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Showing papers by "University of Paderborn published in 1993"


Book ChapterDOI
01 Jan 1993
TL;DR: In this article, a canonical Lie algebra in the direct sum of vector fields and 1-1-tensors, the perturbation bundle, is introduced and extended to a full tensor structure and it is related to the Lie algebra obtained by coupling linear systems to nonlinear ones.
Abstract: We introduce a canonical Lie algebra in the direct sum of vector fields and 1-1-tensors, the perturbation bundle This Lie algebra is extended to a full tensor structure and it is related to the Lie algebra obtained by coupling linear systems to nonlinear ones Using Lie algebra isomorphisms from the original structure to the abstract perturbation bundle, new completely integrable systems are obtained The formalism of Lax pairs is found to be a special case of the new structure

74 citations


Book ChapterDOI
01 Jan 1993
TL;DR: Simulated annealing has proven to be a good technique for solving hard combinatorial optimization problems and parallelizations for certain problems on distributed memory multiprocessor systems are known.
Abstract: Simulated annealing has proven to be a good technique for solving hard combinatorial optimization problems. Some attempts at speeding up annealing algorithms have been based on shared memory multiprocessor systems. Also parallelizations for certain problems on distributed memory multiprocessor systems are known.

59 citations


Journal ArticleDOI
01 Dec 1993
TL;DR: Simulation results show that the equalisers based on the multilayer perceptron provides better bit error rate performance compared with the conventional decision feedback equaliser if the equaliser length corresponds to the time spread of the channel.
Abstract: The paper describes the application of multilayer perceptrons to the problem of adaptive channel equalisation in digital communications systems In particular, the use of decision feedback structures is investigated for time-invariant and time-variant bandlimited channels Simulation results show that the equaliser based on the multilayer perceptron provides better bit error rate performance compared with the conventional decision feedback equaliser if the equaliser length corresponds to the time spread of the channel Increasing the equaliser length leads to equivalent bit error rates for the decision feedback and the multilayer perceptron based equaliser Because of the more complex structure of the multilayer perceptron its adaptive behaviour for time-variant channels is inferior compared with the decision feedback equaliser Nonlinearities on the transmission channel can be equalised much better by the multilayer perceptron based equaliser

57 citations


Proceedings ArticleDOI
Rui Zhao1
01 May 1993
TL;DR: Novel concepts and techniques based on an incremental paradigm of gesture recognition and a cooperative communication between modules for pattern recognition and for diagram parsing are presented.
Abstract: Diagram editing is an attractive application of gestural interfaces and pen-based computers which promise a new input paradigm where users communicate with computers in diagram languages by using gestures. A key problem in building gesture-based diagram editors is the recognition of handsketched diagrams. Existing approaches concentrate either on gesture recognition or on parsing visual languages, there has been a lack of integrated recognition concepts. This paper presents novel concepts and techniques based on an incremental paradigm of gesture recognition and a cooperative communication between modules for pattern recognition and for diagram parsing. These concepts and techniques have been used successfully to build several experimental gesture-based and syntax-directed diagram editors.

56 citations


Proceedings ArticleDOI
20 Jun 1993
TL;DR: In this paper, an averaged modeling and analysis method for resonant power converters is described, which is based on the slowly varying amplitude and phase transformation, which leads to a new transformed model where all state variables are slow variables.
Abstract: An averaged modeling and analysis method for resonant power converters is described. The method is based on the slowly varying amplitude and phase transformation. Application of such a transformation to the state space model of a resonant power converter leads to a new transformed model where all state variables are slow variables. The averaging method is then applied to the transformed model to derive an averaged model. Various kinds of analysis and controller design can be carried out using the averaged model. The method is discussed in detail, and a series resonant power converter is taken as example to demonstrate the application of the method. >

53 citations


Journal ArticleDOI
TL;DR: The preparation of a new mixture oxidation products for patch testing in the diagnosis of contact allergy to colophony allergy is recommended.
Abstract: Degradation of abietic, levopimaric and dehydroabietic acids after exposure to air and light over a period of one to several months, as well its examination of degraded French tall oil rosin and Portuguese colophony, led to the isolation of numerous oxidation products. These compounds were synthesized and consigned to experimental sensitization in guinea pigs. From 20 substances studied as acids or as their methyl esters, in the present and preceding paper, at least 2 can be named: 8.12-peroxydo-δ13(14)-dihydroabietic acid and 12 α-hydroxyabietic acid, that contribute a great deal to colophony allergy by both their sensitizing capacity and their determined concentration in the mixture of degradation products. We recommend the preparation of a new mixture oxidation products for patch testing in the diagnosis of contact allergy to colophony.

