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  • American Geophysical Union  (41)
  • American Institute of Physics (AIP)  (41)
  • 2020-2023  (6)
  • 1990-1994  (76)
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4357-4361 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An ellipsometric study of ambient-reaction-produced BaCO3 overlayer growth on laser-ablated YBa2Cu3O7−x is presented as a function of time. The effects of the anisotropy of YBa2Cu3O7−x on the ellipsometric data inversion process are discussed, and it is concluded that with certain restrictions on the data acquisition method, the anisotropic substrate can be adequately modeled by its isotropic pseudodielectric function for the purpose of overlayer thickness estimation. It is found that after an initial period of rapid growth attributed to the chemical reaction of the exposed surface bonds, the BaCO3 overlayer growth is linear at 1–2 A(ring) per day. This slow growth rate is attributed to the complexity of the BaCO3 forming reaction, together with the need for ambient reactants to diffuse through the overlayer.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6734-6736 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fe2N particles were prepared by nitriding acicular γ-Fe2O3 particles (precoated with sodium silicate to prevent the particles from sintering) at about 450 °C for 3–6 h under a mixed stream of H2-NH3 (1:4 molar ratio). X-ray diffraction showed mostly Fe4N and small amounts of α-Fe and Fe2O3, but no Fe8N(α‘-Fe16N2). The saturation magnetic moment density σS increased to 140–160 emu/g and the coercivity Hc increased to about 1000 Oe. Although the ultimate goal of preparing Fe8N particles was not attained, an impressive combination of magnetization and coercivity was achieved. To obtain Fe8N by chemical doping, the nitrogen content of Fe4N was decreased by coating with metal hydroxides of Ti, Nd, and Sm, and reducing under H2 at 300 °C: the magnetization dropped precipitously, and no Fe8N was formed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5226-5232 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Submonolayer coverages of Au on GaAs(001) substrates prepared by various ex situ chemical cleaning procedures using low-energy ion scattering techniques are investigated. This research is compared with previous results for 1 ML of Au deposited on Si(111). A comparison of the energy spectra showed substantial broadening in the Li+ backscattering ion peak from Au deposited on GaAs, as compared to the Au on Si. Li+ impact collision ion scattering spectroscopy (ICISS) results showed that the gold formed an ordered overlayer above the Si surface, which was thermally stable to 500 °C. Even for depositions on room-temperature GaAs(001), shadowing of Au by substrate atoms at low scattering angles showed that Au penetrated below the GaAs surface. The estimate of the average penetration depth into the room-temperature substrate is two to three atomic planes of the GaAs crystal. An ICISS experiment showed that the Au atoms sampled by the ion beam were not ordered on lattice sites, but appeared to occupy multiple and/or random positions within the substrate. Upon annealing to 300 °C, the gold atoms were more ordered, but did not penetrate significantly further into the GaAs. At higher annealing temperatures, the Au either diffused further into the substrate or became incorporated in islands, and occupied favored subsurface sites.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2313-2321 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Room-temperature measurements of linear and nonlinear photoconductivity in CaF2 containing trace amounts of yttrium, lanthanum, and several rare earths are reported and discussed. Linear spectral photoconductivity scans taken over the 1.55- to 6.20-eV range of photon energies produced significant photocurrents above 3 eV. The results are explained in terms of a combination of 4f-5d absorption in Ce+3 and Pr+3 and photoionization of interstitial F− in both nearest-neighbor charge-compensating defects and anion-Frenkel defects. Peak photocurrents induced by focused 950-ns-wide pulses from a 496.5-nm wavelength dye laser increased nonlinearly with increasing laser pulse energy. These results are interpreted as a transition from two-photon conductivity to electron avalanche and the asymptotic approach to the material's laser damage threshold at approximately 27 GW/cm2.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6016-6016 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: State-of-the-art theoretical and numerical techniques required to simulate the head-disk interface (HDI) of future magnetic storage devices is presented. The severity of operating conditions (i.e., attempts to achieve flying heights as low as 40 nm) pose several challenges. Large transient pressure gradients can be established within air bearing leading to numerical oscillations as well as to increased program execution times. Enhanced gaseous rarefaction effects must also be incorporated into the analysis. In the present study, accurate nonoscillatory air bearing pressure distributions were obtained using a high resolution finite element algorithm to solve the generalized Reynolds equation. Higher order gaseous rarefaction effects are incorporated into generalized Reynolds equations using the total mass flow rate coefficient predicted from the linearized Boltzmann equation. The form of the generalized Reynolds equation that is presented in this paper is an improved version of the continued fraction approximation previously proposed by Crone et al.1 A simple scaling analysis, which is based upon the results of the linearized Boltzmann equation, will also be presented to study the effect of slider miniaturization, as well as to obtain a novel interpretation of accelerated wear and accelerated flyability test results.