Sea flavor content of octet baryons and intrinsic five-quark Fock states

Sea quark contents of the octet baryons are investigated by employing an extended chiral constituent quark approach, which embodies higher Fock five-quark components in the baryons wave-functions. The well-known flavor asymmetry of the nucleon sea $\bar{d}-\bar{u}$, is used as input to predict the probabilities of $\bar{u}$, $\bar{d}$ and $\bar{s}$ in the nucleon, $\Lambda$, $\Sigma$ and $\Xi$ baryons, due to the intrinsic five-quark components in the baryons wave functions.Comment: 22 page

Questions on uncertainties in parton distributions

A discussion is presented of the manner in which uncertainties in parton distributions and related quantities are determined. One of the central problems is the criteria used to judge what variation of the parameters describing a set of partons is acceptable within the context of a global fit. Various ways of addressing this question are outlined

The effect of bedrest on various parameters of physiological function. part xiv- effect of bedrest on plasma levels and urinary excretion of 17-hydroxycorticosteroids

Bed rest effect on plasma levels and urinary excretion of hydroxycorticosteroid

Open Charm Production at STAR

We present the open charm spectra at mid-rapidity from direct reconstruction of D0, D* and D+/- in d+Au collisions at sqrt(sNN)=200 GeV using the STAR detector at RHIC. The indirect electron/positron measurements via charm semileptonic decays in p+p and d+Au collisions are also reported. The total c\bar(c) cross section per nucleon-nucleon collision is extracted from both direct and indirect measurements and are consistent with each other. By combining the D0 and semileptonic measurements together, the cross section of 1.4+/-0.2+/-0.4 mb is higher than expectations from PYTHIA and other pQCD calculations. The open charm pT distribution from direct measurements covers the pT range up to ~10 GeV/c and follows a power-law distribution.Comment: 7 pages, 4 figures, proceedings for Hot Quark 04 Conference. submitted to J. Phys. G: Nucl. Phy

Multi-k magnetic structures in USb_{0.9}Te_{0.1} and UAs_{0.8}Se_{0.2} observed via resonant x-ray scattering at the U M4 edge

Experiments with resonant photons at the U M4 edge have been performed on a sample of USb_{0.9}Te_{0.1}, which has an incommensurate magnetic structure with k = 0.596(2) reciprocal lattice units. The reflections of the form , as observed previously in a commensurate k = 1/2 system [N. Bernhoeft et al., Phys. Rev. B 69 174415 (2004)] are observed, removing any doubt that these occur because of multiple scattering or high-order contamination of the incident photon beam. They are clearly connected with the presence of a 3k configuration. Measurements of the reflections from the sample UAs_{0.8}Se_{0.2} in a magnetic field show that the transition at T* ~ 50 K is between a low-temperature 2k and high-temperature 3k state and that this transition is sensitive to an applied magnetic field. These experiments stress the need for quantitative theory to explain the intensities of these reflections.Comment: submitted to Phys. Rev.

Accurate black hole evolutions by fourth-order numerical relativity

We present techniques for successfully performing numerical relativity simulations of binary black holes with fourth-order accuracy. Our simulations are based on a new coding framework which currently supports higher order finite differencing for the BSSN formulation of Einstein's equations, but which is designed to be readily applicable to a broad class of formulations. We apply our techniques to a standard set of numerical relativity test problems, demonstrating the fourth-order accuracy of the solutions. Finally we apply our approach to binary black hole head-on collisions, calculating the waveforms of gravitational radiation generated and demonstrating significant improvements in waveform accuracy over second-order methods with typically achievable numerical resolution.Comment: 17 pages, 25 figure

Studies of acid deposition and its effects in two small catchments in Hunan, China

