Showing papers by "Johannes Kepler University of Linz published in 1989"
TL;DR: In this paper, the authors consider non-linear ill-posed problems in a Hilbert space setting, and show that Tikhonov regularization is a stable method for solving nonlinear illposed problems and give conditions that guarantee the convergence rate O( square root delta ) for the regularised solutions.
Abstract: The authors consider non-linear ill-posed problems in a Hilbert space setting, they show that Tikhonov regularisation is a stable method for solving non-linear ill-posed problems and give conditions that guarantee the convergence rate O( square root delta ) for the regularised solutions, where delta is a norm bound for the noise in the data. They illustrate these conditions for several examples including parameter estimation problems. In an appendix, they study the connection between the ill-posedness of a non-linear problem and its linearisation and show that this connection is rather weak. A sufficient condition for ill-posedness is given in the case that the non-linear operator is compact.
534 citations
TL;DR: The coexistence of the two contrary signals on the same molecule might be responsible for the versatile features of tenascin.
409 citations
01 Jan 1989
TL;DR: In this article, a more precise control of beam fluxes and growth conditions is proposed for MBE, which is performed under conditions far from thermodynamic equilibrium and is governed mainly by the kinetics of the surface processes occurring when the impinging beams react with the outermost atomic layers of the substrate crystal.
Abstract: MBE is a versatile technique for growing thin epitaxial structures made of semiconductors, metals or insulators [7.1] (see also the definition given in Sect. 6.1.3). What distinguishes MBE from previous vacuum deposition techniques is its significantly more precise control of the beam fluxes and growth conditions. Because of vacuum deposition, MBE is carried out under conditions far from thermodynamic equilibrium and is governed mainly by the kinetics of the surface processes occurring when the impinging beams react with the outermost atomic layers of the substrate crystal. This is in contrast to other epitaxial growth techniques, such as LPE or atmospheric pressure VPE, which proceed at conditions near thermodynamic equilibrium and are most frequently controlled by diffusion processes occurring in the crystallizing phase surrounding the substrate crystal.
231 citations
TL;DR: In this paper, the authors present a table of best-fitted cross sections for protons on all elements from 4Be to 92U, where experimental cross sections are first normalized by the ECPSSR theory of Brandt and Lapicki; then the normalized values are averaged, interpolated and used to produce reference cross sections.
193 citations
TL;DR: In this paper, the use of lasers in the formation and surface processing of high-temperature superconductors (HTS) is reviewed, and thin film fabrication by reactive laser sputtering, and surface patterning by laser-induced reduction/metallization and ablation are the most promising applications.
Abstract: The use of lasers in the formation and surface processing of high-temperature superconductors (HTS) is reviewed. Presently, thin film fabrication by reactive laser sputtering, and surface patterning by laser-induced reduction/metallization and ablation are the most promising applications. The great majority of the investigations have been performed for Y-Ba-Cu-O.
74 citations
TL;DR: In this article, the authors consider a mean field treatment of the catalytic surface of CO and find the phase transition between poisoned and active states using a version of mean field theory for inhomogeneous systems.
58 citations
TL;DR: A survey of the experimental evidence of shear induced lamellar crystallization of polymers is given in this paper, which forms the basis for a theory by two of the authors.
Abstract: A survey is given of the experimental evidence of shear induced lamellar crystallization of polymers. This survey forms the basis for a theory by two of the authors. In this theory elements of polymer melt rheology and polymer crystallization kinetics are combined. In turns out that the capability of the melt of crystallizing in the typical lamellar form, is only gradually developed during flow. Similarly, relaxation occurs after cessation of flow. The obtained expressions are introduced into Avrami’s formalism in order to define an induction time. In principle the model can be applied to any flow and temperature history. The case of isothermal flow at constant shear rate and at a certain level of supercooling is worked out in more detail. The obtained result favorably compares with experiments by Lagasse and Maxwell. Implications for the application in industrial processes are discussed.
