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Important data in the investigation of laser-produced plasmas will be provided by studies of the X-ray emission characteristics in the range 1-10 keV, with time resolution comparable to plasma heating times. Present techniques using conventional photomultipliers or photodiodes are not suitable for time measurements on plasma heated by short optical pulses of several hundred picoseconds or less. The development of new X-ray cameras is also necessary. Their photocathodes must be chosen with care. In this paper we describe an initial study of the characteristics of metallic photocathodes: quantum efficiency, energy distribution of emitted photoelectrons, etc. Then we worked out the provisional sensitivity, spatial and temporal resolution of cameras in the streak mode or in shutter mode.
The emission mechanism studied here, the synchrotron maser instability is based on a gyroresonance of highly energetic electrons. Compared to the cyclotron maser, this mechanism has the great advantage to be a direct amplification process even if the ratio ωp/ωc is not very small; a situation relevant to stellar flares.The high efficiency of the process can be confirm by the non linear study of its saturation.
Case studies show that some energetic particle flux enhancements up to MeV/nuc. observed at 1 AU cannot be treated as a consequence of particle acceleration at shocks or during flares. Atypical energetic particle events (AEPEs) are often detected during crossings of magnetic cavities formed by strong current sheets of various origins in the solar wind. Such cavities confine small-scale magnetic islands (SMIs) produced by magnetic reconnection. SMIs, in turn, trap and re-accelerate energetic particles according to predictions based on the theory of Zank et al. describing stochastic particle energization in the supersonic solar wind via numerous dynamically interacting SMIs. AEPEs possess energies that overlap SEP events and can be an important component in understanding space weather.
In practice cattle may be slaughtered at different combinations of age and weight. As each of these factors could affect meat quality traits, the present work aimed to identify which combination can be expected to increase overall meat quality of m. rectus abdominis of Charolais heifers. Totally, 40 heifers were slaughtered either at 26±1 or at 36±1 months of age. Young heifers were sampled at two different carcass weights (349±12 and 394±8 kg). Old heifers were also sampled at two different carcass weights (397±6 and 451±9 kg). The m. rectus abdominis was excised 24 h postmortem to determine metabolic enzyme activities, myosin heavy-chain isoform proportions, lipid contents, collagen content and collagen solubility. Shear force measurements were evaluated on raw and broiled meat after 14 days of ageing. Meat quality traits scored between 0 and 10 by sensory analysis. Increasing slaughter age from 26 to 36 months had no impact on either raw/broiled shear force (0.31⩽P⩽0.47) and/or meat quality traits (0.62⩽P⩽0.91) or on physicochemical properties of heifer’s meat samples. Increasing carcass weight for a similar slaughter age of 26 months had also impact neither on meat quality traits (0.52⩽P⩽0.91) nor on muscular properties. On the contrary, increasing carcass weight for a similar slaughter age of 36 months had induced a decrease of muscular shear force (raw muscle; P=0.009) and a concomitant decrease of total collagen content (P=0.03). Nevertheless, no significant impact on meat quality traits was revealed by the sensorial panel (0.13⩽P⩽0.49). Metabolic enzyme activities (0.13⩽P⩽0.86) and myosin heavy-chain proportions (0.13⩽P⩽0.96) were not significantly impacted by slaughter age and carcass weight. Thus, the impact of increasing carcass weight and/or slaughter age in young Charolais heifers has a limited impact on meat quality traits and associated muscular characteristics. Modulating heifer’s cycles (age and/or carcass weight in the studied range) appears to be a way to answer to the numerous marketing chains, without penalising meat quality traits.
Research to understand and manage ecosystems to supply services has recently spurred a functional view of their biodiversity. In particular, approaches based on functional traits rather than species diversity are increasingly used to reflect interactions between organisms and their environment. These approaches bring a functional perspective to the study of community structure responses to disturbances and resources, and of their effects on ecosystem functioning and services. From an academic perspective, we propose a conceptual framework based on species functional traits to better infer how grassland management practices (fertilization, defoliation regime) along with abiotic factors influence plant, animal and microbial community composition and a range of services in grassland ecosystems. The core of the framework relies on combinations of plant functional traits and associated microbial features that specifically respond to environmental and management factors and influence ecosystem services. To overcome stakeholders’ difficulty in applying the concept of functional traits, we propose an operational approach implying the mapping of plant communities distributed into five plant functional types (PFTs). The approach was used for fields in grassland-based livestock farms from two French grassland networks. We evaluated its ability to predict a range of services including forage provision and non-market services according to environmental and management drivers. PFT-based plant community composition predicted forage services reasonably well but responded weakly to environmental gradients. To cope with the observed limitations of current predictive approaches, we suggest including soil microbial functional types and adaptive management rather than using a prescriptive scheme.
