Magnetic reversals in a simple model of MHD

We study a simple magnetohydrodynamical approach in which hydrodynamics and MHD turbulence are coupled in a shell model, with given dynamo constrains in the large scales. We consider the case of a low Prandtl number fluid for which the inertial range of the velocity field is much wider than that of the magnetic field. Random reversals of the magnetic field are observed and it shown that the magnetic field has a non trivial evolution linked to the nature of the hydrodynamics turbulence.Comment: 4 pages, submitted to PR

Influence of Ground Reaction Forces and Joint Velocities on Kicking Velocity

Introduction: Kicking is a vital component in the game of soccer. One major factor that influences the success of a scoring attempt is ball velocity. Ground reaction force (GRF) and joint velocities of the lower extremities are variables of interest for increasing kicking velocity. Previous studies have shown exercise programs used to strengthen the muscles used in kicking have been successful in increasing kicking velocity (Manolopoulos, et al., 2013).[GJR1] To date, no known studies have analyzed the specific relationship between GRF, joint velocity and kicking velocity. Purpose: The goal of this pilot study was to analyze the influence of ground reaction forces and joint velocities on kicking velocity. Methods: Four female Division II collegiate soccer players [GJR2] completed 3 instep soccer kicks [GJR3] using their dominant, right leg. Their motion was captured using the Cortex 8.1 Motion Analysis Software. Ball velocity, right and left anterior superior iliac spine (ASIS) and right and left ankle velocities were calculated using the motion analysis software. Ground reaction forces from the plant leg were also measured using force plate data from the Cortex software. Bivariate Pearson correlations with 0.95 confidence intervals were computed using SPSS version 28 for the resultant velocities of the right and left ASIS, right and left ankles, and the velocity of the ball. They were also calculated for the peak GRF in the anteroposterior (X), mediolateral (Y) and vertical (Z) directions and ball velocity. A correlation value of \u3e0.800 or \u3c -0.800 was considered significant. Results: Significant correlations were found between peak resultant ball velocity and GRF in the X direction (-0.907), GRF in the Y direction (0.867), R ASIS velocity (0.950), R ankle velocity (0.855), and L ankle velocity (0.977). No significant correlations were found between peak resultant ball velocity and GRF in the Z direction (0.788), or peak resultant ball velocity and peak joint velocity of the L ASIS (0.692). Conclusion: Braking force of the planting leg is shown to correlate significantly with kicking velocity. Although high braking force allows for a faster ball, this can have other implications to injury [GJR4] (Ball, 2012; Jones & Graham-Smith, 2016). Linear velocity of the hip also allows for greater ball velocity. As a pilot study, this study lacks the statistical power to extrapolate the information to larger populations. Therefore, additional studies are needed to further investigate the relationships between kicking mechanics and the resulting ball velocity

Emergence of pointer states in a non-perturbative environment

We show that the pointer basis distinguished by collisional decoherence consists of exponentially localized, solitonic wave packets. Based on the orthogonal unraveling of the quantum master equation, we characterize their formation and dynamics, and we demonstrate that the statistical weights arising from an initial superposition state are given by the required projection. Since the spatial width of the pointer states can be obtained by accounting for the gas environment in a microscopically realistic fashion, one may thus calculate the coherence length of a strongly interacting gas.Comment: 8 pages, 1 figure; corresponds to published versio

Diffusion and dispersion of passive tracers: Navier-Stokes versus MHD turbulence

A comparison of turbulent diffusion and pair-dispersion in homogeneous, macroscopically isotropic Navier-Stokes (NS) and nonhelical magnetohydrodynamic (MHD) turbulence based on high-resolution direct numerical simulations is presented. Significant differences between MHD and NS systems are observed in the pair-dispersion properties, in particular a strong reduction of the separation velocity in MHD turbulence as compared to the NS case. It is shown that in MHD turbulence the average pair-dispersion is slowed down for $\tau_\mathrm{d}\lesssim t\lesssim 10 \tau_\mathrm{d}$, $\tau_\mathrm{d}$ being the Kolmogorov time, due to the alignment of the relative Lagrangian tracer velocity with the local magnetic field. Significant differences in turbulent single-particle diffusion in NS and MHD turbulence are not detected. The fluid particle trajectories in the vicinity of the smallest dissipative structures are found to be characterisically different although these comparably rare events have a negligible influence on the statistics investigated in this work.Comment: Europhysics Letters, in prin