53 citations
TL;DR: The energy dependence of the local density of states near the vortex axis is found to be in qualitative agreement with recent scanning-tunneling-microscope measurements.
Abstract: The local, direction resolved density of states in the vortex state of clean type-II superconductors is calculated for arbitrary energies and inductions. It is obtained by solving numerically the quasi- classical equations of superconductivity, using parameters corresponding to Nb or V. The excitation spectrum is discussed for arbitrary inductions and, for the special case of large vortex distance, compared with previous theories. Tunneling states of quasiparticles are calculated explicitly for the first time and a shift of continuum states to energies higher than ${\ensuremath{\psi}}_{\mathrm{BCS}}$ is found. Some conclusions specific to the important materials Nb and V are drawn. The energy dependence of the local density of states near the vortex axis is found to be in qualitative agreement with recent scanning-tunneling-microscope measurements.
35 citations
TL;DR: In this article, the authors explored the importance of peer groups, how belonging to different types of groups affects the actual perception of oneself, the peer group and other groups, and the perception of difficulty in coping with developmental tasks.
Abstract: This study aims to exploring the importance of peer groups, how belonging to different types of groups affects the actual perception of oneself, the peer group and other groups, and the perception of difficulty in coping with developmental tasks. 600 adolescents from Bologna, Italy filled out a questionnaire, consisting of three parts. The results show that peer groups are important in adolescence lifes. Overall, 90% of the subjects were members of a peer group; most often they belonged to informal or quasi-informal groups. A smaller percentage belonged to formal groups, like to sport or religious groups. The scopes to meet the groups were most often for amusement and also for talking about one’s personal problems. Surprisingly, the differences of descriptions of oneself and the own group, oneself and the self-defined outgroup, oneself and drug abusers, did not differ considerably among informal and formal groups. Also informal and formal groups described the ingroups equally favorably and outgroups equally unfavorably. Moreover the results show that informal and formal groups did not differ in the perception of difficulty in coping with developmental tasks. These results indicate that the type of groups is not a crucial variable in explaining differences in evolution of the self-system in adolescents.
35 citations
TL;DR: A modular algorithm for computing the greatest common divisor of two polynomials over an algebraic number field using the Weinberger-Rothschild homomorphic scheme with the important change that it avoids factoring the modular image of the minimal polynomial.
32 citations
TL;DR: A fundamentally new view of the sodium channel is shown to seriously challenge the commonly unquestioned conception that 'single-current events' reflect ion passage through only one single pathway and to distinguish between conceptually distinct models of structure-function relationships for a variety of channels which show multiple substates and conserved ion selectivity.
17 Jul 1989
TL;DR: This work shows how the Knuth-Bendix procedure and the Buchberger algorithm can be seen as special cases of a more general completion procedure.
Abstract: The Knuth-Bendix procedure for the completion of a rewrite rule system and the Buchberger algorithm for computing a Grobner basis of a polynomial ideal are very similar in two respects: they both start with an arbitrary specification of an algebraic structure (axioms for an equational theory and a basis for a polynomial ideal, respectively) which is transformed to a very special specification of this algebraic structure (a complete rewrite rule system and a Grobner basis of the polynomial ideal, respectively). This special specification allows to decide many problems concerning the given algebraic structure. Moreover, both algorithms achieve their goals by employing the same basic concepts: formation of critical pairs and completion.Although the two methods are obviously related, the exact nature of this relation remains to be clarified. Based on previous work we show how the Knuth-Bendix procedure and the Buchberger algorithm can be seen as special cases of a more general completion procedure.
TL;DR: In this article, it was shown that for a separable Banach space X failing the Radon-Nikodým property (RNP), ande > 0, there is a symmetric closed convex subsetC of the unit ball of X such that every extreme point of the weak-star closure of C in the bidualX** has distance from X bigger than 1 − e.
