Showing papers by "Vienna University of Technology published in 1993"
TL;DR: In this paper, the authors present an ab initio quantum-mechanical molecular-dynamics calculations based on the calculation of the electronic ground state and of the Hellmann-Feynman forces in the local density approximation.
Abstract: We present ab initio quantum-mechanical molecular-dynamics calculations based on the calculation of the electronic ground state and of the Hellmann-Feynman forces in the local-density approximation at each molecular-dynamics step. This is possible using conjugate-gradient techniques for energy minimization, and predicting the wave functions for new ionic positions using subspace alignment. This approach avoids the instabilities inherent in quantum-mechanical molecular-dynamics calculations for metals based on the use of a fictitious Newtonian dynamics for the electronic degrees of freedom. This method gives perfect control of the adiabaticity and allows us to perform simulations over several picoseconds.
32,798 citations
TL;DR: It is shown that standard feedforward networks with as few as a single hidden layer can uniformly approximate continuous functions on compacta provided that the activation function @j is locally Riemann integrable and nonpolynomial.
529 citations
22 Jun 1993
TL;DR: The Time-Triggered Protocol (TTP), which is intended for use in distributed real-time control applications that require a high dependability and guaranteed timeliness, is discussed.
Abstract: The Time-Triggered Protocol (TTP), which is intended for use in distributed real-time control applications that require a high dependability and guaranteed timeliness, is discussed. It integrates all services that are required in the design of a fault-tolerant real-time system, such as predictable message transmission, message acknowledgment in group communication, clock synchronization, membership, rapid mode changes, redundancy management, and temporary blackout handling. It supports fault-tolerant configurations with replicated nodes and replicated communication channels. TTP provides these services with a small overhead so it can be used efficiently on twisted pair channels as well as on fiber optic networks.
273 citations
01 Jan 1993
TL;DR: Approximation of convex bodies is frequently encountered in geometric convexity, discrete geometry, the theory of finite-dimensional normed spaces, in geometric algorithms and optimization, and in the realm of engineering as discussed by the authors.
Abstract: Publisher Summary This chapter reviews various aspects of approximation of convex bodies. Approximation of convex bodies is frequently encountered in geometric convexity, discrete geometry, the theory of finite-dimensional normed spaces, in geometric algorithms and optimization, and in the realm of engineering. Also, approximation problems in optimization arise often from more practical problems of operations research and pattern recognition. Several effective approximation algorithms formulated for convex functions or convex bodies are described in the chapter. In the former case the approximation is considered with respect to the maximum norm, in the latter case with respect to the Hausdorff metric. The chapter presents more recent developments in approximation, but many older results are also described.
188 citations
TL;DR: The STM data reveal chemical short-range order at the surface, which is in agreement with embedded atom simulations and can be understood as small domains of an L 1 0 ordered phase.
Abstract: We present the first scanning tunneling microscopy (STM) study which allows clear discrimination of two chemical species in a metal alloy. Special tunneling conditions, which we attribute to an adsorbate at the STM tip, cause a difference in corrugation between Pt and Ni atoms of 0.3 \AA{}. The STM data reveal chemical short-range order at the surface, which is in agreement with embedded atom simulations and can be understood as small domains of an L${1}_{0}$ ordered phase.
187 citations
TL;DR: The evidence available favors a model in which conidial bound cellobiohydrolases carry out a first exo-exo-wise attack on the cellulose molecule, and evidence available suggests that they are further metabolized to, rather than being, the "true" inducer.
186 citations
TL;DR: This work proves that the deduction problem for arbitrary propositional theories under the extended closed-world assumption or under circumscription is Π P 2 -complete, i.e., complete for a class of the second level of the polynomial hierarchy.
185 citations
TL;DR: The oscillator presented has the potential for producing sub-10-fs pulses in the 800-nm wavelength region, and the position of the dispersive resonance is used to determine the ratio of the net second- and third-order intracavity dispersions.
Abstract: We report the operating characteristics of a self-mode-locked Ti:sapphire solitary laser at reduced group-delay dispersion. The generation of ≈12.3 fs near-sech2 optical pulses at 775 nm is reported, together with experimental evidence for the dominant role of third-order dispersion (TOD) as a limiting factor to further pulse shortening in the oscillator. At reduced second-order dispersion excessive residual TOD is shown to lead to dispersive wave generation, and the position of the dispersive resonance is used to determine the ratio of the net second- and third-order intracavity dispersions. Since the magnitude of TOD rapidly decreases with increasing wavelength in prism-pair dispersion-compensated resonators, the oscillator presented has the potential for producing sub-10-fs pulses in the 800-nm wavelength region.
