Ornstein-Zernike equation and Percus-Yevick theory for molecular crystals

We derive the Ornstein-Zernike equation for molecular crystals of axially symmetric particles and apply the Percus-Yevick approximation to this system. The one-particle orientational distribution function has a nontrivial dependence on the orientation and is needed as an input. Despite some differences, the Ornstein-Zernike equation for molecular crystals has a similar structure as for liquids. We solve both equations for hard ellipsoids on a sc lattice. Compared to molecular liquids, the tensorial orientational correlators exhibit less structure. However, depending on the lengths a and b of the rotation axis and the perpendicular axes of the ellipsoids, different behavior is found. For oblate and prolate ellipsoids with b >= 0.35 (units of the lattice constant), damped oscillations in distinct directions of direct space occur for some correlators. They manifest themselves in some correlators in reciprocal space as a maximum at the Brillouin zone edge, accompanied by maxima at the zone center for other correlators. The oscillations indicate alternating orientational fluctuations, while the maxima at the zone center originate from nematic-like orientational fluctuations. For a <= 2.5 and b <= 0.35, the oscillations are weaker. For a >= 3.0 and b <= 0.35, no oscillations occur any longer. For many of the correlators in reciprocal space, an increase of a at fixed b leads to a divergence at the zone center q = 0, consistent with nematic-like long range fluctuations, and for some oblate and prolate systems with b ~< 1.0 a simultaneous tendency to divergence of few other correlators at the zone edge is observed. Comparison with correlators from MC simulations shows satisfactory agreement. We also obtain a phase boundary for order-disorder transitions.Comment: 20 pages, 13 figures, submitted to Phys. Rev.

Microscopic theory of glassy dynamics and glass transition for molecular crystals

We derive a microscopic equation of motion for the dynamical orientational correlators of molecular crystals. Our approach is based upon mode coupling theory. Compared to liquids we find four main differences: (i) the memory kernel contains Umklapp processes, (ii) besides the static two-molecule orientational correlators one also needs the static one-molecule orientational density as an input, where the latter is nontrivial, (iii) the static orientational current density correlator does contribute an anisotropic, inertia-independent part to the memory kernel, (iv) if the molecules are assumed to be fixed on a rigid lattice, the tensorial orientational correlators and the memory kernel have vanishing l,l'=0 components. The resulting mode coupling equations are solved for hard ellipsoids of revolution on a rigid sc-lattice. Using the static orientational correlators from Percus-Yevick theory we find an ideal glass transition generated due to precursors of orientational order which depend on X and p, the aspect ratio and packing fraction of the ellipsoids. The glass formation of oblate ellipsoids is enhanced compared to that for prolate ones. For oblate ellipsoids with X <~ 0.7 and prolate ellipsoids with X >~ 4, the critical diagonal nonergodicity parameters in reciprocal space exhibit more or less sharp maxima at the zone center with very small values elsewhere, while for prolate ellipsoids with 2 <~ X <~ 2.5 we have maxima at the zone edge. The off-diagonal nonergodicity parameters are not restricted to positive values and show similar behavior. For 0.7 <~ X <~ 2, no glass transition is found. In the glass phase, the nonergodicity parameters show a pronounced q-dependence.Comment: 17 pages, 12 figures, accepted at Phys. Rev. E. v4 is almost identical to the final paper version. It includes, compared to former versions v2/v3, no new physical content, but only some corrected formulas in the appendices and corrected typos in text. In comparison to version v1, in v2-v4 some new results have been included and text has been change

Premiers apports archéoentomologiques de l'étude des Puces : aspects historiques et anthropologiques (Siphonaptera)

