Showing papers by "Technical University of Berlin published in 1998"

The singlet and triplet states of phenyl cation. A hybrid approach for locating minimum energy crossing points between non-interacting potential energy surfaces

Abstract: The phenyl cation is known to have two low-energy minima, corresponding to 1 A 1 and 3 B 1 states, the first of which is more stable by ca. 25 kcal/mol. The minimum energy crossing point between these two surfaces, located at various levels including a hybrid method first described here, lies just above the minimum of the triplet, 0.12 kcal/mol at the CCSD(T)/cc-pVDZ//B3LYP/SV level, and there is significant spin-orbit coupling between the surfaces at this point. On the basis of these results, the lifetime of the triplet is expected to be very short.

Raman spectroscopy of orthorhombic perovskitelike YMnO 3 and LaMnO 3

Abstract: The Raman-active phonons in orthorhombic perovskitelike ${\mathrm{YMnO}}_{3}$ and ${\mathrm{LaMnO}}_{3}$ were studied by measuring Raman spectra in various scattering configurations. The experimental Raman line wave numbers and the expected shapes for the phonon modes were compared to those reported for other perovskitelike compounds with the $\mathrm{Pnma}$ structure and to the results of lattice dynamical calculations. The observed Raman lines in the spectra of ${\mathrm{YMnO}}_{3}$ and ${\mathrm{LaMnO}}_{3}$ were assigned to definite atomic motions. The much larger linewidths and strong variation of the Raman spectra with increasing laser power in the case of ${\mathrm{LaMnO}}_{3}$ provide evidence for a structural instability that may result in a phase transition under laser annealing.

Granular ferric hydroxide—a new adsorbent for the removal of arsenic from natural water.

Abstract: Granular ferric hydroxide (GFH) is an adsorbent, developed for arsenic removal from natural water. It can be applied in simple fixed bed reactors, similar to those for activated alumina or activated carbon. GFH has a high adsorption capacity in model systems and in natural waters. The application of GFH in test adsorbers showed a high treatment capacity of 30 000–40 000 bed volumes, until the new German and WHO drinking water standard for arsenic of 10 μg/L was exceeded. The residue of this technique is a solid waste, enriched with arsenic. The typical residual mass is in the range of 5–25 g/m 3 treated water. This new technique for arsenic removal provides a simple and effective method, particularly for small water facilities.

Quantum dot heterostructures: Fabrication, properties, lasers (Review)

Abstract: In the present review we summarize original results where 1) we have experimentally discovered a novel class of spontaneously ordered nanostructures, namely equilibrium arrays of threedimensional, coherently strained islands on crystal surfaces; 2) we have developed a theory of spontaneous formation of semiconductor nanostructures in heteroepitaxial systems; 3) we have experimentally demonstrated the existence of a novel class of semiconductor heterostructures, namely perfect quantum dots having an atom-like energy spectrum; we have performed a detailed investigation of the optical properties of quantum dots; 4) we have fabricated quantum dot-based injection lasers demonstrating unique charactristics, namely high-temperature stability of the threshold current and ultra-high material gain.

The effect of genotype on response thresholds to sucrose and foraging behavior of honey bees (Apis mellifera L.)

Abstract: Honey bee foragers were tested for their proboscis extension response (PER) to water and varying solutions of sucrose. Returning pollen and nectar foragers were collected at the entrance of a colony and were assayed in the laboratory. Pollen foragers had a significantly higher probability of responding to water and to lower concentrations of sucrose. Bees derived from artificially selected high- and low-pollen-hoarding strains were also tested using the proboscis extension assay. Returning foragers were captured and tested for PERs to 30% sucrose. Results demonstrated a genotypic effect on PERs of returning foragers. The PERs of departing high- and low-strain foragers were consistent with those of returning foragers. The PERs were related to nectar and water reward perception of foragers. High strain bees were more likely to return with loads of water and lower concentrations of sucrose than foragers from the low pollen strain. Low-strain bees were more likely to return empty. We identified a previously mapped genomic region that contains a variable quantitative trait locus that appears to influence sucrose response thresholds. These studies demonstrate a gene-brain-behavior pathway that can be altered as a consequence of colony-level selection for quantities of stored food.

