract: Nitromethylenes and their analogues are a novel class of insecticidally active molecules of commercial importance. Here we describe the actions of a novel nitroguanidine analogue, l-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine (imidacloprid; NTN 33893) and a nitromethylene, l-(3-pyridylmethyl)-2-nitromethylene-imidazolidine (PMNI) on the cockroach fast coxal depressor motor neurone Df and their effectiveness in displacing [125I]α-bungarotoxin binding to cockroach nerve cord preparations. When tested on the cell body of this identified neurone both imidacloprid and PMNI induce slow depolarizations, which are sensitive to nicotinic receptor antagonists, such as dihydro-β-erythroidine (1.0 × 10−5 M) and mecamylamine (1.0 × 10−4 M). Lower concentrations of imidacloprid (1.0 × 10−8 −1.0 × 10−6 M) and PMNI (1.0 × 10−8 M) show no antagonist action on nicotine-induced depolarization. At concentrations in the range 1.0 × 10−7 −5.0 × 10−7 M, PMNI partially and reversibly blocks nicotine-induced depolarization. Both compounds are more effective displacers of specific [125I]α-bungarotoxin binding than nicotine, with imidacloprid (IC50 = 2.0 × 10−7 M) about tenfold more potent than PMNI (IC50 = 1.3 × 10−6 M).

Acquisition of phosphorus and copper by VA-mycorrhizal hyphae and root-to-shoot transport in white clover

Abstract: White clover (Trifolium repens L.) plants were grown in a calcareous soil in pots with three compartments, a central one for root growth and two outer ones for growth of vesicular-arbuscular (VA) mycorrhizal (Glomus mosseae [Nicol. & Gerd.] Gerdemann & Trappe) hyphae (hyphal compartments). Phosphorus (P) was applied at three levels (0, 20 and 50 mg kg−1 soil) in the outer compartments in mycorrhizal treatments. Root and shoot dry weight were increased in mycorrhizal plants with hyphal access to outer compartments. Growth of the mycorrhizal hyphae in the outer compartments was not significantly affected by variation in P level in these compartments. However, both concentration and amount of P in roots and shoots sharply increased with increasing P supply in the outer (hyphal) compartments. With increasing P levels the calculated delivery of P by the hyphae from the outer compartments increased from 34% to 90% of total P uptake.

Priority management in ATM switching nodes

Abstract: Various space priority mechanisms and their detailed performance evaluation are described. A comparative performance study is given, indicating the excellent performance characteristics of a simple buffer management scheme called partial buffer sharing. The introduction of a second bearer capability provides a 10/sup -6/ cell loss rate instead of 10/sup -10/. >

Siderophores of Pseudomonas putida as an iron source for dicot and monocot plants

Abstract: Iron uptake from ferrated (59Fe) pseudobactin (PSB), a Pseudomonas putida siderophore, by various plant species was studied in nutrient solution culture under short term (10 h) and long term (3 weeks) conditions. In the short term experiments, 59Fe uptake rate from 59FePSB by dicots (peanuts, cotton and sunflower) was relatively low when compared with 59Fe uptake rate from 59FeEDDHA. Iron uptake rate from 59FePSB was pH and concentration dependent, as was the Fe uptake rate from 59FeEDDHA. The rate was about 10 times lower than that of Fe uptake from the synthetic chelate. Results were similar for long term experiments.

