""E muet" et "Schwa" au XVIIIe siècle"

National audienceLa lexicographie française moderne présente les notions de Schwa et e muet comme de strictes équivalents. Ces deux unités, dans notre langue, ont-elles toujours été considérées comme décrivant les mêmes réalités ? Qu'apprenons-nous d'un regard sur les théories grammaticales françaises des siècles antérieurs

Réflexions autour du vocabulaire grammatical dans le dictionnaire de l'Académie française

International audienceCette communication constitue une réflexion autour de la métalangue grammaticale recensée dans les huit premières éditions du Dictionnaire de l'Académie française. En s'appuyant notamment sur la question du marquage du domaine grammatical, l'étude proposée esquisse en quelque sorte les contours de l'histoire interne d'une discipline au sein de l'un des plus importants monuments de la lexicographie française

Une approche historique du concept de "Nasalité"

The present paper provides a brief analysis of the lexicographical history of the concept of "nasalité".Cet article propose une brève analyse de l'histoire du concept de "nasalité" à travers la lexicographie

Charles-Joseph Panckoucke, artisan de l'encyclopédisme français

Article présenté lors d'une réunion de l'équipe METADIF.Cet article esquisse une présentation du rôle déterminant joué par l'éditeur Charles-Joseph Panckoucke dans la diffusion du mouvement encyclopédique des Lumières

Formation and evolution of hydrated surface layers of apatites

Nanocrystalline apatites exhibit a very fragile structured hydrated surface layer which is only observed in aqueous media. This surface layer contains mobile ionic species which can be easily exchanged with ions from the surrounding fluids. Although the precise structure of this surface layer is still unknown, it presents very specific spectroscopic characteristics. The structure of the hydrated surface layer depends on the constitutive mineral ions: ion exchanges of HPO42- ions by CO32- ions or of Ca2+ by Mg2+ ions result in a de-structuration of the hydrated layer and modifies its spectroscopic characteristics. However, the original structure can be retrieved by reverse exchange reaction. These alterations do not seem to affect the apatitic lattice. Stoichiometric apatite also shows HPO42- on their surface due to a surface hydrolysis after contact with aqueous solutions. Ion exchange is also observed and the environments of the surface carbonate ions seem analogous to that observed in nanocrystalline apatites. The formation of a hydrated layer in aqueous media appears to be a property common to apatites which has to be taken into account in their reactivity and biological behavior

Chemical Diversity of Apatites

Apatites can accommodate a large number of vacancies and afford multiple ionic substitutions determining their reactivity and biological properties. Unlike other biominerals they offer a unique adaptability to various biological functions. The diversity of apatites is essentially related to their structure and to their mode of formation. Special charge compensation mechanisms allow molecular insertions and ion substitutions and determine to some extent their solubility behaviour. Apatite formation at physiological pH involves a structured surface hydrated layer nourishing the development of apatite domains. This surface layer contains relatively mobile and exchangeable ions, and is mainly responsible for the surface properties of apatite crystals from a chemical (dissolution properties, ion exchange ability, ion insertions, molecule adsorption and insertions) and a physical (surface charge, interfacial energy) point of view. These characteristics are used by living organisms and can also be exploited in material science

Bone mineral: update on chemical composition and structure

Bone mineral: update on chemical composition and structur

Physico-chemical properties of nanocrystalline apatites: Implications for biominerals and biomaterials

Nanocrystalline apatites play an important role in biomineralisation and they are used as bioactive biominerals for orthopaedic applications. One of the most interesting characteristics of the nanocrystals, evidenced by spectroscopic methods, is the existence of a structured surface hydrated layer, well developed in freshly formed precipitates, which becomes progressively transformed into the more stable apatitic lattice upon ageing in aqueous media. The hydrated layer is very fragile and irreversibly altered upon drying. Several routes leading to different apatite compositions are found in biological systems. The loosely bound ions of the hydrated layer can be easily and reversibly substituted by other ions in fast aqueous ion exchange reactions. These ions can either be included in the growing stable apatite lattice during the ageing process or remain in the hydrated layer. The adsorption properties of nanocrystals appear to be strongly dependent on the composition of the hydrated layer and on ageing. The surface reactivity of the apatite nanocrystals can play a part in different biomaterials and could explain the setting reactions of biomimetic calcium phosphate cements and the possibility of obtaining adherent nanocrystalline coatings on different substrates