Showing papers by "Technical University of Berlin published in 1991"

Large single-mode rib waveguides in GeSi-Si and Si-on-SiO/sub 2/

Abstract: Mode-matching and beam-propagation methods are used to analyze single-mode operation of optical GeSi-Si and Si-SiO/sub 2/ semiconductor rib waveguides. The waveguide dimensions that allow only the fundamental HE/sub 00/ or EH/sub 00/ mode to propagate have been determined. For both material systems, it is found that the rib can be several microns wide and several microns high, thus allowing efficient coupling to single-mode fibers. Numerical examples are given for monomode guiding group-IV materials, but the results apply to III-V rib waveguides. It is shown that single-mode rib guides with large cross sections are feasible as long as the waveguide is at least several millimeters long. >

A correspondence theory for terminological logics: preliminary report

Abstract: We show that the terminological logic ACC comprising Boolean operations on concepts and value restrictions is a notational variant of the propositional modal logic K(m)- To demonstrate the utility of the correspondence, we give two of its immediate by-products, Namely, we axiomatize ACC and give a simple proof that subsumption in ACC is PSPACE-complete, replacing the original six-page one. Furthermore, we consider an extension of ACC additionally containing both the identity role and the composition, union, transitive-reflexive closure, range restriction, and inverse of roles. It turns out that this language, called TSL, is a notational variant of the propositional dynamic logic converse-PDL. Using this correspondence, we prove that it suffices to consider finite TSL-models, show that TSL-subsumption is decidable, and obtain an axiomatization of TSL By discovering that features correspond to deterministic programs in dynamic logic, we show that adding them to TSC preserves decidability, although violates its finite model property. Additionally, we describe an algorithm for deciding the coherence of inverse-free TSC-concepts with features. Finally, we prove that universal implications can be expressed within TSC.

Microbiological characterization of a fuel-oil contaminated site including numerical identification of heterotrophic water and soil bacteria.

Abstract: Seven soil samples and seven groundwater samples from a site contaminated with fuel-oil were investigated using several chemical and microbiological techniques. In soil samples, 500 to 7,500 mg/kg of total hydrocarbons were found. These samples contained no n-alkanes but iso- and branched chain alkanes. No polychlorinated biphenyls could be detected. Microbiological investigations included estimations of total cell counts, viable cell counts on different media, and numbers of methylotrophic, denitrifying, sulphate reducing, anaerobic (with the exception of methanogenic organisms), and hydrocarbon degrading bacteria. Viable and hydrocarbon degrading bacteria were found in all samples. A total of 1,366 pure cultures was characterized morphologically and physiologically and identified by numerical identification using a data base of more than 4,000 reference strains. Groundwater samples were dominated by gram-negative bacteria of the generaPseudomonas, Comamonas, Alcaligenes, andAcinetobacter, which were also found in soil samples. In addition, more grampositive bacteria belonging to the generaArthrobacter, Nocardia, andBacillus could be isolated from soil samples.

ATLAS/ti--A Prototype for the Support of Text Interpretation

Abstract: At the core of ATLAS/ti is an explorative approach to theory-building. With linear textual data, such as transcribed interviews, as a starting point, segmentation and coding (“textual phases”) of the text alternates with the building of conceptual networks and hypertextual structures (“conceptual phase”). The researcher may draw actual “maps,” consisting of boxes and connecting lines, that depict the linkages among concepts as a network. Memos can be written for any entity at any stage in the process. For proceeding to a coherent text-outcome, features like the compilation of text units, and cut & paste operations between different text windows are available. All interaction with the program is through a graphic user interface containing windows, menus and icons, since special emphasis is placed in this program on its “readiness-at-hand.”

