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  • American Institute of Physics  (16)
  • Wiley-Blackwell  (16)
  • American Ceramics Society  (4)
  • 2000-2004  (17)
  • 1990-1994  (19)
  • 1955-1959
  • 1
    Electronic Resource
    Electronic Resource
    Electrical Properties of Boron Nitride Matrix Composites: I, Analysis of McLachlan Equation and Modeling of the Conductivity of Boron Nitride–Boron Carbide and Boron Nitride–Silicon Carbide Composites (2001)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The McLachlan equation, which incorporates both effective medium models and percolation, was used to predict the volume fraction–conductivity relationships of insulator–conductor composites, and results were compared with experimental data. Two composite systems were investigated (BN–B4C and BN–SiC). Both systems are anisotropic, because of the orientation of BN platelets perpendicular to the hot-pressing direction. For BN–B4C composites, with increasing B4C content, the ac and dc conductivities are relatively constant to ∼40% B4C (the critical volume fraction). At this composition, the conductivity suddenly increases to a value closer to that of B4C and then resumes a gradual increase. Little difference is seen for measurements made perpendicular or parallel to the hot-pressing direction, i.e., perpendicular or parallel to the BN platelets. Similar results are found for the BN–SiC composites, except that the critical volume fraction is ∼20% SiC in this case. The experimental curves are in good agreement with those predicted by the McLachlan equation. The parameters s and t of the McLachlan equation relate to the morphology of the phases present in the microstructure. The critical volume fraction relates to the connectivity of the phases in the composites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00866.x
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  • 2
    Electronic Resource
    Electronic Resource
    Electrical Properties of Boron Nitride Matrix Composites: II, Dielectric Relaxations in Boron Nitride–Silicon Carbide Composites (2001)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A low-frequency Maxwell–Wagner relaxation, resulting from space-charge buildup, was observed when BN–SiC composites were subjected to an ac current. This paper discusses the Maxwell–Wagner relaxation and information that it reveals about the microstructure of the composite. A modified Maxwell–Wagner equation for the real part of the permittivity is used to model the data. SiC has a higher dielectric constant than that of BN. The microstructure of these composites is anisotropic, with BN platelets preferentially oriented perpendicular to the hot-pressing direction. Samples measured in this direction exhibit a lower dielectric constant than those measured parallel to the hot-pressing direction. In regard to frequency response, the permittivity of BN shows no dependence on frequency, whereas frequency dependence is seen with increasing SiC content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00867.x
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  • 3
    Electronic Resource
    Electronic Resource
    Volume Fraction and Whisker Orientation Dependence of the Electrical Properties of SiC-Whisker-Reinforced Mullite Composites (2001)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The electrical behavior of hot-pressed mullite composites reinforced with 10, 20, and 30% SiC whiskers (SiCw) was evaluated in the frequency range 100 Hz–10 MHz and compared with 2 GHz data as well as dc resistivity measurements. It is found that the addition of SiCw has a dramatic effect on the dielectric properties as well as the resistivity of these materials. The ac properties (dielectric constant, dielectric loss, and impedance) show a strong dependence on the volume fraction of SiC and on the orientation of the electric field with respect to the hot-pressing direction and hence the whisker orientation. The dc resistivity measurements are sensitive to the whisker volume fraction but cannot easily discriminate between those samples that were measured parallel or perpendicular to the hot-pressing direction as was possible with the ac measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb01010.x
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  • 4
    Electronic Resource
    Electronic Resource
    Electrical Properties of Boron Nitride Matrix Composites: III, Observations near the Percolation Threshold in BN–B4C Composites (2001)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In this third paper of the series, we discuss the electrical resistivity of BN–B4C composites with compositions ranging from 0% to 100% B4C. After establishing the response of samples whose compositions lie far away from the percolation region, where effective medium models apply, we focus attention on samples with compositions at or near the percolation threshold (∼60% BN–40% B4C). The large differences in electrical properties among samples with the same nominal composition can be explained by invoking a connectivity parameter. Since the difference in the electrical resistivity of BN and B4C is about 9 orders of magnitude, the degree of connectivity of the two components at the percolation threshold determines the resultant composite resistivity. Connectivity in these composites was quantified by taking BN peak height ratios in X-ray diffraction patterns of all samples containing 60% BN–40% B4C. The degree of preferred orientation of the BN platelets can be correlated with systematic increases in the electrical resistivity of the composites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb01011.x
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  • 5
    Electronic Resource
    Electronic Resource