140 citations
TL;DR: It is shown that in this compound the instability against small tetragonal distortions, the Invar behavior, and the LM⇄HM transitions are a consequence of the delicate balance of charge distribution and magnetic order from d orbitals having different bonding character.
Abstract: An attempt is made to show the close connection between martensitic transformations, the Invar effect, magnetovolume instabilities, and associated low-moment--high-moment (LM-HM) transitions. For that purpose we study the volume dependence of electron occupation and magnetization of ${\mathit{e}}_{\mathit{g}}$ and ${\mathit{t}}_{2\mathit{g}}$ states in ordered ${\mathrm{Fe}}_{3}$Ni. We show that in this compound the instability against small tetragonal distortions, the Invar behavior, and the LM \ensuremath{\rightleftarrows} HM transitions are a consequence of the delicate balance of charge distribution and magnetic order from d orbitals having different bonding character. Our calculation is a generalization of the cluster calculation of Kaspar and Salahub who have speculated that the Invar effect is a consequence of thermal excitations of electrons from the antibonding majority-spin level to close-lying nonbonding minority-spin orbitals at the Fermi energy ${\mathit{E}}_{\mathit{F}}$. Our fixed-spin-moment (FSM) calculation confirms the presence of these orbitals close to ${\mathit{E}}_{\mathit{F}}$ in ${\mathrm{Fe}}_{3}$Ni. In addition we have extended the FSM calculations to finite temperatures with the help of a semimicroscopic spin-fluctuation theory, which allows the study of the temperature evolution of the HM and LM states of ${\mathrm{Fe}}_{3}$Ni. We find that the states merge with increasing temperature.
137 citations
TL;DR: The authors show that any hyperbolic TF representation is related to both the wideband ambiguity function and a "hyperbolic ambiguity function" and are shown to be the class of all quadratic TF representations which are invariant to "Hyperbolic time-shifts" and TF scalings, operations which are important in the analysis of Doppler-invariant signals and self-similar random processes.
Abstract: The time-frequency (TF) version of the wavelet transform and the "affine" quadratic/bilinear TF representations can be used for a TF analysis with constant-Q characteristic. The paper considers a new approach to constant-Q TF analysis. A specific TF warping transform is applied to Cohen's class of quadratic TF representations, which results in a new class of quadratic TF representations with constant-Q characteristic. The new class is related to a "hyperbolic TF geometry" and is thus called the hyperbolic class (HC). Two prominent TF representations previously considered in the literature, the Bertrand P/sub 0/ distribution and the Altes-Marinovic Q-distribution, are members of the new HC. The authors show that any hyperbolic TF representation is related to both the wideband ambiguity function and a "hyperbolic ambiguity function". It is also shown that the HC is the class of all quadratic TF representations which are invariant to "hyperbolic time-shifts" and TF scalings, operations which are important in the analysis of Doppler-invariant signals and self-similar random processes. The paper discusses the definition of the HC via constant-Q warping, some signal-theoretic fundamentals of the "hyperbolic TF geometry", and the description of the HC by 2D kernel functions. Several members of the HC are considered, and a list of desirable properties of hyperbolic TF representations is given together with the associated kernel constraints. >
129 citations
25 Feb 1993
TL;DR: A comprehensive complexity analysis of relevant problems related to abduction on propositional theories shows that the different variations of abduction provide a rich collection of natural problems populating all major complexity classes between P and Σ 3 P , Π 3 P in the refined polynomial hierarchy.
Abstract: Abduction is an important form of nonmonotonic reasoning allowing one to find explanations for certain symptoms or manifestations. When the application domain is described by a logical theory, we speak about logic- based abduction. Candidates for abductive explanations are usually subjected to minimality criteria such as subset-minimality, minimal cardinality, minimal weight, or minimality under prioritization of individual hypotheses. This paper presents a comprehensive complexity analysis of relevant problems related to abduction on propositional theories. They show that the different variations of abduction provide a rich collection of natural problems populating all major complexity classes between P and Σ 3 P , Π 3 P in the refined polynomial hierarchy. More precisely, besides polynomial, NP-complete and co-NP-complete abduction problems, abduction tasks that are complete for the classes Δ i P , Δ i P [O(logn), Σ i P , and Π i P , for i=2,3, are identified.
