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Showing papers by "Vienna University of Technology published in 1996"


Journal ArticleDOI
TL;DR: An efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set is presented and the application of Pulay's DIIS method to the iterative diagonalization of large matrices will be discussed.
Abstract: We present an efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrices will be discussed. Our approach is stable, reliable, and minimizes the number of order ${\mathit{N}}_{\mathrm{atoms}}^{3}$ operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special ``metric'' and a special ``preconditioning'' optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calculations. It will be shown that the number of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order ${\mathit{N}}_{\mathrm{atoms}}^{2}$ scaling is found for systems containing up to 1000 electrons. If we take into account that the number of k points can be decreased linearly with the system size, the overall scaling can approach ${\mathit{N}}_{\mathrm{atoms}}$. We have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large number of different systems (liquid and amorphous semiconductors, liquid simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable. \textcopyright{} 1996 The American Physical Society.

81,985 citations


Journal ArticleDOI
TL;DR: A detailed description and comparison of algorithms for performing ab-initio quantum-mechanical calculations using pseudopotentials and a plane-wave basis set is presented in this article. But this is not a comparison of our algorithm with the one presented in this paper.

47,666 citations


Proceedings ArticleDOI
06 Oct 1996
TL;DR: In this paper, the authors present the "INFORM" method based on real-time inductance measurements for sensorless control of AC drives, which reduces robustness and increase costs of a drive considerably.
Abstract: The increasing use of AC machines compared to DC motors in electrical drive applications has several reasons. A very important advantage of AC machines is their simple construction. However, AC drives often need mechanical sensors (tachometers, position encoders) for field orientation. In many applications these sensors reduce robustness and increase costs of a drive considerably. The main objective of this paper is to present the "INFORM" method based on real-time inductance measurements for sensorless control of AC drives.

653 citations


Journal ArticleDOI
TL;DR: Calculations reveal that in both systems covalent contributions to the chemical bond determine the change of the s electron density at the Zn nucleus between the different crystallographic phases as well as the electric-field-gradient tensor in ZnO (wurtzite).
Abstract: The II-VI semiconductors ZnO and ZnSe have been investigated by x-ray and $^{67}\mathrm{ssbauer}$ spectroscopy at high external pressures. In ZnSe, the recoilfree fraction f increases from f=0.50% at ambient pressure to 1.19% at 6.1 GPa. It then decreases to f=0.92% as the pressure is further raised to 8.2 GPa. This decrease of f is caused by softening of phonon modes which occurs far below the crystallographic phase transition (13.5 GPa). In the high-pressure phase of ZnO (NaCl structure), low-frequency acoustic-phonon modes become harder and high-frequency optic modes become softer as compared to ZnO (wurtzite structure). Modern theoretical Hartree-Fock cluster and full potential scalar-relativistic linearized-augmented plane-wave calculations have been performed. These calculations reveal that in both systems covalent contributions to the chemical bond determine the change of the s electron density \ensuremath{\rho}(0) at the Zn nucleus between the different crystallographic phases as well as the electric-field-gradient tensor in ZnO (wurtzite). In particular, \ensuremath{\rho}(0) in ZnO (NaCl phase) is reduced compared to \ensuremath{\rho}(0) in ZnO (wurtzite phase) by -1.15e/${\mathit{a}}_{0}^{3}$. Thus, contrary to observation for ZnSe, the electrical conductivity in ZnO (NaCl phase) is not expected to increase in comparison with the low-pressure wurtzite structure. \textcopyright{} 1996 The American Physical Society.

