Mémoire et archive : définitions de la culture visuelle IV

Voici un livre qu’il faudrait lire à l’envers, de Wajcman à Arasse, en commençant par la fin, par sa dernière phrase : » Ce qui ne peut se dire du passé, ce dont on ne peut se souvenir, l’artiste le montre. C’est sa tâche ». Gérard Wajcman conclut ainsi un texte qui rend un vibrant hommage à Jochen Gerz, le seul artiste qui aurait su élever un monument à la shoah parce que « ses œuvres démontrent en quoi seul l’art peut accomplir cette chose essentielle au sujet de la shoah, qui est de transm..

Development and characterization of composite chitosan/active carbon hydrogels for a medical application

International audienceComposite chitosan/active carbon (AC) hydrogels were elaborated by a novel route, consisting in exposing the chitosan solution to ammonia vapors. This vapor-induced gelation method was compared with the conventional elaboration process, a direct immersion of the chitosan solution in liquid ammonia. The hydrogels were characterized to evaluate their potential application as wound-dressings, mostly regarding their morphology, mechanical properties, swelling behavior, and sorption capacities for malodorous compounds emitted from wounds as diethylamine (DEA). The influence of elaboration route, chitosan concentration, and AC incorporation was studied. The results show that freeze-dried hydrogels have a porous asymmetric structure dependent on the chitosan concentration and which promotes exudates drainage. The nanostructure of the parent hydrogel is semi-crystalline and slightly dependent on the gelation conditions. It confers on hydrogel an acceptable mechanical behavior (compressive modulus up to 1.08 center dot 105 Pa). Hydrogels including AC display enhanced sorption kinetics for DEA, with sorption capacities up to 49 mg g1

Preparation of Composite Hydrogels for Medical Applications: Experimental Study and Modeling of Mass Transfers

International audienceThe aim of this work is to prepare wound dressing hydrogels permitting (i) tocure chronicle pathologies; (ii) to remove unsuitable odors coming from healing.Thus, chitosan, a natural polymer with biological properties, and activated carbon(AC), a well-known adsorbent, are mixed within a composite hydrogel. To get asuitable porous structure for healing, the vapor induced phase separation process(VIPS) is used. It permits to slow down mass transfers kinetics compared to otherelaboration processes such as the wet process. Hence, a better control of the finalporous matrix is reached throughout the elaboration process.In this work, the mass transfers occurring through the elaboration of the com-posites were studied thanks to gravimetric measurements carried out during theVIPS process. Results showed there were two main steps in the gelation process.A weight intake, due to an ammonia flux allowing the gelation to happen, wasfollowed by a weight loss, mainly controlled by a water outtake. This second partcould be compared to a slow drying in smooth conditions. Gelation with a colorindicator was also performed, which provided complementary experimental infor-mation on mass transfers barrier.A modeling of mass transfers mechanisms occurring during the gel elaborationis presented to get an overview of limiting phenomena leading to the final com-posite structures. It involves a coupling between chemical reactions, external masstransfers and internal diffusion within the polymeric matrix. Results show that in-ternal diffusion is the main barrier to gelation.To qualify the gel structure, drying kinetics were compared on the elaborated gels.Whatever the gel, the drying kinetics were globally the same and could be dividedinto three steps. Considering the process used and this result, it was believedthat the matrixes prepared were homogeneous and rather symmetric. They couldconstitute the first layer of wound dressings

On the adsorption mechanisms of diethylamine by medically-certified activated carbons: Investigation of critical parameters controlling sorption properties

International audienceThis study investigates the adsorption mechanisms and reaction pathways involved in the adsorption ofdiethylamine (DEA) by medically-certified activated carbons (ACs). DEA is used as a model of aminessecreted during healing process of chronic wounds. DEA adsorption kinetics/isotherms were performedin liquid phase. Based on a preliminary assumption of a sorption favoured by surface chemical functions,it was found that the sorption kinetics followed accurately a pseudo-second order model. In addition, ouranalysis revealed that surface diffusion strongly influenced DEA sorption. If Langmuir and Redlich–Peterson models provided the most accurate fit of the adsorption isotherms, the Freundlich isothermgave a fair representation of experimental data as well. L-type isotherms supported the occurrence ofstrong surface interactions. Also, a negative correlation was drawn between the micropore volumepercentage and adsorption capacity at equilibrium. Further, acid/base reactions were believed to occur,along with the establishment of numerous H-bonds between the sorbent and DEA. This study is ended bya discussion of the effect of AC entrapment within a polymeric matrix on the adsorption properties. IfDEA removal was still observed, a serious decrease of sorption properties was measured. We concludedthat AC must be treated during the activation process in order to possess a high BET surface, an importantmesopore/macropore content and a high content of acidic surface functions, in order to balance thedecreasing of adsorption properties owed to its entrapment

The database of the PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) project

The PREDICTS project—Projecting Responses of Ecological Diversity In Changing Terrestrial Systems (www.predicts.org.uk)—has collated from published studies a large, reasonably representative database of comparable samples of biodiversity from multiple sites that differ in the nature or intensity of human impacts relating to land use. We have used this evidence base to develop global and regional statistical models of how local biodiversity responds to these measures. We describe and make freely available this 2016 release of the database, containing more than 3.2 million records sampled at over 26,000 locations and representing over 47,000 species. We outline how the database can help in answering a range of questions in ecology and conservation biology. To our knowledge, this is the largest and most geographically and taxonomically representative database of spatial comparisons of biodiversity that has been collated to date; it will be useful to researchers and international efforts wishing to model and understand the global status of biodiversity