Showing papers by "Technische Universität Darmstadt published in 1998"
TL;DR: In this article, the authors proposed fracture analysis of structural members made of FRP composites and derived the fracture angle which is the key for this evaluation, which is derived in the present paper.
1,529 citations
TL;DR: In this paper, a colloid method was used to synthesize polymetallic PEM catalysts for anodic anodic oxidation of H2 containing 150ppm CO and of methanol.
449 citations
TL;DR: In this paper, a hexapole corrector system was constructed for compensation of the spherical aberration of the objective lens of a transmission electron microscope, and an improvement of the point resolution from 0.24nm to better than 0.14nm was realized.
380 citations
TL;DR: In this article, the authors analyzed the production cross sections of several hundred nuclei produced in the fragmentation of uranium and lead projectiles with the abrasion-ablation model taking into account fission in the deexcitation chain.
334 citations
TL;DR: An overview of the various kinds of real-time and HIL simulation for relatively slow processes, like those in basic industries or heating systems, is discussed and the required models are described.
331 citations
TL;DR: A new method for eliminating speckles in the far field by using a diffractive optical element is proposed, which can be reduced to a few percent while good beam quality is preserved.
Abstract: In laser projection systems the observer in the far field of the image points on the screen will recognize serious speckle noise There are many methods to reduce or eliminate speckles in the near field by reducing or eliminating temporal or spatial coherence of the laser But for the far field it is hardly possible to change the coherence properties of laser sources so that speckles will disappear We propose a new method for eliminating speckles in the far field by using a diffractive optical element The intensity modulation depth in the far-field speckle pattern can be reduced to a few percent while good beam quality is preserved
262 citations
01 Mar 1998
TL;DR: It is shown how fuzzy logic approaches can be applied to process supervision and to fault diagnosis with approximate reasoning on observed symptoms and a review and classification of the potentials of fuzzy logic in process automation.
Abstract: The degree of vagueness of variables, process description, and automation functions is considered and is shown. Where quantitative and qualitative knowledge is available for design and information processing within automation systems. Fuzzy-rule-based systems with several levels of rules form the basis for different automation functions. Fuzzy control can be used in many ways, for normal and for special operating conditions. Experience with the design of fuzzy controllers in the basic level is summarized, as well as criteria for efficient applications. Different fuzzy control schemes are considered, including cascade, feedforward, variable structure, self-tuning, adaptive and quality control leading to hybrid classical/fuzzy control systems. It is then shown how fuzzy logic approaches can be applied to process supervision and to fault diagnosis with approximate reasoning on observed symptoms. Based on the properties of fuzzy logic approaches the contribution gives a review and classification of the potentials of fuzzy logic in process automation.
259 citations
TL;DR: In this paper, the viscosity of silicoboron carbonitride (Si2B1.0C3.4N2.3), which seems to have a Tg value of >1700°C, was examined.
Abstract: Recently, the viscosity of a predominantly amorphous silicon carbonitride (Si1.7C1.0±0.1N1.5) alloy with an apparent glass-transition temperature (Tg) of 1400°–1500°C was studied. In this study, the creep behavior of silicoboron carbonitride (Si2B1.0C3.4N2.3), which seems to have a Tg value of >1700°C, was examined. Both materials exhibited a three-stage creep behavior. In stage I, the creep rate declined, because of densification. In stage II, the strain rate approaches a steady state. In stage III, it resumes a declining strain rate, which ultimately decreased below the measurement limit of the system. At 1550°C in stage II, the viscosity of silicoboron carbonitride was six orders of magnitude higher than that of fused silica. Among the Si-C-N ceramics, only chemical-vapor-deposited and reaction-bonded silicon carbides seem to have greater creep resistance than the silicoboron carbonitrides at temperatures >1550°C.
231 citations
TL;DR: In this paper, the effect of SiC volume fraction and particle size on the fatigue behavior of 2080 Al was investigated, and it was found that increasing volume fraction resulted in an increase in fatigue resistance.