On the pseudo-elastic hysteresis

Abstract: It is often considered that in solids a non-monotone load-deformation characteristic of the “van der Waals type” may give rise to hysteretic behaviour in a phase transition. Here we consider a pseudo-elastic hysteresis that occurs in the austenitic-martensitic phase transition of shape memory alloys. For demonstrative purposes we let the non-monotone characteristic first be defined by the Landau-Devonshire model, later we even use straight lines. We ask the following questions: (i) How wide is the hysteresis loop? (ii) How does the width of the hysteresis loop change with temperature? (iii) What are the possible processes inside the hysteresis loop? Answers are provided for all three questions, viz. On (i) The width is determined by the interfacial energy of the phases. On (ii) There is no significant dependence on temperature. On (iii) The hysteresis loop contains metastable states that loose their (meta-)stability on a line defining phase equilibrium. The theoretical predictions are qualitative results. They are supported by tensile experiments on a CuZnAl single crystal.

Antimicrobial effect of water‐soluble chitosans with high hydrostatic pressure

Abstract: Two commercially available water‐soluble chitosan salts, chitosan lactate and chitosan hydroglutamate, were examined for antagonistic effect against Escherichia coli V517, Staphylococcus aureus MF‐31 and Saccharomyces cerevisiae 15. Significant inactivation of each population was evident within 2 min of incubation with Chitosan. S. cerevisiae was the most sensitive of the microorganisms examined. Concentration effects varied but chitosan hydroglutamate was usually the more effective of the chitosans for inactivation of these microorganisms. Application of high hydrostatic pressure (2,380 atmospheres) to chitosan‐treated cultures of E. coli V517 or S. aureus MF‐31 resulted in additional inactivation but an amplified or synergistic effect was not found.

Parallelism and concurrency in high-level replacement systems

Abstract: High-level replacement systems are formulated in an axiomatic algebraic framework based on categories pushouts. This approach generalizes the well-known algebraic approach to graph grammars and several other types of replacement systems, especially the replacement of algebraic specifications which was recently introduced for a rule-based approach to modular system design.in this paper basic notions like productions, derivations, parellel and sequential independence are introduced for high-level replacement syetms leading to Church-Rosser, Parallelism and concurrency Theorems previously shown in the literature for special cases only. In the general case of high-level replacement systems specific conditions, called HLR1- and HLR2-conditions, are formulated in order to obtain these results.Several examples of high-level replacement systems are discussed and classified w.r.t. HLR1- and HLR2-conditions showing which of the results are valid in each case.

The three-dimensional Wigner-Poisson problem: existence, uniqueness and approximation

Abstract: We prove the existence of a unique, global classical solution of the quantum Vlasov-Poisson problem posed on the phase space R x 3 xR v 3 . The proof is based on a reformulation of the quantum Vlasov-Poisson problem as a system of countably many Schrodinger equations coupled to a Poisson equation for the potential. The Schrodinger-Poisson problem is first analysed on a bounded domain in R x 3 and the solution of the whole-space problem is then obtained by a limiting procedure in which the domains «tend» to R x 3

Bulky or Supracyclopentadienyl Derivatives in Organometallic Chemistry

Abstract: Publisher Summary This chapter focuses on supracyclopentadienyl derivatives in organometallic chemistry. Within organometallic chemistry—synthetic, analytical, physical, applied, and theoretical chemists are involved in research projects, dealing with highly substituted cyclopentadienylide (Cp)-metal complexes. Supra-Cp's are a major focus of this chapter, whereas for many others they are just a sideline where the bulkiness is a minor feature in the comparative study of certain phenomena. This chapter reveals unifying interest, sometimes with no cross-referencing to similar bulky Cp systems or even different metals carrying the same supra-Cp. The basic bulky Cp systems that are common in organometallic chemistry are discussed in the chapter, in their anionic form as ball-and-stick models with the hydrogens included. Other basic bulky Cp's described in the chapter are di(isobutyl)(tert-buty1)-Cp, penta(isopenty1)- Cp [isopentyl=( H,C2)2CH-], and tris(methoxycarbony1)-Cp. This chapter presents highly substituted Cp's, supracyclopentadienes that so far have escaped attention as ligands in organometallic complexes: tetra(terfbuty1)- Cp, 3,Mimethyl- and 3,5di-n-propyl- 1,2,4-triphenyl-Cp, and 1,2,3,5-tetraphenyl-4-p(7-cycloheptatrienyl)phenyl-Cp. Most of the bulky ring substituents are simple hydrocarbon moities, either alkyl or aryl groups, and consequently the supra-Cp's can be divided into two classes: peralkyl and peraryl systems. The use of bulky cyclopentadienes with functional group substituents causes problems in organometallic synthesis. Although there is a sizable number of Cp- metal complexes with only one functional group on the Carbon, ring examples for persubstituted systems are limited. This chapter also covers tetrasubstituted fulvalenes ethylene-bridged bis(tetrahydroindeny1) complexes and a dibornacyclopentadienyl ligand.