494 citations


Journal ArticleDOI
TL;DR: This article shows how class-based object-oriented systems can be extended to handle evolving objects well, and complemented by role hierarchies, whose nodes represent role types an object classified in the root may take on.
Abstract: In many class-based object-oriented systems the association between as instance and a class is exclusive and permanent Therefore these systems have serious difficulties in representing objects taking on different roles over time Such objects must be reclassified any time they evolve (eg, if a person becomes a student and later an employee) Class hierarchies must be planned carefully and may grow exponentially if entities may take on serveral independent roles The problem is even more servere for object-oriented databases than for common object-oriented programming Databases store objects over longer periods, during which the represented entities evolve This article shows how class-based object-oriented systems can be extended to handle evolving objects well Class hierarchies are complemented by role hierarchies, whose nodes represent role types an object classified in the root may take on At any point in time, an entity is represented by an instance of the root and an instance of every role type whose role it currently plays In a natural way, the approach extends traditional object-oriented concepts, such as classification, object identity, specialization, inheritance, and polymorphism in a natural way The practicability of the approach is demonstrated by an implementation in Smalltalk Smalltalk was chosen because it is widely known, which is not true for any particular class-based object-oriented database programming language Roles can be provided in Smalltalk by adding a few classes There is no need to modify the semantics of Smalltalk itself Role hierarchies are mapped transparently onto ordinary classes The presented implementation can easily be ported to object-oriented database programming languages based on Smalltalk, such as Gemstone's OPAL hierarchies are complemented by role hierarchies, whose nodes represent role types an object classified in the root may take on At any point in time, an entity is represented by an instance of the root and an instance of every role type whose role in currently plays

378 citations


Journal ArticleDOI
TL;DR: In this article, a class of finite-sample optimal tests for the existence of a changepoint at an unknown time in a normal linear multiple regression model with known variance was determined.

313 citations


Journal ArticleDOI
TL;DR: Two characterizations of a minimum-information principle in possibilistic reasoning" Int.
Abstract: Benferhat, S, Dubois D and Prade, H, 1992. \"Representing default rules in possibilistic logic\" In: Proc. of the 3rd Inter. Conf. on Principles of knowledge Representation and Reasoning (KR'92), 673-684, Cambridge, MA, October 26-29. De Finetti, B, 1936. \"La logique de la probabilite\" Actes du Congres Inter, de Philosophic Scientifique, Paris. (Hermann et Cie Editions, 1936, IV1-IV9). Driankov, D, Hellendoorn, H and Reinfrank, M, 1995. An Introduction to Fuzzy Control, Springer-Verlag. Dubois, D and Prade, H, 1988. \"An introduction to possibilistic and fuzzy logics\" In: Non-Standard Logics for Automated Reasoning (P Smets, A Mamdani, D Dubois and H Prade, editors), 287-315, Academic Press. Dubois, D and Prade, H, 1994. \"Can we enforce full compositionality in uncertainty calculi?\" In: Proc. 12th US National Conf. On Artificial Intelligence (AAAI94), 149-154, Seattle, WA. Elkan, C, 1994. \"The paradoxical success of fuzzy logic\" IEEE Expert August, 3-8. Lehmann, D and Magidor. M, 1992. \"What does a conditional knowledge base entail?\" Artificial Intelligence 55 (1) 1-60. Maung, 1,1995. \"Two characterizations of a minimum-information principle in possibilistic reasoning\" Int. J. of Approximate Reasoning 12 133-156. Pearl, J, 1990. \"System Z: A natural ordering of defaults with tractable applications to default reasoning\" Proc. of the 2nd Conf. on Theoretical Aspects of Reasoning about Knowledge (TARK'90) 121-135, San Francisco, CA, Morgan Karfman. Shoham, Y, 1988. Reasoning about Change MIT Press. Smets, P, 1988. \"Belief functions\" In: Non-Standard Logics for Automated Reasoning (P Smets, A Mamdani, D Dubois and H Prade, editors), 253-286, Academic Press. Smets, P, 1990a. \"The combination of evidence in the transferable belief model\" IEEE Trans, on Pattern Anal. Mach. Intell. 12 447-458. Smets, P, 1990b. \"Constructing the pignistic probability function in a context of uncertainty\" Un certainty in Artificial Intelligence 5 (M Henrion et al., editors), 29-40, North-Holland. Smets, P, 1995. \"Quantifying beliefs by belief functions: An axiomatic justification\" In: Procoj the 13th Inter. Joint Conf. on Artificial Intelligence (IJACT93), 598-603, Chambey, France, August 28-September 3. Smets, P and Kennes, R, 1994. \"The transferable belief model\" Artificial Intelligence 66 191-234.

