Showing papers by "Braunschweig University of Technology published in 1992"

Fibronectin-binding protein of Streptococcus pyogenes: sequence of the binding domain involved in adherence of streptococci to epithelial cells.

Abstract: The sequence of the fibronectin-binding domain of the fibronectin-binding protein of Streptococcus pyogenes (Sfb protein) was determined, and its role in streptococcal adherence was investigated by use of an Sfb fusion protein in adherence studies. A 1-kb DNA fragment coding for the binding domain of Sfb protein was cloned into the expression vector pEX31 to produce an Sfb fusion protein consisting of the N-terminal part of MS2 polymerase and a C-terminal fragment of the streptococcal protein. Induction of the vector promoter resulted in hyperexpression of fibronectin-binding fusion protein in the cytoplasm of the recombinant Escherichia coli cells. Sequence determination of the cloned 1-kb fragment revealed an in-frame reading frame for a 268-amino-acid peptide composed of a 37-amino-acid sequence which is completely repeated three times and incompletely repeated a fourth time. Cloning of one repeat into pEX31 resulted in expression of small fusion peptides that show fibronectin-binding activity, indicating that one repeat contains at least one binding domain. Each repeat exhibits two charged domains and shows high homology with the 38-amino-acid D3 repeat of the fibronectin-binding protein of Staphylococcus aureus. Sequence comparison with other streptococcal ligand-binding surface proteins, including M protein, failed to reveal significant homology, which suggests that Sfb protein represents a novel type of functional protein in S. pyogenes. The Sfb fusion protein isolated from the cytoplasm of recombinant cells was purified by fast protein liquid chromatography. It showed a strong competitive inhibition of fibronectin binding to S. pyogenes and of the adherence of bacteria to cultured epithelial cells. In contrast, purified streptococcal lipoteichoic acid showed only a weak inhibition of fibronectin binding and streptococcal adherence. These results demonstrate that Sfb protein is directly involved in the fibronectin-mediated adherence of S. pyogenes to epithelial cells.

Optical properties of rare earth-doped ZBLAN glasses

Abstract: An investigation has been made of the radiative and non-radiative properties of the well known ZBLAN glass composition doped with individual rare earth elements (Pr3+, Nd3+, Dy3+, Ho3+, Er3+ and Tm3+) at levels between 0.1 and 4 mol%. The optical absorption and fluorescence spectra of the samples were measured and also the lifetimes for some transitions. Using the Judd-Ofelt model, the radiative decay rates between the different levels, the lifetimes and the branching ratios were calculated. These results and comparison of calculated and measured lifetimes are discussed with respect to radiative and non-radiative rates and quantum efficiencies. The multiphonon rates below 3200 cm−1 are found to be less in ZBLAN than in other host materials (ZBLA, SiO2, YAG).

Stability of Product Form G-Networks

Abstract: We prove necessary and sufficient conditions for the existence and uniqueness of the stationary solution of the queueing networks (G-networks) with negative and positive customers introduced in Gelenbe [3], which have been shown to have product form. First, the existence of the solution of the nonlinear customer flow equations is established using Brouwer's fixed-point theorem; this result is valid for stable and unstable systems, as well as for certain networks that may not have product form. Then, the result is used to establish general stability related to the usual “load factor less than 1” criterion of queueing systems for G-networks with product form.

Bootstrapping stationary autoregressive moving-average models

Abstract: . In this paper we develop an asymptotic theory for application of the bootstrap to stationary stochastic processes of autoregressive moving-average (ARMA) type, with known order (p, q). We give a proof of the asymptotic validity of the bootstrap proposal applied to M estimators for the unknown parameter vector of the process. For this purpose we derive an asymptotic expansion for M estimators in ARMA models and construct an estimate for the unknown distribution function of the residuals which in principle are not observable. A small simulation study is also included.

Conceptual modelling of database applications using an extended ER model

Abstract: In this paper, we motivate and present a data model for conceptual design of structural and behavioural aspects of databases. We follow an object centered design paradigm in the spirit of semantic data models. The specification of structural aspects is divided into modelling of object structures and modelling of data types used for describing object properties. The specification of object structures is based on an E xtended E ntity- R elationship (EER) model. The specification of behavioural aspects is divided into the modelling of admissible database state evolutions by means of temporal integrity constraints and the formulation of database (trans)actions. The central link for integrating these design components is a descriptive logic-based query language for the EER model. The logic part of this language is the basis for static constraints and descriptive action specifications by means of pre- and postconditions. A temporal extension of this logic is the specification language for temporal integrity constraints. We emphasize that the various aspects of a database application are specified using several appropriate, but yet compatible formalisms, which are integrated by a unifying common semantic.