Gel systems for the Belousov-Zhabotinskii reaction

Abstract: Gel systems and their advantages over an aqueous system for spatial patterns in the Belousov-Zhabotinskii reaction are investigated. Five new gel preparations are introduced in which several ferroin-type catalysts (highly hydrophobic and anionic) are immobilized. Together with previously known systems these are classified into three categories: soluble, immobilized continuous, and immobilized discrete systems

Piezoresistive pressure sensors based on polycrystalline silicon

Abstract: Polycrystalline Si (poly-Si) has found various applications in microelectronics and micromechanical devices such as pressure sensors, accelerometers and actuators. Poly-Si films deposited on an oxidized Si substrate can combine the excellent mechanical properties of Si with the efficient electrical insulation of poly-Si piezoresistors, so that improved stability and high-temperature operation can be obtained. Different poly-Si fabrication techniques are reviewed with emphasis on their applications to pressure sensors. The theoretical interpretation and models of the piezoresistivity in poly-Si and experimental results are presented. The calculation of the longitudinal and transverse gauge factors and their correlation with the crystallographic structure of the poly-Si film are discussed. The possibility of sensor performance optimization including mechanical, temperature and piezoresistive properties of a device is demonstrated. Two examples of commercially manufactured poly-Si sensors and an example of a new poly-Si technology are also presented.

X-ray survey of the Large Magellanic Cloud by ROSAT

Abstract: The central region of the Large Magellanic Cloud (LMC) contains a variety of astrophysical objects including supernova remnants, X-ray binary systems, the 30 Doradus complex of hot stars, as well as supernova 1987A. A survey in X-rays of this region, taken as the 'first light' observations with the Rontgen Observatory Satellite (ROSAT), reveals 45 individual sources. Fifteen of these are new; the brightest is probably a new and strongly variable low-mass X-ray binary.

Two sites of photoinhibition of the electron transfer in oxygen evolving and Tris-treated PS II membrane fragments from spinach.

Abstract: Photoinhibition was analyzed in O2-evolving and in Tris-treated PS II membrane fragments by measuring flash-induced absorption changes at 830 nm reflecting the transient P680+ formation and oxygen evolution. Irradiation by visible light affects the PS II electron transfer at two different sites: a) photoinhibition of site I eliminates the capability to perform a ‘stable’ charge separation between P680+ and QA - within the reaction center (RC) and b) photoinhibition of site II blocks the electron transfer from YZ to P680+. The quantum yield of site I photoinhibition (2–3×10-7 inhibited RC/quantum) is independent of the functional integrity of the water oxidizing system. In contrast, the quantum yield of photoinhibition at site II depends strongly on the oxygen evolution capacity. In O2-evolving samples, the quantum yield of site II photoinhibition is about 10-7 inhibited RC/quantum. After selective elimination of the O2-evolving capacity by Tris-treatment, the quantum yield of photoinhibition at site II depends on the light intensity. At low intensity (<3 W/m2), the quantum yield is 10-4 inhibited RC/quantum (about 1000 times higher than in oxygen evolving samples). Based on these results it is inferred that the dominating deleterious effect of photoinhibition cannot be ascribed to an unique target site or a single mechanism because it depends on different experimental conditions (e.g., light intensity) and the functional status of the PS II complex.

