Controlling Tokamak Geometry with 3D Magnetic Perturbations

It is shown that small externally applied magnetic perturbations can significantly alter important geometric properties of magnetic flux surfaces in tokamaks. Through 3D shaping, experimentally relevant perturbation levels are large enough to influence turbulent transport and MHD stability in the pedestal region. It is shown that the dominant pitch-resonant flux surface deformations are primarily induced by non-resonant 3D fields, particularly in the presence of significant axisymmetric shaping. The spectral content of the applied 3D field can be used to control these effects

ACUTE STATIC STRETCH EFFECTS ON MULTIPLE BOUTS OF VERTICAL JUMP

The purpose of this study was to evaluate the acute effects of static stretching on vertical jumping and the ground reaction force kinetics when stretching was implemented between multiple performance bouts. Fifty-two young adults were randomly assigned to a control or stretch condition, each group performing four sets of three jumps. After the initial jump series, subjects in the stretch condition performed a set of four unilateral lower extremity stretches, holding each stretch for 30 s on each leg. Vertical jump height and time had a significant interaction effect (

Structural Relaxation and Mode Coupling in a Simple Liquid: Depolarized Light Scattering in Benzene

We have measured depolarized light scattering in liquid benzene over the whole accessible temperature range and over four decades in frequency. Between 40 and 180 GHz we find a susceptibility peak due to structural relaxation. This peak shows stretching and time-temperature scaling as known from $\alpha$ relaxation in glass-forming materials. A simple mode-coupling model provides consistent fits of the entire data set. We conclude that structural relaxation in simple liquids and $\alpha$ relaxation in glass-forming materials are physically the same. A deeper understanding of simple liquids is reached by applying concepts that were originally developed in the context of glass-transition research.Comment: submitted to New J. Phy

Continuum description of finite-size particles advected by external flows. The effect of collisions

The equation of the density field of an assembly of macroscopic particles advected by a hydrodynamic flow is derived from the microscopic description of the system. This equation allows to recognize the role and the relative importance of the different microscopic processes implicit in the model: the driving of the external flow, the inertia of the particles, and the collisions among them. The validity of the density description is confirmed by comparisons of numerical studies of the continuum equation with Direct Simulation Monte Carlo (DSMC) simulations of hard disks advected by a chaotic flow. We show that the collisions have two competing roles: a dispersing-like effect and a clustering effect (even for elastic collisions). An unexpected feature is also observed in the system: the presence of collisions can reverse the effect of inertia, so that grains with lower inertia are more clusterized.Comment: Final (strongly modified) version accepted in PRE; 6 pages, 3 figure

A COMPARISON OF HIGH AND LOW VELOCITY PITCHERS IN FASTPITCH SOFTBALL

A two-dimensional biomechanical comparison of 10 “high velocity” and 10 “low velocity” softball pitchers was done to assess kinematic similarities and differences. While angular velocities of the shoulder, wrist, and elbow are often believed to be important in determining ball velocity, they were not different between high and low velocity groups for these data. Significant differences (

Motivations for Underreporting Suspected Concussion in College Athletics

Student-athletes often fail to report concussion signs and symptoms, thereby putting themselves at risk for delayed recovery and permanent impairment. The present study examined motivations for underreporting concussion symptoms among college athletes enrolled at an NCAA Division I university. One hundred and ninety-three student-athletes in high-risk sports completed a multiple-choice survey related to self-reporting of suspected concussion symptoms and reporting of teammates’ symptoms. Results indicated that 45% of participants did not report their own suspected concussions during the present season and 50% did not report suspected concussions in teammates. Responses revealed that the primary reason for underreporting a suspected concussion was the belief that the blow to the head was not serious enough. Suggestions are provided for athletes, athletic staff, and coaches to improve players’ awareness of the signs, symptoms, and consequences of concussions, as well as how to report suspected concussions appropriately

Periodic magnetoconductance fluctuations in triangular quantum dots in the absence of selective probing

We have studied the magnetoconductance of quantum dots with triangular symmetry and areas down to 0.2 square microns, made in a high mobility two-dimensional electron gas embedded in a GaAs-AlGaAs heterostructure. Semiclassical simulations show that the gross features in the measured magnetoconductance are caused by ballistic effects. Below 1 K we observe a strong periodic oscillation, which may be explained in terms of the Aharanov-Bohm flux quantization through the area of a single classical periodic orbit. From a numerical and analytical analysis of possible trajectories in hard- and soft-walled potentials, we identify this periodic orbit as the enscribed triangle. Contrary to other recent experiments, this orbit is not accessible by classical processes for the incoming collimated beam.Comment: RevTex 8 pages, including 5 postscript figure

Gaussian approximation for finitely extensible bead-spring chains with hydrodynamic interaction

The Gaussian Approximation, proposed originally by Ottinger [J. Chem. Phys., 90 (1) : 463-473, 1989] to account for the influence of fluctuations in hydrodynamic interactions in Rouse chains, is adapted here to derive a new mean-field approximation for the FENE spring force. This "FENE-PG" force law approximately accounts for spring-force fluctuations, which are neglected in the widely used FENE-P approximation. The Gaussian Approximation for hydrodynamic interactions is combined with the FENE-P and FENE-PG spring force approximations to obtain approximate models for finitely-extensible bead-spring chains with hydrodynamic interactions. The closed set of ODE's governing the evolution of the second-moments of the configurational probability distribution in the approximate models are used to generate predictions of rheological properties in steady and unsteady shear and uniaxial extensional flows, which are found to be in good agreement with the exact results obtained with Brownian dynamics simulations. In particular, predictions of coil-stretch hysteresis are in quantitative agreement with simulations' results. Additional simplifying diagonalization-of-normal-modes assumptions are found to lead to considerable savings in computation time, without significant loss in accuracy.Comment: 26 pages, 17 figures, 2 tables, 75 numbered equations, 1 appendix with 10 numbered equations Submitted to J. Chem. Phys. on 6 February 200