Stability of Relativistic Matter with Magnetic Fields for Nuclear Charges up to the Critical Value

We give a proof of stability of relativistic matter with magnetic fields all the way up to the critical value of the nuclear charge $Z\alpha=2/\pi$.Comment: LaTeX2e, 12 page

Cartographie des dimères cyclobutyliques de pyrimidines (DCP) induits par les UVA et étude des effets de certains gènes de réparation des mésappariements et du gène P53 muté sur la réparation par excision de nucléotides des DCP

Tableau d’honneur de la Faculté des études supérieures et postdoctorales, 2004-2005Les cancers cutanés sont associés à la formation des dimères cyclobutyliques de pyrimidine (DCP) générés par les ultraviolets (UV) du soleil. Nos résultats indiquent que les transversions T-->G retrouvées suite aux UVA sont dues aux DCP formés majoritairement sur les TT. Nous avons également démontré que, contrairement au dogme établi, les protéines réparant les mésappariements n'influencent pas la réparation des DCP. p53 a indéniablement une influence sur la réparation des DCP. Cependant, la lignée SW480, contenant un gène p53 double-muté, est fonctionnelle en réparation par excision de nucléotides des DCP. Normalement, un stress est nécessaire à l'activation des effecteurs de p53. Cependant, la protéine p53 double-mutée des SW480 active constitutivement p21, un effecteur de p53. L'activation des protéines réparant les DCP par p53 se fait probablement de la même façon que p21. L'éclaircissement de ces mécanismes a amené une meilleure compréhension de l'induction des cancers

In situ multi-frequency measurements of magnetic susceptibility as an indicator of planetary regolith maturity

Space weathering is now generally accepted to modify the optical and magnetic properties of airless planetary regoliths such as those on the Moon and Mercury. Under micrometeorite and ion bombardment, ferrous iron in such surfaces is reduced to metallic iron spheres, found in amorphous coatings on almost all exposed regolith grains. The size and number distribution of these particles and their location in the regolith all determine the nature and extent of the optical and magnetic changes. These parameters in turn reflect the formation mechanisms, temperatures, and durations involved in the evolution of the regolith. Studying them in situ is of intrinsic value to understanding the weathering process, and useful for determining the maturity of the regolith and providing supporting data for interpreting remotely sensed mineralogy. Fine-grained metallic iron has a number of properties that make it amenable to magnetic techniques, of which magnetic susceptibility is the simplest and most robust. The magnetic properties of the lunar regolith and laboratory regolith analogues are therefore reviewed and the theoretical basis for the frequency dependence of magnetic susceptibility presented. Proposed here is then an instrument concept using multi-frequency measurements of magnetic susceptibility to confirm the presence of fine grained magnetic material and attempt to infer its quantity and size distribution. Such an instrument would be invaluable on a future mission to an asteroid, the Moon, Mercury or other airless rocky Solar System body

57Fe Mössbauer spectroscopy studies of chondritic meteorites from the Atacama Desert, Chile: Implications for weathering processes

Some terrestrial areas have climatic and geomorphologic features that favor the preservation, and therefore, accumulation of meteorites. The Atacama Desert in Chile is among the most important of such areas, known as dense collection areas. This desert is the driest on Earth, one of the most arid, uninhabitable locals with semi-arid, arid and hyper-arid conditions. The meteorites studied here were collected from within the dense collection area of San Juan at the Central Depression and Coastal Range of Atacama Desert. [superscript 57]Fe Mössbauer spectroscopy was used for quantitative analysis of the degree of weathering of the meteorites, through the determination of the proportions of the various Fe-bearing phases and in particular the amount of oxidized iron in the terrestrial alteration products. The abundance of ferric ions in weathered chondrites can be related to specific precursor compositions and to the level of terrestrial weathering. The aim of the study was the identification, quantification and differentiation of the weathering products in the ordinary chondrites found in the San Juan area of Atacama Desert