Showing papers by "Johannes Kepler University of Linz published in 1985"
284 citations
TL;DR: In this article, the authors presented an extensive presentation of dynamic mechanical data (complex moduli), as obtained on the melts of a series of standard polystyrenes of narrow molar mass distributions.
Abstract: This paper contains an extensive presentation of dynamic mechanical data (complex moduli), as obtained on the melts of a series of standard polystyrenes of narrow molar mass distributions. It also shows the way of obtaining structural parameters (plateau modulus and friction factor) which are needed for an interpretation of these data in terms of simple theoretical models (Maxwell elements, Doi-Edwards model). A linear mixing rule is used for taking into account the finite width of the molar mass distributions.
100 citations
TL;DR: In this paper, the photophoresis and physical properties of particles are investigated and the dominant photophoretic force is a force (F α ) caused by differences of the thermal accommodation coefficient (α) over the particle surface.
63 citations
01 Dec 1985
49 citations
TL;DR: In this paper, the photoionization energy of substitutional Fe in CdTe was investigated by means of photo-EPR and photoluminescence, and the experimentally determined level energy of Ec − 1.45 eV for Fe2+3+ was in good agreement with recent theoretical predictions.
45 citations
32 citations
01 Jan 1985
TL;DR: In this paper, the authors considered the problem of finding the unique element that has minimal norm among all minimizers of the residual |Tx-y|, i.e., the element that is the smallest element in the residual.
Abstract: Throughout this paper, let X and Y be real Hilbert spaces, T be a bounded linear operator on X into Y, y e Y. We look for the “best-approximate solution” of (1.1) Tx = y, i.e., the unique element that has minimal norm among all minimizers of the residual |Tx-y|. The best-approximate solution is actually given by T†y where T is the Moore-Penrose generalized inverse of T (see e.g. [15], [7]).
24 citations
01 Dec 1985
TL;DR: This work will examine how cascade connections of clock controlled shift registers perform when used as generators of pseudo randan sequences, and derive results for the period, for the linear recursion and for the pseudo-randomness of their output sequences.
Abstract: Shift registers are frequently used in generators of pseudo randan sequences (see [1 ]). We will examine how cascade connections of clock controlled shift registers perform when used as generators of pseudo randan sequences. We will derive results for the period, for the linear recursion and for the pseudo-randomness of their output sequences.
24 citations
01 Dec 1985
TL;DR: An algorithm based on nonlinear constrained optimization which computes values of these control variables such that a desirable solidification front is approximated within an accuracy that is sufficient for practical purposes is described.
Abstract: In continuous casting of steel, the solidification process can be influenced by external cooling and by the casting speed. We describe an algorithm based on nonlinear constrained optimization which computes values of these control variables such that a desirable solidification front is approximated within an accuracy that is sufficient for practical purposes.
24 citations
TL;DR: (GB) is equivalent to the assertion that ‘F has the Church-Rosser property, whose fundamental importance in rewrite systems is well known (see, e.g., [22]).
Abstract: The notion of GrGbner bases for polynomial ideals, which is central to this paper, is given by the following: Definition. A finite set F of polynomials in K[xl, . . . , x,] is called a canonical basis or Grtibner basis (for the ideal generated by F) if and only if (GB) for arbitrary polynomials f, g, h E K[xl, . . . , x,]: if f +F g, f “F h, and g, h are irreducible modulo +F, then g = h. Here, ‘f +‘I? g” means that ‘f may be reduced to g modulo F m by applying a certain reduction process that may be considered as a “generalized division.” For the exact definition of this reduction relation and examples, we refer to [4] and [6]. (GB) is equivalent to the assertion that ‘F has the Church-Rosser property, whose fundamental importance in rewrite systems is well known (see, e.g., [22]). The problem of constructing Grijbner bases for polynomial ideals is characterized by the following:
20 citations
TL;DR: Using hexamethylphosphoric acid triamide (HMPT) as solvent for bilatrienesabc and mainly for 2,3-dihydrobilatriene-abc (which serve as the most suitable models for the biliproteid chromophores) a small hypsochromic shift and a dramatic change of the relative intensities of short and long wavelength absorption bands, as compared to solutions in CCl4, is observed.