The effect of electric fields on blue phases

Abstract: An experimental review on electric field effects in blue phases is presented. Electric fields have a profound effect on these phases which appear in chiral liquid crystals. In addition to producing elec-trostrictive effects on blue phase lattices, they also cause new field induced phases—tetragonal BPX, hexagonal BPH3D and BPH2D, and possible other phases yet to be identified. In recent experiments on BPIII for materials with negative dielectric anisotropy, it was found that electric fields cause a dramatic increase in the otherwise weak BPIII selective reflection. These experimental results were discussed with respect to possible models for the unknown structure of BPIII. Recently, efforts were also made to investigate the dynamics of different electrooptic effects more precisely.

News on Nematic-Biaxial Liquid Crystals1

Abstract: Recent studies have established that not only some polymeric materials exhibit nematic biaxial phases, but that also low molecular weight compounds can do so if certain structural conditions are me...

Charge transfer induced nematic columnar phase in low molecular weight disc-like systems [1]

Abstract: Two large pentakis(phenylethynyl)phenyl alkyl ethers, without side chains as is usual for discotic systems, were synthesized in palladium catalysed one pot coupling reactions. These low molecular weight and non-liquid-crystalline electron donor compounds were doped with 2,4,7-trinitrofluorenone under the formation of charge transfer complexes. The induction of two types of enantiotropic mesophases (i.e. nematic and hexagonal columnar phases (Nc and Dho)) was observed. These charge transfer-induced mesophases were characterized by polarization microscopy, differential scanning calorimetry, and X-ray analysis; phase diagrams of the binary systems were also recorded as well as the hexagonal columnar to nematic columnar transition as a function of the length of the disturbing alkoxy group. It is considered possible now to study low molecular mass Nc phases by tailor-made two component mixtures on the basis of our easily accessible disc-shaped multiynes.

The effect of liming on quantity and chemical composition of soil organic matter in a pine forest in Berlin, Germany

Abstract: The study was carried out in a 40-yr old pine plantation on a Cambic Arenosol within the urban area of Berlin. Lime application (6.1 t ha-1) has led to a pH increase in the forest floor from 3.3 to 5.5 within one year and to a strong stimulation of macrofaunal and microbiological activity. Three years after liming, the C:N ratio of the forest floor decreased from 28 to 25 and P, Pb, Zn, Cu and Cd concentrations in organic matter increased significantly. The organic C pool of the forest floor was almost 7 t ha-1 lower in the limed plot which is attributed to increased microbial respiration. In the mineral soil too, C-pools are lower in the limed plot, amounting to 13.2 t ha-1 or 14% less than in the control. C:N ratios have narrowed significantly from 27–29 to 23 in 10–30 cm depth. The humic acid fraction is lower throughout the limed profile while the percentage of fulvic acids has increased significantly below 10 cm. The results point to severe losses of organic matter and to profound changes in its composition. This may be of consequences for site quality and leaching processes.

Processing and Characterization of Jute Fiber Reinforced Thermoplastic Polymers

Abstract: Jute fibers were investigated to verify their possible application in reinforcement of thermoplastics. A laboratory press was modified and laminates were produced using polymer films of LDPE, HDPE, PE copolymer, and PP as interlayers. Variations of the processing parameters were carried out in order to find optimal adjustment. High molding temperature leads to a decrease of mechanical properties and water absorption ability of the composites. The effect of water treatment on mechanical properties was also studied.

Unusual low reactivity of the water oxidase in redox state S3 toward exogenous reductants. Analysis of the NH2OH- and NH2NH2-induced modifications of flash-induced oxygen evolution in isolated spinach thylakoids.

