Sur quels modèles théoriques une approche communicationnelle en sciences sociales peut-elle s'appuyer?

How to theorize communication in social sciences? This text has two goals. First, to rely on the work of Louis Quéré, revealing the strengths and weaknesses of the two dominant models of two dominant models: an epistemological model enrolling the theory of information and cybernetics in an instrumental aim; a political model that aims at inter-understanding at the service of self-determination of the citizens in the elaboration of norms that govern them. Moreover, we wish to add to this review, two models which go beyond the limits of the first two approaches: a praxeological model that relies on praxis as an organizing activity of shared perspectives; a model of incommunication that reverses the situation and makes the impossibility of achieving intercomprehension the norm

Dynamic aspects of cerium dioxide sintering: HT-ESEM study of grain growth and pore elimination

International audienceSintering of CeO2 is studied in situ by high temperature scanning environmental microscopy (HT-ESEM) at T = 1400 °C. The morphological modifications of a single grains population are recorded for 6 h. Kinetic parameters are extracted from image series. The local grain growth determined from the single population studied in situ is compared to the general grain growth obtained by classical ex situ technique. Using HT-ESEM for sintering study is validated. The grain boundary velocities range between 0 and 5 μm h−1, with a mean value of about 1 μm h−1. The migration of the intragranular surface pores is described. Their velocities range between 0.4 and 1.2 μm h−1 and depend on pore diameters: the smaller the pore, the faster the pore velocity. The time required to fill a pore that arises at the sample surface is determined as a function of pore diameter. The time for pore elimination dependence with the pore diameters is also established

From thorium phosphate hydrogenphosphate hydrate to β\beta-thorium phosphate diphosphate: Structural evolution to a radwaste storage ceramic

$\beta$-Thorium phosphate diphosphate ($\beta$-TPD), considered as a very promising radwaste storage material, was obtained from thorium phosphate hydrogenphosphate hydrate (TPHPH) precursor through dehydration and hydrogen phosphate condensation. The structures of TPHPH, intermediate $\alpha$-thorium phosphate diphosphate ($\alpha$-TPD) and its hydrate ($\alpha$-TPDH) have been resolved ab initio by Rietveld analysis of their synchrotron diffraction patterns. All were found orthorhombic (space group Cmcm) and similarly composed of [ThPO$_4$]$_4^{4+}$ slabs alternating with disordered layers hosting either [HPO$_4$·H$_2$O]$_2^{4-}$ (TPHPH), [P$_2$O$_7$·2H$_2$O]$^{4-} ($\alpha$-TPDH), or [P$_2O_7$]$^{4-}$($\alpha$-TPD), unlike the 3D structure of$\beta$-TPD. The diphosphate groups of$\alpha$-TPD and$\alpha$-TPDH are strongly bent. The irreversible transition to the final$\beta$-TPD consists in a shearing of the slabs and a reduction of the interslabs cavities that explains the stability of this high-temperature form

Solid-State Synthesis of Monazite-type Compounds Containing Tetravalent Elements

International audienceOn the basis of optimized grinding/heating cycles developed for several phosphate-based ceramics, the preparation of brabantite and then monazite/brabantite solid solutions loaded with tetravalent thorium, uranium, and cerium (as a plutonium surrogate) was examined versus the heating temperature. The chemical reactions and transformations occurring when heating the initial mixtures of AnO2/CeO2, CaHPO4·2H2O (or CaO), and NH4H2PO4 were identified through X-ray diffraction (XRD) and thermogravimetric/differential thermal analysis experiments. The incorporation of thorium, which presents only one stabilized oxidation state, occurs at 1100 °C. At this temperature, all the thorium−brabantite samples appear to be pure and single phase as suggested by XRD, electron probe microanalyses, and μ-Raman spectroscopy. By the same method, tetravalent uranium can be also stabilized in uranium−brabantite, i.e., Ca0.5U0.5PO4, after heating at 1200 °C. Both brabantites, Ca0.5Th0.5PO4 and Ca0.5U0.5PO4, begin to decompose when increasing the temperature to 1400 and 1300 °C, respectively, leading to a mixture of CaO and AnO2 by the volatilization of P4O10. In contrast to the cases of thorium and uranium, cerium(IV) is not stabilized during the heating treatment at high temperature. Indeed, the formation of Ca0.5Ce0.5PO4 appears impossible, due to the partial reduction of cerium(IV) into cerium(III) above 840 °C. Consequently, the systems always appear polyphase, with compositions of CeIII1-2xCeIVxCaxPO4 and Ca2P2O7. The same conclusion can be also given when discussing the incorporation of cerium(IV) into La1-2xCeIIIx-yCeIVyCay(PO4)1-x+y. This incomplete incorporation of cerium(IV) confirms the results obtained when trying to stabilize tetravalent plutonium in Ca0.5PuIV0.5PO4 samples

