Showing papers by "Vienna University of Technology published in 1994"
TL;DR: The simulation allows us to study in detail the changes in the structure-property relationship through the metal-semiconductor transition, and a detailed analysis of the local structural properties and their changes induced by an annealing process is reported.
Abstract: We present ab initio quantum-mechanical molecular-dynamics simulations of the liquid-metal--amorphous-semiconductor transition in Ge. Our simulations are based on (a) finite-temperature density-functional theory of the one-electron states, (b) exact energy minimization and hence calculation of the exact Hellmann-Feynman forces after each molecular-dynamics step using preconditioned conjugate-gradient techniques, (c) accurate nonlocal pseudopotentials, and (d) Nos\'e dynamics for generating a canonical ensemble. This method gives perfect control of the adiabaticity of the electron-ion ensemble and allows us to perform simulations over more than 30 ps. The computer-generated ensemble describes the structural, dynamic, and electronic properties of liquid and amorphous Ge in very good agreement with experiment. The simulation allows us to study in detail the changes in the structure-property relationship through the metal-semiconductor transition. We report a detailed analysis of the local structural properties and their changes induced by an annealing process. The geometrical, bonding, and spectral properties of defects in the disordered tetrahedral network are investigated and compared with experiment.
16,744 citations
2,003 citations
TL;DR: Optical thin-film structures exhibiting high reflectivity and a nearly constant negative group-delay dispersion over frequency ranges as broad as 80 THz are presented, making these coatings well suited for intracavity dispersion control in broadband femtosecond solid-state lasers.
Abstract: Optical thin-film structures exhibiting high reflectivity and a nearly constant negative group-delay dispersion over frequency ranges as broad as 80 THz are presented. This attractive combination makes these coatings well suited for intracavity dispersion control in broadband femtosecond solid-state lasers. We address design issues and the principle of operation of these novel devices.
675 citations
TL;DR: When the enzymes and the peptaibols were tested together, an antifungal synergistic interaction was observed and the 50% effective dose values obtained were in the range of those determined in the culture supernatants.
Abstract: Chitinase, beta-1,3-glucanase, and protease activities were formed when Trichoderma harzianum mycelia, grown on glucose as the sole carbon source, were transferred to fresh medium containing cell walls of Botrytis cinerea. Chitobiohydrolase, endochitinase, and beta-1,3-glucanase activities were immunologically detected in culture supernatants by Western blotting (immunoblotting), and the first two were quantified by enzyme-linked immunosorbent assay. Under the same conditions, exogenously added [U-14C]valine was incorporated in acetone-soluble compounds with an apparent M(r) of < 2,000. These compounds comigrated with the peptaibols trichorzianines A1 and B1 in thin-layer chromatography and released [U-14C]valine after incubation in 6N HCl. Incorporation of radioactive valine into this material was stimulated by the exogenous supply of alpha-aminoisobutyric acid, a rare amino acid which is a major constituent of peptaibols. The obtained culture supernatants inhibited spore germination as well as hyphal elongation of B. cinerea. Culture supernatants from mycelia placed in fresh medium without cell walls of B. cinerea did not show hydrolase activities, incorporation of [U-14C]valine into peptaibol-like compounds, and inhibition of fungal growth. Purified trichorzianines A1 and B1 as well as purified chitobiohydrolase, endochitinase, or beta-1,3-glucanase inhibited spore germination and hyphal elongation, but at concentrations higher than those observed in the culture supernatants. However, when the enzymes and the peptaibols were tested together, an antifungal synergistic interaction was observed and the 50% effective dose values obtained were in the range of those determined in the culture supernatants. Therefore, the parallel formation and synergism of hydrolytic enzymes and antibiotics may have an important role in the antagonistic action of T. harzianum against fungal phytopathogens.
450 citations
TL;DR: In this article, a class of two-dimensional field theories, based on (generically degenerate) Poisson structures and generalizing gravity-Yang-Mills systems, is presented.
Abstract: A class of two-dimensional field theories, based on (generically degenerate) Poisson structures and generalizing gravity-Yang–Mills systems, is presented. Locally, the solutions of the classical equations of motions are given. A general scheme for the quantization of the models in a Hamiltonian formulation is found. A BRS-formulation is outlined briefly.
