Showing papers by "University of Erlangen-Nuremberg published in 1980"

The physical interaction potential of gas atoms with single-crystal surfaces, determined from gas-surface diffraction experiments

Abstract: A comprehensive survey and data collection of experimental results achieved from diffracting beams of light gases like H, D, $^{3}\mathrm{He}$, $^{4}\mathrm{He}$, and ${\mathrm{H}}_{2}$ from single-crystal surfaces (alkali halides, oxides, and graphite) is given, and it is shown that gas-surface diffraction is a valuable tool to get detailed information on the physical gas-surface potential: (a) From comparison of diffracted beam intensities with calculations in a corrugated hardwall approximation the periodic structure of the interaction potential is obtained together with information on the atomic structure at the surface. (b) From bound-state resonance investigations one gets information on the different terms of the gas-surface potential in Fourier expansion $v(r) ={\ensuremath{\Sigma}}_{G} {v}_{G}(z)\mathrm{exp}(iG\ifmmode\cdot\else\textperiodcentered\fi{}R)$: the achieved spectrum of binding energies {${E}_{j}$} can be used to construct the main term ${v}_{00}(z)$, whereas observed splitting of degenerate bound states allows evaluation of the strength of the periodic terms ${v}_{\mathrm{G}}(z)$. (c) from ${E}_{j}$ levels near the dissociation limit the constant ${C}_{3}$ of gas-surface long-range dispersion attraction can be determined. Finally, regarding the experimental results on ${C}_{3}$ and the potential well depth $D$, two semiempirical rules are established: ${C}_{3}={K}_{C}\ifmmode\cdot\else\textperiodcentered\fi{}\ensuremath{\alpha}\frac{(\ensuremath{\epsilon}\ensuremath{-}1)}{(\ensuremath{\epsilon}+1)}$ and $D={K}_{D}\ifmmode\cdot\else\textperiodcentered\fi{}\ensuremath{\alpha}\frac{(\ensuremath{\epsilon}\ensuremath{-}1)}{(\ensuremath{\epsilon}+1)}$. These rules allow the calculation of ${C}_{3}$ and $D$ from the static electric polarizability $\ensuremath{\alpha}$ of the atom, the optical dielectric constant $\ensuremath{\epsilon}$ of the solid, and the system-independent constants ${K}_{C}$, ${K}_{D}$ given in the text. Calculated values of $D$ for several gas-surface systems are given in a table.

Bis(pentamethylcyclopentadienyl)germanium und ‐zinn sowie (Pentamethylcyclopentadienyl)germanium‐ und ‐zinn‐Kationen: Synthese, Struktur und Bindungsverhältnisse

Abstract: Synthese und Eigenschaften des Bis(pentamethylcyclopentadienyl)germaniums (2) und -zinns (1) sowie der ionischen (Pentamethylcyclopentadienyl)germanium- und -zinn-tetrafluoroborate 4 und 3 werden beschrieben. Die Strukturen von 1 – 4 resultieren aus spektroskopischen und analytischen Daten sowie im Falle von 1 und 3 auch aus Rontgenstrukturanalysen. Elektronenstruktur und Bindungsverhaltnisse in 1 – 4 werden auf der Basis von MO-Modellrechnungen diskutiert. Bis(pentamethylcyclopentadienyl)germanium and -tin and (Pentamethylcyclopentadienyl)germanium- and -tin Cations: Synthesis, Structure, and Bonding Properties Synthesis and properties of bis(pentamethylcyclopentadienyl)germanium (2) and -tin (1) and of the ionic (pentamethylcyclopentadienyl)germanium- and -tin tetrafluoroborates 4 and 3 are described. The structures of 1 – 4 result from spectroscopic and analytical data and in the case of 1 and 3 also from X-ray structure analyses. The bonding in 1 – 4 is discussed on the basis of model MO calculations.

Fracture behaviour of composites based on Al2O3-TiC

Abstract: The critical stress intensity factor and other related fracture parameters have been measured in three-point bending for pure Al2O3-TiC composites containing 4 to 35 volume fractions of TiC. An increase has been observed for all the parameters with increasing volume fraction of TiC. Following a study of the mode of fracture, the results are explained in terms of a linear variation of the fracture energy with the volume fraction of TiC.

Oxygen effect in the radiolysis of proteins. I. Lactate dehydrogenase.

