Showing papers by "Braunschweig University of Technology published in 1991"

New method for detecting rhamnolipids excreted by Pseudomonas species during growth on mineral agar

Abstract: A new semi-quantitative agar plate test for the detection of extracellular rhamnolipids has been developed. These biological anionic tensides (biosurfactants) form an insoluble ion pair with the cationic tenside cetyltrimethylammonium bromide and the basic dye methylene blue which was included in mineral agar plates. On the light blue agar, productive colonies ofPseudomonas spec. were surrounded by dark blue halos. The test is specific for anionic biosurfactants and can be applied to other glycolipid producing microorganims.

Simulation of recrystallization by cellular automata

Abstract: A cellular automata (CA) model for recrystallization is introduced. Its behviour is investigated under the influence of different model parameters and algorithms that simulate the kinetics of nucleation and growth of recrystallizing grains. The rate of released energy is calculated by the CA-model so that comparisons with calorimetric measurements are possible. The CA-model givesthe same results as the theory of Johnson, Mehl, Avrami and Kolmogorov (JMAK) for the same model assumptions. Systematic deviations of experimental data from the JMAK-theory are simulated by special model assumptions of the CA. This leads to good agreement with experimental data. It is shown that the CA-model is easy to handle, very simple in the basic algorithm and extremely flexible for introducing special model assumptions.

The IgA‐binding β antigen of the c protein complex of Group B streptococci: sequence determination of its gene and detection of two binding regions

Abstract: The beta antigen of the lbc protein complex of Group B streptococci is a cell-surface receptor which binds the Fc region of human immunoglobulin A (IgA). Determination of the nucleotide sequence of the beta antigen gene shows that it encodes a preprotein having a molecular weight of 130,963 daltons and a polypeptide of 1164 amino acid residues that is typical of other Gram-positive cell-wall proteins. There is a long signal sequence of 37 amino acids at the N-terminus. Four of the five C-terminal amino acid residues are basic and are preceded by a hydrophobic stretch that appears to anchor the C-terminus in the cell membrane. To the N-terminal side of this hydrophobic stretch is a putative cell-wall-spanning region containing proline-rich repeated sequences. An unusual feature of these repeated sequences is a three-residue periodicity, whereby every first residue is a proline, the second residue is alternating positively or negatively charged, and the third residue is uncharged. The IgA-binding activity was approximately localized by expressing subfragments of the beta antigen as fusion proteins. Two distinct but adjacent DNA segments specified peptides that bound IgA, which indicates that the IgA-binding activity is located in two distinct regions of the protein.

Qualitative and Quantitative Analysis of the Phenolic Constituents from Orthosiphon aristatus.

Abstract: ORTHOSIPHON ARISTATUS (Orthosiphonis folium DAB 9) was studied with regard to its phenolic constituents. Twenty compounds were isolated and identified on the basis of their spectral characteristics. The compounds included nine lipophilic flavones, two flavonol glycosides, and nine caffeic acid derivatives. The presence of the recently reported methylripariochromene A could not be confirmed. All compounds identified were quantified by HPLC. The caffeic acid derivatives including the major compounds rosmarinic acid and 2,3-dicaffeoyltartaric acid (67% of total identified phenolics) predominated over the flavones (33%) in an aqueous MeOH extract. The predominance of the caffeic acid derivatives was even more pronounced in a hot water extract (94.5% of total identified phenolics) that was comparable to a herbal tea.

30 Years Space Vectors, 20 Years Field Orientation, 10 Years Digital Signal Processing with Controlled AC-Drives, a Review (Part 1)

Abstract: SummaryThe dynamic interactions of AC-machines are far more complex than those of DC-machines and important quantities are not directly measurable. This has given rise to considerable difficulties in designing high performance AC-drive controls. About 20 years ago, they were overcome by the emergence or new methods of control, using moving frames of reference determined by the angular position or flux waves, hence called field orientation. Their application requires extensive on-line signal processing that can only be realised economically with microprocessors or special digital hardware.The paper presents a review of this evolution, which has matured in less than 2 decades from research studies to a universally accepted method for controlling AC-machines. The method of field orientation has proved to be well adaptable to all types of power converters and AC-machines; modifications and extensions to include self-tuning and adaptive features are possible. It now seems to be generally accepted that field or...

Marine biosurfactants, III. Toxicity testing with marine microorganisms and comparison with synthetic surfactants.