TL;DR: In this article, the decomposition of mixed barium titanium oxalates was studied by means of various thermochemical as well as spectroscopic methods, and the results of both IR and the thermochemical analyses suggest that the oxalate are first converted to unidentate carbonate, then to ionic carbonate and finally to mixed oxides of perovskite structure.
Abstract: The decomposition of mixed barium titanium oxalates was studied by means of various thermochemical as well as spectroscopic methods. Infrared (IR) spectra of the mixed oxalates indicate the existence of an octahedral complex with Ti chelated by oxalate groups. In general, the results of both IR and the thermochemical analyses suggest that the oxalates are first converted to unidentate carbonate, then to ionic carbonate, and finally to mixed oxides of perovskite structure. The decomposition processes were found to depend upon the atmosphere. In the presence of oxygen the stoichiometrically mixed oxalates decompose by forming TiO2 and BaCO3 as intermediates. Under vacuum, two routes of decomposition occur in parallel. In one route, TiO2 and BaCO3 are formed as intermediates; in the other, partially reduced TiOx(x < 2) is formed, which further reacts with BaCO3 to produce also BaTiO3, CO2 and CO.
TL;DR: The electron emission yield was found to increase proportionally with the increasing projectile charge state in all cases studied, suggesting no saturation in the ability of the Au target to provide necessary electrons within the above surface interaction time.
Abstract: Total low-energy electron yields for the normal incidence interaction of slow, very highly charged ions ${(}^{136}$${\mathrm{Xe}}^{\mathit{q}+}$, 21\ensuremath{\le}q\ensuremath{\le}51; $^{232}\mathrm{Th}^{\mathit{q}+}$, 51\ensuremath{\le}q\ensuremath{\le}80) with a clean gold surface have been determined from the related measured electron emission statistics. The projectile impact energies could be reduced down to the image charge acceleration limit. The electron emission yield was found to increase proportionally with the increasing projectile charge state in all cases studied, suggesting no saturation in the ability of the Au target to provide necessary electrons within the above surface interaction time (e.g., about 280 electrons/projectile for ${\mathrm{Th}}^{79+}$ in less than ${10}^{\mathrm{\ensuremath{-}}13}$ s). Because of the relatively narrow energy distribution of the incident ions, as well as their very high charge states, the first clear measurements of the image charge acceleration from electron emission yields could be performed. Results of a quantitative study of this acceleration are in good agreement with those of a theoretical model based on classical over the barrier transitions (recently developed by J. Burgd\"orfer et al.).
TL;DR: It is shown that many properties of Bezier and B-spline curves hold for a much wider class of curves, including tensor product surfaces, and a generalization of the blossoming method is derived.
TL;DR: The results stress a hitherto not recognized point of control in the induction of cellulases by T. reesei at the level of uptake of cellulose oligosaccharides.
TL;DR: In this paper, the authors give an easy example of two strictly positive local martingales that fail to be uniformly integrable, but such that their product is a uniformly integral martingale.
Abstract: We give an easy example of two strictly positive local martingales that fail to be uniformly integrable, but such that their product is a uniformly integrable martingale. The example simplifies an earlier example given by the second author. We give applications in mathematical finance and we show that the phenomenon is present in many incomplete markets.
TL;DR: In this article, the generalized Nevanlinna class N(kappa)m x m is considered and the operator representation of matrix functions belonging to this class is discussed. But the results about the operator representations are not discussed in this paper.
Abstract: This paper consists of two chapters. The first chapter concerns matrix functions belonging to the generalized Nevanlinna class N(kappa)m x m. We present results about the operator representation of such functions. These representations are then used to obtain information about the (generalized) poles of generalized Nevanlinna functions. The second chapter may be viewed as a continuation of our paper [DLS3] and treats Hamiltonian systems of differential equations with boundary conditions depending on the eigenvalue parameter. In particular we study the eigenvalues, both isolated and embedded eigenvalues.
TL;DR: Trichoderma reesei RUT C-30 formed an extracellular alpha-galactosidase when it was grown in a batch culture containing lactose or locust bean gum as a carbon source and its action on galactomannan was increased by the presence of beta-mannanase.
