657 research outputs found
A study of colour field distributions in the baryon
The distributions of chromo-electric and chromo-magnetic field associated
with flux tubes in the baryon are studied in SU(3) lattice QCD. Maximal Abelian
projection is used to reduce the statistical fluctuations. For a fixed source
geometry, many different string configurations are possible. We investigated
whether the string configuration, that is the choice of operator, biases the
observed flux distribution.Comment: 3 pages, 3 figures, talk given at Lattice2003(topology
Threshold Photo/Electro Pion Production - Working Group Summary
We summarize the pertinent experimental and theoretical developments in the
field of pion photo- and electroproduction in the threshold region. We discuss
which experiments and which calculations should be done/performed in the
future.Comment: plain TeX (macro included), 6pp, summary talk presented at the
workshop on "Chiral Dynamics: Theory and Experiments", MIT, July 25-29, 199
Phosphorus nutrition and management – overcoming constraints to wider adoption
The importance of phosphorus nutrition for cattle grazing northern Australian rangelands has been well documented and demonstrated. Phosphorus is clearly one of the most important nutritional deficiencies, within the limitations of potential metabolizable energy intakes, of grazing cattle in the seasonally dry tropics. Nevertheless it appears that only a small proportion of cattle grazing phosphorus deficient pastures are supplemented or otherwise managed to alleviate phosphorus deficiency. Estimated requirements for dietary phosphorus by various classes of cattle grazing tropical pastures have recently been revised (CSIRO 2007). The development of faecal near infrared spectroscopy (F.NIRS) allows the routine estimation of metabolizable energy and nitrogen concentrations in the diet, and thus the potential productivity, of cattle grazing northern rangelands.
The concentration of phosphorus in the diet of grazing cattle can be estimated from the concentration of phosphorus in the faeces, at least in cattle not fed phosphorus supplements.
Combining estimates of diet metabolizable energy, nitrogen and phosphorus allows estimation whether current needs of the animal are supplied by the diet. Phosphorus-replete cattle have substantial body reserves of phosphorus which can be mobilized, especially in late pregnancy and lactation, to alleviate a dietary deficiency. However, these body reserves need to be replenished in late lactation or post-lactation if mobilization occurs each year. Diagnosis of subclinical phosphorus deficiency in grazing cattle, and prediction of animal responses to phosphorus supplements is difficult. In growing cattle the concentration of inorganic phosphorus in blood (Pi), in the late wet or early dry season, combined with information on diet metabolizable energy and nitrogen concentrations obtained by F.NIRS, provides the most reliable test. In pregnant or lactating cows measurements of faecal phosphorus concentration and F.NIRS provide the best estimate of whether phosphorus intake meets the current needs of the animal. However, estimates of adequacy of phosphorus supply need to also consider possible mobilization of body phosphorus reserves.
Indicative responses to provision of phosphorus supplements by cattle grazing pastures ranging from marginal to acute deficiency are summarized. Economic evaluation of benchmark enterprises where cattle are expected to be phosphorus deficient indicate that phosphorus supplementation is highly cost-effective. Major obstacles to more widespread adoption of phosphorus supplementation appear to be lack of knowledge and appreciation by managers of the phosphorus status of their cattle, lack of appreciation of the cost-effectiveness of a phosphorus supplementation particularly for some classes of cattle, and the practical difficulties in implementing phosphorus supplementation during the wet season
The Off-diagonal Goldberger-Treiman Relation and Its Discrepancy
We study the off-diagonal Goldberger-Treiman relation (ODGTR) and its
discrepancy (ODGTD) in the N, Delta, pi sector through O(p^2) using heavy
baryon chiral perturbation theory. To this order, the ODGTD and axial vector N
to Delta transition radius are determined solely by low energy constants. Loop
corrections appear at O(p^4). For low-energy constants of natural size, the
ODGTD would represent a ~ 2% correction to the ODGTR. We discuss the
implications of the ODGTR and ODGTD for lattice and quark model calculations of
the transition form factors and for parity-violating electroexcitation of the
Delta.Comment: 11 pages, 1 eps figur
Computation of the Heavy-Light Decay Constant using Non-relativistic Lattice QCD
We report results on a lattice calculation of the heavy-light meson decay
constant employing the non-relativistic QCD approach for heavy quark and Wilson
action for light quark. Simulations are carried out at on a
lattice. Signal to noise ratio for the ground state is
significantly improved compared to simulations in the static approximation,
enabling us to extract the decay constant reliably. We compute the heavy-light
decay constant for several values of heavy quark mass and estimate the
magnitude of the deviation from the heavy mass scaling law . For the meson we find MeV, while
an extrapolation to the static limit yields = MeV.Comment: 34 pages in LaTeX including 10 figures using epsf.sty,
uuencoded-gziped-shar format, HUPD-940
Reconstruction of Black Hole Metric Perturbations from Weyl Curvature
Perturbation theory of rotating black holes is usually described in terms of
Weyl scalars and , which each satisfy Teukolsky's complex
master wave equation and respectively represent outgoing and ingoing radiation.
On the other hand metric perturbations of a Kerr hole can be described in terms
of (Hertz-like) potentials in outgoing or ingoing {\it radiation
gauges}. In this paper we relate these potentials to what one actually computes
in perturbation theory, i.e and . We explicitly construct
these relations in the nonrotating limit, preparatory to devising a
corresponding approach for building up the perturbed spacetime of a rotating
black hole. We discuss the application of our procedure to second order
perturbation theory and to the study of radiation reaction effects for a
particle orbiting a massive black hole.Comment: 6 Pages, Revtex
Broadening of band-gap in photonic crystals with optically saturated media
Due to strong absorption of the incident light, the media with high
refractive index are considered restrictive for applications in photonic
crystals (PhCs). The possibility to resolve this problem by optical saturation
effectively minimizing the absorption of the PhC medium is discussed. Such
approach might be promising for the significant broadening of the photonic
band-gap.Comment: 10 page
Renal pericytes: regulators of medullary blood flow
Regulation of medullary blood flow (MBF) is essential in maintaining normal kidney function. Blood flow to the medulla is supplied by the descending vasa recta (DVR), which arise from the efferent arterioles of juxtamedullary glomeruli. DVR are composed of a continuous endothelium, intercalated with smooth muscle-like cells called pericytes. Pericytes have been shown to alter the diameter of isolated and in situ DVR in response to vasoactive stimuli that are transmitted via a network of autocrine and paracrine signalling pathways. Vasoactive stimuli can be released by neighbouring tubular epithelial, endothelial, red blood cells and neuronal cells in response to changes in NaCl transport and oxygen tension. The experimentally described sensitivity of pericytes to these stimuli strongly suggests their leading role in the phenomenon of MBF autoregulation. Because the debate on autoregulation of MBF fervently continues, we discuss the evidence favouring a physiological role for pericytes in the regulation of MBF and describe their potential role in tubulo-vascular cross-talk in this region of the kidney. Our review also considers current methods used to explore pericyte activity and function in the renal medulla
Nucleon Axial Form Factor from Lattice QCD
Results for the isovector axial form factors of the proton from a lattice QCD
calculation are presented for both point-split and local currents. They are
obtained on a quenched lattice at with Wilson
fermions for a range of quark masses from strange to charm. We determine the
finite lattice renormalization for both the local and point-split currents of
heavy quarks. Results extrapolated to the chiral limit show that the
dependence of the axial form factor agrees reasonably well with experiment. The
axial coupling constant calculated for the local and the point-split
currents is about 6\% and 12\% smaller than the experimental value
respectively.Comment: 8 pages, 5 figures (included in part 2), UK/93-0
- …