Showing papers by "Johannes Kepler University of Linz published in 1984"

An analytical cross-section formula for K X-ray production by protons

Abstract: We present an analytical cross-section formula for the K X-ray production cross section: σax = scσf, where σf approximates σx = ωkσecpssr where ωK is Krause's fluorescence yield; ECPSSR refers to the theoretical ionization cross section by Brandt and Lapicki. sc is a correction factor close to unity, based upon a comparison of about 3200 experimental data points taken from the literature; it is found to depend essentially only on the scaled velocity ξ and can be approximated by an analytical function. We plot log (σxZ22.2) as a function of e = log( E 1 Z 2 2 ) , where Z2 is the atomic number of the target and E1 is the proton energy in MeV, and approximate this function by a sixth order polynomial in e; the expansion coefficients in turn are rational functions of Z2. We thus obtain an analytical cross section for 11 ⩽ Z2 ⩽ 90 and − 3.7 ⩽ e ⩽ − 1.4 which is accurate to 2.5% (standard deviation) for 21 ⩽ Z2 ⩽ 30 if − 3.5 ⩽ e ⩽ −1.8 and less accurate in other regions.

Lateral growth rates in laser CVD of microstructures

Abstract: Lateral growth rates of Ni spots deposited on absorbing substrates by decomposition of Ni(CO)4 with visible Kr+ laser light have been measured. The experimental data are consistent with the calculated temperature distributions. The mechanism of decomposition is thermal with an apparent chemical activation energy of 22±3 kcal/mole for the temperature range 350 K≦T≦500 K.

The Church-Rosser property in computer algebra and special theorem proving: an investigation of critical-pair/completion algorithms (Ph.D. thesis)

Abstract: An important problem both in computer algebra and special theorem proving in connection with automatic program verification is the calculation of canonical forms with respect to some given side relations. If these side relations can be viewed as a rewrite system which has the Church-Rosser property then a normal form algorithm with respect to this system provides a canonical simplifier. For many computational domains there exists a "completion algorithm" for transforming an arbitrary rewrite system into an equivalent one which has the Church-Rosser property. Improvements to the existing completion algorithms are presented. A very general completion algorithm is described which contains all these various algorithms as special cases. A complexity bound for the Buchberger algorithm for trivariate polynomial equations is derived.

Ion implantation in IV–VI semiconductors

Abstract: In this review, ion-implantation doping and ion-implantation damage in IV–VI semiconductors are discussed. Doping can be achieved by implanting impurity atoms as well as the constituent elements themselves since the electrical properties of these compounds are determined not only by impurities but also by deviations from stoichiometry. Results obtained with implantation doping are presented and the applications of ion implantation to the fabrication of infrared photodetectors and laser diodes are summarized. The main feature of the implantation damage is a saturation of the carrier concentration as a function of the dose, independent of the ion species and implantation conditions. This unusual behaviour has been explained recently by a defect-level model, which is discussed in detail. The similarity of the damage caused by ion implantation and by electron irradiation is pointed out.

K-shell ionization due to light ions: The status of cross-sections

Abstract: In earlier papers, we have shown that the bulk of experimental K-shell ionization cross-sections can be well represented by the Brandt-Lapicki theory. Here we discuss the remaining discrepancies: at low reduced velocity ξ, the Brandt cross-section is too high due to its Coulomb correction. For ξ > 0.6 and nitrogen projectiles, electron capture by the projectile and an increased fluorescence yield enhance the cross-section. Between ξ = 0.25 and ξ = 0.6, a small deficiency of Brandt's binding correction is found, using both experimental data and theoretical results. Krause's fluorescence yields are discussed and various theoretical cross-sections are compared. Light target data are discussed separately, and some chemical effects are pointed out.

On the Complexity of the Groebner-Bases Algorithm over K[x, y, z]

Abstract: In /Bu65/, /Bu70/, /Bu76/ B. Buchberger presented an algorithm which, given a basis for an ideal in K[x1,...,xn] (the ring of polynomials in n indeterminates over the field K), constructs a so-called Grobner-basis for the ideal. The importance of Grobner-bases for effectively carrying out a large number of construction and decision problems in polynomial ideal theory has been investigated in /Bu65/, /Wi78/, /WB81/, /Bu83b/. For the case of two variables B. Buchberger /Bu79/, /Bu83a/ gave bounds for the degrees of the polynomials which are generated by the Grobner-bases algorithm. However, no bound has been known until now for the case of more than two variables. In this paper we give such a bound for the case of three variables.

