Showing papers by "University of Marburg published in 1981"

Electron Spin Resonance of Doped Glow-Discharge Amorphous Silicon

Abstract: The influence of doping on the ESR spectra of glow-discharge a-Si:H is systematically investigated in the X- and Q-band for phosphorus- and boron-doped samples up to a high doping level. Whereas for undoped and moderately doped material the well-known line with g = 2.0055 is observed, for highly boron-doped samples the broader line at g = 2.01 predominates as does the g = 2.0043 line in the case of high phosphorus doping. The linewidth of the resonance at g = 2.01, due to holes in localized valence band tail states, is mainly determined by a g-value spectrum. With increasing boron doping the width of this spectrum decreases and its centre of gravity shifts to smaller g-values. The narrower line with g = 2.0043, due to electrons in localized conduction band tail states, however, broadens with increasing phosphorus doping due to hyperfine interaction with the phosphorus nuclei. From these features it is concluded that the wave function of holes in valence band tail states is much more localized than that of electrons in the conduction band tail. At the same high doping level the spin density for the hole resonance at g = 2.01 is a factor of about 102 larger than for the electron line with g = 2.0043. This difference is explained by a different correlation energy U. Besides these lines a relatively weak resonance at g = 2.0026 is found for boron-doped samples and for phosphorus-doped material as well. Measurements on compensated samples indicate that by doping dangling bonds are created. Der Einflus von Dotierung auf die ESR-Spektren von glow-discharge-a-Si:H wird systematisch im X- und Q-Band fur Phosphor- und Bor-dotierte Proben bis herauf zu einem hohen Dotierungsniveau untersucht. Wahrend fur undotiertes und masig dotiertes Material die bekannte Linie mit g = 2,0055 beobachtet wird, ist fur hoch mit Bor dotierte Proben die breitere Linie mit g = 2,01 und fur starke Phosphordotierung die Linie mit 2,0043 vorherrschend. Die Linienbreite der Resonanz mit g = 2,01, die auf Locher in lokalisierten Zustanden des Valenzbandauslaufers zuruckzufuhren ist, wird hauptsachlich durch ein g-Wert-Spektrum bestimmt. Mit zunehmender Bordotierung nimmt die Breite dieses Spektrums ab und sein Schwerpunkt verschiebt sich zu kleineren g-Werten. Die schmalere Linie mit g = 2,0043, die von Elektronen in lokalisierten Zustanden des Leitungsbandauslaufers herruhrt, verbreitert sich dagegen mit wachsender Phosphordotierung durch Hyperfein-Wechselwirkung mit den Phosphorkernen. Aus diesen Eigenschaften wird geschlossen, das die Wellenfunktionen der Locher im Valenzbandauslaufer starker lokalisiert sind als die der Elektronen im Leitungsband-Tail. Bei der gleichen hohen Dotierung ist die Spindichte fur die Locherresonanz bei g = 2,01 um etwa den Faktor 102 groser als fur die Elektronenlinie mit g = 2,0043. Dieser Unterschied wird durch eine verschiedene Korrelationsenergie U erklart. Auser den oben genannten Linien wird noch eine relativ schwache Resonanz bei g = 2,0026 sowohl fur Phosphor- als auch fur Bor-dotiertes Material gefunden. Messungen an kompensierten Proben zeigen, das durch die Dotierung unabgesattigte Bindungen erzeugt werden.

Do the Blind Hear Better? Investigations on Auditory Processing in Congenital or Early Acquired Blindness II. Central Functions

Abstract: The same 18 normally hearing students and 18 matched normal-sighted students, as in part I of this study, were compared in regard to pure-tone integration, speech discrimination ability and late co...

One-Dimensional Wide Energy Bands in a Polydiacetylene Revealed by Electroreflectance

Abstract: Above a region of excitonic transitions the polydiacetylene DCHD [poly 1, 6-di(N-carbazolyl)-2, 4-hexadiyne] shows at the photoconduction edge a large electroreflectance response for fields parallel to the polymer. The signal broadens with field strength indicating a high-field limit for electroreflectance. Evaluation yields ${E}_{g}=2.335$ eV, ${m}^{*}=0.05{m}_{0}$, and $\ensuremath{\mu}=2800$ ${\mathrm{cm}}^{2}$/V sec. The influence of a field perpendicular to the polymer chain is 3 orders of magnitude smaller. This unique anisotropy indicates that delocalization of the electrons occurs only along the polymer.

