335 research outputs found
Errata: First-Principles Theoretical Explanation of Incommensurate Behavior in Rb\u3csub\u3e2\u3c/sub\u3eZnC\u3csub\u3e4\u3c/sub\u3e
Figures 2(a) and 2(b) of this paper have been inadvertently interchanged; thus, the caption for Fig. 2(a) relates to Fig. 2(b) and the caption for Fig. 2(b) relates to Fig. 2(a)
Errata: First-Principles Theoretical Explanation of Incommensurate Behavior in Rb\u3csub\u3e2\u3c/sub\u3eZnC\u3csub\u3e4\u3c/sub\u3e
Figures 2(a) and 2(b) of this paper have been inadvertently interchanged; thus, the caption for Fig. 2(a) relates to Fig. 2(b) and the caption for Fig. 2(b) relates to Fig. 2(a)
Reconstruction of subgrid scale topographic variability and its effect upon the spatial structure of three dimensional river flow
A new approach to describing the associated topography at different scales in computational fluid dynamic applications to gravel bed rivers was developed. Surveyed topographic data were interpolated, using geostatistical methods, into different spatial discretizations, and grain-size data were used with fractal methods to reconstruct the microtopography at scales finer than the measurement (subgrid) scale. The combination of both scales of topography was then used to construct the spatial discretization of a three-dimensional finite volume Computational Fluid Dynamics (CFD) scheme where the topography was included using a mass flux scaling approach. The method was applied and tested on a 15 m stretch of Solfatara Creek, Wyoming, United States, using spatially distributed elevation and grain-size data. Model runs were undertaken for each topography using a steady state solution. This paper evaluates the impact of the model spatial discretization and additional reconstructed-variability upon the spatial structure of predicted three-dimensional flow. The paper shows how microtopography modifies the spatial structure of predicted flow at scales finer than measurement scale in terms of variability whereas the characteristic scale of predicted flow is determined by the CFD scale. Changes in microtopography modify the predicted mean velocity value by 3.6% for a mesh resolution of 5 cm whereas a change in the computational scale modifies model results by 60%. The paper also points out how the spatial variability of predicted velocities is determined by the topographic complexity at different scales of the input topographic model
What do young athletes implicitly understand about psychological skills?
One reason sport psychologists teach psychological skills is to enhance performance in sport; but the value of psychological skills for young athletes is questionable because of the qualitative and quantitative differences between children and adults in their understanding of abstract concepts such as mental skills. To teach these skills effectively to young athletes, sport psychologists need to appreciate what young athletes implicitly understand about such skills because maturational (e.g., cognitive, social) and environmental (e.g., coaches) factors can influence the progressive development of children and youth. In the present qualitative study, we explored young athletes’ (aged 10–15 years) understanding of four basic psychological skills: goal setting, mental imagery, self-talk, and relaxation. Young athletes (n = 118: 75 males and 43 females) completed an open-ended questionnaire to report their understanding of these four basic psychological skills. Compared with the older youth athletes, the younger youth athletes were less able to explain the meaning of each psychological skill. Goal setting and mental imagery were better understood than self-talk and relaxation. Based on these findings, sport psychologists should consider adapting interventions and psychoeducational programs to match young athletes’ age and developmental level
Resonant Impurity Scattering in a Strongly Correlated Electron Model
Scattering by a single impurity introduced in a strongly correlated
electronic system is studied by exact diagonalization of small clusters. It is
shown that an inert site which is spinless and unable to accomodate holes can
give rise to strong resonant scattering. A calculation of the local density of
state reveals that, for increasing antiferromagnetic exchange coupling, d, s
and p-wave symmetry bound states in which a mobile hole is trapped by the
impurity potential induced by a local distortion of the antiferromagnetic
background successively pull out from the continuum.Comment: 10 pages, 4 figures available on request, report LPQTH-93-2
Absolute values of the London penetration depth in YBa2Cu3O6+y measured by zero field ESR spectroscopy on Gd doped single crystals
Zero-field electron spin resonance (ESR) of dilute Gd ions substituted for Y
in the cuprate superconductor YBaCuO is used as a novel
technique for measuring the absolute value of the low temperature magnetic
penetration depth . The Gd ESR spectrum of samples with
substitution was obtained with a broadband microwave technique
that measures power absorption bolometrically from 0.5 GHz to 21 GHz. This ESR
spectrum is determined by the crystal field that lifts the level degeneracy of
the spin 7/2 Gd ion and details of this spectrum provide information
concerning oxygen ordering in the samples. The magnetic penetration depth is
obtained by relating the number of Gd ions exposed to the microwave magnetic
field to the frequency-integrated intensity of the observed ESR transitions.
