Showing papers by "Vienna University of Technology published in 1982"

beta-Glucosidase excretion by Trichoderma pseudokoningii: correlation with cell wall bound beta-1.3-glucanase activities.

Abstract: The formation and excretion of beta-glucosidase from Trichoderma pseudokoningii was studied during growth on different carbon sources. The enzyme was present under all conditions examined, but increased activity was found during growth on carbon sources favouring slow growth. Two different patterns of beta-glucosidase excretion were observed: on carbon sources allowing fast growth a relatively high percentage of total activity was found in the culture fluid, which decreases as the culture grows older, but which increases again during the phase of cell lysis; on carbon sources favouring slow growth, excretion is initially low, but commences at later culture stages. Changes in cell wall composition and cell wall lytic enzyme activities associated with the cell walls were examined during phases of high and low ratios of extracellular to cell-wall bound beta-glucosidase activities. With no component of the cell wall (chitin, alpha-glucan, beta-glucan, galactosamine) could correlation with beta-glucosidase excretion be identified. Among a number of cell-wall lytic, cell-wall associated enzymes (alpha-glucanases, beta-glucanases, glucosaminidase, galactosaminidase), beta-1.3-glucanase activity correlated well with the excretion of beta-glucosidase. The results suggest a possible role of beta-1.3-glucanases in the mechanism of release of beta-glucosidase from cell walls of T. pseudokoningii; this is discussed.

Kinematic-wave theory of sedimentation beneath inclined walls

Abstract: The two-phase flow in settling vessels with walls that are inclined to the vertical is investigated. By neglecting inertial effects and the viscosity of the suspension i t is shown that the particle concentration remains constant on kinematic-wave fronts. The wave fronts are horizontal and propagate in a quasi-one-dimensional manner, but are imbedded in a two-dimensional or three-dimensional basic flow which, in turn, depends on the waves via the boundary conditions. Concentration discontinuities (interfaces) are described by kinematic-shock theory. The kinematic shocks are shown to be horizontal, with the possible exception of discontinuities that separate the suspension from the sediment. At downward-facing inclined walls conservation of mass enforces the existence of a boundary-layer flow with relatively large velocity. As G / R 2 →∞ and G / R 4 → 0, where G and R are respectively a sedimentation Grashof number and a sedimentation Reynolds number, the entrainment of suspended particles into the boundary-layer flow of clear liquid is negligibly small. This provides an appropriate boundary condi- tion for the basic flow of the suspension. Thus, in the double limit considered, a kine- matic theory suffices to determine the convective flow of the suspension due to the presence of inclined walls. As an example batch sedimentation in vessels with inclined plane or conical walls is investigated. The settling process is terminated after a time that can be considerably smaller than the time required in a vertical vessel under the same conditions.Depending on the initial particle concentration, there are centred kinematic waves that are linked to a continuous increase of the particle concentration in the suspension. In an appendix, the flow in the boundary layer at a downward facing, inclined wall is investigated. With G / R 2 →∞ and G / R 4 → 0, the boundary layer consists of an inviscid particle-free main part, a viscous sublayer at the wall, and a free shear sublayer at the liquid/particle interface.

The crystal structure of Liebigite, Ca2UO2(CO3)3·∼11H2O

Abstract: The crystal structure of liebigite, previously only incompletely known from a short note, has been determined from X-ray 4-circle diffractometer data and refined toR=0.030 for 3005 observed reflections. Liebigite from Joachimsthal, Bohmen, was used. It was found to crystallize in the polar orthorhombic space groupBba2−C 2 17 witha=16.699(3),b=17.557(3),c=13.697(3) A,V=4016 A3 and a cell content of 8 Ca2UO2(CO3)3·∼11H2O. The structure contains UO2(CO3)3 units which are linked by two kinds of CaO4(H2O)4 polyhedra and one kind of CaO3(H2O)4 polyhedron to form puckered Ca2UO2(CO3)3·8H2O layers parallel to (010). These layers are interconnected only by hydrogen bonds, both directly as well as via three additional interlayer H2O molecules, two of which show positional disorder.

