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  • 1
    Electronic Resource
    Electronic Resource
    Geometric phases in dissipative systems (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 1 (1991), S. 455-461 
    Details
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that a phenomenon analogous to the geometric phase shifts of Berry and Hannay occurs for dissipative oscillatory systems and can be detected in numerical simulations of chemical oscillators. The approach herein to the theory of geometric phases begins with a study of simple first-order differential equations on the circle (circle dynamics). It is shown how more complicated systems exhibit geometric phases through reduction to a circle dynamics. In this way, the various manifestations of the phenomenon are seen from a single unified perspective. The results are illustrated in numerical experiments on several model systems ranging from analytically solvable, but contrived, to realistic models of chemical oscillators.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.165855
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  • 2
    Electronic Resource
    Electronic Resource
    An analysis of RNG-based turbulence models for homogeneous shear flow (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2278-2281 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.857963
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  • 3
    Electronic Resource
    Electronic Resource
    Optical and magneto-optical constants of Pr substituted TbFeCo films : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 7087-7089 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optimization of tri- or quadrilayer magneto-optic recording media requires knowledge of the optical and/or magneto-optical constants for all of the individual active or passive layers that together comprise the complete disk structure. The optical (n+ik) and first-order magneto-optical (Q1+iQ2) constants for two series (i) (Tb23Fe72.5Co4.5)100−xPrx, (ii) (Tb27Fe65Co8)100−xPrx of Pr substituted TbFeCo films, for which x varies between 0 and 30, have been determined by a combination of ellipsometry and Kerr polarimetry. Ellipsometry has also been used to determine independently the optical constants of the optimized SiN passivation layers developed to protect these samples. Using constants determined experimentally on thick samples, the variation of the polar Kerr rotation and ellipticity as a function of magnetic film thickness has been calculated for light incident from both the air and substrate side of a typical trilayer magneto-optic disk structure in which material from the above series, the magnetic and thermomagnetic properties of which have been previously reported [Carey et al., J. Magn. Magn. Mater. (to be published)], forms the active storage layer. The agreement obtained with measurements demonstrates the self-consistency of the modeling process and the validity of the determined constants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356737
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  • 4
    Electronic Resource
    Electronic Resource
    Compositional dependence of the structural and magnetic properties of PtMnSb films : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 7081-7083 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nonstoichiometric, Pt deficient, PtMnSb films have been investigated for evidence of the increase in coercivity suggested by the work of Marinero [Appl. Surf. Sci. 43, 117 (1989)]. Structural, magnetic, and magneto-optic properties of thin PtMnSb films of different compositions annealed in under 30 s using a rapid thermal processing (RTP) system [Carey et al., IEEE Meeting on Current Topics in Applied Magnetism, Keele University, 4 November 1992 (unpublished), Paper 15; J. Magn. Soc. Jpn. 17, 290 (1993)], have been determined. It is shown that the crystalline texture of the films can be controlled by adjustments in composition and RTP time and that Pt deficiency produces increases in coercivity. The production of coercivity does not correlate with the marked changes in texture but appears to be associated with the development of MnSb phases within the PtMnSb microstructure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356735
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  • 5
    Electronic Resource
    Electronic Resource
    The magnetic and magneto-optical properties of Co, Cr, Mn, and Ni substituted barium ferrite films : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6789-6791 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356831
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  • 6
    Electronic Resource
    Electronic Resource
    Self-similar supersonic variable-density shear layers in binary systems (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 662-673 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Some characteristic features of supersonic/supersonic, laminar, variable-density shear layers are studied by examining the self-similar behavior of five nitrogen/hydrogen streams. With the Levy–Lees transformation, the flow-field variables, which include the transverse velocity and dilatation, are obtained through the solution of the coupled set of nonlinear conservation equations. The issue of the appropriate "third boundary condition,'' first given for the supersonic/supersonic case by Ting [J. Math. Phys. 28, 153 (1959)], is addressed and implemented in the present formulation. Expressions for the thermal conductivity, viscosity, specific heat, and binary diffusion coefficients of an arbitrary mixture are utilized so that the Prandtl and Lewis numbers and the Chapman–Rubesin parameter can vary freely across the shear layer. In the particular cases considered, these three quantities varied by factors of approximately 3, 7, and 22, respectively. The region of high vorticity moves toward the less-dense hydrogen stream for large density ratios (∼9:1), and becomes nearly decoupled from the density profile. Because the vorticity is responsible for the kinematic mixing of the two streams, this mixing of the two laminar streams is likely to be inhibited. Even though laminar flows are considered here, this effect is consistent with the experimental observation that as density ratios become very large, further increases in the density ratio have no effect on the turbulent shear layer growth rate. The density and hydrogen mass-fraction profiles are quite elongated in the transverse direction. An increase in the velocity ratio exaggerates both of these effects. Results obtained in this work are compatible with earlier work on incompressible, variable-density flows; more importantly, these results qualitatively resemble those from experiments of compressible and incompressible turbulent flows.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868306
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  • 7
    Electronic Resource
    Electronic Resource
    Inhibition of corneal epithelial cell migration by cadmium and mercury (1991)
    Springer
    Bulletin of environmental contamination and toxicology 46 (1991), S. 230-236 
    Details
    ISSN: 1432-0800
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01691942
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  • 8
    Electronic Resource
    Electronic Resource
    Pito Rift: How a large-offset rift propagates (1991)
    Springer
    Marine geophysical researches 13 (1991), S. 287-309 
    Details
    ISSN: 1573-0581
    Keywords: SeaMARC II ; side-scan ; bathymetry ; magnetics microplates ; rift propagation ; East Pacific Rise