Long- and short-term effects of crop residues on aluminum toxicity, phosphorus availability and growth of pearl millet in an acid sandy soil

Abstract: In a long-term field experiment millet straw application (+CR) increased soil pH and base saturation and strongly improved pearl millet (Pennisetum glaucum L) growth on acid sandy soils Aluminum (Al) toxicity may be responsible for poor millet growth in plots without crop residues (−CR) Laboratory experiments were conducted to verify this assumption The concentrations of labile Al (8-hydroxyquinoline, 15 sec) in equilibrium soil solutions of top soil samples from field plots were 140 and 06 μM in unfertilized samples of −CR and +CR soil, respectively The corresponding values for labile Al in fertilized (NPK) samples were 518 and 110 μM, respectively A short-term (14 days) incubation of −CR soil with ground millet straw (01% w/w) increased soil solution pH and decreased total and labile Al in the soil solution by more than 44% In a water-culture experiment with increasing concentrations of Al (0–60 μM) pearl millet proved to be very Al-tolerant compared to cowpea, peanut and soybean A short-term (12 days) pot experiment with the incubated soil showed that root growth of pearl millet is not restricted by Al toxicity in the acid soils from Niger, but that after millet straw incubation root growth is considerably enhanced Phosphorus (P) concentration in the soil solution was about three times higher in +CR (175 μM) than in −CR (052 μM) top soil Since P is the most growth-limiting nutrient in those soils, the beneficial effect of crop residues on pearl millet is likely due to improvement of P nutrition by both increase in P mobility in the soil and enhancement of root growth

Energy-adjustedab initio pseudopotentials for the second and third row transition elements: Molecular test for M2 (M=Ag, Au) and MH (M=Ru, Os)

Abstract: Recently published nonrelativistic and quasirelativistic energy-adjustedab initio pseudopotentials representing the M(Z−28)+ cores of the second row transition metal atoms and the M(Z−60)+ cores of the third row transition metal atoms have been tested in SCF, CI(SD) and CEPA1 calculations of the spectroscopic constants (R e ,D e , and ω e ) of the ground states of the neutral and singly charged silver and gold dimers, and in state averaged CASSCF and multi-reference CI(SD) calculations of the spectroscopic constants (R e ,D e , ω e , μ e , ∂μ/∂R). Comparison is made with experimental and reliable theoretical data where available; in the case of the hydrides, additional calculations with pseudopotentials published by other groups have been made for comparison.

Refractive-index measurements for the correction of particle sizing methods

Abstract: For many optical methods in liquid particle sizing the refractive index of the liquid must be known. There is no problem if the data are available in the literature. If the liquid is unknown or if the refractive index changes because of a heating process or chemical reactions, the refractive index must be measured to achieve accurate sizing. A method is presented to determine the real part of the refractive index of droplets using the shift in the position of the first rainbow. Results from the application of this method to burning droplet streams are presented.

Common sense entailment: a modal theory of nonmonotonic reasoning

Abstract: In this paper, we use the Stalnaker-Lewis semantics for conditional logic to construct a truth conditional semantics for generic sentences. The resulting notion of logical entailment captures intuitively valid argument forms involving generics. A dynamic semantics is built on top of the truth conditional one, and the resulting inference notion captures nonmonotonic argument patterns familiar from the artificial intelligence literature. The theory developed here extends that of Asher and Morreau (1991). That theory enables specific information to prevail over more general information by using techniques familiar from prioritized circumscription; this theory uses a constraint on modal frames to achieve the same effect.

Oligonucleotide fingerprinting using simple repeat motifs: a convenient, ubiquitously applicable method to detect hypervariability for multiple purposes.

