Showing papers by "Vienna University of Technology published in 1978"

The role of the tricarboxylic acid cycle in citric acid accumulation by Aspergillus niger

Abstract: Determinations of the momentary levels of various intermediates related to the activity of the tricarboxylic acid cycle have been made during citric acid production in high-accumulating (manganese deficient) and lowaccumulating (manganese supplemented) mycelia of Aspergillus niger. During the growth period the levels of almost all TCA cycle acids, with the exception of 2-oxo-acids, were unusually high; during the induction phase of citrate accumulation malate, fumarate, and isocitrate decreased, whereas pyruvate, oxalacetate, and citrate increased. The presence of succinate could not be demonstrated. The interrelations of the momentary concentrations of the intermediates mainly demonstrate a lack in activity of 2-oxoglutarate dehydrogenase, representing a block in the TCA cycle concomitant with a strongly operating glycolysis as a prerequisite for citrate accumulation. Inhibition studies with crude enzyme preparations suggest that an inhibition of malate dehydrogenase by citrate and also inhibition of isocitrate dehydrogenase by citrate and 2-oxoglutarate occur during the production phase as additional factors.

On the reliability of amorphous chalcogenide switching devices

Abstract: Switching devices consisting of a thin amorphous AsTeGe film sandwiched between two molybdenum electrodes were prepared by electron-beam evaporation and investigated by subsequent switching. The number of switching events from the beginning of the test until a prefixed change in switching voltage appeared, was defined as the “lifetime”. Samples which were subjected to an ageing process showed relatively stable operation, and longer lifetime than unaged samples. In addition, the lifetime was found to depend strongly on device geometry and to be limited by the formation of crystalline regions in the amorphous film. This was explained to be due to heating effects during the preswitching region, during the transition from off-state to on-state, and during the on-state, although the underlying switching model is assumed to be non-thermal.

Iterated defect correction for differential equations part I: theoretical results

Abstract: Iterated Defect Correction (IDeC) is a technique for improving successively an approximate solution of a given problemFy=0. One of the most important fields of application of this principle are differential equations. Here, IDeC can be used as a technique for increasing the order of a discretization method and thus for improving the accuracy. In this paper a metalgorithm for the class of IDeC-methods for differential equations is presented and analyzed. For every component of this metalgorithm conditions are given which guarantee a certain order of accuracy. These conditions are of particular importance for practical applications, as far as the implementation of IDeC-methods is concerned.

Light waves guided by a single curved metallic surface.

Abstract: Propagation of TE-waves along a single curved metallic surface with radius of curvature much larger than wavelength is investigated both theoretically and experimentally. Approximate analytic expressions for the field configuration yield that power concentrates in a small region near the metal. The attenuation constant per unit angle of bend (radian) is given by the real part of the inverse of the refractive index, independent of the radius of curvature and of the mode number. In agreement with theory experiments with 10-μm radiation showed that low loss guiding can be realized.

Determination of metastable fractions in noble-gas-ion beams

Abstract: Yields and kinetic energy distributions of secondary electrons emitted by potential emission due to impact of slow singly or multiply charged noble-gas ions on a clean polycrystalline tungsten target have been determined. An empirical relation for the secondary-electron yield of ground-state ions is applied to obtain the secondary-electron yield of corresponding metastably excited ions. By this technique metastable fractions of noble-gas-ion beams could be evaluated. Results for singly and doubly charged ions of Ar, Kr, and Xe, are presented.

Eine semiempirische Gleichung zur Beschreibung des Lösungsmitteleinflusses auf Statik und Kinetik chemischer Reaktionen. Teil I

Abstract: A model has been developed for calculating the enthalpy, entropy and free energy change associated with the creation of cavities in a liquid the size of which corresponds to the volume occupied by a solvent molecule. The molar enthalpy change ΔHcav equals the molar enthalpy of vaporization of the liquid, the free energy change ΔGcav is given by ΔGcav=−RT ln (V m ·p eq /RT) (V m =molar volume,p eq =equilibrium vapor pressure) and is related to the standard free energy of vaporization. This relationship provides an estimate of the free energy of cavity formation required to accomodate a substrate in the liquid. It has been shown, that the free energy of solvation of a substrate can be dissected into different contributions accounting for (1) the concentration dependence of partial molar free energy quantities, (2) the formation of holes in the solvent, (3) the existence of specific, short range solute-solvent interactions and (4) the dielectric polarization of the medium. Application of this concept leads to an equation of the general form ΔG S −ΔG R =a(DN S −DN R )+b(AN S −AN R )+c(ΔG vp oS −ΔG vp oR ), where ΔG represents the free energy of reaction or activation,DN the donor number,AN the acceptor number and ΔG vp o the standard free energy of vaporization of a solventS and a reference solventR, resp.