REACTION MECHANISMS AND RATE LIMITATIONS IN DRY ETCHING OF SILICON DIOXIDE VITH ANHYDROUS HYDROGEN FLUORIDE

A novel dry etching process for silicon dioxide has been developed. This process, carried out at ambient temperature and pressure, uses anhydrous hydrogen fluoride, water vapor in a nitrogen carrier, and a unique processing sequence to achieve etch rates of about 200A/second, with 5 percent or better uniformity. The overall reaction is a complicated sequence of surface hydration and surface fluorlnation by adsorption, reaction, and product desorptlon. This paper presents two proposed reaction mechanisms and describes how experimental data from a laminar flow reactor were used to evaluate the mechanisms

Cytokine Profiles of Stimulated Blood Lymphocytes in Asthmatic and Healthy Adolescents Cross the School Year

T cell cytokines play an important role in mediating airway inflammation in asthma. The predominance of a Th2 cytokine profile, particularly interleukin (IL)-4 and IL-5, is associated with the pathogenesis and course of asthma. The aim of this study was to test the hypothesis that a stressful life event alters the pattern of cytokine release in asthmatic individuals. Thirteen healthy controls and 21 asthmatic adolescents gave blood samples three times over a semester: midsemester, during the week of final examinations, and 2-3 weeks after examinations. Interferon-γ (IFN-γ), IL-2, IL-4, and IL-5 were measured from supernatants of cells stimulated with PHA/PMA for 24 h. Cells from asthmatic subjects released significantly more IL-5 during the examination and postexamination periods, whereas cells from healthy controls released significantly more IL-2 during the midsemester and examination periods, thereby indicating a bias for a Th2-like pattern in asthmatics and a Th 1-like pattern in healthy controls. IL-4 and IL-5 production showed a marked decrease during and after examinations in healthy controls, whereas this decline was absent in asthmatics. The ratios of IFN-γ:IL-4 and IFN-γ:IL-5 also revealed significant changes in the profile of cytokine release across the semester. These results indicate differential cytokine responses in asthmatics that may become pronounced during periods of cellular activation

Variational bound on energy dissipation in plane Couette flow

We present numerical solutions to the extended Doering-Constantin variational principle for upper bounds on the energy dissipation rate in turbulent plane Couette flow. Using the compound matrix technique in order to reformulate this principle's spectral constraint, we derive a system of equations that is amenable to numerical treatment in the entire range from low to asymptotically high Reynolds numbers. Our variational bound exhibits a minimum at intermediate Reynolds numbers, and reproduces the Busse bound in the asymptotic regime. As a consequence of a bifurcation of the minimizing wavenumbers, there exist two length scales that determine the optimal upper bound: the effective width of the variational profile's boundary segments, and the extension of their flat interior part.Comment: 22 pages, RevTeX, 11 postscript figures are available as one uuencoded .tar.gz file from [email protected]

Variational bound on energy dissipation in turbulent shear flow

We present numerical solutions to the extended Doering-Constantin variational principle for upper bounds on the energy dissipation rate in plane Couette flow, bridging the entire range from low to asymptotically high Reynolds numbers. Our variational bound exhibits structure, namely a pronounced minimum at intermediate Reynolds numbers, and recovers the Busse bound in the asymptotic regime. The most notable feature is a bifurcation of the minimizing wavenumbers, giving rise to simple scaling of the optimized variational parameters, and of the upper bound, with the Reynolds number.Comment: 4 pages, RevTeX, 5 postscript figures are available as one .tar.gz file from [email protected]

An integrating factor matrix method to find first integrals

In this paper we developed an integrating factor matrix method to derive conditions for the existence of first integrals. We use this novel method to obtain first integrals, along with the conditions for their existence, for two and three dimensional Lotka-Volterra systems with constant terms. The results are compared to previous results obtained by other methods

Fabrication of 2-2 Connectivity PZT/Thermoplastic Composites for High Frequency Linear Arrays

An alternate approach for fabricating PZT/polymer composites with 2-2 connectivity with fine scales is described. Thin (less than or equal to 20 micrometers) sintered PZT plates and sheets of a thermoplastic polymer film (less than or equal to 10 micrometers) were bonded together via thermal processing. Stack sintering of tape cast PZT generated the necessary PZT plates, while tape cast polymers were used to control the thermoplastic thickness. Composite blocks were cut to required dimensions for linear arrays, electroded, and poled. Electromechanical properties were measured to evaluate the composites. The significance of this fabrication technique is that it is able to generate 2-2 structures at a scale level unachievable by conventional dice-and-fill fabrication methods