Abstract: Eight synthetic and nine biogenetic surfactants were tested on their toxicity. Because of their possible application as oil dispersants against oil slicks on sea, the test organisms used were marine microorganisms (mixed and pure cultures of bacteria, microalgae, and protozoa). Bacterial growth was hardly effected or stimulated, whilst that of algae and flagellates was reduced. All substances tested were biodegraded in sea water. The bioluminescence of Photobacter phosphoreum (Microtox test) was the most sensitive test system used. A ranking shows that most biogenetic surfactants were less toxic than synthetic surfactants. No toxicity could be detected with the glucose-lipid GL, produced by the marine bacterium Alcaligenes sp. MM1.

The Effect of Ultraviolet and Solar Radiation and Temperature on Survival of Fungal Propagules

Abstract: Survival of spores, spore aggregates, sclerotia, and pycnidia of fungi was evaluated after exposure to high temperature in the dark, or exposure to ultraviolet (UV) radiation or sunlight. Under most conditions survival decreased from the most resitant Sclerotium rolfsii to Alternaria macrospora, Mycosphaerella pinodes, Aspergillus niger and Botrytis cinerea, in that order. There was no difference in survival among organisms stored in darkness at 45°C as single spores or aggregated into a mass of spores; or between spores of M. pinodes exposed before and after being released from pycnidia. Exposure to UV reduced survival much more than exposure in darkness. Longevity under UV ranged from more than 7 days for S. rolfsii to approximately 50 min for A. macrospora and 3 min for B. cinerea. Much longer survival occurred for spores of all fungi aggregated together; of spores of M. pinodes irradiated when inside rather than outside pycnidia; and in bigger, darker and older rather than in smaller, paler and younger sclerotia of S. rolfsii. Survival of sclerotia cut into slices and exposed to UV increased with thickness, irrespective of exposure to UV with the outer pigmented or innernonpigmented side. As tested with spore aggregates of A. niger, the rate of survival was linearly proportional to the number of conidia aggregated in each body. Irradiation by sunlight affected survival as described for irradiation by UV. The best protection from the detrimental effects of sun and UV radiation was provided by the infected host tissue.

Influence of sewage sludge and heavy metals on nematodes in an arable soil

Abstract: The abundance of nematodes was investigated in agricultural plots treated in three different ways, the first with no treatment, the second with 300 m3 ha-1 a-1 raw sewage sludge and the third with 300 m3 ha-1 a-1 sewage sludge with the addition of heavy metals. The nematodes were determined down to the genus and were assigned to five feeding groups. Total nematode numbers were highest in the site treated with sewage sludge and heavy metals. The smallest total numbers were found in the control site. The plant-feeding nematode genera showed different patterns of abundance depending on the sludge treatment and heavy metal content. For the mycophagic and bacteriophagic nematodes, numbers increased with the amount of sludge, especially in the sites with a higher heavy metal content. The family Rhabditidae was the most numerous group in the sludge plus heavy metals treatment. In contrast to these findings, the omnivorous nematodes were very rare in the sludgetreated plots and were completely absent in plots treated with sludge plus heavy metals, whereas predatory nematodes were numerous only after the application of sludge alone.

Reductive dechlorination of Tri- and tetrachloroethylenes depends on transition from aerobic to anaerobic conditions.

Abstract: Aerobic enrichment cultures from contaminated groundwaters dechlorinated trichloroethylene (TCE) (14.6 mg/liter; 111 mumol/liter) and tetrachloroethylene (PCE) (16.2 mg/liter; 98 mumol/liter) reductively within 4 days after the transition from aerobic to anaerobic conditions. The transformation products were equimolar amounts of cis-1,2-dichloroethylene and traces of 1,1-dichloroethylene. No other chlorinated product and no methane were detected. The change was accompanied by the release of sulfide, which caused a decrease in the redox potential from 0 to -150 mV. In sterile control experiments, sulfide led to the abiotic formation of traces of 1,1-dichloroethylene without cis-1,2-dichloroethylene production. The reductive dechlorination of PCE via TCE depended on these specific transition conditions after consumption of the electron acceptor oxygen or nitrate. Repeated feeding of TCE or PCE to cultures after the change to anaerobic conditions yielded no further dechlorination. Only aerobic subcultures with an air/liquid ratio of 1:4 maintained dechlorination activities; anaerobic subcultures showed no transformation. Bacteria from noncontaminated sites showed no reduction under the same conditions.