First archeoentomological contribution to Fleas study in France : historical and anthropological aspects (Siphonaptera). The authors give a review of recent developments of fossil Siphonaptera (Fleas) study in archaeological contexts in France. These new data are compared with previous investigations carried out elsewhere in Europe but mainly in Britain, and their contribution as regards Siphonaptera biogeography and biology is mentioned. At last, the role of Pulex irritans as vector of plague is underlined.Les auteurs présentent un bilan des récentes découvertes de Siphonaptères fossiles (Puces) en France dans des contextes archéologiques. Ces nouveaux faits sont confrontés aux données anciennes et récentes, surtout britanniques, et leur apport en matière de biogéographie et de biologie des Siphonaptères est évoqué. Enfin, le rôle de Pulex irritans comme probable vecteur de la peste est à nouveau souligné.Yvinec J.-H., Ponel Philippe, Beaucournu Jean-Claude. Premiers apports archéoentomologiques de l'étude des Puces : aspects historiques et anthropologiques (Siphonaptera). In: Bulletin de la Société entomologique de France, volume 105 (4), octobre 2000. pp. 419-425

Les approches environnementales sur le sanctuaire antique de Sains-du-Nord chez les Nerviens (Nord)

International audienceDie Notausgrabung des antiken Heiligtums von Sains-du-Nord (Nord) hat drei pläoökologsiche Studein mit sich gebracht (Holzkohlstudien, Archäozoologie, Bodenkunde). Jede lieferte Elemente zur besseren Kenntnis des Heiligtums. Die Holzkohlstudie erlaubt unter anderem die Diversität der Waldnutzung zu erkennen, Archäozoologie den Vergleich mit anderen Heiligtümern Nordgalliens, Bodenkunde die Abwesenheit anthropogener Verschmutzung und die Anwesenheit verschiedener Typen von Oberflächengestaltung im Heiligtum.The rescue excavation of the antique sanctuary of Sains-du-Nord (Nord) allowed the realization of three archaeo-environmental studies (anthracology ; archaeozoology ; pedology). They each brought elements contributing to a better understanding of the site. Among others, the anthracological study allowed to observe the diversity of the exploited woodland ; the archaeozoological study authorized the establishment of comparisons with other sanctuaries of the north of Gaul ; as for the pedological study, highlighted the absence of anthropogenic pollution on the site.La fouille préventive du sanctuaire antique de Sains-du-Nord (Nord) a permis la réalisation de trois études archéo-environnementales (anthracologie ; archéozoologie ; pédologie). Elles ont chacune apporté des éléments contribuant à une meilleure compréhension du site. Ainsi, pour l’essentiel, l’étude anthracologique a permis d’observer la diversité des milieux exploités ; l’étude archéozoologique a autorisé l’établissement de comparaisons avec d’autres sanctuaires du nord de la Gaule ; quant à l’étude pédologique, a mis en évidence l’absence de pollution anthropique sur le site

Les approches environnementales sur le sanctuaire antique de Sains-du-Nord chez les Nerviens (Nord)

International audienceDie Notausgrabung des antiken Heiligtums von Sains-du-Nord (Nord) hat drei pläoökologsiche Studein mit sich gebracht (Holzkohlstudien, Archäozoologie, Bodenkunde). Jede lieferte Elemente zur besseren Kenntnis des Heiligtums. Die Holzkohlstudie erlaubt unter anderem die Diversität der Waldnutzung zu erkennen, Archäozoologie den Vergleich mit anderen Heiligtümern Nordgalliens, Bodenkunde die Abwesenheit anthropogener Verschmutzung und die Anwesenheit verschiedener Typen von Oberflächengestaltung im Heiligtum.The rescue excavation of the antique sanctuary of Sains-du-Nord (Nord) allowed the realization of three archaeo-environmental studies (anthracology ; archaeozoology ; pedology). They each brought elements contributing to a better understanding of the site. Among others, the anthracological study allowed to observe the diversity of the exploited woodland ; the archaeozoological study authorized the establishment of comparisons with other sanctuaries of the north of Gaul ; as for the pedological study, highlighted the absence of anthropogenic pollution on the site.La fouille préventive du sanctuaire antique de Sains-du-Nord (Nord) a permis la réalisation de trois études archéo-environnementales (anthracologie ; archéozoologie ; pédologie). Elles ont chacune apporté des éléments contribuant à une meilleure compréhension du site. Ainsi, pour l’essentiel, l’étude anthracologique a permis d’observer la diversité des milieux exploités ; l’étude archéozoologique a autorisé l’établissement de comparaisons avec d’autres sanctuaires du nord de la Gaule ; quant à l’étude pédologique, a mis en évidence l’absence de pollution anthropique sur le site