Bootstrap procedures for AR (∞) — processes

Abstract: In this paper we will deal with an application of Efron’s 1979 bootstrap to stationary stochastic processes in discrete time. In many applications it is assumed that these processes are of autoregressive or more generally of autoregressive moving average type, i.e. the underlying stationary process X = (X t: t ∈ Z = {0, ±1, ±2,…}) is assumed to satisfy the following stochastic difference equation $$ {X_t} = \sum\limits_{{v = 1}}^p {{a_v}{X_{{t - v}}} + {\varepsilon_t} + \sum\limits_{{\mu = 1}}^q {{b_{\mu }}{\varepsilon_{{t - \mu }}},\;t \in Z} } $$ Here e = (e t: t ∈ Z) denotes a white noise, that is a sequence of uncorrelated, zero mean random variables with finite variance σ 2 .

Spatial distribution of earthworms and soil properties in an arable loess soil

Abstract: The spatial distribution of earthworms and soil properties under sugar beet and winter-barley was investigated in 1987 and 1989, respectively, in an arable loess soil near Hannover, Germany. In a pattern of a 10 × 10 square grid on an area of 1 ha earthworms were collected with the formalin expulsion method. Three species were determined: Lumbricus terrestris, Allolobophora caliginosa and Allolobophora rosea . Different stages of development, biomass and abundance were recorded. At all 100 points of the square grid, soil samples were taken at three depths. Carbon content, bulk and aggregate density, hydraulic conductivity and gas diffusion coefficients were measured. Maps of the distribution of all properties were computed with geostatistical interpolation methods. Earthworms showed a spatial dependence in a range of 20–50 m. The larger the average size of the respective species, the more the spatial distribution of biomass and abundance of a population differed. Earthworm abundance and biomass in 1987 and 1989 were correlated. For the tilled Ap-horizon only the carbon content showed a spatial dependence and a significant correlation between both years. Further correlations between soil properties and earthworms are: L. terrestris and carbon content in the Ap; L. terrestris and aggregate density in the Al-horizon; and a negative correlation of Allolobophora species and the aggregate density in the Al.

Enhanced glucan formation of filamentous fungi by effective mixing, oxygen limitation and fed-batch processing

Abstract: Glucan formation ofSchizophyllum commune andSclerotium glucanicum were investigated. Process data obtained during batch cultivation are presented. Glucan release can be improved by oxygen limitation. Thus, growth and glucan release are influenced by oxygen in opposite ways. Possible pathways of this oxygen-dependent regulation are discussed. A draft-tube/propeller system, rushtonturbine-, fan- and helicon-ribbon-impeller as well as a fundaspi and intermig agitator were tested. The 4-bladed fan impeller withd *=0.64 yielded the best results, since effective bulk mixing is much more important than bubble break up (micromixing) with regard to this system. Fed-batch cultivation always resulted in higher rates of glucan formation than the batch process.

Molecular phylogenies of plastid origins and algal evolution

Abstract: An overview of recent molecular analyses regarding origins of plastids in algal lineages is presented. Since different phylogenetic analyses can yield contradictory views of algal plastid origins, we have examined the effect of two distance measurement methods and two distance matrix tree-building methods upon topologies for the ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit nucleotide sequence data set. These results are contrasted to those from bootstrap parsimony analysis of nucleotide sequence data subsets. It is shown that the phylogenetic information contained within nucleotide sequences for the chloroplast-encoded gene for the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase, integral to photosynthesis, indicates an independent origin for this plastid gene in different plant taxa. This finding is contrasted to contrary results derived from 16S rRNA sequences. Possible explanations for discrepancies observed for these two different molecules are put forth. Other molecular sequence data which address questions of early plant evolution and the eubacterial origins of algal organelles are discussed.

The dynamic of belief in the transferable belief model and specialization-generalization matrices

Abstract: The fundamental updating process in the transferable belief model is related to the concept of specialization and can be described by a specialization matrix. The degree of belief in the truth of a proposition is a degree of justified support. The Principle of Minimal Commitment implies that one should never give more support to the truth of a proposition than justified. We show that Dempster's rule of conditioning corresponds essentially to the least committed specialization, and that Dempster's rule of combination results essentially from commutativity requirements. The concept of generalization, dual to the concept of specialization, is described.