50 citations


Journal ArticleDOI
TL;DR: In this article, phase fields intersected by three joins in the System CaO-MgO-SiO-CO_2-H_2O at 2 kbar were investigated experimentally to determine the melting relationships and the sequences of crystallization of liquids co-precipitating silicate minerals and carbonates.
Abstract: Phase fields intersected by three joins in the System CaO-MgO-SiO_2-CO_2-H_2O at 2 kbar were investigated experimentally to determine the melting relationships and the sequences of crystallization of liquids co-precipitating silicate minerals and carbonates. These joins connect SiO_2 to three mixtures of CaCO_3-MgCO_3-Mg(OH)_2 with compositions on the primary field for calcite, between the composition CaCO_3 and the low-temperature (650°C eutectic liquid co-precipitating calcite, dolomite and periclase. In the pseudo-quaternary tetrahedron calcite-magnesite-brucite-diopside, two of the significant reactions found are: (1) a eutectic at 650°C, calcite + dolomite + periclase + forsterite + vapor = liquid, and (2) a peritectic at 1038°C which is either calcite + akermanite + forsterite + vapor = monticellite + liquid calcite + monticellite + forsterite + vapor = akermanite + liquid. The eutectic liquid has high MgO/CaO and CO_2/H_2O and only 2–3% SiO_2 (estimated 15–20% MgCO_3, 35–40% CaCO_3, 40–45% Mg(OH)_2, and 5–6% Mg_2SiO_4). The composition joins intersect a thermal maximum for akermanite + forsterite + vapor = liquid, which separates high-temperature liquids precipitating silicates together with a little calcite, from low-temperature liquids precipitating carbonates with a few percent of forsterite; there is no direct path between the silicate and synthetic carbonatite liquids on these joins, but it is possible that fractionating liquid paths diverging from the joins may connect them. More complex relationships involving the precipitation of monticellite and akermanite are also outlined. Magnetite-magnesioferrite may replace periclase in natural magmatic systems. The results indicate that the assemblage calcite-dolomite-magnetite-forsterite represents the closing stages of crystallization of carbonatites, whereas assemblages such as calcite-magnetite-forsterite and dolomite-magnetite-forsterite span the whole range of carbonatite evolution in terms of temperature and composition, and provide the link between liquids precipitating silicates and those precipitating carbonates.

49 citations


Journal ArticleDOI
TL;DR: A theoretical scheme for interpretation of phase transitions in smectic films is proposed and on its basis a conjecture on tension-induced phase transitions is formulated.
Abstract: Shifting and destruction of phase transitions due to the finite thickness of free-standing smectic films are examined. The behavior of smectic films is studied as a function of the temperature and the thickness in a material showing a first-order smectic-A (Sm-A)\ensuremath{\rightarrow}smectic-${\mathit{C}}^{\mathrm{*}}$ (Sm-${\mathit{C}}^{\mathrm{*}}$) bulk phase transition. Measurements of the optical reflectivity and direct observations in an inverted polarizing microscope reveal that the first-order phase transition between Sm-A- and Sm-${\mathit{C}}^{\mathrm{*}}$-like structures takes place in films that are thick enough (Ng${\mathit{N}}_{\mathit{c}}$=90). In thin films (N${\mathit{N}}_{\mathit{c}}$) this transition disappears. For N\ensuremath{\approxeq}${\mathit{N}}_{\mathit{c}}$, a critical behavior is detected. A theoretical scheme for interpretation of phase transitions in smectic films is proposed and on its basis a conjecture on tension-induced phase transitions is formulated.

47 citations



Book ChapterDOI
01 Jan 1993
TL;DR: Various modelling techniques are discussed and a specific model, extended Pr/T-Nets are introduced in detail and a short overview of other system level activities concludes this paper.
Abstract: In this contribution, some aspects of system level design are discussed. After a short characterization of the term system level, most emphasis is laid on modelling aspects. Various modelling techniques are discussed and a specific model, extended Pr/T-Nets are introduced in detail. A short overview of other system level activities concludes this paper.

