Showing papers by "Braunschweig University of Technology published in 1995"

The molecular architecture of focal adhesions

Abstract: This article outlines the present knowledge of the architecture, molecular composition, and dynamics of focal contacts of adhesive animal cells. These structures, developed at the plasma membrane at sites where cells touch their substratum, are essential for cellular attachment in tissue formation during embryogenesis and wound healing. In tissue culture, they are particularly prominent and thus amenable to detailed investigation. Focal contacts consist of a cytoplasmic face, comprising cytoskeletal elements, a transmembrane connecting region, and a extracellular face composed of proteins of the extracellular matrix. The molecular anatomy of the numerous proteins involved, the basis for classifying them as structural or regulatory components, and their in vitro interactions are described. Based on this information, current models on the dynamics of their assembly and of possible regulatory mechanisms involving a variety of signal transduction pathways are discussed.

Characterization of a new lipopeptide surfactant produced by thermotolerant and halotolerant subsurface Bacillus licheniformis BAS50.

Abstract: Strain BAS50, isolated from a petroleum reservoir at a depth of 1,500 m and identified as Bacillus licheniformis, grew and produced a lipopeptide surfactant when cultured on a variety of substrates at salinities of up to 13% NaCl. Surfactant production occurred both aerobically and anaerobically and was optimal at 5% NaCl and temperatures between 35 and 45 degrees C. The biosurfactant, termed lichenysin A, was purified and chemically characterized. A tentative structure and composition for the surfactant are described. Lichenysin A is a mixture of lipopeptides, with the major components ranging in size from 1,006 to 1,034 Da. The lipid moiety contains a mixture of 14 linear and branched beta-hydroxy fatty acids ranging in size from C12 to C17. There are seven amino acids per molecule. The peptide moiety is composed of the following amino acids: glutamic acid as the N-terminal amino acid, asparagine, valine, leucine, and isoleucine as the C-terminal amino acid, at a ratio of 1.1:1.1:1.0:2.8:1.0, respectively. Purified lichenysin A decreases the surface tension of water from 72 mN/m to 28 mN/m and achieves the critical micelle concentration with as little as 12 mg/liter, characterizing the product as a powerful surface-active agent that compares favorably to others surfactants. The antibacterial activity of lichenysin A has been demonstrated.

CELIAS — Charge, Element and Isotope Analysis System for SOHO

Abstract: The CELIAS experiment on SOHO is designed to measure the mass, ionic charge and energy of the low and high speed solar wind, of suprathermal ions, and of low energy flare particles. Through analysis of the elemental and isotopic abundances, the ionic charge state, and the velocity distributions of ions originating in the solar atmosphere, the investigation focuses on the plasma processes on various temporal and spatial scales in the solar chromosphere, transition zone, and corona. CELIAS includes 3 mass- and charge-discriminating sensors based on the time-of-flight technique: CTOF for the elemental, charge and velocity distribution of the solar wind, MTOF for the elemental and isotopic composition of the solar wind, and STOF for the mass, charge and energy distribution of suprathermal ions. The instrument will provide detailed in situ diagnostics of the solar wind and of accelerated particles, which will complement the optical and spectroscopic investigations of the solar atmosphere on SOHO. CELIAS also contains a Solar Extreme Ultraviolet Monitor, SEM, which continously measures the EUV flux in a wide band of 17 – 70 nm, and a narrow band around the 30.4 nm He II line.

Structure and properties of plasma-nitrided stainless steel

Abstract: A series of plasma-nitriding experiments has been conducted on AISI 304L austenitic stainless steel at temperatures ranging from 400 to 600 °C using a pulsed d.c. plasma with various pulse duration/repetition ratios in an N2H2 gas mixture. The structure and composition of the plasma-nitrided surface layer were analysed by means of X-ray diffraction (XRD), scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), optical microscopy and microhardness testing. The corrosion behaviour of the S phase was also investigated. The maximum Knoop hardness after plasma nitriding is about 1400 HK 0.01 and the maximum thickness of the compound layer is 34 μm. XRD patterns show that the surface layer consists of the S phase only. The corrosion performance was tested in 0.05 M Na2SO4 solution at pH 3.3 and in neutral 3.5% NaCl solution at ambient temperature. Potentiostatic and potentiodynamic experiments yielded slightly higher passive corrosion currents for plasma-nitrided 304L. Pitting corrosion in neutral electrolytes containing chloride ions was observed only for untreated 304L. The passive layers formed on both types of samples were similar in constitution and thickness as determined from XPS sputter profiles.