Dispersive hopping transport via sites having a Gaussian distribution of energies

Abstract: The Monte Carlo technique has been employed to simulate hopping transport through a Gaussian energy distribution of hopping sites located on a cubic lattice having a nearest-neighbour distance of 10−7 cm. Dispersive transport is observed at temperatures where the width of the Gaussian [sgrave] > kT and for electric fields where eE x 10−7/[sgrave] < 1. The dispersive regime is observed over a considerable range in the average number of jumps and in this range both ⟨x⟩ and ⟨x 2⟩ can be described by a mobility and a diffusion constant which are proportional to t α–1 and where α is a function of electric field and [sgrave]/kT.

Coordinate induction by UV light of stilbene synthase, phenylalanine ammonia-lyase and cinnamate 4-hydroxylase in leaves of vitaceae.

Abstract: A stilbene synthase catalyzing the formation of resveratrol from 4-hydroxycinnamoyl-CoA and malonyl-CoA was found in the leaves of several Vitaceae. This stilbene synthase and two other enzymes functioning on the route from phenylalanine to stilbenes were induced concurrently upon irradiation of the leaves with UV light. With leaves of Cissus antarctica, an increase of stilbene synthase activity, more than hundred-fold, was observed with a maximum appearing 15 h after the induction with UV light.

Ultrasonically guided fine‐needle biopsies in neoplastic liver disease: Cytohistologic diagnoses and echo pattern of lesions

Abstract: Sixty consecutive percutaneous fine-needle aspiration biopsies guided by ultrasound were performed without complications in patients with ultrasonically suspected focal or diffuse neoplastic liver disease. Evaluations of aspirated samples were based on cytologic examination of smear preparations (100%) combined with histologic examination of serial sectioned tissue fragments (81.7%). The overall accuracy rate of cytohistologic evaluations was 91.6% with a sensitivity of 92.2%, a specificity of 88.9%, and a high predictive value of positive results (cytology; 97.8%; histology, 100%). Percutaneous fine-needle aspiration biopsy guided by sonography proved to be a safe, useful, and highly accurate technique for making cytohistologic diagnoses of hepatic masses suspected of being malignant. No relationship was found between the various echo patterns of intrahepatic neoplastic lesions and cell type or primary site of tumor origin.

Sodium dependence of growth and methane formation in Methanobacterium thermoautotrophicum

Abstract: Methanobacterium thermoautotrophicum was found to require sodium for growth and for CO2 reduction to methane. The dependence of the rate of growth and methane formation on the sodium concentration was hyperbolic with an apparent K s for sodium of approximately 1 mM. The findings indicate that sodium has a specific function in the energy metabolism of this bacterium.

The Blue Light Receptor(s): Primary Reactions and Subsequent Metabolic Changes

Abstract: The growing awareness of blue-light-induced phenomena in plants and microorganisms is reflected in the increased research activity into an ever-increasing variety of blue light effects in biological systems. In the early 1930s the first publications dealing with specific effects of blue light on biological processes in plants were those on phototropism (Galston, 1959). Closely related were other studies on the blue-light-induced photooxidation of indole-3-acetic acid, the plant growth hormone (Galston and Baker, 1959). More than 20 years were to elapse, however, before the discovery that blue light could specifically influence carbon metabolism in higher plants and algae (Hauschild et al., 1962; Kowallik, 1962; Voskresenskaya, 1953); this finding then triggered an avalanche of research into blue light effects on plant metabolism, photomorphogenesis, development, and algal photomovement.