35 citations


Journal ArticleDOI
TL;DR: Indium can be classified as a «simple» solid under strong compression, and no structural phase transitions are observed in the present experimental range up to 67 GPa.
Abstract: The crystal structure of indium is studied by energy-dispersive x-ray diffraction with diamond anvil cells at ambient temperature under pressures up to 67 GPa. The present results are compared with previous volumetric data for the lower-pressure region as well as with data from shock-wave measurements extending to higher pressures. A comparison of these data with different forms representing equations of state for solids under strong compression shows that indium can be classified as a ``simple'' solid. No structural phase transitions are observed in the present experimental range up to 67 GPa.

Journal ArticleDOI
01 Oct 1993
TL;DR: In this article, the well-known microscopic model for spontaneous polarization of smectic C* phases has been extended by taking into account different orientations of the considered molecular transverse axes.
Abstract: The well-known microscopic model from Žeks et al. for the spontaneous polarization of smectic C* phases has been extended by taking into account different orientations of the considered molecular transverse axes. A stronger temperature dependence of the tilt angle reduced polarization P0 = PS/θ results. The extended model explains differences between the quadrupolar order parameters calculated from P0(T) and from 14N-NQR measurements. Additionally, temperature induced sign inversions of PS, described in the literature, can be explained by considering a possible competition between polar and quadrupolar ordering.


Proceedings ArticleDOI
20 Jun 1993
TL;DR: In this paper, state space models of high frequency multiwinding transformers are presented, suitable for circuit simulation with all kinds of excitation and loads, based on a field and network theoretical analysis.
Abstract: State space models of high frequency multiwinding transformers are presented, suitable for circuit simulation with all kinds of excitation and loads. The elements of these state space models are calculated based on a field and network theoretical analysis. A simulation of a switched mode power supply and a comparison with measurements demonstrates the accuracy of the analysis. >

Journal ArticleDOI
TL;DR: The main result of the paper is the precise estimation of the gossip-problem complexity in cycles, which leads to an optimal lower bound on the number of rounds, and also to the design of an optimal algorithm for gossiping in cycles.
Abstract: The problems of gossiping and broadcasting in one-way communication mode are considered for some prominent families of graphs. The complexity is measured as the number of communication rounds in the gossip and broadcast algorithms. The main result of the paper is the precise estimation of the gossip-problem complexity in cycles. To obtain this result a new combinatorial analysis of gossiping in cycles is developed. This analysis leads to an optimal lower bound on the number of rounds, and also to the design of an optimal algorithm for gossiping in cycles. The optimal algorithm for gossiping is later used to design new, effective algorithms for gossiping in important families of interconnection networks (cube connected cycles, butterfly networks). Furthermore, a new, effective algorithm for broadcasting in shuffle-exchange networks is developed.

Book ChapterDOI
30 Sep 1993
TL;DR: This paper proves that the designed two-way gossip algorithms on d-dimensional grids, d≥3, are almost optimal, and it also shows that the 2-dimensional grid belongs to the best gossip graphs among all planar graphs.
Abstract: The communication modes (one-way and two-way mode) used for sending messages to processors of interconnection networks via vertex-disjoint paths in one communication step are investigated. The complexity of communication algorithms is measured by the number of communication steps (rounds). Here, the complexity of gossiping in grids and in planar graphs is investigated. The main results are the following: 1. Effective one-way and two-way gossip algorithms for d-dimensional grids, d≥2, are designed. 2. The lower bound 2 log2n −log2k −log2 log2n −2 is established on the number of rounds of every two-way gossip algorithm working on any graph of n nodes and vertex bisection k. This proves that the designed two-way gossip algorithms on d-dimensional grids, d≥3, are almost optimal, and it also shows that the 2-dimensional grid belongs to the best gossip graphs among all planar graphs. 3. Another lower bound proof is developed to get some tight lower bounds on one-way “well-structured” gossip algorithms on planar graphs (note that all gossip algorithms designed until now in vertexdisjoint paths mode are “well-structured”).

Journal ArticleDOI
TL;DR: This work proves the first superlinear lower bound for a concrete, polynomial time recognizable decision problem on a Turing machine with one work tape and a two-way input tape.
Abstract: We prove the first superlinear lower bound for a concrete, polynomial time recognizable decision problem on a Taring machine with one work tape and a two-way input tape (also called off-line 1-tape Turing machine). In particular, for offline Turing machines we show that two tapes are better than one and that three pushdown stores are better than two (both in the deterministic and in the nondeterministic case).