Globally Convergent Decomposition Methods for Nonconvex Optimization Problems

Abstract: In this paper we consider nonlinear optimization problems of a separable form with nonconvex objective and convex constraints. A convexification procedure preserving separability is given in order that primal-dual methods are applicable. A globally convergent algorithm observing computational aspects is given. This algorithm was applied to a real world problem with 1007 variables and 4030 constraints for controlling the heads of a hydroenergy power station.

Beiträge zur Chemie der Pyrrolpigmente, 52. Mitt.

Abstract: The Δ-4 bond of 2,3-dihydrobilatrienes is susceptible to nucleophilic attack. This is verified by using an intramolecular reaction which provides as a model an entropic situation comparable to the natural protein environment of the phytochrome-chromophore. A carboxylic group can be added to Δ-4 yielding a lactone which vice versa may be opened by a base catalysed elimination reaction. The chromophoric group is thereby transformed forth and back from the bilatriene to the violin type. The mechanistic implications are discussed using deuteriation experiments as well as derivatives methylated in strategic positions. Reactions of this type may be involved in the dark reaction sequences of phytochrome transformation.

On the annealing behaviour of the Staebler-Wronski effect in a-Si:H

Abstract: The kinetics of the Staebler-Wronski effect ina-Si:H were investigated experimentally. The rate of recovery from the illuminated state B to the annealed state A was observed at various temperatures in undoped,n- andp-dopeda-Si:H. The data can be characterized by a thermally activated relaxation time with an activation energy decreasing with increasing doping concentration. The results are compared with previous data and existing models.

Zur Chemie der Pyrrolpigmente, 56. Mitt.

Abstract: From an investigation of the ICD of bilatrienes-abc and 2,3-dihydrobilatrienes-abc induced by mixtures of CCl4 with (+)-cis-Pinane, (−)-lactic and (+)-tartaric acid esters it is concluded that specific interactions between chromophore and the chiral reagents afford a partial resolution of the labile racemate of helices. Attaching chiral residues covalently to the chromophore induces very low resolution of the same kind in case of apolar ligands like a cholesteryl-residue. However, with polar ligands as in the case ofBoc-lysyl derivatives enantiomeric excesses up to 90% are achieved depending on the solvent used.

On imbedding and parametric optimization-- a concept of a globally convergent algorithm for nonlinear optimization problems

Abstract: The imbedding technique known for the numerical solution of nonlinear equations is applied to nonlinear optimization problems. The parametric optimization problem induced by the imbedding is analyzed. The results of this analysis are the basis for the proposed globally convergent algorithm using Robinson’s method as the local iteration method. To pass over critical points a suitable quadratic approximation is used to obtain the new index set of active constraints. For the case of convex problems a concrete imbedding is proposed based on the theory of parametric optimization.

The role of gravitophotophoresis for stratospheric and mesospheric particulates

Abstract: Gravitophotophoresis, a type of photophoresis related to the direction of gravity, is examined in view of its possible importance to some aerosols in stratosphere and mesosphere. particles of various materials from about 1 to 100 μm in size show levitation by photophoretic forces under laboratory simulation of irradiation by the sun at air densities of the middle atmosphere. Minimum air densities for levitation are about 2–3 g m−3 with mineral and metallic powders, about 0.08 g m−3 with carbonaceous powders. The fraction of rising particles can be about 0.01 to 1%. Velocities of ascent are in the range of 0.001 to 0.01 m s−1 at a pressure of several mbar. The magnitude and the mechanical character of the force of gravitophotophoresis can be explained if it is identified with a radiometer force caused by a difference of the accommodation coefficient on the surface. It is suggested that gravitophotophoresis can be important to the residence time and the maximum altitude of carbonaceous and mineral particles, such as volcanic ash or products of meteorite impact, and to the presence of microorgnisms in the middle atmosphere.

Least-squares fitting of PIXE spectra with a digital filter treatment of the continuum

Abstract: A set of aerosol spectra have been fitted both by HEX and by a new Guelph program that uses a top-hat filter; agreement is good. Improvements to lineshape descriptions and to the L X-ray intensity data base are suggested.

Optimization strategies for hydro energy storage plants

Abstract: This paper is concerned with the optimization of base load production of hydro energy storage plants within a given time interval at a varying tariff rate. For three real world storage plants in Austria, each of them presenting some characteristic difficulty we discuss both mathematical models and numerical techniques. Beside classical techniques as Dynamic Programming and Simulation two newly developed nonlinear optimization methods were used.