Abstract: Using hexamethylphosphoric acid triamide (HMPT) as solvent for bilatrienesabc and mainly for 2,3-dihydrobilatrienes-abc (which serve as the most suitable models for the biliproteid chromophores) a small hypsochromic shift and a dramatic change of the relative intensities of short and long wavelength absorption bands, as compared to solutions in CCl4, is observed. Applying NMR-spectroscopic techniques (15N-,13C-,1H-) a predominance of the (4Z,9E,15Z) diastereomer forming a 5syn-, 10anti-, 14syn-periplanar orclinal conformation is deduced. The stabilisation of this configuration and conformation arises from strong hydrogen bonds between the acidic protons of the bilins andHMPT. Interactions of this kind seem to be the main source of energy to stretch the otherwise coiled bilin chromophore of (4Z,9Z,15Z)-5sp,10sp,14sp geometry. Stretched systems of the type bilin-HMPT may serve as a valuable model for the natural biliproteides.
TL;DR: In this paper, the title compound was prepared by acid catalyzed condensation of the appropriate pyrrole-2,5-dialdehyde and two equivalents of the corresponding pyrromethenone and its solution structure was deduced by15N-,13C- and1H-NMR to be the bislactam form with a fixation as the N27-H-tautomer and configuration (4Z, 9Z, 15Z, 20Z) at the exocyclic double bonds.
Abstract: The title compound was prepared by acid catalyzed condensation of the appropriate pyrrole-2,5-dialdehyde and two equivalents of the corresponding pyrromethenone. Its solution structure was deduced by15N-,13C- and1H-NMR to be the bislactam form with a fixation as the N27-H-tautomer and configuration (4Z, 9Z, 15Z, 20Z) at the exocyclic double bonds. From NOE measurements and a comparison of its UV-VIS spectrum andPPP-SCF-LCAO-MO-CI spectra calculations an overall helical 5sp, 10sp, 14sp, 19sp-conformation with a dihedral angle of 20° at the exocyclic single bonds was deduced. Judging from spin—lattice relaxation times of the methyl groups its flexibility is lowered as compared to bilatrienes-abc. However, its helix interconversion barrier is still low enough to prohibit an identification of the enantiomeric helices, as shown by means of a chiral shift reagent.
TL;DR: The molecular and crystal structures of two 2,3-dihydrobilatrienes-abc1 and2, representing model compounds for the phytochrome chromophore, were determined by X-ray crystallography at 97 K as discussed by the authors.
Abstract: The molecular and crystal structures of the two 2,3-dihydrobilatrienes-abc1 and2, representing model compounds for the phytochrome chromophore, were determined by X-ray crystallography at 97 K. Crystals of the racemate1 contain disordered regions. Both molecules are found to be ofall-(Z) configuration, assuming a helical conformation. The acidic hydrogen atoms are localized at the nitrogen atoms of rings A, C and D. A summary of the geometries of unsaturated five-membered rings as observed in four accurate low-temperature crystal structures of bilatrienes-abc is given.
TL;DR: In this article, a 3,4-dihydropyrromethenone of known conformation is used to check the parameters of a PPP-SCF-LCAO-MO-CI treatment adjusted earlier for studies in the bilatriene-abc series.