433 citations
TL;DR: In this paper, the propagation of electromagnetic wave packets through 1D photonic band gap materials has been studied using 12 fs optical pulses and the measured transit time is paradoxically short (implying superluminal tunneling) and independent of the barrier thickness for opaque barriers.
Abstract: Propagation of electromagnetic wave packets through 1D photonic band gap materials has been studied using 12 fs optical pulses. The measured transit time is found to be paradoxically short (implying superluminal tunneling) and independent of the barrier thickness for opaque barriers, in analogy to the behavior of electrons tunneling through potential barriers. Shortening of Fourier-limited incident wave packets is observed upon transmission through these linear systems. Although in apparent conflict with causality and the uncertainty principle, neither of these general principles is violated because of the strong attenuation suffered by the transmitted signals.
355 citations
TL;DR: In this paper, a generalized gradient approximation (GGA) based on the exchange-correlation potential (ECP) was proposed to obtain the equilibrium lattice constants in comparison to experiment, but the total energy aspect is unsatisfactory.
Abstract: Recently, Engel and Vosko have proposed an alternative form of a generalized gradient approximation (GGA) [Phys. Rev. B 47, 13 164 (1993)] within density-functional theory. This version of the GGA (EV93) was obtained by optimizing the exchange-correlation potential ${\mathit{V}}_{\mathrm{xc}}$ instead of the corresponding energy ${\mathit{E}}_{\mathrm{xc}}$. We have applied this functional to various solids and found that equilibrium lattice constants generally are far too large in comparison to experiment, so that the total-energy aspect is unsatisfactory. However, EV93 describes FeO and CoO as antiferromagnetic insulators, while the local-spin-density approximation or the Perdew-Wang version of the GGA yields a metallic ground state. EV93 favors magnetism, e.g., the spin susceptibility of V is increased, but Pd remains nonmagnetic in agreement with experiment.
335 citations
TL;DR: Adding generalized-gradient corrections to the LDA results in a crystal structure, equilibrium volume, and binding energy in better agreement with experiment, and shows that the effect of the GGC's is to add a uniform internal pressure to the system, the local bonding properties at constant volume are unchanged.
Abstract: The crystal structure and phase stability of selenium and tellurium have been investigated by total-energy calculations within the local-density approximation (LDA), without and including generalized-gradient corrections (GGC). We find that the LDA underestimates the equilibrium volume by as much as 15% and predicts a crystal structure that is much more isotropic than observed: the nearest-neighbor distances in the helical chains are increased, but the interchain distances are reduced. Adding generalized-gradient corrections to the LDA results in a crystal structure, equilibrium volume, and binding energy in better agreement with experiment. We show that the effect of the GGC's is to add a uniform internal pressure to the system, the local bonding properties at constant volume, however, are unchanged.
321 citations
TL;DR: In this article, the structural, cohesive, and electronic properties of various polymorphic forms of carbon and boron nitride have been analyzed using a variational approach to the solution of the Kohn-Sham equations.
Abstract: We present ab initio calculations of the structural, cohesive, and electronic properties of various polymorphic forms of carbon and boron nitride. Our calculations are based on ultrasoft pseudopotentials and a variational approach to the solution of the Kohn-Sham equations. Optimization of the atomic geometries is performed using total energy calculations and by minimizing the energy via a quasi-Newton quench using the Hellmann-Feynman forces. Special attention is devoted to the convergence of the results with respect to the plane-wave basis. The entire set of structural energy differences calculated in our work is in good agreement with the most accurate results obtained using a variety of different techniques---our results represent a consistent set of data based all on the same potential. We show that the use of ultrasoft potentials allows one to achieve accurate results with low cutoff energies (and hence small basis sets).
308 citations
TL;DR: In this article, the photochemical mineralization of 4-chlorophenol (4-CP) and of a wastewater from dyehouse industry by the methods UV/O3, UV/H2O2 and UV/TiO2 (photo-Fenton reaction) were compared.
