1,728 research outputs found
Evolution rĂ©cente de la population, de lâoccupation des sols et de la diversitĂ© floristique sur un terroir agricole du Sud-Ouest du Niger
Au cours des 50 derniĂšres annĂ©es, un fort accroissement de la population a Ă©tĂ© enregistrĂ© dans la partie Sud-Ouest du Niger. Ce phĂ©nomĂšne a entraĂźnĂ© de profonds changements dans lâoccupation des sols et une pression accrue sur les ressources naturelles qui ont eu une incidence importante sur lâallure de la vĂ©gĂ©tation. Lâobjectif de cette Ă©tude est de faire le point sur la richesse spĂ©cifique du terroir au regard de cette Ă©volution. Les rĂ©sultats montrent que la richesse floristique est assez Ă©levĂ©e Ă Ticko. Ainsi, 400 espĂšces, rĂ©parties entre 66 familles ont Ă©tĂ© recensĂ©es. Parmi celles-ci, on compte 85 espĂšces ligneuses regroupĂ©es en 32 familles et 315 espĂšces herbacĂ©es, ou ligneuses basses, rĂ©parties entre 44 familles, dont 64% de ThĂ©rophytes. Cette flore reprĂ©sente 65% des espĂšces et 71% des familles prĂ©sentes dans la rĂ©gion du Liptako. AprĂšs 25 ans de forte croissance dĂ©mographique Ă Ticko, la diversitĂ© floristique reste encore Ă peu prĂšs intacte dans ce terroir. On note cependant une rĂ©gression des populations dâespĂšces herbacĂ©es et ligneuses, autrefois bien reprĂ©sentĂ©es sur le terroir, qui pourrait conduire dans les annĂ©es Ă venir Ă la disparition de ces taxons, et plus particuliĂšrement dâune vingtaine de taxons ligneux.Mots clĂ©s : population humaine, diversitĂ© floristique, Ticko, Niger
Magnetic imaging with an ensemble of Nitrogen Vacancy centers in diamond
The nitrogen-vacancy (NV) color center in diamond is an atom-like system in
the solid-state which specific spin properties can be efficiently used as a
sensitive magnetic sensor. An external magnetic field induces Zeeman shifts of
the NV center levels which can be measured using Optically Detected Magnetic
Resonance (ODMR). In this work, we exploit the ODMR signal of an ensemble of NV
centers in order to quantitatively map the vectorial structure of a magnetic
field produced by a sample close to the surface of a CVD diamond hosting a thin
layer of NV centers. The reconstruction of the magnetic field is based on a
maximum-likelihood technique which exploits the response of the four intrinsic
orientations of the NV center inside the diamond lattice. The sensitivity
associated to a 1 {\mu}m^2 area of the doped layer, equivalent to a sensor
consisting of approximately 10^4 NV centers, is of the order of 2
{\mu}T/sqrt{Hz}. The spatial resolution of the imaging device is 400 nm,
limited by the numerical aperture of the optical microscope which is used to
collect the photoluminescence of the NV layer. The versatility of the sensor is
illustrated by the accurate reconstruction of the magnetic field created by a
DC current inside a copper wire deposited on the diamond sample.Comment: 11 pages, 5 figures, figure 4 added, results unchange
Perfect preferential orientation of nitrogen-vacancy defects in a synthetic diamond sample
We show that the orientation of nitrogen-vacancy (NV) defects in diamond can
be efficiently controlled through chemical vapor deposition (CVD) growth on a
(111)-oriented diamond substrate. More precisely, we demonstrate that
spontaneously generated NV defects are oriented with a ~ 97 % probability along
the [111] axis, corresponding to the most appealing orientation among the four
possible crystallographic axes. Such a nearly perfect preferential orientation
is explained by analyzing the diamond growth mechanism on a (111)-oriented
substrate and could be extended to other types of defects. This work is a
significant step towards the design of optimized diamond samples for quantum
information and sensing applications.Comment: 6 pages, 4 figure
Forward-backward multiplicity correlations and leakage parameter behaviour in asymmetric high energy collisions
Continuing previous work, forward-backward multiplicity correlations are
studied in asymmetric collisions in the framework of the weighted superposition
mechanism of different classes of events. New parameters for the asymmetric
clan distribution and for the particle leakage from clans in one hemisphere to
the opposite one are introduced to effectively classify different classes of
collisions. This tool should be used to explore forward-backward multiplicity
correlations in AB and pA collisions in present and future experiments at RHIC
and LHC.Comment: 14 pages, 2 figures, latex 2e with amsmat
Good Learning and Implicit Model Enumeration
MathSBML is an open-source, freely-downloadable Mathematica package that facilitates working with Systems Biology Markup Language (SBML) models. SBML is a toolneutral,computer-readable format for representing models of biochemical reaction networks, applicable to metabolic networks, cell-signaling pathways, genomic regulatory networks, and other modeling problems in systems biology that is widely supported by the systems biology community. SBML is based on XML, a standard medium for representing and transporting data that is widely supported on the internet as well as in computational biology and bioinformatics. Because SBML is tool-independent, it enables model transportability, reuse, publication and survival. In addition to MathSBML, a number of other tools that support SBML model examination and manipulation are provided on the sbml.org website, including libSBML, a C/C++ library for reading SBML models; an SBML Toolbox for MatLab; file conversion programs; an SBML model validator and visualizer; and SBML specifications and schemas. MathSBML enables SBML file import to and export from Mathematica as well as providing an API for model manipulation and simulation
Ruthenium(II) and Iridium(III) complexes featuring NHC-Sulfonate chelate
International audienc
Rare decay Z --> neutrino antineutrino photon photon via quartic gauge boson couplings
We present a detailed calculation of the rare decay Z --> neutrino
antineutrino photon photon via the quartic neutral gauge boson coupling
Z-Z-photon-photon in the framework of the effective Lagrangian approach. The
current experimental bound on this decay mode is then used to constrain the
coefficients of this coupling. It is found that the bounds obtained in this
way, of the order of , are weaker than the ones obtained from the
analysis of triple-boson production at LEP-2Comment: 5 pages, 2 figures, to appear in Physical Review D Brief Report
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