Dwarf (Kogia sima) and pygmy (K. breviceps) sperm whales occur in pelagic waters around southern Africa. Here we report the first record of K. sima from Namibia and provide information on the basic morphometrics and diet of that record and of two recent strandings of K. breviceps. All known records (N = 29) of K. breviceps from Namibia are also collated. Eight families of cephalopod were identified in the stomach contents of the K. sima but no fish remains and few crustacean parts were present. Nine and ten families of cephalopod were identified in the stomachs of the two K. breviceps specimens respectively. This report expands the known range of K. sima by more than 1000 km from previous published records in the region. The sparsely populated nature of the Namibian coast and bias of records towards centres of human habitation suggest Kogia strandings are under reported. The low number of stranded specimens of K. sima from Namibia and west South Africa, in comparison to K. breviceps suggests that K. sima occur rarely or at very low densities in the area influenced by the Benguela current ecosystem. Specimens from Namibia are valuable due to uncertainties about taxomony of kogiids in the region.
Nanoparticles (NPs) have attracted a considerable interest in the last decades, owing to their remarkable physical and chemical properties. The most important characteristic of NPs is the size effect, that is, their properties differ from that of the corresponding bulk material. We will focus here on Electron Energy-Loss Spectroscopy (EELS) investigations of Gd2O3 NPs of different and controlled sizes. EELS spectra near the O-K edge of Gd2O3 were recorded and compared with feff8.2 ELNES simulations. The calculation of the EELS response from small particles by the feff code raises some particular problems which have been carefully examined and partially solved. The simulations are in fair agreement with experiment and reveal the existence of size effects.
The sol-gel process opens new possibilities in the field of biotechnologies. Sol-gel glasses are formed at room temperature via the polymerization of molecular precursors. Enzymes can be added to the solution of precursors and trapped within the growing silica network. Small substrate molecules can diffuse through the pores allowing reactions to be performed in-situ, within the silica gels. Enzyme are encased by the hydrated silica in a cage tailored to their size, they retain their biocatalytic activity and may even be stabilized within the sol-gel matrix.
Whole cell bacteria have also been immobilized within sol-gel glasses. They behave as a "bag of enzymes" and their membrane protects enzymes against denaturation and leaching. The cellular organization of bacteria cells is preserved upon encapsulation. Experiments performed with Escherichia coli induced to β-galactosidase show that they still exhibit noticeable enzymatic activity. Some degradation of the cell walls may even occur increasing the “measured” activity. However silica gels made from aqueous precursors seem to prevent bacteria from natural degradation upon ageing.
Antibody-antigen recognition has been shown to be feasible within sol-gel matrices. Trapped antibodies bind specifically the corresponding haptens and can be used for the detection of traces of chemicals. Even whole cell protozoa have been encapsulated without any alteration of their cellular organization. For medical applications, trapped parasitic protozoa have been used as antigens for blood tests with human sera. Antigen-antibody interactions were followed by the so-called Enzyme Linked ImmunoSorbent Assays (ELISA).
Comparative tests on SGN and Radon simulated ILW vitrification with a cold crucible based experimental plant were performed. The batch was fed as paste with 20 wt.% moisture. An operation conditions, the ability of the cold crucible to maintain the differential pressure during the operation, process variables, product properties, off-gas and condensate compositions, the effect of melt agitation on melter capacity and cesium loss have been determined. Melt viscosity and resistivity have been measured. Material structures were studied using infra-red spectroscopy and electron microscopy. Leach rates of sodium and potassium cations as well as Cs-137 have been measured. The behavior of sulfate and chloride ions in the vitrification process as well as their solubility in SGN and “Radon” glasses have been investigated.
The technique of ball milling has been applied to various phases of superionic PbSnF4, namely on (i): highly stressed tetragonal α-PbSnF 4(aq1) obtained by precipitation from aqueous solutions, (ii): highly stressed tetragonal α-PbSnF4(aq2) obtained by reaction of a solid with an aqueous solution, (iii): stressed orthorhombic o-PbSnF4 obtained by precipitation from aqueous solutions, (iv): non-stressed tetragonal α-PbSnF4(ssr) obtained by direct reaction between SnF2 and
PbF2 at high temperature, and on (v): non-stressed tetragonal β-PbSnF4 obtained by direct reaction between SnF2 and PbF2 at high temperature. In all cases, transformation to microcrystalline cubic γ-PbSnF4 is observed very rapidly. This is a unique method for stabilizing high temperature γ-PbSnF4 at ambient temperature, which cannot be done by conventional methods, such as quenching. The phases obtained are totally disordered, microcrystalline, and have the memory of their origin.