Thermodynamics and Stability of Rhabdophanes, Hydrated Rare Earth Phosphates REPO4 · n H2O

Rare earth phosphates comprise a large family of compounds proposed as possible nuclear waste disposal forms. We report structural and thermodynamic properties of a series of rare earth rhabdophanes and monazites. The water content of the rhabdophanes, including both adsorbed and structural water, decreases linearly with increase in ionic radius of the rare earth. The energetics of the transformation of rhabdophane to monazite plus water and the enthalpy of formation of rhabdophane from the constituent oxides was determined by high temperature drop solution calorimetry. The former varies linearly with the ionic radius of the lanthanide, except for cerium. By combining the enthalpy of formation determined by high temperature drop solution calorimetry and the free energy of formation determined previously by solubility experiments, a complete set of thermodynamic data was derived for the rhabdophanes. They are thermodynamically metastable with respect to the corresponding monazites plus water at all temperatures under ambient pressure conditions. This conclusion strengthens the case for monazites being an excellent nuclear waste form

TFK1, a basal body transition fibre protein that is essential for cytokinesis in Trypanosoma brucei

In Trypanosoma brucei, transition fibres (TFs) form a nine-bladed pattern-like structure connecting the base of the flagellum to the flagellar pocket membrane. Despite the characterization of two TF proteins, CEP164C and T. brucei (Tb)RP2, little is known about the organization of these fibres. Here, we report the identification and characterization of the first kinetoplastid-specific TF protein, named TFK1 (Tb927.6.1180). Bioinformatics and functional domain analysis identified three distinct domains in TFK1 – an N-terminal domain of an unpredicted function, a coiled-coil domain involved in TFK1–TFK1 interaction and a C-terminal intrinsically disordered region potentially involved in protein interaction. Cellular immunolocalization showed that TFK1 is a newly identified basal body maturation marker. Furthermore, using ultrastructure expansion and immuno-electron microscopies we localized CEP164C and TbRP2 at the TF, and TFK1 on the distal appendage matrix of the TF. Importantly, RNAi-mediated knockdown of TFK1 in bloodstream form cells induced misplacement of basal bodies, a defect in the furrow or fold generation, and eventually cell death. We hypothesize that TFK1 is a basal body positioning-specific actor and a key regulator of cytokinesis in the bloodstream form Trypanosoma brucei

Murine Models for Trypanosoma brucei gambiense Disease Progression—From Silent to Chronic Infections and Early Brain Tropism

Trypanosoma brucei gambiense is responsible for more than 90% of reported cases of human African trypanosomosis (HAT). Infection can last for months or even years without major signs or symptoms of infection, but if left untreated, sleeping sickness is always fatal. In the present study, different T. b. gambiense field isolates from the cerebrospinal fluid of patients with HAT were adapted to growth in vitro. These isolates belong to the homogeneous Group 1 of T. b. gambiense, which is known to induce a chronic infection in humans. In spite of this, these isolates induced infections ranging from chronic to silent in mice, with variations in parasitaemia, mouse lifespan, their ability to invade the CNS and to elicit specific immune responses. In addition, during infection, an unexpected early tropism for the brain as well as the spleen and lungs was observed using bioluminescence analysis. The murine models presented in this work provide new insights into our understanding of HAT and allow further studies of parasite tropism during infection, which will be very useful for the treatment and the diagnosis of the disease

A MAP6-Related Protein Is Present in Protozoa and Is Involved in Flagellum Motility

In vertebrates the microtubule-associated proteins MAP6 and MAP6d1 stabilize cold-resistant microtubules. Cilia and flagella have cold-stable microtubules but MAP6 proteins have not been identified in these organelles. Here, we describe TbSAXO as the first MAP6-related protein to be identified in a protozoan, Trypanosoma brucei. Using a heterologous expression system, we show that TbSAXO is a microtubule stabilizing protein. Furthermore we identify the domains of the protein responsible for microtubule binding and stabilizing and show that they share homologies with the microtubule-stabilizing Mn domains of the MAP6 proteins. We demonstrate, in the flagellated parasite, that TbSAXO is an axonemal protein that plays a role in flagellum motility. Lastly we provide evidence that TbSAXO belongs to a group of MAP6-related proteins (SAXO proteins) present only in ciliated or flagellated organisms ranging from protozoa to mammals. We discuss the potential roles of the SAXO proteins in cilia and flagella function

New insights in the description of the dissolution of actinide dioxides: better understanding for their reprocessing

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