Transformation of industrial dyes by manganese peroxidases from Bjerkandera adusta and Pleurotus eryngii in a manganese-independent reaction.

Abstract: We investigated the transformation of six industrial azo and phthalocyanine dyes by ligninolytic peroxidases from Bjerkandera adusta and other white rot fungi. The dyes were not oxidized or were oxidized very little by Phanerochaete chrysosporium manganese peroxidase (MnP) or by a chemically generated Mn3+-lactate complex. Lignin peroxidase (LiP) from B. adusta also showed low activity with most of the dyes, but the specific activities increased 8- to 100-fold when veratryl alcohol was included in the reaction mixture, reaching levels of 3.9 to 9.6 U/mg. The B. adusta and Pleurotus eryngii MnP isoenzymes are unusual because of their ability to oxidize aromatic compounds like 2,6-dimethoxyphenol and veratryl alcohol in the absence of Mn2+. These MnP isoenzymes also decolorized the azo dyes and the phthalocyanine complexes in an Mn2+-independent manner. The reactions with the dyes were characterized by apparent Km values ranging from 4 to 16 microM and specific activities ranging from 3.2 to 10.9 U/mg. Dye oxidation by these peroxidases was not increased by adding veratryl alcohol as it was in LiP reactions. Moreover, the reaction was inhibited by the presence of Mn2+, which in the case of Reactive Black 5, an azo dye which is not oxidized by the Mn3+-lactate complex, was found to act as a noncompetitive inhibitor of dye oxidation by B. adusta MnP1.

Power-saving mechanisms in emerging standards for wireless LANs: the MAC level perspective

Abstract: This article provides an overview of mechanisms used for power saving in the upcoming standards for wireless LANs: IEEE 80211 and ETSI RES 10 HIPERLAN Power saving on the MAC level is addressed by these standards in a quite different way We outline the main features of the mechanisms in both standards in terms of power saving In addition we present simulation studies of the power-saving mechanism in ad hoc configurations of IEEE 80211 networks, which demonstrate the optimization potential and some performance trade-offs quantitatively

Electronic Structure Makes a Difference: Cytochrome P-450 Mediated Hydroxylations of Hydrocarbons as a Two-State Reactivity Paradigm

Abstract: This paper describes a reactivity paradigm called two-state reactivity (TSR) in C ± H bond activation by metal oxenoid cations (e.g., FeO‡). The paradigm is applied to the hydroxylation of alkanes by the active species of the enzyme cytochrome P-450, and a mechanistic scheme is proposed based on the competition between TSR pathways and single-state-reactivity (SSR) pathways. Generally, the oxide cations of the late transition metals (MO‡) possess the same bonding patterns as the O2 molecule, having a high-spin ground state and an adjacent low-spin excited state. The adjacency of the spin states, together with the poor bonding capability of the high-spin state and the good bonding capability of the low-spin state, leads to a spin crossover along the reaction coordinate and opens a low-energy TSR path for hydroxylation. The competing pathway is SSR, in which the reaction starts, occurs and ends in the same spin state. The TSR/SSR competition is modulated by the probability of spin crossover. Generally, TSR involves concerted pathways that conserve stereochemical information, while SSR results in stepwise mechanisms that scramble this information. The TSR/SSR competition is used to shed some light on recent results which are at odds with the commonly accepted mechanism of P-450 hydroxylation. The fundamental features of the paradigm are outlined and the theoretical and experimental challenges for its articulation are spelled out.

Vitellogenin : a biomarker for endocrine disruptors

Abstract: The increasing preponderance of females in fish populations has become a matter of concern not only for scientists but also for environmental authorities. For example, in the extensive waterways in Berlin, Germany, 70% of the fish population is female. A twofold question should be asked: is the biomarker vitellogenin (vitellogenin-synthesis assay) an appropriate tool for determining endocrine effects (European Commission 1996) and of chemical pollutants in effluents (Castillo et al. 1997), such as estradiols, phthalates, alkyl-phenols, and alkyl-ethoxylates, influence sex differentiation in fish?