Abstract: SummaryDose survival curves of lactate dehydrogenase irradiated under aerobic and anaerobic conditions show a sensitizing effect of oxygen for the inactivation of the enzyme. The oxygen effect in the radiolysis of lactate dehydrogenase was analysed by gel filtration and polyacrylamide gel electrophoresis. Under anaerobic conditions the main reaction is the aggregation caused by covalent and non-covalent interaction of the protein molecules. Oxygen prevents both kinds of aggregation and instead it enhances peptide chain breakage. Protein fragments became obvious only after reduction of the irradiated proteins and could be separated by electrophoresis.

Contingency and Choice in Organization Theory

Abstract: From reconstructing and reviewing the paradigm of contingency theory, its inherent economic determinism is rejected as being misleading Supported by considerable evidence, 'scope of choice' is suggested to be crucial for the understanding of the nexus between environmental circumstances and organizational structure Using the idea of 'scope of choice', consequences for further theorizing are outlined An action-oriented approach is suggested which also allows for rational reasoning on normative issues Some proposals for interpreting organizational structure as a subject of decision pro cesses are discussed Special attention is given to the concept of strategic choice as a possible means of orienting organization research Finally, issuing from the idea of 'scope of choice', normative questions are considered in an attempt to 'recall' the obligation of practical (normative) reasoning in organizational choice

Fazielle und paläontologische Untersuchungen in oberrhätischen Riffen (Feichtenstein- und Gruberriff bei Hintersee, Salzburg, Nördliche Kalkalpen)

Abstract: Im Hangenden der Kossener Schichten sind in den Nordlichen Kalkalpen zahlreiche kleine Riffe (“patch-reefs”) eingeschaltet, die in der Literatur verschieden benannt werden und im allgemeinen als “Oberrhat”-Riffe bekannt sind (vgl. Fabricius 1966:20; Tollmann 1976:258).

The time temperature position of the glass-rubber transition of amorphous polymers and the free volume

Abstract: Accurate measurements of the shear creep compliance in the glass rubber transition region have been performed by means of a combined torsional pendulum and torsional creep apparatus over a broad experimental window for commercial PS, PMMA and PVC and for two slightly crosslinked rubbers, NR and PU. For the three plastic materials, specific volume vs. temperature curves were obtained by volume dilatometry under different rates of cooling.

Unequal Opportunity Structure and Labour Market Segmentation

Abstract: Sociology of social stratification and labour market economics have developed in isolation from one another. The present paper attempts to bring these two traditions closer together. The starting point is a critique of the very notion of social `stratification'. A return to Max Weber's idea of `class situation as market situation' and to his concept of `social closure' is advocated. On this basis, a conception of structured social inequality in advanced capitalist societies is developed which is open for conceptual innovations to be taken from labour market economics. A number of approaches to labour market analysis are discussed, and the special significance of several recent contributions related to the so-called `dual labour market theory' is emphasized. This leads up to the construction of a typological model supposed to supersede the traditional notion of social inequality as a system of hierarchically superposed strata. This model comprises eight levels of labour market structuration characterizing ...

Palaeoisopus, Palaeopantopus andPalaeothea, pycnogonid arthropods from the Lower Devonian Hunsriick Slate, West Germany

Abstract: Palaeoisopus problematicus andPalaeopantopus maucheri are redescribed and found to be primitive pycnogonids belonging to extinct orders.Palaeoisopus is particularly primitive in retaining a long abdomen with a telson. It differs from other forms also in having flattened limbs indicating a swimming mode of life and in having the ocelli differently arranged.Palaeothea devonica nov. gen. et nov. spec. is a tiny pycnogonid, the only hitherto known fossil representative of the extant order Pantopoda, indicating that entirely modern forms were in existence already in the Early Devonian. A derivation of pycnogonids from early merostomes is regarded as likely.

Chromosome studies on lymphocytes of patients under cytostatic therapy. I. Conventional chromosome studies in cytostatic interval therapy.

Abstract: Chromosome studies were performed on lymphocyte cultures from the peripheral blood of 43 patients undergoing a cytostatic interval therapy with a regimen of methyl-CCNU, 5-fluorouracil, and vincristine. From a total of 229 individual examinations (30 prior to the start of therapy, the rest at different stages of the therapy) more than 23 000 metaphases were analysed for structural chromosome aberrations (i.e., gaps, breaks, and interchanges).