Journal ArticleDOI
TL;DR: In this article, the first amino-alkylation of a ketone using terpyridines with peripheral substituents is described. But the reaction produces only two isomers: S-shaped and U-shaped isomers.

Journal ArticleDOI
TL;DR: In this paper, the kinking behavior of cracks is investigated and the J-integral and the mixed-mode components were determined after having performed several finite element analyses for different loading conditions.
Abstract: Cracks in structures are often subjected to complex loading conditions. The direction of the crack extension depends on the normal and the shear components of the load. This paper is based on the kinking behaviour of cracks taking elastic-plastic behaviour of materials into account. The J-integral and the mixed-mode components J I and J II were determined after having performed several finite element analyses for different loading conditions. The path independence of J, J I and J II is investigated for both, the line integral proposed by Rice and the volume integral proposed by deLorenzi. For correctly determined crack deflection angles the J II-component vanishes when a FE-model with a kinked crack is considered. Hence, cracks propagate perpendicularly to the local mode I load.

Proceedings ArticleDOI
14 Jul 1993
TL;DR: In this paper, the use of structure information is emphasized and some aspects of its integration into a vision system are demonstrated.
Abstract: This paper describes a hierarchical vision system for the detection and classification of traffic signs on freeways. The structure and color information of an image is used for detection of traffic signs in the image and coarse classification. Regions-of-interest (RoI) each of them containing only one hypothetical traffic sign, are investigated using pixel classification methods. In this paper, the use of structure information is emphasized and some aspects of its integration into a vision system are demonstrated.

Journal ArticleDOI
TL;DR: The influence of different humic substances and linear alkylbenzene sulfonate on chemical treatment of a synthetic wastewater was investigated at pH=6-6.5 as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this article, the authors investigated low temperature Raman scattering and luminescence in AgBr microcrystals produced in reversed micelles and found that the strong confinement of the exciton and the statistical size distribution result in a blue shift and strong inhomogeneous broadening of the luminecence.

Proceedings ArticleDOI
23 Mar 1993
TL;DR: The guaranteed bandwidth (GBW) protocol for connection oriented data service is a very promising candidate for variable bit rate communication with predictable bandwidth requirements.
Abstract: The distributed queue dual bus (DQDB) standard accepted by the IEEE Standards Board in 1990 is incomplete in the sense that it does not specify details of isochronous service and connection oriented data service. The authors discuss the performance of a protocol which has been studied in all meetings of IEEE 802.6 since 1991. The guaranteed bandwidth (GBW) protocol for connection oriented data service is a very promising candidate for variable bit rate communication with predictable bandwidth requirements. Simulation results of the GBW protocol are presented for various traffic scenarios. >


Journal ArticleDOI
01 Oct 1993
TL;DR: In this paper, a mean-field theory describing the process of surface ordering in smectic membranes is presented, where the critical point where the first order phase transition disappears is observed, by decreasing the thickness of the films.
Abstract: High precision optical reflectivity measurements and optical image analyses are applied to investigate the first order SmA-SmC* phase transition in free-standing films. By decreasing the thickness of the films the critical point is observed, where the first order phase transition disappears. A mean-field theory describing the process of surface ordering in smectic membranes is presented.

01 Sep 1993
TL;DR: The goal of this project was to support the scientific analysis of multi-spectral astrophysical data by means of scientific visualization, and the software system STAR (Scientific Toolkit for Astrophysical Research) was developed during the course of the project to better understand the pragmatic concerns raised in the project.
Abstract: The goal of this project was to support the scientific analysis of multi-spectral astrophysical data by means of scientific visualization. Scientific visualization offers its greatest value if it is not used as a method separate or alternative to other data analysis methods but rather in addition to these methods. Together with quantitative analysis of data, such as offered by statistical analysis, image or signal processing, visualization attempts to explore all information inherent in astrophysical data in the most effective way. Data visualization is one aspect of data analysis. Our taxonomy as developed in Section 2 includes identification and access to existing information, preprocessing and quantitative analysis of data, visual representation and the user interface as major components to the software environment of astrophysical data analysis. In pursuing our goal to provide methods and tools for scientific visualization of multi-spectral astrophysical data, we therefore looked at scientific data analysis as one whole process, adding visualization tools to an already existing environment and integrating the various components that define a scientific data analysis environment. As long as the software development process of each component is separate from all other components, users of data analysis software are constantly interrupted in their scientific work in order to convert from one data format to another, or to move from one storage medium to another, or to switch from one user interface to another. We also took an in-depth look at scientific visualization and its underlying concepts, current visualization systems, their contributions and their shortcomings. The role of data visualization is to stimulate mental processes different from quantitative data analysis, such as the perception of spatial relationships or the discovery of patterns or anomalies while browsing through large data sets. Visualization often leads to an intuitive understanding of the meaning of data values and their relationships by sacrificing accuracy in interpreting the data values. In order to be accurate in the interpretation, data values need to be measured, computed on, and compared to theoretical or empirical models (quantitative analysis). If visualization software hampers quantitative analysis (which happens with some commercial visualization products), its use is greatly diminished for astrophysical data analysis. The software system STAR (Scientific Toolkit for Astrophysical Research) was developed as a prototype during the course of the project to better understand the pragmatic concerns raised in the project. STAR led to a better understanding on the importance of collaboration between astrophysicists and computer scientists. Twenty-one examples of the use of visualization for astrophysical data are included with this report. Sixteen publications related to efforts performed during or initiated through work on this project are listed at the end of this report.

