17,102 research outputs found
Energy evolution of the moments of the hadron distribution in QCD jets including NNLL resummation and NLO running-coupling corrections
The moments of the single inclusive momentum distribution of hadrons in QCD
jets, are studied in the next-to-modified-leading-log approximation (NMLLA)
including next-to-leading-order (NLO) corrections to the alpha_s strong
coupling. The evolution equations are solved using a distorted Gaussian
parametrisation, which successfully reproduces the spectrum of charged hadrons
of jets measured in e+e- collisions. The energy dependencies of the maximum
peak, multiplicity, width, kurtosis and skewness of the jet hadron distribution
are computed analytically. Comparisons of all the existing jet data measured in
e+e- collisions in the range sqrt(s)~2-200 GeV to the NMLLA+NLO* predictions
allow one to extract a value of the QCD parameter Lambda_QCD, and associated
two-loop coupling constant at the Z resonance alpha_s(m_Z^2)= 0.1195 +/-
0.0022, in excellent numerical agreement with the current world average
obtained using other methods.Comment: 40 pages, 15 figures. Minor changes. Matches published version in
JHE
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Solidification Morphology Analysis of SLM of Cu Powder
The solidification morphology analysis of fine Cu powder melted by a raster
scanned energy beam from a focused Nd:YAG laser is presented here. The powder was
processed inside of sealed chamber where it was subjected to a high vacuum cycle. The
laser fusion process consisted raster scanning a narrow rectangular pattern with a high
density of scanning lines, the chamber was purged with inert gas during the process. Up
to a 3.3 mm/s laser travel speed and maximum laser power level of 240 W were used to
melt a 2 mm thick bed of loose powder. The resulting solidified ingots were separated
into categories based on their shape integrity. Metallographic analysis by means of
optical microscopy and scanning electron microscopy was performed on the cross section
and longitudinal section of the ingots with homogeneous surface and complete shape
integrity. Characterization revealed an elongated columnar grain structure with a grain
orientation along the direction of the laser travel direction, some degree of porosity was
observed too in some of the specimens. It was observed that grains diameter ranged from
10 to 100 µm and contained a two phase eutectic microstructure of copper and it oxides.
Oxygen content was accounted from a 5.5 up to 8.1 atomic percent, a small percentage of
chlorine was present, too. A 2 to 8 percent variation in the Vickers microhardness values
were found between the different specimens when measured along the longitudinal
section. These HV values corresponded to approximate 20-25% cold rolled oxygen free
copper (80-90 HV). The ingots thus produced suggest that a multilayer structure from Cu
powder could be build by the SLM process having sufficiently adequate compositional,
microstructure and mechanical properties for functional applications.Mechanical Engineerin
The Yang-Mills gradient flow and SU(3) gauge theory with 12 massless fundamental fermions in a colour-twisted box
We perform the step-scaling investigation of the running coupling constant,
using the gradient-flow scheme, in SU(3) gauge theory with twelve massless
fermions in the fundamental representation. The Wilson plaquette gauge action
and massless unimproved staggered fermions are used in the simulations. Our
lattice data are prepared at high accuracy, such that the statistical error for
the renormalised coupling, g_GF, is at the subpercentage level. To investigate
the reliability of the continuum extrapolation, we employ two different lattice
discretisations to obtain g_GF. For our simulation setting, the corresponding
gauge-field averaging radius in the gradient flow has to be almost half of the
lattice size, in order to have this extrapolation under control. We can
determine the renormalisation group evolution of the coupling up to g^2_GF ~ 6,
before the onset of the bulk phase structure. In this infrared regime, the
running of the coupling is significantly slower than the two-loop perturbative
prediction, although we cannot draw definite conclusion regarding possible
infrared conformality of this theory. Furthermore, we comment on the issue
regarding the continuum extrapolation near an infrared fixed point. In addition
to adopting the fit ansatz a'la Symanzik for performing this task, we discuss a
possible alternative procedure inspired by properties derived from low-energy
scale invariance at strong coupling. Based on this procedure, we propose a
finite-size scaling method for the renormalised coupling as a means to search
for infrared fixed point. Using this method, it can be shown that the behaviour
of the theory around g^2_GF ~ 6 is still not governed by possible infrared
conformality.Comment: 24 pages, 6 figures; Published version; Appendix A added for
tabulating data; One reference included; Typos correcte
Protecting mobile money customer funds in civil law jurisdictions
The provision of financial services through mobile phones is a powerful tool to foster financial inclusion, and thus economic growth, in developing countries. However, it raises important regulatory issues. Given the vulnerability of most potential customers of these services, the protection of customer funds is important. In common law countries, trust accounts are an effective response to these concerns. In civil law jurisdictions however, in the absence of trusts, protection of customer funds is more difficult. This paper identifies the theoretical and practical problems that regulators in civil law jurisdictions might face when trying to protect customer funds and explores how fiduciary contracts, mandate contracts and direct regulation might be used to achieve this goal. It offers a series of practical recommendations for policymakers in developing countries that provide a range of regulatory options that combine private law and regulation
The magnetic field configuration of a solar prominence inferred from spectropolarimetric observations in the He I 10830 A triplet
Context: The determination of the magnetic field vector in quiescent solar
prominences is possible by interpreting the Hanle and Zeeman effects in
spectral lines. However, observational measurements are scarce and lack high
spatial resolution. Aims: To determine the magnetic field vector configuration
along a quiescent solar prominence by interpreting spectropolarimetric
measurements in the He I 1083.0 nm triplet obtained with the Tenerife Infrared
Polarimeter installed at the German Vacuum Tower Telescope of the Observatorio
del Teide. Methods. The He I 1083.0 nm triplet Stokes profiles are analyzed
with an inversion code that takes into account the physics responsible of the
polarization signals in this triplet. The results are put into a solar context
with the help of extreme ultraviolet observations taken with the Solar Dynamic
Observatory and the Solar Terrestrial Relations Observatory satellites.
Results: For the most probable magnetic field vector configuration, the
analysis depicts a mean field strength of 7 gauss. We do not find local
variations in the field strength except that the field is, in average, lower in
the prominence body than in the prominence feet, where the field strength
reaches 25 gauss. The averaged magnetic field inclination with respect to the
local vertical is 77 degrees. The acute angle of the magnetic field vector with
the prominence main axis is 24 degrees for the sinistral chirality case and 58
degrees for the dextral chirality. These inferences are in rough agreement with
previous results obtained from the analysis of data acquired with lower spatial
resolutions.Comment: Accepted in A&
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