Carbenes and Nitrenes in Heterocyclic Chemistry: Intramolecular Reactions

Abstract: Publisher Summary The chapter reviews the literature of carbenes and nitrenes. It accounts for vinylnitrenes, 2H-azirines, iminocarbenes, imidoylcarbenes, 1H-azirin, oxocarbenes, oxiren, thioxocarbenes, thiirenes, selenium analog, acylnitrenes and Thio Analogs, and imidoylnitrenes and nitrilimines (Azocarbenes). The chapter discusses arylcarbenes and arylnitrenes wherein mechanism of carbine–nitrene rearrangements, matrix photochemistry, formations of azepines, o-Diamines, and pyridines are also discussed. Cyclization onto an adjacent ring is done in two ways: direct cyclization and carbine–carbene and carbine–nitrene rearrangement. Cyclization between bridged rings are carried out for methylene bridging group, sulfur bridging group, and O,N, SO2, or CO bridging groups. Undoubtedly there are still innumerable arrangements and synthetic application of carbenes and nitrenes to be discovered. This together with the flourishing chemistry of silylenes and the emerging chemistry monovalent boron and phosphorous compounds give the entire field of electron-deficient reactive intermediates enormous synthetic potential.

Correlations and spectra of periodic chaos generated by the logistic parabola

Abstract: We consider the one-parameter family of mappingsfa(x)=4ax(1−x), a, x e[0, 1] and define an infinite countable set of parameter values a for which the solutions show observable chaos. Their properties are investigated by means of correlation functions and spectra, which can be interpreted and approximated by separating periodic and chaotic components in the solutions and introducing two simple assumptions on the statistics of the chaotic component.

Simulation of carrier transport and energy relaxation in a macroscopic hopping system of sites with a Gaussian energy distribution

Abstract: The transport properties within a cubic lattice consisting of 70 × 30 × 30 hopping sites subject to a Gaussian energy distribution [sgrave]=0.1 eV wide, have been simulated by a Monte Carlo technique. Transit pulse shapes, the time evolution of the energy of the hopping carrier and number of new sites visited as a function of time are analysed. It is found that within the time regime of dispersive transport the energy loss per carrier per jump is inversely proportional to the previous number of new sites visited. This is consistent with a t α-1 behaviour of the jump rate. After a time τe, dynamic equilibrium is established leading to Gaussian transport. For disordered molecular solids in which hopping transport dominates and which are characterized by [sgrave]/kT 0.5, τe is found to be less than 10−8 s. This value would prevent detection of the dispersive regime employing conventional electrical circuitry. The mean carrier displacement at t=τe is typically ten lattice planes. In the...

Phosphorylative fumarate reduction in Vibrio succinogenes: Stoichiometry of ATP synthesis

Abstract: 1. Cells of Vibrio succinogenes, treated with EDTA at pH 8, catalyze the phosphorylation of their endogenous ADP and AMP as a function of the electron transport from formate to fumarate. The P/fumarate ratio obtained from the initial velocity of the phosphorylation on initiation of the electron transport and from the activity of fumarate reduction in the steady state was 0.90. The phosphorylation was prevented by 10μmol/g protein carbonylcyanide-3-chlorophenylhydrazone. 2. The esterification of external phosphate in the presence of ADP, hexokinase and glucose is catalysed by a membrane preparation of V. succinogenes in the steady state of fumarate reduction by H2. The phosphorylation was fully abolished by either 5μmol/g protein carbonylcyanide-4-trifluoromethoxyphenylhydrazone or 30μmol/g protein carbonylcyanide-3-chlorphenylhydrazone. Phosphorylation was blocked also by dicyclohexylcarbodiimide, an inhibitor of the Mg2+-dependent membrane bound ATP synthase, and by low concentrations of the inhibitors of electron transport 2-(n-nonyl)-4-hydroxyquinoline-N-oxide or 4-chloromercuriphenylsulfonate. 3. The P/fumarate ratios, measured with the membrane preparation, were found to increase with progressive inhibition of the electron transport from hydrogen to fumarate by means of 4-chloromercuriphenylsulfonate. The extrapolated ratio at vanishing electron transport activity was 0.47. 4. About 50% of the membrane preparation was found to consist of inverted vesicles with the hydrogenase and formate dehydrogenase oriented to the inside. The residual part is considered as being incapable of performing energy transduction. The extrapolated P/fumarate ratio valid for the inverted vesicles was 0.94.

Photoaffinity labeling of steroid binding proteins with unmodified ligands.