A non-destructive method for the morphological assessment of earthworm burrow systems in three dimensions by X-ray computed tomography

Abstract: Earthworm burrows of endogeic species (Allolobophora caliginosa, Octolasium cyaneum) in artificially packed soil columns were examined using X-ray computed tomography. By means of digital image processing, it was possible to reconstruct and visualize the burrow system in three dimensions. The reconstruction revealed morphological features of the burrows which were not obvious from two-dimensional section images.

Normal and deviant lexical processing: Reply to Dell and O'Seaghdha (1991).

Abstract: In their comment, Dell and O'Seaghdha (1991) adduced any effect on phonological probes for semantic alternatives to the activation of these probes in the lexical network. We argue that that interpretation is false and, in addition, that the model still cannot account for our data. Further­ more, and different from Dell and O'Seaghda, we adduce semantic rebound to the lemma level, where it is so substantial that it should have shown up in our data. Finally, we question the function of feedback in a lexical network (other than eliciting speech errors) and discuss Dell's (1988) notion of a unified production-comprehension system. Until recently, models of lexical access in speech production were almost exclusively based on speech error data. This is true both for the modular two-stage models and for the interactive connectionist models of lexical access. Both kinds of models were initially designed to account for the distributions of natu­ rally observed or experimentall y elicited speech errors. From the start, however, they were conceived as process models of normal speech production. Therefore, the ultimate test of such models cannot lie in their account of infrequent derailments of the process. Rather, the proof of their efficacy should be sought in the account of the normal process itself. An exclusively errorbased approach to lexical access in speech production is as ill-conceived as an exclusively illusion-based approach in vision research. One should, of course, hope that an ultimate theory of the normal process also has the potential of explaining ob­ served error distributions (or visual illusions, for that matter), but it should not be one's main concern.

Determination of flavanols, theogallin, gallic acid and caffeine in tea using HPLC

Abstract: An RP-HPLC method for the determination of flavanols (catechins), theogallin, gallic acid and caffeine, including the sample preparation using a solid-phase extraction technique, has been developed. HPLC separation was performed on a Hypersil-ODS column using a gradient method with 2% acetic acid (aq) and acetonitrile as solvents. The method has been applied to green, oolong and black tea samples as well as tea extracts. The contents in different kinds of tea were 0.93–5.74 g/100 g dry mass for epigallocatechin gallate, 0.73–3.25 g/100 g dry mass for epigallocatechin, 0.17–1.16 g/100 g dry mass for epicatechingallate, 0.04–0.48 g/100 g dry mass for catechin, 0.1–0.8 g/100 g dry mass for epicatechin, 0.17–0.97 g/100 g dry mass for theogallin, 0.06–0.62 g/100 g dry mass for gallic acid and 2.25–4.33 g/100 g dry mass for caffeine. Instant tea contained 2–3-fold higher amounts. As expected the contents of flavanols in green teas were higher than in black teas, for gallic acid it was the opposite. Furthermore, the influence of different extraction methods on the contents of these compounds has been investigated.

Sequestration of plant pyrrolizidine alkaloids by chrysomelid beetles and selective transfer into the defensive secretions

Abstract: Oreina cacaliae andO. speciosissima (Coleoptera, Chrysomelidae) sequester in their elytral and pronotal defensive secretions pyrrolizidine alkaloids (PAs) as Noxides (PA N-oxides). The PA N-oxide patterns found in the beetles and their host plants were evaluated qualitatively and quantitatively by capillary gas chromatography/mass spectrometry (GC-MS). Of the three host plantsAdenostyles alliariae (Asteraceae) is the exclusive source for PA N-oxide sequestration in the defensive secretions of the beetles. With the exception of O-acetylseneciphylline the N-oxides of all PAs ofA. alliariae, i.e. senecionine, seneciphylline, spartioidine, integerrimine, platyphylline and neoplatyphylline were identified in the secretion. PA N-oxides typical ofSenecio fuchsii (Asteraceae) were detected in the bodies of the beetles but not in their secretion. No PAs were found in the leaves of the third host plant,Petasites paradoxus (Asteraceae). The results suggest the existence of two distinctive storage compartments for PA N-oxides in the beetle: (1) the defensive secretion, containing specifically PA N-oxides acquired fromA. alliariae; (2) the body of the beetle, sequestering additionally but less selectively PA N-oxides from other sources,e.g. S. fuchsii or monocrotaline N-oxide fed in the laboratory. The concentration of PA N-oxides in the defensive secretion is in the range of 0.1 to 0.3 mol/1, which is more than 2.5 orders of magnitude higher than that found in the body of the beetle. No significant differences exist in the ability of the two species of beetles to sequester PA N-oxides fromA. alliariae, althoughO. speciosissima, but notO. cacaliae, produces autogenous cardenolides. A negative correlation seems to exist between the concentrations of plant-derived PA N-oxides andde novo synthesized cardenolides in the defensive secretion ofO. speciosissima.

