Material independent crack arrest statistics

The propagation of (planar) cracks in a heterogeneous brittle material characterized by a random field of toughness is considered, taking into account explicitly the effect of the crack front roughness on the local stress intensity factor. In the so-called strong-pinning regime, the onset of crack propagation appears to map onto a second-order phase transition characterized by universal critical exponents which are independent of the local characteristics of the medium. Propagation over large distances can be described by using a simple one-dimensional description, with a correlation length and an effective macroscopic toughness distribution that scale in a non-trivial fashion with the crack front length. As an application of the above concepts, the arrest of indentation cracks is addressed, and the analytical expression for the statistical distribution of the crack radius at arrest is derived. The analysis of indentation crack radii on alumina is shown to obey the predicted algebraic expression for the radius distribution and its dependence on the indentation load

Alien Registration- Roux, Charles (Lewiston, Androscoggin County)

https://digitalmaine.com/alien_docs/27753/thumbnail.jp

Artificial Keys to the Genera of Living Stalked Crinoids (Echinodermata)

Two practical, illustrated, dichotomous keys to the 29 genera of living stalked crinoids are provided: one for entire animals and one for stalk ossicles and fragments. These are accompanied by (1) an overview of taxonomically important morphology, and (2) an alphabetical list by family and genus of the ∼95 nominal living species and their distribution by region. This is the first compilation of such data for all living stalked crinoids since Carpenter (1884) recognized 27 species in six genera in his monograph based on the H.M.S. CHALLENGER Expedition collection

Material-independent crack arrest statistics: Application to indentation experiments

An extensive experimental study of indentation and crack arrest statistics is presented for four different brittle materials (alumina, silicon carbide, silicon nitride, glass). Evidence is given that the crack length statistics can be described by a universal (i.e. material independent) distribution. The latter directly derives from results obtained when modeling crack propagation as a depinning phenomenon. Crack arrest (or effective toughness) statistics appears to be fully characterized by two parameters, namely, an asymptotic crack length (or macroscopic toughness) value and a power law size dependent width. The experimental knowledge of the crack arrest statistics at one given scale thus gives access to its knowledge at all scales

Large scale numerical simulations of "ultrametric" long-range depinning

The depinning of an elastic line interacting with a quenched disorder is studied for long range interactions, applicable to crack propagation or wetting. An ultrametric distance is introduced instead of the Euclidean distance, allowing for a drastic reduction of the numerical complexity of the problem. Based on large scale simulations, two to three orders of magnitude larger than previously considered, we obtain a very precise determination of critical exponents which are shown to be indistinguishable from their Euclidean metric counterparts. Moreover the scaling functions are shown to be unchanged. The choice of an ultrametric distance thus does not affect the universality class of the depinning transition and opens the way to an analytic real space renormalization group approach.Comment: submitted to Phys. Rev.

Revision of the Pentacrinid Stalked Crinoids of the Genus Endoxocrinus (Echinodermata, Crinoidea), with a Study of Environmental Control of Characters and Its Consequences for Taxonomy

