2,069 research outputs found
Properties of WNh stars in the Small Magellanic Cloud: evidence for homogeneous evolution
We derive the physical properties of three WNh stars in the SMC to constrain
stellar evolution beyond the main sequence at low metallicity and to
investigate the metallicity dependence of the clumping properties of massive
stars. We compute atmosphere models to derive the stellar and wind properties
of the three WNh targets. A FUV/UV/optical/near-infrared analysis gives access
to temperatures, luminosities, mass loss rates, terminal velocities and stellar
abundances. All stars still have a large hydrogen mass fraction in their
atmosphere, and show clear signs of CNO processing in their surface abundances.
One of the targets can be accounted for by normal stellar evolution. It is a
star with initial mass around 40-50 Msun in, or close to, the core He burning
phase. The other two objects must follow a peculiar evolution, governed by fast
rotation. In particular, one object is likely evolving homogeneously due to its
position blue-ward of the main sequence and its high H mass fraction. The
clumping factor of one star is found to be 0.15+/-0.05. This is comparable to
values found for Galactic Wolf-Rayet stars, indicating that within the
uncertainties, the clumping factor does not seem to depend on metallicity.Comment: 16 pages. A&A accepte
Gravitational solution to the Pioneer 10/11 anomaly
A fully relativistic modified gravitational theory including a fifth force
skew symmetric field is fitted to the Pioneer 10/11 anomalous acceleration. The
theory allows for a variation with distance scales of the gravitational
constant G, the fifth force skew symmetric field coupling strength omega and
the mass of the skew symmetric field mu=1/lambda. A fit to the available
anomalous acceleration data for the Pioneer 10/11 spacecraft is obtained for a
phenomenological representation of the "running" constants and values of the
associated parameters are shown to exist that are consistent with fifth force
experimental bounds. The fit to the acceleration data is consistent with all
current satellite, laser ranging and observations for the inner planets.Comment: 14 pages, 3 figures, 3 tables. typo's were corrected at Equations (4)
and (12) and a third table including our predictions for the anomalous
perihelion advance of the planets was adde
Summary Report on 2018 Residue Monitoring of Irish Farmed Finfish & 2018 Border Inspection Post Fishery Product Testing undertaken at the Marine Institute
On behalf of the Department of Agriculture, Food and Marine (DAFM), the Marine Institute carries out monitoring of chemical residues in finfish for aquaculture sector. This monitoring is set out in the annual National Residue Control Plan, which is approved by the European Commission, and is an important component of the DAFM food safety controls and is implemented under a service contract with the Food Safety Authority of Ireland. Since 1999, the Marine Institute has implemented the National Residues Monitoring Programme for aquaculture. This is carried out on behalf of the Sea Fisheries Protection Authority, which is the responsible organisation for residue controls on farmed finfish.
In 2018, in excess of 920 tests and a total of 2,611 measurements were carried out on 171 samples of farmed finfish for a range of residues. Implementation of the Aquaculture 2018 Plan involves taking samples at both farm and processing plant:
• 123 target samples taken at harvest: 110 farmed salmon and 13 freshwater trout.
• 48 target samples were taken at other stages of production: 40 salmon smolts and 8 freshwater trout.
All 2018 samples were compliant. For target sampling of farmed fish, a summary table of the residue results from 2005 - 2018 is outlined in Table 1. Overall, the outcome for aquaculture remains one of consistently low occurrence of residues in farmed finfish, with no non-compliant target residues results for the period 2006-2014, 0.11% and 0.10% non-compliant target residues results in 2015 and 2016 respectively and no non-compliant target results in 2017 and 2018
What Are the Low-Q and Large-x Boundaries of Collinear QCD Factorization Theorems?
Familiar factorized descriptions of classic QCD processes such as deeply inelastic scattering (DIS) apply in the limit of very large hard scales, much larger than nonperturbative mass scales and other nonperturbative physical properties like intrinsic transverse momentum. Since many interesting DIS studies occur at kinematic regions where the hard scale, Q ∼ 1-2 GeV, is not very much greater than the hadron masses involved, and the Bjorken scaling variable xbj is large, xbj ≳ 0.5, it is important to examine the boundaries of the most basic factorization assumptions and assess whether improved starting points are needed. Using an idealized field-theoretic model that contains most of the essential elements that a factorization derivation must confront, we retrace the steps of factorization approximations and compare with calculations that keep all kinematics exact. We examine the relative importance of such quantities as the target mass, light quark masses, and intrinsic parton transverse momentum, and argue that a careful accounting of parton virtuality is essential for treating power corrections to collinear factorization. We use our observations to motivate searches for new or enhanced factorization theorems specifically designed to deal with moderately low-Q and large-xbj physics. © 2017 American Physical Society
What Are the Low-Q and Large-x Boundaries of Collinear QCD Factorization Theorems?
