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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 31 (1996), S. 2647-2652 
    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 Dimensional argument analysis and near-tip singular in-plane shear stress of a continuum model have been employed to derive the expression for mode II fracture toughness of brittle cellular materials. It was found that both mode I and II fracture toughnesses have the same dependence on cell size, relative density and modulus of rupture of solid cell walls, except a microstructure coefficient included in their expressions. In addition, the linear superposition principle was applied to calculate the bending moment exerted at the first unbroken cell wall for brittle cellular materials under a combined loading of uniform tensile and in-plane shear stresses. The resulting mixed-mode fracture criterion was compared to existing experimental data in PVC foams; agreement was found to be good.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 26 (1991), S. 637-647 
    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 The linear and non-linear creep of polymeric foams are analysed. Measurements of the creep of rigid polyurethane foams under constant shear indicate that their behaviour is linear at stresses up to half the shear strength; the model describes the data well.
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  • 3
    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 The different microstructure of the fibre–cement interface might result in different failure mechanisms. It is expected that improvement of strength and toughness in fibre-reinforced cementitious composites will depend on their interfacial thickness and stiffness. A three-phase model, subject to a transversely uniform tensile stress, was utilized to investigate the effect of interfacial thickness and stiffness on the stress distributions near the fibre–cement interface and the corresponding failure mechanism. The results suggest that optimum interfacial microstructure of fibre-reinforced cementitious composites can be tailored to obtain a higher strength and toughness. Optimum interfacial thickness and stiffness was evaluated for various reinforcements, including steel, carbon, glass and polypropylene fibres.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 12 (1993), S. 602-604 
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1435-1536
    Keywords: Neutron spin-echo ; relaxation dynamics ; molecular aggregates ; microemulsions ; block copolymers
    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 Neutron spin-echo (NSE) spectroscopy is a tool to close the gap between light scattering and more conventional neutron spectroscopies. It may also be viewed as an augmentation of small-angle scattering with inelastic, dynamical information. Using a microemulsion system as example for a system of molecular aggregates and a block-copolymer system forming macromolecular aggregates, it is shown what type of dynamics is observable by NSE-spectroscopy. The lamellar phase of a SDS-pentanol-water microemulsion allows for the investigation of different layer modes (undulation, peristaltic mode) the dynamics of which are determined by elastic properties of the interface layers and by the friction due to fluid flow between the layers. Platelet-like aggregates of polyethylene-polyethylenebutylene (PE-PEP) copolymers formed upon cooling a decane solution exhibit a polymeric brush of PEP-hairs on their surface. The fluctuation dynamics of this brush determined by a balance of solvent friction and entropie restoring forces has been observed by NSE spectroscopy. Besides, the direct dynamical information the NSE data allow for the separation of static scattering due to the average structure from the scattering contributions due to mobile fluctuating parts of the sample.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 2370-2377 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Stability of contacts in shallow junction devices against high current density is a reliability issue for very large scale integration technology. We have observed a strong polarity effect on failure at nickel and nickel silicide contacts on both n- and p-type Si under high stress conditions. In a pair of cathode and anode contacts the Ni/n+-Si contact pair fails at the anode, while the Ni/p+-Si pair fails at the cathode. The Ni/Ni2Si/n+-Si and Ni/Ni2Si/p+-Si were found to fail preferentially at the cathode. Microbeam Rutherford backscattering spectrometry and Auger electron spectroscopy depth profiles show that a silicide reaction occurs between Ni and Si during current stressing, especially at the failed contacts. In situ resistance data indicate that the resistance of the failed contact increases with time while that of the other contact in the pair remains constant. Transmission electron microscopy shows that the silicide formation