Evaluation of the volumetric erosion of spherical electrical contacts using the defect removal method

Volumetric erosion is regarded as a significant index for studying the erosion process of electrical switching contacts. Three-dimensional (3-D) surface measurement techniques provide an approach to investigate the geometric characteristics and volumetric erosion of electrical contacts. This paper presents a concrete data-processing procedure for evaluating volumetric erosion of spherical electrical contacts from 3-D surface measurement data using the defect removal method (DRM). The DRM outlined by McBride is an algorithm for evaluating the underlying form (prior to erosion) parameters of the surfaces with localized erosion and allowing the erosion characteristics themselves to be isolated. In this paper, a number of spherical electrical contacts that had undergone various electrical operations were measured using a 3-D surface profiler, the underlying form parameters of the eroded contacts were evaluated using the DRM, and then the volumetric erosions were isolated and calculated. The analysis of the correlations between the volumetric erosion and the number of switching cycles of electrical operation that the contacts had undergone showed a more accurate and reliable volumetric erosion evaluation using the DRM than that without using the DRM

Exploring choking experiences in elite sport: The role of self- presentation

Objectives The aims of this study were twofold: first, to examine the role of self-presentation within the lived-experience of choking in sport; and second, to explore whether the 2 × 2 framework of self-presentation (Howle, Jackson, Conroy, & Dimmock, 2015) holds the potential to further our understanding of acute sporting failure under pressurized conditions. Design and Method An empirical phenomenological research design was adopted to address the research aims. Purposefully selected participants completed phenomenological interviews, which explored in detail their experiences of choking and clutch performance under pressure. The sample consisted of 9 elite athletes (6 male and 3 female) (Mage = 27.14; SD = 5.27) from a range of sports (netball, rugby union, golf, tennis, and cricket). Results Participants reported a tendency to hold protective-agentic self-presentation motives, low self-presentation efficacy, and self-presentational concerns prior to, and during the choke. Conversely, acquisitive-agentic self-presentation motives, and self-presentation efficacy were experienced before and during clutch performances. However, alongside self-presentation, other psychological constructs also preceded and accompanied the choking experience (e.g., unfamiliarity and perceived control). Conclusion This exploratory study is the first to identify the value of examining choking in sport through the lens of the 2 × 2 self-presentation framework, with self-presentation motives appearing to influence the choking experience. Yet, it is also evident that self-presentation may not explain all choking episodes

A Quantum-Mechanical Equivalent-Photon Spectrum for Heavy-Ion Physics

In a previous paper, we calculated the fully quantum-mechanical cross section for electromagnetic excitation during peripheral heavy-ion collisions. Here, we examine the sensitivity of that cross section to the detailed structure of the projectile and target nuclei. At the transition energies relevant to nuclear physics, we find the cross section to be weakly dependent on the projectile charge radius, and to be sensitive to only the leading momentum-transfer dependence of the target transition form factors. We exploit these facts to derive a quantum-mechanical ``equivalent-photon spectrum'' valid in the long-wavelength limit. This improved spectrum includes the effects of projectile size, the finite longitudinal momentum transfer required by kinematics, and the response of the target nucleus to the off-shell photon.Comment: 19 pages, 5 figure

Can Increased Training and Awareness Take Forest Research to New Heights?

Forest canopies contribute significantly to global forest biodiversity and ecosystem functioning, yet are declining and understudied. One reason for a knowledge gap is that accessing forest canopies can be difficult and dangerous. Thus, lack of relevant canopy access skills may compromise knowledge gain and personal safety. We assessed skill levels in canopy access methods and self-perception of skills amongst ecologists worldwide via a web-based survey, available in four languages. We obtained responses from expert arborists as a control group. From 191 respondents who said canopy access is relevant to their research (of 1,070 total responses), we found that ecologists are not attaining the full potential provided by existing methods of canopy access. Specifically, most respondents are unable to access much of the forest canopy, especially areas away from the trunk and between trees. The survey further revealed the common use of unsafe and inefficient practices among ecologists and that few are adequately equipped with aerial rescue skills. Importantly, ecologists with the lowest skill levels overestimate their expertise the most. Proper field techniques are key components of good science: they can improve study design, increase potential for data collection, and ultimately reveal greater knowledge on canopy organisms and processes. By safely allowing greater access to the forest canopy, proper techniques can reduce bias in our scientific understanding of forest ecology. To facilitate safe and effective canopy access for ecological research, we recommend increasing instruction and collaboration, implementing certification programs, and conducting audits of canopy research programs. With increased access to such opportunities, ecologists will acquire improved skills in accessing forest canopies, develop a greater appreciation for the full breadth of possibilities among methods of canopy access, and more safely and effectively gather the data needed to better understand forest ecosystems

