The purpose of this study is to analyze a long term database of the chemical composition of precipitation at three African dry savanna sites in the Sahel. The precipitation samples were collected ...during the monsoon season at Agoufou (15°20′N, 01°29′W, Mali) from 2004 to 2006, Banizoumbou (13°31′N, 02°38′E, Niger) from 1994 to 2009 and Katibougou (12°56′N, 07°32′ W, Mali) from 1997 to 2008. pH and major inorganic and organic ions in precipitation were analyzed by ionic chromatography. A characterization of mean precipitation chemistry with the associated wet deposition fluxes for each species is presented. The first important result is that interannual variability of all volume-weighted mean (VWM) concentrations is low, ranging between ±5% and ±25%. Acidity in dry savannas is low and indicates the strong alkaline nature of the precipitation. The average annual pH at Agoufou is 6.28, 5.75 at Banizoumbou and 5.54 at Katibougou. This result is correlated with the important terrigenous contribution measured in the chemical content of precipitation, implying acidity neutralization by mineral species such as Ca2+ and NH4+. Mg2+ and K+ are found to play a minor role in neutralization. Enrichment factor calculations for Ca2+, SO42−, K+ and Mg2+ with respect to the sea reference reveal a significant influence of Saharan and Sahelian crustal sources. VWM concentrations of these species dominate the composition of measured precipitation. An estimation of the potential particulate and gas contribution to the total precipitation composition is given for each site: At Agoufou, the mean relative contribution in rainwater is 80% for particles and 20% for gases, while at the Banizoumbou and Katibougou sites, results indicate 70% for particles and 30% for gases. The high particulate phase contribution to precipitation emphasizes the importance of multiphase processes between gases and particles in the atmospheric chemistry typical of African semi-arid savanna ecosystems. The second highest contribution is nitrogenous, with high VWM concentrations of NO3− and NH4+ measured at the three sites. Monthly evolution of NO3− and NH4+ concentrations are studied in relation to gaseous emission sources in the Sahelian region, i.e. biogenic soil emission and ammonia sources from animals. The calculated wet nitrogen deposition flux presents a regular increase throughout the wet season at the three sites. Results suggest total mean nitrogen deposition fluxes of 1.80 kg N ha−1 yr−1 at Agoufou, 2.10 kg N ha−1 yr−1 at Banizoumbou, and 3.30 kg N ha−1 yr−1 at Katibougou. The marine contribution is lower, 23% at Agoufou, 17% at Banizoumbou and 13% at Katibougou. The last contribution concerns organic acidity, which ranges from 5% at Agoufou, 10% at Banizoumbou to 14% at Katibougou. Terrigenous and marine contributions present a negative gradient, whereas nitrogenous and organic contributions a positive gradient along the Sahelian transect defined by Agoufou–Banizoumbou–Katibougou.
► Analysis of quality controlled rain chemical data for three sahelian savannas in Africa. ► Characterization of mean precipitation chemistry composition for each chemical species. ► Characterization of mean deposition fluxes for each chemical species. ► Interannual and seasonal variability of concentrations and deposition. ► Focus on nitrogen deposition fluxes in Sahelian ecosystems.
Aims: This 12-week, open-label, primary care study (NCT02195817) evaluated the efficacy and safety of nalmefene, taken as needed, to reduce alcohol consumption in adults with a diagnosis of alcohol ...dependence and drinking at least at high drinking risk levels (DRL, > 60 g/day for men, > 40 g/day for women). Methods: Following the Screening Visit, patients recorded their daily alcohol consumption for 2 weeks. Patients were then categorised by their self-reported drinking levels; those who maintained at least a high DRL in the 2-week period were included in Cohort-A, and those who reduced their alcohol consumption below high DRL were included in Cohort-B. Cohort-A received simple psychosocial interventions and were supplied with nalmefene 18 mg to be taken on days when they perceived a risk of drinking alcohol. Patients in Cohort-B received a simple psychosocial intervention and were treated per normal practice. Results: Of the 378 enrolled patients, 330 were included in Cohort-A and 48 in Cohort-B. For patients in Cohort-A, the mean change from screening to Week-12 in the number of heavy drinking days/month was –13.1 days/month (95% CI –14.4 to –11.9, p < 0.0001). Overall, 55% of patients reduced their DRL by ≥2 risk levels and 44% of patients reduced to a low DRL. The most common adverse events were nausea (18.3%) and dizziness (17.7%). Patients in Cohort-B maintained their lower level alcohol consumption at the 12-week follow-up. Conclusions: Patients with alcohol dependence treated in primary care with nalmefene, taken as needed, in conjunction with simple psychosocial support, significantly reduced their alcohol consumption. Treatment was well tolerated.