Analysis of Breakdown Phenomena in MOSFET's

Abstract: An accurate two-dimensional self-consistent numerical model for MOS transistors which is able to predict avalanche behavior is presented. This model aims at a more principal understanding of the physical processes which arise from the avalanche effect and which eventually lead to breakdown. The system of the fundamental semiconductor equations with several generation/recombination mechanisms is solved. To improve the description of the ionization process, correction terms are introduced which account for the fact that the gate induced field does not cause ionization. Holes which are generated in the pinch-off region by impact ionization cause a bulk current; the voltage drop at the parasitic bulk resistance initiates an internal feedback mechanism. Thus a negative resistance branch of the drain current characteristic can arise. However, at high current levels, introduced by a high gate bias and/or a short channel, this snap-back effect is often counterbalanced by strong recombination. Snapback voltage can be estimated with this model.

Investigation of parameter sensitivity of short channel mosfets

Abstract: A strategy to examine the sensitivity of electrical device parameters on geometrical and technological tolerances is described. An approach is offered to determine the limit of device miniaturzation for a given fabrication process and a desired operating condition. As a didactic example of practical relevance the minimum channel length for a modern silicon gate, double implant process due to threshold uncertainty is estimated. A method to calculate global sensitivity numbers for the reproducability of miniaturized devices is suggested. As an experimental determination of sensitivities is extremely difficult and expensive, numerical simulations are ideally suited for this purpose.

Energy band structure and X-ray emission spectra of ZrC and ZrN

Abstract: Self-consistent augmented plane wave calculations are performed for ZrC and ZrN. The charge distributions resulting from valence bands in different regions of the unit cell are discussed and compared with related compounds, where the transition metal is varied between a 3d and 4d element of group IV and V. The limitations of the rigid band model are illustrated and general trends in the chemical bonding are discussed. In connection with X-ray emission spectra (XES) matrix element effects are shown for the three spectra Zr-LIII,-MIII, and-NIII. Further, comparison between theoretical and experimental XES is made with all data available for both ZrC and ZrN.

Approximation of convex bodies by polytopes

Abstract: LetC be a convex body ofE d and consider the symmetric difference metric. The distance ofC to its best approximating polytope having at mostn vertices is 0 (1/n 2/(d−1)) asn→∞. It is shown that this estimate cannot be improved for anyC of differentiability class two. These results complement analogous theorems for the Hausdorff metric. It is also shown that for both metrics the approximation properties of «most» convex bodies are rather irregular and that ford=2 «most» convex bodies have unique best approximating polygons with respect to both metrics.

Effect of Fresnel ripples on sidelobe suppression in low time-bandwidth product linear FM pulse compression

Abstract: The paper discusses the effects of Fresnel ripples on the suppression of peak time sidelobes in low time-bandwidth (TB) product linear-FM pulse compression systems employing internally Hamming weighted compression filters. Two methods for the reduction of these effects are investigated. The first, amplitude tapering of the rectangular FM pulse, yields significantly diminished sidelobes for TB products less than about 100 and is of particular interest for spectrum analysis. The second, applicable to short risetime high-power radar transmitters, is cubic phase predistortion of the rectangular transmitted pulse. This procedure is found to be very effective for TB products less than about 50 (e.g. about 10 dB improvement for TB=10 compared with usual chirp). Both techniques force the fall-off of far sidelobes. Computed results on the achievable sidelobe suppression are presented as a function of the TB product and compared with conventional Hamming weighting. Finally, it is shown that the superior Doppler performance of linear FM is not affected by the discussed waveform modifications.

Die Kristallstruktur des Johannits, Cu(UO2)2(OH)2(SO4)2·8H2O

Abstract: Die Kristallstruktur des Johannits wurde anhand eines verzwillingten Kristalls von Joachimsthal, Bohmen, mit dreidimensionalen Rontgendaten bestimmt und fur 2005 unabhangige Reflexe aufR=0,039 verfeinert. Johannit kristallisiert triklin, RaumgruppeP1, mita=8,903 (2),b=9,499 (2),c=6,812 (2) A, α=109,87 (1) β=112,01 (1), γ=100,40 (1)° undV=469,9 A3. Chemische Formel und Zellinhalt lauten Cu(UO2)2(OH)2(SO4)2·8H2O, das ist um zwei H2O-Molekule mehr als bisher angenommen. In der Struktur sind pentagonal dipyramidale (UO2)(OH)2O3-Polyeder paarweise uber eine von zwei OH-Gruppen gebildete Kante zu Doppelpolyedern und diese wiederum durch SO4-Gruppen zu (UO2)2(OH)2(SO4)2-Schichten parallel (100) verknupft. Die Schichten sind parallel α uber gestreckte Cu(H2O)4O2-Oktaeder und Wassermolekule miteinander verbunden. Folgende Bindungslangen wurden gefunden: U−O=1,78 A (2x) und 2,34–2,39 A (5x); Cu−O=1,97 A (4x) und 2,40 A (2x); =1,47 A; O−O in Wasserstoffbrucken 2,71–2,91 A (8x) und 3,30 A.

