Sputter ejection of matter from Io

The direct collisional interaction of magnetospheric particles with Io will lead to sputtering of atoms and molecules from the satellite into circum-Jovian space. The ∼520-eV S (and ∼260-eV O) ions composing the Io torus are the most effective agents for net sputter removal of matter from the satellite. An incident flux of ∼10^(10) cm^(−2) s^(−1) is estimated to provide ∼5 × 10^(10) S atoms cm^(−2) s^(−1) from sputtering of a (dayside) atmosphere with an exobase at a few hundred kilometers and up to ∼10^(12) S atoms cm^(−2) s^(−1) from an atmosphere at 1500°K with an exobase at ∼2.2 R_(Io). The supply of S (and O) required to stabilize the torus has been estimated by others to be from 10^(10) to 10^(12) cm^(−2) s^(−1). If Na and K are present in the atmosphere at a concentration level of 1%, the corresponding sputtering rates are calculated to be a few times 10^8 cm^(−2) s^(−1) for an exobase at several hundred kilometers. These numbers are large enough to supply the 10^7 cm^(−2) s^(−1) fluxes required to maintain the Na and K clouds. Sputtering can also remove heavy molecules, like Sn, from the atmosphere. At night, direct S sputtering of the unprotected surface is calculated to eject S and Na (1% concentration) at rates given approximately by ∼10^(10) and ∼10^8 cm^(−2) s^(−1), respectively. All atomic species residing on the surface must be ejected into circum-Jovian space at a rate approximately proportional to their (surface) abundances, if direct surface sputtering occurs, so that the particle content of the inner Jovian magnetosphere should map rather faithfully all species present on Io's surface. The processes of plume sputtering, avalanche cascading, and ionic saltation may lead to spatial and temporal variations in the number of ejected particles

National Strength and Conditioning Association position statement on weightlifting for sports performance

The origins of weightlifting and feats of strength span back to ancient Egypt, China, and Greece, with the introduction of weightlifting into the Olympic Games in 1896. However, it was not until the 1950s that training based on weightlifting was adopted by strength coaches working with team sports and athletics, with weightlifting research in peer-reviewed journals becoming prominent since the 1970s. Over the past few decades, researchers have focused on the use of weightlifting-based training to enhance performance in nonweightlifters because of the biomechanical similarities (e.g., rapid forceful extension of the hips, knees, and ankles) associated with the second pull phase of the clean and snatch, the drive/thrust phase of the jerk and athletic tasks such as jumping and sprinting. The highest force, rate of force development, and power outputs have been reported during such movements, highlighting the potential for such tasks to enhance these key physical qualities in athletes. In addition, the ability to manipulate barbell load across the extensive range of weightlifting exercises and their derivatives permits the strength and conditioning coach the opportunity to emphasize the development of strength-speed and speed-strength, as required for the individual athlete. As such, the results of numerous longitudinal studies and subsequent meta-analyses demonstrate the inclusion of weightlifting exercises into strength and conditioning programs results in greater improvements in force-production characteristics and performance in athletic tasks than general resistance training or plyometric training alone. However, it is essential that such exercises are appropriately programmed adopting a sequential approach across training blocks (including exercise variation, loads, and volumes) to ensure the desired adaptations, whereas strength and conditioning coaches emphasize appropriate technique and skill development of athletes performing such exercises

Hyperfine Populations Prior to Muon Capture

It is shown that the 1S level hyperfine populations prior to muon capture will be statistical when either target or beam are unpolarised independent of the atomic level at which the hyperfine interaction becomes appreciable. This assertion holds in the absence of magnetic transitions during the cascade and is true because of minimal polarisation after atomic capture and selective feeding during the cascade.Comment: (revtex, 6 preprint pages, no figures

Can the cross-education of strength attenuate the impact of detraining after a period of strength training? A quasi-randomized trial

