2,238 research outputs found

    Données sur les transferts du 137Cs et du 60Co dans un écosystème fluvial : le Rhône

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    L'étude radioécologique du Rhône permet d'évaluer qualitativement et quantitativement les radionucléides présents dans le fleuve. Les études menées in situ posent des questions concernant les modalités de transfert des radionucléides. Dans ce travail des expériences sont mises au point, afin d'analyser les mécanismes de bioconcentration dans les écosystèmes aquatiques. Pour le césium-137 les échanges entre l'eau, le sédiment et divers organismes aquatiques ont permis d'élaborer un modèle mathématique que l'on peut confronter aux valeurs mesurées sur le terrain. En ce qui concerne le Cobalt-60 les auteurs décrivent des expériences permettant l'évaluation de la contribution relative de l'eau et de la nourriture dans l'accumulation du radionucléide par un poisson.The radioecology of the Rhone Basin has been studied for the last 15 years. This has been an opportunity to make a quantitative and qualitative evaluation of radionuclides as a function of their different sources. Special attention is given to 137Cs (present both in fallout and liquid wastes) and 60Co, which characterize the liquid wastes of pressurised water reactors. In order to assess the transfer and bioconcentration of these two radionuclides in freshwater ecosystems, several experimental studies were undertaken.The 137Cs transfer studies were carried out with a 5-component experimental ecosystem and the data were included in a mathematical model. For 60Co, the experimental study concerns the relative contribution of water and food in the accumulation of the radionuclide by Cyprinus carpio.Water, sediment, plants and fishes were taken from 60 sampling stations set up along the river (figure 1). Water was filtrated, then percolated on resin columns. Sediment, plants and fishes were dried and burnt to ashes in an oven at 500° C. Radioactivity was measured by gamma spectrometry and radiochemistry.137Cs experimental transfers were studied between water, sediment, midge larvae, daphnid and carp. These components were taken in pairs in order to estimate the radionuclide transfer from one to the other. Thus ten experiments were carried out (figure 2). In order to study the relative importance of food and water as 60Co sources for the carp, an experiment was carried out simultaneously on three homogeneous groups of ten juvenile fishes. The individuals of the first group were maintained in separate aquaria and offered 45 daily rations of labelled food over a 63-day period. Bach carp of the other two groups was placed in a compartment of a large tank with contaminated water. One group was fed with radioactive food, the other with non-radioactive food (table 1).Natural radioactivity remained steady all along the river. It ranged around 1 Bq.l-1 in water, 2250 Bq.kg-1 DW in sediment, 1700 Bq.kg-1 DW in aquatic plants, 110 Bq.kg-1 WW in fish. The fallout impact was characterized by 137Cs presence. PWR liquid wastes contained mainly, 58Co, 60Co, 134 Cs, 137Cs. The Chernobyl fallout gave an increase of Cs and the presence of 103Ru and 106RU+Rh specially during May and June 1986 which later decreased (tables 2, 3 and 4).137Cs transfer between water and sediment was very fast and important. Less than 2 % of the radionuclide was released from sediment into a non-radioactive water. During the transfer from water to chironomids the larvae radioactivity increased steadily (figure 3). Conversely, the transfer from the sediment to larvae did not seem to depend on the contact time. The transfer from water to carp was regular without any steady state during the 63 days of the experiment (figure 3). Then the fish concentration factor was less than 5. For 42 days, the transfer factor from sediment to carp was 3.6.10-3. The retention factor from food to carp was 0.03 when fishes were fed with daphnids and 0.13 with chironomids. An experiment showed that the various ways of 137Cs transfer could have an added impact. Thus the carp radioactivity was the sum of the separate transfers. Water was responsible for 4 % of the fish 137 Cs concentration, sediment for 45 % and chironomids for 51 %.It is possible to include the different kinetic equations in a mathematical model. If the radioactivity of one of the components is known, the nuclide concentration can be computed in others, as a relation of the contact time, the quantity and quality of ingested food, etc... This model gives a concentration factor for juvenile carp of 1000 in 180 days and 500 for 3-year old fish. Considering the field conditions (e.g. seasonal nutritive cycles) the computed concentration factor in fish was between 200 and 350. For a 1 mBq.l-1 137Cs concentration in water, the model gave a concentration of 0.2 to 0.35 Bq.kg-1 WW in carp, which was the 137Cs radioactivity level measured in the Rhone fish before the Chernobyl accident.During the 60Co accumulation phase, the mean weight of the fish in the three groups increased exponentially and the resultant relative weight gain was 52-59 % after 63 days (table 5).The 60Co accumulation kinetics showed that the steady state should be reached after 165 days for fish exposed to 60Co in food, 92 days for fish exposed to radiocobalt in water and 120 days for fish exposed to 60Co in both sources (figure 4). According to the 60Co concentration in the fish in the three treated groups, the accumulation from water accounted for 75 % of the total radioactivity and the accumulation of the radionuclide from both water and food was in addition.Depuration of 60Co from carp was a relatively intensive process reflecting a high Co turnover. Biological half-lives for loss from the long-lived compartment ranged from 35d in fish previously contaminated by food, to 87d in fish previously contaminated by food, to 87d in fish previously contaminated by water (figure 5).137Cs and 60Co are the most concentrated radionuclides in liquid wastes of the pressurised water reactors, and they are often measured in the aquatic ecosystem components. Though it accounts for the highest fraction of total radioactivity in the liquid wastes, 60Co cobalt is not the most concentrated radionuclide in fish. Experimental studies show that it is primarily transferred from the water so it is logical that its concentration in fish remains at a low level. Conversely the 137Cs has a low concentration in water but as it is transferred simultaneously from water, sediment and food, its concentration in fish is still important. Moreover its 30 years half-life means that the cesium contamination of fish is a long and important process, all the more so as the source terms can add their own effects during time and space