225 citations
TL;DR: Information obtained by immunoelectron microscopy and differential staining led to the conclusion that the biopulping effect obtained after 2 weeks of incubation cannot be explained by the direct action of enzymes on lignin or polysaccharides, and a low molecular mass agent is considered to be responsible for the biopsies.
Abstract: Treatment of wood chips with lignin-degrading fungi prior to pulping has been shown to have great potential for mechanical as well as chemical pulping on a laboratory scale. Ceriporiopsis subvermispora, when grown on aspen or loblolly pine for 4 weeks, was found to be superior to other fungi. On aspen there was an energy savings of 47%, and an increase in burst and tear indices of 22% and 119%, respectively. With loblolly pine, energy savings amounted to 37%, while burst and tear indices increased by 41% and 54%, respectively. The weight loss was only 6%, but a decrease in optical properties had to be accepted. After sulfite cooking of wood chips pretreated for 2 weeks, the Kappa number decreased by 30% with hard- and softwood. Tensile and tear indices decreased by only 10%, while the brightness of unbleached pulp increased by 4% with birch. Information obtained by immunoelectron microscopy and differential staining led to the conclusion that the biopulping effect obtained after 2 weeks of incubation cannot be explained by the direct action of enzymes on lignin or polysaccharides. Instead, a low molecular mass agent is considered to be responsible for the biopulping effect. These results have changed the aims of biopulping from an emphasis on removing the bulk of lignin to an emphasis on a short-term process, lasting 2 weeks and yielding a low mass loss. Data on these kinetics of fungal development and the degree of asepsis will help to scale-up the process. An advanced chip pile is assumed to be the most feasible process design, rather than a controlled enclosed reactor.
TL;DR: The structural development of HfO2 thin films grown from HfCl4 and water onto glass substrates by atomic layer epitaxy at 500 °C was studied with X-ray diffraction, atomic force microscopy and scanning electron microscopy.
TL;DR: A review on energy and angular distributions of atomic, molecular and cluster particles sputtered from solid surfaces under ion bombardment is presented in this article, which is preferentially focused on experimental results and corresponding experimental methods.
TL;DR: The method provided a simple and reliable screening procedure that distinguishes between fungi that cause decay by selectively removing lignin and those that degrade both cellulose and lignIn simultaneously.
Abstract: Cryostat microtome sections of birch wood degraded by white rot fungi were examined by light microscopy after treatment with two stains: astra-blue, which stains cellulose blue only in the absence of lignin, and safranin, which stains lignin regardless of whether cellulose is present. The method provided a simple and reliable screening procedure that distinguishes between fungi that cause decay by selectively removing lignin and those that degrade both cellulose and lignin simultaneously. Moreover, morphological characteristics specific to selective delignification were revealed.
TL;DR: Mitotically-stable transformants contained the hph gene and the regulatory sequences of the pkil promoter and the cbh2 terminator integrated into the genome and evidence for preferentially ectopic integration is given.
Abstract: Trichoderma reesei was transformed to hygromycin B resistance using a novel vector, which contains the E. coli hygromycin B phosphotransferase gene (hph) fused between promoter and terminator elements of the homologous Trichoderma pki1 (coding for pyruvate kinase) and cbh2 (coding for cellobiohydrolase II) genes, respectively. Transformation frequencies of over 1,800--2,500 transformants/micrograms DNA were obtained, which is a 15--20-fold increase over that with pAN7-1, which contains hph between A. nidulans expression signals. Mitotically-stable transformants contained the hph gene and the regulatory sequences of the pki1 promoter and the cbh2 terminator integrated into the genome. Evidence for preferentially ectopic integration is given.
TL;DR: The generation of highly stable optical pulses as short as 11 fs from a Kerr-lens mode-locked Ti:sapphire laser containing no intracavity prisms is demonstrated and novel dielectric mirrors provide broadband dispersion control for solitonlike pulse formation.
Abstract: The generation of highly stable optical pulses as short as 11 fs from a Kerr-lens mode-locked Ti:sapphire laser containing no intracavity prisms is demonstrated. In the femtosecond oscillator design reported, novel dielectric mirrors provide broadband dispersion control for solitonlike pulse formation.