On the chemistry of pyrrole pigments: 57—Phytochrome model studies: Complete assignments of the 13C NMR spectra of phytochrome model compounds

Abstract: A strategy for the assignment of aromatic 13C NMR resonances of pyrrole pigments is presented which makes use of two-dimensional chemical shift correlation spectroscopy via one-bond and long-range C,H coupling constants. The complete 13C NMR assignments for a 3,4-dihydropyrromethenone and three phytochrome model compounds (2,3-dihydrobilatrienes-abc) are given.

Investigation of hydrogen stopping in noble metals around the stopping power maximum

Abstract: The stopping cross sections of copper, silver and gold for protons and deuterons were measured in the energy range from 50 keV/amu to 500 keV/amu. All measurements were performed on supported films evaporated onto polished backings employing both transmission and backscattering type techniques. By use of different hydrogen isotopes — assuming velocity scaling — and of different target thicknesses we showed that plural and multiple scattering do not influence our results within the experimental uncertainties of ± 3%. As a cross check the stopping ratios were also measured by evaluation of the heights of the backscattering spectra and were found to be consistent with the absolute values. Our results are compared to the theory of Lindhard-Winther using different solid state charge distributions and to the binary encounter theory of Kuhrt and Wedell. Best agreement is achieved for those calculations which take the correct density of the valence electrons into account. Furthermore, our results are compared to the fitted data by Andersen and Ziegler (1977), by Janni (1982) and by Ziegler (to be published). In general, better agreement with the more recent fit-data was found.

Measurement of the stopping cross section for protons in copper by backscattering using various methods for foil-thickness determination

Abstract: Copper films evaporated on pyrolitic carbon are used to determine the stopping cross section of copper for protons in the energy range from 60 to 500 keV by evaluating the energy width of Rutherford backscattering (RBS)-spectra. For this purpose we need both the number of atoms per unit area of the copper-foils and the spectrum widths. The number of atoms per unit area is determined for all copper films by a quartz-thickness monitor during evaporation, by weighing on a microbalance and by RBS, where a reference target of known thickness has been used to obtain absolute values without the input of stopping cross section data. The results of the quartz monitor and of RBS always agree within 2%, they agree with the results obtained by weighing within a mean relative error of less than 6% for each target. From the width of the RBS-spectra the stopping cross section is extracted by an iteration procedure which starts with Warters' approximation [1] and afterwards corrects for the small systematic errors arising there. The resulting stopping cross section data lead to a maximum at 125 keV. They are in excellent agreement with the data of Luomajarvi [2] and in fair agreement with the data of Mertens and Krist [3], In comparison with the Andersen and Ziegler curve, our data are lower in the whole energy range.

Einsatz mathematischer Methoden bei der Hydroenergiegewinnung

Abstract: Presentation de quatre modeles mathematiques utilises pour l'optimisation de differents types de centrales hydroelectriques

Zur Chemie der Pyrrolpigmente, 54. Mitt.: Phytochrommodellstudien: Ein 2,3-Dihydrobilatrien-abc-3-Cholesterylderivat

Abstract: The diastereomeric 2,3-Dihydrobilatrienes-abc derivatives (4Z, 9Z, 15Z)-7 and (4Z, 9Z, 15E)-7 bearing a cholesterylacetate moiety in position 3 of the chromophore are prepared. The reaction sequence contains an isomerisation step providing quantitative enantioselective formation of the chiral center in position 3. Configurations and conformations of the diastereomers are elucidated using1H- and13C-NMR spectra, NOE-difference spectra, 2D-NMR experiments (NOESY) and arguments from UV-VIS and CD data. It is concluded that the hydrophobic interactions between chromophore and cholesteryl-fragment yield a “compact” conformation where the two substructures are in close contact with each other. On the other hand these interactions seem to be too weak to induce significant changes in the chemistry, absorption spectra and conformational characterics of the bile pigment chromophore. Therefore hydrophobic interactions between chromophor and apolar amino acid residues of the protein in phytochrome should be of minor relevance for determining spectroscopic shifts.

Kinetics of distant-pair recombination: II. Tunnelling non-radiative recombination

Abstract: The kinetics of competitive tunnelling recombination paths are treated theoretically, and solutions are obtained for tunnelling radiative and non-radiative recombination mechanisms. A general solut...

