Détermination du niveau de toxicité des sédiments de rivière par le test de bioluminescence bactérienne

A partir de références bibliographiques encore réduites, les auteurs ont mis au point un protocole expérimental d'évaluation de la toxicité des sédiments de rivière, après extraction au dichlorométhane et mesure de la toxicité par le lest de Bioluminescence Bactérienne.Ce protocole simple appliqué à quarante-trois prélèvements correspondant à des situations de pollution diversifiées, a permis d'établir et de proposer une typologie des sédiments en fonction de leur niveau de toxicité.Correspondant à une approche nouvelle (tests biologiques de toxicité sur sédiments), la méthodologie apparaît particulièrement intéressante pour la gestion patrimoniale des cours d'eau (réseaux de surveillance, mise en évidence de situations de pollutions), et devrait être intégrée dans les opérations de mesure de l'impact des pollutions toxiques sur les écosystèmes aquatiques.As toxic substances in river water are not easy to detect and to measure, sediments able to precipitate them have been userd, successfully, to quaintly metals and a limited number of organics. Actually, analytical determinations, very expansive, time consuming and never exhaustive, are not an adequate means for a general estimation of the presence of toxic organic substances.Another developing approach consists in determining effects not the substances themselves (contained in the sediments) but their toxic effects on biotests applied directly on all the sediments or on the extracts. This approach has been used by relatively few teams, principally in North-America and in The Netherlands, in limited areas, to evaluate the local impacts of industrial effluents on sea and-or river waters. On the contrary, the object of this work is to measure the interest of this kind of approach, at a large Water Basin, first to establish the toxic profiles of rivers with areas of pollution, and second to constitute a memorization, susceptible of being compared at regular intervals for an estimation of general depollution policies .Based on data taken from the literature, an organic extraction of sediments with dichloromethane as solvent (without pretreatment) and photobacterium phosphoreum luminescence inhibition test were chosen. Actually, according to the literature, dichloromethane is the must convenient solvant and toxic activities of extracts are well correlated with organic toxic contents in the few cases where, exceptionally, the two approaches have been carried out simultaneously. Similarly, the bacterial luminescence test, Microtox (commercial name), quick and inexpensive, is well correlated with results from other biotests when, occasionally, both were utilised. Moreover, Microtox was well tested in the Agence laboratory.Different conditions of extraction were carefully tested, before the adoption of the definite protocol : whole sediments (10-g) are mixed (slow agitation in rolling flasks) for 6 hours with dichloromethane (100-mL) and sodium sulphate (50 g). Dichloromethane is then eliminated and the remaining solid materials are washed twice with fresh dichloromethane (2 x 20 mi). Dichloromethane extract and washings are collected, dried over sodium sulphate and concentrated (below 40 °C) to 1 mL, further adjusted to 3 mL. A portion measured accurately of this concentrate is added to ethanol and concentrated to remove dichloromethane.Bacterial bioluminescence tests, in duplicate, are performed on ethanol extracts, diluted (1 %) in salified (sodium chloride 2 %) distilled water. Estimates of the EC 50 (concentration causing a 50 % reduction in bioluminescence) obtained using linear regression analysis are converted into Toxic Units and referred to the net organic weight, measured separately, at 550 °C. This expression of results is particularly relevant when sediments with different organic net weights are compared.The protocol has been applied to sediments collected at 43 sites in the principal rivers of Rhône Méditerranée Corse Basin and in special distant from significant domestic and industrial activities.The toxic amplitude observed (ratio of l/200 between lowest and highest toxic units obtained with the panel) and the good reproductibility of the whole process (10 % to 25 %) were consistent with a trial subdivision in 5 classes as follow :Class 1 : Out of pollution - Class 2 : Moderate toxicity - Class 3 : Important toxicity - Class 4 : Very important toxicity - Class 5 : Exceptional toxicity.The relevancy of this classification was estimated when sediments were classed according to their toxic content. The classification proves to be correct in must cases. Exceptionally toxic sediments were collected in sites affected by large industries and agglomerations as (CHASSE and SAINT-VALLIER) on River Rhone near Lyon and important chemical plants, or GIVORS, on the small River GIER, markedly affected by many various industries. On the contrary sediments of moderate toxicity corresponded to sites relatively far from sources of important pollutions, e.g., ARLES on the River RHONE near the sea and a number of sites on the River SAONE. Moreover, when repeated sampling was performed on the same sites, the results were consistent, belonging to the same class of toxicity.The general object of this work was not to determine a definite classification of sediment toxicities, but to assess the relevancy of this approach. In our opinion, it was proved that bioassays on sediment extracts, and specially the bacterial bioluminescence assay, are a valuable tool, before the material impossibility to determine the toxic substances content. Moreover this approach could be used at the Basin. More investigations are necessary to define more accurately the number and level of toxic classes and e.g. to establish correlations with perturbations of benthic communities living in the sediments. It is also a contribution to the general knowledge and action based on biotests performed on effluents and different compartments of rivers

Laser offset welding of AZ31B magnesium alloy to 316 stainless steel

In this paper, the feasibility of using a fiber laser to perform a dissimilar metal joining was explored. AZ31B magnesium and 316 stainless steel were autogenously joined in butt configuration. The weldability between different materials is often compromised by a large difference in thermal properties and poor metallurgical compatibility. Thus, the beam was focused onto the top surface of the magnesium plate, at a certain distance from the interfaces (offset), and without using any interlayer or groove preparation. Such a method was called laser offset welding (LOW). Results proved a very good capability. The ultimate tensile strength exceeded the value of 100 MPa, since a resistant and thin layer of hard intermetallic compounds is formed within the fusion zone. The rupture was observed within the magnesium side, far from the centerline. The metallurgy of fusion zone indicated the effectiveness of phases coalescence, without mixing at liquid states. LOW was demonstrated to be a promising technique to join dissimilar metal welds, being capable to produce an effective bonding with good tensile strength

