Line mixing effects in isotropic Raman spectra of pure N2: A classical trajectory study

International audienceLine mixing effects in the Q branch of pure N2 isotropic Raman scattering are studied at room temperature using a classical trajectory method. It is the first study using an extended modified version of Gordon's classical theory of impact broadening and shift of rovibrational lines. The whole relaxation matrix is calculated using an exact 3D classical trajectory method for binary collisions of rigid N2 molecules employing the most up-to-date intermolecular potential energy surface (PES). A simple symmetrizing procedure is employed to improve off-diagonal cross-sections to make them obeying exactly the principle of detailed balance. The adequacy of the results is confirmed by the sum rule. The comparison is made with available experimental data as well as with benchmark fully quantum close coupling [F. Thibault, C. Boulet, and Q. Ma, J. Chem. Phys. 140, 044303 (2014)] and refined semi-classical Robert-Bonamy [C. Boulet, Q. Ma, and F. Thibault, J. Chem. Phys. 140, 084310 (2014)] results. All calculations (classical, quantum and semi-classical) were made using the same PES. The agreement between classical and quantum relaxation matrices is excellent, opening the way to the analysis of more complex molecular systems

Comparison of quantum, semi-classical and classical methods in the calculation of nitrogen self-broadened linewidths

International audienceWe perform dynamical calculations on two robust N2-N2 potential energy surfaces in order to intercompare pressure broadening coefficients derived from close coupling and coupled states quantum dynamical methods, the semi-classical model of Robert and Bonamy and a full classical method. The coupled states and full classical results compare well with the experimental results or with close coupling values when available. This study confirms that the classical method is a good alternative at room and high temperatures to quantum dynamical methods. The results obtained using the semi-classical method however deviate from the other sets of data at all temperatures considered here (77-2400 K)

Interaction of surface acoustic waves with a two-dimensional electron gas in the presence of spin splitting of the Landau bands

The absorption and variation of the velocity of a surface acoustic wave of frequency $f$= 30 MHz interacting with two-dimensional electrons are investigated in GaAs/AlGaAs heterostructures with an electron density $n=(1.3 - 2.8) \times 10^{11} cm^{-2}$ at $T$=1.5 - 4.2 K in magnetic fields up to 7 T. Characteristic features associated with spin splitting of the Landau level are observed. The effective g factor and the width of the spin-split Landau bands are determined: $g^* \simeq 5$ and $A$=0.6 meV. The greater width of the orbital-split Landau bands (2 meV) relative to the spin-split bands is attributed to different shielding of the random fluctuation potential of charged impurities by 2D electrons. The mechanisms of the nonlinearities manifested in the dependence of the absorption and the velocity increment of the SAW on the SAW power in the presence of spin splitting of the Landau levels are investigated.Comment: Revtex 5 pages + 5 EPS Figures, v.2 - minor corrections in text and pic

Electron localization in sound absorption oscillations in the quantum Hall effect regime

The absorption coefficient for surface acoustic waves in a piezoelectric insulator in contact with a GaAs/AlGaAs heterostructure (with two-dimensional electron mobility $\mu= 1.3\times 10^5 cm^2/V\cdot s)$ at T=4.2K) via a small gap has been investigated experimentally as a function of the frequency of the wave, the width of the vacuum gap, the magnetic field, and the temperature. The magnetic field and frequency dependencies of the high-frequency conductivity (in the region 30-210 MHz) are calculated and analyzed. The experimental results can be explained if it assumed that there exists a fluctuation potential in which current carrier localization occurs. The absorption of the surface acoustic waves in an interaction with two-dimensional electrons localized in the energy "tails" of Landau levels is discussed.Comment: RevTeX 6 pages+6 EPS pic

Room temperature cathodoluminescence quenching of Er3+ in AlNOEr

This paper reports a cathodoluminescence (CL) spectroscopic study of nanogranular AlNOEr x samples with erbium content, x, in the range 0.5–3.6 at%. A wide range of erbium concentration was studied with the aim of understanding the concentration quenching of CL. The composition of thin films, deposited by radiofrequency reactive magnetron sputtering, was accurately determined by Energy Dispersive X-ray Spectroscopy (EDS). CL emission was investigated in the extended visible spectral range from 350 nm to 850 nm. The critical concentration of luminescent activator Er 3+ above which CL quenching occurs is 1%; the corresponding critical distance between Er 3+ ions in AlNOEr x is about 1.0 nm. The quenching mechanism is discussed. We discount an exchange-mediated interaction in favour of a multipole-multipole phonon-assisted interaction

The ABCD (Agriculture Biologique, Conseil et Développement), a French professional degree in organic farming, consulting and development

The creation of a professional degree in organic farming, known as an ABCD, is the result of the desire to provide training at the national level that is supported by the agriculture sector and that brings together the know-how of universities and higher education institutions specialised in agronomy and those of a network of teaching establishments specialised in technical education in the field. This degree aims at forming agents and advisors capable of working in a wide range of fields such as production, processing, distribution, control-certification and marketing. It is mainly intended for adults interested in career development and students who would like to further their education. Four training sites are involved and all teaching is done through a virtual digital university using information and communication technologies

Extended X-ray absorption fine structure study of Er bonding in AlNO:Erx films with x <= 3.6%