Abstract: Photoactivation of the alpha,beta-unsaturated ketones of natural and synthetic steroid molecules by light of lambda greater than or equal to 330 nm allows their covalent attachment to steroid-binding proteins. The general validity of this method is demonstrated with two steroid hormone receptors and the steroid-binding protein uteroglobin. Progesterone can be covalently attached to the partially purified progesterone receptor and to uteroglobin, and comigrates with the binding proteins upon electrophoresis in polyacrylamide gels containing sodium dodecyl sulfate. Similarly the synthetic glucocorticoid triamcinolone acetonide can be covalently bound to the partially purified glucocorticoid of rat liver. This method allows the identification of steroid hormone receptors after electrophoresis in polyacrylamide gels containing sodium dodecyl sulfate. Labeling with radioactive steroids is specific since it can be prevented by the addition of an excess of non-radioactive ligand. Digestion of the labeled binding proteins with trypsin or chymotrypsin yields a defined pattern of radioactive peptides, demonstrating that covalent attachment takes place at specific binding sites.

Lipomatosis of the pancreas. A morphometrical investigation.

Abstract: The study was performed in 50 human autoptic pancreata. After postmortem ductography and formalin fixation the organs were cut in slices of 8 mm thickness. After paraffinembedding histological sections were made from these slices. In photographical magnification (20 X) of these sections the amount of adipose tissue and pancreatic parenchyma were measured by morphometric means. The length of the pancreatic duct was determined in the radiographs. The data were evaluated by statistical methods. The share of the adipose tissue and the total weight of the pancreata are positively correlated depending on age and body weight. In contrast the weight of the pancreatic parenchyma shows no correlation to age, body length and weight. The amount of lipomatosis is the same in the various parts of the dorsal pancreatic anlage. On the other hand, the amount is clearly diminished in the ventral anlage. In the lipomatous pancreata the main duct is longer than in the normal. The lipomatosis of the pancreas is not correlated with a loss of parenchyma, which means, that there is not a true lipomatous atrophy. Even if the parenchyma in the lipomatous pancreata is replaced by fat tissue, which includes the undestroyed pancreatic islets, the parenchymal weight of the pancreas remains unchanged. This and the lengthening of the pancreatic duct in lipomatous organs allow the conclusion that the loss of parenchyma may be compensated by new parenchymal growth.

The Function fo the Subunits of the Fumarate Reductase Complex of Vibrio succinogenes

Abstract: The membrance-bound fumarate reductase complex of Vibrio succinogenes catalyzes the reduction fo fumarate by 2,3-dimethyl-1,4-naphthohydrquinone (dimethylnaphthohydroquinone) and consists of three different keptides (Mr 79000, Mr 31000 and Mr 25000), the smallest of which is cytochrome b [Unden, G., Hackenberg, H. and Kroger, A.(1980) Biochem. Biophys.Acta 591, 275–288]. The complex was cleaved with guanidinium chloride, the resulting subunits characterized and their functions within the complex investigated by reconstitutional experiments. 1 The Mr-79000 subunits catalyzed the reduction fo fumarate by benzylviologen radicals as well as the oxidation of succinate by methylene blue, but not fumarate reduction by dimethylnaphthohydroquinone. 2 The spectral and the redox properties of the isolated cytochrome b(Mr 25000) were equivalent to those of the high-protential cytochrome b of the bacteria. The isolated cytochrome b had a midpoint potential of -15 mV and was reducible by dimethylnaphthohydroquinone in the absence of the other subunits. 3 The Mr-31000 subunit did not catalyze any of the ractions mentioned above. For the reduction of cytochrome b by succinate in the presence of the Mr-79000 subunits, an amount of the Mr-31000 subunits was required which was equimolar to cytochrome b. 4 The activity of fumarate reduction by dimethylnaphthohydroquinone could be restord by coprecipitation of the three subunits. It is concluded that the fumarate reductase complex has two different reactive sites, which are essential for its function in the phosphorylative electron transport of the bacterium. The site reacting with the substrates fumarate and succinate is situated on the Mr-79000 subunit, and that reacting with dimethylnaphthohydroquinone is cytochrome b. The Mr-31000 subunit mediates the electron transport between cytochrome b and the Mr-31000 subunits mediates the electron transport between cytochrome b and the Mr-79000 subunit.