Abstract: Trichoderma reesei RUT C-30 formed an extracellular alpha-galactosidase when it was grown in a batch culture containing lactose or locust bean gum as a carbon source. Short-chain alpha-galactosides (melibiose, raffinose, stachyose), as well as the monosaccharides galactose, dulcitol, arabinose, and arabitol, also induced alpha-galactosidase activity both when they were used as carbon sources (at a concentration of 1%) in batch cultures and in resting mycelia (at concentrations in the millimolar range). The addition of 50 mM glucose did not affect the induction of alpha-galactosidase formation by galactose. alpha-Galactosidase from T. reesei RUT C-30 was purified to homogeneity from culture fluids of galactose-induced mycelia. The active enzyme was a 50 +/- 3-kDa, nonglycosylated monomer which had an isoelectric point of 5.2. It was active against several alpha-galactosides (p-nitrophenyl-alpha-D-galactoside, melibiose, raffinose, and stachyose) and galactomannan (locust bean gum) and was inhibited by the product galactose. It released galactose from locust bean gum and exhibited synergism with T. reesei beta-mannanase. Its activity was optimal at pH 4, and it displayed broad pH stability (pH 4 to 8). Its temperature stability was moderate (60 min at 50 degrees C resulted in recovery of 70% of activity), and its highest level of activity occurred at 60 degrees C. Its action on galactomannan was increased by the presence of beta-mannanase. Images
TL;DR: It is argued that introducing computers in a female occupation is not simply a case of imposing ‘male’ technology on ‘female’ care-oriented practices and values, but rather the already technology-driven cure aspect.
Abstract: This paper looks at the cultural transformation of nursing. It argues that introducing computers in a female occupation is not simply a case of imposing ‘male’ technology on ‘female’ care-oriented practices and values. In order to understand current changes of nursing practice, three points of view have to be simultaneously kept in focus: 1) the differences between women's interests and ambitions; 2) the readings of a technology that have already been established through previous examples of design and use (in hospitals up to date primarily for the purpose of establishing discipline and management control); and 3) the social practices that dominate a field of work (in the case of health work the already technology-driven cure aspect).
01 Jan 1993
TL;DR: In this article, the authors focus on Baire categories in convexity, and present a Baire category type result for any complete metric and any locally compact space, together with its proof.
Abstract: This chapter focuses on Baire categories in convexity. A topological space X is called Baire if each of its meager sets has a dense complement; a subset of X is meager or of first (Baire) category if it is a countable union of dense sets. All other sets are called non-meager or of second (Baire) category; in particular, a set with meager complement is called residual. One version of the category theorem of Baire shows that any complete metric and any locally compact space is Baire. The chapter presents a Baire category type result in convexity together with its proof. A boundary point x of a convex body C is smooth if there is a unique supporting hyperplane of C containing x . C is called smooth if all its boundary points are smooth. A geodesic segment on the boundary of a convex body C is a continuous curve on bd C connecting two points of bd C and having minimum length among all such curves. For any two points of bd C , there is at least one geodesic segment connecting them. A geodesic is a continuous curve on bd C that locally consists of geodesic segments.
TL;DR: It is proposed that ACVS is located either within or bound to the vacuolar membrane, and that the precursor amino acids for penicillin biosynthesis are withdrawn from the vacUolar amino acid pool.
TL;DR: The enzyme responsible for the major β-mannanolytic activity from T. reesei was purified to physical homogeneity by preparative chromatofocusing and anion exchange fast protein liquid chromatography, and has an optimal temperature for activity at 75° C.
Abstract: Trichoderma reesei was studied for its ability to produce β-mannanase activity on a variety of carbon sources. The highest β-mannanase activity was produced on cellulose, whereas β-mannan-containing carbon sources (such as kojac powder or locust bean gum) gave lower enzyme titres. The enzyme responsible for the major β-mannanolytic activity from T. reesei was purified to physical homogeneity by preparative chromatofocusing and anion exchange fast protein liquid chromatography. This β-mannanase is a glycoprotein, with a molecular mass of 46 (±2) kDa and an isoelectric point of 5.2. It has an optimal pH at 5.0 and broad pH stability (2.5–7.0). It is stable for 60 min at 55° C, and has an optimal temperature for activity at 75° C. During incubation with locust bean gum, the enzyme releases mainly tri- and disaccharides.
TL;DR: Passive mode locking initiated with a moving mirror is demonstrated in a neodymium fiber laser for what is to the authors' knowledge the first time.
Abstract: Passive mode locking initiated with a moving mirror is demonstrated in a neodymium fiber laser for what is to our knowledge the first time Near-bandwidth-limited pulses with a width of 42 fs and energies as high as 1 nJ are generated
Proceedings Article•
28 Aug 1993TL;DR: This paper gives a formal foundation of interchangeabilities by the notion of domain partitions induced by equivalence relations and shows how these domain partitions can be used in a very accurate manner by the majority of existing constraint propagation algorithms and introduces a novel back-track procedure exploiting such interchangeabi-lities of domain values.