Book ChapterDOI
25 Feb 1993
TL;DR: A lower bound on the time required by the ROBUST PRAM to compute Boolean functions in terms of the number of different values each memory cell of the PRAM can contain and the degree of the function when expressed as a polynomial over a finite field is proved.
Abstract: The ROBUST PRAM is a concurrent-read concurrent-write (CRCW) parallel random access machine in which any value might appear in a memory cell as a result of a write conflict. This paper addresses the question of whether a PRAM with such a weak form of write conflict resolution can compute functions faster than the concurrent-read exclusive-write (CREW) PRAM. We prove a lower bound on the time required by the ROBUST PRAM to compute Boolean functions in terms of the number of different values each memory cell of the PRAM can contain and the degree of the function when expressed as a polynomial over a finite field. In the case of 1-bit memory cells, our lower bound for the problem of computing the OR of n Boolean variables exactly matches Cook, Dwork, and Reischuk's upper bound on the CREW PRAM. We extend our result to obtain a lower bound, depending on the number of processors, for computing Boolean functions on the ROBUST PRAM, even with memory cells of unbounded size. A particular consequence is that the ROBUST PRAM with 2 O( log n) processors requires 0(log n) steps to compute OR. These results are obtained by defining a class of CRCW PRAMs, the fixed adversary PRAMs, all of which are at least as powerful as the ROBUST PRAM. We prove our lower bounds using carefully chosen PRAMs from this class. We also show the limitations of this technique by describing how, with n-bit memory cells, any fixed adversary PRAM can compute OR and, more generally, simulate a PRIORITY PRAM in constant time. Finally, we consider the effect of adding randomization to the ROBUST PRAM. For any algorithm that computes OR without error, its expected running time on its worst input is no better than the worst case deterministic time complexity of computing OR. However, allowing a small probability of error enables the ROBUST PRAM with single bit memory cells to compute OR in almost constant time. ] 1996 Academic Press, Inc.

Journal ArticleDOI
TL;DR: In this paper, the magnetic circular dichroism of the absorption (MCDA) and optically detected electron paramagnetic resonance (EPR) of a vandium impurity in 6H-silicon carbide were measured.

Journal ArticleDOI
TL;DR: In this article, the equations of caustics for dynamically extending curvilinear interface cracks are derived where optical isotropy and anisotropy of the material have been considered, respectively.

Journal ArticleDOI
TL;DR: Evidence is given to identify this As antisite-related defect with an anti-structure-pair in GaAs electron irradiated at room temperature using optically detected electron-nuclear double resonance (ODENDOR).
Abstract: The microscopic structure of a paramagnetic arsenic antisite-related defect in GaAs electron irradiated at room temperature has been studied using optically detected electron-nuclear double resonance (ODENDOR). In addition to the ODENDOR lines of the nearest and next-nearest As ligands those of a Ga atom have been observed. The analysis of the Ga ODENDOR lines gives evidence to identify this As antisite-related defect with an anti-structure-pair ${\mathrm{As}}_{\mathrm{Ga}\mathrm{\ensuremath{-}}}$${\mathrm{Ga}}_{\mathrm{As}}$, where the ${\mathrm{Ga}}_{\mathrm{As}}$ is diamagnetic and located in the next-nearest As shell of the As antisite.