Abstract: The effect of redox-active amines NH2R (R = OH or NH2) on the period-four oscillation pattern of oxygen evolution has been analyzed in isolated spinach thylakoids as a function of the redox state Si (i = 0, ..., 3) of the water oxidase. The following results were obtained: (a) In dark-adapted samples with a highly populated S1 state, NH2R leads via a dark reaction sequence to the formal redox state "S-1"; (b) the reaction mechanism is different between the NH2R species; NH2OH acts as a one-electron donor, whereas NH2NH2 mainly functions as a two-electron donor, regardless of the interacting redox state Si (i = 0, ..., 3). For NH2NH2, the modified oxygen oscillation patterns strictly depend upon the initial ratio [S0(0)]/[S1(0)] before the addition of the reductant; while due to kinetic reasons, for NH2OH this dependence largely disappears after a short transient period. (c) The existence of the recently postulated formal redox state "S-2" is confirmed not only in the presence of NH2NH2 [Renger, G., Messinger, J., & Hanssum, B. (1990) in Current Research in Photosynthesis (Baltscheffsky, M., Ed.) Vol. 1, pp 845-848, Kluwer, Dordrecht] but also in the presence of NH2OH. (d) Activation energies, EA, of 50 kJ/mol were determined for the NH2R-induced reduction processes that alter the oxygen oscillation pattern from dark-adapted thylakoids. (e) Although marked differences exist between NH2OH and NH2NH2 in terms of the reduction mechanism and efficiency (which is about 20-fold in favor of NH2OH), both NH2R species exhibit the same order of rate constants as a function of the redox state Si in the nonperturbed water oxidase: kNH2R(S0) greater than kNH2R(S1) much less than kNH2R(S2) much greater than kNH2R(S3) The large difference between S2 and S3 in their reactivity toward NH2R is interpreted to indicate that a significant change in the electronic configuration and nuclear geometry occurs during the S2----S3 transition that makes the S3 state much less susceptible to NH2R. The implications of these findings are discussed with special emphasis on the possibility of complexed peroxide formation in redox state S3 postulated previously on the basis of theoretical considerations [Renger, G. (1978) in Photosynthetic Water Oxidation (Metzner, H., Ed.) pp 229-248, Academic Press, London].

Cell-free biosynthesis of surfactin, a cyclic lipopeptide produced by Bacillus subtilis

Abstract: The lipopeptide antibiotic surfactin is a potent extracellular biosurfactant produced by various Bacillus subtilis strains. Biosynthesis of surfactin was studied in a cell-free system prepared from B. subtilis ATCC 21332 and OKB 105, which is a transformant producing surfactin in high yield [Nakano, M. M., Marahiel, M. A., & Zuber, P. (1988) J. Bacteriol. 170, 5662-5668]. Cell material was disintegrated by treatment with lysozyme and French press. A cell-free extract was prepared by ammonium sulfate fractionation, which catalyzed the formation of surfactin at the expense of ATP. Lipopeptide biosynthesis required the L-amino acid components of surfactin and D-3-hydroxytetradecanoyl-coenzyme A thioester. D-Leucine which is present in surfactin was not utilized but inhibited the biosynthetic process. The structure of surfactin, synthesized enzymatically in vitro, was confirmed by chromatographic comparison with the authentic compound and by amino acid analyses. An enzyme fraction was prepared by gel permeation chromatography which catalyzed ATP/pyrophosphate exchange reactions dependent on the component amino acids of surfactin. This enzyme fraction was capable of binding substrate amino acids covalently, probably via thioester linkages. The formation of these intermediates was inhibited by various thiol blocking reagents and phenylmethanesulfonyl fluoride. De novo synthesis of the lipopeptide was not observed with this partially purified enzyme fraction most likely due to the lack of an acyltransferase activity required for linking the beta-hydroxy fatty acid to the peptide moiety.