Familiar factorized descriptions of classic QCD processes such as deeply inelastic scattering (DIS) apply in the limit of very large hard scales, much larger than nonperturbative mass scales and other nonperturbative physical properties like intrinsic transverse momentum. Since many interesting DIS studies occur at kinematic regions where the hard scale, Q ∼ 1-2 GeV, is not very much greater than the hadron masses involved, and the Bjorken scaling variable xbj is large, xbj ≳ 0.5, it is important to examine the boundaries of the most basic factorization assumptions and assess whether improved starting points are needed. Using an idealized field-theoretic model that contains most of the essential elements that a factorization derivation must confront, we retrace the steps of factorization approximations and compare with calculations that keep all kinematics exact. We examine the relative importance of such quantities as the target mass, light quark masses, and intrinsic parton transverse momentum, and argue that a careful accounting of parton virtuality is essential for treating power corrections to collinear factorization. We use our observations to motivate searches for new or enhanced factorization theorems specifically designed to deal with moderately low-Q and large-xbj physics. © 2017 American Physical Society
Collinear factorization in wide-angle hadron pair production in e+e-annihilation
We compute the inclusive unpolarized dihadron production cross section in the far from back-to-back region of e+e-annihilation in leading order pQCD using existing fragmentation function fits and standard collinear factorization, focusing on the large transverse momentum region where transverse momentum is comparable to the hard scale (the center-of-mass energy). We compare with standard transverse-momentum-dependent (TMD) fragmentation function-based predictions intended for the small transverse momentum region with the aim of testing the expectation that the two types of calculation roughly coincide at intermediate transverse momentum. We find significant tension, within the intermediate transverse momentum region, between calculations done with existing nonperturbative TMD fragmentation functions and collinear factorization calculations if the center-of-mass energy is not extremely large. We argue that e+e-measurements are ideal for resolving this tension and exploring the large-to-small transverse momentum transition, given the typically larger hard scales (~10 GeV) of the process as compared with similar scenarios that arise in semi-inclusive deep inelastic scattering and fixed-target Drell-Yan measurements
Qualitative Analysis of Universes with Varying Alpha
Assuming a Friedmann universe which evolves with a power-law scale factor,
, we analyse the phase space of the system of equations that describes
a time-varying fine structure 'constant', , in the
Bekenstein-Sandvik-Barrow-Magueijo generalisation of general relativity. We
have classified all the possible behaviours of in ever-expanding
universes with different and find new exact solutions for . We
find the attractors points in the phase space for all . In general, will be a non-decreasing function of time that increases logarithmically in
time during a period when the expansion is dust dominated (), but
becomes constant when . This includes the case of negative-curvature
domination (). also tends rapidly to a constant when the
expansion scale factor increases exponentially. A general set of conditions is
established for to become asymptotically constant at late times in an
expanding universe.Comment: 26 pages, 6 figure
Time Delay Predictions in a Modified Gravity Theory
The time delay effect for planets and spacecraft is obtained from a fully
relativistic modified gravity theory including a fifth force skew symmetric
field by fitting to the Pioneer 10/11 anomalous acceleration data. A possible
detection of the predicted time delay corrections to general relativity for the
outer planets and future spacecraft missions is considered. The time delay
correction to GR predicted by the modified gravity is consistent with the
observational limit of the Doppler tracking measurement reported by the Cassini
spacecraft on its way to Saturn, and the correction increases to a value that
could be measured for a spacecraft approaching Neptune and Pluto.Comment: 5 pages, LaTex file, no figures. Corrections to Table
Geodesic and Path Motion in the Nonsymmetric Gravitational Theory
We study the problem of test-particle motion in the Nonsymmetric
Gravitational Theory (NGT) assuming the four-velocity of the particle is
parallel-transported along the trajectory. The predicted motion is studied on a
static, spherically symmetric background field, with particular attention paid
to radial and circular motions. Interestingly, it is found that the proper time
taken to travel between any two non-zero radial positions is finite. It is also
found that circular orbits can be supported at lower radii than in General
Relativity for certain forms of motion.
We present three interactions which could be used as alternate methods for
coupling a test-particle to the antisymmetric components of the NGT field. One
of these takes the form of a Yukawa force in the weak-field limit of a static,
spherically symmetric field, which could lead to interesting phenomenology.Comment: 17 pages, REVTeX 3.0 with amssymb.st
Spectroscopy of SMC Wolf-Rayet Stars Suggests that Wind-Clumping does not Depend on Ambient Metallicity
The mass-loss rates of hot, massive, luminous stars are considered a decisive
parameter in shaping the evolutionary tracks of such stars and influencing the
interstellar medium on galactic scales. The small-scale structures (clumps)
omnipresent in such winds may reduce empirical estimates of mass-loss rates by
an evolutionarily significant factor of >=3. So far, there has been no direct
observational evidence that wind-clumping may persist at the same level in
environments with a low ambient metallicity, where the wind-driving opacity is
reduced. Here we report the results of time-resolved spectroscopy of three
presumably single Population I Wolf-Rayet stars in the Small Magellanic Cloud,
where the ambient metallicity is ~1/5 Z_Sun.We detect numerous small-scale
emission peaks moving outwards in the accelerating parts of the stellar
winds.The general properties of the moving features, such as their velocity
dispersions,emissivities and average accelerations, closely match the
corresponding characteristics of small-scale inhomogeneities in the winds of
Galactic Wolf-Rayet stars.Comment: 9 pages, 3 figures; accepted by ApJ Letter
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