301 citations


Journal ArticleDOI
TL;DR: A miniaturized device for simultaneous measurement of glucose and lactate levels was produced by means of photopatterning of enzyme-containing photosensitive membrane precursors and subcutaneous measurements of glucose levels in pigs were close to the corresponding blood levels obtained without in vivo calibration.
Abstract: A miniaturized device for simultaneous measurement of glucose and lactate levels was produced by means of photopatterning of enzyme-containing photosensitive membrane precursors. This device shows no cross-talk and a lifetime for both the glucose and the lactate sensors of more than 2 weeks when continuously operated in undiluted bovine serum. Linear response ranges of up to 40 mM for glucose and 25 mM for l-lactate, in combination with 95% response times of 0.98 with respect to laboratory techniques. Subcutaneous measurements of glucose levels in pigs were close to the corresponding blood levels obtained without in vivo calibration.

282 citations


Journal ArticleDOI
TL;DR: The influence of the Coulomb focusing, in combination with multiple returns, focuses parts of the electron wave function, increasing the efficiency of such intense field processes as multiphoton double ionization.
Abstract: In the intense field (long-wavelength) limit, the oscillating motion of an electron wave packet leads to multiple passes by the scattering Coulomb center. The influence of the Coulomb focusing, in combination with multiple returns, focuses parts of the electron wave function, increasing the efficiency of such intense field processes as multiphoton double ionization. Our calculations show enhancement by more than an order of magnitude for multiphoton double ionization of He at 0.8 \ensuremath{\mu}m.

249 citations


Journal ArticleDOI
TL;DR: The detailed analysis of the layer-resolved local densities of states and of the dispersion of the surface states demonstrates that the results are in good agreement with recent photoemission experiments.
Abstract: We present ab initio investigations of the structural and electronic properties of clean and hydrogen-covered diamond (100) surfaces within local-density-functional theory. Our calculations are based on a variational solution of the Kohn-Sham equations using a preconditioned conjugate-gradient approach and on the optimization of the atomic structure via a quasi-Newton quench based on the exact Hellmann-Feynman forces. The computations are performed in a plane-wave basis, the electron-ion interaction is described by optimized ultrasoft pseudopotentials. We find that the clean and the monolayer-covered surfaces reconstruct in a (2\ifmmode\times\else\texttimes\fi{}1) cell via the formation of rows of symmetric \ensuremath{\pi}-bonded dimers. Further hydrogenation to a coverage of 1.5 ML stabilizes a surface with a (1\ifmmode\times\else\texttimes\fi{}1) periodicity in the C layers, albeit with a low H-desorption energy for the formation of the reconstructed monohydride surface. The two-step desorption process is in good agreement with experimental observations. Electronic surface states within the bulk gap are predicted for the clean surface, but not for the monohydride case. The detailed analysis of the layer-resolved local densities of states and of the dispersion of the surface states demonstrates that the results are in good agreement with recent photoemission experiments. A negative electron affinity is predicted for the monohydride surface, but not for the clean surface. \textcopyright{} 1996 The American Physical Society.