    Evidence accumulation in the magnitude system

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    Perceptual interferences in the estimation of quantities (time, space and numbers) have been interpreted as evidence for a common magnitude system. However, if duration estimation has appears sensitive to spatial and numerical interferences, space and number estimation tend to be resilient to temporal manipulations. These observations question the relative contribution of each quantity in the elaboration of a representation in a common mental metric. Here, we elaborated a task in which perceptual evidence accumulated over time for all tested quantities (space, time and number) in order to match the natural requirement for building a duration percept. For this, we used a bisection task. Experimental trials consisted of dynamic dots of different sizes appearing progressively on the screen. Participants were asked to judge the duration, the cumulative surface or the number of dots in the display while the two non-target dimensions varied independently. In a prospective experiment, participants were informed before the trial which dimension was the target; in a retrospective experiment, participants had to attend to all dimensions and were informed only after a given trial which dimension was the target. Surprisingly, we found that duration was resilient to spatial and numerical interferences whereas space and number estimation were affected by time. Specifically, and counter-intuitively, results revealed that longer durations lead to smaller number and space estimates whether participants knew before (prospectively) or after (retrospectively) a given trial which quantity they had to estimate. Altogether, our results support a magnitude system in which perceptual evidence for time, space and numbers integrate following Bayesian cue-combination rules

    The Witness-Aimed First Account (WAFA): a new technique for interviewing autistic witnesses and victims

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    Autistic people experience social communication difficulties alongside specific memory difficulties that can impact their ability to recall episodic events. Police interviewing techniques do not take account of these differences, and so are often ineffective. Here we introduce a novel Witness-Aimed First Account (WAFA) interview technique, designed to better support autistic witnesses by diminishing socio-cognitive and executive demands through encouraging participants to generate and direct their own discrete, parameter-bound event topics, before freely recalling information within each parameter-bound topic. Since witnessed events are rarely cohesive stories with a logical chain of events, we also explored witnesses’ recall when the narrative structure of the to-be-remembered event was lost. Thirty-three autistic and 30 typically developing (TD) participants were interviewed about their memory for two videos depicting criminal events. Clip segments of one video were ‘scrambled’, disrupting the event’s narrative structure; the other video was watched intact. Although both autistic and TD witnesses recalled fewer details with less accuracy from the scrambled video, WAFA interviews resulted in more detailed and accurate recall from autistic and TD witnesses, for both scrambled and unscrambled videos. The WAFA technique may be a useful tool to improve autistic and TD witnesses’ accounts within a legally appropriate, non-leading framework

    Behavioural and oceanographic isolation of an island‑based jellyfish (Copula sivickisi, Class Cubozoa) population

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    Cubozoan jellyfish are classified as plankton despite the strong swimming and orientation abilities of cubomedusae. How these capabilities could affect cubozoan population structures is poorly understood. Medusae of the cubozoan Copula sivickisi can uniquely attach to surfaces with the sticky pads on their bells. Biophysical modelling was used to investigate the spatial scales of connectivity in a C. sivickisi population. When the medusae were active at night they could maintain their observed distribution on fringing reef if they attached to the reef when the current speed exceeded a moderate threshold. This behaviour facilitated the isolation of a C. sivickisi population on reefs fringing Magnetic Island, Queensland, Australia. Within this distribution, there was considerable within bay retention and medusae rarely travelled > 3 km. The few (< 0.1%) medusae lost from the island habitat were largely advected into open water and away from the mainland coast which lies 8 km from the island. Given that successful emigration is unlikely, the island population probably represents a stock that is ecologically distinct from any mainland populations. The cosmopolitan distribution of C. sivickisi could contain incipient or cryptic species given the small scales of connectivity demonstrated here

    Fingermark age determinations: Legal considerations, review of the literature and practical propositions.

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    The question of the age of fingermarks is often raised in investigations and trials when suspects admit that they have left their fingermarks at a crime scene but allege that the contact occurred at a different time than the crime and for legal reasons. In the first part of this review article, examples from American appellate court cases will be used to demonstrate that there is a lack of consensus among American courts regarding the admissibility and weight of testimony from expert witnesses who provide opinions about the age of fingermarks. Of course, these issues are not only encountered in America but have also been reported elsewhere, for example in Europe. The disparity in the way fingermark dating cases were managed in these examples is probably due to the fact that no methodology has been validated and accepted by the forensic science community so far. The second part of this review article summarizes the studies reported on fingermark dating in the literature and highlights the fact that most proposed methodologies still suffer from limitations preventing their use in practice. Nevertheless, several approaches based on the evolution of aging parameters detected in fingermark residue over time appear to show promise for the fingermark dating field. Based on these approaches, the definition of a formal methodological framework for fingermark dating cases is proposed in order to produce relevant temporal information. This framework identifies which type of information could and should be obtained about fingermark aging and what developments are still required to scientifically address dating issues

    M. Kontsevich's graph complex and the Grothendieck-Teichmueller Lie algebra

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    We show that the zeroth cohomology of M. Kontsevich's graph complex is isomorphic to the Grothendieck-Teichmueller Lie algebra grt_1. The map is explicitly described. This result has applications to deformation quantization and Duflo theory. We also compute the homotopy derivations of the Gerstenhaber operad. They are parameterized by grt_1, up to one class (or two, depending on the definitions). More generally, the homotopy derivations of the (non-unital) E_n operads may be expressed through the cohomology of a suitable graph complex. Our methods also give a second proof of a result of H. Furusho, stating that the pentagon equation for grt_1-elements implies the hexagon equation
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