is not uniform at the damaged contacts. A mixture of dominant epitaxial NiSi2 and a minor amount of polycrystalline NiSi2 phases was identified. We have proposed mechanisms to explain the polarity effect on failure: wear-out mechanism for the damaged positive contacts of Ni/n+-Si, electromigration enhanced silicide formation for the damaged negative contacts of Ni/Ni2Si/n+-Si and electron-hole recombination mechanism for the damaged negative contacts of Ni/p+-Si and Ni/Ni2Si/p+-Si. © 1997 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5443-5445 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the oxidation kinetics of Cu and Cu3Ge thin films in air using in situ resistivity measurement and x-ray photoelectron spectroscopy. Thin films of Cu oxidize in air around 250 °C to form CuO with an activation energy of 0.74 eV. In contrast to Cu, thin films of Cu3Ge oxidize only above 450 °C. The excellent oxidation resistance of Cu3Ge is due to the thin GeO2 layer which protects Cu3Ge from oxidation below 450 °C. Above 510 °C, GeO2 evaporates and the oxidation protection is lost. Besides the excellent oxidation resistance and low resistivity, we also found Cu3Ge to have a better adhesion to SiO2 than Cu. It has the potential to be used as an adhesion layer and passivation layer in Cu metallization. © 1995 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5981-5988 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two-dimensional simulations of amorphous silicon thin-film transistors are presented for the case when source-drain voltage is turned on long before gate voltage is turned on. Discrepancies between these results and the one-dimensional results of M. F. Willums, M. Hack, P. G. LeComber, and J. G. Shaw [MRS Symp. Proc. 258, 985 (1992)] are discussed. Valid reasons for drain current decay are provided, and occupation dynamics for the trap states are shown in order to distinguish these from the one-dimensional results of C. van Berkel, J. R. Hughes, and M. J. Powell [J. Appl. Phys. 66, 4488 (1989)] where a two-fluid model occupation function was assumed. The invalidity of such approximation is explicitly demonstrated. The mean trap-filling energy level moves up in three stages: First, the level varies with log t, then varies linearly with t, and finally, with log (log t) to a steady-state level.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 644-649 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cu3Ge films have been found to have a low resistivity, good adhesion onSiO2, good thermal stability on Si, and good oxidation resistance. It has the potential as an ideal adhesion/barrier/passivation layer for Cu ultralarge scale integration metallization. The kinetics of Cu3Ge formation and the thermal stability ofCu3Ge against Al were studied by in situ resistivity measurement, Rutherford backscattering spectrometry, and transmission electron microscopy. We found that Cu reacted with Ge in the temperature range of 100–200 °C. The activation energy of the Cu–Ge compound formation was found to be 1.1±0.1 eV. The Cu–Ge compound was identified asε-Cu3Ge from transmission electron microscope diffraction patterns. Upon annealing theε-Cu3Ge became unstable on Al at the temperature range of 300–350 °C. In the reaction between Al andCu3Ge, Cu preferentially reacted with Al to form anε-Al2Cu3 compound. The activation energy of formation of the Al–Cu compound was found to be 2.1±0.1 eV. © 1997 American Institute of Physics.
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  • 10
    ISSN: 0959-8103
    Keywords: organolithium ; anionic polymerization ; propagation reaction orders ; 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: A long held assumption in hydrocarbon based anionic polymerization involving organolithiums is that the aggregated species are unreactive and thus serve only as reservoirs from which the active singlet species momentarily emerge to participate in the initiation or propagation events. This work demonstrates that contrary to the notion of aggregate dormancy such species can participate in monomer addition. The approach involved freeze-dried vitrified polystyryllithium which was found to be reactive toward butadiene and methanol vapors. The sub-glass transition state of the polystyryllithium eliminates the establishment of the aggregate: singlet equilibrium as a result of the inability of chains to undergo diffusion. Furthermore, it is shown that the lower bound gradient for the dependence of propagation rate on active center concentration, within experimental error, is about 1/5 for the majority of those diene systems where the active center concentration covers at least two decades. A computer evaluation of the propagation rate: active center data was done with the aim of testing and determining the equilibrium constants of these aggregated systems.
    Additional Material: 13 Ill.
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