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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 29 (1994), S. 1097-1100 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Conductive silicon carbide particles were incorporated into an insulating cristobalite ceramic matrix to produce composite materials with a sizeable positive temperature coefficient (PTC) effect. A large drop in resistivity with silicon carbide content at room temperature, or percolation behaviour, was observed. The PTC effect of the composites, which resulted from the thermal expansion of the cristobalite ceramic matrix, was a maximum with five orders of magnitude for the specimen with 25 vol% silicon carbide. The PTC transition temperature of the composites was at 260 °C, which coincided exactly the reversible high-low phase inversion temperature of the cristobalite ceramic matrix.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 1994-02-01
    Print ISSN: 0022-2461
    Electronic ISSN: 1573-4803
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of mathematical biology 56 (1994), S. 323-336 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A simple chemical model of the idiotypic network of immune systems, namely the AB model, has been developed by De Boeret al. The complexity of the system, such as the steady states, periodic oscillations and chaotic motions, has been examined by the authors mentioned above. In the present paper, the periodic motions and chaotic behaviours exhibited by the system are intuitively described. To clarify in which parameter domains concerned the system exhibits periodic oscillations and in which parameter domains the system demonstrates chaotic behaviours the Lyapounov exponent is explored. To characterize the strangeness of the attractors, the fractal dimension problem is worked out.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Polymer bulletin 27 (1992), S. 607-613 
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Polysilanes containing cyclodisilazane units in the backbone were synthesized by the modified Wurtz-type coupling of available dichlorosilanes with N,N′-bis (chlorodimethylsilyl)tetramethylcyclodisilazane in the mixture of solvents. The effect of solvent additives on the polymerization process was examined. These polymers are soluble in common solvents and very easily handled by molding or casting.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Optical and quantum electronics 24 (1992), S. S1095 
    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract In this paper a statistical ensemble of laser light is defined. The lasing field is treated as a classical variable, the spontaneous emission is considered phenomenally by using a random function. Special attention is paid to the transverse mode behaviour. To calculate the ensemble elements, an approach based on Fresnel integration has been developed. Theoretical investigations into some stripe stable resonators have been carried out. Some results for the intensity, the mode spectrum, the correlation between transverse modes, the beam quality, and the spectra of the intensity and the output power fluctuation are presented and discussed.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Optical and quantum electronics 24 (1992), S. S1081 
    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Taking the modal behaviours of the laser field into account, the coherence properties of laser light can be characterized by mode coherence functions (MCFs) and mode coherence coefficients (MCCs). Changes in laser light properties due to optical operations can be described by transformation laws for the MCFs and the MCCs. The transformation laws as well as transformation matrices for propagation in free space, phase transformations, spatial amplitude modulations and aperturizing are given. Furthermore, intensity distributions and intensity moments in the spatial and in the spatial frequency domains are expressed in terms of the MCCs. General expressions for the beam quality factors,M 2s, obtained using the intensity moments and some useful expressions for intensity moments of higher order are discussed.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Optical and quantum electronics 24 (1992), S. S1119 
    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Based on average intensity distributions at two axial positions, an experimental approach to determine the mode coherence coefficients was developed. Using this approach, investigations were carried out for a CO2 laser with a stripe resonator. The power partitions of, and cross-correlations between, modes at different aperture widths and the dependence of the beam quality on the aperture width were studied. The measuring principle, an iterative fit method, and some experimental results are presented and discussed.
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  • 8
    ISSN: 1572-8862
    Keywords: Cubane-like ; double cubane-like ; Molybdenum-copper-sulphur clusters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Two novel heterometallic cubane-like and double cubane-like clusters, {MoCu3S3(S2COEt)}(O)(Ph3P)3 I and {Mo2Cu6S6(SCMe3)2}(O)2(Ph3P)4 II, were synthesized by reaction of {MoCu2S3}(O)(Ph3P)3 with CuS2COEt and CuSCMe3, respectively. ClusterI crystallized in the triclinic space group $$P\overline 1 $$ (2) witha=12.766(6) Å,b=22.904(5) Å,c=10.522(3) Å, α=99.86(2)°, β=109.68(2)°, γ=86.84(3)°,V=2854(2) Å3,Z=2,R=0.049 for 6622 observed reflections (I〉5σ(I)) and 410 variables. ClusterII crystallized in the triclinic space group $$P\overline 1 $$ (2) with dimensionsa=14.212(4) Å,b=14.725(5) Å,c=12.396(8) Å, α=110.32(4)°, β=90.40(5)°, γ=62.88(2)°,V=2129(2) Å3,Z=1,R=0.039 for 6020 observed reflections (I〉3σ(I)) and 461 variables. ClusterI consists of a neutral cubane-like molecule with the core {MoCu3S3(S2COEt)}2+, in which one corner of the cubane-like core is a novel triply bridging bidentate 1,1-dithiolato (xanthate, S2COEt−) ligand. ClusterII is a double cubane-like one, in which two cubane-like cores {MoCu3S3(SCMe3)}2+ are connected by two Cu-S bonds of the triply bridging monothiolato (SCMe 3 − ) ligand. Two different pathways of unit construction from a small heterometallic cluster {MoCu2S3}(O)(Ph3P)3 have been outlined. Comparisons of the selected bond lengths and bond angles for the cubane-like core {MoCu3S3 X} (X=Cl−, Br−, S2COEt−, SCMe 3 − ) are given. Spectroscopic properties of the title clusters are also reported.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of cluster science 5 (1994), S. 265-285 
    ISSN: 1572-8862
    Keywords: Designed synthesis ; transition metal clusters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Designed synthesis for some transition metal clusters involving bridging-sulfido ligands is reviewed. The basic concept with the use of reactive fragments as building blocks is described. It is shown that the sulfido ligands with lone-pair electrons and the unsaturated coordination sites play important roles in this rational synthesis. The relationship between the metallic coordination types of the sulfido ligands and their assembling activity in the compounds is summarized. Examples of the six kinds of “unit construction” with reactive fragments as building blocks are shown, indicating clearly that the “unit construction” is a reasonable way in the synthesis of transition metal clusters involving bridging sulfido ligands. Finally, the potential application of the “unit construction” schemes in the synthesis of transition metal clusters involving other bridging ligands is presented.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 57 (1992), S. 193-202 
    ISSN: 1436-4646
    Keywords: Steiner trees ; approximation performance ratio
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Finding a shortest network interconnecting a given set of points in a metric space is called the Steiner minimum tree problem. The Steiner ratio is the largest lower bound for the ratio between lengths of a Steiner minimum tree and a minimum spanning tree for the same set of points. In this paper, we show that in a metric space, if the Steiner ratio is less than one and finding a Steiner minimum tree for a set of size bounded by a fixed number can be performed in polynomial time, then there exists a polynomialtime heuristic for the Steiner minimum tree problem with performance ratio bigger than the Steiner ratio. It follows that in the Euclidean plane, there exists a polynomial-time heuristic for Steiner minimum trees with performance ratio bigger than $${\textstyle{1 \over 2}}\sqrt 3 $$ . This solves a long-standing open problem.
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