Abstract: A panel of simple repetitive oligonucleotide probes has been designed and tested for multilocus DNA fingerprinting in some 200 fungal, plant and animal species as well as man. To date at least one of the probes has been found to be informative in each species. The human genome, however, has been the major target of many fingerprinting studies. Using the probe (CAC)5 or (GTG)5, individualization of all humans is possible except for monozygotic twins. Paternity analyses are now performed on a routine basis by the use of multilocus fingerprints, including also cases of deficiency, i.e. where one of the parents is not available for analysis. In forensic science stain analysis is feasible in all tissue remains containing nucleated cells. Depending on the degree of DNA degradation a variety of oligonucleotides are informative, and they have been proven useful in actual case work. Advantages in comparison to other methods including enzymatic DNA amplification techniques (PCR) are evident. Fingerprint patterns of tumors may be changed due to the gain or loss of chromosomes and/or intrachromosomal deletion and amplification events. Locus-specific probes were isolated from the human (CAC)5/(GTG)5 fingerprint with a varying degree of informativeness (monomorphic versus truly hypervariable markers). The feasibility of three different approaches for the isolation of hypervariable mono-locus probes was evaluated. Finally, one particular mixed simple (gt)n(ga)m repeat locus in the second intron of the HLA-DRB genes has been scrutinized to allow comparison of the extent of exon-encoded (protein-) polymorphisms versus intronic hypervariability of simple repeats: adjacent to a single gene sequence (e.g. HLA-DRB1*0401) many different length alleles were found. Group-specific structures of basic repeats were identified within the evolutionarily related DRB alleles. As a further application it is suggested here that due to the ubiquitous interspersion of their targets, short probes for simple repeat sequences are especially useful tools for ordering genomic cosmid, yeast artificial chromosome and phage banks.

Performance analysis of buffered Banyan networks

Abstract: The authors give a classification of the most common Banyan networks and outline an analysis approach for the rather general class of delta-b networks with multiple buffers. On the basis of this approach, they discuss the effects of the approximation involved and present a refined analysis algorithm for the special case of a single buffered delta-2 network. The results of both algorithms are compared with simulation results to assess their accuracy. The comparison shows clearly that the accuracy of the analysis is mainly determined by the modeling of the dependencies between consecutive clock cycles. >

Isolation and characterization of a methyl chloride utilizing, strictly anaerobic bacterium

Abstract: From sludge obtained from the sewage digester plant in Stuttgart-Mohringen a strictly anaerobic bacterium was enriched and isolated with methyl chloride as the energy source. The isolate, which was tentatively called strain MC, was nonmotile, gram-positive, and occurred as elongated cocci arranged in chains. Cells of strain MC formed about 3 mol of acetate per 4 mol of CH3Cl consumed, indicating that the organism was a homoacetogenic bacterium fermenting methyl chloride plus CO2 according to: $$\begin{gathered} 4 CH_3 Cl + 2 CO_2 + 2 H_2 O \to 3 CH_3 COO^ - \hfill \\ + 7 H^ + + 4 Cl^ - . \hfill \\ \end{gathered} $$ The organism grew with 2–3% methyl chloride in the gas phase at a doubling time of near 30 h. Dichloromethane was not utilized. The bacterium also grew on carbon monoxide, H2 plus CO2, and methoxylated aromatic compounds. Optimal growth with methyl chloride was observed at 25°C and pH 7.3–7.7. The G+C-content of the DNA was 47.5±1.5%. The methyl chloride conversion appeared to be inducible, since H2 plus CO2-grown cells lacked this ability. From the morphological and physiological characteristics, the isolate could not be affiliated to a known species.

Two methods of constructing contractions and revisions of knowledge systems

Abstract: The theory of nonmonotonic reasoning and the theory of belief revision share a very important subject. Both theories help to understand how it is possible rationally to pass from one knowledge system into another knowledge system that is in contradiction with the former one. In nonmonotonic reasoning this transition is accomplished by distinguishing between axioms ("explicit beliefs") and theorems ("implicit beliefs") and giving up the doctrine that more axioms must always yield more theorems. Thus my old (implicit) belief that Tweety can fly may well turn into disbelief after getting the information (acquiring the explicit belief) that Tweety is a penguin. A considerable limitation of this approach is that the new axiom must be (monotonica!ly) consistent with the previous axioms, or else we get an inconsistent knowledge base. The theory of belief revision on which I shall focus my attention is not subject to this restriction. In fact, it does not at all distinguish between axioms and theorems, or between beliefs and their reasons. The knowledge systems it takes into consideration are whole theories, where a theory, or knowledge set, is understood as a set of sentences closed under some appropriate logic Cn. We shall assume that this logic includes classical propositional logic, that it is compact (i.e., if

An investigation of a finite rotation four node assumed strain shell element

Abstract: The paper presents a shell formulation based on the ‘degenerated solid approach’. The theory employs covariant strains and performs explicit integration through the shell thickness. The rigid body motion is exactly represented. The consistent tangent stiffness matrix is evaluated for the four node quadrilateral. It is shown, in the final part, that this type of element, which distinguishes itself by a very simple and easily understandable theory, gives good answers for linear as well as non-linear applications.

