4,898 research outputs found
Light meson form factors at high from lattice QCD
Measurements and theoretical calculations of meson form factors are essential
for our understanding of internal hadron structure and QCD, the dynamics that
bind the quarks in hadrons. The pion electromagnetic form factor has been
measured at small space-like momentum transfer ~GeV by pion
scattering from atomic electrons and at values up to ~GeV by
scattering electrons from the pion cloud around a proton. On the other hand, in
the limit of very large (or infinite) , perturbation theory is
applicable. This leaves a gap in the intermediate where the form factors
are not known.
As a part of their 12 GeV upgrade Jefferson Lab will measure pion and kaon
form factors in this intermediate region, up to of ~GeV. This is
then an ideal opportunity for lattice QCD to make an accurate prediction ahead
of the experimental results. Lattice QCD provides a from-first-principles
approach to calculate form factors, and the challenge here is to control the
statistical and systematic uncertainties as errors grow when going to higher
values.
Here we report on a calculation that tests the method using an
meson, a 'heavy pion' made of strange quarks, and also present preliminary
results for kaon and pion form factors. We use the ensembles made
by the MILC collaboration and Highly Improved Staggered Quarks, which allows us
to obtain high statistics. The HISQ action is also designed to have small
discretisation errors. Using several light quark masses and lattice spacings
allows us to control the chiral and continuum extrapolation and keep systematic
errors in check.Comment: Presented at Lattice 2017, the 35th International Symposium on
Lattice Field Theory at Granada, Spain (18-24 June 2017
Quantifying the Topology of Large-Scale Structure
We propose and investigate a new algorithm for quantifying the topological
properties of cosmological density fluctuations. We first motivate this
algorithm by drawing a formal distinction between two definitions of relevant
topological characteristics, based on concepts, on the one hand, from
differential topology and, on the other, from integral geometry. The former
approach leads one to concentrate on properties of the contour surfaces which,
in turn, leads to the algorithms CONTOUR2D and CONTOUR3D familiar to
cosmologists. The other approach, which we adopt here, actually leads to much
simpler algorithms in both two and three dimensions. (The 2D algorithm has
already been introduced to the astronomical literature.) We discuss the 3D case
in some detail and compare results obtained with it to analogous results using
the CONTOUR3D algorithm.Comment: 10 pages, LaTex using mn.sty, 3 figures available on request from
[email protected]; MNRAS, in pres
Origin of magnetic moments in carbon nanofoam
A range of carbon nanofoam samples was prepared by using a high-repetition-rate laser ablation technique under various Ar pressures. Their magnetic properties were systematically investigated by dc magnetization measurements and continuous wave (cw) as well as pulsed EPR techniques. In all samples we found very large zero-field cooled-field-cooled thermal hysteresis in the susceptibility measurements extending up to room temperature. Zero-field cooled (ZFC) susceptibility measurements also display very complex behavior with a susceptibility maximum that strongly varies in temperature from sample to sample. Low-temperature magnetization curves indicate a saturation magnetization MS ≈0.35 emu g at 2 K and can be well fitted with a classical Langevin function. MS is more than an order of magnitude larger than any possible iron impurity, proving that the observed magnetic phenomena are an intrinsic effect of the carbon nanofoam. Magnetization measurements are consistent with a spin-glass type ground state. The cusps in the ZFC susceptibility curves imply spin freezing temperatures that range from 50 K to the extremely high value of >300 K. Further EPR measurements revealed three different centers that coexist in all samples, distinguished on the basis of g -factor and relaxation time. Their possible origin and the role in the magnetic phenomena are discussed
Comparisons between intragastric and small intestinal delivery of enteral nutrition in the critically ill: a systematic review and meta-analysis
INTRODUCTION: The largest cohort of critically ill patients evaluating intragastric and small intestinal delivery of nutrients was recently reported. This systematic review included recent data to compare the effects of small bowel and intragastric delivery of enteral nutrients in adult critically ill patients. METHODS: This is a systematic review of all randomised controlled studies published between 1990 and March 2013 that reported the effects of the route of enteral feeding in the critically ill on clinically important outcomes. RESULTS: Data from 15 level-2 studies were included. Small bowel feeding was associated with a reduced risk of pneumonia (Relative Risk, RR, small intestinal vs. intragastric: 0.75 (95% confidence interval 0.60 to 0.93); P = 0.01; I(2 )= 11%). The point estimate was similar when only studies using microbiological data were included. Duration of ventilation (weighted mean difference: -0.36 days (-2.02 to 1.30); P = 0.65; I(2 )= 42%), length of ICU stay (WMD: 0.49 days, (-1.36 to 2.33); P = 0.60; I(2 )= 81%) and mortality (RR 1.01 (0.83 to 1.24); P = 0.92; I(2 )= 0%) were unaffected by the route of feeding. While data were limited, and there was substantial statistical heterogeneity, there was significantly improved nutrient intake via the small intestinal route (% goal rate received: 11% (5 to 16%); P = 0.0004; I(2 )= 88%). CONCLUSIONS: Use of small intestinal feeding may improve nutritional intake and reduce the incidence of ICU-acquired pneumonia. In unselected critically ill patients other clinically important outcomes were unaffected by the site of the feeding tube