Measurement of velocity mismatch in traveling-wave electrooptic modulators

Abstract: For traveling-wave electrooptic modulators, we describe an experimental method to determine the sign and magnitude of velocity mismatch between electrical and optical wave. To this end the waves are counterpropagated and frequencies yielding modulation nulls are determined. Such a measurement does also reveal dispersion of the modulator structure.

Band theory for the magnetic moment in the bcc Fe-Co alloy

Abstract: Magnetic moments and equilibrium lattice constants for the bcc Fe-Co alloy are obtained by means of band-structure calculations using the augmented-spherical-wave method and the local-spin-density scheme. The calculated magnetic moment in Fe-Co does not vary linearly with composition, in agreement with experiment. A rigid-band picture is found to be inadequate; i.e., chemical effects are very important.

Projective invariance of shaky structures

Abstract: A framework consisting of rigid rods which are connected in freely moveable knots, in general is stable if the number of knots is sufficiently large. In exceptional cases, however, the rodwork may allow an infinitesimal deformation. Due to a theorem of Liebmann, this apparently metric property of existing shakiness in fact is a projective one, as it does not vanish if the structure is transformed by an affine or projective collineation. The paper presents a new analytic proof of this remarkable phenomenon. The developments are applicable also to polyhedra with rigid plates and to closed chains of rigid links.

Fracture initiation and stress wave diffraction at cracked interfaces in layered media I. brittle/brittle transition

Abstract: Fracture Initiation and Stress Wave Diffraction at Cracked Interfaces in Layered Media — I. Brittle/Brittle Transition Stress wave scattering about the tips of stationary interface cracks at a brittle-brittle junction in a layered medium and the associated stress-wave induced fracture were investigated. Dynamic photoelasticity was employed to visualize the highly complex interaction process between stress waves and cracks. Methods of linear elastic fracture mechanics were used to analyze regions of high stress intensity as possible sources for crack initiation. The phenomenon of partial load transmission across closed crack walls and imperfect joints and its effect on fracture initiation was also studied.

Acid-base properties of Al2O3/MgO oxides, II. Infrared study of adsorption of pyridine

Abstract: Mixed oxides of alumina and magnesia were characterized by an IR study of pyridine adsorption. Three different Lewis acid sites, but no Bronsted acid sites were detected. The strongest adsorption sites are attributed to Al3+ cations of the alumina phase (1455 cm−1), the weaker Lewis acid sites were assumed to be due to cations of the MgAl2O4 phase (1449–1443 cm−1) and the MgO phase (1440–1438 cm−1).

Transient SH-waves in a wedge-shaped layer

Abstract: Summary. A generalized ray theory for transient SH-waves in a wedge-shaped layer over an elastic half-space is developed in this paper. The ray integrals for multiply reflected waves in the layer are derived in terms of two systems of coordinates and two sets of local wavenumbers, one along the free surface and the other along the sloped interface. All local wavenumbers are then transformed to a common wavenumber in all ray integrals which are evaluated by the Cagniard method. Results for the first motion approximation are in agreement with previous investigations.

Einführung in die Methode der Finiten Elemente

Abstract: Viele Rand- und Anfangswertaufgaben zur Beschreibung komplexer naturwissenschaftlicher bzw. technischer Probleme sind derart schwierig, das an analytische Losungen von Anfang an nicht zu denken ist. Nicht selten bietet schon die Aufstellung der entsprechenden Differentialgleichungen bzw. Differentialgleichungssysteme uberaus grose Schwierigkeiten. Dies gilt nicht zuletzt auch fur komplizierte Probleme der Strukturmechanik. Ohne Anspruch auf Vollstandigkeit zu erheben, werden im folgenden einige Grunde fur die Schwierigkeit, zu analytischen Losungen strukturmechanischer Probleme zu gelangen, aufgezahlt. Im einzelnen handelt es sich um (a) „Unregelmasigkeiten“ in der Struktur (abrupte Anderungen der Wandstarke, Aussparungen, Versteifungen, usw.) (b) Komplizierte geometrische Form der Berandung der Struktur (Berandung nicht oder nur unter grosen Schwierigkeiten mathematisch beschreibbar) (c) Komplizierte Lagerung der Struktur (elastische bzw. elasto-plastische Stutzennachgiebigkeiten verschiedener Art, zeitlich veranderliche Randbedingungen)