Abstract: The effect of SiC volume fraction and particle size on the fatigue behavior of 2080 Al was investigated. Matrix microstructure in the composite and the unreinforced alloy was held relatively constant by the introduction of a deformation stage prior to aging. It was found that increasing volume fraction and decreasing particle size resulted in an increase in fatigue resistance. Mechanisms responsible for this behavior are described in terms of load transfer from the matrix to the high stiffness reinforcement, increasing obstacles for dislocation motion in the form of S’ precipitates, and the decrease in strain localization with decreasing reinforcement interparticle spacing as a result of reduced particle size. Microplasticity was also observed in the composite, in the form of stress-strain hysteresis loops, and is related to stress concentrations at the poles of the reinforcement. Finally, intermetallic inclusions in the matrix acted as fatigue crack initiation sites. The effect of inclusion size and location on fatigue life of the composites is discussed.
219 citations
TL;DR: In this article, the transmission and reflection of the multilayers were measured, as well as the film thickness and the sheet resistance, and the complex indices of refraction both of ITO and of AgCu were calculated from the measured data.
216 citations
TL;DR: In this article, a DC-magnetron reactive sputtering in an vertical Inline sputtering system was used to produce indium-tin-oxide (ITO) thin films.
01 Jan 1998
TL;DR: ACO is a new algorithmic approach, inspired by the foraging behavior of real ants, that can be applied to the solution of combinatorial optimization problems.
Abstract: In this article we present an Ant Colony Optimization approach to the Flow Shop Problem. ACO is a new algorithmic approach, inspired by the foraging behavior of real ants, that can be applied to the solution of combinatorial optimization problems. Artificial ants are used to construct solutions for Flow Shop Problems that subsequently are improved by a local search procedure. Comparisons with other heuristics for the Flow Shop Scheduling problem show that with our approach very promising results are obtained.
TL;DR: Borophosphates (intermediate compounds of the system MxOy−B2O3−P2O5−(H2O)) contain complex anionic structures built of BO4, BO3, and PO4 groups and their partially protonated species, respectively as discussed by the authors.
Abstract: Borophosphates (intermediate compounds of the system MxOy−B2O3−P2O5−(H2O)) contain complex anionic structures built of BO4, BO3, and PO4 groups and their partially protonated species, respectively....
07 Jun 1998
TL;DR: A new spread-spectrum multiple- access scheme applicable for both the uplink and the downlink of a mobile radio communications system is proposed, which is termed "interleaved frequency-division multiple-access", which combines the advantages of spread-Spectrum and multicarrier transmission.
Abstract: A new spread-spectrum multiple-access scheme applicable for both the uplink and the downlink of a mobile radio communications system is proposed, which is termed "interleaved frequency-division multiple-access". This scheme combines the advantages of spread-spectrum and multicarrier transmission. Moreover, it can be viewed as a special kind of a multicarrier spread-spectrum scheme where user discrimination is carried out using frequency-division multiple-access. The multiple-access capability is achieved by assigning to each user a different set of orthogonal subcarriers. The orthogonality between the different users is maintained at the receiver, even in time-dispersive channels resulting in no multiple-access interference. However, the cost to avoid multiple-access interference is to allow for intersymbol interference and therefore equalization is required at the receiver.
27 Sep 1998
TL;DR: The empirical tests are performed applying MAX-MIN Ant System, one of the most efficient ACO algorithms, to the Traveling Salesman Problem and show that using parallel independent runs is very effective.
Abstract: Ant Colony Optimization (ACO) is a new population oriented search metaphor that has been successfully applied to NP-hard combinatorial optimization problems. In this paper we discuss parallelization strategies for Ant Colony Optimization algorithms. We empirically test the most simple strategy, that of executing parallel independent runs of an algorithm. The empirical tests are performed applying MAX-MIN Ant System, one of the most efficient ACO algorithms, to the Traveling Salesman Problem and show that using parallel independent runs is very effective.
TL;DR: The intention of this paper is to introduce a marching method to build a mesh of triangles successively by starting with a point or a prescribed polygon, applicable to any surface for which foot points can be determined.