NEFCLASSmdash;a neuro-fuzzy approach for the classification of data

Abstract: In this paper we present NEFCLASS, a neuro-fuzzy system for the classification of data. This approach is based on our generic model of a fuzzy perceptron which can be used to derive fuzzy neural networks or neural fuzzy systems for specific domains. The presented model derives fuzzy rules from data to classify patterns into a number of (crisp) classes. NEFCLASS uses a supervised learning algorithm based on fuzzy error backpropagation that is used in other derivations of the fuzzy perceptron. Introduction Combinations of neural networks and fuzzy systems are very popular (for an overview see [4, 6]), but most of the approaches are not easy to compare because they use very different architectures, activation functions, propagation and learning algorithms, etc. In [s] we presented a fuzzy perceptron as a generic model of multilayer fuzzy neural networks. It can be used as a common base for neuro-fuzzy architectures in order to ease the comparision of different approaches. By applying additional constraints to the definition of the fuzzy perceptron one can e.g. obtain a structure that can be interpreted as a usual fuzzy controller, and easily create a neuro-fuzzy controller this way [3, 8, 91. In thii paper we present an approach to neuro-fuzzy data analysis. The goal is to derive fuzzy rules from a set of data that can be separated in different crisp classes, i.e. at this moment we do not consider data where the patterns belong to overlapping or fuzzy categories. The fuzziness involved is due to an imperfect or incomplete measurement of features thus rendering it difficult to assign a pattern to the correct category. “Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commerical advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission.” @ 19% ACM O-89791-658-1 95 COO2 3.50 The fuzzy rules describing the data are of the form: if ~~ is g1 and zz is ~2 and . . . end zn is p, then the pattern (21,22, . . . ,z,) belongs to class i, where~l,... , pn are fuzzy sets. The task of the NEFCLASS model is to discover these rules and to learn the shape of the membership functions. We will first briefly present the fuzzy perceptron model in section II, and in section III we show how the NEFCLASS model is derived from it. We also present the supervised learning algorithm. In the fourth section we discuss the learning results we got by applying NEFCLASS to the SRIS data set, and we compare the results to other approaches. The Fuzzy Perceptron A fuzzy perceptron has the architecture of an usual multilayer perceptron, but the weights are modelled as fuzzy sets and the activation, output, and propagation functions are changed accordingly. The intention of this model is to be interpretable in form of linguistic rules and to be able to use prior rule based knowledge, so the learning has not to start from scratch. In [s] we suggested a generic model for fuzzy neural networks based on a 3-layer fuzzy perceptron. By using it to derive neural fuzzy systems for special domains, it would be possible to evaluate these diierent neuro-fuzzy approaches by means of the same underlying model. The fuzzy perceptron was used to derive the NEFCON model [3, 8, 91 for neuro-fuzzy controll applications, and it is now used to define the NEFCLASS model discussed in this paper. We will therefore shortly present the definition of the generic fuzzy perceptron. Definition 1 A %-layer fuzzy perceptron is D S-layer feedforward neural network (U, W, NET, A, 0, ex) with the following specifications: (i) I! = U U; is a non-empty set of units (neurons) igM andM={1,2,3} is theindezsetofu. Foralli,jE M, U; # B and U; n Uj = t? with i # j holds. U1 is called input layer, Us rule layer (hidden layer), and Ii3 output layer. (ii) The structure of the network (connections) is defined as W : U x U --+ T(R), such that there are only connections W(u, w) with u E Cr,, u E U,+I : E all fuzzy subsets of L). {1,2)) (T(R) is the set of

Morphological and orthographic similarity in visual word recognition.

Abstract: The differential impact of orthographic and morphological relatedness on visual word recognition was investigated in a series of priming experiments in Dutch and German. With lexical decision and naming tasks, repetition priming and contiguous priming procedures, and masked and unmasked prime presentation, a pattern of results emerged with qualitative differences between the effects of morphological and form relatedness. With lexical decision, mere orthographic similarity between primes and targets (e.g., keller-KELLER, cellar-ladle) produced negative effects, whereas morphological relatedness (e.g., kellen-KELLE, ladles-ladle) consistently resulted in facilitation. With the naming task, positive priming effects were found for morphological as well as for mere form similarity. On the basis of these results, a model of the lexicon is proposed in which information about word form is represented separately from morphological structure and in which processing at the form level is characterized in terms of activation of, and competition between, form-related entries.