Multiband superconductivity in NbSe_2 from heat transport

The thermal conductivity of the layered s-wave superconductor NbSe_2 was measured down to T_c/100 throughout the vortex state. With increasing field, we identify two regimes: one with localized states at fields very near H_c1 and one with highly delocalized quasiparticle excitations at higher fields. The two associated length scales are most naturally explained as multi-band superconductivity, with distinct small and large superconducting gaps on different sheets of the Fermi surface.Comment: 2 pages, 2 figures, submitted to M2S-Rio 2003 Proceeding

Electromagnetic Dissociation of Nuclei in Heavy-Ion Collisions

Large discrepancies have been observed between measured Electromagnetic Dissociation(ED) cross sections and the predictions of the semiclassical Weiz\"acker-Williams-Fermi(WWF) method. In this paper, the validity of the semiclassical approximation is examined. The total cross section for electromagnetic excitation of a nuclear target by a spinless projectile is calculated in first Born approximation, neglecting recoil. The final result is expressed in terms of correlation functions and convoluted densities in configuration space. The result agrees with the WWF approximation to leading order(unretarded electric dipole approximation), but the method allows an analytic evaluation of the cutoff, which is determined by the details of the electric dipole transition charge density. Using the Goldhaber-Teller model of that density, and uniform charge densities for both projectile and target, the cutoff is determined for the total cross section in the nonrelativistic limit, and found to be smaller than values currently used for ED calculations. In addition, cross sections are calculated using a phenomenological momentum space cutoff designed to model final state interactions. For moderate projectile energies, the calculated ED cross section is found to be smaller than the semiclassical result, in qualitative agreement with experiment.Comment: 28 page

Microstructural Shear Localization in Plastic Deformation of Amorphous Solids

The shear-transformation-zone (STZ) theory of plastic deformation predicts that sufficiently soft, non-crystalline solids are linearly unstable against forming periodic arrays of microstructural shear bands. A limited nonlinear analysis indicates that this instability may be the mechanism responsible for strain softening in both constant-stress and constant-strain-rate experiments. The analysis presented here pertains only to one-dimensional banding patterns in two-dimensional systems, and only to very low temperatures. It uses the rudimentary form of the STZ theory in which there is only a single kind of zone rather than a distribution of them with a range of transformation rates. Nevertheless, the results are in qualitative agreement with essential features of the available experimental data. The nonlinear theory also implies that harder materials, which do not undergo a microstructural instability, may form isolated shear bands in weak regions or, perhaps, at points of concentrated stress.Comment: 32 pages, 6 figure

Theoretical Evaluations of the Fission Cross Section of the 77 eV Isomer of 235-U

We have developed models of the fission barrier (barrier heights and transition state spectra) that reproduce reasonably well the measured fission cross section of $^{235}$U from neutron energy of 1 keV to 2 MeV. From these models we have calculated the fission cross section of the 77 eV isomer of $^{235}$U over the same energy range. We find that the ratio of the isomer cross section to that of the ground state lies between about 0.45 and 0.55 at low neutron energies. The cross sections become approximately equal above 1 MeV. The ratio of the neutron capture cross section to the fission cross section for the isomer is predicted to be about a factor of 3 larger for the isomer than for the ground state of $^{235}$U at keV neutron energies. We have also calculated the cross section for the population of the isomer by inelastic neutron scattering form the $^{235}$U ground state. We find that the isomer is strongly populated, and for $E_n = 1 MeV$ the $(n,n'\gamma)$ cross section leading to the population of the isomer is of the order of 0.5 barn. Thus, neutron reaction network calculations involving the uranium isotopes in a high neutron fluence are likely to be affected by the 77 eV isomer of $^{235}$U. With these same models the fission cross sections of $^{233}$U and $^{237}$U can be reproduced approximately using only minor adjustments to the barrier heights. With the significant lowering of the outer barrier that is expected for the outer barrier the general behavior of the fission cross section of $^{239}$Pu can also be reproduced.Comment: 17 pages including 8 figure

Anomalous Scaling of Structure Functions and Dynamic Constraints on Turbulence Simulations

The connection between anomalous scaling of structure functions (intermittency) and numerical methods for turbulence simulations is discussed. It is argued that the computational work for direct numerical simulations (DNS) of fully developed turbulence increases as $Re^{4}$, and not as $Re^{3}$ expected from Kolmogorov's theory, where $Re$ is a large-scale Reynolds number. Various relations for the moments of acceleration and velocity derivatives are derived. An infinite set of exact constraints on dynamically consistent subgrid models for Large Eddy Simulations (LES) is derived from the Navier-Stokes equations, and some problems of principle associated with existing LES models are highlighted.Comment: 18 page