597 research outputs found
Evaluation of three tools for assessing infection by gastrointestinal parasites in pasture-fed organic lambs
Organic meat sheep producers have a very limited array of efficient alternative drugs and limited access to synthetic drugs for controlling internal parasites. The use of targeted selective treatments, e.g., treating only the lambs that cannot cope with infection, would be of interest. The difficulty is to identify those lambs in need of treatment. FAMACHA© (based on an anaemia indicator) has been used with success in tropical areas where the bloodsucker worm Haemonchus contortus is the main gastrointestinal strongyle. The appearance of the wool is sometimes used to determine the necessity of treatment, and a spectrofluorometric analysis of the wool was tested. Shepherds may also detect lambs with poor, medium and good body conditions, on the basis of experience. In our study, the three estimators for gastrointestinal parasites were not related to parasite faecal egg or oocyste counts, which are the usual laboratory tools for assessing infection
Animal health strategies in organic and conventional meat sheep production
Sixteen meat sheep farms (nine conventional and seven organic) in the centre of France were surveyed to evaluate their economic and production performances (previous interviews) and their strategies related to animal health with particular attention to internal parasites (present interview on health strategies). The organic farms were surveyed in mid-September 2006 and the conventional ones in October 2007. Each interview (1Âœ or 2 h) included a visit of the farm (with the collection of faeces for evaluation of internal parasites), followed by an open discussion on sheep production and health problems, and parasitic infections, in particular. The discussion was recorded and then transcribed into a word processor file and analysed. The farmers agreed on the fragile health of their animals (with special attention to internal parasites)and were confronted with the low value of each lamb or ewe, which does not allow for high health costs. Even under this limited economic situation, the farmers developed different health strategies. Conventional farmers rely on systematic treatments to prevent parasitic infection; they use low-cost effective synthetic drugs and accept lamb mortality rates ranging from five to eight percent. Their practices are homogeneous, which is possibly due to frequent exchanges with colleagues or veterinarians. The healthcare strategy of organic farmers may be divided into two distinct categories: autonomous (âself-made farmerâ) and âcreativeâ. The organic self-made farmers are experienced and aim at a sustainable flock (âcruiser flockâ). The creative ones do not seem to easily handle the health strategy aspect and often spend more money on healthcare than their conventional or organic self-made colleagues. Health strategy is therefore not completely dependent on the type of production - conventional versus organic - but on the farmerâs conception of life and nature.
The creative farmers believe that disease is a dysfunction that may be corrected with treatments
(conventional or alternative ones), whereas the self-made farmers consider health as the result of a
dynamic equilibrium between the many forces that interact within a flock. The latter is somewhat similar
to the idea put forth in the book âThe normal and the pathologicalâ by Canguilhem
First-principles calculations of X-ray absorption spectra at the K-edge of 3d transition metals: an electronic structure analysis of the pre-edge
International audienceWe first present an extended introduction of the various methods used to extract electronic and structural information from the K pre-edge X-ray absorption spectra of 3d transition metal ions. The K pre-edge structure is then modelled for a selection of 3d transition metal compounds and analyzed using first-principles calculations based on the density functional theory (DFT) in the local density approximation (LDA). The selected compounds under study are presented in an ascending order of electronic structure complexity, starting with the Ti K-edge of rutile and anatase, and finishing with the Fe K-edge of the cyanomet-myoglobin. In most cases, the calculations are compared to polarized experimental spectra. It is shown that DFT-LDA methods enable us to reproduce satisfactorily the experimental features and to understand the nature of the electronic transitions involved in the pre-edge region. The limiting aspects of such methods in modelling the core-hole electron interaction and the 3d electron-electron repulsion are also pointed out
Inventaire des mollusques d'eau douce en Ituri (Haut-Zaïre) : conséquences sanitaires pour l'homme et le bétail
Cent soixante-dix points d'abreuvement pour le bétail ont été prospectés de juin 1986 à août 1988 en Ituri (nord-est du Zaïre) afin de déterminer les principaux mollusques d'eau douce pouvant intervenir dans la transmission des trématodoses animales et humaines. Dix-neuf espÚces de gastéropodes ont été rencensées. Quatre gßtes sur dix n'hébergent pas ou trÚs peu de mollusques. Les trois espÚces les plus fréquemment rencontrées sont #Lymnaea natalensis, #Biomphalaria pfeifferi (15,3 %). La distribution des deux premiÚres espÚces semble trÚs homogÚne au niveau régional et ne permet pas l'établissement d'une relation avec le risque parasitaire (#Fasciola gigantica et #Schistosoma mansoni). Inversement, la répartition de #Bulinus africanus (et secondairement celle de #B. forskalii) correspond globalement à la distribution de #Schistosoma bovis chez les bovins. L'association de #Lymnaea natalensis et de #Bulinus africanus au sein des gßtes rend compte de l'association des infestations à #Fasciola gigantica et #Schistosoma bovis$ chez les bovins. (Résumé d'auteur
Hydrogen Energy Storage: New Techno-Economic Emergence Solution Analysis
International audienceThe integration of various renewable energy sources as well as the liberalization of electricity markets are established facts in modern electrical power systems. The increased share of renewable sources within power systems intensifies the supply variability and intermittency. Therefore, energy storage is deemed as one of the solutions for stabilizing the supply of electricity to maintain generation-demand balance and to guarantee uninterrupted supply of energy to users. In the context of sustainable development and energy resources depletion, the question of the growth of renewable energy electricity production is highly linked to the ability to propose new and adapted energy storage solutions. The purpose of this multidisciplinary paper is to highlight the new hydrogen production and storage technology, its efficiency and the impact of the policy context on its development. A comprehensive techno/socio/economic study of long term hydrogen based storage systems in electrical networks is addressed. The European policy concerning the different energy storage systems and hydrogen production is explicitly discussed. The state of the art of the techno-economic features of the hydrogen production and storage is introduced. Using Matlab-Simulink for a power system of rated 70 kW generator, the excess produced hydrogen during high generation periods or low demand can be sold either directly to the grid owners or as filled hydrogen bottles. The affordable use of Hydrogen-based technologies for long term electricity storage is verified
