1,048 research outputs found
Detailed Balance and Sea-Quark Flavor Asymmetry of Proton
In this study, the proton is taken as an ensemble of quark-gluon Fock states.
Using the principle of detailed balance, the probabilities of finding every
Fock states of the proton are obtained without any parameter. A new origin of
the light flavor sea quark asymmetry, i.e., , is given
as a pure statistical effect. It is found that ,
which is in surprisingly agreement with the experimental observation.Comment: significant changes in title and content, 12 latex pages, to appear
in PL
Flavor Structure of the Nucleon Sea
The recent progress on our understanding of the flavor structure of
unpolarized and polarized nucleon sea is reviewed. The large flavor asymmetry
between the up and down sea quark distributions is now well established. This
asymmetry strongly suggests the importance of the mesonic degrees of freedom in
the description of the nucleon sea. The strong connection between the flavor
structure and the spin structure of the nucleon sea is emphasized. Possible
future measurements for testing various theoretical models are also discussed.Comment: 5pages, 4 figures, Invited talk presented at the QNP2002 conference,
Julich, June 200
Sigma Meson Cloud and Proton's Light Flavor Sea Quarks
We take into account the sigma meson cloud effect in the meson cloud model to
calculate the distributions of light flavor sea quarks in the proton. Our
calculation gives a better description of the data for .
We also provide a picture that the probability of finding a physical proton in
a Fock state is reasonable small with a smaller cutoff
.Comment: 10 latex pages, 4 figures. Version to appear in PL
Principle of Balance and the Sea Content of the Proton
In this study, the proton is taken as an ensemble of quark-gluon Fock states.
Using the principle of balance that every Fock state should be balanced with
all of the nearby Fock states (denoted as the balance model), instead of the
principle of detailed balance that any two nearby Fock states should be
balanced with each other (denoted as the detailed balance model), the
probabilities of finding every Fock state of the proton are obtained. The
balance model can be taken as a revised version of the detailed balance model,
which can give an excellent description of the light flavor sea asymmetry
(i.e., ) without any parameter. In case of
sub-processes not considered, the balance model and the
detailed balance model give the same results. In case of
sub-processes considered, there is about 10 percent difference between the
results of these models. We also calculate the strange content of the proton
using the balance model under the equal probability assumption.Comment: 32 latex pages, 4 ps figures, to appear in PR
Neurocognitive function in HIV infected patients on antiretroviral therapy
OBJECTIVE
To describe factors associated with neurocognitive (NC) function in HIV-positive patients on stable combination antiretroviral therapy.
DESIGN
We undertook a cross-sectional analysis assessing NC data obtained at baseline in patients entering the Protease-Inhibitor-Monotherapy-Versus-Ongoing-Triple therapy (PIVOT) trial.
MAIN OUTCOME MEASURE
NC testing comprised of 5 domains. Raw results were z-transformed using standard and demographically adjusted normative datasets (ND). Global z-scores (NPZ-5) were derived from averaging the 5 domains and percentage of subjects with test scores >1 standard deviation (SD) below population means in at least two domains (abnormal Frascati score) calculated. Patient characteristics associated with NC results were assessed using multivariable linear regression.
RESULTS
Of the 587 patients in PIVOT, 557 had full NC results and were included. 77% were male, 68% Caucasian and 28% of Black ethnicity. Mean (SD) baseline and nadir CD4+ lymphocyte counts were 553(217) and 177(117) cells/µL, respectively, and HIV RNA was <50 copies/mL in all. Median (IQR) NPZ-5 score was -0.5 (-1.2/-0) overall, and -0.3 (-0.7/0.1) and -1.4 (-2/-0.8) in subjects of Caucasian and Black ethnicity, respectively. Abnormal Frascati scores using the standard-ND were observed in 51%, 38%, and 81%, respectively, of subjects overall, Caucasian and Black ethnicity (p<0.001), but in 62% and 69% of Caucasian and Black subjects using demographically adjusted-ND (p = 0.20). In the multivariate analysis, only Black ethnicity was associated with poorer NPZ-5 scores (P<0.001).
CONCLUSIONS
In this large group of HIV-infected subjects with viral load suppression, ethnicity but not HIV-disease factors is closely associated with NC results. The prevalence of abnormal results is highly dependent on control datasets utilised.
TRIAL REGISTRY
ClinicalTrials.gov, NCT01230580
Testing the meson cloud in the nucleon in Drell-Yan processes
We discuss the present status of the \bar u-\bar d asymmetry in the nucleon
and analize the quantities which are best suited to verify the asymmetry. We
find that the Drell-Yan asymmetry is the quantity insensitive to the valence
quark distributions and very sensitive to the flavour asymmetry of the sea. We
compare the prediction of the meson cloud model with different experimental
data including the Fermilab E772 data and recent data of the NA51 Collaboration
at CERN and make predictions for the planned Drell-Yan experiments.Comment: written in ReVTeX, 26 pages + 10 PS-figure
Nuclear EMC Effect in a Statistical Model
A simple statistical model in terms of light-front kinematic variables is
used to explain the nuclear EMC effect in the range , which
was constructed by us previously to calculate the parton distribution functions
(PDFs) of the nucleon. Here, we treat the temperature as a parameter of the
atomic number , and get reasonable results in agreement with the
experimental data. Our results show that the larger , the lower thus the
bigger volume , and these features are consistent with other models.
Moreover, we give the predictions of the quark distribution ratios,
\emph{i.e.}, , , and , and also the gluon ratio for iron as an example. The
predictions are different from those by other models, thus experiments aiming
at measuring the parton ratios of antiquarks, strange quarks, and gluons can
provide a discrimination of different models.Comment: 26 latex pages, 3 figure
Flavor Asymmetry of the Nucleon Sea and W Boson Production
The advantage and feasibility of using -boson production to extract unique
information on the flavor asymmetry of the and sea-quark
distributions in the proton are examined. The and production cross
section ratios in collisions are shown to be sensitive to the ratios, and they are free from charge-symmetry-breaking and
nuclear-binding effects. The feasibility for measuring these ratios at the RHIC
and LHC proton-proton colliders, as well as the expected sensitivity to the
ratios, are also presented.Comment: 7 pages, 4 figures (updated figures
Reversal of Tetracycline Resistance by Cepharanthine, Cinchonidine, Ellagic Acid and Propyl Gallate in a Multi-drug Resistant Escherichia coli
Bacterial resistance to antibiotics is an increasing threat to global healthcare systems. We therefore sought compounds with potential to reverse antibiotic resistance in a clinically relevant multi-drug resistant isolate of Escherichia coli (NCTC 13400). 200 natural compounds with a history of either safe oral use in man, or as a component of a traditional herb or medicine, were screened. Four compounds; ellagic acid, propyl gallate, cinchonidine and cepharanthine, lowered the minimum inhibitory concentrations (MICs) of tetracycline, chloramphenicol and tobramycin by up to fourfold, and when combined up to eightfold. These compounds had no impact on the MICs of ampicillin, erythromycin or trimethoprim. Mechanistic studies revealed that while cepharanthine potently suppressed efflux of the marker Nile red from bacterial cells, the other hit compounds slowed cellular accumulation of this marker, and/or slowed bacterial growth in the absence of antibiotic. Although cepharanthine showed some toxicity in a cultured HEK-293 mammalian cell-line model, the other hit compounds exhibited no toxicity at concentrations where they are active against E. coli NCTC 13400. The results suggest that phytochemicals with capacity to reverse antibiotic resistance may be more common in traditional medicines than previously appreciated, and may offer useful scaffolds for the development of antibiotic-sensitising drugs
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