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  • 1
    Digitale Medien
    Digitale Medien
    Strain Tolerant Porous Silicon Nitride (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: An approach to material strain tolerance, which basically makes it possible to lower the elastic modulus while retaining strength, was experimentally confirmed using as an example a porous silicon nitride composed of oriented anisotropic grains and pores. The porous structure consisting of tightly tangled rodlike grains and anisotropic pores was obtained by using β-Si3N4 whiskers. This material exhibited a low Youngs modulus while retaining a relatively high fracture stress, even though it contained 14.4% porosity. Consequently, the strain to failure of silicon nitride was appreciably increased.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02856.x
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  • 2
    Digitale Medien
    Digitale Medien
    Deterring nuclear weapons proliferation (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Economic affairs 17 (1997), S. 0 
    Details
    ISSN: 1468-0270
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Wirtschaftswissenschaften
    Notizen: In the wake of the dissolution of the Soviet Union and the end of the Cold War, the problem of nuclear proliferation has become one of the primary issues of strategic concern The proliferation problem is an old one, but the problem today is very different from that of even a few years ago. calling for new approaches. By considering demand and supply factors, the old approaches that rely on limits on the technology or supply appear inadequate in the current situation Rather, the best approaches today are those that influence demand, making it less attractive for nations to develop nuclear weapons. The constraints on the United States that inhibit it from using its nuclear weapons to threaten new nuclear states make both nuclear deterrence and guarantees to countries not acquiring such weapons ineffectual in preventing further proliferation. The use of conventional forces to prevent proliferation or to protect threatened nations may also be politically difficult unless there are clear national interests at stake.A possible way out of this dilemma is to develop a system of conventional deterrence using precision guided munitions and other recent technological developments that have increased the accuracy of weapons delivery systems. Such a system of conventional deterrence could play an important role in making nuclear weapons of less perceived value to potentially proliferating nations and in protecting regions that these nations threaten.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/1468-0270.00051
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  • 3
    Digitale Medien
    Digitale Medien
    Auger decay of the molecular field split S 2p core excited states in HS radical (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 18-23 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Using synchrotron radiation, very high resolution electron spectra at the 2p→6a1 and 2p→3b2 resonances of H2S have been recorded. Auger transitions from molecular field split S 2p hole states of HS* fragment, created by fast dissociation of the core excited H2S, are found to reveal different partial rates depending on the symmetry of the final state. The experiments have made it possible to determine, for the first time, the molecular field splitting of the core levels in a free radical. The molecular field splitting between the 3σ1/2 and 1π3/2 ("2p3/2'') levels in the HS* fragment is found to be 90(5) meV, which significantly differs from the molecular field splitting of the "S 2p3/2'' levels in the H2S molecule. Resonant Auger decay in the molecule before dissociation is also observed. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.473035
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  • 4
    Digitale Medien
    Digitale Medien
    N-(5-Nitro-2-pyrrolidinylphenyl)trifluoroacetamide (1997)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 53 (1997), S. 492-493 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270196014679
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  • 5
    Digitale Medien
    Digitale Medien
    Isothermal Structural Evolution of SnO2 Monolithic Porous Xerogels (1997)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 30 (1997), S. 664-669 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: Monolithic samples of SnO2 xerogel were produced by careful control of the gelation and drying steps of material preparation. In these samples, small and nanoporous aggregates stick together, yielding a monolithic (nonpowdered) material. The material was analyzed by in situ small-angle X-ray scattering (SAXS) during isothermal treatment at temperatures ranging from 473 to 773 K. At 473 K, the SAXS intensity does not change significantly with time. All experimental scattering intensity functions for T 〉 473 K are composed of two wide peaks, which evolve with increasing time. Each of them was associated with one of the modes of a bimodal distribution of pore sizes corresponding to a fine (intra-aggregate) and a coarse (inter-aggregate) porosity. The SAXS intensities of the maxima of both peaks increase with increasing treatment time, while the position of their maxima, associated with an average correlation distance, decreases. The time dependences of the SAXS intensity corresponding to both families of pores qualitatively agree with those expected for a two-phase separating system exhibiting dynamic scaling properties. The time evolutions of the several moments of the structure function of samples heat treated at 773 K exhibit a good quantitative agreement with the theory of dynamic scaling for systems evolving by a coagulation mechanism. The kinetic parameters are the same for both peaks, indicating that the same mechanism is responsible for the structural evolution of both families of pores.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889897002434
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  • 6
