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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 1238-1243 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Ultra-short-pulse reflectometry is studied by means of the numerical integration of one- and two-dimensional full-wave equations for ordinary and extraordinary modes propagating in a plasma. The numerical calculations illustrate the use of the reflection of ultra-short-pulse microwaves as an effective probe of the density or magnetic profile in the presence of density or magnetic fluctuations in the plasma. Bragg resonance effects can be identified in the reflected signals, which give information on fluctuations. It is also demonstrated that ultra-short-pulse reflectometry can be used to perform correlation reflectometry measurements in which correlation lengths for density fluctuations are deduced from the observed cross-correlation function of phase shifts as a function of frequency. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Ultra-short-pulse reflectometry is studied by means of the numerical integration of one- and two-dimensional full-wave equations for ordinary and extraordinary modes propagating in a plasma. The numerical calculations illustrate the use of the reflection of ultra-short-pulse microwaves as an effective probe of the density or magnetic profile in the presence of density or magnetic fluctuations in the plasma. Bragg resonance effects can be identified in the reflected signals, which give information on fluctuations. It is also demonstrated that ultra-short-pulse reflectometry can be used to perform correlation reflectometry measurements in which correlation lengths for density fluctuations are deduced from the observed cross-correlation function of phase shifts as a function of frequency. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 1089-1090 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The lifetime of the lowest quasibound state localized between the barriers of a GaAs/AlGaAs double-barrier structure is calculated as a function of barrier and well dimensions. The results are consistent with high-frequency experiments.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using rapid thermal processing (RTP) we recently demonstrated the production of high quality well ordered barium ferrite films in times much shorter than those required by a conventional annealing process. Influence over the magnetic and structural properties developed in annealed samples was also achieved by variation of the RTP heating profile (R. Carey, P. A. Gago-Sandoval, D. M. Newman, and B. W. J. Thomas, presented at Intermag-93, Stockholm, April 13–16, 1993). It is known that the magneto-optic properties of barium ferrite can be enhanced by selective substitution of some of the Fe by Co2+ and Ti4+ albeit at the expense of reducing the magnetic anisotropy. A multitarget scanning cosputtering process has been used in conjunction with rapid thermal processing to produce a series of barium ferrite films in which Co, Cr, Mn, Ni are selectively introduced to substitute for between 5 and 20 at. % of the Fe. A corresponding percentage of Ti is also added to maintain charge compensation. The magnetic and magneto-optic properties of these films are presented and discussed with reference to their composition and treatment respect to the properties of barium ferrite.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4129-4137 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Neural networks provide an efficient, general interpolation method for nonlinear functions of several variables. This paper describes the use of feed-forward neural networks to model global properties of potential energy surfaces from information available at a limited number of configurations. As an initial demonstration of the method, several fits are made to data derived from an empirical potential model of CO adsorbed on Ni(111). The data are error-free and geometries are selected from uniform grids of two and three dimensions. The neural network model predicts the potential to within a few hundredths of a kcal/mole at arbitrary geometries. The accuracy and efficiency of the neural network in practical calculations are demonstrated in quantum transition state theory rate calculations for surface diffusion of CO/Ni(111) using a Monte Carlo/path integral method. The network model is much faster to evaluate than the original potential from which it is derived. As a more complex test of the method, the interaction potential of H2 with the Si(100)-2×1 surface is determined as a function of 12 degrees of freedom from energies calculated with the local density functional method at 750 geometries. The training examples are not uniformly spaced and they depend weakly on variables not included in the fit. The neural net model predicts the potential at geometries outside the training set with a mean absolute deviation of 2.1 kcal/mole. © 1995 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6513-6525 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a simple model of the signals transmitted by global positioning system (GPS) satellites and of the reception of these signals by a GPS receiver, neglecting atmospheric effects. The model idealizes the receiver and transmitter as electric dipole antennas. We derive the open-circuit voltage induced in the antenna of the receiver as a function of time, position, velocity, and orientation of the respective antenna. As an application of this model, we show that by using a single dipole antenna, a user of the GPS can compute his position, time, and two angles of attitude, by tracking the phases of the open-circuit antenna voltages for six GPS satellites.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 9834-9840 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An equilibrated model glass-forming liquid is studied by mapping successive configurations produced by molecular dynamics simulation onto a time series of inherent structures (local minima in the potential energy). Using this "inherent dynamics" approach we find direct numerical evidence for the long held view that below a crossover temperature, Tx, the liquid's dynamics can be separated into (i) vibrations around inherent structures and (ii) transitions between inherent structures [M. Goldstein, J. Chem. Phys. 51, 3728 (1969)], i.e., the dynamics become "dominated" by the potential energy landscape. In agreement with previous proposals, we find that Tx is within the vicinity of the mode-coupling critical temperature Tc. We further find that near Tx, transitions between inherent structures occur via cooperative, stringlike rearrangements of groups of particles moving distances substantially smaller than the average interparticle distance. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 385-388 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Sources producing beams of spin-polarized atoms and ions are now widely used in nuclear physics. Modern systems are increasingly expensive and complex. They provide a variety of species and beam polarizations with intensities often sufficient for experimental needs. The laboratory seeking such a device for its program must evaluate a variety of options and match them to its accelerator, experimental program, and expected resources. The major systems and techniques used are surveyed and criteria dictating the choice of source for particular experimental applications are discussed briefly.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2887-2899 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct simulations of homogeneous turbulence have, in recent years, come into widespread use for the evaluation of models for the pressure–strain correlation of turbulence. While work in this area has been beneficial, the increasingly common practice of testing the slow and rapid parts of these models separately in uniformly strained turbulent flows is shown in this paper to be unsound. For such flows, the decomposition of models for the total pressure–strain correlation into slow and rapid parts is ambiguous. Consequently, when tested in this manner, misleading conclusions can be drawn about the performance of pressure–strain models. This point is amplified by illustrative calculations of homogeneous shear flow where other pitfalls in the evaluation of models are also uncovered. More meaningful measures for testing the performance of pressure–strain models in uniformly strained turbulent flows are proposed and the implications for turbulence modeling are discussed.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2278-2281 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In a recent paper [Phys. Fluids A 2, 1678 (1990)], the authors compared the performance of a variety of turbulence models including the K-ε model and the second-order closure model derived by Yakhot and Orszag based on renormalization group (RNG) methods. The performance of these RNG models in homogeneous turbulent shear flow was found to be quite poor, apparently due to the value of the constant Cε1 in the modeled dissipation rate equation, which was substantially lower than its traditional value. However, recently a correction has been made in the RNG-based calculation of Cε1. It is shown herein that, with the new value of Cε1, the performance of the RNG K-ε model is substantially improved. On the other hand, while the predictions of the revised RNG second-order closure model are better, some lingering problems still remain that can be remedied by the addition of higher-order terms.
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