197 citations


Book
29 Jan 1996
TL;DR: Theorem for Non-Precise a priori Distribution and Non- precise Data Bayesian Decisions Based on Non- Precise Information Outlook References List of Symbols Index.
Abstract: Non-Precise Data and Their Formal Description Non-Precise Data Non-Precise Numbers and Characterizing Functions Construction of Characterizing Functions Non-Precise Vectors Functions of Non-Precise Quantities and Non-Precise Functions Descriptive Statistics with Non-Precise Data Non-Precise Samples Histograms for Non-Precise Data Cumulative Sums for Non-Precise Data Empirical Distribution Function for Non-Precise Data Empirical Fractiles for Non-Precise Data Foundations for Statistical Inference with Non-Precise Data Combination of Non-Precise Observations Sample Moment for Non-Precise Observations Sequences of Non-Precise Observations Classical Statistical Inference for Non-Precise Data Point Estimators for Parameters Confidence Regions for Parameters Nonparametric Estimation Statistical Tests and Non-Precise Data Bayesian Inference for Non-Precise Data Bayes' Theorem for Non-Precise Data Bayesian Confidence Regions Based on Non-Precise Data Non-Precise Predictive Distributions Non-Precise a priori Distributions Bayes Theorem for Non-Precise a priori Distribution and Non-Precise Data Bayesian Decisions Based on Non-Precise Information Outlook References List of Symbols Index

Journal ArticleDOI
TL;DR: An essentially complete characterization is given of the H(z) allowing such a realization, in terms of the location of the pole or poles of H(Z) with maximum modulus.
Abstract: Let H(z) be a rational transfer function, with associated nonnegative impulse response sequence. The paper considers the question: When does there exist a triple A/spl isin/R/sup N/spl times/N/, b/spl isin/R/sup N/, c/spl isin/R/sup N/ with all nonnegative entries H(z)=c'(zI-A)/sup -1/b? An essentially complete characterization is given of the H(z) allowing such a realization, in terms of the location of the pole or poles of H(z) with maximum modulus.

Journal ArticleDOI
TL;DR: The molecular basis of the absence of xylanase I formation on glucose was studied to postulate that basal transcription of xyn1 is repressed by glucose and mediated by an inverted repeat of the consensus motif for Cre1‐mediated carbon catabolite repression.
Abstract: The filamentous fungus Trichoderma reesei forms two specific, xylan-inducible xylanases encoded by xyn1 and xyn2 to degrade the beta-1,4-D-xylan backbone of hemicelluloses. This enzyme system is formed in the presence of xylan, but not glucose. The molecular basis of the absence of xylanase I formation on glucose was the purpose of this study. Northern blotting of the xyn1 transcript as well as the use of the Escherichia coli hygromycin B phosphotransferase-encoding gene (hph) as a reporter consistently showed that the basal expression of xyn1 was affected by glucose, whereas its induction by xylan remained uninfluenced. The repression of basal xyn1 transcription is mediated by the carbon catabolite repressor protein Cre1, which in vivo binds to two of four consensus sites (5'-SYG-GRG-3') in the xyn1 promoter, which occurred in the form of an inverted repeat. T. reesei strains, bearing a xyn1::hph reporter construct, in which four nucleotides from the middle of the inverted repeat had been removed, expressed hph on glucose at a level comparable to that observed during growth on a carbon catabolite derepressing carbon source. Northern analysis of xyn1 expression in a T. reesei mutant strain (RUT C-30), which contains a truncated, non-functional cre1 gene, also confirmed basal transcription of xyn1. In this strain, xyn1 transcription was still inducible by xylose or xylan to an even higher degree than in the wild-type strain, suggesting that induction overcomes glucose repression at the level of xyn1 expression. Based on these data, we postulate that basal transcription of xyn1 is repressed by glucose and mediated by an inverted repeat of the consensus motif for Cre1-mediated carbon catabolite repression.

Journal ArticleDOI
TL;DR: In this paper, an extension of well-founded semantics for logic programs with two types of negation is described, in which information about preferences between rules can be expressed in the logical language and derived dynamically.
Abstract: The paper describes an extension of well-founded semantics for logic programs with two types of negation. In this extension information about preferences between rules can be expressed in the logical language and derived dynamically. This is achieved by using a reserved predicate symbol and a naming technique. Conflicts among rules are resolved whenever possible on the basis of derived preference information. The well-founded conclusions of prioritized logic programs can be computed in polynomial time. A legal reasoning example illustrates the usefulness of the approach.

