1,758 research outputs found
Determination of the strange quark mass from Cabibbo-suppressed tau decays with resummed perturbation theory in an effective scheme
We present an analysis of the m_s^2-corrections to Cabibbo-suppressed tau
lepton decays employing contour improved resummation within an effective scheme
which is an essential new feature as compared to previous analyses. The whole
perturbative QCD dynamics of the tau-system is described by the beta-function
of the effective coupling constant and by two gamma-functions for the effective
mass parameters of the strange quark in different spin channels. We analyze the
stability of our results with regard to high-order terms in the perturbative
expansion of the renormalization group functions. A numerical value for the
strange quark mass in the MS scheme is extracted m_s(M_\tau)=130\pm 27_{exp}\pm
9_{th} MeV. After running to the scale 1 GeV this translates into m_s(1
GeV)=176 \pm 37_{exp}\pm 13_{th} MeV.Comment: 32 pages, latex, 4 postscript figures, revised version to appear in
European Physical Journal C, discussion of the choice of the moments added,
some errors correcte
Asymptotic structure of perturbative series for tau lepton observables
We analyze tau lepton decay observables, namely moments of the hadronic
spectral density in the finite energy interval (0,M_\tau), within finite order
perturbation theory including \alpha_s^4 corrections. The start of asymptotic
growth of perturbation theory series is found at this order in a scheme
invariant manner. We establish the ultimate accuracy of finite order
perturbation theory predictions and discuss the construction of optimal
observables.Comment: 21 page
Asymptotic structure of perturbative series for lepton decay observables: corrections
In a previous paper we performed an analysis of asymptotic structure of
perturbation theory series for semileptonic -lepton decays in massless
limit. We extend our analysis to the Cabibbo suppressed decay
modes of the lepton. In particular we address the problem of
corrections to theoretical formulas. The properties of the asymptotic behavior
of the finite order perturbation theory series for the coefficient functions of
the corrections are studied.Comment: 25 page
Mechanism of the fluxional behaviour in (1–5-η-cycloheptadienyl)-(1–5-η-cycloheptatrienyl)iron
Evidence for a 1.2-shift mechanism of the 1-5-η-cycloheptatrienyl moiety with respect to the central iron atom of the title compound is presented together with absolute assignments of the ^(13)C n.m.r. chemical shifts of the C_(7)H_(7) ring. A low-temperature rocking motion of both rings can be frozen out at -70 °C
A systematic review and meta-analysis of the effectiveness of antiseptics for meatal cleaning in the prevention of catheter associated urinary tract infections
Background: Catheter-associated urinary tract infections (CAUTIs) are among the most common healthcare-associated infections. Antiseptic cleaning of the meatal area before and during catheter use may reduce the risk of CAUTIs.
Aim: To undertake a systematic review of the literature and meta-analysis of studies investigating the effectiveness of antiseptic cleaning before urinary catheter insertion and during catheter use for prevention of CAUTIs.
Methods: Electronic databases were searched to identify randomized controlled trials. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated and compared across intervention and control groups using DerSimonian–Laird random-effects model. Subgroup analyses were performed. Heterogeneity was estimated using the I2 statistic.
Findings: In total, 2665 potential papers were identified; of these, 14 studies were eligible for inclusion. There was no difference in the incidence of CAUTIs when comparing antiseptic and non-antiseptic agents (pooled OR 0.90, 95% CI 0.73–1.10; P=0.31), or when comparing different agents: povidone-iodine vs routine care; povidone-iodine vs soap and water; chlorhexidine vs water; povidone-iodine vs saline; povidone-iodine vs water; and green soap and water vs routine care (P > 0.05 for all). Comparison of an antibacterial agent with routine care indicated near significance (P=0.06). There was no evidence of heterogeneity (I2=0%; P > 0.05). Subgroup analyses showed no difference in the incidence of CAUTIs in terms of country, setting, risk of bias, sex and frequency of administration.