A nuclear gene of eubacterial origin in Euglena gracilis reflects cryptic endosymbioses during protist evolution

Abstract: Genes for glycolytic and Calvin-cycle glyceraldehyde-3-phosphate dehydrogenase (GAPDH) of higher eukaryotes derive from ancient gene duplications which occurred in eubacterial genomes; both were transferred to the nucleus during the course of endosymbiosis. We have cloned cDNAs encoding chloroplast and cytosolic GAPDH from the early-branching photosynthetic protist Euglena gracilis and have determined the structure of its nuclear gene for cytosolic GAPDH. The gene contains four introns which possess unusual secondary structures, do not obey the GT-AG rule, and are flanked by 2- to 3-bp direct repeats. A gene phylogeny for these sequences in the context of eubacterial homologues indicates that euglenozoa, like higher eukaryotes, have obtained their GAPDH genes from eubacteria via endosymbiotic (organelle-to-nucleus) gene transfer. The data further suggest that the early-branching protists Giardia lamblia and Entamoeba histolytica--which lack mitochondria--and portions of the trypanosome lineage have acquired GAPDH genes from eubacterial donors which did not ultimately give rise to contemporary membrane-bound organelles. Evidence that "cryptic" (possibly ephemeral) endosymbioses during evolution may have entailed successful gene transfer is preserved in protist nuclear gene sequences.

Characterization of a novel fibronectin‐binding surface protein in group A streptococci

Abstract: Streptococcus pyogenes interacts with host fibronectin via distinct surface components. One of these components is the Sfbl protein (streptococcal fibronectin-binding protein, now specified as class I), an adhesin that represents a protein family with characteristic features. Here we present the complete structure of a novel fibronectin-binding protein of S. pyogenes, designated SfbII, which is distinct from the previously described Sfbl proteins. The sfbII gene originated from a λ EMBL3 library of chromosomal DNA from group A streptococcal strain A75 and coded for a 113kDa protein exhibiting features of membrane-anchored surface proteins of Gram-positive cocci. The expression of biologically active fusion proteins allowed the determination of the location of the fibronectin-binding domain within the C-terminal part of the protein. It consisted of two and a half repeats which share common motifs with fibronectin-binding repeats of other streptococcal and staphylococcal proteins. Purified recombinant fusion protein containing this domain competitively inhibited the binding of fibronectin to the parental S. pyogenes strain. Furthermore, polyclonal antibodies against the binding domain specifically blocked the Sfbll receptor site on the streptococcal surface. No cross-reactivity could be detected between anti-Sfbll antibodies and the sfbl gene product, and vice versa, indicating that the two proteins do not share common immunogenic epitopes. Southern hybridization experiments performed with specific sfbll gene probes revealed the presence of the sfbll gene in more than 55% of 93 streptococcal isolates tested. The majority of the strains also harboured the sfbl gene, and 86% carried at least one of the two sfb genes.

The solar WIND and suprathermal ion composition investigation on the WIND spacecraft

Abstract: The Solar Wind and Suprathermal Ion Composition Experiment (SMS) on WIND is designed to determine uniquely the elemental, isotopic, and ionic-charge composition of the solar wind, the temperatures and mean speeds of all major solar-wind ions, from H through Fe, at solar wind speeds ranging from 175 kms−1 (protons) to 1280 kms−1 (Fe+8), and the composition, charge states as well as the 3-dimensional distribution functions of suprathermal ions, including interstellar pick-up He+, of energies up to 230 keV/e. The experiment consists of three instruments with a common Data Processing Unit. Each of the three instruments uses electrostatic analysis followed by a time-of-flight and, as required, an energy measurement. The observations made by SMS will make valuable contributions to the ISTP objectives by providing information regarding the composition and energy distribution of matter entering the magnetosphere. In addition SMS results will have an impact on many areas of solar and heliospheric physics, in particular providing important and unique information on: (i) conditions and processes in the region of the corona where the solar wind is accelerated; (ii) the location of the source regions of the solar wind in the corona; (iii) coronal heating processes; (iv) the extent and causes of variations in the composition of the solar atmosphere; (v) plasma processes in the solar wind; (vi) the acceleration of particles in the solar wind; and (vii) the physics of the pick-up process of interstellar He as well as lunar particles in the solar wind, and the isotopic composition of interstellar helium.