Journal ArticleDOI
TL;DR: An ab initio study based on local-density-functional (LDF) theory is presented for the chemisorption of hydrogen on the Pd(111) surface, and both geometries and the electronic structure obtained are in good agreement with experimental results.
Abstract: An ab initio study based on local-density-functional (LDF) theory is presented for the chemisorption of hydrogen on the Pd(111) surface. Our calculation uses the Vienna ab initio molecular-dynamics program (VAMP) based on (i) finite-temperature LDF, (ii) exact calculation of the electronic ground state and Hellmann-Feynman forces after each ionic move, and (iii) ultrasoft pseudopotentials for the electron-ion interaction. Complete geometry optimization for different adsorption sites are carried out. The energetic stability of the adsorption site correlates with the coordination number of the site. The larger the coordination number, the more stable the site. Both geometries and the electronic structure obtained from our theoretical calculations are in good agreement with experimental results. \textcopyright{} 1996 The American Physical Society.

Journal ArticleDOI
TL;DR: Electrophoretic mobility shift assays, using cell-free extracts, identified induction-specific protein-DNA complexes: one complex of high mobility was observed under basal, noninduced conditions (glucose) with xyn2, which was in part replaced by a slow-migrating complex upon induction by xylan or sophorose.

Journal ArticleDOI
TL;DR: Four subspace algorithms which are based on an initial estimate of the state are considered and an algorithm which is essentially equal to the N4SID algorithm by Van Overschee and De Moor is compared.

Journal ArticleDOI
TL;DR: In this paper, a quasiclassical approach to correct electron motion following tunneling ionization in intense laser fields, for the presence of the Coulomb potential, is described.
Abstract: We describe a quasiclassical approach to correct electron motion following tunneling ionization in intense laser fields, for the presence of the Coulomb potential. The technique is applied to model the dependence of high-harmonic generation on the ellipticity of the incident laser field. We present experimental data on the harmonics with photon energies close to the ionization potential of an atom, identify their source, and explain their unusual dependence on the ellipticity of the incident laser field. Our calculations are in good agreement with experimental data. \textcopyright{} 1996 The American Physical Society.

Posted Content
TL;DR: Information about preferences between rules can be expressed in the logical language and derived dynamically by using a reserved predicate symbol and a naming technique to extend well-founded semantics for logic programs with two types of negation.
Abstract: The paper describes an extension of well-founded semantics for logic programs with two types of negation. In this extension information about preferences between rules can be expressed in the logical language and derived dynamically. This is achieved by using a reserved predicate symbol and a naming technique. Conflicts among rules are resolved whenever possible on the basis of derived preference information. The well-founded conclusions of prioritized logic programs can be computed in polynomial time. A legal reasoning example illustrates the usefulness of the approach.

Journal ArticleDOI
01 Jan 1996
TL;DR: In this paper, the formation rates of NO, N 2 O, and HCN were studied by using a high performance FT-IR spectrometer in combination with a long-path, low-volume gas cell.
Abstract: In an exclusively electrically heated, laboratory-scale, fluidized-bed compustor (MM-FBC) made of quartz glass, the formation rates of NO, N 2 O, and HCN are studied by using a high performance FT-IR spectrometer in combination with a long-path, low-volume gas cell. The emission characteristics of single, spherical fuel particles (5–15 mm in diameter) of bituminous coal, subbituminous coal, and beech wood are studied. The bed temperature is varied between 600 and 900°C. The fluidizing velocity is 0.68 m/s and the oxygen partial pressure is varied between 0.05 and 21 kPa. The bed material is silica sand with a mean diameter of 225 μm. Besides changing combustion conditions and fuel type and diameter, an iodine addition technique is applied to study the relative importance of the homogeneous and the heterogeneous chemistry during devolatilization and char combustion. Iodine addition suppresses the radical concentrations to equilibrium level and has proven as a very effective method for kinetic measurements. With a semitheoretical model, the measurement results are discussed and reaction paths are evaluated. The formation characteristics during devolatilization can be explained mainly by the homogeneous HCN oxidation and NO and N 2 O formation. NO and N 2 O formation during char combustion consists of two different paths. NO is mainly heterogeneously formed by char-nitrogen oxidation. But a volatile species, which has been identified as HCN, is simultaneously released in low concentrations. This species is homogeneously oxidized to NCO which further reacts with the heterogeneously produced NO to form N 2 O.