Synthesis and structural characterization of gold-(I), -(III) and silver(I) complexes of the ylide ligand Ph3PCHC(O)NMe2. Crystal structure of [(AuPPh3)2{µ-C(PPh3)C(O)NMe2}]ClO4

Abstract: The reaction between [AuCl(tht)](tht = tetrahydrothiophene) and the ylide Ph3PCHC(O)NMe2 gives [AuCl{CH(PPh3)C(O)NMe2}]1, which reacts with chlorine to gives [AuCl3{CH(PPh3)C(O)NMe2}]2 and with the same ylide and NaClO4 to form [Au{CH(PPh3)C(O)NMe2}2]ClO43. The analogous silver complex [Ag{CH(PPh3)C(O)NMe2}2]ClO44 is obtained by the reaction of AgClO4 with the ylide in molar ratio 1 : 2. The phosphonium salt [Ph3PCH2C(O)NMe2]ClO4 reacts with [Au(acac)(PPh3)](acac = acetylacetonate) to gives [Au{CH(PPh3)C(O)NMe2}(PPh3)]ClO45 or [(AuPPh3)2{µ-C(PPh3)C(O)NMe2}]ClO46 depending on the reaction conditions. The structure of 6 was confirmed by an X-ray diffraction study at –95 °C [space group P, a= 11.572(3), b= 11.836(3), c= 21.627(7)A, α= 78.29(2), β= 87.19(2), γ= 75.65(2)°, R= 0.076]; the Au ⋯ Au bond length is 2.938(1)A.

Toxicity testing of synthetic and biogenic surfactants on marine microorganisms

Abstract: The toxicity of four synthetic surfactants, two commercial oil dispersants, and six biosurfactants have been examinated. The test systems were (a) bacterial growth inhibition, (b) microalgae growth inhibition, (c) microflagellate growth inhibition, (d) biodegradation, and (e) bioluminescence inhibition (Microtox test). The multiplication of bacteria was stimulated by surfactants, while that of microflagellates and microalgae was inhibited. This may be due to the metabolic usage of surfactants, especially biosurfactants, by bacteria. The bioluminescence was very sensitive to surfactants. No toxicity could be detected with glucose-lipid, produced by the marine bacterium Alcaligenes sp. MM1. Most biosurfactants were degraded faster and possessed higher EC50 values than synthetic dispersants.

Modelling nitrogen dynamics in a plant-soil system with a simple model for advisory purposes

Abstract: A simple functional computer model for advisory purposes is described. Results of simulation indicate some limitations of the model especially in handling the water regime in soils with fluctuating water tables. A major problem seems to be the ‘disappearance’ of fertilizer N. Measurements by the fumigation-extraction method of microbial N during the growing season show that disappearance of fertilizer N can partly be explained by immobilization by the microbial biomass.

Descriptive specification of database object behaviour

Abstract: Traditional database design methodologies are not appropriate for the specific requirements of object-oriented database systems and new database application areas. Apart from semantic complications arising from object-oriented database structures with complex objects, arbitrary data types as attribute domains, or generalization hierarchies, specification and semantics of dynamic database behaviour has to be of main interest for typical object-oriented applications, too. We propose the use of a temporal logic as a specification language for dynamic object behaviour and point out the formal semantics of such database dynamics specifications. A layered conceptual database design methodology is presented together with a discussion on design support techniques for behaviour specifications. Finally, implementation aspects are treated.

Neue planare π-Systeme, II1) Zur Darstellung und Struktur von Tetrakis(phenylethinyl)ethen

Abstract: New Planar π-Systems, II1). - On the Preparation and Structure of Tetrakis(phenylethynyl)ethene The preparation of tetrakis(phenylethynyl)ethene (1 b) has been repeated. Among various routes to this highly unsaturated cross-conjugated π-system, the dimerization of bromide 2 via the carbene 3 is the most simple one. Full spectroscopic data for 1 b are reported for the first time, as is its X-ray structural analysis at - 95°C.

