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  • 1
    ISSN: 1573-4854
    Keywords: macropore formation ; illumination ; temperature dependence ; anodic potential ; doping dependence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Applying an anodic bias on a silicon HF contact and illuminating the backside of a n-type silicon wafer allows to create macropores. The formation of “random macropores” is studied in this paper by determination of the influences of the potential, the temperature and the doping level. A statistical approach is used to evaluate the micrographs. The formation of the macroporous layer consists of two phases. Beginning with a plane surface and homogeneous dissolution of silicon, first pores occur after some time. In this nucleation phase the thickness of the homogeneously dissolved Si depends strongly on the doping level and the temperature but only weakly on the applied bias. In a second phase of stable pore growth the density of pores is investigated as a function of temperature and anodic potential. For low doped material we find a strong stabilisation influence of the deep space charge region (SCR) in the nucleation as well as in the stable pore growth phase. Thus an increased anodic bias decreases the density of pores. For highly doped silicon no stabilisation influence of the SCR is found. The pore growth is dominated by the electrochemical dissolution rate, i.e. increasing the potential increases the density of the macropores.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In Parts I to V of the present work, the formulation and finite element implementation of a non-linear stress resultant shell model are considered in detail. This paper is concerned with the extension of these results to incorporate completely general non-linear dynamic response. Of special interest here is the dynamics of very flexible shells undergoing large overall motion which conserves the total linear and angular momentum and, for the Hamiltonian case, the total energy. A main goal of this paper is the design of non-linear time-stepping algorithms, and the construction of finite element interpolations, which preserve exactly these fundamental constants of motion. It is shown that only a very special class of algorithms, namely a formulation of the mid-point rule in conservation form, exactly preserves the total linear and angular momentum. For the Hamiltonian case, a somewhat surprising result is proved: regardless of the degree of non-linearity in the stored-energy function, a generalized mid-point rule algorithm always exists which exactly conserves energy The conservation properties of a time-stepping algorithm need not, and in general will not, be preserved by the spatial discretization. Precise conditions which ensure preservation of these conservation properties are derived. A number of numerical simulations are presented which illustrate the exact conservation properties of the proposed methodology.
    Additional Material: 22 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A three-field mixed formulation in terms of displacements, stresses and an enhanced strain field is presented which encompasses, as a particular case, the classical method of incompatible modes. Within this frame-work, incompatible elements arise as particular ‘compatible’ mixed approximations of the enhanced strain field. The conditions that the stress interpolation contain piece-wise constant functions and be L2-ortho-gonal to the enhanced strain interpolation, ensure satisfaction of the patch test and allow the elimination of the stress field from the formulation. The preceding conditions are formulated in a form particularly convenient for element design. As an illustration of the methodology three new elements are developed and shown to exhibit good performance: a plane 3D elastic/plastic QUAD, an axisymmetric element and a thick plate bending QUAD. The formulation described herein is suitable for non-linear analysis.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1435-4373
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  To determine the value of ahpC promoter mutations for the rapid prediction of isoniazid resistance, this genomic region was characterized in 50 isoniazid-resistant and 12 isoniazid-sensitive Mycobacterium tuberculosis isolates. Of the resistant isolates, 12 had ahpC promoter mutations, but only one possessed both an ahpC promoter mutation and a katG codon 315 substitution, although the latter was found in the majority (54%) of the isoniazid-resistant isolates investigated. This investigation presents empirical evidence that the central portion of the ahpC promoter is the most valuable genetic locus to complement katG codon 315 characterizations in order to increase the sensitivity of molecular tests for the prediction of isoniazid resistance.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1435-4373
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To determine the value ofahpC promoter mutations for the rapid prediction of isoniazid resistance, this genomic region was characterized in 50 isoniazid-resistant and 12 isoniazid-sensitiveMycobacterium tuberculosis isolates. Of the resistant isolates, 12 hadahpC promoter mutations, but only one possessed both anahpC promoter mutation and akatG codon 315 substitution, although the latter was found in the majority (54%) of the isoniazid-resistant isolates investigated. This investigation presents empirical evidence that the central portion of theahpC promoter is the most valuable genetic locus to complementkatG codon 315 characterizations in order to increase the sensitivity of molecular tests for the prediction of isoniazid resistance.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0021-8995
    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
    Notes: The effect of stabilizers on the mechanical properties of UPVC and how these are affected by different formulations has been studied. Three stabilizers, tin mercaptide MT, lead system Pb, and Ba/Cd/Zn complex BCZ, were used. A high -intensity blender was used for dry blend compounding, and the blend was injection -molded on a Kuasy single Screw injection molding machine. A two -cavity mold was made for forming the specimens. The specimens were tested for their impact strength, fracture toughness, tensile strength, and flexural strength. Increasing MT stabilizer was shown to increase the tensile strength and to decrease fracture toughness, impact strength, and ductility; this was attributed to antiplasticization. Increasing the Pb stabilizer conferred ductility and improved fracture toughness and impact strength. It is concluded that stabilizers have a marked effect on the mechanical behavior of rigid PVC.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0021-8995
    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
    Notes: The determination of the effectiveness of lead (Pb) and mercaptotin (MT) stabilizers on the useful service life of poly(vinyl chloride) PVC in outdoor applications, necessitates testing the mechanical properties of the polymer before and after weathering, to learn its behavior in the outdoor environment. Artificial weathering was used, and four mechanical tests were carried out, namely tensile, flexure, impact, and fracture toughness tests. The Pb stabilizer system used gave better fracture toughness and impact strength after exposure. The tensile strength and modulus of elasticity of MT-stabilized specimens increased significantly after exposure, unlike Pb-stabilized specimens. Brittleness in unplastisized PVC can be attributed to a number of factors, such as unsaturation, carbonyl group concentration, stabilized concentration, crystallinity, and extent of dehydrochlorination. The tensile strength and modulus of elasticity increase in tin mercaptide stabilizers significantly with increased UV exposure, while the increase in Pb specimens is less significant. There is a continuous diminution of the percent of elongation at break in both types of Pb or MT specimens, with increased exposure. The ductility of Pb may be accounted for by PbO and Pb stearate (C17H35COO)2Pb. One of the possible causes for the brittleness of tin mercaptide stabilized specimens is antiplasticization.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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