Showing papers by "Vienna University of Technology published in 1987"

Geometry of Numbers

Abstract: The geometry. of numbers can be traced back at least to Lagrange [1773], who proved important results about quadratic forms in two variables. The proofs as well as the formulations of results were purely arithmetic. Reviewing a book of Seeber [1831B] on ternary quadratic forms, Gaus [1831] introduced for the first time geometric methods. Geometric methods were predominant in the work of Dirichlet [1850]. On the other hand Hermite [1850] and Korkine and Zolotareff [1872], [1873], [1877] gave arithmetic proofs for their results on quadratic forms in more than three variables. Finally Minkowski [1891] noticed that a simple geometric argument which he used to give a new proof of a theorem of Hermite could be adapted to much more general situations. Then Minkowski [1896B], [7B], [11B] started a systematic study of geometric methods in number theory and called this new branch of number theory geometry of numbers. Many results and most concepts of modern geometry of numbers have their origin in the work of Minkowski. After Minkowski many eminent mathematicians made contributions to this field. In order to avoid controversies I will not mention any of them. Geometry of numbers is closely related to other branches of number theory such as algebraic number theory and Diophantine approximation. A flourishing offspring is discrete geometry, developed mainly by Fejes Toth and his school.

Involvement of a Conidial Endoglucanase and a Plasma-membrane-bound β-Glucosidase in the Induction of Endoglucanase Synthesis by Cellulose in Trichoderma reesei

Abstract: Summary: The induction of endo-1,4-β-glucanase synthesis by Trichoderma reesei QM 9414 was investigated in conidia, mycelia and protoplasts. Cellulose induced endoglucanase synthesis only in conidia, but not in glucose-grown mycelia or protoplasts. Cellooligosaccharides and sophorose induced endoglucanase synthesis in mycelia, conidia and protoplasts. Only conidia exhibited detectable basal endoglucanase levels, whereas β-glucosidase activity was found in conidia, mycelia and protoplasts. The β-glucosidase was inhibited in vitro by nojirimycin and glucono-δ-lactone. Addition of either of these inhibitors to the induction medium blocked de novo synthesis of endo-1,4 β-glucanase with cellulose (conidia) or cellooligosaccharides (protoplasts and mycelia) as inducer, whereas induction by sophorose remained unaffected. The results are consistent with the assumption that basal constitutive levels of endoglucanase and β-glucosidase are involved in the induction of cellulase synthesis by cellulose in T. reesei.

Electron emission from a metal surface bombarded by slow highly charged ions.

Abstract: We have measured total electron-emission yields \ensuremath{\gamma} for clean tungsten bombarded with various multiply charged ions: ${Z}^{q+}$ up to ${\mathrm{N}}^{6+}$, ${\mathrm{Ne}}^{7+}$, ${\mathrm{Ar}}^{12+}$, and ${\mathrm{Kr}}^{11+}$. At low impact energy (\ensuremath{\le}10 eV/amu) a linear dependence of \ensuremath{\gamma} versus ion potential energy could be observed up to the respectively highest q, for which a pronounced decrease appeared superimposed on the gradual decrease of all \ensuremath{\gamma} toward higher impact energy. Our results are discussed within a multiple-step ion-neutralization model.

The Kleene and the Parikh theorem in complete semirings

Abstract: The Kleene and the Parikh Theorem are generalized to complete semirings with the additional property that limits can be defined by infinite sums.

The role of the citric acid cycle in fungal organic acid fermentations.

Abstract: Filamentous fungi are well known for their potential to accumulate organic acids in the medium when supplied with large amounts of sugar. Commercial applications of this are the production of citric and itaconic acids. The present review attempts to present the current state of knowledge on the biochemical basis of organic acid accumulation by filamentous fungi (citric, itaconic, fumaric and oxalic acids), particularly with respect to the role of citric acid cycle reactions. The explanations offered are based on recent advances in understanding the compartmentation of the fungal cell, and regulation of some key enzymes. The general conclusion is that fungi accumulate organic acids by mechanisms which avoid the channeling of substrates into the citric acid cycle under conditions of strongly active glycolysis.