Abstract: Surface triangulations are necessary in applying finite element methods for solving mechanical problems and for displaying surfaces by ray tracing or other hidden line algorithms. A parametric surface can be a triangulated by triangulating its (plane) area of definition. However, the images of these triangles in object space may vary unacceptably for the application. Thus we need suitable methods of triangulation even for parametric surfaces. Triangulation algorithms for implicit surfaces are available in the literature. [ALGN'91; BL'88; LO'87; SC'93; WY'86]. All these methods divide the space into suitable polyhedrons (cubes, tetrahedrons) and determine the section of the given implicit surface with the edges of these polyhedrons. The intention of this paper is to introduce a marching method to build a mesh of triangles successively by starting with a point or a prescribed polygon. The triangulation is terminated by several bounding polygons (on the given surface) or a global bounding box. (A similar idea is used in the recently published paper [BAXU'97] on algebraic surfaces.) The method will be established for implicit surfaces. With the idea of numerical implicitization introduced in [HA'97], the triangulation is applicable to any surface for which foot points (i.e., points of minimal distance to the surface) can be determined.The main advantages of the triangulation presented in this paper are:
TL;DR: In this article, pore formers are added to the electrocatalyst slurry which is used for the hot spraying process to obtain additional coarse porosity for better access of oxygen from air to the depth of the cathode.
Abstract: Better performance of and higher electrocatalyst utilization in proton-exchange membrane fuel cells equipped with thin film electrodes is achieved by exploiting pore forming additives in the electrode recipe formulation. Preparing the membrane–electrode assembly by a hot spraying procedure already provides 35% porosity. Additional coarse porosity is obtained by adding pore formers to the electrocatalyst slurry which is used for the hot spraying process. This allows for a better access of oxygen from air to the depth of the cathode. For air operation at ambient pressure and low catalyst loading of 0.15mgPtcm-2 a current density of 200mAcm-2 at 0.7V cell voltage can be obtained with such electrodes.
Proceedings Article•
24 Jul 1998TL;DR: A novel methodology for evaluating the performance of LVAs, based on the identification of empirical run-time distributions is proposed, and is exemplified by applying it to Stochastic Local Search algorithms for the satisfiability problem (SAT) in propositional logic.
Abstract: Stochastic search algorithms are among the most sucessful approaches for solving hard combinatorial problems. A large class of stochastic search approaches can be cast into the framework of Las Vegas Algorithms (LVAs). As the run-time behavior of LVAs is characterized by random variables, the detailed knowledge of run-time distributions provides important information for the analysis of these algorithms. In this paper we propose a novel methodology for evaluating the performance of LVAs, based on the identification of empirical run-time distributions. We exemplify our approach by applying it to Stochastic Local Search (SLS) algorithms for the satisfiability problem (SAT) in propositional logic. We point out pitfalls arising from the use of improper empirical methods and discuss the benefits of the proposed methodology for evaluating and comparing LVAs.
TL;DR: It could be shown that the micro-organism produces a protease which cleaves pro-transglutaminase at the C-side of Pro45, and Rapid transformation of the mature enzyme also occurs by addition of other proteases.
Abstract: The zymogen of bacterial transglutaminase was found during cultivation of Streptoverticillium mobaraense (DSMZ strain) using rabbit antibodies raised against the active enzyme. Ion-exchange chromatography at pH 5.0 yielded a highly purified pro-enzyme. Structure information was obtained by means of Edman degradation and analysis of PCR amplified nucleotide fragments. The data revealed an excess of negatively charged amino acids in the pro-region resulting in a decreased isoelectric point of the zymogen. Additionally, the new sequence gave rise to some modifications to the previously published hypothetical structure of prepro-transglutaminase derived from genomic DNA [Washizu, K., Ando, K., Koikeda, S., Hirose, S., Matsuura, A., Takagi, H., Motoki, M. & Takeuchi, K. (1994) Biosci. Biotechnol. Biochem. 58, 82−87]. Inactive transglutaminase, which carries an activation peptide of 45 amino acids, has a calculated molecular mass of 42 445 Da. Its pro-region provides for both suppression of activity and increased thermostability. Furthermore, it could be shown that the micro-organism produces a protease which cleaves pro-transglutaminase at the C-side of Pro45. Rapid transformation of the mature enzyme also occurs by addition of other proteases. During conversion, 43 and 41 amino acid peptides are released by bovine trypsin and dispase from Bacillus polymyxa, respectively. The detection of endogenous substrates in the murein layer makes discussion of the physiological role of bacterial transglutaminases necessary.