Abstract: We show that for a separable Banach spaceX failing the Radon-Nikodým property (RNP), ande > 0, there is a symmetric closed convex subsetC of the unit ball ofX such that every extreme point of the weak-star closure ofC in the bidualX** has distance fromX bigger than 1 −e. An example is given showing that the full strength of this theorem does not carry over to the non-separable case. However, admitting a renorming, we get an analogous result for this theorem in the non-separable case too. We also show that in a Banach space failing RNP there is, fore > 0, a convex setC of diameter equal to 1 such that each slice ofC has diameter bigger than 1 −e. Some more related results about the geometry of Banach spaces failing RNP are given.
01 Oct 1989
TL;DR: This paper points out the disadvantages of that organization, introduces a new way of version management - the “orthogonal organization” - and compares the two organizations by means of an example, and calls this form of organization “intermixed organization’ of variants and revisions.
Abstract: One part of the “Software Configuration Management” — software version control — is the task of controlling different versions of documents. Most existing version control systems accomplish this task by managing variant and revision trees of single documents. The structure of these trees depends on the chronological evolution of the software project. We call this form of organization “intermixed organization” of variants and revisions. This paper points out the disadvantages of that organization, introduces a new way of version management - the “orthogonal organization” - and then compares the two organizations by means of an example.
TL;DR: An easy general construction for uniform oriented matroids with disconnected realization space is given that disproves the longstanding isotopy conjecture for simple line arrangements or order types in the plane.
Abstract: We give an easy general construction for uniform oriented matroids with disconnected realization space. This disproves the longstanding isotopy conjecture for simple line arrangements or order types in the plane.
TL;DR: In this paper, a superconducting film of BiSr-Ca-Cu-O on (100) MgO substrates was fabricated by XeCl-excimer-laser sputtering from ceramic targets of Bi2.5Sr2Ca2Cu3Oy in O2 atmosphere.
Abstract: Superconducting films of Bi-Sr-Ca-Cu-O on (100) MgO substrates have been fabricated by XeCl-excimer-laser sputtering from ceramic targets of Bi2.5Sr2Ca2Cu3Oy in O2 atmosphere. The films were polycrystalline with the c-axis (30.80±0.02A) preferably oriented normal to the substrate surface. Without post-annealing the films showed metallic resistance behavior with zero resistance temperatures of up to Tc(0) }- 79 K. The critical current density of the films had values of up to jc(50K)}- 104 A/cm2.
TL;DR: In this paper, a representation of polynomial identities promised by Hilbert's Nullstellensatz has been studied independently by Bokowski [2,3,4] and Whiteley [23] to derive invariant algebraic proofs for statements in geometry.
Abstract: Final polynomials and final syzygies provide an explicit representation of polynomial identities promised by Hilbert’s Nullstellensatz. Such representations have been studied independently by Bokowski [2,3,4] and Whiteley [23,24] to derive invariant algebraic proofs for statements in geometry.
TL;DR: In this article, the Grad's moment method was applied to several boundary layer problems for the Klein-Kramers equation, the kinetic equation for noninteracting Brownian particles, and study its convergence properties as the number of moments is increased.
Abstract: We apply Grad's moment method, with Hermite moments and Marshak-type boundary conditions, to several boundary layer problems for the Klein-Kramers equation, the kinetic equation for noninteracting Brownian particles, and study its convergence properties as the number of moments is increased. The errors in various quantities of physical interest decrease asymptotically as inverse powers of this number; the exponent is roughly three times as large as in an earlier variational method, based on an expansion in the exact boundary layer eigenfunctions. For the case of a fully absorbing wall (the Milne problem) we obtain full agreement with the recent exact solution of Marshall and Watson; the relevant slip coefficient, the Milne length, is reproduced with an accuracy better than 10−6. We also consider partially absorbing walls, with specular or diffuse reflection of nonabsorbed particles. In the latter case we allow for a temperature difference between the wall and the medium in which the particles move. There is noa priori reason why our method should work only for Brownian dynamics; one may hope to extend it to a broad class of linear transport equations. As a first test, we looked at the Milne problem for the BGK equation. In spite of the completely different analytic structure of the boundary layer eigenfunctions, the agreement with the exact solution is almost as good as for the Klein-Kramers equation.
