5,189 research outputs found
Relevance of the observation of UHE gammas to hard X-ray astronomy
A number of consequences of the presence of sources of ultra high energy (UHE) gamma rays, exemplified by Cygnus X-3, are examined. It is shown that there should be a flux of hard X-rays at all Galactic latitudes; a significant flux of extragalactic hard X-rays may also result. Relevance to theories of cosmic ray particle origin and propagation is discussed
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Farmers' management of rice varietal diversity in the mid-hills of Nepal: implications for on-farm conservation and crop improvement
Season-long monitoring of on-farm rice (Oryza sativa, L.) plots in Nepal explored farmers' decision-making process on the deployment of varieties to agroecosystems, application of production inputs to varieties, agronomic practices and relationship between economic return and area planted per variety. Farmers deploy varieties [landraces (LRs) and modern varieties (MVs)] to agroecosystems based on their understanding of characteristics of varieties and agroecosystems, and the interaction between them. In marginal growing conditions, LRs can compete with MVs. Within an agroecosystem, economic return and area planted to varieties have positive relationship, but this is not so between agroecosystems. LRs are very diverse on agronomic and economic traits; therefore, they cannot be rejected a priori as inferior materials without proper evaluation. LRs have to be evaluated for useful traits and utilized in breeding programmes to generate farmer-preferred materials for marginal environments and for their conservation on-farm
The Heavy Quark Form Factors at Two Loops
We compute the two-loop QCD corrections to the heavy quark form factors in
case of the vector, axial-vector, scalar and pseudo-scalar currents up to
second order in the dimensional parameter . These terms are
required in the renormalization of the higher order corrections to these form
factors.Comment: 131 pages, 3 figure
Heavy quark form factors at two loops in perturbative QCD
We present the results for heavy quark form factors at two-loop order in
perturbative QCD for different currents, namely vector, axial-vector, scalar
and pseudo-scalar currents, up to second order in the dimensional
regularization parameter. We outline the necessary computational details,
ultraviolet renormalization and corresponding universal infrared structure.Comment: 13 pages Latex, Proceedings of XLI International Conference of
Theoretical Physics "Matter to the Deepest", Podlesice, Poland, September
3-8, 2017 and RADCOR 2017, St.~Gilgen Austria, Sept 24-29, 201
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Improvement in Renal Function and Reduction in Serum Uric Acid with Intensive Statin Therapy in Older Patients: A Post Hoc Analysis of the SAGE Trial.
BackgroundImprovement in renal function and decreases in serum uric acid (SUA) have been reported following prolonged high-intensity statin (HMG-CoA reductase inhibitor) therapy. This post hoc analysis of the SAGE trial examined the effect of intensive versus less intensive statin therapy on renal function, safety, and laboratory parameters, including SUA, in elderly coronary artery disease (CAD) patients (65-85 years) with or without chronic kidney disease (CKD).MethodsPatients were randomized to atorvastatin 80 mg/day or pravastatin 40 mg/day and treated for 12 months. Patients were stratified using Modification of Diet in Renal Disease (MDRD) estimated glomerular filtration rates (eGFRs) in CKD (eGFR <60 mL/min/1.73 m(2)) and non-CKD populations.ResultsOf the 893 patients randomized, 858 had complete renal data and 418 of 858 (49%) had CKD (99% Stage 3). Over 12 months, eGFR increased with atorvastatin and remained stable with pravastatin (+2.38 vs. +0.18 mL/min/1.73 m(2), respectively; p < 0.0001). MDRD eGFR improved significantly in both CKD treatment arms; however, the increased eGFR in patients without CKD was significantly greater with atorvastatin (+2.08 mL/min/1.73 m(2)) than with pravastatin (-1.04 mL/min/1.73 m(2)). Modest reductions in SUA were observed in both treatment arms, but a greater fall occurred with atorvastatin than with pravastatin (-0.52 vs. -0.09 mg/dL, p < 0.0001). Change in SUA correlated negatively with changes in eGFR and positively with changes in low-density lipoprotein cholesterol. Reports of myalgia were rare (3.6% CKD; 5.7% non-CKD), and there were no episodes of rhabdomyolysis. Elevated serum alanine and aspartate transaminase to >3 times the upper limit of normal occurred in 4.4% of atorvastatin- and 0.2% of pravastatin-treated patients.ConclusionIntensive management of dyslipidemia in older patients with stable coronary heart disease may have beneficial effects on renal function and SUA