Electronic excitation in sputtered atoms and the oxygen effect

Abstract: Bombardment of surfaces by ions gives rise to a variety of inelastic collision events leading to the ejection of excited atoms and ions. Such excited sputtered particles have been studied since more than 80 years through their optical emission, when they decay in front of the target to the electronic ground state, having lifetimes of 10−9 to 10−7 s, typically. Information on the energy distribution of such excited states can be obtained by two different techniques: light vs distance measurements (LvD) and by studying line profile broadening in light emission due to the Doppler effect. Only recently it has become possible to study in addition metastable excited atoms using laser induced fluorescence spectroscopy (LIF). Relative sputtering yields and energy distributions have been measured for such metastable states and two types can be distinguished. States with a very low excitation energy (0–0.3 eV), being sublevels of the electronic ground state, were found to have yields and energy distributions comparable to the electronic ground state, while metastable states at higher excitation energies (above 1 eV) seem to behave similar to short lived excited states, typically observed in secondary photon emission (BLE) with excitation energies in the range of 2–6 eV. This behaviour is also clearly visible with respect to oxygen surface coverage or increased near surface oxygen concentration where, similar to secondary ion emission, drastic changes in the yield by orders of magnitude have been found for excited atoms as well as for ions. In addition, under the same conditions a strong decrease in the sputtering yield of neutral ground state atoms has been observed for a number of metals. LIF results for highly excited metastable states are compared with recent results obtained by studying line profile broadening in light emission for Ca, Al and Cr targets. Different mechanisms that have been proposed to account for the observations will be discussed.

Is it Necessary to Develop a Fuzzy Bayesian Inference

Abstract: In applications data used for updating a-priori information are often fuzzy. These fuzzy data are usually not described by standard Bayesian inference. Statistical analysis has to take care of this fuzzyness which can be described by fuzzy numbers. Therefore the resulting fuzzyness of a-posteriori distributions has to be modelled and an analogue of predictive distributions under fuzzyness must be developed. Moreover for a fuzzy observation it is not always possible to decide if it is a member of a certain event. This kind of uncertainty states the following question: Is additivity for the measurement of uncertainty in general valid or a generalization of probability, postulating superadditivity, necessary.

Accumulation and partial re-consumption of polyols during citric acid fermentation by Aspergillus niger

Abstract: Quantitative balances have been made for sugar and oxygen uptake rates during citric acid accumulation by Aspergillus niger: during the first phase of citric acid accumulation (up to 130 h) more sugar is taken up than the production of biomass, CO2 and citric acid account for. In contrast, during later phases of fermentation more citric acid, CO2 and biomass are formed than sugar uptake would theoretically allow. A similar pattern is obtained for oxygen uptake, where less uptake occurs during the early phase of fermentation than needed for complete balance, and the reverse is observed during the late stage of fermentation. It could subsequently be shown that this is caused by the intermediate accumulation and partial re-consumption of a number of polyhydric alcohols (glycerol, arabitol, erythritol and mannitol) during citric acid fermentation.

Magnetic anisotropy in Pr2(Fe1−xCox)14B compounds

Abstract: We have measured the concentration dependence of the Curie temperature, magnetization, anisotropy field and lattice parameters in Pr2(Fe1−xCox)14B for 0 ⩽ x ⩽ 1. The Curie temperature strongly increases with x. The saturation magnetization at 4.2 K decreases with x after remaining approximately concentration independent up to x = 0.2. The room temperature anisotropy field first decreases with x but after passing through a minimum at about x = 0.7 strongly increases with x. The experimental results are compared with results obtained previously for Nd2(Fe1−xCox)14B and are discussed in terms of crystal-field effects.