Marine biosurfactants. IV. Production, characterization and biosynthesis of an anionic glucose lipid from the marine bacterial strain MM1

Abstract: During screening for biosurfactants among marine, n-alkane-utilizing bacteria, low- and high-molecular surface-active substances were detected. The marine bacterial strain MM1 was found to synthesize a novel glycolipid that has not so far been cited in the literature. Both 1H, 13C-nuclear magnetic resonance spectroscopic and positive ion fast atom bombardment mass spectrometer studies led to the identification of a glucose lipid consisting of four 3-OH-decanoic acids, which are linked together by ester bonds. The lipophilic moiety is coupled glycosidically with C-1 of glucose. The glucolipid reduced the surface tension from 72 mN/m to 30 mN/m while the minimum interfacial tension towards n-hexadecane was lowered to values smaller than 5 mN/m.

Entrapment of microbial cells within polyurethane hydrogel beads with the advantage of low toxicity

Abstract: A new method is described for the entrapment of microbial cells in polyurethane (PUR) hydrogel beads. This hydrogel is produced from a hydrophilic pre-polymer blocked with bisulphite by adjusting the pH between 4 and 6.5. Bisulphite-blocked isocyanate has a substantially lower toxicity against living cells than unblocked (conventional) isocyanates. The poly(carbamoylsulfonate) (PCS) hydrogels have optimal elastic properties and therefore can be used for a matrix of biocatalysts in an agitated reactor as well as in a fluid-bed reactor. The results of ethanol fermentation ofSaccharomyces cerevisiae entrapped in PCS hydrogel beads, and of the denitrification activity of immobilizedParacoccus denitrificans are promising. In contrast, entrapped cells in conventional PUR hydrogels didn’t show any activity.

The switching gene swi6 affects recombination and gene expression in the mating-type region of Schizosaccharomyces pombe.

Abstract: The products of 11 switching (swi) genes are required for efficient mating-type (MT) switching in homothallic (h 90) strains of Schizosaccharomyces pombe. The MT region of h 90 comprises three cassette genes: the expression site mat1: 1 and two silent loci, mat2: 2 and mat3: 3. Besides reducing MT switching, the swi6 mutation leads to deletions in the MT region caused by intrachromosomal cross-overs between two paired cassettes. These deletions only arise if DNA double-strand breaks are present at mat1: 1, which initiate MT switching. Furthermore, swi6 allows meiotic recombination in the K region, a region of 16 kb between mat2: 2 and mat3: 3; in wild-type strains no recombination occurs in K. swi6 also allows the simultaneous expression of two different cassettes in the same haploid cell. Thus swi6 may have an influence on the general chromatin structure in the MT region.

On the flow stress of [100]- and [111]-oriented Cu-Mn single crystals: A transmission electron microscopy study

Abstract: Cu-Mn single crystals oriented for multiple slip with [111] and [100] axis have been deformed in tension at room temperature. The Mn content was 0.8 at.% for the [111] and 3at.% for the [100] crystals. The observed decrease in the workhardening rate with increasing reduced shear stress τ—τ0 coincides with the linear decrease in pure Cu for τ—τ0 15–20 MPa (τ0 is the critical resolved shear stress). The total dislocation density measured for τ—τ0 between 5 and 58 MPa increases proportional to (τ—τ0)2 with a slope which increases with increasing Mn content. The higher dislocation density in the alloys is stored in a cell structure of higher volume fraction of the walls compared with pure Cu. For τ—τ0 exceeding 15—20 MPa, the dislocation density within the walls depends only on τ—τ0 and not on orientation and Mn content. Furthermore, it alone determines, in the pure and alloyed crystals, the flow stress, which is additively composed of contributions from solid-solution and strain hardening. In the sy...

Individual somatotopy of primary sensorimotor cortex revealed by intermodal matching of MEG, PET, and MRI.

Abstract: A method for comparing estimated magnetoencephalographic (MEG) dipole localizations with regional cerebral blood flow (rCBF) activation areas is presented. This approach utilizes individual intermodal matching of MEG data, of rCBF measurements with [15O]-butanol and positron emission tomography (PET), and of anatomical information obtained from magnetic resonance (MR) images. The MEG data and the rCBF measurements were recorded in a healthy subject during right-sided simple voluntary movements of the foot, thumb, index finger, and mouth. High resolution 3D-FLASH MR images of the brain consisting of 128 contiguous sagittal slices of 1.17-mm thickness were used. MEG/MR integration was performed by superimposing the 3D head coordinate system constructed during the MEG measurement onto the MR image data using identical anatomical landmarks as references. PET/MR integration was achieved by a phantom-validated iterative front-to-back-projection algorithm resulting in one integrated MEG/PET/MR image. The estimated dipole locations followed the somatotopic organisation of the task-specific rCBF increases as evident from PET, although they did not match point-to-point. Our results demonstrate that intermodal matching of MEG, PET and MR data provides a tool for relating estimated neuromagnetic field locations to task-specific rCBF changes in individual subjects. Our method offers the perspective of refined dipole modelling.