A revision of the stalked crinoid species attributed to the genus Endoxocrinus A.H. Clark, 1908 (Diplocrininae, Pentacrinitidae, Crinoidea, Echinodermata) is conducted using studies on phenotype variation and its relation with environment. Specimens collected via submersible at five sites in the Bahamas exhibit distinct phenotypes that correlate with different apparent ecological niches and serve as references for interpreting specimens dredged in Atlantic and Pacific Oceans where detailed information on their benthic environment is unknown. Documentation of ecophenotypic convergences or divergences allows us to distinguish between adaptive characters and those revealing genetic affinities, and to discuss allopatric evolution and bathymetric zonation. The results suggest the following taxonomy: the genus Endoxocrinus is subdivided into two subgenera, i.e., Endoxocrinus A.H. Clark, 1908 and Diplocrinus Döderlein, 1912 (Annacrinus A. H. Clark, 1923 becomes a junior synonym of Diplocrinus); the subgenus Endoxocrinus is monospecific with E. (E.) parrae [Gervais (in Guérin, 1835)] from the western tropical Atlantic; the subgenus Diplocrinus includes E. (D.) alternicirrus (Carpenter, 1882) from the western and central Pacific, E. (D.) maclearanus (Thomson, 1872) from the western tropical Atlantic, and E. (D.) wyvillethomsoni (Jeffreys, 1870) from the northeastern Atlantic. Endoxocrinus (E.) parrae includes three subspecies adapted to different habitats and depths: E. (E.) parrae parrae usually in 154–518 m with moderate to high current velocity and moderate turbulence to laminar flow, E. (E.) parrae carolinae (A.H. Clark, 1934) in 504–724 m with moderate current velocity and high turbulence, and E. (E.) parrae prionodes H.L. Clark, 1941 in 402–832 m with high current velocity in laminar flow. E. (D.) alternicirrus includes two subspecies, E. (D.) alternicirrus alternicirrus in 625–1476 m and E. (D.) alternicirrus sibogae (Döderlein, 1907) usually in 364–800 m. E. (D.) maclearanus has a depth range of 432–878 m and occurs as a dwarf variety minimus n. var. in high current velocities and high turbulence. E. (D.) wyvillethomsoni from depths of 1214–2070 m lives on various substrates under a variety of hydrodynamic conditions

As placas de xisto gravadas (e os baculos) do sitio do Monte da Barca (Coruche)

En 1971, des terrassements liés aux aménagements d’une coopérative agricole mirent au jour un remarquable ensemble de plaques et de crosses gravées en schiste. La découverte survint à 20 km à l’est de Lisbonne et 8 km au sud du Tage, en bordure sud de la plaine alluviale de la rivière Soria, face au bourg de Coruche et non loin d’un camp chalcolithique bien connu pour avoir abrité une fabrique de telles plaques. Les conditions dans lesquelles deux amateurs purent recueillir ce matériel furent..

Les nouveaux patrimoines en Pays de la Loire

Publié avec le soutien de la Région Pays de la Loire, ce fort (et beau) volume est le fruit du travail de plus de quarante auteurs (relevant de huit laboratoires répartis dans trois universités), durant trois ans et sur un projet (NEOPAT) lui-même retenu par ladite région dans le cadre d’un appel à projets de recherche. Sans être une « commande » à proprement parler, il est clair que l’ouvrage répond, dans le domaine patrimonial, à un légitime souhait de lisibilité générale de leur région, re..

F. Carrera Ramirez, et r. Fabregas Valcace, (dir.),Arte parietal megalitico en el Noroeste peninsular. Conocimiento y conservacion

Ce livre présente le bilan d’un projet de recherche soutenu par le Ministère espagnol de la Science et de la Technologie (au titre du FEDER) et par le Conseil régional de Galice. Après une présentation liminaire, l’ouvrage s’articule en sept chapitres, chacun étant précédé d’un résumé en anglais (parfois un peu succinct) et suivi de sa propre bibliographie. Au chapitre 1, R. Fabregas et I. Vilaseco présentent les mégalithes galiciens dans leur contexte - humain essentiellement, l’environnemen..

C. Marcigny, E. Ghesquière, et J. Desloges, (avec la coll. de C. Riche, et G. San Juan), 2007 – La hache et la meule. Les premiers paysans du Néolithique en Normandie (6000-2000 avant notre ère)

* Par suite d’une regrettable erreur matérielle, ce compte rendu avait été attribué à J.-L. Monnier dans notre n° 24 (2007, p. 214-216). Nous le redonnons ici sous la signature de son véritable auteur. Nous prions nos lecteurs de bien vouloir rectifier cette référence et présentons nos plus vives excuses aux intéressés. (NDLR). Ce ne sont pas moins de sept partenaires institutionnels qui se sont associés pour permettre l’élaboration de ce beau volume au format « carré » (23 x 28 cm), préparé ..