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The Pito Rift area is the site of actively deforming oceanic lithosphere that has been primarily under extension for at least the past million years, based on kinematic reconstructions. The major morphologic features, Pito Deep and Pito Seamount, are aligned toward the Euler pole for relative motion between the Easter and Nazca plates. SeaMARC II side-scan and bathymetry data indicate that there are two general modes of faulting currently active in the Pito Rift area. One is associated with incipient rifting of old (∼3 Ma) Nazca lithosphere by large NW-SE normal faults, and the other is associated with a broad area of right-lateral transform shear between the Nazca and Easter plates. This transform shear is distributed over a broad region because of the northward growth of the East Rift and parallel tectonic rifting within the Pito Rift area. The majority of the Pito Rift area is composed of preexisting blocks of Nazca plate that are back-tilted away from Pito Deep and strike perpendicular to present and previous relative plate motions. This observation suggests that block-faulting and back-tilting are the primary mechanisms responsible for the distributed lithospheric extension, in agreement with gravity and magnetic analyses (Martinez et al., this issue). The only recent volcanic flows observed in side-scan data are from the Pito Seamount area and to the outside of the outer pseudofault of the East Rift. The significance of the young flows near the outer pseudofault is not understood. We interpret the flows extending northwest from the Pito Seamount as representing a newly formed seafloor spreading axis within the Pito Rift area. Gravity and magnetic analyses (Martinez et al., this issue) together with SeaMARC II bathymetry and side-scan data support this interpretation. Based on the tectonic evolution of the Easter microplate, we propose an evolutionary model for the formation of the Pito Rift area, where new ‘tectonic’ grabens form immediately west of the previous graben and with slightly more counterclockwise orientation. The duration and history of tectonic activity for each graben are not well constrained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366280
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  • 9
    Electronic Resource
    Electronic Resource
    Three-dimensional SeaMARC II, gravity, and magnetics study of large-offset rift propagation at the Pito Rift, Easter microplate (1991)
    Springer
    Marine geophysical researches 13 (1991), S. 255-285 
    Details
    ISSN: 1573-0581
    Keywords: Magnetic inversion ; Bouguer anomalies ; block faulting ; modelling ; microplate ; rift propagation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We present results from a SeaMARC II bathymetry, gravity, and magnetics survey of the northern end of the large-offset propagating East Rift of the Easter microplate. The East Rift is offset by more than 300 km from the East Pacific Rise and its northern end has rifted into approximately 3 Ma lithosphere of the Nazca Plate forming a broad (70–100 km) zone of high (up to 4 km) relief referred to as the Pito Rift. This region appears to have undergone distributed and asymmetric extension that has been primarily accommodated tectonically, by block faulting and tilting, and to a lesser degree by seafloor spreading on a more recently developed magmatic accretionary axis. The larger fault blocks have dimensions of 10–15 km and have up to several km of throw between adjacent blocks suggesting that isostatic adjustments occur on the scale of the individual blocks. Three-dimensional terrain corrected Bouguer anomalies, a three-dimensional magnetic inversion, and SeaMARC II backscatter data locate the recently developed magmatic axis in an asymmetric position in the western part of the rift. The zone of magmatic accretion is characterized by an axis of negative Bouguer gravity anomalies, a band of positive magnetizations, and a high amplitude magnetization zone locating its tip approximately 10 km south of the Pito Deep, the deepest point in the rift area. Positive Bouguer gravity anomalies and negative magnetizations characterize the faulted area to the east of the spreading axis supporting the interpretation that this area consists primarily of pre-existing Nazca plate that has been block faulted and stretched, and that no substantial new accretion has occurred there. The wide zone of deformation in the Pito Rift area and the changing trend of the fault blocks from nearly N-S in the east to NW-SE in the west may be a result of the rapidly changing kinematics of the Easter microplate and/or may result from ridge-transform like shear stresses developed at the termination of the East Rift against the Nazca plate. The broad zone of deformation developed at the Pito Rift and its apparent continuation some distance south along the East Rift has important implications for microplate mechanics and kinematic reconstructions since it suggests that initial microplate boundaries may consist in part of broad zones of deformation characterized by the formation of lithospheric scale fault blocks, and that what appear to be pseudofaults may actually be the outer boundaries of tectonized zones enclosing significant amounts of stretched pre-existing lithosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366279
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  • 10
    Electronic Resource
    Electronic Resource
    Binding by temporal structure in multiple feature domains of an oscillatory neuronal network (1994)
    Springer
    Biological cybernetics 70 (1994), S. 397-405 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract. An important step in visual processing is the segregation of objects in a visual scene from one another and from the embedding background. According to current theories of visual neuroscience, the different features of a particular object are represented by cells which are spatially distributed across multiple visual areas in the brain. The segregation of an object therefore requires the unique identification and integration of the pertaining cells which have to be “bound” into one assembly coding for the object in question. Several authors have suggested that such a binding of cells could be achieved by the selective synchronization of temporally structured responses of the neurons activated by features of the same stimulus. This concept has recently gained support by the observation of stimulus-dependent oscillatory activity in the visual system of the cat, pigeon and monkey. Furthermore, experimental evidence has been found for the formation and segregation of synchronously active cell assemblies representing different stimuli in the visual field. In this study, we investigate temporally structured activity in networks with single and multiple feature domains. As a first step, we examine the formation and segregation of cell assemblies by synchronizing and desynchronizing connections within a single feature module. We then demonstrate that distributed assemblies can be appropriately bound in a network comprising three modules selective for stimulus disparity, orientation and colour, respectively. In this context, we address the principal problem of segregating assemblies representing spatially overlapping stimuli in a distributed architecture. Using synchronizing as well as desynchronizing mechanisms, our simulations demonstrate that the binding problem can be solved by temporally correlated responses of cells which are distributed across multiple feature modules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004220050043
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