Technology aspects related to microorganisms in functional foods

Abstract: Processing of microbial systems for functional foods can be organized into processing of starter cultures, processing of products with desired functional characteristics and processing of foods containing probiotics. Technology aspects as related to microorganisms in functional foods are highly complex and diverse since they have to deal with the productivity and viability of probiotic strains as well as with the production of functional foods and food constituents by microbial systems. However, limited data are available on the impact of processing, distribution and storage on microbial cell viability. Technological challenges include the necessity to obtain high initial productivity and viability as starter cultures as well as high stability, viability and productivity as probiotic strains.

Overexpression of a cytosolic hydroxymethylglutaryl-CoA reductase leads to squalene accumulation in yeast

Abstract: The enzyme 3-hydroxy-3-methylglutaryl-coenzyme-A (HMG-CoA) reductase is known as the rate-limiting enzyme in early sterol biosynthesis in eukaryotic cells. To eliminate this regulation in the yeast Saccharomyces cerevisiae, a truncated HMG1 gene, producing a form of the enzyme that lacks the membrane-binding region (i.e. amino acids 1–552), was constructed and overexpressed in this yeast. The transformed strains accumulated large amounts of the sterol precursor squalene, while the levels of ergosterol and a number of other sterol compounds were only slightly elevated. These findings suggest that HMG-CoA reductase is not the only rate-limiting step in sterol synthesis and its overexpression cannot significantly influence this pathway beyond the sterol precursor squalene.

Carrier dynamics in type-II GaSb/GaAs quantum dots

Abstract: The optical properties and dynamics of charge carriers in self-organized arrays of type-II (staggered band lineup) GaSb/GaAs quantum dots are studied. Interband absorption from type-II quantum dots is evidenced; the energetic positions of quantum dot absorption peaks coincide with those apparent in photoluminescence spectra. (Sb,As) intermixing with an antimony diffusion length of about 1 nm is found to make an important contribution to the observed transition energies. Dipole layer formation and quantum dot state filling contribute to the luminescence blueshift with increasing excitation density. The recombination rate of electrons with localized holes drastically depends on the average carrier density. When several carriers are localized at each dot, decay time constants around 5 ns, quite similar to type-I systems, are observed. Individual, spatially indirect excitons decay with much larger time constants close to 1 \ensuremath{\mu}s. The decay time of quantum dot luminescence is independent of the temperature in the measured range $Tl~65\mathrm{K}$ as expected for zero-dimensional excitons.

Excited states and energy relaxation in stacked InAs/GaAs quantum dots

Abstract: Excited states and energy relaxation processes are studied for stacked InAs/GaAs QD's with GaAs cap layers grown by migration enhanced epitaxy. Photoluminescence excitation (PLE) spectra reveal the excited state spectrum as a function of size for self-assembled InAs QD's in multilayered samples with 36-ML spacers. The observed energy shifts and splittings are consistent with those of hole states numerically calculated for pyramidal QD's supporting assignment to the transition between the electron ground |000〉 and the |001〉 excited hole state. The optical results suggest the island shape uniformity to improve in multilayered samples, which is attributed to the contribution of the buried islands to the surface strain altering the island formation kinetics and energetics that also underlie vertical self-organization. Time-resolved photoluminescence (TRPL) results yield a lifetime of 40 ps for the first excited |001〉 hole state, attributed to multiphonon relaxation processes bridging the approximately 100 meV level separation, and ground-state lifetimes around 700 ps independent of the detection energy. At high excitation densities saturation of QD states leads to long-living excited-state PL and up to 1 ns delay in the ground-state PL decay, showing radiative decay to be the dominant recombination process in the QD's. The results presented contribute to the understanding of PLE spectra of an inhomogeneous QD ensemble, which is argued to be sensitive to the shape uniformity, the excited-state spectrum, and competing recombination processes.

