Initial investigation of the wavelength dependence of optical properties measured with a new multi-pass Aerosol Extinction Differential Optical Absorption Spectrometer (AE-DOAS)

Atmospheric aerosols directly affect climate by scattering and absorbing radiation. The magnitude of the impact is dependent upon the wavelength of light, but is often estimated near 550 nm. When light scattering and absorption by aerosols is approximated, the wavelength dependence of the refractive index for specific components is lost. As a result, climate models would have inherent uncertainties for aerosol contributions to radiative forcing when considering the entire solar spectrum. An aerosol extinction differential optical absorption spectrometer has been developed to directly measure aerosol extinction at mid-ultraviolet to near infrared wavelengths. The instrument consists of a spectrometer coupled to a closed White-type multi-pass gas cell with an adjustable path length of up to approximately 20 m. Laboratory measurements of various gases are compared with known absorption cross sections. Additionally, the extinction of monodisperse samples of polystyrene latex spheres are measured and compared to Mie theory generated with refractive index values from the literature to validate the new instrument. The polystyrene experiments also emphasize the ability of the new instrument to retrieve the wavelength dependent refractive index, especially in the ultraviolet wavelength regions where variability is expected. The spectrometer will be a significant advancement for determining wavelength dependent complex refractive indices in future laboratory studies as well as provide the ability to monitor ambient aerosol light extinction

La Fièvre de la Vallée du Rift en Afrique de l'Ouest

Des enquêtes sérologiques ont été réalisées entre 1981 et 1986 dans différents pays d'Afrique de l'Ouest (Sénégal, Gambie, Guinée, Mauritanie, Burkina et Niger) afin d'apprécier l'importance de la circulation du virus RVF (Rift Valley Fever), et son incidence en pathologie animale et humaine. Au total, 5 315 sérums prélevés chez des chèvres, des moutons, des boeufs, des dromadaires et dans les populations humaines, ont été testés par IFI. Les sérums trouvés posisitifs ont été contrôlés par les tests de neutralisation par réduction des plages. Un important foyer de circulation du virus RVF a été découvert dans le Sud de la Mauritanie : 17, 8 p. 100 (83 sérums positifs/466 tests réalisés) du bétail représentait des anticorps pour le virus RVF. En outre dans cette région, 13,3 p. 100 (32/240) des éleveurs se sont révélés positifs. Dans d'autres régions d'Afrique de l'Ouest, la prévalence des anticorps est trés faible (0,4 p. 100 à 6,3 p. 100). Aucune souche de virus RVF n'a pu être isolée des 1478 rongeurs, capturés au Sénégal et en Mauritanie. La prévalence en anticorps s'avère faible chez les rongeurs (2 sérums/287 testés), et nulle chez les singes (0/88 testés). Une étude portant sur 461 avortements dans le bétail de Mauritanie a permis de montrer l'abscence de corrélation entre les sérologies positifs pour le virus RVF et les avortements. Les données préliminaires receuillies au cours de cette étude permettent d'opposer la situation épidémiologique de la fiévre de la vallée du Rift en Afrique de l'Ouest à celle de l'Afrique de l'Est et du Sud et de suggérer soit une résistance particulière du bétail de cette région, soit un pouvoir pathogène atténué des souches de virus RVF circulant en Afrique de l'Ouest. (Résumé d'auteur

Reducing the Effects of Unequal Number of Games on Rankings

Ranking is an important mathematical process in a variety of contexts such as information retrieval, sports and business. Sports ranking methods can be applied both in and beyond the context of athletics. In both settings, once the concept of a game has been defined, teams (or individuals) accumulate wins, losses, and ties, which are then factored into the ranking computation. Many settings involve an unequal number of games between competitors. This paper demonstrates how to adapt two sports rankings methods, the Colley and Massey ranking methods, to settings where an unequal number of games are played between the teams. In such settings, the standard derivations of the methods can produce nonsensical rankings. This paper introduces the idea of including a super-user into the rankings and considers the effect of this fictitious player on the ratings. We apply such techniques to rank batters and pitchers in Major League baseball, professional tennis players, and participants in a free online social game. The ideas introduced in this paper can further the scope that such methods are applied and the depth of insight they offer

A micropillar for cavity optomechanics

We present a new micromechanical resonator designed for cavity optomechanics. We have used a micropillar geometry to obtain a high-frequency mechanical resonance with a low effective mass and a very high quality factor. We have coated a 60-$\mu$m diameter low-loss dielectric mirror on top of the pillar and are planning to use this micromirror as part of a high-finesse Fabry-Perot cavity, to laser cool the resonator down to its quantum ground state and to monitor its quantum position fluctuations by quantum-limited optical interferometry

High-precision measurement of the half-life of 62^{62}Ga

The beta-decay half-life of 62Ga has been studied with high precision using on-line mass separated samples. The decay of 62Ga which is dominated by a 0+ to 0+ transition to the ground state of 62Zn yields a half-life of T_{1/2} = 116.19(4) ms. This result is more precise than any previous measurement by about a factor of four or more. The present value is in agreement with older literature values, but slightly disagrees with a recent measurement. We determine an error weighted average value of all experimental half-lives of 116.18(4) ms.Comment: 9 pages, 5 figures, accepted for publication in PR

Overview of (pro-)Lie group structures on Hopf algebra character groups

Character groups of Hopf algebras appear in a variety of mathematical and physical contexts. To name just a few, they arise in non-commutative geometry, renormalisation of quantum field theory, and numerical analysis. In the present article we review recent results on the structure of character groups of Hopf algebras as infinite-dimensional (pro-)Lie groups. It turns out that under mild assumptions on the Hopf algebra or the target algebra the character groups possess strong structural properties. Moreover, these properties are of interest in applications of these groups outside of Lie theory. We emphasise this point in the context of two main examples: The Butcher group from numerical analysis and character groups which arise from the Connes--Kreimer theory of renormalisation of quantum field theories.Comment: 31 pages, precursor and companion to arXiv:1704.01099, Workshop on "New Developments in Discrete Mechanics, Geometric Integration and Lie-Butcher Series", May 25-28, 2015, ICMAT, Madrid, Spai

Neutron Transfer Studied with a Radioactive beam of 24Ne, using TIARA at SPIRAL

A general experimental technique for high resolution studies of nucleon transfer reactions using radioactive beams is briefly described, together with the first new physics results that have been obtained with the new TIARA array. These first results from TIARA are for the reaction 24Ne(d,p)25Ne, studied in inverse kinematics with a pure radioactive beam of 100,000 pps from the SPIRAL facility at GANIL. The reaction probes the energies of neutron orbitals relevant to very neutron rich nuclei in this mass region and the results highlight the emergence of the N=16 magic number for neutrons and the associated disappearance of the N=20 neutron magic number for the very neutron rich neon isotopes.Comment: Proceedings of the Carpathian Summer School of Physics, Mamaia-Constanta, Romania, 13-24 June 200