Calculated iron L2,3L_{2,3} x-ray absorption and XMCD of spin-crossover Fe(phen)2_{2}(NCS)2_{2} molecule adsorbed on Cu(001) surface

The PAW method has been used to compute the iron L$_{2,3}$ edges of x-ray absorption spectra (XAS) and x-ray magnetic circular dichroism (XMCD) of the spin-crossover Fe(phen)$_{2}$(NCS)$_{2}$ molecule when adsorbed on Cu(001) surface and in the gas phase, for both the high spin (HS) and low spin (LS) states. It is found that the calculated XAS and XMCD with the static core hole or the Slater transition state half hole are in less good agreement with experiment than those using the so called initial state. This disagreement is due to the reduction of the iron spin magnetic moment caused by the static screening of the core hole by the photo-electron. The L$_{2,3}$ XAS formula is found to be directly related to the unoccupied $3d$ density of states (DOS), and hence the symmetry broken $e_g$ and the $t_{2g}$ iron DOS are used to explain the XAS and XMCD results. It is demonstrated that the dependence of the HS XMCD on the direction of incident x-ray circularly polarized light with respect to the magnetization direction can be used to determine the iron octahedron deformation, while the XMCD for various magnetization directions is directly related to the anisotropy of the orbital magnetic moment and the magneto-crystalline energy. It is also shown that the magnetic dipole moment $T_z$ is very large due to the strong distortion of the iron octahedron and is necessary for an accurate determination of the sum rule computed spin magnetic moment.Comment: 39 pages, 5 figure

Huge excitonic effects in layered hexagonal boron nitride

The calculated quasiparticle band structure of bulk hexagonal boron nitride using the all-electron GW approximation shows that this compound is an indirect-band-gap semiconductor. The solution of the Bethe-Salpeter equation for the electron-hole two-particle Green function has been used to compute its optical spectra and the results are found in excellent agreement with available experimental data. A detailed analysis is made for the excitonic structures within the band gap and found that the excitons belong to the Frenkel class and are tightly confined within the layers. The calculated exciton binding energy is much larger than that obtained by Watanabe {\it et al} using a Wannier model to interpret their experimental results and assuming that h-BN is a direct-band-gap semiconductor.Comment: 4 pages, 3 figure

Comment on "Origin of Giant Optical Nonlinearity in Charge-Transfer--Mott Insulators: A New Paradigm for Nonlinear Optics"

Comment on Phys. Rev. Lett. 86, 2086 (2001)Comment: 1 page, 1 eps figur

A new web-based system to improve the monitoring of snow avalanche hazard in France

International audienceSnow avalanche data in the French Alps and Pyrenees have been recorded for more than 100 years in several databases. The increasing amount of observed data required a more integrative and automated service. Here we report the comprehensive web-based Snow Avalanche Information System newly developed to this end for three important data sets: an avalanche chronicle (Enquete Permanente sur les Avalanches, EPA), an avalanche map (Carte de Localisation des Phenomenes d'Avalanche, CLPA) and a compilation of hazard and vulnerability data recorded on selected paths endangering human settlements (Sites Habites Sensibles aux Avalanches, SSA). These data sets are now integrated into a common database, enabling full interoperability between all different types of snow avalanche records: digitized geographic data, avalanche descriptive parameters, eyewitness reports, photographs, hazard and risk levels, etc. The new information system is implemented through modular components using Java-based web technologies with Spring and Hibernate frameworks. It automates the manual data entry and improves the process of information collection and sharing, enhancing user experience and data quality, and offering new outlooks to explore and exploit the huge amount of snow avalanche data available for fundamental research and more applied risk assessment

Pressure Tuning of the Charge Density Wave in the Halogen-Bridged Transition-Metal (MX) Solid Pt2Br6(NH3)4Pt_2Br_6(NH_3)_4

We report the pressure dependence up to 95 kbar of Raman active stretching modes in the quasi-one-dimensional MX chain solid $Pt_2Br_6(NH_3)_4$. The data indicate that a predicted pressure-induced insulator-to-metal transition does not occur, but are consistent with the solid undergoing either a three-dimensional structural distortion, or a transition from a charge-density wave to another broken-symmetry ground state. We show that such a transition cacan be well-modeled within a Peierls-Hubbard Hamiltonian. 1993 PACS: 71.30.+h, 71.45.Lr, 75.30.Fv, 78.30.-j, 81.40.VwComment: 4 pages, ReVTeX 3.0, figures available from the authors on request (Gary Kanner, [email protected]), to be published in Phys Rev B Rapid Commun, REVISION: minor typos corrected, LA-UR-94-246