The microstructure of fibrous networks in low density wood-based fibreboards elaborated with various processes is observed by X-ray tomography. Image analysis tools derived from mathematical ...morphology are used to process 3D images obtained and to recover 3D information on the fibres and the fibre network. A 3D model of random fibre networks developed by means of experimental information is presented. The parameters of the model correspond to internal architecture properties. Their influence on a local thermal conductivity is studied through finite element method.
African biomass burning emission inventories for gaseous and particulate species have been constructed at a resolution of 1 km by 1km with daily coverage for the 2000-2007 period. These inventories ...are higher than the GFED2 inventories, which are currently widely in use. Evaluation specifically focusing on combustion aerosol has been carried out with the ORISAM-TM4 global chemistry transport model which includes a detailed aerosol module. This paper compares modeled results with measurements of surface BC concentrations and scattering coefficients from the AMMA Enhanced Observations period, aerosol optical depths and single scattering albedo from AERONET sunphotometers, LIDAR vertical distributions of extinction coefficients as well as satellite data. Aerosol seasonal and interannual evolutions over the 2004-2007 period observed at regional scale and more specifically at the Djougou (Benin) and Banizoumbou (Niger) AMMA/IDAF sites are well reproduced by our global model, indicating that our biomass burning emission inventory appears reasonable.
Ambient PM10 and PM2.5 aerosols were monitored in Toulouse from March 2004 to February 2005 (Extensive Observed Period (EOP)) as part of the research project CAPITOUL (Canopy and Aerosol Particles ...Interaction in TOulouse Urban Layer). Concentrations of 8 major ions (Na⁺, NH₄ ⁺, K⁺, Mg⁺², Ca⁺², Cl⁻, NO₃ ⁻, SO₄ ²⁻), 15 metal elements (Al, Ba, Cd, Ce, Cr, Cu, Fe, La, Mn, Ni, Pb, Sr, Th, Ti, Zn), and carbonaceous aerosols TC, POM and EC (total carbon, organic carbon and elemental carbon, respectively) were measured in a total of 52 samples of each size. Inter-seasonal variations were analyzed. Weekly PM2.5 and PM10 total mass concentrations (major ions + carbon + metal elements) were 4.4-18.0 μg m⁻³ and 6.5-23.5 μg m⁻³, with an annual average concentration of 11.0 ± 3.6 μg m⁻³ and 13.2 ± 4.3 μg m⁻³, respectively. The highest concentration for sulfate was found in summer and fall, whereas the highest NO₃ ⁻ concentration was observed in winter. This study is strengthened by Kruskal-Wallis and Mann-Whitney statistical tests. On average, carbonaceous species constitute between 49% and 75% of the monthly concentration registered, POM concentration always remaining higher (ratio more than 51%) than EC in both size ranges. The average OC/EC ratios were 2.70 ± 0.81 and 2.70 ± 0.60 for PM2.5 and PM10, respectively. Secondary organic carbon concentrations were significantly higher in the warmer seasons reaching in summer average ratios of 65.9% and 64.5% of the total OC concentration for PM2.5 and PM10, respectively. Secondary organic carbon was produced in the fine fraction of the aerosol. Metal elements analysis and enrichment factor calculations show that traffic emissions were the major influence on the chemical composition of the urban aerosol. A receptor modeling study was conducted using Principal Component Factor Analysis followed by multi-linear regression analysis in order to provide quantitative insights into the sources of specific chemical components in PM10.
