433 research outputs found
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
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
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 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
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
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
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
The Granular Phase Diagram
The kinetic energy distribution function satisfying the Boltzmann equation is
studied analytically and numerically for a system of inelastic hard spheres in
the case of binary collisions. Analytically, this function is shown to have a
similarity form in the simple cases of uniform or steady-state flows. This
determines the region of validity of hydrodynamic description. The latter is
used to construct the phase diagram of granular systems, and discriminate
between clustering instability and inelastic collapse. The molecular dynamics
results support analytical results, but also exhibit a novel fluctuational
breakdown of mean-field descriptions.Comment: 15 pages, 4 figure
The Agreement Between a Portable Contact-Mat and Force-Plates During Bilateral Vertical Jumps
International Journal of Exercise Science 15(1): 632-644, 2022. Force plates are commonly used when assessing vertical jumping performance but are not always affordable or practical tools for all testing situations. Twenty-four participants volunteered to take part in a study investigating the agreement between bilateral force plates and a new commercially available contact mat that records jump height, flight-time (FT), and FT of individual limbs during both countermovement (CMJ) and squat (SJ) jumps. Each participant performed six jumps of each type while standing on a contact mat placed upon a pair of in-ground force plates. When compared to the force plate via ordinary least products regression, the contact mat agreed with force plate CMJ and SJ jump height, individual limb FT during CMJs, and left-leg FT during SJs. The bilateral contact mat provided valid assessment of individual limb FT during CMJs, but not SJs. Practitioners can therefore use a bilateral contact mat interchangeably with bilateral force plates to measure SJ and CMJ performance
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