Evolution of the Rubisco operon from prokaryotes to algae: structure and analysis of the rbcS gene of the brown alga Pylaiella littoralis.

Abstract: The rbcS gene coding for the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) of the brown alga Pylaiella littoralis is located within the plastid genome and is transcribed as a single polycistronic mRNA with the gene for the large subunit of Rubisco, rbcL. The structure of the Rubisco operon from P. littoralis was determined. Molecular phylogenies for rbcS and rbcL with a wide range of prokaryotes and eukaryotes were constructed which are congruent with recent evidence for polyphyletic plastid origins. Both rbcL and rbcS of the beta-purple bacterium Alcaligenes eutrophus clearly cluster with the rhodophyte and chromophyte proteins. The data suggest that the Rubisco operons of red algal and chromophytic plastids derive from beta-purple eubacterial antecedents, rather than the cyanobacterial lineage of eubacteria from which other of their genes derive. This implies a lateral transfer of Rubisco genes from beta-purple eubacterial ancestors to the cyanobacterial ancestor of rhodophyte and chromophyte plastids.

A time domain integral formulation of dynamic poroelasticity

Abstract: In this paper, a direct boundary element approach for solving three-dimensional problems of dynamic poroelasticity in the time domain is developed. Based on Biot's theory of wave propagation in poroelastic media, and on Cleary's reciprocal theorem, the complete set of necessary time-dependent fundamental solutions has been derived. Then, after an analytical time integration, a time stepping Boundary Element procedure for the numerical solution of wave propagation problems is established.

The origin of Kibaran (late Mid-Proterozoic) tin, tungsten and gold quartz vein deposits in Central Africa: a fluid inclusions study

Abstract: Composition and evolution of fluids depositing tin and tungsten ores in Kibaran quartz vein deposits allow the modelling of devolatizing evolved granites as their source at depth. Fluids forming gold quartz veins and breccias are different from the first, especially by showing characteristics of a high-pressure environment. All deposits are controlled by compressional deformation whose fading phases affect earlier formed veins. These findings lead to the conclusion that both anatectic melting resulting in intrusion of fertile granites, and the generation of fluids forming gold deposits are the final consequence of deep crustal metamorphism. The latter was caused by crustal thickening immediately preceding the metallogenetic climax.

Stress-strain fields at the tunnelling face—Three-dimensional analysis for two-dimensional technical approach

Abstract: For tunnelling in rock, the original stress field in the ground is changed considerably before a first lining is participating in stabilizing the opening. Depending on this stress release at the tunnel face, only a small portion of the primary stresses is acting on the lining. Only a three-dimensional approach is able to determine the stresses and the deformations of the ground and the lining realistically. The paper presents some results of elastic three-dimensional finite-element-analyses in consecutive steps of the sectional excavation of circular and non-circular tunnels. From these results an equivalent two-dimensional approach is derived for technical applications, given in diagrams.

On the use of the BEM for wave propagation in infinite domains

Abstract: The use of the Boundary Element Method for the analysis of wave propagation in boundless domains is discussed. Attention is paid to the difficulties that the method may present in the context of external regions, uniform half-spaces, boundless layer systems and infinite channels. In cases where the model should include boundaries extending to infinity the circumstances that allow the truncation of the boundary discretization are analysed. Several examples of wave propagation problem in boundless domains are presented. An artificial closing boundary is shown to be necessary for the case of standing waves propagating in an infinite three or two-dimensional channel. The closing boundary is formulated and tested.

Theoretical foundations of handling large substitution sets in temporal integrity monitoring

Abstract: Temporal integrity constraints describe long-term data dependencies in databases to be satisfied by each correct database evolution. They can be formulated in a temporal logic. For a runtime monitoring of temporal integrity the problem arises to handle the historical information necessary to monitor the long-term dependencies. This paper extends the already known techniques for minimizing the stored information for a single substitution of the free constraint variables using transition graph construction. Our extension allows to decrease also the amount of handled substitutions for constraint monitoring. For this purpose, the notion of substitution descriptions is formally introduced allowing to monitor simultaneously whole substitution sets. The notions of formula validity and of stepwise monitoring potential validity of temporal constraints are redefined for descriptions. Based on these notions an algorithm for monitoring temporal integrity by handling descriptions is presented.