    Preparation of [5 + 6]-, [6 + 6]-, and [6 + 7]-Bicyclic Guanidines from C,C'-Bis(iminophosphoranes) (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1641-1652 
    Details
    ISSN: 0009-2940
    Keywords: Bis(iminophosphoranes) ; Guanidines, bicyclic ; Aza Wittig reaction ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A one-pot synthesis of [5 + 6]-, [6 + 6]-, and [6 + 7]-rigid bicyclic guanidines (6, 8, 19, 21, 23) based on a bis(iminophosphorane)-mediated annulation strategy is reported. The crystal and molecular structure of the parent [5 + 6]-bicyclic guanidine 8 has been established by X-ray diffraction. The crystallographically independent molecule forms dimers through a centre of symmetry by N-H-N hydrogen bonds. The molecule, and therefore the dimer, is statistically disordered in a 65/35 ratio. A statistical study of N-H-N hydrogen bonds of this kind of dimers has been carried out by using the Cambridge Structural Database.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270916
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  • 6
    Electronic Resource
    Electronic Resource
    α,β-Unsaturated Fischer Carbene Complexes vs. 1,3-Dipoles: Reactions with Nitrones and Nitrilimines (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1773-1783 
    Details
    ISSN: 1434-193X
    Keywords: Cycloadditions ; Carbenes ; Nitrones ; Nitrilimines ; Pyrazolines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The reaction of tert-butylalkynyl chromium Fischer carbene complex 1 with nitrones 2 affords β-enamino-ketoaldehydes 4 by the light-promoted rearrangement of the corresponding [3+2] cycloadduct carbene complexes 3. On the other hand, [3+2] cycloaddition of chiral nonracemic Fischer alkenyl carbene complexes 19 with nitrilimines 10 yields enantiomerically pure Δ2-pyrazolines with high regio- and diastereoselectivity.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Broadband dielectric spectroscopy on an oxovanadium metallomesogen compoundThis work was supported by the CICYT (Spain, project MAT-91-0962-C02-02) and the EC Human Capital and Mobility Programme (ERB4050 PL922749). (1994)
    Weinheim : Wiley-Blackwell
    Advanced Materials 6 (1994), S. 941-944 
    Details
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/adma.19940061208
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  • 8
    Electronic Resource
    Electronic Resource
    Behaviour of a silica filler surface-modified with boron-amine groups (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 217 (1994), S. 107-117 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Das Verhalten von mit primären Boramingruppen modifizierten Silikat-Füllstoffen wurde unter verschiedenen Reaktionsbedingungen untersucht. Der Füllstoff mit den besten Verstärkungseigenschaften wurde eingesetzt, um zwei unterschiedliche Vulkanisationssysteme zu vergleichen: ein wirksames Vulkanisationsverfahren (EV), das nach ISO als Methode zur Untersuchung des Verstärkungsverhaltens neuer Silikate empfohlen wird, sowie ein konventionelles Verfahren. Die besten Ergebnisse werden mit Silikat erhalten, welches 3 h bei 500°C behandelt wurde; unter diesen Bedingungen werden die meisten der primären Boramingruppen fixiert. Die Eigenschaften des nach dem EV-Verfahren modifizierten Silikats ähneln denen von mit Silan modifizierten Silikaten und sind in einigen Fallen besser als jene, welche nach dem konventionellen Verfahren erhalten werden. In allen Fallen wird die verstarkende Wirkung von gefällten Silikat-Füllstoffen durch die Boraminbehandlung verbessert.
    Notes: The behaviour of silica fillers modified with primary boron-amine groups has been studied under different reaction conditions. The filler with the best reinforcing properties was used to compare two different vulcanization systems: an efficient vulcanization system, EV, which is the recommended ISO Standards method to study the reinforcing behaviour of new silicas, and a conventional vulcanization system.The results indicate that the best properties are obtained with silica treated for 3 h at 500°C, reaction conditions which fix most of the primary boron-amine groups. Using the EV system, the properties of this modified silica are similar to those of silane-modified silica, and in some cases better than those obtained with a conventional vulcanization system. In all cases, the boron-amination treatment significantly improves the behaviour of precipitated silica as a reinforcing filler.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052170111
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  • 9
    Electronic Resource
    Electronic Resource
    Targeting of aequorin for calcium monitoring in intracellular compartments (1994)
    New York : Wiley-Blackwell
    Journal of Bioluminescence and Chemiluminescence 9 (1994), S. 177-184 
    Details
    ISSN: 0884-3996
    Keywords: Photoproteins ; calcium ; organelles ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: We have recently developed a new method for monitoring Ca2+ concentrations in defined cell compartments. The cDNA encoding the Ca2+-sensitive photoprotein aequorin has been modified in order to include specific targeting sequences and expressed in eukaryotic cells; the recombinant protein, specifically located inside the cells, has allowed the direct study of mitochondrial and nuclear Ca2+ concentrations in living cells. The principles, and the application, of this new methodology are discussed in this article.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bio.1170090312
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  • 10
    Electronic Resource
    Electronic Resource
    A novel preparation route of aromatic poly(amido-imide)s (1994)
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 15 (1994), S. 95-98 
    Details
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/marc.1994.030150201
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