216 research outputs found
UV luminescence characterisation of organics in Mars-analogue substrates
This project was supported by a Leverhulme Trust Research Project Grant (RPG-2015-071). C Cousins also wishes to acknowledge funding by the Royal Society of Edinburgh.Detection of organic matter is one of the core objectives of future Mars exploration. The ability to probe rocks, soils, and other geological substrates for organic targets is a high priority for in situ investigation, sample caching, and sample return. UV luminescence – the emission of visible light following UV irradiation – is a tool that is beginning to be harnessed for planetary exploration. We conducted UV photoluminescence analyses of (i) Mars analogue sediments doped with polyaromatic hydrocarbons (PAHs; <15 ppm), (ii) carbonaceous CM chondrites and terrestrial kerogen (Type IV), and (iii) synthetic salt crystals doped with PAHs (2 ppm). We show that that detection of PAHs is possible within synthetic and natural gypsum, and synthetic halite. These substrates show the most apparent spectral modifications, suggesting that the most transparent minerals are more conducive to UV photoluminescence detection of trapped organic matter. Iron oxide, ubiquitously present on Mars surface, hampers but does not completely quench the UV luminescence emission. Finally, the maturity of organic carbonaceous material influences the luminescence response, resulting in a reduced signal for UV excitation wavelengths down to 225 nm. This study demonstrates the utility of UV luminescence spectroscopy for the analysis of mixed organic-inorganic materials applicable to Mars exploration.PostprintPeer reviewe
Relaxation kinetics in two-dimensional structures
We have studied the approach to equilibrium of islands and pores in two
dimensions. The two-regime scenario observed when islands evolve according to a
set of particular rules, namely relaxation by steps at low temperature and
smooth at high temperature, is generalized to a wide class of kinetic models
and the two kinds of structures. Scaling laws for equilibration times are
analytically derived and confirmed by kinetic Monte Carlo simulations.Comment: 6 pages, 7 figures, 1 tabl
Standard Model Matrix Elements for Neutral B-Meson Mixing and Associated Decay Constants
We present results of quenched lattice calculations of the matrix elements
relevant for B_d-\bar B_d and B_s-\bar B_s mixing in the Standard Model.
Results for the corresponding SU(3)-breaking ratios, which can be used to
constrain or determine |V_{td}|, are also given. The calculations are performed
at two values of the lattice spacing, corresponding to \beta = 6.0 and \beta =
6.2, with quarks described by a mean-field-improved Sheikholeslami-Wohlert
action. As a by-product, we obtain the leptonic decay constants of B and D
mesons. We also present matrix elements relevant for D^0-\bar D^0 mixing. Our
results are summarized in the Introduction.Comment: 27 pages (RevTeX), 26 figures, version published in Phys. Rev. D:
improved estimate of the systematic error associated with the uncertainty on
the strange quark mass and other small improvements to analysis (results
change only slightly); correction of typos and minor changes to text; RevTeX
formattin
Metabolic Network Fluxes in Heterotrophic Arabidopsis Cells: Stability of the Flux Distribution under Different Oxygenation Conditions
Come back Marshall, all is forgiven? : Complexity, evolution, mathematics and Marshallian exceptionalism
Marshall was the great synthesiser of neoclassical economics. Yet with his qualified assumption of self-interest, his emphasis on variation in economic evolution and his cautious attitude to the use of mathematics, Marshall differs fundamentally from other leading neoclassical contemporaries. Metaphors inspire more specific analogies and ontological assumptions, and Marshall used the guiding metaphor of Spencerian evolution. But unfortunately, the further development of a Marshallian evolutionary approach was undermined in part by theoretical problems within Spencer's theory. Yet some things can be salvaged from the Marshallian evolutionary vision. They may even be placed in a more viable Darwinian framework.Peer reviewedFinal Accepted Versio
Semi-automatic enrichment of crowdsourced synonymy networks: the WISIGOTH system applied to Wiktionary