The Fine Structure of Colonic Submucosal Nerves in Patients with Chronic Laxative Abuse

Abstract: Ultrastructural studies of colonic biopsies from patients with a history of long-term laxative abuse, predominantly with stimulant cathartics such as anthraquinone derivatives or bisacodyl, indicated that submucosal nerve fibres may be severely damaged in relation to dosage and time of addiction. The main pathological features found were ballooning of axons, reduction of nerve-specific cell organelles, lysosomal activity, and increase of melanin-loaded macrophages. Morphometric analysis revealed a significant increase (P less than 0.01) in axonal area, with simultaneous reduction of neurotubules. Nerve endings showed a significant decrease of neurosecretory granules when compared with those of normals. It is concluded that these alterations might be a morphological correlation to the clinically evident disturbance of gut motility in patients with chronic laxative abuse, because the intact enteric plexus system is a prerequisite for coordination of normal gut peristalsis.

Kumulierte Ylide, VI. Eine neue Synthese des (Triphenylphosphoranyliden)ketens, seines Thioanalogen und stabiler Propadienylidentriphenylphosphorane

Abstract: Die Einwirkung von Natrium-bis(trimethylsilyl)amid (2) auf (Methoxycarbonylmethylen)triphenylphosphoran (1a) bzw. sein Dithioanaloges 1b fuhrt unter β-Eliminierung zu (Triphenylphosphoranyliden)keten (3a) bzw. -thioketen (3b). Die analoge Reaktion von 2 mit den (α-Ethoxyallyliden)-triphenylphosphoranen 8 liefert die stabilen Propadienylidentriphenylphosphorane 9. Cumulated Ylides, VI. A New Synthesis of (Triphenylphosphoranylidene)ketene, its Thio Analogue, and Stable Propadienylidenetriphenylphosphoranes Reaction of sodium bis(trimethylsilyl)amide (2) with (methoxycarbonylmethylene)triphenyl-phosphorane (1a) or its dithio analogue 1b leads to β-elimination and formation of (triphenyl-phosphoranylidene)ketene (3a) and -thioketene (3b), respectively. The analogous reaction of 2 with the (α-ethoxyallylidene)triphenylphosphoranes 8 gives rise to the formation of the stable propadienylidenetriphenylphosphoranes 9.

Mössbauer study of Ni 0.25 Zn 0.75 Fe 2 O 4 . I. Spin fluctuations

Abstract: A M\"ossbauer study of ${\mathrm{Ni}}_{0.25}$${\mathrm{Zn}}_{0.75}$${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$ has been made in the temperature range from 4.2 to 300 K, in the presence of longitudinal fields up to 80 kG. It is possible to distinguish between the effects of ionic spin relaxation and superparamagnetism on the shape of a M\"ossbauer spectrum using an external magnetic field, and effects of ionic spin relaxation are found to dominate the spectra of the ferrite. The N\'eel temperature is found to be higher than 350 K, although the collapse of the magnetic splitting in the absence of an external field occurs at \ensuremath{\sim}250 K. Ionic spin relaxation cannot give rise to the collapse of the magnetic splitting below ${T}_{N}$. This is concluded to be due to superparamagnetism.

On the theory of irreversible processes in molecular liquids and liquid crystals, nonequilibrium phenomena associated with the second and fourth rank alignment tensors

Abstract: A theory for nonequilibrium phenomena primarily associated with the molecular orientation in liquids and liquid crystals is developed within the framework of irreversible thermodynamics. The alignment tensors of rank 2 and 4 are taken into consideration as additional macroscopic variables. With appropriate assumptions concerning the dependence of the internal energy, specific volume and the entropy on the alignment, a dynamic Landau theory is obtained. Nonlinear relaxation equations are derived for the alignment tensors. They possess zero and nonzero stable stationary solutions corresponding to the isotropic and nematic phases of a liquid crystal when the temperature is above or below the transition temperature. Some further applications of the relaxation equations are discussed, in particular fluctuations of the intensity of the depolarized component of scattered light.