Spontaneous volume magnetostriction in R2Fe14B compounds

Abstract: We have measured the thermal expansion in ternary compounds of the type R2Fe14B (R  La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Lu) in the temperature range 4.2–1000 K. Data were also obtained above room temperature for Th2Fe14B. At temperatures well above the corresponding Curie temperatures we found a linear high temperature slope of Δ l l equal to α = 16 × 10−6 K−1, excepting Ce2Fe14B for which the slope was slightly higher (α = 20 × 10−6 K−1). The spontaneous volume magnetostriction derived from our data extends to temperatures considerably above the corresponding Curie temperatures. The spontaneous volume magnetostriction at 4.2 K ranges from 2.5% to 3.5% in the various compounds investigated and consists of contributions due to the iron sublattice and the rare earth sublattice.

Second-harmonic generation in centro-symmetric media

Abstract: We have studied the magnetic-dipole and electric-quadrupole contributions to second-harmonic generation (SHG) of centro-symmetric media. It can be shown that the phenomenological parameters α, β, γ can be arranged to form an effective\(\bar \chi _s^{(2)} \)-tensor, which describes dipole-forbidden SHG as the effect of a surface layer upon excitation with a single plane electromagnetic wave. An experimental technique is proposed allowing a determination of the usually very small γ term due to magnetic-dipole interaction using coherent compensation of its contribution by a coverage with an appropriate dye monolayer.

Two-dimensional modeling of ion implantation with spatial moments

Abstract: We present a two-dimensional model of ion implantation which allows for position dependent lateral moments. The lateral standard deviation and the lateral kurtosis as a function of depth have been calculated by 2-D Monte-Carlo simulations for boron, phosphorus, arsenic, and antimony in silicon for energies in the range of 10–300 keV. The lateral moments as a function of depth and energy as well as the vertical moments as a function of energy have been fitted by simple formulae. We specify two types of distribution functions the parameters of which can be adjusted to given values of standard deviation and kurtosis. In this way the depth dependent lateral moments can be included into analytical distribution functions.

Presence and regulation of ATP:citrate lyase from the citric acid producing fungus Aspergillus niger.

Abstract: ATP:citrate lyase (EC 4.1.3.8) has been identified in cell-free extracts from the filamentous fungus Aspergillus niger. The enzyme was located in the cytosol. It exhibits an activity at least ten times that of acetate-CoA-kinase (EC 6.2.1.1) during growth on carbohydrates as carbon sources, and is thus considered responsible for acetyl-CoA formation under these conditions. It is formed constitutively and its biosynthesis does not appear to be controlled by changes in the nitrogen or carbon source or type. ATP:citrate-lyase appears to be very labile during conventional purification procedures; a method involving fast protein liquid anion exchange chromatography was thus developed in order to obtain enzyme preparations sufficiently free of enzymes which could interfere with kinetic investigations. This preparation displays commonly known characteristics of ATP:citrate lyase with respect to substrate affinities and cofactor requirements, with the exception that the affinity for citrate is rather low (2.5 mM). No activator was found. The enzyme is inhibited by nucleoside diphosphates, nucleoside monophosphates and palmitoyl-CoA. Regulation of ATP:citrate lyase be the energy charge of the cytosol in relation to lipid or citric acid accumulation is discussed in view of these findings.

Auger electron emission from slow multicharged ions near a metal surface

Abstract: Electron energy spectra from multicharged ion (N5+, N6+, Ar9+) impact on clean tungsten (impact energies ≥ 500 eV) revealed Auger electron emission from the projectile particles. The impact energy dependence of emission yield and kinetic-energy shift for these Auger electrons lead to a fairly detailed explanation of slow multicharged ion neutralization near metal surfaces.

A boundary element method for eigenvalue problems of polygonal membranes and plates

Abstract: An advanced Boundary Element formulation for eigenvalue problems of membranes and plates is developed. Polygonal membranes are considered, and are embedded into a proper basic domain in order to satisfy boundary conditions exactly as far as possible. Hence, boundary integrals have to be applied at the not coinciding boundaries only. Eigenvalues of the underlying Dirichlet's Helmholtz problem are calculated from frequency response functions evaluated by that “method with Green's functions of finite domains”, and natural frequencies of corresponding membranes and simply supported plates are determined by analogy. A numerical investigation is performed for parallelogram Mindlin plates. Natural frequencies and critical buckling eigenvalues are graphically represented in a nondimensional form, where the influence of skew angle and plate thickness is studied.