Heavy Quark Form Factors at Three Loops in the Planar Limit
We compute the color-planar and complete light quark non-singlet
contributions to the heavy quark form factors in the case of the axialvector,
scalar and pseudoscalar currents at three loops in perturbative QCD. We
evaluate the master integrals applying a new method based on differential
equations for general bases, which is applicable for all first order
factorizing systems. The analytic results are expressed in terms of harmonic
polylogarithms and real-valued cyclotomic harmonic polylogarithms.Comment: 9 pages, 4 figure
Ultrafast Optical-Pump Terahertz-Probe Spectroscopy of the Carrier Relaxation and Recombination Dynamics in Epitaxial Graphene
The ultrafast relaxation and recombination dynamics of photogenerated
electrons and holes in epitaxial graphene are studied using optical-pump
Terahertz-probe spectroscopy. The conductivity in graphene at Terahertz
frequencies depends on the carrier concentration as well as the carrier
distribution in energy. Time-resolved studies of the conductivity can therefore
be used to probe the dynamics associated with carrier intraband relaxation and
interband recombination. We report the electron-hole recombination times in
epitaxial graphene for the first time. Our results show that carrier cooling
occurs on sub-picosecond time scales and that interband recombination times are
carrier density dependent.Comment: 4 pages, 5 figure
Cosmic Needles versus Cosmic Microwave Background Radiation
It has been suggested by a number of authors that the 2.7K cosmic microwave
background (CMB) radiation might have arisen from the radiation from Population
III objects thermalized by conducting cosmic graphite/iron needle-shaped dust.
Due to lack of an accurate solution to the absorption properties of exceedingly
elongated grains, in existing literature which studies the CMB thermalizing
process they are generally modelled as (1) needle-like spheroids in terms of
the Rayleigh approximation; (2) infinite cylinders; and (3) the antenna theory.
We show here that the Rayleigh approximation is not valid since the Rayleigh
criterion is not satisfied for highly conducting needles. We also show that the
available intergalactic iron dust, if modelled as infinite cylinders, is not
sufficient to supply the required opacity at long wavelengths to obtain the
observed isotropy and Planckian nature of the CMB. If appealing to the antenna
theory, conducting iron needles with exceedingly large elongations (10^4)
appear able to provide sufficient opacity to thermalize the CMB within the iron
density limit. But the applicability of the antenna theory to exceedingly thin
needles of nanometer/micrometer in thickness needs to be justified.Comment: 13 pages, 4 figures; submitted to ApJ
On the Similarity between Cluster and Galactic Stellar Initial Mass Functions
The stellar initial mass functions (IMFs) for the Galactic bulge, the Milky
Way, other galaxies, clusters of galaxies, and the integrated stars in the
Universe are composites from countless individual IMFs in star clusters and
associations where stars form. These galaxy-scale IMFs, reviewed in detail
here, are not steeper than the cluster IMFs except in rare cases. This is true
even though low mass clusters generally outnumber high mass clusters and the
average maximum stellar mass in a cluster scales with the cluster mass. The
implication is that the mass distribution function for clusters and
associations is a power law with a slope of -2 or shallower. Steeper slopes,
even by a few tenths, upset the observed equality between large and small scale
IMFs. Such a cluster function is expected from the hierarchical nature of star
formation, which also provides independent evidence for the IMF equality when
it is applied on sub-cluster scales. We explain these results with analytical
expressions and Monte Carlo simulations. Star clusters appear to be the relaxed
inner parts of a widespread hierarchy of star formation and cloud structure.
They are defined by their own dynamics rather than pre-existing cloud
boundaries.Comment: 22 pages, 2 figures, ApJ, 648, in press, September 1, 200
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