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  • 1
    Electronic Resource
    Electronic Resource
    Investigation of local current flow in polycrystalline, anisotropic superconductors using finite element simulation (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 5283-5288 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A finite element program was used to calculate current distributions in superconductors, assuming a nonlinear (power-law or percolation-type) local dependence of the electrical field on current density. A bicrystal geometry, which forms the basic building block of (Bi,Pb)2Sr2Ca2Cu3Ox powder-in-tube tapes and other polycrystalline conductors, was studied. Current–voltage curves and critical currents were calculated for different geometrical and electromagnetic parameters. Bicrystals of "brick-wall" and "railway-switch" geometry were compared, and it was found that in both cases anisotropy is the dominating factor determining the overall critical current. Strong anisotropy leads to current concentration around grain boundaries, thereby reducing the critical current. Addition of a grain boundary with finite resistance does not significantly change the current distribution within the grains. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1314332
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  • 2
    Electronic Resource
    Electronic Resource
    Current transfer at superconducting Bi2Sr2CaCu2O8+δ–Ag joints (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1569-1573 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Composite reaction textured Bi2Sr2CaCu2O8+δ superconducting samples were made by partial melt processing, with aligned MgO fibers as seeding and texturing interfaces. The electric contacts were in situ processed thick silver tapes of the same width as the sample. The voltage drop at the metal–superconductor joint was measured in liquid nitrogen during continuous current ramp in self fields and applied fields. The contact resistivity and current transfer length were estimated by applying a transmission line model for current transport across the joint. The calculated and estimated transfer length, corresponding to 〉95% current transfer, occurs over only 0.75 mm of the contact in the case of a 0.125-mm-thick Ag current lead. At currents, I, below critical, IC, this approach was satisfactory. However, at higher currents nonohmic behavior is observed. The apparent contact resistance increased with increasing current, and with applied magnetic field. This contribution to the contact resistance arises from flux flow effects in the superconductor and is shown to vary nonlinearly with both increasing current and increasing applied field. Consequently the current transfer length increased progressively over the whole contact, approaching a rather uniform current distribution at about I∼12IC. The results are compared with a nonlinear finite element model of current flow in an in situ current element; the agreement of the model with experiment is good. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370929
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  • 3
    Electronic Resource
    Electronic Resource
    Preliminary stock assessment of the Patagonian toothfish longline fishery around the Falkland Islands (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 49 (1996), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: An experimental fishery for Patagonian toothfish Dissostichus eleginoides was opened in Falkland Island waters briefly in 1992 and then from April 1994. One to two longlines per vessel were usually deployed at night, mostly fishing for 12–30 h at depths between 600 and 2000 m. The characteristics of the vessel, gear, fishing activities and the data collection and analyses methods are described. An initial evaluation of the authors' current understanding of toothfish biology and population dynamics in Falkland Island waters is given. A first analysis of toothfish numbers caught in 1994 suggests that these are changing at rates faster than expected from simple demographic processes. Therefore, despite an intensive monitoring of catch and fishing effort of each vessel, it is still not possible to derive reliable estimates for the size of the toothfish population currently exploited around the Falkland Islands. Migration patterns in and out of the fishery need to be understood before a reliable assessment of the fishery can be made. These results, together with current and future lines of research, are discussed in the light of data available from other toothfish fisheries in austral waters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1996.tb06072.x
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  • 4
    Electronic Resource
    Electronic Resource
    A new thermal emission cesium primary ion source for secondary ion mass spectrometer : Proceedings of the fourth International Conference on Ion Sources (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 2414-2416 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A thermal emission cesium primary ion source for investigation of solid-state surface layers by the SIMS method is described. The characteristics of the constructed ion source are presented. The optimal values of accelerating, focusing, and stopping potentials for the primary ions focusing system are found (Va = 4500 V, Vf = 2500 V, and Vs = 2560 V, respectively). This thermal emission cesium primary ion source is used in the secondary ion mass spectrometer constructed at the Institute of Physics of the M. Curie-Skl(Slashthrough accent mark)odowska University in Lublin. To illustrate the application of the described ion source, the mass spectrum of GaAs secondary ions and the concentration profile of indium implanted into stainless steel at an energy of 150 keV and dose 5×1016 ions/cm2 are presented. The maximum concentration of In is at about 240-A(ring) depth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142947
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  • 5
    Electronic Resource
    Electronic Resource
    Theory of the structure of adsorbed block copolymers: Detailed comparison with experiment (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 2343-2353 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a numerical, self-consistent field study of adsorbed diblock copolymers in thermal solvents, with a detailed and quantitative comparison with recent experiments performed on poly(dimethylsiloxane-block-styrene) copolymer spread as a monolayer at the free surface of ethyl benzoate [M. S. Kent, L. T. Lee, B. Farnoux, and F. Rondelez, Macromolecules 25, 6240 (1992); M. S. Kent, L. T. Lee, B. J. Factor, F. Rondelez, and G. S. Smith, J. Chem. Phys. 103, 2320 (1995)]. These neutron reflectivity experiments, for the first time, independently varied both the molecular weight and surface density, and probed the size and nature of the depletion layer at the surface. In the calculations, the polymer and solvent are characterized by realistic values of the pure component densities, the Kuhn length and the Flory interaction parameter. We examine the properties of the dangling block, specifically the depletion layer, the thickness of the brush, the maximum polymer concentration and its location, and the dependence of these properties on surface density and molecular weight. We obtain very good agreement with the experiments, especially for the functional dependences, which indicate that these systems are not in the asymptotic brush limit. We also argue that this conclusion applies to many experiments, some of which were previously thought to be in the asymptotic limit. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469656