Occurrence and Distribution of Organic Contaminants in the Aquatic System in Berlin. Part I: Drug Residues and other Polar Contaminants in Berlin Surface and Groundwater

Abstract: Several polar contaminants were found in screening analyses of 30 representative surface water samples collected from rivers, lakes, and canals in Berlin. Residues of pharmaceuticals and N-(phenylsulfonyl)-sarcosine originating from various sewage treatment plants effluents were found at concentrations up to the μg/L-level in the surface water, whereas the concentrations of polar pesticides such as dichlorprop and mecoprop were always below 0.1 μg/L. The pharmaceuticals most frequently detected in the surface water samples include clofibric acid, diclofenac, ibuprofen, propiphenazone, and two other drug metabolites. Additional investigations of groundwater wells of a drinking water plant have shown that polar contaminants such as drug residues or N-(phenylsulfonyl)-sarcosine easily leach through the subsoil into the groundwater aquifers when contaminated surface water is used for groundwater recharge in drinking water production. Vorkommen und Verteilung organischer Kontaminanten im aquatischen System in Berlin. Teil I: Arzneimittelruckstande und weitere polare Kontaminanten im Berliner Oberflachen- und Grundwasser Im Rahmen eines Screenings von 30 reprasentativen Oberflachenwasserproben aus Flussen, Seen und Kanalen Berlins wurden eine Reihe polarer organischer Kontaminanten detektiert. Ruckstande von Arzneimitteln und von N-(Phenylsulfonyl)-sarcosin, die uber die verschiedenen Klarwerke in die Oberflachengewasser eingetragen werden, wurden in Konzentrationen bis in den μg/L-Bereich in den Proben gefunden. Zu den am haufigsten gefundenen Pharmazeutika gehorten Clofibrinsaure, Diclofenac, Ibuprofen und Propiphenazon sowie zwei weitere Metabolite von Arzneimitteln. Die Konzentrationen der ebenfalls gefundenen polaren Pestizide Dichlorprop und Mecoprop lagen hingegen immer unterhalb von 0.1 μg/L. Zusatzliche Untersuchungen von Wasserproben, die den Grundwasserbrunnen bzw. den Grundwasserbeobachtungsrohren eines Wasserwerkes entnommen wurden, zeigten, das polare Kontaminanten wie Arzneimittelruckstande oder N-(Phenylsulfonyl)-sarcosin aus kontaminierten Oberflachengewassern in die Grundwasseraquifere eingetragen werden konnen, wenn die Uferfiltration oder die kunstliche Grundwasseranreicherung zur Trinkwassergewinnung eingesetzt wird.

Numerical Methods for Semi-Infinite Programming: A Survey

Abstract: This paper provides a review of numerical methods for the solution of smooth semi-infinite programming problems. Fundamental and partly new results on level sets, discretization, and local reduction are presented in a primary section. References to algorithms for real and complex continuous Chebyshev approximation are given for historical reasons and in order to point out connections.

Peptide mass fingerprint sequence coverage from differently stained proteins on two‐dimensional electrophoresis patterns by matrix assisted laser desorption/ionization‐mass spectrometry (MALDI‐MS)

Abstract: Identification of proteins separated by two-dimensional electrophoresis (2-DE) is a necessary task to overcome the purely descriptive character of 2-DE and a prerequisite to the construction of 2-DE databases in proteome projects. Matrix assisted laser desorption/ionization-mass spectrometry (MALDI-MS) has a sensitivity for peptide detection in the lower fmol range, which should be sufficient for an analysis of even weakly silver-stained protein spots by peptide mass fingerprinting. Unfortunately, proteins are modified by the silver staining procedure, leading to low sequence coverage. Omission of glutaraldehyde increased the sequence coverage, but this improved sequence coverage is still clearly below the sequence coverage starting with Coomassie Brilliant Blue (CBB) R-250-stained spots. Other factors additionally seem to modify proteins during silver staining. By decreasing the protein amount, the advantage of very sensitive detection on the gel is lost during identification, because the resulting low sequence coverage is not sufficient for secure identification. Low-quantity proteins can be identified better starting with CBB G-250 or Zn-imidazol-stained proteins. In contrast, for high-quantity CBB R-250-stained spots, a sequence coverage of up to 90% can be obtained by using only one cleaving enzyme, and up to 80% was reached for medium-quantity spots after combination of tryptic digest with Asp-N- and Glu-C digest.

Error resilience support in H.263

Abstract: Version 2 of ITU Recommendation H.263, better known as H.263+, includes a number of new mechanisms to improve coding efficiency and support various types of networks more efficiently. This paper provides an overview of the error resilience optional modes of H.263+ and describes the use of such modes in various multimedia network scenarios.

