A consistent approach for mixed detailed and statistical calculation of opacities in hot plasmas

Absorption and emission spectra of plasmas with multicharged-ions contain transition arrays with a huge number of coalescent electric-dipole (E1) lines, which are well suited for treatment by the unresolved transition array and derivative methods. But, some transition arrays show detailed features whose description requires diagonalization of the Hamiltonian matrix. We developed a hybrid opacity code, called SCORCG, which combines statistical approaches with fine-structure calculations consistently. Data required for the computation of detailed transition arrays (atomic configurations and atomic radial integrals) are calculated by the super-configuration code SCO (Super-Configuration Opacity), which provides an accurate description of the plasma screening effects on the wave-functions. Level energies as well as position and strength of spectral lines are computed by an adapted RCG routine of R. D. Cowan. The resulting code provides opacities for hot plasmas and can handle mid-Z elements. The code is also a powerful tool for the interpretation of recent laser and Z-pinch experimental spectra, as well as for validation of statistical methods.Comment: submitted to "High Energy Density Physics

Paiements pour services environnementaux et pays du Sud. La conservation de la nature rattrapée par le développement ?

Le concept de paiement pour services environnementaux (PSE) suscite beaucoup d'espoirs pour la conservation des écosystèmes dans les pays du Sud. Jusqu'à présent, de nombreux PSE concernaient le maintien de la qualité de l'eau, et faisaient l'objet de négociations bilatérales entre des " acheteurs " et des " fournisseurs " de service. Avec la perspective de l'inclusion du mécanisme REDD (Réduction des Emissions issues de la Déforestation et de la Dégradation) dans les accords post-Kyoto sur le climat, les PSE se voient investis d'un rôle clé pour la mise en oeuvre de la " déforestation évitée ", et se développent rapidement dans le cadre de " projets REDD ". Les PSE constituent un instrument aux contours qui restent flous. Les critères d'accord volontaires et de conditionnalité ne sont pas toujours vérifiés dans les initiatives qui se présentent comme des PSE. Les définitions des PSE qui mettent l'accent sur l'achat et la vente de services, introduisent une ambigüité quant à la propriété des services " vendus ", lesquels sont en général des biens publics. La revendication de droits de propriété sur le " carbone " introduit une logique de rente associée à une situation " business as usual " alors que les PSE visent d'abord à modifier les pratiques qui dégradent les écosystèmes. Les paiements pour le maintien d'activités conservatoires de l'écosystème risquent de ne pas répondre au principe d'additionnalité (l'écosystème aurait été conservé même sans les paiements), et la vérification de celle-ci engendre des coûts de transaction qui peuvent devenir très importants. Il y a une dissociation entre les exercices d'évaluation monétaire des services écosystémiques et la pratique des PSE, tout comme en économie on peut établir une distinction entre la valeur et le prix. Le problème fondamental des PSE est de savoir à quoi correspondent les paiements : la pratique tend à les aligner sur le coût d'opportunité d'un renoncement à certains droits d'usage ou de propriété (on parle d'ailleurs de " compensations "). Seul le mécanisme de développement propre, qui occupe une place à part dans les PSE, fait exception: la tonne de CO2 ayant une valeur de marché, les paiements s'aligner sur elle (qui n'est pas la valeur du service de régulation climatique - bien difficile à connaître - mais un prix d'équilibre offre/demande très spécifique). La mesure du coût d'opportunité des fournisseurs du service tend à devenir une question centrale pour évaluer la faisabilité des PSE envisagés, et cette problématique de l'efficacité se double également de questions autour de l'équité des contrats proposés. La seule logique de la compensation du coût d'opportunité a peu de chances d'aboutir à des résultats durables. Il faut passer d'une logique de compensation à une perspective d'investissement. Ceci conduit à évaluer le besoin de financement de ces programmes bien au-delà du seul coût d'opportunité, et réinsère l'instrument PSE dans l'orbite du développement rural. (Résumé d'auteur

A reverse chemical ecology approach to explore wood natural durability

The natural durability of wood species, defined as their inherent resistance to wood‐destroying agents, is a complex phenomenon depending on many biotic and abiotic factors. Besides the presence of recalcitrant polymers, the presence of compounds with antimicrobial properties is known to be important to explain wood durability. Based on the advancement in our understanding of fungal detoxification systems, a reverse chemical ecology approach was proposed to explore wood natural durability using fungal glutathione transferases. A set of six glutathione transferases from the white‐rot Trametes versicolor were used as targets to test wood extracts from seventeen French Guiana neotropical species. Fluorescent thermal shift assays quantified interactions between fungal glutathione transferases and these extracts. From these data, a model combining this approach and wood density significantly predicts the wood natural durability of the species tested previously using long‐term soil bed tests. Overall, our findings confirm that detoxification systems could be used to explore the chemical environment encountered by wood‐decaying fungi and also wood natural durability

Acute appendicitis: prospective evaluation of a diagnostic algorithm integrating ultrasound and low-dose CT to reduce the need of standard CT