Superconductive properties of vanadium and their impurity dependence

Abstract: We report on a comprehensive study of the magnetic properties of the super-conductor vanadium. Starting from a high-purity sample (RRR=1900), we use magnetization measurements to evaluate the primary superconductive parameters of vanadium and their impurity dependence up to α⋍3.1. For the clean limit we findT c0 =5.47 K and κ 0 =0.78. From the impurity dependence of the transition temperature an rms gap anisotropy of ≈16% is obtained. Furthermore, for Ginzburg-Landau parameters ≲1.5 an attractive flux line interaction is found. The experiments on Hc2 anisotropy show results comparable to those for niobium, i.e., a slow decrease of the anisotropy coefficient a4 with increasing impurity parameter and a much faster decrease of the 1=6 component. A detailed analysis of these results awaits further progress of theory.

A numerical analysis of bulk-barrier diodes

Abstract: A selfconsistent numerical analysis of bulk-barrier diodes (BBD) is presented. The principal way of operation of a BBD is explained. A computer program which can accurately model second order effects is used to achieve basic understanding of the internal electric behaviour of a BBD. The distributions of the relevant physical quantities in the interior of a BBD are discussed. Measured and simulated characteristics which show good agreement, owing to the carefully modeled physical parameters, are compared. The sensitivity of electrical properties to minute variations of the doping profile is presented. This can only be done by a program simulating the characteristics of a BBD. The advantages and disadvantages of a BBD compared to a standard silicon diode and a Schottky diode are discussed.

Raman spectra of Na3AsS4·8(D, H)2O and Na3SbS4·9(D, H)2O and O ? D(H)…S bonds in salt hydrates

Abstract: Raman spectra, measured in the temperature range T =75–295 K, are reported for H2O, D2O and isotopically dilute samples of Na3AsS4·8(D, H)2O and Na3SbS4·9(D, H)2O. At T =75 K the uncoupled OD(H) stretching frequencies are observed in the range ν = 2433–2664(3279–3618) cm−1 and ν = 2461–2528(3318–3417) cm−1 for the thioarsenate and the thioantimonate, respectively. Plausible assignments to the distinct crystallographically non-equivalent OD(H) groups are given. The correlation between the uncoupled OD stretching frequencies and the hydrogen bond distances R(D…S) of approximately linear OD…S bonds in salt hydrates is discussed. The frequency shifts upon H-bond formation are shown to depend strongly on the chemical nature of the sulphur proton acceptors.

The microbiological aspects of grape marc humification

Abstract: The microbiological aspects of a novel process of grape marc composting have been investigated. It has been possible to determine the succession of populations during the process which are required to obtain the required final product. The initial population comprises exclusively yeasts which, by autolysis and subsequent binding of the residual alcohol by esterifying reactions, enable rapid appearance of a mixed population of bacteria. The temperature increase continued by this bacterial flora favours growth of a thermophilic fungal flora, which is mainly responsible for the microbial decomposition process. The most important organism is Thermomyces lanuginosus Tsiklinski. Final humification is effected by a mixed population of Streptomycetes. It was possible to optimize the process by installing heat exchangers, thereby creating optimum conditions for the most important organism, T. lanuginosus.

Electrooptic gigahertz light-pipe modulator for CO 2 laser wavelength

Abstract: We have built a traveling-wave electrooptic modulator for 10.6 μm where the optical beam propagates in a highly oversized waveguide. Three CdTe-crystals measuring 35 \times 0.8 \times 0.8 mm3each are cascaded to yield an aspect ratio of 131. Velocity matching between optical and modulating waves and a line impedance of 100 Ω are achieved by proper choice of dielectric embedding and of electrode width. Measured characteristics are: optical transmission 96 percent, maximum input VSWR 1.25:1, half-wave voltage 450 V, and frequency response ±1.1 dB over a 0.006-1 GHz range.

Effect of dilution rate on β-glucosidase secretion and cell wall metabolism in Trichoderma aureoviride cultivated in a continuous air lift fermenter

Abstract: Trichoderma aureoviride was grown in continuous culture under glucose limitation in an airlift fermenter at dilution rates (D) varying between 0.06–0.21 h−1. Autoradiography showed a high incorporation of 3H-GlcNAc into hyphal tips under these conditions, indicating that the hyphae were not suffering from physical stress.