The structural properties of Er-doped AlNO epilayers grown by radio frequency magnetron sputtering were studied by Extended X-ray Absorption Fine Structure (EXAFS) spectra recorded at the Er L3 edge. The analysis revealed that Er substitutes for Al in all the studied samples and the increase in Er concentration from 0.5 to 3.6 at.% is not accompanied by formation of ErN, Er2O3 or Er clusters. Simultaneously recorded X-ray Absorption Near Edge Structure (XANES) spectra verify that the bonding configuration of Er is similar in all studied samples. The Er-N distance is constant at 2.18-2.19 Å i.e. approximately 15% larger than the Al-N bondlength, revealing that the introduction of Er in the cation sublattice causes considerable local distortion. The Debye-Waller factor, which measures the static disorder, of the second nearest shell of Al neighbors, has a local minimum for the sample containing 1% Er that coincides with the highest photoluminescence efficiency of the sample set

The SPARSE model for the prediction of water stress and evapotranspiration components from thermal infra-red data and its evaluation over irrigated and rainfed wheat

Evapotranspiration is an important component of the water cycle, especially in semi-arid lands. A way to quantify the spatial distribution of evapotranspiration and water stress from remote-sensing data is to exploit the available surface temperature as a signature of the surface energy balance. Remotely sensed energy balance models enable one to estimate stress levels and, in turn, the water status of continental surfaces. Dual-source models are particularly useful since they allow derivation of a rough estimate of the water stress of the vegetation instead of that of a soil&#8211;vegetation composite. They either assume that the soil and the vegetation interact almost independently with the atmosphere (patch approach corresponding to a parallel resistance scheme) or are tightly coupled (layer approach corresponding to a series resistance scheme). The water status of both sources is solved simultaneously from a single surface temperature observation based on a realistic underlying assumption which states that, in most cases, the vegetation is unstressed, and that if the vegetation is stressed, evaporation is negligible. In the latter case, if the vegetation stress is not properly accounted for, the resulting evaporation will decrease to unrealistic levels (negative fluxes) in order to maintain the same total surface temperature. This work assesses the retrieval performances of total and component evapotranspiration as well as surface and plant water stress levels by (1) proposing a new dual-source model named Soil Plant Atmosphere and Remote Sensing Evapotranspiration (SPARSE) in two versions (parallel and series resistance networks) based on the TSEB (Two-Source Energy Balance model, Norman et al., 1995) model rationale as well as state-of-the-art formulations of turbulent and radiative exchange, (2) challenging the limits of the underlying hypothesis for those two versions through a synthetic retrieval test and (3) testing the water stress retrievals (vegetation water stress and moisture-limited soil evaporation) against in situ data over contrasted test sites (irrigated and rainfed wheat). We demonstrated with those two data sets that the SPARSE series model is more robust to component stress retrieval for this cover type, that its performance increases by using bounding relationships based on potential conditions (root mean square error lowered by up to 11 W m&#8722;2 from values of the order of 50&#8211;80 W m&#8722;2), and that soil evaporation retrieval is generally consistent with an independent estimate from observed soil moisture evolution

Magnetism, Spin-Orbit Coupling, and Superconducting Pairing in UGe2_2

A consistent picture on the mean-field level of the magnetic properties and electronic structure of the superconducting itinerant ferromagnet UGe$_2$ is shown to require inclusion of correlation effects beyond the local density approximation (LDA). The "LDA+U" approach reproduces both the magnitude of the observed moment, composed of strongly opposing spin and orbital parts, and the magnetocrystalline anisotropy. The largest Fermi surface sheet is comprised primarily of spin majority states with orbital projection $m_{\ell}$=0, suggesting a much simpler picture of the pairing than is possible for general strong spin-orbit coupled materials. This occurrence, and the quasi-two-dimensional geometry of the Fermi surface, support the likelihood of magnetically mediated p-wave triplet pairing.Comment: accepted for publication in Phys. Rev. Lett; URL for better quality image of Fig.3 (2MB) at http://yammer.ucdavis.edu/public/UGe2/fig3.ep

HIV/AIDS Drugs for Sub-Saharan Africa: How Do Brand and Generic Supply Compare?

BACKGROUND: Significant quantities of antiretroviral drugs (ARVs) to treat HIV/AIDS have been procured for Sub-Saharan Africa for the first time in their 20-year history. This presents a novel opportunity to empirically study the roles of brand and generic suppliers in providing access to ARVs. METHODOLOGY/PRINCIPAL FINDINGS: An observational study of brand and generic supply based on a dataset of 2,162 orders of AIDS drugs for Sub-Saharan Africa reported to the Global Price Reporting Mechanism at the World Health Organization from January 2004-March 2006 was performed. Generic companies supplied 63% of the drugs studied, at prices that were on average about a third of the prices charged by brand companies. 96% of the procurement was of first line drugs, which were provided mostly by generic firms, while the remaining 4%, of second line drugs, was sourced primarily from brand companies. 85% of the generic drugs in the sample were manufactured in India, where the majority of the drugs procured were ineligible for patent protection. The remaining 15% was manufactured in South Africa, mostly under voluntary licenses provided by brand companies to a single generic company. In Sub-Saharan African countries, four first line drugs in the dataset were widely patented, however no general deterrent to generic purchasing based on a patent was detected. CONCLUSIONS/SIGNIFICANCE: Generic and brand companies have played distinct roles in increasing the availability of ARVs in Sub-Saharan Africa. Generic companies provided most of the drugs studied, at prices below those charged by brand companies, and until now, almost exclusively supplied several fixed-dose combination drugs. Brand companies have supplied almost all second line drugs, signed voluntary licenses with generic companies, and are not strictly enforcing patents in certain countries. Further investigation into how price reductions in second line drugs can be achieved and the cheapest drugs can actually be procured is warranted