International audienceAcid deposition and its effects were studied by analysing the chemistry in precipitation, stream water, soil water and soils in two catchments in Hunan. One site, Linkesuo (denoted LKS), is on the outskirts of Changsha, the provincial capital of Hunan, the other (Bailutang, denoted BLT) on the outskirts of Chenzhou in southern Hunan. Volume-weighted average pH values and sulphate concentrations in wet deposition were 4.58 (BLT) and 4.90 (LKS) and 174 ?molc L-1 and 152 ?molc L-1, respectively. Wet deposition of sulphate has been estimated as 4.3 gS m-2yr-1 and 3.4 gS m-2yr-1 at BLT and LKS, respectively. Estimates of the corresponding total depositions (dry + wet) are 6.1 gS m-2yr-1 and 5.3 gS m-2yr-1. In precipitation and throughfall, sulphate was the major anion and calcium the major cation. In stream and soil water, nitrate was slightly higher than sulphate on an equivalent basis and magnesium (Mg) not much lower than calcium (Ca). Important soil properties, such as soil pH, soil organic matter (SOM) content, exchangeable acidic cations, exchangeable base cations, effective cation exchange capacity (CECe), base saturation (BS), and aluminium (Al) and iron (Fe) pools, were determined for five forest soil profiles (consisting of four horizons) in each of the two catchments. The soils in BLT are generally more acid, have lower BS and higher Al and Fe pools than the LKS soils. The Al- and Fe-pools were generally higher in the topsoils (i.e. the O and A horizons) than in deeper soils (i.e. E and B horizons) especially at the most acidic site (BLT). There are significant correlations between Fe-pools and the corresponding Al-pools in both catchments except between the amorphous Feox and Alox. Considering the long-term high deposition of sulphate, there is a risk of future ecological damage due to acidification, especially in the BLT catchment, although vegetation damage has yet to be observed in the catchments. This condition appears to be representative of a large part of Hunan. Keyword: acid deposition, soil acidification, catchment, Al-pools, Fe-pools, Hunan</p

Heavy Flavor Production at STAR

e present measurements on $D^0$ meson production via direct reconstruction of its hadronic decay channel $D^0\to K\pi$ in minimum bias $d$+Au and Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV with $p_T$ up to $\sim$3 GeV/$c$. Non-photonic electron spectra from the charm semi-leptonic decays are analyzed from the same data set as well as in $p$+$p$ collision at $\sqrt{s}$=200 GeV using the STAR Time-of-Flight (TOF) and Barrel EMC (BEMC) detectors, respectively. Results of the charm-decayed single muon (prompt muon) spectra are also presented at low $p_T$ in Au+Au collisions measured by the TOF detector. The charm production total cross-section per nucleon-nucleon collision is measured to be 1.26$\pm$0.09(stat.)$\pm$0.23(sys.) mb in minimum bias Au+Au collisions, which is consistent with the $N_{bin}$ scaling compared to 1.4$\pm0.2\pm$0.4 mb in minimum bias $d$+Au collisions, and supports the idea that charm quarks should be produced mostly via parton fusion at early stage in relativistic heavy-ion collisions. A Blast-Wave model fit to the low $p_T$ ($<2$ GeV/c) non-photonic electrons, prompt muons and $D^0$ spectra shows that charm hadrons may kinetically freeze-out earlier than light hadrons with a smaller collective velocity. The nuclear modification factors ($R_{AA}$) of the non-photonic electrons in central Au+Au collisions are significantly below unity at $p_T>\sim$2 GeV/$c$, which indicates a significant amount of energy loss for heavy quarks in Au+Au collisions. The charm transverse momentum distribution must have been modified by the hot and dense matter created in central Au+Au collisions at RHIC.Comment: 7 pages, 4 figures, proceedings for the Strange Quark Matter 2006 conferenc

Constraining the Metallicity of the Low Density Lyman-alpha Forest Using OVI Absorption

We search for OVI absorption in a Keck HIRES spectrum of the z=3.62 quasar Q1422+231. Comparison of CIV measurements to cosmological simulations shows that \lya forest absorbers with N_HI > 10^{14.5} have [C/H]~=-2.5, for the UV background spectrum of Haardt & Madau (HM). Lower column density absorption arises in lower density gas, where OVI is the most sensitive metal tracer. Since OVI lines lie at wavelengths contaminated by Lyman series absorption, we interpret our Q1422 results by comparing to artificial spectra drawn from an SPH simulation of a Lambda-dominated CDM model. A search for deep, narrow features in Q1422 yields only a few candidate OVI lines, statistically consistent with the number in artificial spectra with no metals; spectra generated with the HM background and [O/H] >= -2.5 predict too many narrow lines. However, applying the optical depth ratio technique of Songaila (1998), we DO find significant OVI associated with CIV systems; matching Q1422 requires [O/C]~=+0.5, implying [O/H]~=-2.0. Taken together these results imply that (a) the metallicity in the low density IGM is at least a factor of three below that in the overdense regions where CIV absorption is detectable, and (b) oxygen is overabundant in these regions, consistent with the enrichment pattern of old halo stars. If the UV background is heavily truncated above 4 Ry, an implausibly high oxygen overabundance ([O/C]>+2) is required by the data; thus a majority of the volume of the universe must have undergone helium reionization by z=3.(Abridged)Comment: Submitted to ApJ, 48 pp including 14 ps figures, uses aaspp4.st