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 8-13 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 3-methyl-4-nitropyridine-1-oxide is an organic material presenting high optical nonlinear behavior especially for second-harmonic generation. Single crystals are obtained by spontaneous nucleation and grown by slow cooling in tetramethoxysilane gel. Coupled phase-matched second-harmonic generation and x-ray topography experiments allow one to relate nonlinear optical performance to crystalline quality.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 9239-9240 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 8568-8577 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Solutions of polystyrene in toluene in the concentration range 0.1–1.0 g/ml have been examined using polarized Rayleigh–Brillouin scattering and dynamic light scattering. The purpose was to extend measurements to the hitherto little studied interval between semidilute solutions and the bulk polymer. The Brillouin shift increases monotonically with polymer volume fraction (Φp) and a linewidth maximum is observed at about Φp=0.6. Up to Φp=0.56, a single cooperative diffusion mode is found, which passes through a broad maximum at Φp=0.5. For the sample with Φp=0.78, the nature of the main component depends sensitively on temperature. At 17 °C it is purely relaxational (q independent), while at 40 and 50 °C, it is diffusive. At intermediate temperatures, mixed behavior is noted where the dynamic processes overlap because the slower relaxational mode has a stronger temperature dependence. At Φp=0.89, the correlation functions are highly nonexponential and strongly temperature dependent. The bimodal correlation function contains contributions from both concentration fluctuations due to cooperative diffusion and density fluctuations arising from segmental motions in the polymer.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 6644-6659 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We compute energy levels and wave functions of Ne, Ar, Kr, and Xe trimers, modeled by pairwise Lennard-Jones potentials, using the discrete variable representation (DVR) and the successive diagonalization-truncation method. For the Ne and Ar trimers, we find that almost all of the energy levels lie above the energy required classically to achieve a collinear configuration. For the Kr and Xe trimers, we are able to determine a number of energy levels both below the classical transition energy as well as above it. Energy level statistics for these heavier clusters reveal behavior that correlates well with classical chaotic behavior that has previously been observed above the transition energy. The eigenfunctions of these clusters show a wide variety of behavior ranging from very regular behavior for low lying eigenstates to a combination of regular and irregular behavior at energies above the transition energy. These results, along with quantum Monte Carlo calculations of the ground states for a variety of small clusters, lead to the construction of a local mode model for the eigenstates of these clusters. This simple model reproduces quite well many of the calculated energy levels. From the findings here, a simple picture emerges for quantum mechanical clusters of Ne, Ar, Kr, and Xe that correlates very strongly to classical models of these systems.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6800-6803 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An analytic expression is derived for the interfacial profile of a liquid–vapor or a liquid–liquid phase equilibrium by assuming, in accord with current ideas, that the equilibrium interface consists of an intrinsic interface of the nonclassical van der Waals type broadened by capillary wave fluctuations. It is shown that in two dimensions of space, the interfacial thickness exhibits a crossover with change of critical exponent from capillary wave behavior at low and near-critical temperatures, to van der Waals behavior at temperatures very close to the critical temperature. The location of the crossover temperature is determined by the ratio of the critical amplitudes of the root-mean squared interfacial thickness and the bulk correlation length. From available experimental data and theory, an estimate of the order of magnitude of the critical amplitude ratio is made, from which the crossover is found to occur in the temperature range 3×10−4 K〈(Tc−T)〈0.3 K. In the currently accessible temperature range, the capillary wave prediction prevails, in contrast to the case of three-dimensional systems.
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