Search results for "SHELL"
showing 10 items of 748 documents
Pmarg-pearlin is a matrix protein involved in nacre framework formation in the pearl oyster Pinctada margaritifera.
2011
11 pages; International audience; The shell of pearl oysters is organized in multiple layers of CaCO(3) crystallites packed together in an organic matrix. Relationships between the components of the organic matrix and mechanisms of nacre formation currently constitute the main focus of research into biomineralization. In this study, we characterized the pearlin protein from the oyster Pinctada margaritifera (Pmarg); this shares structural features with other members of a matrix protein family, N14/N16/pearlin. Pmarg pearlin exhibits calcium- and chitin-binding properties. Pmarg pearlin transcripts are distinctively localized in the mineralizing tissue responsible for nacre formation. More s…
Changes in eggshell ultrastructure of Falco naumanni and Tyto alba exposed to pesticides and polychlorinated biphenyls (PCBs)
2014
Changes in the quality of eggs of birds exposed to environmental contaminants have been described, but few reports concern eggshell ultrastructure. In this study, infertile or addled Lesser Kestrels (Falco naumanni) and Barn owls (Tyto alba) eggs were collected from the polluted area of Gela plain (Sicily) during 2007, and compared in terms of organophosphate and organochlorine pesticides, and PCBs levels, and eggshell ultrastructure as determined by scanning electron microscopy. Pesticide and PCB residues in eggs were determined by Gas chromatography/ mass spectrometry (GC/MS) [GC Agilent 7890A/MS Agilent 5975C (Agilent technologies) using a DB-5 capillary column in the selected ion monito…
Reconstruction of the internal structure of the pore system of a complex dinosaur eggshell (Megaloolithus siruguei)
2013
Despite the many reconstructions of fossil material that have recently appeared in the literature, dinosaur eggshells have never been reconstructed using computing techniques. Using the EMAC 3-D modelling methodology, we reconstruct a section of the Late Cretaceous Megaloolithus siruguei eggshell, which has a particularly complex pore system, exhibiting an intricate network of vertical, oblique, and horizontal pores.
Embryonic Ammonoid Shell Features: Intraspecific Variation Revisited
2001
Two samples of ammonoids belonging to the Oppeliidae, Sublunuloceras virguloidesHecticoceras (Brightii) canaliculatum, are analyzed to estimate the intraspecific variability of embryonic shell features. The study of embryonic shell characters reveals two main shapes of protoconch, flattened and round. Prosiphons may be straight or slightly curved. New parameters for area are added to the linear parameters commonly found in the literature. Prosiphon length and caecum area vary greatly whereas protoconch and ammonitella diameter vary only slightly, and the ammonitella angle is almost constant. The protoconch-to-ammonitella size ratio behaves differently in each species, suggesting different p…
MIL-53(Al) under reflux in water: Formation of γ-AlO(OH) shell and H2BDC molecules intercalated into the pores
2014
Abstract It is shown that treatment of MIL-53(Al) (Al(OH)BDC·H2O, BDC = 1,4-benzene dicarboxylate) under reflux in water results in a progressive transformation of the solid into a new well crystallized phase. After reflux for 10 h or more the new phase is obtained in a pure form and its XRD pattern was indexed in a monoclinic system with the following cell parameters: a = 19.47 A, b = 8.98 A, c = 6.60 A, β = 107.7°. Characterization of the obtained solid by TGA, FT-IR, NMR, TEM and XRD has revealed that its composition is [0.8Al(OH)BDC·0.2H2BDC] + 0.2γ-AlO(OH). Formation of this material indicates that under reflux in water a partial hydrolysis of the MOF network occurs producing H2BDC mol…
Shell Extracts from the Marine Bivalve Pecten maximus Regulate the Synthesis of Extracellular Matrix in Primary Cultured Human Skin Fibroblasts
2014
International audience; Mollusc shells are composed of more than 95% calcium carbonate and less than 5% of an organic matrix consisting mostly of proteins, glycoproteins and polysaccharides. Previous studies have elucidated the biological activities of the shell matrices from bivalve molluscs on skin, especially on the expression of the extracellular matrix components of fibroblasts. In this work, we have investigated the potential biological activities of shell matrix components extracted from the shell of the scallop Pecten maximus on human fibroblasts in primary culture. Firstly, we demonstrated that shell matrix components had different effects on general cellular activities. Secondly, …
Spectral theory of a Neumann-Poincare-type operator and analysis of cloaking due to anomalous localized resonance
2011
The aim of this paper is to give a mathematical justification of cloaking due to anomalous localized resonance (CALR). We consider the dielectric problem with a source term in a structure with a layer of plasmonic material. Using layer potentials and symmetrization techniques, we give a necessary and sufficient condition on the fixed source term for electromagnetic power dissipation to blow up as the loss parameter of the plasmonic material goes to zero. This condition is written in terms of the Newtonian potential of the source term. In the case of concentric disks, we make the condition even more explicit. Using the condition, we are able to show that for any source supported outside a cr…
Conformations and orientational ordering of semiflexible polymers in spherical confinement.
2017
Semiflexible polymers in lyotropic solution confined inside spherical nanoscopic “containers” with repulsive walls are studied by molecular dynamics simulations and density functional theory, as a first step to model confinement effects on stiff polymers inside of miniemulsions, vesicles, and cells. It is shown that the depletion effects caused by the monomer-wall repulsion depend distinctly on the radius R of the sphere. Further, nontrivial orientational effects occur when R, the persistence length ℓp, and the contour length L of the polymers are of similar magnitude. At intermediate densities, a “shell” of wall-attached chains is forming, such that the monomers belonging to those chains a…
Investigation of various shellac grades: additional analysis for identity.
2009
Background: A number of different grades of shellac are commercially available and most of them are known only as generic shellac and are not further differentiated. The investigated grades of shellac in this study are based on different insect strains, host trees, refining methods, and products from different suppliers. Method: The Gardner/Iodine color values of alcoholic and aqueous solutions of the various shellac grades were measured. Glass transition temperatures and pKa-values were determined. To assess chemical differences in the tested shellac grades, MALDI-TOF analysis was performed. Results: Differences were found in color, TG, and pKa-values and in the mass spectra by MALDI-TOF a…
Cation Environment of BaCeO3−Based Protonic Conductors II: New Computational Models
2011
Quantum chemical calculations have been carried out to simulate Y-doped BaCeO(3) derivatives. Hartree-Fock energy functional was used to study octahedral site environments embedded in a Pmcn orthorhombic framework, showing local arrangement characterized by Ce-O-Ce, Ce-O-Y, and Y-O-Y (Z-O-Ξ) configurations and including or not hydrogen close to the moieties encompassing those configurations. The latter are, in fact, representative of - and, in our modeling approach, were treated as - local arrangements that could be found in Y:BaCeO(3)-doped materials. The geometrical optimizations performed on the structural models and a detailed orbital analysis of these systems allowed us to confirm and …