TL;DR: The lattice parameter of titanium nitride is also a linear function of the nitrogen/metal ratio in the temperature range investigated in this article, where the lattice parameters were obtained from high-temperature X-ray diffraction (HTXRD) measurements made with high-dimensional (X-ray) in the range of 298-1473 K.
TL;DR: In this article, an exact linear integral relation between the Fukui functions of insulators or molecules and the probability density of the frontier orbitals of Kohn-Sham theory was obtained.
Abstract: The local softness and the Fukui function emerge from density functional theory as measures of local electronic reactivity. We obtain here an exact linear integral relation between the Fukui functions of insulators or molecules and the probability density of the frontier orbitals of Kohn–Sham theory. The same linear map holds between the local softness and the local Kohn–Sham density of states at the Fermi level for metals. The kernel in those relations is the inverse of the transpose of the potential response function (PRF) of Kohn–Sham theory. The PRF has the form of the static Hartree dielectric function with an exchange and correlation interaction added to the bare Coulomb interaction. The exact static dielectric function also has the Hartree form, but with a renormalized polarization propagator. The map is norm preserving for systems with energy gaps such as insulators and molecules and norm reducing or screening for systems with a finite density of states above the ground state such as normal metals...
TL;DR: Two types of flow‐through cell retention devices based on the concept of layered piezoelectric resonators are described, which could be used as systems to retain biomass within the fermentor or as a substitute for centrifugation, with the major advantage of eliminating high‐speed rotational motion.
Abstract: This article describes two types of flow-through cell retention devices based on the concept of layered piezoelectric resonators. A single-chamber device is compared to a novel optimized steam-sterilizable prototype ultrasonic cell separator with improved acoustic design and an integrated cooling circuit, eliminating the problem of local temperature increase caused by the high amplitudes necessary to achieve the separation of animal cells with low acoustic contrast. This setup yields highly reproducible results and is ideal for studying the long-term effects of ultrasonic sound fields and separation efficiency. The novel two-chamber system has the potential for scaleability due to the reduction in thermal and acoustic flow, increased field stability, and separation efficiency. Finally, the effect of power input on separation and cell viability is reported. Such flow-through cell retention systems could be used as systems to retain biomass within the fermentor or as a substitute for centrifugation, with the major advantage of eliminating high-speed rotational motion.
TL;DR: A Green's-function technique is presented that describes the electronic properties of surfaces and interfaces in the framework of multiple-scattering theory as based on localized structure constants.
Abstract: A Green's-function technique is presented that describes the electronic properties of surfaces and interfaces in the framework of multiple-scattering theory as based on localized structure constants Results of self-consistent calculations are presented for the Cu (111), (110), and (100) surfaces The obtained surface densities of states and work functions are in good agreement with previous calculations
TL;DR: In this article, the authors used scanning tunneling microscopy to reveal surface alloy formation of Pb deposited on Cu ( 111 ), even at 300 K. At low tunneling voltages, standing waves of surface-state electrons scattered by embedded Pb atoms could be observed.
TL;DR: In this paper, a survey of SAW sensor systems is given, where three categories of sensors are defined as transit-time, resonator and chirp-type devices and each category is subdivided into active and passive signal processing systems.
Abstract: A survey is given of SAW sensor systems. Three categories of sensors are defined as transit-time, resonator and chirp-type devices and each category is subdivided into active and passive signal-processing systems. In these, the mechanical change of the SAW device is evaluated by difference measurements of the transit time, phase or resonance frequency, which are described quantitatively. To show the high resolution of active sensor systems, an electronic spirit level (based on SAW resonators) is described. New SAW chirp sensors allow the dispersive interdigital transducer or reflector geometry to be adjusted to the sensor system resolution and measurement range. In passive systems the sensor device is connected to an antenna. The SAW is excited by an interrogating radio impulse. After a SAW transit time, the sensor radiates back to the interrogator an impulse containing the sensor's information. The time and frequency response of all sensor categories and the possibilities of temperature compensation are discussed.