Purification and characterization of peroxidases from the dye-decolorizing fungus Bjerkandera adusta

Abstract: A peroxidase oxidizing Mn2+ (MnP) is described for the first time in Bjerkandera adusta, a fungus efficiently degrading xenobiotic compounds. The MnP appeared as two isoenzymes, which were purified to homogeneity together with two lignin peroxidases (LiP). Their N-terminal sequences were identical, but the MnP isoenzymes showed more basic isoelectric points and differences in amino acid composition and catalytic properties. The B. adusta LiP is similar to LiP from Phanerochaete chrysosporium. However, the interest of the MnP described here is related to its ability to catalyze Mn2+-mediated as well as Mn2+-independent reactions on aromatic compounds, which may be of use for applications in biotechnology and environmental technology.

Electronic absorption by Ti 3+ ions and electron delocalization in synthetic blue rutile

Abstract: Polarized absorption spectra, σ and π, in the spectral range 30000–400 cm−1 (3.71–0.05 eV) were obtained on crystal slabs // [001] of deep blue rutile at various temperatures from 88 to 773 K. The rutile crystals were grown in Pt-capsules from carefully dried 99.999% TiO2 rutile powder at 50 kbar/1500 °C using graphite heating cells in a belt-type apparatus. Impurities were below the detection limits of the electron microprobe (about 0.005 wt% for elements with Z≥13). The spectra are characterized by an unpolarized absorption edge at 24300 cm−1, two weak and relatively narrow (Δν1/2≈3500–4000 cm−1), slightly σ-polarized bands ν1 at 23500 cm−1 and ν2 at 18500 cm−1, and a complex, strong band system in the NIR (near infra red) with sharp weak peaks in the region of the OH stretching fundamentals superimposed on the NIR system in the σ-spectra. The NIR band system and the UV edge produce an absorption minimum in both spectra, σ and π, at 21000 cm−1, i.e. in the blue, which explains the colour of the crystals. Bands ν1 and ν2 are assigned to dd transitions to the Jahn-Teller split upper Eg state of octahedral Ti3+. The NIR band system can be fitted as a sum of three components. Two of them are partly π-polarized, nearly Gaussian bands, both with large half widths 6000–7000 cm−1, ν3 at 12000 cm–1 and the most intense ν4 at 6500 cm−1. The third NIR band ν5 of a mixed Lorentz-Gaussian shape with a maximum at 3000 cm−1 forms a shoulder on the low-energy wing of ν4. Energy positions, half band widths and temperature behaviour of these bands are consistent with a small polaron type of Ti3+Ti4+ charge transfer (CT). Polarization dependence of CT bands can be explained on the basis of the structural model of defect rutile by Bursill and Blanchin (1983) involving interstitial titanium. Two OH bands at 3322 and 3279 cm−1 in σ-spectra show different stability during annealing, indicating two different positions of proton in the rutile structure, one of them probably connected with Ti3+ impurity. Total water concentration in blue rutile determined by IR spectroscopy is 0.10 wt-% OH. The EPR spectra measured in the temperature interval 20–295 K show the presence of an electron centre at temperatures above 100 K and Ti3+ ions in more than one structural position, but predominantly in compressed interstitial octahedral sites, at lower temperatures. These results are in good agreement with the conclusions based on the electronic absorption data.

Classification on Pairwise Proximity Data

Abstract: We investigate the problem of learning a classification task on data represented in terms of their pairwise proximities. This representation does not refer to an explicit feature representation of the data items and is thus more general than the standard approach of using Euclidean feature vectors, from which pairwise proximities can always be calculated. Our first approach is based on a combined linear embedding and classification procedure resulting in an extension of the Optimal Hyperplane algorithm to pseudo-Euclidean data. As an alternative we present another approach based on a linear threshold model in the proximity values themselves, which is optimized using Structural Risk Minimization. We show that prior knowledge about the problem can be incorporated by the choice of distance measures and examine different metrics W.r.t. their generalization. Finally, the algorithms are successfully applied to protein structure data and to data from the cat's cerebral cortex. They show better performance than K-nearest-neighbor classification.