TL;DR: Alumina was found to be a highly selective stationary phase for the preconcentration of sulphate from complex matrices, and owing to its selectivity, which is different from that of R4N+-type anion-exchange materials, it is well suited for on-line column-coupling techniques.
TL;DR: Des melanges de poudres de Al 2 O 3 and TiB 2 contenant de 0 a 40% en poids de TiB2 ont ete frittes entre 1400 and 1800 o C as mentioned in this paper.
Abstract: Des melanges de poudres de Al 2 O 3 et TiB 2 contenant de 0 a 40% en poids de TiB 2 ont ete frittes entre 1400 et 1800 o C. On etudie les proprietes mecaniques et electriques des echantillons frittes et on examine la microstructure par MEB
TL;DR: In this paper, a MIMIC compatible transferred electron oscillator is investigated, which utilizes the frequency-independent negative resistance of the stationary charge dipole domain that forms in the channel of a MESFET.
Abstract: A MIMIC-(millimeter wave monolithic integrated circuit) compatible transferred electron oscillator is investigated which utilizes the frequency-independent negative resistance of the stationary charge dipole domain that forms in the channel of a MESFET. The device structure, analysis, and simulation are described. Devices fabricated from GaAs and InP exhibit very high power levels of 56 mW at 29 GHz and 55 mW at 34 GHz, respectively. Continuous wave power levels are somewhat lower (30 mW). >
TL;DR: In this paper, the authors considered the problem of estimating the growth rate of a droplet in a supersaturated vapor when the droplet radius is not large compared to the mean free path of a vapor molecule.
Abstract: Deviations from the classical Smoluchowski expression for the growth rate of a droplet in a supersaturated vapor can be expected when the droplet radius is not large compared to the mean free path of a vapor molecule. The growth rate then depends significantly on the structure of the kinetic boundary layer around a sphere. We consider this kinetic boundary layer for a dilute system of Brownian particles. For this system a large class of boundary layer problems for a planar wall have been solved. We show how the spherical boundary layer can be treated by a perturbation expansion in the reciprocal droplet radius. In each order one has to solve a finite number ofplanar boundary layer problems. The first two corrections to the planar problem are calculated explicitly. For radii down to about two velocity persistence lengths (the analog of the mean free path for a Brownian particle) the successive approximations for the growth rate agree to within a few percent. A reasonable estimate of the growth rate for all radii can be obtained by extrapolating toward the exactly known value at zero radius. Kinetic boundary layer effects increase the time needed for growth from 0 to 10 (or 2 1/2) velocity persistence lengths by roughly 35% (or 175%).
TL;DR: In this paper, a gas chromatographie method with electron capture detection is described for the simultaneous determination of bromide and iodide in biological matrices such as serum and urine.
Abstract: A gas chromatographie method with electron capture detection is described for the simultaneous determination of bromide and iodide in biological matrices such as serum and urine. Samples are purified by passing them through a disposable C-18 reversed phase silica cartridge; bromide and iodide are derivatized in acid medium to 2-bromoethanol and 2-iodoethanol by ethylene oxide and the derivatives are extraced into ethyl acetate. Detection limits are in the low ng/ml-range.
TL;DR: In this article, the intermolecular interactions of biliverdin with apomyoglobin were investigated using UV-VIS spectroscopy and chiroptical methods, and the structural implications of the spectroscopic findings are discussed.