TL;DR: In this article, a new class of micro lasers based on nanoporous molecular sieve host-guest systems is presented, where organic dye guest molecules of 1-ethyl-4-[4]-4-( $p$-dimethylaminophenyl)-1,3-butadienyl]-pyridinium perchlorat were inserted into the 073-nm wide channel pores of a zeolite host.
Abstract: We present a new class of micro lasers based on nanoporous molecular sieve host-guest systems Organic dye guest molecules of 1-ethyl-4-[4-( $p$-dimethylaminophenyl)-1,3-butadienyl]-pyridinium Perchlorat were inserted into the 073-nm-wide channel pores of a zeolite $\mathrm{AlPO}{}_{4}\ensuremath{-}5$ host The zeolitic microcrystal compounds were hydrothermally synthesized according to a particular host-guest chemical process The dye molecules are found not only to be aligned along the host channel axis, but to be oriented as well Single mode laser emission at $687\mathrm{nm}$ was obtained from a whispering gallery mode oscillating in a $8\ensuremath{-}\ensuremath{\mu}\mathrm{m}\ensuremath{-}\mathrm{diameter}$ monolithic microresonator, in which the field is confined by total internal reflection at the natural hexagonal boundaries inside the zeolitic microcrystals
21 Jun 1998
TL;DR: New iterating functions for computing discrete logarithms with the rho method are defined and compared and it is shown that one of these functions is expected to reduce the number of steps by a factor of approximately 0.8, in comparison with Pollard's originally used function.
Abstract: In Pollard's rho method, an iterating function f is used to define a sequence (y i) by y i+1=f(y i) for i=0,1, 2,..., with some starting value y0. In this paper, we define and discuss new iterating functions for computing discrete logarithms with the rho method. We compare their performances in experiments with elliptic curve groups. Our experiments show that one of our newly defined functions is expected to reduce the number of steps by a factor of approximately 0.8, in comparison with Pollard's originally used function, and we show that this holds independently of the size of the group order. For group orders large enough such that the run time for precomputation can be neglected, this means a real-time speed-up of more than 1.2.
TL;DR: This paper derives the transition rules for an abstract machine from a continuation semantics which appears as a generalization of the ¬¬-translation known from logic.
Abstract: One of the goals of this paper is to demonstrate that denotational semantics is useful for operational issues like implementation of functional languages by abstract machines. This is exemplified in a tutorial way by studying the case of extensional untyped call-by-name λ-calculus with Felleisen's control operator C. We derive the transition rules for an abstract machine from a continuation semantics which appears as a generalization of the ¬¬-translation known from logic. The resulting abstract machine appears as an extension of Krivine's machine implementing head reduction. Though the result, namely Krivine's machine, is well known our method of deriving it from continuation semantics is new and applicable to other languages (as e.g. call-by-value variants). Further new results are that Scott's D∞-models are all instances of continuation models. Moreover, we extend our continuation semantics to Parigot's λμ-calculus from which we derive an extension of Krivine's machine for λμ-calculus. The relation between continuation semantics and the abstract machines is made precise by proving computational adequacy results employing an elegant method introduced by Pitts.
23 Sep 1998
TL;DR: It is clarified that CKDD can be understood as a human-centered approach of Knowledge Discovery in Databases, which led to the software system TOSCANA, which is presented as a CKDD tool in this paper.
Abstract: In this paper we discuss Conceptual Knowledge Discovery in Databases (CKDD) as it is developing in the field of Conceptual Knowledge Processing (cf. [29],[30]). Conceptual Knowledge Processing is based on the mathematical theory of Formal Concept Analysis which has become a successful theory for data analysis during the last 18 years. This approach relies on the pragmatic philosophy of Ch.S. Peirce [15] who claims that we can only analyze and argue within restricted contexts where we always rely on pre-knowledge and common sense. The development of Formal Concept Analysis led to the software system TOSCANA, which is presented as a CKDD tool in this paper. TOSCANA is a flexible navigation tool that allows dynamic browsing through and zooming into the data. It supports the exploration of large databases by visualizing conceptual aspects inherent to the data. We want to clarify that CKDD can be understood as a human-centered approach of Knowledge Discovery in Databases. The actual discussion about human-centered Knowledge Discovery is therefore briefly summarized in Section 1.