Abstract: The parameters of aPPP-SCF-LCAO-MO-CI treatment adjusted earlier for studies in the bilatriene-abc series are checked by means of a 3,4-dihydropyrromethenone of known conformation. This method is then applied to the calculation of π-electron densities, bond orders, reactivities and absorption spectra of the various tautomeric forms, diastereomers and conformations of the 2,3-dihydrobilatrieneabc chromophor, which is of interest as the prosthetic group of the plant photoreceptor phytochrome and of antenna pigments of algae. The results are compared to13C-,15N-NMR and X-ray data as well as absorption spectra of available tautomeric model compounds and diastereomers with conformations known from experiment. The monomeric nature of the absorbing species is checked in some cases by vapour pressure osmometry. In case of the 2,3-dihydrobilatrienes-abc in their N23-H tautomeric form (which was consolidated experimentally earlier) isomerization of the (Z,Z,Z) configured parent compound doesnot yield significant changes of the type of absorption spectra. The “stretched chromophore criterion” deduced byMoscowitz et al. for bilatrienes-abc (i.e., the intensity of the long wavelength band exceeds that of the short wavelength band) is refined for the 2,3-dihydro-derivatives, as only conformational changes fromsyn toanti at the single bonds 10–11 and 14–15 yield this effect. This change at 10–11 may be discriminated from the one at 14–15 by a strong secondary band in the long wavelength region.
01 Dec 1985
TL;DR: In this paper, an analytical formula for the photophoretic force acting on an arbitrary body in the free molecule regime is presented, provided the source function is known, and the force vector can be calculated by integration without solving the heat transfer equation.
Abstract: Previous calculations of the photophoretic force due to unequal heating of gas-suspended, illuminated particles have been restricted to spheres. An analytical formula for the photophoretic force acting on an arbitrary body in the free molecule regime is presented. Provided the source function is known, the force vector can be calculated by integration without solving the heat transfer equation. In general, the photophoretic force deviates from the direction of light. Three extreme, idealized cases are discussed: a particle with uniform source function, a perfectly opaque particle, and a perfectly transparent particle with an adsorbing core.
01 Aug 1985-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, the authors compared the stopping powers available in the literature by accurately measured copper data, for proton energies from 50 keV to 1 MeV, and compared the tabulations by Northcliffe and Schilling, Biersack et al., Andersen and Ziegler, Janni, Zieglers, Lindhard and Winther, Sugiyama, Burenkov, Komarov and Temkin.
Abstract: We test predictions of stopping powers available in the literature by our accurately measured copper data, for proton energies from 50 keV to 1 MeV. In particular, we compare the tabulations by Northcliffe and Schilling; Biersack et al.; Andersen and Ziegler; Janni; Ziegler and the theories by Lindhard and Winther; Sugiyama; Burenkov, Komarov and Temkin; Sigmund; Kuhrt, Wedell, Semrad and Bauer; McGuire. The models used in our calculations to describe the electron density in the solid are discussed.
01 Aug 1985-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, the authors investigated how the energy loss data in these types of measurements are influenced by the different projectile paths due to impact-parameter selection, plural and multiple scattering, by target properties such as bulk and surface impurities, texture and desity differences and by the use of different energy analyzers.
Abstract: The stopping cross section data measured by foil transmission often show an energy dependence different from that of RBS measurements. This cannot be due to problems connected with foil thickness-determination. Therefore, we investigate in this contribution, how the energy loss data in these types of measurements are influenced by the different projectile paths due to impact-parameter selection, plural and multiple scattering, by target properties such as bulk and surface impurities, texture and desity differences and by the use of different energy analyzers. Experiments have been performed which prove the reliability of our target preparation, stopping cross section measurements and data evaluation with respect to these influences.
TL;DR: In this paper, a new model based on a spatial electrical inhomogeneity of the material is presented to describe the ac conductivity of disordered solids, and the model calculation fits quantitatively the ac response against both temperature and frequency of some different amorphous solids.
Abstract: A new model based on a spatial electrical inhomogeneity of the material is presented to describe the ac conductivity of disordered solids. With the central assumption that both the dc and the ac conductivity are due to the same mechanism, the model calculation fits quantitatively the ac response against both temperature and frequency of some different amorphous solids. The analysis accentuates the difficulties and uncertainties which arise in deducing microscopic properties from ac conduction data. The model calculation suggests that at least in the high temperature regime processes working at the Fermi-level do not determine the ac behaviour of disordered solids.