Degradation of chlorinated lignin compounds in a bleach plant effluent by the white-rot fungus trametes versicolor

Abstract: Chlorinated lignin derivatives in a combined bleach plant effluent from sulphite pulping were degraded by several white-rot fungi among which Trametes versicolor (Coriolus versicolor) strains were the most efficient. With glucose as co-substrate, about 90% colour reduction was achieved within 3 days. Simultaneously, the concentration of chloro-organic compounds measured as adsorbable organic halogens decreased by about 45%. As shown by gel chromatography, the high-molecular-weight fraction in the effluent was completely depolymerized while over 50% of total aromatic compounds were degraded. The presence of a co-substrate was necessary for all these activities of the fungus. The residue obtained after degradation was extremely recalcitrant and not further degradable.

Discretization methods for the solution of semi-infinite programming problems

Abstract: In the first part of this paper, we prove the convergence of a class of discretization methods for the solution of nonlinear semi-infinite programming problems, which includes known methods for linear problems as special cases. In the second part, we modify and study this type of algorithms for linear problems and suggest a specific method which requires the solution of a quadratic programming problem at each iteration. With this algorithm, satisfactory results can also be obtained for a number of singular problems. We demonstrate the performance of the algorithm by several numerical examples of multivariate Chebyshev approximation problems.

Growth of Wolinella succinogenes with polysulphide as terminal acceptor of phosphorylative electron transport

Abstract: Polysulphide was formed according to reaction (1), when tetrathionate was $${\text{S}}_4 {\text{O}}_6^{2 - } + {\text{HS}}^ - \to 2{\text{S}}_2 {\text{O}}_3^{2 - } + {\text{S(O)}} + {\text{H}}^ + $$ (1) added to an anaerobic buffer (pH 8.5) containing excess sulphide. S(O) denotes the zero oxidation state sulphur in the polysulphide mixture Sinfnsup2-. The addition of formate to the polysulphide solution in the presence of Wolinella succinogenes caused the reduction of polysulphide according to reaction (2). The bacteria grew in a medium containing formate and sulphide, $${\text{HCO}}_2^ - + {\text{S(O)}} + {\text{H}}2{\text{O}} \to {\text{HCO}}_3^ - + {\text{HS}}^ - + {\text{H}}^ + $$ (2) when tetrathionate was continuously added. The cell density increased proportional to reaction (3) which represents the sum of reactions (1) and $${\text{HCO}}_2^ - + {\text{S}}_{\text{4}} {\text{O}}_6^{2 - } + {\text{H}}2{\text{O}} \to {\text{HCO}}_3^ - + 2{\text{S}}_{\text{2}} {\text{O}}_3^{2 - } + 2{\text{H}}^ + $$ (3) (2). The cell yield per mol formate was nearly the same as during growth on formate and elemental sulphur, while the velocity of growth was greater. The specific activities of polysulphide reduction by formate measured with bacteria grown with tetrathionate or with elemental sulphur were consistent with the growth parameters. The results suggest that W. succinogenes grow at the expense of formate oxidation by polysulphide and that polysulphide is an intermediate during growth on formate and elemental sulphur.

Elastic Properties of Pyrope

Abstract: Brillouin spectroscopy was used to measure the single crystal elastic properties of a pure synthetic pyrope and a natural garnet containing 89.9 mol% of the pyrope end member (Mg_3Al_2Si_3O_(12)). The elastic moduli, c_(ij) , of the two samples are entirely consistent and agree with previous estimates of the elastic properties of pyrope based upon the moduli of solid solutions. Our results indicate that the elastic moduli of pyrope end-member are c_(11)=296.2±0.5, c_(12)=111.1±0.6, c_(44)=91.6±0.3, K_s=172.8±0.3, μ=92.0±0.2, all in units of GPa. These results differ by several percent from those reported previously for synthetic pyrope, but are based upon a much larger data set. Although the hydrous components of the two samples from the present study are substantially different, representing both ‘dry’ and ‘saturated’ samples, we find no discernable effect of structurally bound water on the elastic properties. This is due to the small absolute solubility of water in pyrope, as compared with other garnets such as grossular.