International audienceSemantic lexical resources are a mainstay of various Natural Language Processing applications. However, comprehensive and reliable resources are rare and not often freely available. Handcrafted resources are too costly for being a general solution while automatically-built resources need to be validated by experts or at least thoroughly evaluated. We propose in this paper a picture of the current situation with regard to lexical resources, their building and their evaluation. We give an in-depth description of Wiktionary, a freely available and collaboratively built multilingual dictionary. Wiktionary is presented here as a promising raw resource for NLP. We propose a semi-automatic approach based on random walks for enriching Wiktionary synonymy network that uses both endogenous and exogenous data. We take advantage of the wiki infrastructure to propose a validation "by crowds". Finally, we present an implementation called WISIGOTH, which supports our approach
Inclusive cross section and double helicity asymmetry for \pi^0 production in p+p collisions at sqrt(s)=200 GeV: Implications for the polarized gluon distribution in the proton
The PHENIX experiment presents results from the RHIC 2005 run with polarized
proton collisions at sqrt(s)=200 GeV, for inclusive \pi^0 production at
mid-rapidity. Unpolarized cross section results are given for transverse
momenta p_T=0.5 to 20 GeV/c, extending the range of published data to both
lower and higher p_T. The cross section is described well for p_T < 1 GeV/c by
an exponential in p_T, and, for p_T > 2 GeV/c, by perturbative QCD. Double
helicity asymmetries A_LL are presented based on a factor of five improvement
in uncertainties as compared to previously published results, due to both an
improved beam polarization of 50%, and to higher integrated luminosity. These
measurements are sensitive to the gluon polarization in the proton, and exclude
maximal values for the gluon polarization.Comment: 375 authors, 7 pages, 3 figures. Submitted to Phys. Rev. D, Rapid
Communications. Plain text data tables for the points plotted in figures for
this and previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
System Size and Energy Dependence of Jet-Induced Hadron Pair Correlation Shapes in Cu+Cu and Au+Au Collisions at sqrt(s_NN) = 200 and 62.4 GeV
We present azimuthal angle correlations of intermediate transverse momentum
(1-4 GeV/c) hadrons from {dijets} in Cu+Cu and Au+Au collisions at sqrt(s_NN) =
62.4 and 200 GeV. The away-side dijet induced azimuthal correlation is
broadened, non-Gaussian, and peaked away from \Delta\phi=\pi in central and
semi-central collisions in all the systems. The broadening and peak location
are found to depend upon the number of participants in the collision, but not
on the collision energy or beam nuclei. These results are consistent with sound
or shock wave models, but pose challenges to Cherenkov gluon radiation models.Comment: 464 authors from 60 institutions, 6 pages, 3 figures, 2 tables.
Submitted to Physical Review Letters. Plain text data tables for the points
plotted in figures for this and previous PHENIX publications are (or will be)
publicly available at http://www.phenix.bnl.gov/papers.htm
D* Production in Deep Inelastic Scattering at HERA
This paper presents measurements of D^{*\pm} production in deep inelastic
scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The
data have been taken with the ZEUS detector at HERA. The decay channel
(+ c.c.) has been used in the study. The
cross section for inclusive D^{*\pm} production with
and is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region
{ GeV and }. Differential cross
sections as functions of p_T(D^{*\pm}), and are
compared with next-to-leading order QCD calculations based on the photon-gluon
fusion production mechanism. After an extrapolation of the cross section to the
full kinematic region in p_T(D^{*\pm}) and (D^{*\pm}), the charm
contribution to the proton structure function is
determined for Bjorken between 2 10 and 5 10.Comment: 17 pages including 4 figure
Recommended from our members
Measurement of Bottom versus Charm as a Function of Transverse Momentum with Electron-Hadron Correlations in p+p Collisions at sqrt(s)=200 GeV
The momentum distribution of electrons from semi-leptonic decays of charm and
bottom for mid-rapidity |y|<0.35 in p+p collisions at sqrt(s)=200 GeV is
measured by the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC)
over the transverse momentum range 2 < p_T < 7 GeV/c. The ratio of the yield of
electrons from bottom to that from charm is presented. The ratio is determined
using partial D/D^bar --> e^{+/-} K^{-/+} X (K unidentified) reconstruction. It
is found that the yield of electrons from bottom becomes significant above 4
GeV/c in p_T. A fixed-order-plus-next-to-leading-log (FONLL) perturbative
quantum chromodynamics (pQCD) calculation agrees with the data within the
theoretical and experimental uncertainties. The extracted total bottom
production cross section at this energy is \sigma_{b\b^bar}= 3.2
^{+1.2}_{-1.1}(stat) ^{+1.4}_{-1.3}(syst) micro b.Comment: 432 authors, 6 pages text, 3 figures. Submitted to Phys. Rev. Lett.
Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
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