Purpose: Unilateral strength training may attenuate the decline in muscle strength and size in homologous, contralateral muscles. This study aimed to determine whether the cross-education of strength could specifically attenuate the effects of detraining immediately after a short (prehabilitation-type) period of strength training. Methods: Twenty-six strength-trained participants were assigned to either four weeks of unilateral strength training of the stronger arm (UNI) or detraining (Detrain). Motor evoked potential (MEP) and cortical silent period (cSP) responses, muscle cross-sectional area (CSAFlexor; peripheral quantitative computed tomography) and maximal strength, rate of force development (RFD) and muscle activation (EMG) were examined in both elbow flexors before and after the intervention period. Results: In UNI, one-repetition maximum (1-RM) strength improved in both the trained (∆ = 2.0 ± 0.9 kg) and non-trained (∆ = 0.8 ± 0.9 kg) arms despite cessation of training of the weaker arm, whereas 1-RM strength was unchanged in Detrain. Maximal voluntary isometric contraction, isokinetic peak torque, and RFD did not change in either group. No neural changes were detected in UNI, but cSP increased in Detrain (∆ = 0.010 ± 0.015 s). CSAFlexor increased in the trained arm (∆ = 51 ± 43 mm2) but decreased in the non-trained arm (∆ = -53 ± 50 mm2) in UNI. CSAFlexor decreased in both arms in Detrain and at a similar rate to the non-trained arm in UNI. Conclusion: UNI attenuated the effects of detraining in the weaker arm as shown by the improvement in 1-RM strength. However, the cross-education of strength did not attenuate the decline in muscle size in the contralateral arm

Towards granular hydrodynamics in two-dimensions

We study steady-state properties of inelastic gases in two-dimensions in the presence of an energy source. We generalize previous hydrodynamic treatments to situations where high and low density regions coexist. The theoretical predictions compare well with numerical simulations in the nearly elastic limit. It is also seen that the system can achieve a nonequilibrium steady-state with asymmetric velocity distributions, and we discuss the conditions under which such situations occur.Comment: 8 pages, 9 figures, revtex, references added, also available from http://arnold.uchicago.edu/?ebn

Low-energy three-body charge transfer reactions with Coulomb interaction in the final state

Three-body charge transfer reactions with Coulomb interaction in the final state are considered in the framework of coordinate-space integro-differential Faddeev-Hahn-type equations within two- and six-state close coupling approximations. The method is employed to study direct muon transfer in low-energy collisions of the muonic hydrogen H$_\mu$ by helium (He$^{++}$) and lithium (Li$^{+++}$) nuclei. The experimentally observed isotopic dependence is reproduced.Comment: 14 pages REVTeX, accepted for publication in Journal of Physics

A Systematic Review Evaluating the New Media Landscape and its Effects on Skin Cancer Diagnostics, Prognostics, and Prevention

https://openworks.mdanderson.org/sumexp23/1078/thumbnail.jp

Granular Rheology in Zero Gravity

We present an experimental investigation on the rheological behavior of model granular media made of nearly elastic spherical particles. The experiments are performed in a cylindrical Couette geometry and the experimental device is placed inside an airplane undergoing parabolic flights to cancel the effect of gravity. The corresponding curves, shear stress versus shear rate, are presented and a comparison with existing theories is proposed. The quadratic dependence on the shear rate is clearly shown and the behavior as a function of the solid volume fraction of particles exhibits a power law function. It is shown that theoretical predictions overestimate the experiments. We observe, at intermediate volume fractions, the formation of rings of particles regularly spaced along the height of the cell. The differences observed between experimental results and theoretical predictions are discussed and related to the structures formed in the granular medium submitted to the external shear.Comment: 10 pages, 6 figures to be published in Journal of Physics : Condensed Matte

Nontrivial Velocity Distributions in Inelastic Gases

We study freely evolving and forced inelastic gases using the Boltzmann equation. We consider uniform collision rates and obtain analytical results valid for arbitrary spatial dimension d and arbitrary dissipation coefficient epsilon. In the freely evolving case, we find that the velocity distribution decays algebraically, P(v,t) ~ v^{-sigma} for sufficiently large velocities. We derive the exponent sigma(d,epsilon), which exhibits nontrivial dependence on both d and epsilon, exactly. In the forced case, the velocity distribution approaches a steady-state with a Gaussian large velocity tail.Comment: 4 pages, 1 figur

Steady state representation of the homogeneous cooling state of a granular gas

The properties of a dilute granular gas in the homogeneous cooling state are mapped to those of a stationary state by means of a change in the time scale that does not involve any internal property of the system. The new representation is closely related with a general property of the granular temperature in the long time limit. The physical and practical implications of the mapping are discussed. In particular, simulation results obtained by the direct simulation Monte Carlo method applied to the scaled dynamics are reported. This includes ensemble averages and also the velocity autocorrelation function, as well as the self-diffusion coefficient obtained from the latter by means of the Green-Kubo representation. In all cases, the obtained results are compared with theoretical predictions