H c2 anisotropy in the system niobium-nitrogen

Abstract: Systematic experiments on the impurity and temperature dependence of the H c2anisotropy in niobium are reported. A combined evaluation of these two dependences within the framework of a recent nonlocal theory is shown to permit a separation of different sources contributing to the H c2anisotropy. Whereas the l = 4 component of the anisotropy is mainly due to band-structure anisotropies of the normal state, the l = 6 component in pure niobium originates predominantly from anisotropies of the energy gap. The rms anisotropy of the energy gap in niobium is estimated to be 0.08. The anisotropy of the flux line lattice predicted on the basis of the microscopic anisotropy parameters as deduced from the H c2measurements is in agreement with experimental observations.

Interpretation of soft X-ray emission spectra in terms of relativistic electric dipole transition probabilities

Abstract: The emission process for eigenstates of a model Dirac Hamiltonian of “muffintin” type is described in terms of relativistic electric dipole (E1) transitions with the assumption that the final state is a localized core eigenstate of the system. The proposed method is applied to theL-emission spectrum of V in VC and to theL- andM-emission spectrum of Nb in NbC. Resulting theoretical spectra are compared with experimental data.

Eine semiempirische Gleichung zur Beschreibung des Lösungsmitteleinflusses auf Statik und Kinetik chemischer Reaktionen, Teil II: Praktische Anwendungen

Abstract: Based on the model developed in Part I1, equilibrium and rate data have been calculated for various chemical reactions in a variety of dipolar aprotic solvents of medium to high dielectric constants. Examples include solubility determinations, complex formation equilibria, ion pair equilibria and a nucleophilic substitution reaction with changes in the standard free energies of reaction or activation between about 3 and 8 kcal/mole. Experimental data were analyzed by the method of multiple linear regression. The physical meaning of the individual constants of the regression equations are discussed. Deviations observed between calculated and experimental free energies in structured solvents like water, methanol, formamide and N-methyl-formamide are indicative of changes in solvent structure associated with the solvation process and can be interpreted in terms of the structure making or breaking properties of the solutes.

Transition from Type-II to Type-I Superconductivity with Magnetic Field Direction

Abstract: We report on a new effect in superconductivity and demonstrate experimentally that, because of the correlation of the upper critical field ${H}_{c2}$ with crystal directions in single-crystalline $\mathrm{Ta}\mathrm{N}$ samples (anisotropy effect), at certain fixed temperatures the material is a type-I superconductor near the [100] and a type-II superconductor near the [111] directions.

Symbolik in der Analytischen Chemie

Abstract: Die moderne problemorientierte Analytische Chemie braucht nicht nur Automaten, standardisierte Verfahren und breite Bewertungsmerkmale wie Fehlergrosen, Selektivitatsverhaltnisse, Erfassungsgrenzen usw. Sie verlangt ein hochgeordnetes System fur ubersichtliche und informationsreiche Beschreibung dieser Automaten, Verfahren und Leistungskenngrosen. Wir sind der Meinung, das ein symbolisches System mit entsprechenden Ikonen dieses Verlangen erfullen kann, da es alle notwendigen Parameter eines modernen analytischen Prozesses enthalt.

Neue Erkenntnisse über den Abbau der Stärke mit Hypochlorit. 7. Untersuchung der Wirkung der Hypochloritoxydation auf Amylose mit Hilfe des Abbaues mit β-Amylase und Bestimmung des Jodbindungsvermögens†

Abstract: Mit Hilfe des Abbaues der hypochloritoxydierten Kartoffelstarke mit β-Amylase wurde versucht, die Wirkung des Oxydationsmittels auf die Amylose zu untersuchen. Durch Bestimmung des Jodbindungsvermogens der Oxydationsprodukte konnte der Amylosegehalt quantitativ erfast werden. Auf Grund der Ergebnisse kann auf starkeren Abbau der Amylose im Kornverband der Starke bei der Oxydation mit Hypochlorit geschlossen werden. New Knowledge on Degradation of Starch by Hypochlorite. Part 7. Study on the Effect of Hypochlorite Oxidation on Amylose by Means of Degradation by β-Amylase and Determination of the Iodine Binding Capacity. By degradation of hypochlorite-oxidized potato starch with β-amylase an examination of the effect of the oxidation agent on the amylose was attempted. By determining the iodine binding capacity of oxidation products the amylose content could be established quantitatively. Based on the results stronger degradation of amylose in the grain structure of starch during oxidation with hypochlorite may be assumed to occur.