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  • 6
    Electronic Resource
    Electronic Resource
    Molecular-dynamics study of rotational alignment of NO+ drifting in helium—velocity and angular momentum distribution functions (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 10061-10068 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Collision-induced rotational alignment of NO+ ions drifting in a helium buffer gas is studied with molecular dynamics using the ab initio potential surface of S. K. Pogrebnya et al. [Int. J. Mass Spectrom. Ion Proc. 149/150, 207 (1995)], obtained via a coupled-cluster singles–doubles approximation. We examine average translational and rotational temperatures, velocity and angular momentum distributions, and the dependence of these quantities on the applied electric field. The distributions show that angular momentum is preferentially aligned perpendicular to the electric field vector. We investigate the mechanism of this alignment through a multipolar moment expansion, and propose and demonstrate the accuracy of a bi-Maxwellian analytic form for describing the angular momentum distribution. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480357
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  • 7
    Electronic Resource
    Electronic Resource
    Mobilities of NO+ drifting in helium: A molecular dynamics study (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 11383-11389 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new molecular dynamics (MD) method is introduced, and used to study NO+ ions drifting in helium under the influence of a uniform electric field. Mobilities, average values of squared velocities, and self-diffusion coefficients parallel and perpendicular to the electric field are reported for two recent ab initio potential surfaces: a coupled cluster singles–doubles with perturbative treatment of triple excitations [CCSD(T)] surface [S. K. Pogrebnya et al., Int. J. Mass Spectrom. Ion Processes 149/150, 207 (1995)] and a MP4SDTQ/6-311+G(2df,p) surface [L. A. Viehland et al., Chem. Phys. 211, 1 (1996)]. Average values of angular momentum and alignment parameters are also reported and compared. In all cases, no significant differences were found in the calculated values for the two different potential surfaces. Finally, mobility values are compared with experimental measurements [J. A. de Gouw et al., J. Chem. Phys. 105, 10398 (1996)] and good agreement is obtained for both potential surfaces. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479079
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  • 8
    Electronic Resource
    Electronic Resource
    Numerical self-consistent field study of tethered chains in aitch-theta solvent (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 9885-9892 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a numerical, self-consistent field (SCF) study of tethered polymers in aitch-theta solvent, over the range of anchoring densities found in most experiments. We examine the properties of the dangling block, including the thickness of the brush, the density profile, the depletion layer, the maximum polymer concentration and its location, and the dependence of these properties on surface density and molecular weight. In the calculations, the polymer and solvent are characterized by realistic values of the pure component densities, the statistical segment length, and the Flory interaction parameter, and we make quantitative comparison with recent experiments [M. S. Kent, G. S. Smith, J. Majewski, L. T. Lee, and S. Satija, J. Chem. Phys. 108, 5635 (1998)] and with the asymptotic analytic SCF theory. In agreement with these experiments, our results add to the growing body of evidence that many of these systems are not well described by the asymptotic theories. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476427
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  • 9
    Electronic Resource
    Electronic Resource
    Collision-induced alignment of NO+ drifting in argon: Calculated distribution functions and microscopic quadrupole alignment parameters (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 6605-6613 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics simulations of NO+ drifting in argon are presented. In this system, the ion–bath gas mass ratio is close to but less than unity, thus increasing the importance of inelastic collisions. Strong velocity–angular momentum coupling is found, and in particular the quadrupolar alignment parameter as a function of the velocity parallel with the field takes on, with decreasing velocities, values that start as negative, become positive, and subsequently decay toward negative. To the best of our knowledge, this is the first report of the decay of this alignment towards negative values at the low end of the velocity distribution. The accuracy of an approximate distribution function [R. Baranowski and M. Thachuk, Phys. Rev. A 63, 032503 (2001)] is also examined in detail. It is found to give results that are generally qualitatively correct, and for many properties, semiquantitatively correct as well. The agreement, however, is not as good as that found for systems with ion–bath gas ratios greatly exceeding unity. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1461826
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  • 10
    Electronic Resource
    Electronic Resource
    Molecular dynamics study of the collision-induced rotational alignment of N2+ drifting in helium (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 6662-6671 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The full velocity-angular momentum distribution function for gas-phase N2+ drifting in helium is calculated using a molecular dynamics method, and utilized to examine collision-induced rotational alignment in detail. These results are also compared with experimental measurements, most especially those of Anthony et al. [J. Chem. Phys. 112, 10269 (2000)] and those appearing in the preceding article [Anthony et al., J. Chem. Phys. 114, 6654 (2001)]. Both the calculations and experiments show a number of interesting features including, drift velocities which depend upon rotational state, and quadrupolar alignment parameters which change from negative at high velocities to positive at low velocities. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1354177
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