Influence of agricultural traffic and crop management on collembola and microbial biomass in arable soil

Abstract: Collembola and microbial biomass C were investigated in a field experiment with controlled agricultural traffic and crop rotation over a period of 27 months. The wheel-induced compactive efforts were applied according to management practices within the crop rotation of sugar beet, winter wheat, and winter barley. Increasing wheel traffic produced increasing soil compaction, mainly due to a reduction in surface soil porosity. Increasing soil compaction was accompanied by a decrease in microbial biomass C and the density of collembola. The influence of soil compaction on microbial biomass C was smaller than that of the standing crop. However, for collembola, especially euedaphic species, a reduction in pore space appeared to be of more importance than the effects of a standing crop. Within the crop rotation, microbial biomass C and the density of collembola increased in the order sugar beet, winter wheat, and winter barley.

Purification and cDNA cloning of anthranilate synthase from Ruta graveolens: modes of expression and properties of native and recombinant enzymes.

Abstract: Ruta graveolens utilizes anthranilate synthase (AS) for the synthesis both of tryptophan in primary metabolism and acridone alkaloids in secondary metabolism. AS has been purified from plants and cell cultures of R. graveolens 670- and 1700-fold, respectively. Glutamine- and ammonia-dependent AS activities were strictly co-purified in all steps. Through cDNA cloning and complementation of Escherichia coli deletion mutants defective for AS, it is shown that young Ruta plants express two genes for functional AS alpha subunits, AS alpha 1 and AS alpha 2. The data indicate that AS alpha from Ruta requires an AS beta subunit with a native molecular weight of 60-65 kDa for the glutamine-dependent reaction. Protein synthesized in vitro from cloned cDNA is processed upon import into isolated chloroplasts, indicating that mature AS alpha subunits are active in plastids in vivo. AS alpha 1 and AS alpha 2 are constitutively expressed in Ruta cell cultures, but AS alpha 1 steady-state mRNA levels are increased 100-fold 6 h subsequent to elicitation whereas AS alpha 2 expression remains constitutive. Increased AS alpha 1 transcription corresponds to elicitor-induced alkaloid accumulation. The data indicate that Ruta regulates anthranilate flux into primary and secondary metabolism through differential regulation of AS genes specific to these pathways.

Molybdenum co‐factor biosynthesis: the Arabidopsis thaliana cDNA cnx1 encodes a multifunctional two‐domain protein homologous to a mammalian neuroprotein, the insect protein Cinnamon and three Escherichia coli proteins

Abstract: The molybdenum co-factor (Moco) is an essential part of all eukaryotic molybdoenzymes. It is a molybdopterin and reveals the same principal structure in eubacteria, archaebacteria and eukaryotes. This paper reports the isolation of cnx1, a cDNA clone of Arabidopsis thaliana which complements the Escherichia coli Moco mutant mogA. The mapping data of this cDNA correlate well with the mapping position of the A. thaliana molybdenum co-factor locus chl6. As mutants in chl6 are known to be repairable by high concentrations of molybdate, the defective gene is very likely to be involved in the last step of Moco biosynthesis, that is, the insertion of molybdenum into molybdopterin. The protein encoded by cnx1 shows a two-domain structure: the N-terminal domain is homologous to the E. coli Moco protein MoeA, the C-terminal domain is homologous to the E. coli Moco proteins MoaB and MogA, respectively. These homologies show that part of the prokaryotic Moco biosynthetic pathway accomplished by monofunctional proteins in E. coli, is performed by a single multifunctional protein in eukaryotes. In addition Cnx1 is homologous to the eukaryotic proteins Gephyrin, a rat neuroprotein, and Cinnamon, a Drosophila protein with a function in Moco biosynthesis. These proteins also show a two-domain structure but the order of the domains is inversed as compared with Cnx1. Southern analysis indicates the existence of at least one further member, in addition to the cnx1 gene, of this novel gene family in the Arabidopsis genome.

Practical Experiences in Schedule Synchronization

Abstract: In complex networks schedule synchronization has a major importance when constructing timetables. Restrictions in this field are based on the structure and the complexity of the existing network, different headways, and the origin-destination pairs of the demand structure. With respect to service quality one main objective coming to mind consists of minimizing the sum of all waiting times of all passengers at transfer nodes in a transit system. Furthermore, modifications of such an objective function incorporating the maximum waiting time may have to be observed as well as interrelationships between service level and operating cost.