Towards a numerical simulation of direct manufacturing of thermoplastic parts by powder laser sintering COMPLAS XI

Direct manufacturing technology using Selective Laser Sintering (SLS) on thermoplastic powders allows obtaining final parts in a short time, with classical polymer density and a high flexibility of shape and evolution of parts. The physical base of this process is the coalescence of grains, which initiates the densification of powder during SLS. This study presents a 2D C-NEM simulation of the whole process. We firstly focus on the chosen method and its advantages. We present the simulation details and validate the modeling through a 2D infinite cylinders coalescence simulation. The mesh of the grain interface is continuously adapted to the local curvature to better capture the coalescence phenomenon. We are able to simulate the sintering of twelve particles laying on a support within some hours

Splines and Wavelets on Geophysically Relevant Manifolds

Analysis on the unit sphere $\mathbb{S}^{2}$ found many applications in seismology, weather prediction, astrophysics, signal analysis, crystallography, computer vision, computerized tomography, neuroscience, and statistics. In the last two decades, the importance of these and other applications triggered the development of various tools such as splines and wavelet bases suitable for the unit spheres $\mathbb{S}^{2}$, $\>\>\mathbb{S}^{3}$ and the rotation group $SO(3)$. Present paper is a summary of some of results of the author and his collaborators on generalized (average) variational splines and localized frames (wavelets) on compact Riemannian manifolds. The results are illustrated by applications to Radon-type transforms on $\mathbb{S}^{d}$ and $SO(3)$.Comment: The final publication is available at http://www.springerlink.co

Shapes of leading tunnelling trajectories for single-electron molecular ionization

Based on the geometrical approach to tunnelling by P.D. Hislop and I.M. Sigal [Memoir. AMS 78, No. 399 (1989)], we introduce the concept of a leading tunnelling trajectory. It is then proven that leading tunnelling trajectories for single-active-electron models of molecular tunnelling ionization (i.e., theories where a molecular potential is modelled by a single-electron multi-centre potential) are linear in the case of short range interactions and "almost" linear in the case of long range interactions. The results are presented on both the formal and physically intuitive levels. Physical implications of the obtained results are discussed.Comment: 14 pages, 5 figure

Feasibility of trial procedures for a randomised controlled trial of a community based group exercise intervention for falls prevention for visually impaired older people: the VIOLET study

Background Visually impaired older people (VIOP) have a higher risk of falling than their sighted peers, and are likely to avoid physical activity. The aim was to adapt the existing Falls Management Exercise (FaME) programme for VIOP, delivered in the community, and to investigate the feasibility of conducting a definitive randomised controlled trial (RCT) of this adapted intervention. Methods Two-centre randomised mixed methods pilot trial and economic evaluation of the adapted group-based FaME programme for VIOP versus usual care. A one hour exercise programme ran weekly over 12 weeks at the study sites (Newcastle and Glasgow), delivered by third sector (voluntary and community) organisations. Participants were advised to exercise at home for an additional two hours over the week. Those randomised to the usual activities group received no intervention. Outcome measures were completed at baseline, 12 and 24 weeks. The potential primary outcome was the Short Form Falls Efficacy Scale – International (SFES-I). Participants’ adherence was assessed by reviewing attendance records and self-reported compliance to the home exercises. Adherence with the course content (fidelity) by instructors was assessed by a researcher. Adverse events were collected in a weekly phone call. Results Eighteen participants, drawn from community-living VIOP were screened; 68 met the inclusion criteria; 64 participants were randomised with 33 allocated to the intervention and 31 to the usual activities arm. 94% of participants provided data at the 12 week visit and 92% at 24 weeks. Adherence was high. The intervention was found to be safe with 76% attending nine or more classes. Median time for home exercise was 50 min per week. There was little or no evidence that fear of falling, balance and falls risk, physical activity, emotional, attitudinal or quality of life outcomes differed between trial arms at follow-up. Conclusions The intervention, FaME, was implemented successfully for VIOP and all progression criteria for a main trial were met. The lack of difference between groups on fear of falling was unsurprising given it was a pilot study but there may have been other contributory factors including suboptimal exercise dose and apparent low risk of falls in participants. These issues need addressing for a future trial

Active animal health surveillance in European Union Member States: gaps and opportunities

Animal health surveillance enables the detection and control of animal diseases including zoonoses. Under the EU-FP7 project RISKSUR, a survey was conducted in 11 EU Member States and Switzerland to describe active surveillance components in 2011 managed by the public or private sector and identify gaps and opportunities. Information was collected about hazard, target population, geographical focus, legal obligation, management, surveillance design, risk-based sampling, and multi-hazard surveillance. Two countries were excluded due to incompleteness of data. Most of the 664 components targeted cattle (26·7%), pigs (17·5%) or poultry (16·0%). The most common surveillance objectives were demonstrating freedom from disease (43·8%) and case detection (26·8%). Over half of components applied risk-based sampling (57·1%), but mainly focused on a single population stratum (targeted risk-based) rather than differentiating between risk levels of different strata (stratified risk-based). About a third of components were multi-hazard (37·3%). Both risk-based sampling and multi-hazard surveillance were used more frequently in privately funded components. The study identified several gaps (e.g. lack of systematic documentation, inconsistent application of terminology) and opportunities (e.g. stratified risk-based sampling). The greater flexibility provided by the new EU Animal Health Law means that systematic evaluation of surveillance alternatives will be required to optimize cost-effectiveness