Untersuchung über das Korrosionsverhalten von Zirkoniumlegierungen. IV. Das Lochfraßverhalten Zirkoniumlegierungen

Abstract: Untersuchungen der Lochfrasbestandigkeit einer grosen Anzahl von Zr-Legierungen in verschiedenen Losungen durch elektrochemische Methoden ergaben, das durch Zusatze von Va- und VIa-Metallen, vor allem aber von Ti, die Lochfrasanfalligkeit des Zr vermindert werden kann. Lokalelementbildende Metalle verschlechtern das Lochfrasverhalten; kleinere Mengen Fe, Ni und Cr haben praktisch keinen Einflus. Die Lochfrasanfalligkeit nimmt mit steigendem Chloridnengehalt der Losung zu; Zusatze an Sulfationen hemmen die Lochentstehung, verandern jedoch die Durchbruchspotentiale nicht. Dagegen haben Nitrationen echt inhibierende Wirkung. Fur die Untersuchungen der Lochfrasdurchbruchspotentiale haben sich neu entwickelte Schnellmethoden gut bewahrt. Investigation into corrosion behaviour of zirconium alloys. IV-Pitting behaviour of zirconium alloys Electrochemical investigations into the resistance of a number of Zr-alloys in different solutions against pitting corrosion have shown that additions of Va- and VIa-group metals and in particular Ti improve the resistance of pure Zr. Metals forming local elements decrease pitting corrosion resistance. Minor amounts of Fe, Ni and Cr have practically no influence. The pitting corrosion resistance of Zr and its alloys decreases with increasing concentration of chloride ions in the solutions. Additions of SO4-ions retard the beginning of the pitting but do not shift the pitting corrosion potential. NO3-ions on the other hand produce a real inhibition. Newly developed methods for the quick determination of the pitting corrosion potential were very useful for the described investigations.

The Tectonic Significance of Joints in the Canary Islands

Abstract: The orientations of joints were measured on four islands of the Canary Archipelago: Lanzarote, Gran Canaria, Tenerife and La Gomera. Although the rocks on these islands are mostly of volcanic origin, evidence is adduced that many joints can be considered as of tectonic origin and that those not of tectonic origin, viz. those caused by shrinking of lava during cooling, can be expected to cancel out in a statistical evaluation procedure due to their random orientations. Accordingly, the data were processed by a statistical method of Kohlbeck and Scheidegger and preferential joint strikes were determined for the islands mentioned. It was found that one of the strike directions is consistent on all the islands; the conjugate one is less so, but it agrees with the direction of the Bouguer-anomaly axes in the area. From the preferred joint-orientations, one can calculate the maximum tectonic compression directions. There is somewhat less consistency here because of the variability of one of the joint-sets; however, for the area as a whole, one obtains essentially an EW compression. This is in conformity with the idea of an Atlantic tectonic plate moving eastward away from the mid-Atlantic ridge toward Africa.

Beiträge zur Chemie der Pyrrolpigmente, 21. Mitt.: Röntgenphotoelektronenspektrometrische Untersuchungen des N1s-Niveaus von Gallenpigmenten

Abstract: N1s-X-ray photoelectron spectra of bilatrienes-abc exhibit two peaks with intensities of 3:1 and differing in bonding energy by approximatly two eV. By comparison with the spectra of model compounds representing certain bile pigment partial structures these peaks could be assigned to the lactam-, pyrrole- and the pyrrolenine type nitrogen atoms. From these results it could be established that bilatrienes-abc exist in the crystalline state as bis-lactam forms, having an unsymmetrical canonical dipyrromethene partial structure. By the same procedure the bis lactam structure of biladienes-ac (e.g. bilirubin) was deduced.

Mass shell behaviour of quantum chromodynamics in the axial gauge

Abstract: It is shown that, in the noncovariant axial gauge, quark and gluon mass shell renormalization constants (if suitably defined) obey the classic Ward identity of quantum electrodynamicsZ1=Z2. Similar relations hold for the pure gluon sector. The validity of such identities in covariant gauges has been proven recently in the literature. The derivation in the axial gauge is considerably simpler than in covariant gauges.