Zum Phänomen der induzierten optischen Aktivität: Der induzierte Circulardichroismus in Mischungsreihen

Abstract: The induced circular dichroism (ICD) of 4-Nitroso-N,N-dimethylaniline in a series of mixtures of CCl4, lactic and tartaric acid methylesters andcis-pinane, resp., was determined. From the dependence of the ICD on the concentration of chiral components the existence of a strong intermolecular interaction can be deduced—even in the case of apolarcis-pinane. Obviously the border line between associate induced CD (AICD) and dispersion induced CD (DICD) cannot be drawn unequivocally by experiment. The general phenomenology together with mechanistic models of ICD are discussed. It is proposed to use the term ICD exclusively, instead of others like AICD and DICD, which are only applicable when the predominant mechanism can be derived from experimental data. The term SICD (solvent induced CD) should be avoided for similar reasons.

The influence of multiple ionization upon fluorescence yield

Abstract: A short summary is given of calculations and experimental measurements of the K-fluorescence yield for multiple ionization in the K- and L-shell. It is shown that electron transfer processes into the L-shell can change the K-fluorescence yield and for Ne values of this effect are given. Further, nonstatistical population of multiplet states and the influence of outer shell electrons are discussed. Finally an upper limit is given of the effect of multiple ionization on the fluorescence yield for light ion bombardment.

Decision-making of industrial tribunals as described by professional and lay judges

Abstract: Several years of laboratory research on group decision-making undertaken at the University of Augsburg (cf., Brandstatter, 1978) made it clear that we should look for more empirical evidence from natural settings in order to assess the generalizability of our experimental results. Our first field-study focused on videotaped discussions of twenty organizational groups making decisions of pressing importance (Ruttinger, 1978; Peltzer, 1979). A second study, of which some results are reported here, focused on the deliberation stage of industrial tribunals composed ofa professional judge and two lay judges. We wanted to find out by interviews 1) on 'the last controversial case', and 2) on 'a resume of their general experiences', how judges describe and evaluate the process and outcome of court deliberation. This report centres on differences in perspectives between professional and lay judges. Nach einer Beschreibung der Struktur und Bedeutung von Arbeitsgerichten in der Bundesrepublik Deutschland wird uber die Befragung von 21 Arbeitsrichtern und 24 Beisitzern (Laienrichter) an Arbeitsgerichten, von denen jeweils zwolf von der Arbeitgeber- beziehungsweise von der Arbeitnehmerseite bestellt waren, berichtet. Im Zentrum der Interviews stehen Beschreibungen und Bewertungen arbeitsgerichtlicher Prozesse und Urteile. Die Ergebnisdarstellung bezieht sich auf eine Vielzahl von Unterschieden zwischen diesen drei Gruppen von Richtern, die zwar formal gleichgestellt sind, aber den Prozess der Entscheidungsfindung zum grosen Teil unterschiedlich erleben, beschreiben und bewerten.

Defect States in Pb1−xSnxTe

Abstract: New experimental data of trap centres in Pb1−xSnxTe are presented. The chemical trend of the trap activation energy is determined for 0 ≦ x ≦ 0.11. The optical ionization energy of the defect level is obtained from the threshold wavelength of impurity photoconductivity and the results are compared with the thermal activation energy of the trap states. The cross sections of the defects for electron and hole capture, which were not measured in PbTe so far, are obtained from an analysis of photoconductivity transients. Our new data indicate a strong localization of the observed trap states in real space and bonding by the short range central-cell defect potential. Es wird uber neue experimentelle Daten von Haftstellen in Pb1−xSnxTe berichtet. Der chemische Trend der Aktivierungsenergie der Haftstellen wird fur einen Mischungsbereich 0 ≦ x ≦ 0,11 bestimmt. Die optische Ionisierungsenergie des Defektniveaus wird aus der Einsatzenergie der Storstellenphotoleitung bestimmt und mit der thermischen Aktivierungsenergie der Haftstellen verglichen. Eine Analyse des Abklingverhaltens der Photoleitung ergibt die Einfangsquerschnitte dieser Defekte fur Elektronen und Locher, die bisher noch nicht bekannt waren. Die neuen Daten deuten auf geringe raumliche Ausdehnung der Haftstellenzustande im Ortsraum und eine Bindung durch das kurzreichweitige zentrale Zellenpotential hin.

Partial realization by discrete-time internally bilinear systems: An algorithm

Abstract: We propose an algorithm for the partial realization of a finite sequence of Volterra kernels by a discrete-time internally bilinear system. The algorithm is recursive. Given a realization of a finite sequence of Volterra kernels and an extension of this sequence the relaization of the extended sequence includes the given realization. I.e. the matrices defining the given realization are submatrices of the matrices defining the new realization.