Epstein-Barr virus-positive Burkitt's lymphoma in a german woman during pregnancy

Abstract: A fatal case of a Burkitt's lymphoma which occurred in a 34-year-old German woman during pregnancy is described. Nearly all organs showed either diffuse or nodular infiltration by tumor cells. Placenta and fetus were free of detectable tumor tissue. The patient had extremely high antibody titers (1∶ 2056), both against Epstein-Barr virus capsid antigen (VCA) and the early antigen complex (EA). Within the tumor cells the Epstein-Barr virus-specific nuclear antigen EBNA and viral DNA was detected. A cell line established from a tumor biopsy displayed a translocation involving chromosomes 2 and 8. The role of Epstein-Barr virus in the development of Burkitt's lymphoma is discussed.

Small elemental clusters. I. The structures of Be2, Be3, Be4, and Be5

Abstract: The geometries and energies of beryllium clusters up to Be5 are examined using ab initio molecular orbital theory. Allowances are made for electron correlation with Moller—Plesset perturbation theory to fourth order. Correlation is found to have a dramatic effect on the relative energies of the several structures examined for Be4 and Be5. Furthermore, the effect of d-type basis functions on the correlation energy results in an increased binding energy for the clusters. Be2 is only weakly bound. For Be3, the best estimate of the binding energy is 6 kcal/mole for the singlet equilateral triangle. Be4 is tetrahedral in its ground state and the estimated binding is 56 kcal/mole. The best structure for Be5 is a singlet trigonal bipyramid, and the binding energy is 88 kcal/mole at the highest level of theory used.

On the Classification of Stable Rank-r Vector Bundles over the Projective Plane

Abstract: Though quite a lot is known on the classification of stable rank-2 vector bundles over the projective plane, this is not the case for arbitrary rank. In my talk I wanted to give some results concerning the moduli of rank-r vector bundles. We shall restrict ourselves to c1 (ℱ) = 0. The reason is that though most of the ideas should also work for c1 (ℱ) ≠=0 the technical modifications which are necessary, are quite substantial, and so far I have not been able to bring them into a unified theory.

Oxygen and silicon diffusion-controlled processes in vitreous silica

Abstract: Transport phenomena in silica glass are considered which are rate-controlled by the diffusivity of either oxygen or silicon Oxygen self-diffusion data are reviewed and a diffusion mechanism for oxygen transport is discussed which consists of an interaction between molecularly dissolved oxygen and oxygen of the silica network This interaction is also responsible for the kinetics of silica glass layer formation Data on silicon tracer diffusion in vitreous silica indicate a close correlation with viscous flow phenomena

Hauser-Feshbach calculations in the presence of weakly absorbing channels with special reference to the elastic enhancement factor and the factorization assumption

Abstract: In an extension of previous work on the theory of statistical cross sections model calculations have been performed in the presence of weakly absorbing channels, a case which is of particular interest in applied work involving neutron capture or neutron scattering at low energies. Improved formulas for calculating the elastic enhancement factor and compound nucleus cross sections are presented. In our model calculations we find that the factorization condition for cross sections is not satisfied in cases where a few strongly and many weakly absorbing channels are mixed. However, even in these extreme cases, the formulas provide a good description of the computer-generated cross sections involving at least one strong channel. In addition, the structure of the formula for the elastic enhancement factor has been chosen so as to reproduce all known limiting values and to describe cases where many weakly absorbing channels contribute.

X-ray microanalysis and chlorotetracycline staining of calcium vesicles in the green alga Mougeotia.

Abstract: Calcium ions have been proposed to play a key role in the sensory transduction of phytochrome-governed chloroplast movement in the green alga Mougeotia. To test this hypothesis, the intracellular pattern of calcium distribution was studied in this alga by two independent techniques, namely, X-ray microanalysis of fixed and of unfixed frozen-hydrated cells, as well as in vivo fluorescence by chlorotetracycline. Both methods of detection reveal a significant compartmentation of calcium in vesicles close to the chloroplast edge and, less frequently, in the cortical cytoplasm. Microfilaments, presumably actin, which could function in driving chloroplast movement, have been observed running between the chloroplast edge and the cortical cytoplasm (Wagner, G., Klein, K. (1978) Photochem. Photobiol. 27, 137). The vesicular calcium concentration is stable and decays only slowly in the absence of extracellular calcium much in the same way as the ability of the chloroplast to perform movements decreases. A functional relationship between vesicular calcium compartmentation and phytochrome-governed chloroplast movement in the green alga Mougeotia seems indicated.