The energy deposition during the return stroke phase of a pulsed surface discharge is driven by the electrical circuit and the electrical properties of the discharge. To control these factors, a ...parametric study is performed with varying the circuit parameters, for different discharge lengths and voltages between -19 to -26 kV. The electrical characteristics of the discharge are then simulated using different plasma resistance models, which assume a time-varying resistance: the Toepler model, the Rompe-Weizel model, and the Vlastós model. The model parameters are optimized to fit the experimental results. The analysis shows that for long pulses obtained with large inductance, the three models fare equally well, since the discharge resistance is mainly constant during the pulse. In low-inductance cases, the Toepler model leads to larger errors during the initial current pulse, whereas the Rompe-Weizel and Vlastós models describe with a good agreement the experiments. The discharge resistance evolves during the first 300 ns, then remains mostly constant until the end of the pulse. The constant part of the resistance gives the surface-averaged conductivity of the discharge, which increases linearly with the linear energy dissipated in the discharge. Finally, theoretical estimates of the varying resistance parameters are in fair agreement with the parameters obtained while fitting the experiments, in particular in the Rompe-Weizel case. These findings can be used to estimate the channel resistance of a pulsed surface discharge, and to help optimizing the high-voltage circuit.
We demonstrate carbon dioxide sensing using a random-modulation continuous-wave differential absorption lidar transmitter based on an indium phosphide photonic integrated circuit. We have designed ...and characterized the photonic circuit that has been fabricated through an open access generic integration platform based on standard building blocks. It consists of three four-section distributed Bragg reflector lasers, two fast photodiodes, two electro-absorption modulators and five semiconductor optical amplifiers integrated together with several couplers and waveguides. The circuit contains two interrelated subsystems, one for performing the differential absorption lidar measurement, and the other for stabilizing the emission wavelength of the different lasers. We characterize the individual integrated devices, especially lasers, photodiodes and modulators. The carbon dioxide sensing is done by measuring a gas cell in a fiber setup emulating a lidar configuration. Our promising results pave the way to miniaturized differential absorption lidar systems, while highlighting some of the main challenges to overcome.
Here, we present measurements of electrons and positrons from the semileptonic decays of heavy-flavor hadrons at midrapidity (|y| < 0.35) in Au + Au collisions at √sNN = 62.4 GeV. The data were ...collected in 2010 by the PHENIX experiment that included the new hadron-blind detector. The invariant yield of electrons from heavy-flavor decays is measured as a function of transverse momentum in the range 1 < peT < 5 GeV/c. The invariant yield per binary collision is slightly enhanced above the p + p reference in Au + Au 0%–20%, 20%–40%, and 40%–60% centralities at a comparable level. At this low beam energy this may be a result of the interplay between initial-state Cronin effects, final-state flow, and energy loss in medium. The v2 of electrons from heavy-flavor decays is nonzero when averaged between 1.3 < peT < 2.5 GeV/c for 0%–40% centrality collisions at √sNN = 62.4 GeV. For 20%–40% centrality collisions, the v2 at √sNN = 62.4 GeV is smaller than that for heavy-flavor decays at √sNN = 200 GeV. The v2 of the electrons from heavy-flavor decay at the lower beam energy is also smaller than v2 for pions. Both results indicate that the heavy quarks interact with the medium formed in these collisions, but they may not be at the same level of thermalization with the medium as observed at √sNN = 200 GeV.
Neutral-pion pi(0) spectra were measured at midrapidity (vertical bar y vertical bar < 0.35) in Au + Au collisions at root s(NN) = 39 and 62.4 GeV and compared with earlier measurements at 200 GeV in ...a transverse-momentum range of 1 < p(T) < 10 GeV/c. The high-p(T) tail is well described by a power law in all cases, and the powers decrease significantly with decreasing center-of-mass energy. The change of powers is very similar to that observed in the corresponding spectra for p + p collisions. The nuclear modification factors (RAA) show significant suppression, with a distinct energy, centrality, and p(T) dependence. Above p(T) = 7 GeV/c, R-AA is similar for root sNN = 62.4 and 200 GeV at all centralities. Perturbative-quantum-chromodynamics calculations that describe R-AA well at 200 GeV fail to describe the 39 GeV data, raising the possibility that, for the same p(T) region, the relative importance of initial-state effects and soft processes increases at lower energies. The p(T) range where pi(0) spectra in central Au + Au collisions have the same power as in p + p collisions is approximate to 5 and 7 GeV/c for root sNN = 200 and 62.4 GeV, respectively. For the root sNN = 39 GeV data, it is not clear whether such a region is reached, and the x(T) dependence of the x(T)-scaling power-law exponent is very different from that observed in the root sNN = 62 and 200 GeV data, providing further evidence that initial-state effects and soft processes mask the in-medium suppression of hardscattered partons to higher p(T) as the collision energy decreases.
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