Theory of rigid-plane phonon modes in layered crystals

The lattice dynamics of low-frequency rigid-plane modes in metallic (graphene multilayers, GML) and in insulating (hexagonal boron-nitride multilayers, BNML) layered crystals is investigated. The frequencies of shearing and compression (stretching) modes depend on the layer number {\EuScript N} and are presented in the form of fan diagrams. The results for GML and BNML are very similar. In both cases only the interactions (van der Waals and Coulomb) between nearest-neighbor planes are effective, while the interactions between more distant planes are screened. A comparison with recent Raman scattering results on low-frequency shear modes in GML [Tan {\it et al.}, arXiv:1106.1146v1 (2011)] is made. Relations with the low-lying rigid-plane phonon dispersions in the bulk materials are established. Master curves which connect the fan diagram frequencies for any given {\EuScript N} are derived. Static and dynamic thermal correlation functions for rigid-layer shear and compression modes are calculated. The results might be of use for the interpretation of friction force experiments on multilayer crystals

The Multidimensional Pseudo Spin Model and its Application to Phase Transitions in Layered Perovskites

Pseudo spins with dimensionality larger than two may be used to describe disordered molecular, or ionomolecular, crystals in which the molecules have several equivalent orientations. We show that such models predict complex ordering schemes for these crystals, we describe the various problems related to the construction of these schemes and apply this technique in detail to the case of NH3(CH2)sNH3CdC1an4d briefly to other similar layered perovskites

Hyper-Raman scattering analysis of the vibrations in vitreous boron oxide

Hyper-Raman scattering has been measured on vitreous boron oxide, $v-$B$_2$O$_3$. This spectroscopy, complemented with Raman scattering and infrared absorption, reveals the full set of vibrations that can be observed with light. A mode analysis is performed based on the local D$_{3h}$ symmetry of BO$_3$ triangles and B$_3$O$_3$ boroxol rings. The results show that in $v-$B$_2$O$_3$ the main spectral components can be succesfully assigned using this relatively simple model. In particular, it can be shown that the hyper-Raman boson peak arises from external modes that correspond mainly to librational motions of rigid boroxol rings.Comment: 13 pages, 11 figures, 2 table

A Pressure-Induced Incommensurate Phase in Ammonium Hydrogen Oxalate Hemihydrate

We report evidence for the existence of a new incommensurate phase in a crystal of ammonium hydrogen oxalate hemihydrate. This phase is remarkable in two aspects: it exists only above a critical pressure Pc, and the incommensurate wave vector, which is parallel to the vector c* of the reciprocal lattice, has the largest variation ever reported, varying continuously from 0.147c* at 4.3 kbar to ~ 0.25c* at the maximum pressure (8 kbar) used to date

Sexually dimorphic tibia shape is linked to natural osteoarthritis in STR/Ort mice

Human osteoarthritis (OA) is detected only at late stages. Male STR/Ort mice develop knee OA spontaneously with known longitudinal trajectory, offering scope to identify OA predisposing factors. We exploit the lack of overt OA in female STR/Ort and in both sexes of parental, control CBA mice to explore whether early divergence in tibial bone mass or shape are linked to emergent OA

A New syndrome of the charolais neonatal calf : paralysis in gastroenteritis

Un nouveau syndrome diarrhéique associé à des symptômes nerveux généraux et locomoteurs a été identifié en Charoláis chez des veaux de moins de deux semaines d’âge. Il présente des analogies avec une maladie congénitale liée à un trouble du métabolisme des aminoacides ramifiés mais le rôle plus probable de colibacilles produisant des cytotoxines neu rotoxiques est à confirmer.A new diarrheic syndrome associated with general and locomotor nervous symptoms has been identified in the charoláis area in calves under 2 weeks of age. This condition presents some similarities to a congenital disease related to impaired branched-aminoacid metabolism, but the more probable involvment of neurotoxic cytotoxin-producing E. Coli bacteria remains to be confirmed

Standardisation des piégeages en ligne pour quelques espèces de rongeurs

Une méthode standardisée de piégeage en ligne a été expé rimentée pour les rongeurs suivants : Eliomys quercinus, Pitymys multiplex, Clethrionomys glareolus, Microtus arvalis, Apodemus sylvaticus et Taterillus pygargus. Toutes ces expériences confir ment l’idée générale qu’il existe une relation de proportionnalité entre la densité de population et le nombre de captures en un temps donné sur une longueur donnée de ligne. Mais cette relation dépend étroitement des caractères de l’activité des Rongeurs. Il est montré que le coefficient de ligne est une fonction puissance négative de la moyenne des distances entre recaptures successives de la catégorie considérée. Des coefficients de ligne d’usage pra tique sont indiqués.A standard line trapping technique has been tested with the following Rodent species : Eliomys quercinus, Pitymys multiplex, Clethrionomys glareolus, Microtus arvalis, Apodemus sylvaticus and Taterillus pygargus. A proportional relation occurs between population density and number of catches during a given time- period, along a given length of trap-line. However this rela tionship depends also on the activity pattern and daily movements of the species studied. The « Line coefficient » is a negative power function of the average distance between successive catches (« average-D »)