The protein sequence and some intron positions are conserved between the switching gene swi10 of Schizosaccharomyces pombe and the human excision repair gene ERCC1

Abstract: The switching gene swi10+ has a function in mating-type switching as well as in the repair of radiation damages. We have cloned the genomic swi10+ gene by functional complementation of the switching defect of the swi10-154 mutant. The swi10+ gene is not essential for viability. The DNA sequence revealed an open reading frame of 759 nucleotides interrupted by three introns of 127, 52 and 60 bp, respectively. The positions of intron I as well as of intron III of swi10 are evolutionary conserved in comparison to the introns III and IV of the human ERCC1 gene. The analysis of cDNA clones isolated by PCR amplification confirmed the structure of the swi10 gene. The putative Swi10 protein has homologies to the human and mouse ERCC1 protein, to Rad10 of Saccharomyces cerevisiae and to parts of UvrA and UvrC of E. coli. All these proteins are essential components for excision repair of damaged DNA. The Swi10 protein contains a putative DNA binding domain previously found in other proteins. Northern blot experiments and the analyses of cDNA clones indicate that intron I of the swi10 gene is not efficiently spliced.

Growth Characteristics and Elicitor‐induced Reactions of Photosynthetically Active and Heterotrophic Cell Suspension Cultures of Lycopersicon peruvianum (Mill.)*

Abstract: Cell suspension cultures of Lycopersicon peruvianum (Solanaceae) were established as well-growing photoautotrophic, photomixotrophic and heterotrophic cultures and their growth parameters were characterized. Elicitor-induced responses of these cultures to the tomato pathogen Fusarium oxysporum f. sp. lycopersici were investigated after treatment of cells with autoclaved mycelium and culture filtrate of this fungus. The dominant reaction was an enhanced incorporation of phenolic constituents in the plant cell wall. Among the nine phenolics released by alkaline hydrolysis the most prominent compounds were p-hydroxybenzaldchyde, vanillin, p-coumaroyltryamine, feruloyltyramine, p-coumaric acid and ferulic acid. Phenolic incorporation in cell walls resulted in increased stability of cells against protoplasting with microbial enzymes. Chlorogenic acid, as the main soluble phenolic compound, showed differential accumulation in the three cell cultures lines as well as an elicitor-induced transient decrease. In heterotrophic cells decrease of chlorogenate occurred concomitant with accumulation of caffeoyl- and p-coumaroylshikimate as well as increased activities of p-coumaroyleoenzyme A: shikimic acid p-coumaroyltransferase. Upon elicitation increased activities of phenylalanine ammonia lyase and changes in peroxidase activities wore also detected. Sesquiterpenoid phytoalexines were not produced by either one of the cell culture lines and levels of tomatine were not significantly affected by elicitation.

Pseudomonas cepacia lipase: Studies on aggregation, purification and on the cleavage of olive oil

Abstract: To purify the extracellular lipase ofPseudomonas cepacia DSM 50181 and to disintegrate molecular aggregation, the presence of i-propanol (70% per volume) was necessary. The molecular weight was determined to be 33,000 D. Concerning the hydrolytic activity of the pure enzyme towards olive oil additional free fatty acids inhibited the reaction.

The swi4+ gene of Schizosaccharomyces pombe encodes a homologue of mismatch repair enzymes

Abstract: The swi4+ gene of Schizosaccharomyces pombe is involved in termination of copy-synthesis during mating-type switching The gene was cloned by functional complementation of a swi4 mutant transformed with a genomic library Determination of the nucleotide sequence revealed an open reading frame of 2979 nucleotides which is interrupted by a 68 bp long intron The putative Swi4 protein shows homology to Duc-1 (human), Rep-3 (mouse), HexA (Streptococcus pneumoniae) and MutS (Salmonella typhimurium) The prokaryotic proteins are known as essential components involved in mismatch repair A strain with a disrupted swi4+ gene was constructed and analysed with respect to the switching process As in swi4 mutants duplications occur in the mating-type region of the swi4 (null) strain, reducing the efficiency of switching

On the axiomatic justification of Dempster's rule of combination

Abstract: Within the theory of belief functions Dempster's rule of combination is of particular importance for the integration of different bodies of evidence. In this article a set of axioms is presented that uniquely determines this rule. As the axioms reflect just the intuitive idea of partially moveable evidence masses the presented results emphasize the unicity of Dempster's rule. © 1992 John Wiley & Sons. Inc.