Objectives: To evaluate an algorithm integrating ultrasound and low-dose unenhanced CT with oral contrast medium (LDCT) in the assessment of acute appendicitis, to reduce the need of conventional CT. Methods: Ultrasound was performed upon admission in 183 consecutive adult patients (111 women, 72 men, mean age 32) with suspicion of acute appendicitis and a BMI between 18.5 and 30 (step 1). No further examination was recommended when ultrasound was positive for appendicitis, negative with low clinical suspicion, or demonstrated an alternative diagnosis. All other patients underwent LDCT (30mAs) (step 2). Standard intravenously enhanced CT (180mAs) was performed after indeterminate LDCT (step 3). Results: No further imaging was recommended after ultrasound in 84 (46%) patients; LDCT was obtained in 99 (54%). LDCT was positive or negative for appendicitis in 81 (82%) of these 99 patients, indeterminate in 18 (18%) who underwent standard CT. Eighty-six (47%) of the 183 patients had a surgically proven appendicitis. The sensitivity and specificity of the algorithm were 98.8% and 96.9%. Conclusions: The proposed algorithm achieved high sensitivity and specificity for detection of acute appendicitis, while reducing the need for standard CT and thus limiting exposition to radiation and to intravenous contrast medi

First direct observation of two protons in the decay of 45^{45}Fe with a TPC

The decay of the ground-state two-proton emitter 45Fe was studied with a time-projection chamber and the emission of two protons was unambiguously identified. The total decay energy and the half-life measured in this work agree with the results from previous experiments. The present result constitutes the first direct observation of the individual protons in the two-proton decay of a long-lived ground-state emitter. In parallel, we identified for the first time directly two-proton emission from 43Cr, a known beta-delayed two-proton emitter. The technique developped in the present work opens the way to a detailed study of the mechanism of ground-state as well as beta-delayed two-proton radioactivity.Comment: 4 pages, 5 figure

Isotopic distribution of fission fragments in collisions between 238U beam and 9Be and 12C targets at 24 MeV/u

Inverse kinematics coupled to a high-resolution spectrometer is used to investigate the isotopic yields of fission fragments produced in reactions between a 238U beam at 24 MeV/u and 9Be and 12C targets. Mass, atomic number and isotopic distributions are reported for the two reactions. These informations give access to the neutron excess and the isotopic distribution widths, which together with the atomic-number and mass distributions are used to investigate the fusion-fission dynamics.Comment: Submitted to PR

Probing Nuclear forces beyond the drip-line using the mirror nuclei 16^{16}N and 16^{16}F

Radioactive beams of $^{14}$O and $^{15}$O were used to populate the resonant states 1/2$^+$, 5/2$^+$ and $0^-,1^-,2^-$ in the unbound $^{15}$F and $^{16}$F nuclei respectively by means of proton elastic scattering reactions in inverse kinematics. Based on their large proton spectroscopic factor values, the resonant states in $^{16}$F can be viewed as a core of $^{14}$O plus a proton in the 2s$_{1/2}$ or 1d$_{5/2}$ shell and a neutron in 1p$_{1/2}$. Experimental energies were used to derive the strength of the 2s$_{1/2}$-1p$_{1/2}$ and 1d$_{5/2}$-1p$_{1/2}$ proton-neutron interactions. It is found that the former changes by 40% compared with the mirror nucleus $^{16}$N, and the second by 10%. This apparent symmetry breaking of the nuclear force between mirror nuclei finds explanation in the role of the large coupling to the continuum for the states built on an $\ell=0$ proton configuration.Comment: 6 pages, 3 figures, 2 tables, accepted for publication as a regular article in Physical Review

Crystallization in mass-asymmetric electron-hole bilayers

We consider a \textit{mass-asymmetric} electron and hole bilayer. Electron and hole Coulomb correlations and electron and hole quantum effects are treated on first princles by path integral Monte Carlo methods. For a fixed layer separation we vary the mass ratio $M$ of holes and electrons between 1 and 100 and analyze the structural changes in the system. While, for the chosen density, the electrons are in a nearly homogeneous state, the hole arrangement changes from homogeneous to localized, with increasing $M$ which is verified for both, mesoscopic bilayers in a parabolic trap and for a macroscopic system.Comment: 10 pages, latex (styles files included

New pathway to bypass the 15O waiting point

We propose the sequential reaction process $^{15}$O($p$,$\gamma)(\beta^{+}$)$^{16}$O as a new pathway to bypass of the $^{15}$O waiting point. This exotic reaction is found to have a surprisingly high cross section, approximately 10$^{10}$ times higher than the $^{15}$O($p$,$\beta^{+}$)$^{16}$O. These cross sections were calculated after precise measurements of energies and widths of the proton-unbound $^{16}$F low lying states, obtained using the H($^{15}$O,p)$^{15}$O reaction. The large $(p,\gamma)(\beta^{+})$ cross section can be understood to arise from the more efficient feeding of the low energy wing of the ground state resonance by the gamma decay. The implications of the new reaction in novae explosions and X-ray bursts are discussed.Comment: submitte

Thermal Density Functional Theory in Context

This chapter introduces thermal density functional theory, starting from the ground-state theory and assuming a background in quantum mechanics and statistical mechanics. We review the foundations of density functional theory (DFT) by illustrating some of its key reformulations. The basics of DFT for thermal ensembles are explained in this context, as are tools useful for analysis and development of approximations. We close by discussing some key ideas relating thermal DFT and the ground state. This review emphasizes thermal DFT's strengths as a consistent and general framework.Comment: Submitted to Spring Verlag as chapter in "Computational Challenges in Warm Dense Matter", F. Graziani et al. ed