TL;DR: In this paper, the surface smoothness of TiO2 films grown by atomic layer epitaxy was improved by incorporating thin intermediate Al2O3 layers into them and the elimination of light scattering from the film surface caused a marked increase in specular transmittance.
TL;DR: The authors describe the elements of the Bootstrap method, how it can be used to determine readiness for ISO 9001 certification, and how it was applied in two instances to substantially improve processes.
Abstract: Bootstrap was a project done as part of the European Strategic Program for Research in Information Technology. Its goal was to develop a method for software-process assessment, quantitative measurement, and improvement. In executing that goal, Bootstrap enhanced and refined the Software Engineering Institute's process-assessment method and adapted it to the needs of the European software industry-including nondefense sectors like banking, insurance, and administration. This adaptation provided a method that could be applied to a variety of software-producing units, small to medium software companies or departments that produce software within a large company. Although the Bootstrap project completed in 1993, its attribute-based method for assessing process maturity continues to evolve. The authors describe the elements of the method, how it can be used to determine readiness for ISO 9001 certification, and how it was applied in two instances to substantially improve processes. >
TL;DR: In this paper, different transition states for the Bronsted acid catalyzed reactions of alkanes involving carbonium ions as intermediates are proposed based on data of n-butane conversion over HZSM5.
Abstract: Based on data ofn-butane conversion over HZSM5, different transition states are proposed for the Bronsted acid catalyzed reactions of alkanes involving carbonium ions as intermediates. Hydrogen-deuterium exchange, dehydrogenation and cracking are proposed to proceed via pentacoordinated carbonium ions that are stabilized by the zeolite lattice.
TL;DR: In this paper, generalized gradient approximation (GGA) was used to find the difluorides to be insulators, while in CoO the GGA splits the bands near the E and F bands and opens a direct gap.
Abstract: The local-spin-density approximation yields a metallic ground state for the antiferromagnetic insulators CoO, FeO, ${\mathrm{FeF}}_{2}$, and ${\mathrm{CoF}}_{2}$ By using the generalized gradient approximation (GGA) we find the difluorides to be insulators, while in CoO the GGA splits the bands near ${\mathit{E}}_{\mathit{F}}$ and opens a direct gap, but a small indirect band overlap remains For FeO a significant improvement is found but not quite enough to make it an insulator The magnetic moments and gaps increase The GGA improves angular (and also in-out) correlations and thus affects the energy bands, a feature in addition to the total-energy improvement
TL;DR: The impact of Skolemization on the complexity of proofs in the sequent calculus is investigated and it is shown that restricting the range of quantifiers never increases Herbrand complexity.
Abstract: The impact of Skolemization on the complexity of proofs in the sequent calculus is investigated. It is shown that prefix Skolemization may result in a nonelementary increase of Herbrand complexity (i. e. the minimal number of constituents in a Herbrand disjunction) versus structural Skolemization. Moreover it is shown that restricting the range of quantifiers never increases Herbrand complexity. The results provide a general mathematical justification for minimizing the range of quantifiers (by means of shifting) before Skolemization of formulas.
TL;DR: The problem of replica determinism enforcement under real-time constraints is surveyed in the context of the communication problem for distributed systems.
Abstract: Replication of entities is a convenient technique to achieve fault-tolerance. The problem of replica determinism thereby is to assure, that replicated entities show consistent behavior in the absence of failures. Possible sources for replica non-determinism as well as basic requirements and strategies to enforce replica determinism are presented. The problem of replica determinism enforcement under real-time constraints is surveyed in the context of the communication problem for distributed systems. Furthermore the close interdependence between replica determinism on the one side and synchronization strategies, handling of failures and redundancy preservation on the other side is reviewed. The impact of synchronous or asynchronous approaches on replication strategies is also discussed.
TL;DR: Using the Kerr-Schild decomposition of the metric tensor that employs the algebraically special nature of the Kerr--Newman spacetime family, the energy-momentum tensor was calculated in this article.
Abstract: Using the Kerr--Schild decomposition of the metric tensor that employs the algebraically special nature of the Kerr--Newman spacetime family, we calculate the energy--momentum tensor. The latter turns out to be a well defined tensor distribution with disc-like support.