01 Sep 1998
TL;DR: This work presents a trivial scheme that provides similar protection for the content but be used efficiently with multicasting and caching, and introduces receiver-sided introduction of watermarks into the video.
Abstract: 1. ABSTRACT Various on-demand systems require that large numbers of customers are provided with the same multimedia stream content or different but closely related content in short temporary sequence but not at exactly the same time. This includes video on demand and news on demand. A typical approach to increase the performance of such systems is caching. However in current commercial on-demand streaming applications in the Internet caches are used very rarely because a mechanism to protect the content from resale by the cache owners does not exist. A typical solution is to transfer all content via protected unicast transmissions, which is an approach that does not scale. We want to present a trivial scheme that provides similar protection for the content but be used efficiently with multicasting and caching. In this approach, the major part of the video is intentionally corrupted and can be distributed via multicast connections, while the part for reconstruction of the original is delivered to each receiver individually. We propose also means to discourage resale of the multimedia content by customers. One proposal introduces receiver-sided introduction of watermarks into the video, the other uses infrequent corrupt bytes to achieve uniqueness of each copy.
TL;DR: In this paper, a single bubble in water is excited by a standing ultrasound wave and at high intensity the bubble starts to emit light, together with the emitted light pulse, a shock wave is generated in the liquid at collapse time.
Abstract: A single bubble in water is excited by a standing ultrasound wave. At high intensity the bubble starts to emit light. Together with the emitted light pulse, a shock wave is generated in the liquid at collapse time. The time-dependent velocity of the outward-traveling shock is measured with an imaging technique. The pressure in the shock and in the bubble is shown to have a lower limit of 5500 bars. Visualization of the shock and the bubble at different phases of the acoustic cycle reveals previously unobserved dynamics during stable and unstable sonoluminescence.
TL;DR: In this paper, the authors investigate the interaction of mutually incoherent spatial solitons in photorefractive media with anisotropic nonlocal nonlinear response, and show that the photore-fractive nonlinearity leads to an anomalous interaction between soliton pairs, which may experience both attractive and repulsive forces, depending on their mutual separation.
Abstract: We investigate the interaction of mutually incoherent spatial solitons in photorefractive media with anisotropic nonlocal nonlinear response. We show that the photorefractive nonlinearity leads to an anomalous interaction between solitons. Theoretical and experimental results reveal that an incoherent soliton pair may experience both attractive and repulsive forces, depending on their mutual separation. [S0031-9007(98)05808-6]
TL;DR: This paper gives a counterexample to Graham's proof and describes its own attempts at proving a closure result for the probabilistic powerdomain construction, and gives a new proof of Jones' Splitting Lemma.
TL;DR: In this article, the synthesis, characterization, and thermal stability of element carbodiimides are discussed. But the main part of this paper is focused on polymeric silicon-based carbodiIMides obtained by the reaction of chloro(organo)silanes with bis(trimethylsilyl) carbodiaminide.
Abstract: Organosilicon carbodiimides have been successfully applied as single-source precursor compounds for the synthesis of novel ternary Si-, C-, and N-containing solid phases. Their thermally induced decomposition gives either amorphous silicon carbonitrides or polycrystalline silicon nitride and silicon carbide mixtures, materials that are presently of technological interest for their exceptional hardness, strength, toughness, and high temperature resistance even in corrosive environments. This review is concerned with the synthesis, characterization, and thermal stability of element carbodiimides. The main part of this paper is focused on polymeric silicon-based carbodiimides obtained by the reaction of chloro(organo)silanes with bis(trimethylsilyl)carbodiimide. In the case of RSiCl3, novel poly(silylcarbodiimide) gels are formed. Starting from silicon tetrachloride, new crystalline SiCN phases (namely, SiC2N4 and Si2CN4), have been isolated. Their crystal structures as well as their thermal behavior in the ...