Beitrag zur Kenntnis des Systems Vanadin—Chrom—Stickstoff

Abstract: The System V−Cr−N has been investigated at 1100 and 1400 °C and at nitrogen pressures between 1 and 1000 atmospheres by X-ray techniques. VN and CrN on the one hand and V2N and Cr2N on the other are forming complete series of solid solutions. The phase field of the mononitride solid solution is dependent on nitrogen pressure and temperature conditions.

Electron recombination between Landau-levels in n-InSb

Abstract: Experimental and theoretical investigations of electron recombination between Landau levels and associated impurity levels have been performed for n -InSb. The electronic lifetime in the first Landau level is found to be determined by electron-electron scattering what is experimentally confirmed by an inversely linear dependence on the electron concentration n 1 in the 1st Landau level. Values of 10 −10 sec are obtained for n 1 ∼ 10 13 cm −3 . For n 1 ≤ 10 10 cm −1 acoustic phonon scattering determines the lifetime in the first Land level. For the recombination of electrons between the lowest Landau level and the impurity ground state times between 200 nsec and 50 nsec dependent on the magnetic field but independent of electron concentration are found indicating a phonon capture process. These times are also responsible for the observation that relaxation times from the (110) impurity level to the (000) ground state are the bottle neck in a three step process.

Deformation und Stabilität windbeanspruchter Kühlturmschalen

Abstract: Nach der Formulierung des Deformations- und des Stabilitatsproblems auf der Grundlage ursprunglich nicht-konformer, dreiecksformiger, gekrummter finiter Elemente wird zunachst das Deformationsproblem fur eine ausgefuhrte Kuhlturmschale numerisch gelost Die nachfolgende Stabilitatsanalyse dieser Kuhlturmschale zeigt gute Ubereinstimmung der mittels der Methode der finiten Elemente errechneten Beulsicherheit mit dem aufgrund des Munganschen Beulkriteriums erhaltenen Kleinstwert der Beulsicherheit

Joints in Eastern North America and their geotectonic significance

Abstract: Sufficient data on joint orientations in the general region of Eastern North America have now been accumulated for a global picture to emerge. As is well known, the preferred joint orientations can be calculated for a region by a statistical maximum likelihood procedure and the directions of the principal neotectonic stresses can be inferred there-from. For the individual regions investigated, the postulated stresses are in conformity with those expectable from plate-tectonic theory. In the large-scale picture, the most startling characteristic is the indication of an E-W unconformity in the stress-orientation just below a latitude of 40°N.

Beitrag zur Kenntnis des Systems Chrom-Mangan-Stickstoff

Abstract: The system Cr−Mn−N has been investigated by X-ray technique in three isothermal sections at 800, 1,000 and 1,200°C and at nitrogen pressures ranging from 1 to 800 atm. The binary compounds Cr2N and Mn2N form a complete series of solid solutions. The mononitride phase field extends from CrN to (Cr0.21Mn0.79)N0.80 at 1,000°C and 800 atm N2, whereas at normal pressure only a small portion of chromium atoms in CrN can be substituted by manganese atoms.

Imidazo- und Diazino-Anellierungen an das [1]Benzothieno[2,3?d]pyrimidin-System

Abstract: Derivatives of the following six ring systems were synthesized: 1. 3,10-Dihydro-[1]benzothieno[2,3-d]imidazo[1,5-a]-pyrimidine (I) 2. 6H-[1]Benzothieno[2,3-d]pyrazino[1,2-a]pyrimidine (II) 3. 1,5-Dihydro-[1]benzothieno[2,3-d]imidazo[1,2-a]-pyrimidine (III) 4. 6H-[1]Benzothieno[2,3-d]pyrimido[1,2-a]pyrimidine (IV) 5. 1,5-Dihydro-imidazo[1,2-a]thieno[2,3-d]pyrimidine (V) 6. 4H-Pyrimido[1,2-a]thieno[2,3-d]pyrimidine (VI)

Two-dimensional modelling of s.o.s. transistors

Abstract: The paper presents a 2-dimensional numerical model used to analyse the silicon-on-sapphire transistor under various geometries, doping levels and bias conditions. The model accounts for the thin-film structure and the finite interface charge at the silicon-sapphire interface. The model also includes the possibility of simulating nonisothermal effects, and is shown to be applicable to prediction of the transistor behaviour in the high-voltage region. The complete system of four coupled partial differential equations describing the internal behaviour of the s.o.s. transistor is solved exactly. Typical results for an n-channel double-implanted inversion-layer s.o.s. transistor are shown. The agreement between theory and experiment is found to be excellent.