Abstract: The intermolecular interactions of biliverdin with apomyoglobin were investigated using UV-VIS spectroscopy and chiroptical methods. Biliverdin is bound reversibly in the heme pocket of the apoprotein. The structural implications of the spectroscopic findings are discussed.
TL;DR: In this paper, the authors describe experiments on gravitophotophoresis at ground level atmospheric pressure with varied irradiance including the solar constant and show that the effect of photophoretic forces can extend towards the earth's surface.
TL;DR: In this paper, 1,19-Bilindiones bearing a phenanthryl, mesityl, tert-butyl, and isopropyl substituent at the C-10 position were synthesized.
Abstract: 1,19-Bilindiones bearing a phenanthryl, mesityl,tert-butyl, and isopropyl substituent at the C-10 position were synthesized. Conformational analysis using13C- and1H-NMR spectroscopic techniques and absorption spectroscopy together with semiempirical calculations revealed that the aryl derivatives adopt the common circular helical geometry, whereas thetert-butyl derivative is heavily distorted. The mean planes of the two dipyrrinone moieties are orthogonally positioned to each other. The 10-isopropyl-bilindione tautomerizes to the 10-isopropyliden-biladiene-ac.
02 Jul 1989-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this paper, the authors compared various sophisticated theories (relativistic plane wave Born approximation (RPWBA), semi-classical approximation (SCA), coupled-channels codes (CCS) and coupled-channel codes (CCC) for K-shell ionization cross sections for protons.
Abstract: Various sophisticated theories (relativistic plane wave Born approximation (RPWBA), semi-classical approximation (SCA), coupled-channels codes) are tested by comparison to our recent extended list of empirical K-shell ionization cross sections for protons. Differences between the theories are outlined. Surprisingly, the elaborate coupled-channels codes appear low compared to experiment, especially for light targets. Possible reasons for this are discussed. The RPWBA calculations describe the data better in a large projectile velocity range, in spite of the fact that binding and Coulomb effects are only treated as corrections. The SCA calculations by Hansteen et al. appear closer to the data than those by Trautmann; this is surprising since both codes should give identical results. Systematic comparisons are still severely hampered by the fact that most published cross sections describe different targets or different energies.
TL;DR: In this paper, it was shown that the concentration of photogenerated species and reaction rates depend not only on the electronic properties of precursor molecules and on the wavelength and intensity of the laser excitation, but also on the size of laser focus, the type of the substrate material and the material and geometry of the reaction chamber.
Abstract: Model calculations on laser-induced photolytic gas-phase processing have shown that the concentrations of photogenerated species and the reaction rates depend not only on the electronic properties of precursor molecules and on the wavelength and intensity of the laser excitation, but also on the size of the laser focus, the type of the substrate material and, significantly, on the material and geometry of the reaction chamber. In particular, it has been demonstrated that a dependence of the reaction rate,W, on the radius of the laser beam on the substrate surface,w o, according toW∝w 0 −n cannot be employed, in general, in a simple way to separate adsorbed-phase and gas-phase contributions to the reaction rate as claimed in previous investigations. Even in pure photolytic gas-phase processing, the exponentn can vary within the range 0
TL;DR: In this paper, the dependence of the etch rate on laser power can be interpreted in terms of a thermally activated chemical reaction involving Cl 2 molecules, and the formation of regular structures is observed.
TL;DR: A 15-thia- and a 15-nor hexapyrrin derivative were prepared and their structural features were analyzed by 1-H-NMR and absorption spectroscopy as mentioned in this paper.
Abstract: A 15-thia- and a 15-nor hexapyrrin derivative were prepared. Their structural features were analyzed by1H-NMR and absorption spectroscopy. All-(Z) configurations and all-syn conformations were found throughout. Carrier mediated transport efficiencies of these compounds in bulk membranes were studied and compared with those of a recently synthesized pentapyrrin-dione and their tripyrrinone partial structure. The pentapyrrin-dione derivative turned out to be one of the most efficient Hg(II) carriers known so far.