This technique has allowed us to determine precise values of for
screening currents flowing in the three crystallographic orientations (, and ) in samples of GdYBaCuO of three different oxygen contents ( K), ( K) and
( K). The in-plane values are found to depart substantially from the
widely reported relation .Comment: 14 pages, 12 figures; version to appear in PR
Distinguishing d-wave from highly anisotropic s-wave superconductors
Systematic impurity doping in the Cu-O plane of the hole-doped cuprate
superconductors may allow one to decide between unconvention al ("d-wave") and
anisotropic conventional ("s-wave") states as possible candidates for the order
parameter in these materials. We show that potential scattering of any strength
always increases the gap minima of such s-wave states, leading to activated
behavior in temperature with characteristic impurity concentration dependence
in observable quantities such as the penetration depth. A magnetic component to
the scattering may destroy the energy gap and give rise to conventional gapless
behavior, or lead to a nonmonotonic dependence of the gap on impurity
concentration. We discuss how experiments constrain this analysis.Comment: 5 page
Perspectives on the clonal persistence of presumed ‘ghost’ genomes in unisexual or allopolyploid taxa arising via hybridization
Although hybridization between non-sibling species rarely results in viable or fertile offspring, it occasionally produces self-perpetuating or sexually-parasitic lineages in which ancestral genomes are inherited clonally and thus may persist as 'ghost species' after ancestor extinction. Ghost species have been detected in animals and plants, for polyploid and diploid organisms, and across clonal, semi-clonal, and even sexual reproductive modes. Here we use a detailed investigation of the evolutionary and taxonomic status of a newly-discovered, putative ghost lineage (HX) in the fish genus Hypseleotris to provide perspectives on several important issues not previously explored by other studies on ghost species, but relevant to ongoing discussions about their detection, conservation, and artificial re-creation. Our comprehensive genetic (allozymes, mtDNA) and genomic (SNPs) datasets successfully identified a threatened sexual population of HX in one tiny portion of the extensive distribution displayed by two hemi-clonal HX-containing lineages. We also discuss what confidence should be placed on any assertion that an ancestral species is actually extinct, and how to assess whether any putative sexual ancestor represents a pure remnant, as shown here, or a naturally-occurring resurrection via the crossing of compatible clones or hemi-clones.P. J. Unmack, M. Adams, J. Bylemans, C. M. Hardy, M. P . Hammer, A. George
Recent developments in unconventional superconductivity theory
The review of recent developments in the unconventional superconductivity
theory is given. In the fist part I consider the physical origin of the Kerr
rotation polarization of light reflected from the surface of superconducting
. Then the comparison of magneto-optical responses in
superconductors with orbital and spin spontaneous magnetization is presented.
The latter result is applied to the estimation of the magneto-optical
properties of neutral superfluids with spontaneous magnetization. The second
part is devoted to the natural optical activity or gyrotropy properties of
noncentrosymmetric metals in their normal and superconducting states. The
temperature behavior of the gyrotropy coefficient is compared with the
temperature behavior of paramagnetic susceptibility determining the noticeable
increase of the paramagnetic limiting field in noncentrosymmetric
superconductors. In the last chapter I describe the order parameter and the
symmetry of superconducting state in the itinerant ferromagnet with
orthorhombic symmetry. Finally the Josephson coupling between two adjacent
ferromagnet superconducting domains is discussed.Comment: 15 page
Statistics of Atmospheric Correlations
For a large class of quantum systems the statistical properties of their
spectrum show remarkable agreement with random matrix predictions. Recent
advances show that the scope of random matrix theory is much wider. In this
work, we show that the random matrix approach can be beneficially applied to a
completely different classical domain, namely, to the empirical correlation
matrices obtained from the analysis of the basic atmospheric parameters that
characterise the state of atmosphere. We show that the spectrum of atmospheric
correlation matrices satisfy the random matrix prescription. In particular, the
eigenmodes of the atmospheric empirical correlation matrices that have physical
significance are marked by deviations from the eigenvector distribution.Comment: 8 pages, 9 figs, revtex; To appear in Phys. Rev.
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