Cavitation-generated free radicals during shock wave exposure: investigations with cell-free solutions and suspended cells

Abstract: Extracorporeally generated shock waves as used in lithotripsy of urinary and biliary stones exhibit side effects in vivo. Furthermore, these shock waves destroy eukaryotic cells during in vitro treatment in suspension. A possible cause of these damaging effects might be cavitation, the growth and collapse of bubbles in liquids exposed to tensile stresses. During the collapse, temperature inside these cavitation bubbles rises up to several thousand K, leading to the formation of free radicals. We demonstrated the occurrence of cavitation-generated free radicals by direct reaction with fluorescent dyes in solution after shock wave treatment and investigated the resulting cell killing by variation of the cellular antioxidative defense status. We present evidence for the generation of intracellular free radicals during shock wave treatment of suspended cells.

Molekül‐ und Kristallstrukturen des dimeren Calcium‐bis[bis(trimethylsilyl)amids] und des Calcium‐bis[bis(trimethylsilyl)‐amids] · DME

Abstract: Die Molekul- und Kristallstrukturen des dimeren Calcium-bis[bis(trimethylsilyl)amids] 1 und des Calcium-bis[bis(trimethylsilyl)amids] · DME 2 werden beschrieben. {Ca[N(SiMe3)2]2}21 kristallisiert in der triklinen Raumgruppe P1 mit {a = 890,9(2); b = 1259,3(4); c = 2158,8(7) pm; α = 88,13(2); β = 88,49(2); γ = 72,25(2)°; Z = 2}. Die Calciumatome sind dreifach koordiniert mit CaNt-Bindungslangen von 227 pm zu den terminalen Liganden und CaNb-Bindungen von 247 pm zu den verbruckenden Amidogruppen. Ca[N(SiMe3)2]2 · DME 2 kristallisiert aus n-Hexan in der monoklinen Raumgruppe C2/c mit {a = 854,9(3); b = 1738,2(6); c = 2042,1(6) pm; β = 101,27(2)°; Z = 4}. Das Calciumatom hat die Koordinationszahl 4 mit CaN-Bindungslangen von 227 pm und CaO-Abstanden von 240 pm; das Molekul von Verbindung 2 weist C2-Symmetrie auf. Molecular and Crystal Structures of dimeric Calcium-bis[bis(trimethylsilyl)amide] and Calcium-bis[bis(trimethylsilyl)amide] · DME X-ray crystal structures are reported for dimeric Calcium-bis[bis(trimethylsilyl)amide] 1 and Calcium-bis[bis(trimethylsilyl)amide] · DME 2. {Ca[N(SiMe3)2]2}21 crystallizes in the triclinic space group P1 with {a = 890.9(2); b = 1259.3(4); c = 2158.8(7) pm; α = 88.13(2); β = 88.49(2); γ = 72.25(2)°; Z = 2}. The calcium atoms are three-coordinate with CaNt-bonds of 227 pm to the terminal ligand and CaNb-bonds of 247 pm to the bridging amido groups. Ca[N(SiMe3)2]2 · DME 2 crystallizes from n-hexane in the monoclinic space group C2/c with {a = 854.9(3); b = 1738.2(6); c = 2042.1(6) pm; β = 101.27(2)°; Z = 4}. The calcium atom has the coordination number four with CaN-bonds of 227 pm and CaO-distances of 240 pm. The molecule of compound 2 possesses C2-symmetry.