Conclusions: There were no differences in CAUTI rates, although methodological issues hamper generalizability of this finding. Antibacterial agents may prove to be significant in a well-conducted study. The present results provide good evidence to inform infection control guidelines in catheter management
Mid-infrared Imaging of a Circumstellar Disk Around HR 4796: Mapping the Debris of Planetary Formation
We report the discovery of a circumstellar disk around the young A0 star, HR
4796, in thermal infrared imaging carried out at the W.M. Keck Observatory. By
fitting a model of the emission from a flat dusty disk to an image at
lambda=20.8 microns, we derive a disk inclination, i = 72 +6/-9 deg from face
on, with the long axis of emission at PA 28 +/-6 deg. The intensity of emission
does not decrease with radius as expected for circumstellar disks but increases
outward from the star, peaking near both ends of the elongated structure. We
simulate this appearance by varying the inner radius in our model and find an
inner hole in the disk with radius R_in = 55+/-15 AU. This value corresponds to
the radial distance of our own Kuiper belt and may suggest a source of dust in
the collision of cometesimals. By contrast with the appearance at 20.8 microns,
excess emission at lambda = 12.5 microns is faint and concentrated at the
stellar position. Similar emission is also detected at 20.8 microns in residual
subtraction of the best-fit model from the image. The intensity and ratio of
flux densities at the two wavelengths could be accounted for by a tenuous dust
component that is confined within a few AU of the star with mean temperature of
a few hundred degrees K, similar to that of zodiacal dust in our own solar
system. The morphology of dust emission from HR 4796 (age 10 Myr) suggests that
its disk is in a transitional planet-forming stage, between that of massive
gaseous proto-stellar disks and more tenuous debris disks such as the one
detected around Vega.Comment: 9 pages, 4 figures as LaTex manuscript and postscript files in
gzipped tar file. Accepted for publication in Astrophysical Journal Letters.
http://upenn5.hep.upenn.edu/~davidk/hr4796.htm
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ODTX Measurements and Simulations on Ultra Fine TATB and PBX-9502
We measure the time to explosion of 12.7 mm diameter spheres of ultra fine TATB and PBX-9502 (95 wt% TATB, 5 wt% Kel-F 800) at 85.0, 92.5, and 98.0 percent of theoretical maximum density (TMD) in confined and unconfined configurations and at several elevated temperatures with the Lawrence Livermore National Laboratory (LLNL) One Dimensional Time to Explosion (ODTX) apparatus. Time to explosion data provide insight into the relative ease of thermal ignition and allow for the calibration of kinetic parameters. The measurements show that PBX-9502 is more thermally stable than ultra fine TATB, that unconfined samples are slightly more thermally stable than confined ones, and that lower density samples are more thermally stable than higher density ones. 'Go/no go' data at the lowest temperatures yield an experimental measurement of the critical temperature, which is the temperature at which an explosive can be heated indefinitely without undergoing self-heating and concomitant rapid and violent decomposition. Critical temperatures ranges for 12.7 mm diameter spheres of 98% TMD ultra fine TATB and PBX-9502 are 213-230 C and 234-239 C, respectively. Experimental data are modeled with ALE3D and kinetic parameters are determined. These kinetic parameters, when coupled with thermal property data, provide good prediction of the time to explosion
The Solar Neighborhood. XXXIV. A Search for Planets Orbiting Nearby M Dwarfs using Astrometry
Astrometric measurements are presented for seven nearby stars with previously
detected planets: six M dwarfs (GJ 317, GJ 667C, GJ 581, GJ 849, GJ 876, and GJ
1214) and one K dwarf (BD 10 3166). Measurements are also presented for six
additional nearby M dwarfs without known planets, but which are more favorable
to astrometric detections of low mass companions, as well as three binary
systems for which we provide astrometric orbit solutions. Observations have
baselines of three to thirteen years, and were made as part of the RECONS
long-term astrometry and photometry program at the CTIO/SMARTS 0.9m telescope.
We provide trigonometric parallaxes and proper motions for all 16 systems, and
perform an extensive analysis of the astrometric residuals to determine the
minimum detectable companion mass for the 12 M dwarfs not having close stellar
secondaries. For the six M dwarfs with known planets, we are not sensitive to
planets, but can rule out the presence of all but the least massive brown
dwarfs at periods of 2 - 12 years. For the six more astrometrically favorable M
dwarfs, we conclude that none have brown dwarf companions, and are sensitive to
companions with masses as low as 1 for periods longer than two years.
In particular, we conclude that Proxima Centauri has no Jovian companions at
orbital periods of 2 - 12 years. These results complement previously published
M dwarf planet occurrence rates by providing astrometrically determined upper
mass limits on potential super-Jupiter companions at orbits of two years and
longer. As part of a continuing survey, these results are consistent with the
paucity of super-Jupiter and brown dwarf companions we find among the over 250
red dwarfs within 25 pc observed longer than five years in our astrometric
program.Comment: 18 pages, 5 figures, 4 tables, accepted for publication in A
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