Ausgehend von einer raumlichen elektrischen Inhomogenitat des Materials wird ein neues Modell zur Beschreibung der Wechselstromleitfahigkeit in umgeordneten Festkorpern vorgestellt. Mit der grundlegenden Annahme, das sowohl die Gleich-als auch die Wechselstromleitfahigkeit vom selben Mechanismus verursacht werden. beschreibt die Modellrechnung sowohl die Temperatur- als auch die Frequenzabhangigkeit der Leitfahigkeit verschiedener amorpher Festkorper quantitativ. Die Analyse betont die Schwierigkeiten und Unsicherheiten, die sich aus der Herleitung mikroskopischer Eigenschaften aus Wechselstromleitfahigkeitsdaten ergeben. Die Modellrechnung weist darauf hin, das zumindest im Hochtemperaturbereich des Wechselstromverhalten amorpher Festkorper nicht durch Prozesse bestimmtu wird, die in der Nahe der Fermi-Energie ablaufen.
TL;DR: In this article, a relatively simple experiment is described: in a “unilateral” quench a melted disk-like polymer sample is partially solidified, and conditions are discussed which lead either to a sharp crystallization front or to the occurrence of dispersed spherulitic crystallites.
Abstract: A relatively simple experiment is described: In a “unilateral” quench a melted disk-like polymer sample is partially solidified. The conditions are discussed which lead either to a sharp crystallization front or to the occurrence of dispersed spherulitic crystallites. The importance of this basic experiment for the understanding of industrial moulding processes is stressed.
TL;DR: An outline of the architecture of a multiprocessor machine for deduction in first-order logic and its functional behavior, which fully exploits the parallelism inherent in the deductive process is given.
01 Jan 1985
TL;DR: In this article, the Kuhn-Tucker curves of one-parameter optimization problems P(t), t ǫ IR are discussed using an active index set strategy.
Abstract: In this paper Kuhn-Tucker curves of one-parameter optimization problems P(t), t ɛ IR are discussed. Using an active index set strategy, path following procedures for P(t) are developed. One-parameter optimization problems naturally arise if a nonlinear optimization problem P is solved by a homotopy method. Under certain conditions on P it is shown that the proposed homotopy method is constructive with probability one in the sense of Chow, Mallet-Paret, Yorke [4].
TL;DR: In this article, the chiroptical properties of diastereomeric 2,3-dihydrobilatrienes-abc substituted in position 3 with various chiral ligands were used as a monitor for the conformational influence of the various ligands.
Abstract: Sixteen diastereomeric 2,3-dihydrobilatrienes-abc substituted in position 3 with various chiral ligands, seven chiral derivatives of a 2,3-dihydrobilatriene-abc-12-propionic acid and a chiral derivative of a 8,12-bilatriene-abc-dipropionic acid were prepared. The chiroptical properties (CD) of these compounds were used as a monitor for the conformational influence of the various ligands. Therefrom it could be deduced that steric effects play a minor role in determining the topology of the chromophore. On the contrary, dipole-dipole interactions of the various partial moments of bile pigments and of the attached ligands crucially influence the conformational situation of the chromophore. This fact may be significant for the stabilization of certain chromophore conformations in biliproteids.
TL;DR: A modified version of the binary encounter approximation by Kuhrt and Wedell is presented in this paper, where the motion of the target electrons is described in a more rigorous way Moreover, the use of an alternative energy transfer cut-off now makes it possible to describe the contribution of the outer electrons to the stopping cross section better.