Drying of complex suspensions
We investigate the 3D structure and drying dynamics of complex mixtures of
emulsion droplets and colloidal particles, using confocal microscopy. Air
invades and rapidly collapses large emulsion droplets, forcing their contents
into the surrounding porous particle pack at a rate proportional to the square
of the droplet radius. By contrast, small droplets do not collapse, but remain
intact and are merely deformed. A simple model coupling the Laplace pressure to
Darcy's law correctly estimates both the threshold radius separating these two
behaviors, and the rate of large-droplet evacuation. Finally, we use these
systems to make novel hierarchical structures.Comment: 4 pages, 4 figure
Cell migration in response to the amino-terminal fragment of urokinase requires epidermal growth factor receptor activation through an ADAM-mediated mechanism
BackgroundCell migration is an integral component of intimal hyperplasia development and proteases are pivotal in the process. Understanding the role of urokinase signaling within the cells of vasculature remains poorly defined. The study examines the role of amino-terminal fragment (ATF) of urokinase on a pivotal cross-talk receptor, epidermal growth factor receptor (EGFR). EGFR is transactivated by both G-protein-coupled receptors and receptor tyrosine kinases and is key to many of their responses. We hypothesize that A Disintegrin and Metalloproteinase Domains (ADAM) allows the transactivation of EGFR by ATF.ObjectiveTo determine the role of ADAM in EGFR transactivation by ATF in human vascular smooth muscle cells (VSMC) during cell migration.MethodsHuman coronary VSMC were cultured in vitro. Assays of EGFR phosphorylation were examined in response to ATF (10 nM) in the presence and absence of the matrix metalloprotease (MMP) inhibitor GM6001, the ADAM inhibitors TAPI-0 and TAPI-1, heparin binding epidermal growth factor (HB-EGF) inhibitor, CRM197, HB-EGF inhibitory antibodies, epidermal growth factor (EGF) inhibitory antibodies, and the EGFR inhibitor AG1478. The small interference ribonucleic acid (siRNA) against EGFR and ADAM-9, ADAM-10, ADAM-12, and adenoviral delivered Gbg inhibitor, βARKCT were also used.ResultsATF produced concentration-dependent VSMC migration (by wound assay and Boyden chamber), which was inhibited by increasing concentrations of AG1478. ATF was shown to induce time-dependent EGFR phosphorylation, which peaked at fourfold greater than control. Pre-incubation with the Gβγ inhibitor βARKCT inhibited EGFR activation by ATF. This migratory and EGFR response was inhibited by AG1478 in a concentration-dependent manner. Incubation with siRNA against EGFR blocked the ATF-mediated migratory and EGFR responses. EGFR phosphorylation by ATF was blocked by inhibition of MMP activity and the ligand HB-EGF. The presence of the ADAM inhibitors, TAPI-0 and TAPI-1 significantly decreased EGFR activation. EGFR phosphorylation by EGF was not interrupted by inhibition of MMP, ADAMs, or HB-EGF. Direct blockade of the EGFR prevented activation by both ATF and EGF. Incubation with siRNA to ADAM-9 and -10 significantly reduced HB-EGF release from VSMC and EGFR activation in response to ATF. The siRNA against ADAM-12 had no effect.ConclusionATF can induce transactivation of EGFR by an ADAM-mediated, HB-EGF-dependent process. Targeting a pivotal cross-talk receptor such as EGFR is an attractive molecular target to inhibit cell migration.Clinical RelevanceCell migration is an integral component of intimal hyperplasia development and proteases are pivotal in the process. Understanding the role of urokinase signaling within the cells of vasculature remains poorly defined. The study examines the role of ATF of urokinase on a pivotal cross-talk receptor, EGFR. EGFR is transactivated by both G-protein-coupled receptors and receptor tyrosine kinases and is key to many of their responses. ATF can induce transactivation of EGFR by an ADAM-mediated, HB-EGF-dependent process. Targeting a pivotal cross-talk receptor such as EGFR, which can be transactivated by both G-protein-coupled receptors and receptor tyrosine kinases is an attractive molecular target
A laterally-fused N-heterocyclic carbene framework from polysubstituted aminoimidazo[5,1-b]oxazol-6-ium salts
A polysubstituted 3-aminoimidazo[5,1-b]oxazol-6-ium framework has been accessed from a new nitrenoid reagent by a two-step ynamide annulation and imidazolium ring-formation sequence. Metalation with Au(I), Cu(I) and Ir(I) at the C2 position provides an L-shaped NHC ligand scaffold that has been validated in gold-catalysed alkyne hydration and arylative cyclisation reactions
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