Plasma surface treatment and PACVD on Ti alloys for surgical implants

Abstract: To improve the poor surface hardness and wear resistance of titanium alloys used for surgical implants undergoing wear TiA16V4 and TiA15Fe2.5 have been plasma nitrided. TiN and other sublayers are formed by plasma nitriding. To increase the thickness of the outermost TiN layer the samples have been coated with TiN by PACVD following plasma nitriding. The produced layers have been characterized in terms of microstructure, layer composition, hardness depth profiles. The evaluation of corrosion resistance and biocompatibility revealed that the good properties of the untreated alloys have been well preserved.

Determination of dispersion relations in quasi-stationary plasma turbulence using dual satellite data

Abstract: The joint frequency-wavenumber spectrum is one of the basic quantities for analyzing plasma turbulence It is shown how the full spectrum can be recovered from wavefields measured by two or more satellites via spectral methods based on wavelet transforms Compared to standard cross-correlation techniques, different branches in the dispersion relation can be resolved and quasi-stationary wavefields can be accessed Using this new approach, low frequency magnetic field data from the AMPTE-UKS and AMPTE-IRM spacecraft are investigated and the impact of nonlinear processes on wave propagation at the Earth's foreshock is revealed

Fluorescence spectroscopy of polynuclear aromatic compounds in environmental monitoring.

Abstract: The occurrence of polynuclear aromatic compounds (PAC) in the environment and experimental techniques suitable for the detection of PAC in environmental compartments are briefly reviewed. The specific requirements for on-site andin situ environmental analysis are outlined. Particular emphasis is given to fluorescence spectroscopic techniques for the investigation of humic acid- and soil-containing samples. Some examples of studies in the literature on Shpol'skii and jet spectroscopy and on laser-induced fluorescence (OF) measurements of PAC and mineral oils are highlighted. Contaminants in the environment are usually encountered as multicomponent mixtures in very complex matrices. Total fluorescence analysis in combination with the chemometrical technique of rank annihilation factor analysis (RAFA) was employed for the evaluation of a six-component PAC mixture in toluene. It was shown that even in the presence of strong spectral overlap the qualitative identification of all compounds and the reliable quantification of five substances was possible. Results are presented from our stationary and time-resolved fluorescence investigations of the interactions between pyrene and humic acid in water. The Stern-Volmer analysis showed a significant effect of pH on the static quenching efficiency which can be explained by the pH-dependent macromolecular structure of humic acids. Preliminary results from studies of the deactivation of triplet PAC and quenching of delayed fluorescence by humic acid are reported. LIF measurements of mineral oils directly from soil surfaces and of a model oil in a soil column were performed with a fiber-optic coupled multichannel spectrometer. The fluorescence intensity/ concentration relationships were established for a crude and a fuel oil; the corresponding lower limits of detection (LOD) were determined to be 0.025 and 0.125% m/m (mass/mass percentages). These detection limits are compared with realistic oil contaminations of soils. In a soil column designed to mimic fixed-bed bioreactors the distributions of fluorescence signal intensities from a perylene-doped model oil before and after water flooding were determined. These results fromin situ measurements can provide a quantitative basis for the modelling of temporal and spatial contaminants' distributions in reactor design.

Grazing preferences of some collembola for endomycorrhizal fungi

Abstract: The ability of five collembolan species to distinguish and graze selectively on vesicular-arbuscular mycorrhiza (VAM) has been verified Four species preferred the food infected by VAM fungi All collembolan species showed more of less significant preferences for one species/isolate of the VAM fungi

Preparation and physicochemical characterization of aqueous dispersions of coenzyme Q10 nanoparticles

Abstract: The present study describes a novel pharmaceutical formulation of coenzyme Q10, viz. submicron-sized dispersions of the substance prepared by emulsification of molten coenzyme Q10 in an aqueous phase. Photon correlation spectroscopy reveals mean diameters of 60 to 300 nm depending on process parameters. Coenzyme Q10 nanoparticles remain stable on storage for more than 30 months. Lipophilic drugs can be incorporated into the nanoparticles demonstrating their potential use as a drug carrier system. Transmission electron micrographs of freeze-fractured replica show spherical particles with an amorphous core. Cryo-electron microscopy reveals the coexistence of small unilamellar vesicles in phospholipid stabilized dispersions. Thermoanalysis and X-ray studies indicate that the dispersed and emulsified coenzyme Q10 does not recrystallize even at 4°C over 30 months. These agree with 1H NMR data which demonstrate that coenzyme Q10 molecules have a high mobility when formulated as nanoparticles and that colloidally dispersed coenzyme Q10 remains in the state of a supercooled melt. Despite the high melting point of the bulk material, coenzyme Q10 dispersions represent no suspensions but O/W emulsions according to the IUPAC definition (1).