Images du quotidien et patrimoines sociaux : la mise en images d’archives

L’objet du chapitre est de faire émerger des éléments de convergence quant aux étapes de la mise en images d’archives. D’abord, la conservation. Que l’on se situe dans une dialectique du passé à travers des images anciennes ou que l’on ait affaire au désir de transmission d’images récentes, l’impératif de la pérennisation joue et l’injonction des archives est à l’œuvre. Ensuite, la monstration. Que l’image originelle soit intégrée au décor d’un restaurant ou partagée dans une communauté virtuelle, il n’est guère d’image d’archives que vue et offerte au regard. Le statut d’image d’archives est conféré par un regard extérieur, en dehors du cercle de production et de diffusion initial – la famille par exemple. Enfin, la modification. L’image d’archives ne se conçoit que médiatisée, insérée dans un discours et presque toujours modifiée : découpée, agrandie, teintée, détournée de son objet initial, décryptée, c’est véritablement une autre image qui est produite à partir de l’image primaire. L\u27image créée et mise en scène joue sur des codes convenus, dans une allusion explicite ou plus discrète, à ceux des patrimoines savants. Les procédés de médiation co-construisent l\u27image d\u27archives parce qu\u27ils la mettent en exposition et ainsi déclenchent son accréditation comme objet patrimonial. Le statut d\u27image d\u27archives ne serait donc que transitoire, valable uniquement au moment et dans l’instant de son usage, contrairement à celui de document d’archives ou d’image archivée, défini par un lieu de conservation fixe et des modalités d’accès stables

Images archivées, images d’archives : fortunes terminologiques

On ne peut manquer d’être frappé de la quasi-totale absence dans l’institution archivistique française et dans les milieux professionnels qui l’animent, du moins jusqu’à une date récente, non seulement de l’expression « image d’archives » mais encore du mot même « image ». Cette constatation constitue le point de départ d’une enquête terminologique et lexicologique : d’où vient cette expression « images d’archives » ? Quelles sont les étapes et les raisons de sa diffusion 

Natural Nuclear Reactor Oklo and Variation of Fundamental Constants Part 1: Computation of Neutronics of Fresh Core

Using modern methods of reactor physics we have performed full-scale calculations of the natural reactor Oklo. For reliability we have used recent version of two Monte Carlo codes: Russian code MCU REA and world wide known code MCNP (USA). Both codes produce similar results. We have constructed a computer model of the reactor Oklo zone RZ2 which takes into account all details of design and composition. The calculations were performed for three fresh cores with different uranium contents. Multiplication factors, reactivities and neutron fluxes were calculated. We have estimated also the temperature and void effects for the fresh core. As would be expected, we have found for the fresh core a significant difference between reactor and Maxwell spectra, which was used before for averaging cross sections in the Oklo reactor. The averaged cross section of Sm-149 and its dependence on the shift of resonance position (due to variation of fundamental constants) are significantly different from previous results. Contrary to results of some previous papers we find no evidence for the change of the fine structure constant in the past and obtain new, most accurate limits on its variation with time: -4 10^{-17}year^{-1} < d alpha/dt/alpha < 3 10^{-17} year^{-1} A further improvement in the accuracy of the limits can be achieved by taking account of the core burnup. These calculations are in progress.Comment: 25 pages, 14 figures, 12 tables, minor corrections, typos correcte

Porewater methane transport within the gas vesicles of diurnally migrating Chaoborus spp.: An energetic advantage

We show that diurnally migrating Chaoborus sp. (phantom midge larvae), which can be highly abundant in eutrophic lakes with anoxic bottom, utilises sediment methane to inflate their tracheal sacs, which provides positive buoyancy to aid vertical migration. This process also effectively transports sediment methane bypassing oxidation to the upper water column, adding to the total methane outflux to the atmosphere

Effects of agricultural land use on fluvial carbon dioxide, methane and nitrous oxide concentrations in a large European river, the Meuse (Belgium)

peer reviewedWe report a data-set of CO2, CH4, and N2O concentrations in the surface waters of the Meuse river network in Belgium, obtained during four surveys covering 50 stations (summer 2013 and late winter 2013, 2014 and 2015), from yearly cycles in four rivers of variable size and catchment land cover, and from 111 groundwater samples. Surface waters of the Meuse river network were over-saturated in CO2, CH4, N2O with respect to atmospheric equilibrium, acting as sources of these greenhouse gases to the atmosphere, although the dissolved gases also showed marked seasonal and spatial variations. Seasonal variations were related to changes in freshwater discharge following the hydrological cycle, with highest concentrations of CO2, CH4, N2O during low water owing to a longer water residence time and lower currents (i.e. lower gas transfer velocities), both contributing to the accumulation of gases in the water column, combined with higher temperatures favourable to microbial processes. Inter-annual differences of discharge also led to differences in CH4 and N2O that were higher in years with prolonged low water periods. Spatial variations were mostly due to differences in land cover over the catchments, with systems dominated by agriculture (croplands and pastures) having higher CO2, CH4, N2O levels than forested systems. This seemed to be related to higher levels of dissolved and particulate organic matter, as well as dissolved inorganic nitrogen in agriculture dominated systems compared to forested ones. Groundwater had very low CH4 concentrations in the shallow and unconfined aquifers (mostly fractured limestones) of the Meuse basin, hence, should not contribute significantly to the high CH4 levels in surface riverine waters. Owing to high dissolved concentrations, groundwater could potentially transfer important quantities of CO2 and N2O to surface waters of the Meuse basin, although this hypothesis remains to be tested

Ir. J. Maeck

Vibration monitoring of civil engineering structures has gained a lot of interest over the past few years, due to the relative ease of instrumentation and the development of new powerful system identification techniques. The damage assessment step consists of relating the dynamic characteristics to a damage pattern of the structure. The presented technique makes use of the calculation of modal bending moments and curvatures to derive the bending stiffness at each location. The basic assumption is that damage can be directly related to a decrease of stiffness in the structure. Eigenfrequencies are sensitive damage indicators. Modal curvatures seem to be more sensitive to local damage than the modal displacements. The technique is validated on a reinforced concrete beam, which is gradually damaged and is instrumented with accelerometers, displacement transducers and strain gauges

Evaluation of verification methods for input-accountability measurements

As part of TASTEX related programs two independent methods have been evaluated for the purpose of providing verification of the amount of Pu charged to the head-end of a nuclear fuel processing plant. The first is the Pu/U (gravimetric method), TASTEX Task-L, and the second is the Tracer Method, designated Task-M. Summaries of the basic technology, results of various studies under actual plant conditions, future requirements, are given for each of the Tasks