Abstract: A modified version of the binary encounter approximation by Kuhrt and Wedell is presented, where the motion of the target electrons is described in a more rigorous way Moreover, the use of an alternative energy transfer cut-off now makes it possible to describe the contribution of the outer electrons to the stopping cross section better The very good agreement of this theory with experimental data is shown for a variety of target elements of different electronic structure (insulators, semiconductors, and metals)
Es wird eine Erweiterung der Zwei-Teilchen-Stos-Naherung von Kuhrt und Wedell erlautert, bei der die Bewegung der Targetelektronen genauer berucksichtigt wird Daruber hinaus ermoglicht es die Einfuhrung eines anderen Abschneidewertes fur den Energieubertrag, den Beitrag der auseren Elektronen zum Bremsquerschnitt besser zu beschreiben An Hand von Targetelementen unterschiedlicher Elektronenstruktur (Isolatoren, Halbleiter, und Metalle) wird die sehr gute Ubereinstimmung dieser Theorie mit Experimenten gezeigt
TL;DR: In this paper, the authors calculate the implicit price indexes for both countries and show that official data grossly understate price inflation and overstate real growth of consumption in Poland, and the causes of this discrepancy are mainly seen in the systemic difficulty of properly measuring price changes in Poland's shortage economy.
TL;DR: In this article, the authors used DLTS measurements to investigate defects in laser-annealed CdTe epilayers and showed that laser annealing with sub-threshold powers increases both the electron concentration and the mobility.
TL;DR: In this paper, the implications of 15N chemical shifts on structural features, especially tautomerism, are discussed and compared with results obtained by x-ray photoelectron spectroscopy.
Abstract: 15N NMR spectra, at natural isotopic abundance, of synthetic bilatrienes-abc and 2,3-dihydrobilatrienes-abc and also those of partial structures are presented. The implications of the 15N chemical shifts on structural features, especially tautomerism, are discussed and compared with results obtained by x-ray photoelectron spectroscopy.
TL;DR: In this article, a criterion for the fixation of tautomerism was deduced: if there is a signal in the otherwise unoccupied shift region between 157 and 170 ppm corresponding to an azomethine fragment, tautomers are fixed.
Abstract: By investigation of bilatrienes-abc possessing a rigid tautomeric structure within their pyrromethene fragment, using13C-NMR spectroscopy, a criterion for the fixation of tautomerism was deduced: if there is a signal in the otherwise unoccupied shift region between 157 and 170 ppm corresponding to an azomethine fragment, tautomerism is fixed. If there is no signal in this region there is a rapidly equilibrating system of the two possible tautomers. This criterion may be used as well for natural substitution patterns. Moreover, assignment of the13C-signals by correlation with the easily assigned1H-NMR signals establishes the position of the fixed tautomeric system. The criterion is applied as well to the 2,3-dihydrobilatrienes-abc where it is in accord with the results gained from a coupling criterion reported earlier.
TL;DR: In this article, the effective thermal conductivity, the thermal diffusion ratio, the mass diffusion and the second sound damping without adjustable parameters were calculated within the model of Siggia and Nelson.
TL;DR: A tutorial to introduce the reader to the concept of Denavit-Hartenberg matrices, which are widely used in robotics, and a simple transformation problem in the plane will characterize the principles of this concept in a familar context.
01 Apr 1985
TL;DR: This lecture reports on the present state of a parallel machine project pursued in the CAMP-LINZ working group since 1978, and some proposals are made for using the L-machine as a parallel inference machine.
Abstract: In this lecture we report on the present state of a parallel machine project pursued in the CAMP-LINZ working group since 1978 (see (Buchberger 1978)). Four basic components have been developed that can be combined f lex ib ly for building large parallel machines of arbitrary interconnection topology (Buchberger 1983). On these machines the parallelism inherent in (symbolic) algorithms should be completely exploitable. For example, in (Bibel, Buchberger 19B4) and (Aspetsberger 1985) some proposals are made for using the L-machine as a parallel inference machine. The design easily lends i t se l f to LSI, VLSI and wafer implementation. Recent considerations are also directed towards optoelectronic implementation of parts of the concept. The L-modules defined below have been realized in tradit ional TTL logic already in 1978. A p i lo t implementation of a 8 processors by 8 memories L-machine (see below) in TTL logic has been successfully finished in October 1984, (Buchberger 1984).