Experimental evidence of thermal fluctuations on the X-ray absorption near-edge structure at the aluminum K-edge
After a review of temperature-dependent experimental x-ray absorption
near-edge structure (XANES) and related theoretical developments, we present
the Al K-edge XANES spectra of corundum and beryl for temperature ranging from
300K to 930K. These experimental results provide a first evidence of the role
of thermal fluctuation in XANES at the Al K-edge especially in the pre-edge
region. The study is carried out by polarized XANES measurements of single
crystals. For any orientation of the sample with respect to the x-ray beam, the
pre-edge peak grows and shifts to lower energy with temperature. In addition
temperature induces modifications in the position and intensities of the main
XANES features. First-principles DFT calculations are performed for both
compounds. They show that the pre-edge peak originates from forbidden 1s to 3s
transitions induced by vibrations. Three existing theoretical models are used
to take vibrations into account in the absorption cross section calculations:
i) an average of the XANES spectra over the thermal displacements of the
absorbing atom around its equilibrium position, ii) a method based on the crude
Born-Oppenheimer approximation where only the initial state is averaged over
thermal displacements, iii) a convolution of the spectra obtained for the atoms
at the equilibrium positions with an approximate phonon spectral function. The
theoretical spectra so obtained permit to qualitatively understand the origin
of the spectral modifications induced by temperature. However the correct
treatment of thermal fluctuation in XANES spectroscopy requires more
sophisticated theoretical tools
Assessing temperature effects on multipole contributions and angular dependence in core-level spectroscopies
This study aims at assessing the thermal nuclei motion effects on the multipole transition channels involved in two core-level spectroscopies, x-ray absorption spectroscopy (XAS) and x-ray Raman scattering (XRS). Temperature effects on the 1s -> s monopole, 1s -> p dipole, and 1s -> d quadrupole transitions are investigated using two reference systems for which we present original experimental data: alpha-Al2O3 at the Al K edge probed by XRS at room temperature and rutile TiO2 at the Ti K pre-edge probed by XAS at temperatures ranging from 6 to 700 K. Through the latter, this work enlightens the part of the pre-edge peak enhancement due to temperature in the K pre-edge region of 3d transition metal, which is known to be routinely used to determine the concentration, valence or symmetry of the probed element in a given sample. Nuclear thermal fluctuations are taken into account using a method based on density functional theory that consists in averaging spectra over atomic configurations, generated within the harmonic approximation and obeying quantum statistics at finite temperature. Since only a finite number of such configurations are used, the numerically averaged spectra generally lose the symmetry of the equilibrium crystal positions. In this paper, we demonstrate that the physical average has to be symmetric and propose a method to restore the physical angular dependence of the spectra. The approach is successfully applied to investigate the angular dependent XAS spectra in rutile as a function of temperature. The two systems under study allow to draw general conclusions regarding the effect of nuclear quantum fluctuations on the different transition channels available to both core-level spectroscopies.Peer reviewe
Influence of the 6^1S_0-6^3P_1 Resonance on Continuous Lyman-alpha Generation in Mercury
Continuous coherent radiation in the vacuum-ultraviolet at 122 nm
(Lyman-alpha) can be generated using sum-frequency mixing of three fundamental
laser beams in mercury vapour. One of the fundamental beams is at 254 nm
wavelength, which is close to the 6^1S_0-6^3P_1 resonance in mercury.
Experiments have been performed to investigate the effect of this one-photon
resonance on phasematching, absorption and the nonlinear yield. The efficiency
of continuous Lyman-alpha generation has been improved by a factor of 4.5.Comment: 8 pages, 7 figure
Risk-based inspection as a cost-effective strategy to reduce human exposure to cysticerci of Taenia saginata in low-prevalence settings
Taenia saginata cysticercus is the larval stage of the zoonotic parasite Taenia saginata, with a life-cycle involving both cattle and humans. The public health impact is considered low. The current surveillance system, based on post-mortem inspection of carcasses has low sensitivity and leads to considerable economic burden. Therefore, in the interests of public health and food production efficiency, this study aims to explore the potential of risk-based and cost-effective meat inspection activities for the detection and control of T. saginata cysticercus in low prevalence settings
X-ray Absorption Near-Edge Structure calculations with pseudopotentials. Application to K-edge in diamond and alpha-quartz
We present a reciprocal-space pseudopotential scheme for calculating X-ray
absorption near-edge structure (XANES) spectra. The scheme incorporates a
recursive method to compute absorption cross section as a continued fraction.
The continued fraction formulation of absorption is advantageous in that it
permits the treatment of core-hole interaction through large supercells
(hundreds of atoms). The method is compared with recently developed
Bethe-Salpeter approach. The method is applied to the carbon K-edge in diamond
and to the silicon and oxygen K-edges in alpha-quartz for which polarized XANES
spectra were measured. Core-hole effects are investigated by varying the size
of the supercell, thus leading to information similar to that obtained from
cluster size analysis usually performed within multiple scattering
calculations.Comment: 11 pages, 4 figure
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