In the diffraction community, the goniometer is the main part of the diffractometer, essential for orienting the samples. To characterize the goniometer, the sphere of confusion (SoC) has been measured. The SoC describes the minimal sphere that enclosed the measurements. This essential information is very important for the diffractometer users. In collaboration with Symetrie Inc., Soleil Synchrotron and the CEA, the SoC has been measured with three different metrology methods. These three measurement techniques and the associated results are discussed in this article.
Airborne 137Cs level in France is not decreasing significantly anymore (mean yearly value around 0,25 µ Bq.m-3 contrarily to what was noticed in the past decades. This observation points out the role of processes that delay the atmospheric cleaning and participate to the persistence of radionuclide in the air at ground-level after a deposit, in the frame of medium as well as long-dated post-accidental contexts. The current background level also yields to consider 137Cs in the atmosphere as a tracer of atmospheric processes like resuspension and re-emission from biomass burnings. This allows us to explain 2/3 of the peaks observed over the last six years. The remaining 1/3 is mainly noticed in winter when spreading of pollutants in the atmosphere is often weak due to temperature gradient inversion. On average, continental air masses are responsible for increases by a factor of 3 while oceanic air masses are characterised by levels 3 times lower, compared to the mean value. Feeding of 137Cs in air at ground-level is the result of both local resuspension that signs 137Cs activity levels in soils to which is added a remote contribution from time to time (resuspension of Saharan dust or re-emission from fires occurring in eastern territories with high 137Cs deposition level). Finally, 137Cs activity levels in air masses crossing over France can be described on average by a longitudinal gradient.
To describe the features of hepatitis B virus (HBV) infection in Madagascar, a randomized sero-epidemiological survey was undertaken in the general population ≥ 1 year old of two provinces which represents 45% of the total population. In the 921 sera tested, the prevalence of HBV markers was 20·5% for HBsAg, 38·2% for anti-HBc and 6·9% for HBeAg. HBsAg and anti-HBc prevalence rates were significantly higher in males. A large difference in HBsAg prevalence was observed between urban (5·3%) and rural areas (26·0%). The same contrast in prevalence was noticed for the other HBV markers. In rural areas, HBV infection was more frequently acquired early in infancy, which suggests predominantly perinatal or postnatal transmission. The presence of HBV markers was not significantly associated with a history of blood transfusion, surgery or parenteral injection. High infectivity carriers represented 5·3% and the overall frequency of chronic carriers was 10·4%. These results place Madagascar among areas of high endemicity.
The Gattini-DomeC project, part of the IRAIT site testing campaign and ongoing since January 2006, consists of two cameras for the measurement of optical sky brightness, large area cloud cover, and auroral detection above the DomeC site, home of the French-Italian Concordia station. The cameras are transit in nature and are virtually identical except for the nature of the lenses. The cameras have operated throughout the past two Antarctic winter seasons and here we present the results obtained from the 2006 winter-time dataset of the wide field “All-sky camera".
Despite the growing geological evidence that fluid boiling and vapour-liquid separation affect the distribution of metals in magmatic-hydrothermal systems significantly, there are few experimental data on the chemical status and partitioning of metals in the vapour and liquid phases. Here we report on an in situ measurement, using X-ray absorption fine structure (XAFS) spectroscopy, of antimony speciation and partitioning in the system Sb2O3-H2O-NaCl-HCl at 400°C and pressures 270—300 bar corresponding to the vapour-liquid equilibrium. Experiments were performed using a spectroscopic cell which allows simultaneous determination of the total concentration and atomic environment of the absorbing element (Sb) in each phase. Results show that quantitative vapour-brine separation of a supercritical aqueous salt fluid can be achieved by a controlled decompression and monitoring the X-ray absorbance of the fluid phase. Antimony concentrations in equilibrium with Sb2O3 (cubic, senarmontite) in the coexisting vapour and liquid phases and corresponding SbIII vapour-liquid partitioning coefficients are in agreement with recent data obtained using batch-reactor solubility techniques. The XAFS spectra analysis shows that hydroxy-chloride complexes, probably Sb(OH)2Cl0, are dominant both in the vapour and liquid phase in a salt-water system at acidic conditions. This first in situ XAFS study of element fractionation between coexisting volatile and dense phases opens new possibilities for systematic investigations of vapour-brine and fluid-melt immiscibility phenomena, avoiding many experimental artifacts common in less direct techniques.