Journal ArticleDOI
TL;DR: The appearance of the corresponding N-acetyl-β-D-glucosaminidase protein paralleled the pattern of nag 1 expression, thereby suggesting that its formation is regulated at the level of transcription.
Abstract: A 72-kDa N-acetyl-β-D-glucosaminidase was purified from the mycoparasitic fungus Trichoderma harzianum P1; antibodies were raised against it, and aa-sequences were obtained. The antibody reacted with a single 72-kDa protein band in culture filtrates of T. harzianum grown on chitin, and was subsequently used to clone the corresponding nag1 gene from a λgt11 cDNA expression library. It was interrupted by two short introns and encoded a protein of 580 amino acids. The deduced protein sequence contained aa-sequence areas of high similarity to N-acetyl-glucosaminidases from other eukaryotes such as Candida albicans, and invertebrate and vertebrate animal tissues. The highest similarity was observed with the corresponding gene from the silkworm. The aa-sequence of a tryptic fragment of purified N-acetyl-β-D-glucosaminidase from T. harzianum corresponded to a deduced aa sequence from a portion of the cloned gene, thus verifying that the protein is encoded by nag 1. Southern analysis showed that nag 1 is present as a single-copy gene in T. harzianum. Expression of nag1-mRNA was strongly induced upon growth on chitin, N-acetyl-glucosamine and the cell walls of Botrytis cinerea used as a carbon source. The appearance of the corresponding N-acetyl-β-D-glucosaminidase protein, as determined by Western analysis, paralleled the pattern of nag 1 expression, thereby suggesting that its formation is regulated at the level of transcription.

Journal ArticleDOI
TL;DR: In this paper, the authors provide a concise approach to generalized dilaton theories with and without torsion and coupling to Yang-Mills fields, and set the stage for a thorough global investigation of classical and quantum aspects of more or less all available 2D gravity - Yang - Mills models.
Abstract: We provide a concise approach to generalized dilaton theories with and without torsion and coupling to Yang - Mills fields. Transformations on the space of fields are used to trivialize the field equations locally. In this way their solution becomes accessible within a few lines of calculation only. In this first of a series of papers we set the stage for a thorough global investigation of classical and quantum aspects of more or less all available 2D gravity - Yang - Mills models.

Journal ArticleDOI
TL;DR: In this paper, the authors compare the wavelet soft universal thresholding algorithm described by Donoho, to Fourier filters and to polynomial smoothers such as the Savitzky-Golay filters (SG).

Journal ArticleDOI
TL;DR: This paper presents a meta-analyses of the chiral stationary phase transition of the response of the Higgs boson to the E-modulus of the electron.
Abstract: We perform fully relativistic spin-polarized local spin density calculations for Au covered Co monolayer on Au(111). In accord with a trend observed in experiments we obtain an enhancement of perpendicular magnetic anisotropy as a function of the Au coverage. The close relationship found between the anisotropies of orbital magnetic moments and the anisotropy energies leads to an interpretation of our results in terms of familiar perturbation theory. By using this framework the anomalous behavior of the magnetic anisotropy energies can be well explained due to changes in the sp-d hybridization at the interface of Co monolayer and Au cap.

Journal ArticleDOI
TL;DR: Scanning tunneling microscopy on Ar ion bombarded and annealed aluminum surfaces shows interference between the surface and subsurface bubbles of implanted gas that indicates the bubbles have a shape given Wulff construction.
Abstract: Scanning tunneling microscopy on Ar ion bombarded and annealed aluminum surfaces shows electron interference between the surface and subsurface bubbles of implanted gas. The depth of the bubbles as determined from the energy dependence of the standing waves indicates a minimum around 6--7 layers on Al(111). The appearance and energy dependence of the interference pattern is in good agreement with scattering theory based on free electrons, and indicates the bubbles have a shape given by the Wulff construction.