Abstract: Constraint satisfaction-a method for representing and solving many AI problems in a very elegant manner-is a well-studied research area of recent years. Freuder observed that some constraint satisfaction problems are fashioned so that certain domain values of constraint variables are interchangeable. The use of such knowledge can increase search efficiency drastically by reducing the problem. In this paper we carry on these considerations and give a formal foundation of interchangeabilities by the notion of domain partitions induced by equivalence relations. We show how these domain partitions can be used in a very accurate manner by the majority of existing constraint propagation algorithms and introduce a novel back-track procedure exploiting such interchangeabi-lities of domain values. Both theoretical analysis and experiments indicate that our proposed approach is an improvement of Freuder's use of neighborhood interchangeability and has very good behavior for certain problem types. Constraint Satisfaction is a well-studied research area of recent years. Using constraint satisfaction methods, many problems-especially in AI-can be represented in a very declarative way by identifying the variables of interest for the problem, laying down the domains for the variables and restricting the variable assignments by constraints. More formally, a constraint network R consists of a finite set of variables and a set of constraints. Associated with each variable v; is a finite, discrete domain. A constraint c on the variables is in its extensional form a subset of the Cartesian product of the domains of the afflicted variables. The expression var(c) denotes the tuple of variables the constraint is defined on, and is the relational information of the constraint c. 1 The assignment of a value to a *This work was supported by Siemens Austria AG under project grant CSS (GR 21/96106/4). 1 Our notation is similar to the one used in [Dechter, 1992]. variable v is denoted by v<—d. A tuple t of assignments of variables _ satisfies a constraint c, if and only if A constraint satisfaction problem (CSP) is the task of finding one or all variable assignments for a constraint network R such that all the constraints of R are satisfied. There are various techniques (like network consistency techniques or backtrack search procedures) for the handling and solving of constraint networks (good descripti-it is well-known that the use of special methods for certain problem types can reduce search effort. In this paper we focus on problems where the domain values are structured …
TL;DR: In this article, the flow properties of dense gases in the throat area of slender nozzles were investigated and a novel form of the viscous transonic small-perturbation equation was derived.
Abstract: The paper deals with the flow properties of dense gases in the throat area of slender nozzles. Starting from the Navier–Stokes equations supplemented with realistic equations of state for gases which have relatively large specific heats a novel form of the viscous transonic small-perturbation equation is derived. Evaluation of the inviscid limit of this equation shows that three sonic points rather than a single sonic point may occur during isentropic expansion of such media, in contrast to the case of perfect gases. As a consequence, a shock-free transition from subsonic to supersonic speeds cannot, in general, be achieved by means of a conventional converging–diverging nozzle. Nozzles leading to shock-free flow fields must have an unusual shape consisting of two throats and an intervening antithroat. Additional new results include the computation of the internal thermoviscous structure of weak shock waves and a phenomenon referred to as impending shock splitting. Finally, the relevance of these results to the description of external transonic flows is discussed briefly.
TL;DR: A weak but significant similarity was demonstrated between these two families suggesting that these enzymes share the same molecular mechanism and catalytic residues and that they have related 3D folds.
TL;DR: In this article, the authors define the set of convex compact sets with nonempty interior in the uniform distribution of points in a convex body and show that the ellipsoids are the worst approximated convex bodies.
Abstract: Write ~.-"d for the set of all convex bodies (convex compact sets with nonempty interior) in ~d. Define o@g~l d as the set of those K E 5 b "~d with vol K = 1. Fix K E .~g-i d and choose points X l , . . . , x~ E K randomly, independently, and according to the uniform distribution on K. Then K,~ = c o n v ( x l , . . . , xn} is a random polytope in K . Write E(K, n) for the expectation of the random variable v o l ( K \ K n ) . E(K, n) shows how well K,~ approximates K in volume on the average. Groemer [Grl] proved that, among all convex bodies K E o@g~l d, the ellipsoids are approximated worst, i.e.
TL;DR: In this article, a planar miniaturized Clark-type oxygen sensor based on the Ross principle has been produced by means of thin-film technology using a polarizable counter electrode in a three-electrode configuration.
TL;DR: In this article, it was shown that coherent wave packets remain coupled even in the case of wide spatial separation, which has consequences for any EPR situation and for the discussion of nonlocality in quantum physics.
TL;DR: In this paper, the meaning and occurrence of quantum Zeno effects are discussed by making use of a simple experimental proposal involving neutron spins and the role of quantum measurements and the collapse of the wave function.