Rhizospheric solutions: Pseudomonas isolates counter Botrytis cinerea on tomato

La moisissure grise causée par Botrytis cinerea provoque des dégâts sur plus de 200 espèces de cultures dans le monde. B. cinerea sporule pour former une pourriture grise sur les feuilles, les tiges et les fruits. Pour lutter contre B. cinerea, des fongicides synthétiques sont utilisés. Ces derniers mettent en danger la santé humaine et environnementale en plus de la résistance qu'ils peuvent occasionner chez les souches de B. cinerea. Les alternatives écologiques sont des solutions appropriées pour contrôler la moisissure grise tout en maintenant l’équilibre environnemental. L’objectif de cette étude est d'évaluer l’effet des isolats de Pseudomonas issus de la rhizosphère de la tomate sur B. cinerea. Les résultats ont montré que les 76 isolats testés inhibent le développement de B. cinerea in vitro. Cinq isolats de Pseudomonas (Q6B, Q13B, Q7B, Q14B et Q1B) ont provoqué des niveaux d'inhibition significatifs allant de 65 à 73%. Par ailleurs, ces isolats ont également inhibé B. cinerea sur les feuilles et le fruit de la tomate. Pour tenter d'élucider les mécanismes d'action, les cinq isolats ont montré une production des métabolites antifongiques tels que les sidérophores, le cyanure d'hydrogène et d’autres enzymes. Les résultats de cette étude ont montré que les isolats de Pseudomonas Q6B, Q13B, Q7B, Q14B et Q1B ont une forte efficacité dans la lutte biologique contre B. cinerea et peuvent être utilisés pour une lutte écologique durable.Gray mold caused by Botrytis cinerea causes serious losses in more than 200 crop species worldwide. The necrotrophic fungus sporulates to effect a grey covering on leaves, stems and flowers. B. cinerea is controlled by chemical synthetic fungicides, endangering human and environmental health. Synthetic fungicides stimulate emergence of pathogen resistance. Organic alternatives which may be present or introduced into the edaphic environment are suitable solutions to control outbreaks. This study was done in order to elucidate the mode of action involved in the control of B. cinerea using fluorescent Pseudomonas isolates from tomato roots. The results show that all 76 isolates inhibit fungal growth during in vitro bioassay using dual culture technique. Five isolates of Pseudomonas (Q6B, Q13B, Q7B, Q14B and Q1B) cause significant inhibition levels ranging from 65 to 73%. These isolates inhibit fungal growth in both fruits and leaves. Each isolate tested produced antifungal metabolites (siderophores, hydrogen cyanide and enzymes). Results of this study show that all tested Pseudomonas isolates have a strong efficacy in biological control against B. cinerea and can be used for environmentally sustainable control

Structural relaxation effects on interface and transport properties of Fe/MgO(001) tunnel junctions

The interface structure of Fe/MgO(100) magnetic tunnel junctions predicted by density functional theory (DFT) depends significantly on the choice of exchange and correlation functional. Bader analysis reveals that structures obtained by relaxing the cell with the local spin-density approximation (LSDA) display a different charge transfer than those relaxed with the generalized gradient approximation (GGA). As a consequence, the electronic transport is found to be extremely sensitive to the interface structure. In particular, the conductance for the LSDA-relaxed geometry is about one order of magnitude smaller than that of the GGA-relaxed one. The high sensitivity of the electronic current to the details of the interface might explain the discrepancy between the experimental and calculated values of magnetoresistance.Comment: Submitted to PRL, 5 figure

P-[N-(Diphenyl­phospho­rothio­yl)iso­propyl­amino]-N-isopropyl-P-phenyl­thio­phosphinic amide

The title compound, C24H30N2P2S2, was obtained by the reaction of Ph2PN(iPr)P(Ph)N(iPr)H with elemental sulfur in tetra­hydro­furan. In the solid state, intra­molecular N—H⋯S hydrogen bonding influences the mol­ecular conformation; a P—N—P—N torsion angle of 2.28 (9)° is observed. The two phenyl rings attached to one P atom form a dihedral angle of 74.02 (4)°