Journal ArticleDOI
TL;DR: In this paper, the atomic and electronic structure of the clean and hydrogen-covered one dangling-bond diamond (111) surfaces was analyzed and it was shown that the clean C(111) surface reconstructs in a (2 × 1) geometry with symmetric, unbuckled π bonded Pandey chains.

Journal ArticleDOI
TL;DR: In this article, a set of simple rules for constructing maximal extensions for any metric with a Killing field in an (effectively) two-dimensional spacetime is formulated, and the application of these rules is extremely straightforward, as demonstrated at various examples and illustrated with numerous figures.
Abstract: A set of simple rules for constructing the maximal (e.g. analytic) extensions for any metric with a Killing field in an (effectively) two-dimensional spacetime is formulated. The application of these rules is extremely straightforward, as is demonstrated at various examples and illustrated with numerous figures. Despite the resulting simplicity we also comment on some subtleties concerning the concept of Penrose diagrams. Most noteworthy among these, maybe, is that (smooth) spacetimes which have both degenerate and non-degenerate (Killing) horizons do not allow for globally smooth Penrose diagrams. Physically speaking this obstruction corresponds to an infinite relative red/blueshift between observers moving across the two horizons. – The present work provides a further step in the classification of all global solutions of the general class of two-dimensional gravity-Yang-Mills systems introduced in Part I [1], comprising, e.g., all generalized (linear and nonlinear) dilaton theories. In Part I we constructed the local solutions, which were found to always have a Killing field; in this paper we provide all universal covering solutions (the simply connected maximally extended spacetimes). A subsequent Part III [2] will treat the diffeomorphism inequivalent solutions for all other spacetime topologies. Part II is kept entirely self-contained; a prior reading of Part I is not necessary.

Journal ArticleDOI
TL;DR: This strategy combines several techniques, including levels of detail, progressive refinement and graceful degradation to deliver the data "just in time" over the network to the rendering process, which allows operate on a tight resource budget.
Abstract: We present a strategy for rendering in distributed virtual environments. A geometry database is maintained by a server, while users invoke individual clients to interact with the environment. Instead of downloading a complete copy of the geometry data, the data is distributed on demand, thus gaining signifcant savings in network bandwidth. Our strategy combines several techniques, including levels of detail, progressive refinement and graceful degradation to deliver the data “just in time” over the network to the rendering process. The method allows operate on a tight resource budget, which important if attempting to use low cost systems for virtual reality applications.

Journal ArticleDOI
TL;DR: In this paper, the structural and electronic properties of the low-index surfaces of rhodium have been investigated via fully self-consistent ab initio local density functional (LDF) calculations.

Journal ArticleDOI
11 Mar 1996
TL;DR: A new combination of fuzzy set based constraints and iterative improvement repair based heuristics that help to model real-world scheduling problems are explained and a new consistency test for configuration changes is introduced.
Abstract: Real-world scheduling is decision making under vague constraints of different importance, often using uncertain data, where compromises between antagonistic criteria are allowed. The author explains in theory and by detailed examples a new combination of fuzzy set based constraints and iterative improvement repair based heuristics that help to model these scheduling problems. The mathematics needed for a method of eliciting the criteria's importances from human experts are simplified. The author introduces a new consistency test for configuration changes. This test also helps to evaluate the sensitivity to configuration changes. The implementation of these concepts in the fuzzy logic inference processor library FLIP++, in the fuzzy constraint library ConFLIP++, in the dynamic constraint generation library DynaFLIP++, and in the heuristic repair library Deja Vu is described. All these libraries are implemented in a layered framework enhanced by the common user interface InterFLIP++. The benchmark application to compare the fuzzy constraint iterative improvement repair heuristic with constructive method based on classic constraints is a scheduling system for a continuous caster unit in a steel plant.