17,426 research outputs found
The effect of farming system on dairy cow cleanliness in the UK and implications to udder health
The cleanliness of dairy cows was assessed using a 20 point hygiene score system at different times in the year on 14 organic and 14 conventional farms in the UK. Overall, cows were dirtier during winter housing compared to summer grazing. Farming system had no effect on cow cleanliness when cows were at grass, but when housed in the winter, organic cows were more likely to be cleaner. There was a link between cow hygiene scores and milk hygiene, with herds having lower bulk tank somatic cell counts (BTSCC) tending to have cleaner cows. This relationship was strongest for the organic herds. There was no significant link between hygiene score and Bactoscan (BS) count or mastitis incidence
Random walks of molecular motors arising from diffusional encounters with immobilized filaments
Movements of molecular motors on cytoskeletal filaments are described by
directed walks on a line. Detachment from this line is allowed to occur with a
small probability. Motion in the surrounding fluid is described by symmetric
random walks. Effects of detachment and reattachment are calculated by an
analytical solution of the master equation in two and three dimensions. Results
are obtained for the fraction of bound motors, their average velocity and
displacement. The diffusion coefficient parallel to the filament becomes
anomalously large since detachment and subsequent reattachment, in the presence
of directed motion of the bound motors, leads to a broadening of the density
distribution.
The occurrence of protofilaments on a microtubule is modeled by internal
states of the binding sites. After a transient time all protofilaments become
equally populated.Comment: 20 pages Phys Rev E format + 11 figure
Effective Potential of a Black Hole in Thermal Equilibrium with Quantum Fields
Expectation values of one-loop renormalized thermal equilibrium stress-energy
tensors of free conformal scalars, spin- fermions and U(1) gauge
fields on a Schwarzschild black hole background are used as sources in the
semi-classical Einstein equation. The back-reaction and new equilibrium metric
are solved for at for each spin field. The nature of the modified
black hole spacetime is revealed through calculations of the effective
potential for null and timelike orbits. Significant novel features affecting
the motions of both massive and massless test particles show up at lowest order
in , where is the renormalized black hole mass,
and is the Planck mass. Specifically, we find the tendency for
\underline{stable} circular photon orbits, an increase in the black hole
capture cross sections, and the existence of a gravitationally repulsive region
associated with the black hole which is generated from the U(1) back-reaction.
We also consider the back-reaction arising from multiple fields, which will be
useful for treating a black hole in thermal equilibrium with field ensembles
belonging to gauge theories.Comment: 25 pages (not including seven figures), VAND-TH-93-6. Typed in Latex,
uses RevTex macro
Paper Session III-B - Development of a Microgravity-Rated Hydroponic Plant Culture Apparatus
Porous tubes provide a novel means of growing plants hydroponically under conditions of microgravity. The experimental strategy for a spaceflight experiment utilizing this technology (anticipated in the 2000-2001 timeframe) is presented. The primary question to be addressed relates to the control of optimal rates of water provision, and how it can be expected to differ between the spaceflight and earth-based environments
Thermal divergences on the event horizons of two-dimensional black holes
The expectation value of the stress-energy tensor \langleT_{\mu\nu}\rangle
of a free conformally invariant scalar field is computed in a general static
two-dimensional black hole spacetime when the field is in either a zero
temperature vacuum state or a thermal state at a nonzero temperature. It is
found that for every static two-dimensional black hole the stress-energy
diverges strongly on the event horizon unless the field is in a state at the
natural black hole temperature which is defined by the surface gravity of the
event horizon. This implies that both extreme and nonextreme two-dimensional
black holes can only be in equilibrium with radiation at the natural black hole
temperature.Comment: 13 pages, REVTe
Design definition study of a NASA/Navy lift/cruise fan technology V/STOL airplane: Risk assessment addendum to the final report
An assessment of risk, in terms of delivery delays, cost overrun, and performance achievement, associated with the V/STOL technology airplane is presented. The risk is discussed in terms of weight, structure, aerodynamics, propulsion, mechanical drive, and flight controls. The analysis ensures that risks associated with the design and development of the airplane will be eliminated in the course of the program and a useful technology airplane that meets the predicted cost, schedule, and performance can be produced
An Eccentric Hot Jupiter Orbiting the Subgiant HD 185269
We report the detection of a Jupiter-mass planet in a 6.838 day orbit around
the 1.28 solar mass subgiant HD 185269. The eccentricity of HD 185269b (e =
0.30) is unusually large compared to other planets within 0.1 AU of their
stars. Photometric observations demonstrate that the star is constant to
+/-0.0001 mag on the radial velocity period, strengthening our interpretation
of a planetary companion. This planet was detected as part of our radial
velocity survey of evolved stars located on the subgiant branch of the H-R
diagram--also known as the Hertzsprung Gap. These stars, which have masses
between 1.2 and 2.5 solar masses, play an important role in the investigation
of the frequency of extrasolar planets as a function of stellar mass.Comment: 18 pages, 4 figures, 3 tables, ApJ in press (scheduled for Dec 2006,
v652n2
Optimal control of entanglement via quantum feedback
It has recently been shown that finding the optimal measurement on the
environment for stationary Linear Quadratic Gaussian control problems is a
semi-definite program. We apply this technique to the control of the
EPR-correlations between two bosonic modes interacting via a parametric
Hamiltonian at steady state. The optimal measurement turns out to be nonlocal
homodyne measurement -- the outputs of the two modes must be combined before
measurement. We also find the optimal local measurement and control technique.
This gives the same degree of entanglement but a higher degree of purity than
the local technique previously considered [S. Mancini, Phys. Rev. A {\bf 73},
010304(R) (2006)].Comment: 10 pages, 5 figure
State-dependent diffusion: thermodynamic consistency and its path integral formulation
The friction coefficient of a particle can depend on its position as it does
when the particle is near a wall. We formulate the dynamics of particles with
such state-dependent friction coefficients in terms of a general Langevin
equation with multiplicative noise, whose evaluation requires the introduction
of specific rules. Two common conventions, the Ito and the Stratonovich,
provide alternative rules for evaluation of the noise, but other conventions
are possible. We show the requirement that a particle's distribution function
approach the Boltzmann distribution at long times dictates that a drift term
must be added to the Langevin equation. This drift term is proportional to the
derivative of the diffusion coefficient times a factor that depends on the
convention used to define the multiplicative noise. We explore the consequences
of this result in a number examples with spatially varying diffusion
coefficients. We also derive path integral representations for arbitrary
interpretation of the noise, and use it in a perturbative study of correlations
in a simple system.Comment: 18 pages, 8 figures, Accepted to PR
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