939 research outputs found
Vascular perfusion chilling of red meat carcasses - A feasibility study.
Meat carcasses must be chilled to below 7°C before leaving the slaughterhouse. Typically this is done by passing cold air over the surfaces of eviscerated and de-hided carcasses. This surface cooling can take many hours to reduce centre temperatures to below 7°C. In vascular perfusion chilling (VPC), a cold fluid is circulated through the intact vascular system, offering significant reductions in cooling time. This paper describes a small feasibility study to evaluate vascular perfusion techniques for rapid chilling of lamb carcasses using a proprietary Flo-ice(™) system. This produces pumpable ice slurries containing very fine ice particles, suitable for circulating through vascular systems. VPC was found to be capable of rapid initial reduction of carcass temperatures in comparison with air chilling (mean times to 20°C in deep legs were reduced from 2.6 to 1.3h, which was significantly different at P<0.05). In all cases however, uptake of perfusate into the carcasses occurred. This limited the duration of the perfusion treatment and as a result restricted the period of enhanced cooling. Samples from carcasses treated with VPC were lighter (P<0.05, with mean measured L value increasing from 43.4 to 46.8) and more yellow (P<0.05, with mean measured b value increasing from 6.7 to 7.9) than samples from conventionally chilled carcasses, and had lower shear force values when cooked (P<0.05, with mean force reducing from 10.0 to 6.8kg). This was most probably due to the added water in the meat. Microbial quality of the meat was not significantly affected by the perfusion treatments
Morse theory of the moment map for representations of quivers
The results of this paper concern the Morse theory of the norm-square of the
moment map on the space of representations of a quiver. We show that the
gradient flow of this function converges, and that the Morse stratification
induced by the gradient flow co-incides with the Harder-Narasimhan
stratification from algebraic geometry. Moreover, the limit of the gradient
flow is isomorphic to the graded object of the
Harder-Narasimhan-Jordan-H\"older filtration associated to the initial
conditions for the flow. With a view towards applications to Nakajima quiver
varieties we construct explicit local co-ordinates around the Morse strata and
(under a technical hypothesis on the stability parameter) describe the negative
normal space to the critical sets. Finally, we observe that the usual Kirwan
surjectivity theorems in rational cohomology and integral K-theory carry over
to this non-compact setting, and that these theorems generalize to certain
equivariant contexts.Comment: 48 pages, small revisions from previous version based on referee's
comments. To appear in Geometriae Dedicat
Free expansion of lowest Landau level states of trapped atoms: a wavefunction microscope
We show that for any lowest-Landau-level state of a trapped, rotating,
interacting Bose gas, the particle distribution in coordinate space in a free
expansion (time of flight) experiment is related to that in the trap at the
time it is turned off by a simple rescaling and rotation. When the
lowest-Landau-level approximation is valid, interactions can be neglected
during the expansion, even when they play an essential role in the ground state
when the trap is present. The correlations in the density in a single snapshot
can be used to obtain information about the fluid, such as whether a transition
to a quantum Hall state has occurred.Comment: 5 pages, no figures. v2: discussion of neglect of interactions during
expansion improved, refs adde
Microbial sulfate reduction and metal attenuation in pH 4 acid mine water
Sediments recovered from the flooded mine workings of the Penn Mine, a Cu-Zn mine abandoned since the early 1960s, were cultured for anaerobic bacteria over a range of pH (4.0 to 7.5). The molecular biology of sediments and cultures was studied to determine whether sulfate-reducing bacteria (SRB) were active in moderately acidic conditions present in the underground mine workings. Here we document multiple, independent analyses and show evidence that sulfate reduction and associated metal attenuation are occurring in the pH-4 mine environment. Waterchemistry analyses of the mine water reveal: (1) preferential complexation and precipitation by H2S of Cu and Cd, relative to Zn; (2) stable isotope ratios of 34S/32S and 18O/16O in dissolved SO4 that are 2–3 ‰ heavier in the mine water, relative to those in surface waters; (3) reduction/oxidation conditions and dissolved gas concentrations consistent with conditions to support anaerobic processes such as sulfate reduction. Scanning electron microscope (SEM) analyses of sediment show 1.5-micrometer, spherical ZnS precipitates. Phospholipid fatty acid (PLFA) and denaturing gradient gel electrophoresis (DGGE) analyses of Penn Mine sediment show a high biomass level with a moderately diverse community structure composed primarily of iron- and sulfate-reducing bacteria. Cultures of sediment from the mine produced dissolved sulfide at pH values near 7 and near 4, forming precipitates of either iron sulfide or elemental sulfur. DGGE coupled with sequence and phylogenetic analysis of 16S rDNA gene segments showed populations of Desulfosporosinus and Desulfitobacterium in Penn Mine sediment and laboratory cultures
Near threshold eta meson production in the d+d->alpha+eta reaction
The d+d->alpha+eta reaction has been investigated near threshold using the
ANKE facility at COSY-Juelich. Both total and differential cross sections have
been measured at two excess energies, Q=2.6 MeV and 7.7 MeV, with a
subthreshold measurement being undertaken at Q=-2.6 MeV to study the physical
background. While consistent with isotropy at the lower energy, the angular
distribution reveals a pronounced anisotropy at the higher one, indicating the
presence of higher partial waves. Options for the decomposition into partial
amplitudes and their consequences for determination of the s-wave eta-alpha
scattering length are discussed.Comment: 8pp, fig.3 added, normalisation in eq.4.1 correcte
Fragmented Condensate Ground State of Trapped Weakly Interacting Bosons in Two Dimensions
The ground state and its structure for a rotating, harmonically trapped
N-Boson system with a weak repulsive contact interaction are studied as the
angular momentum L increases up to 3N. We show that the ground state is
generally a fragmented condensate due to angular momentum conservation. In
response to an (arbitrarily weak) asymmetric perturbation of the trap, however,
the fragmented ground state can be transformed into a single condensate state.
We manifest this intrinsic instability by calculating the conditional
probability distributions, which show patterns analogous to the boson density
distributions predicted by mean-field theory.Comment: 4 pages, 4 ps figure
Scaling in high-temperature superconductors
A Hartree approximation is used to study the interplay of two kinds of
scaling which arise in high-temperature superconductors, namely critical-point
scaling and that due to the confinement of electron pairs to their lowest
Landau level in the presence of an applied magnetic field. In the neighbourhood
of the zero-field critical point, thermodynamic functions scale with the
scaling variable , which differs from the variable
suggested by the gaussian approximation.
Lowest-Landau-level (LLL) scaling occurs in a region of high field surrounding
the upper critical field line but not in the vicinity of the zero-field
transition. For YBaCuO in particular, a field of at least 10 T is needed to
observe LLL scaling. These results are consistent with a range of recent
experimental measurements of the magnetization, transport properties and,
especially, the specific heat of high- materials.Comment: 22 pages + 1 figure appended as postscript fil
Pion interferometry with pion-source-medium interactions
An extended pion source, which can be temporarily created by a high energy
nuclear collision, will also absorb and distort the outgoing pions. We discuss
how this effect alters the interferometric pattern of the two-pion momentum
correlation function. In particular, we show that the two-pion correlation
function decreases rapidly when the opening angle between the pions increases.
The opening-angle dependence should serve as a new means of obtaining
information about the pion source in the analysis of experimental data.Comment: 14 pages (revtex) and 9 figures (uuencoded), Caltech preprint
MAP-175, Indiana Univ. preprint IU/NTC 914-1
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