Simulated annealing to locate various stationary points in semiempirical methods

Abstract: In this work, an algorithm was developed to study the potential energy surfaces in the coordinate spaces of molecules by a nonlocal way, in contrast to classic energy minimizers as the BFGS or the DFP method. This algorithm, based on the specificities of semiempirical methods, mixes simulated annealing and local searches to reduce computation costs. By this technique, the global energy minimum can be localized. Moreover, local minima that are close in energy to the global minimum are also obtained. If the search is not only for minima but for all stationary points (minima, saddle points…), then the energy is replaced by the gradient norm, which reaches its minimum values at stationary points. The annealing process is stopped before having accurately reached the global minimum and generates a list of geometries whose energies (respectively, whose gradients) are optimized by local minimizers. This list of geometries is shortened from the nearly equivalent geometries by a dynamic single-clustering analysis. The energy/gradient local minimizers act on the clustered list to produce a set of minima/stationary points. A targeted search of these points and reduction of the costs are reached by the way of several penalty functions. They eliminate—without energy calculation—most of the points generated by random walks on the potential energy surface. These penalty functions (on the total moment of inertia or on interatomic distances) are specific to the class of problem studied. They account for the nonrupture of either specific chemical bonds or rings in cyclic molecules, they assure that molecular systems are kept bonded, and they avoid the collapsing of atoms. © 1992 John Wiley & Sons, Inc.

Mössbauer effect studies on amorphous and nanocrystalline Fe73.5Cu1Nb3Si13.5B9

Abstract: Amorphous and nanocrystalline Fe73.5Cu1Nb3Si13.5B9 were studied by conversion electron and transmission Mossbauer effect measurements. The Curie temperatureTc of the ferromagnetic amorphous phase was determined to (602±2) K. The formation of nanocrystals from the amorphous alloy can be initiated by annealing the sample at 520 °C. The kinetics of crystallization was observed by annealing the samples for 2, 4, 8, 16, 32 and 60 min and studying the state of the alloy by Mossbauer spectroscopy. The sample annealed for 60 min consisted of about 50% of the amorphous and about 50% crystalline phase. The structure of the crystalline phase is dominated by Fe-Si (DO3) with 21% Si. Other crystalline phases such as Fe-B were found. For the remaining amorphous phase a description is given. It consists of a phase with a hyperfine field distribution like the as-quenched alloy and of a new “emaciated” amorphous phase that develops during the crystallization.

Effect of soil compaction on activity and biomass of endogeic lumbricids in arable soils

Abstract: Between June 1988 and October 1989 the effect of soil compaction on abundance and biomass of active lumbricids was investigated in a longterm field experiment under spring-wheat and winter-barley. Seven plots were subjected to loads by agricultural machinery under conditions simulating three common kinds of agricultural practice and compared to an unloaded control plot (Table 1). The dominant species of the investigation area, Aporrectodea caliginosa and A. rosea (99.3% of total individual number) had their highest activity and biomass in the uncompact control plot. Lowest individual numbers were found in the extremely loaded wheel-track and the conservation tillage area. The extensive cultivation of this area began just at the start of the field experiment, so that a greater earthworm population had not had time to establish itself. In pot experiments the activity of the endogeic species A. caliginosa was investigated in tripartioned soil columns (40 cm long × 19 cm wide), each differently compact to pore volumes (pv) of 37.5, 42.5, 47.5 and 56%. A significantly higher activity, measured as the length and the number of the burrows visible from outside, was found in the lighter substrates. The volume number extent of earthworm burrows was as much as 2 times higher in the 47.5 and 56% pv columns than in the more compact 42.5 and 37.5% pv columns.

Requirements for Airborne Vector Gravimetry

Abstract: The objective of airborne vector gravimetry is the determination of the full gravity disturbance vector along the aircraft trajectory. The paper briefly outlines the concept of this method using a combination of inertial and GPS-satellite data. The accuracy requirements for users in geodesy and solid earth geophysics, oceanography and exploration geophysics are then specified. Using these requirements, accuracy specifications for the GPS subsystem and the INS subsystem are developed. The integration of the subsystems and the problems connected with it are briefly discussed and operational methods are indicated that might reduce some of the stringent accuracy requirements.