Zur Einzigkeit der Bricardschen Oktaeder

Abstract: In 1896 R. BRICARD gave a complete description of all flexible octahedra; a different approach is due to R. CONNELLY (1978). In this paper a new proof is given using methods of classical projective geometry. The proof is based on the observation that by a converse of the theorem of IVORY each pair of incongruent octahedra with the same edge lengths is connected with a certain pair of confocal guadrics.

On the behaviour of the new Kondo lattice CeCuAl3

Abstract: The temperature dependence of the electrical resistivity, thermopower, specific heat, susceptibility and magnetization of CeCuAl3 are presented. CeCuAl3 behaves as a Kondo lattice system with antiferromagnetic ground state properties (TN∼2.8 K). The valency of Ce in this tetragonal compound is close to 3 and the overall crystal field splitting found from our results is about 150 K. The Kondo temperatureTK in the crystal field ground state, estimated from the magnetic susceptibility and the specific heat, is of the order of 8 K.

Potential emission for multicharged ion impact on clean tungsten above the kinetic emission threshold

Abstract: Apparent electron emission yields for impact of Nq+ (q = 4–6) and Neq+ (q = 4–7) on polycrystalline tungsten at impact velocities of 0.5 − 3 × 105 ms−1 are presented. For ν >νt ≈ 105 ms−1 with νt being threshold velocity for kinetic electron emission the data have been corrected for the latter contribution, which permits investigation of potential emission toward higher impact velocities.

A method for determining the mass thickness of thin films using electron probe microanalysis

Abstract: A method is proposed for easy determination of the mass thickness of thin films using electron-probe microanalysis. The model is based on the function of the depth distribution O(qz) of the characteristic x-ray production and emphasizes the treatment of the physical phenomena in the transition area between the film and the substrate. The method is applicable to a wide range of elements and element combinations (Z>5) and electron acceleration energies. It has been tested by comparing results obtained using this method with data taken from the literature. Errors are small, generally, not exceeding 5%.

Stimulation of protein secretion in Trichoderma reesei by Tween surfactants is not correlated with changes in enzyme localization or membrane fatty acid composition

Abstract: Tween surfactants (Tween 20, 40, 60 and 80) stimulated the excretion of protein by Trichoderma reesei QM9414 during growth on cellulose. Tween 60 gave maximal secretion of protein. The presence of Tween decreased the lag time of growth and weakly stimulated growth. Almost the same proportion of cell-wall-bound activity was found in cultures supplemented with Tween for β-glucosidase, acid phosphatase and β-N-acetyl-glucosaminidase. The addition of various Tweens (20, 40, 60 or 80) had only a small effect on the fatty acid composition of the mycelium of T. reesei. Among 5 mutant strains with different secretory capacity, all but one showed stimulation of protein secretion by Tween surfactants. There was no observable correlation between the stimulation of secretion by Tween and the degree of unsaturation of mycelial fatty acids. It is concluded that the stimulation of protein secretion by Tween surfactants does not involve release of surface bound enzymes or changes in membrane fatty acid unsaturation.

A 90 degrees optical fiber hybrid for optimal signal power utilization.

Abstract: An optical 90 degrees hybrid comprising a single-mode fiber coupler and a polarization beam splitter was made at 0.82 microm. It relies on the phase retardation intentionally induced in one of the input fiber leads of the coupler. By properly choosing the transmission/coupling coefficient as well as the orientation of the polarization beam splitter following the coupler, optimum distribution of the available optical fields can be obtained in a Costas loop.

Forced vibrations of an elasto-plastic and deteriorating beam

Abstract: A solution method for elastoplastic vibrating beams including damage accumulation is shown, where inelastic behavior of the structure is represented by an additional loading due to sources of selfstresses acting upon the linear elastic structure of time-invariant stiffness. Response due to this additional loading is evaluated using proper Green's functions. Thus, integral relations are set up, similar to Maysel's formula. Theory is applied to a two span sandwich beam with elastoplastic degrading flanges and elastic core material.