33,014 research outputs found
Dispersion of biased swimming microorganisms in a fluid flowing through a tube
Classical Taylor-Aris dispersion theory is extended to describe the transport
of suspensions of self-propelled dipolar cells in a tubular flow. General
expressions for the mean drift and effective diffusivity are determined exactly
in terms of axial moments, and compared with an approximation a la Taylor. As
in the Taylor-Aris case, the skewness of a finite distribution of biased
swimming cells vanishes at long times. The general expressions can be applied
to particular models of swimming microorganisms, and thus be used to predict
swimming drift and diffusion in tubular bioreactors, and to elucidate competing
unbounded swimming drift and diffusion descriptions. Here, specific examples
are presented for gyrotactic swimming algae.Comment: 20 pages, 4 figures. Published version available at
http://rspa.royalsocietypublishing.org/content/early/2010/02/09/rspa.2009.0606.short?rss=
Magnetic Properties of LaCr1−xMxSb3 (M=V, Mn, Fe, Cu, and Al)
The influence of Cr substitution by various metals (M=V, Mn, Fe, Cu and Al) on the magnetic state of the itinerant intermetallics La(Cr,M)Sb3 was studied by magnetization and magnetic susceptibility measurements up to 55 kG at 5 K and from 4.2 to 400 K, in a magnetic field of 1000 G, respectively. It was found that the Curie temperature (TC) and magnetization (M) of these compounds depend nonlinearly on the concentration, remaining in the vicinity of the values of TC and M measured for LaCrSb3. Curie temperatures and magnetization values at 55 kG are suppressed by Mn, Fe, V, and Cu, and have a slight maximum at low Al concentration (about 5%)
N=1 Supersymmetric Moose Theories
We study the quantum moduli spaces and dynamical superpotentials of four
dimensional linear and ring moose theories with
supersymmetry and link chiral superfields in the fundamental representation.
Nontrivial quantum moduli spaces and dynamical superpotentials are produced.
When the moduli space is perturbed by generic tree level superpotentials, the
vacuum space becomes discrete. The ring moose is in the Coulomb phase and we
find two singular submanifolds with a nontrivial modulus that is a function of
all the independent gauge invariants needed to parameterize the quantum moduli
space. The massive theory near these singularities confines. The Seiberg-Witten
elliptic curve that describes the quantum moduli space of the ring moose is
produced.Comment: 26 pages, 4 figures. A few comments and references added. To appear
in PR
Charge and spin Hall conductivity in metallic graphene
Graphene has an unusual low-energy band structure with four chiral bands and
half-quantized and quantized Hall effects that have recently attracted
theoretical and experimental attention. We study the Fermi energy and disorder
dependence of its spin Hall conductivity. In the metallic regime we find that
vertex corrections enhance the intrinsic spin Hall conductivity and that skew
scattering can lead to its values that exceed the quantized ones expected when
the chemical potential is inside the spin-orbit induced energy gap. We predict
that large spin Hall conductivities will be observable in graphene even when
the spin-orbit gap does not survive disorder.Comment: 4 pages, 2 figure
A game for all shapes and sizes? Changes in anthropometric and performance measures of elite professional rugby union players 1999-2018
Background: Rugby union player size has increased since the game turned professional in 1995. Changes in physical and performance capability over this period have yet to be fully described. Hypothesis: Increases in player momentum would result from changes in body mass. Methods: Within-player rates of change in anthropometric and kinetic variables with season played were sampled in three successively studied professional rugby union club cohorts playing at the highest level of European competition between 1999-2019. Data comprised 910 seasons of observation for 291 elite male players. Most players had 2, 3 or 4 seasons of observation. Mixed-effects modelling distinguished changes independent of position played, club and international status. Results: With each season played, player body mass, fat-free mass, and maximum speed increased significantly, while percent fat decreased. The mean maximal velocity of a rugby player in 1999 was 8.2 (±0.18) m/s, which in 2019 had risen to 9.1 (±0.10) m/s. Player’s momentum in 2019 was 14% more than those playing in 1999. In the Front Five, momentum increased in this period by more than 25%, mainly driven by greater running speed, disproving our hypothesis. Conclusions: The momentum of players, particularly forwards, increased markedly over 20 seasons of professional rugby. The resulting forces generated in collisions are thus significantly greater, although these may be mitigated by better player conditioning. Proactive regulation to address player safety may be required to address the changing nature of anthropometric measures and physical performance, minimising injury rates and potential long-term sequelae
Length Scales of Acceleration for Locally Isotropic Turbulence
Length scales are determined that govern the behavior at small separations of
the correlations of fluid-particle acceleration, viscous force, and pressure
gradient. The length scales and an associated universal constant are quantified
on the basis of published data. The length scale governing pressure spectra at
high wave numbers is discussed. Fluid-particle acceleration correlation is
governed by two length scales; one arises from the pressure gradient, the other
from the viscous force.Comment: 2 figures, 4 pages. Physical Review Letters, accepted August 200
Dynamical equations for high-order structure functions, and a comparison of a mean field theory with experiments in three-dimensional turbulence
Two recent publications [V. Yakhot, Phys. Rev. E {\bf 63}, 026307, (2001) and
R.J. Hill, J. Fluid Mech. {\bf 434}, 379, (2001)] derive, through two different
approaches that have the Navier-Stokes equations as the common starting point,
a set of steady-state dynamic equations for structure functions of arbitrary
order in hydrodynamic turbulence. These equations are not closed. Yakhot
proposed a "mean field theory" to close the equations for locally isotropic
turbulence, and obtained scaling exponents of structure functions and an
expression for the tails of the probability density function of transverse
velocity increments. At high Reynolds numbers, we present some relevant
experimental data on pressure and dissipation terms that are needed to provide
closure, as well as on aspects predicted by the theory. Comparison between the
theory and the data shows varying levels of agreement, and reveals gaps
inherent to the implementation of the theory.Comment: 16 pages, 23 figure
Conjoint Analysis of Breaded Catfish Nuggets: Consumer Preferences for Price, Product Color, Cooking Method and Country of Origin
A new product, marinated, breaded catfish nuggets, was developed. This conjoint study was designed to evaluate consumers’ preferences for certain attributes of the nuggets. An in-store survey was conducted to collect data. The data collected will be used to determine the market potential for the catfish nuggets.Food Consumption/Nutrition/Food Safety,
Deformation Energy Minima at Finite Mass Asymmetry
A very general saddle point nuclear shape may be found as a solution of an
integro-differential equation without giving apriori any shape parametrization.
By introducing phenomenological shell corrections one obtains minima of
deformation energy for binary fission of parent nuclei at a finite (non-zero)
mass asymmetry. Results are presented for reflection asymmetric saddle point
shapes of thorium and uranium even-mass isotopes with A=226-238 and A=230-238
respectively.Comment: 5 pages, 2 Postscript figures, REVTeX, Version 4.
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