    Digitale Medien
    Digitale Medien
    Self-diffusion in simple models: Systems with long-range jumps (1997)
    Springer
    Journal of statistical physics 87 (1997), S. 1131-1144 
    Details
    ISSN: 1572-9613
    Schlagwort(e): Self-diffusion ; long-range jumps ; diffusion constant ; meanfield limit
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We review some exact results for the motion of a tagged particle in simple models. Then, we study the density dependence of the self-diffusion coefficientD N(ρ) in lattice systems with simple symmetric exclusion in which the particles can jump, with equal rates, to a set ofN neighboring sites. We obtain positive upper and lower bounds onF N(ρ)=N{(1−ρ)−[DN(ρ)/DN(0)]}/[ρ(1−ρ)]x for ρ∈[0, 1]. Computer simulations for the square, triangular, and one-dimensional lattices suggest thatF N becomes effectively independent ofN forN≥20.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02181276
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  • 7
    Digitale Medien
    Digitale Medien
    Introduction (1997)
    Springer
    Journal of statistical physics 87 (1997), S. 975-979 
    Details
    ISSN: 1572-9613
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02181265
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  • 8
    Digitale Medien
    Digitale Medien
    Theory for diffusion-limited oscillating chemical reactions (1997)
    Springer
    Journal of statistical physics 87 (1997), S. 1165-1178 
    Details
    ISSN: 1572-9613
    Schlagwort(e): Reaction-diffusion ; lattice-gas automata ; non-detailed balance ; Hopf bifurcation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract A kinetic description of lattice-gas automaton models for reaction-diffusion systems is presented. It provides corrections to the mean-field rate equations in the diffusion-limited regime. When applied to the two-species Maginu model, the theory gives an excellent quantitative prediction of the effect of slow diffusion on the periodic oscillations of the average concentrations in a spatially homogeneous state.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02181278
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  • 9
    Digitale Medien
    Digitale Medien
    Net nitrogen mineralization and net nitrification rates in soils following deforestation for pasture across the southwestern Brazilian Amazon Basin landscape (1997)
    Springer
    Oecologia 110 (1997), S. 243-252 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Key words Brazilian Amazon  ;  Tropical forest  ; Tropical pasture  ;  Nitrification  ;  Nitrogen mineralization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Previous studies of the effect of tropical forest conversion to cattle pasture on soil N dynamics showed that rates of net N mineralization and net nitrification were lower in pastures compared with the original forest. In this study, we sought to determine the generality of these patterns by examining soil inorganic N concentrations, net mineralization and nitrification rates in 6 forests and 11 pastures 3 years old or older on ultisols and oxisols that encompassed a wide variety of soil textures and spanned a 700-km geographical range in the southwestern Brazilian Amazon Basin state of Rondônia. We sampled each site during October-November and April-May. Forest soils had higher extractable NO3 −-N and total inorganic N concentrations than pasture soils, but substantial NO3 −-N occurred in both forest and pasture soils. Rates of net N mineralization and net nitrification were higher in forest soils. Greater concentrations of soil organic matter in finer textured soils were associated with greater rates of net N mineralization and net nitrification, but this relationship was true only under native forest vegetation; rates were uniformly low in pastures, regardless of soil type or texture. Net N mineralization and net nitrification rates per unit of total soil organic matter showed no pattern across the different forest sites, suggesting that controls of net N mineralization may be broadly similar across a wide range of soil types. Similar reductions in rates of net N transformations in pastures 3 years old or older across a range of textures on these soils suggest that changes to soil N cycling caused by deforestation for pasture may be Basin-wide in extent. Lower net N mineralization and net nitrification rates in established pastures suggest that annual N losses from largely deforested landscapes may be lower than losses from the original forest. Total ecosystem N losses since deforestation are likely to depend on the balance between lower N loss rates from established pastures and the magnitude and duration of N losses that occur in the years immediately following forest clearing.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004420050157
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  • 10
    Digitale Medien
    Digitale Medien
    Parametrized variational principles in dynamics applied to the optimization of dynamic models of plates (1997)
    Springer
    Computational mechanics 20 (1997), S. 285-294 
    Details
    ISSN: 1432-0924
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract We investigate the use of Parametrized Variational Principles (PVP) in linear structural dynamics. Our main objective is to assess whether the free parameters can be used to enhance the accuracy of dynamic models on a fixed mesh. Consistent, boundary-consistent and lumped mass matrices are defined within the framework of the PVP. The accuracy provided by three different mass matrices in the computation of plate frequencies is numerically studied. A method to update the free parameters on an element by element basis to improve the dynamic model is presented. Numerical experiments that characterize that improvement for the vibration and transient-response analysis of plates are presented. These experiments suggest that such update is primarily beneficial for modes in the intermediate frequency range.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004660050251
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