Search results for "Calcar"

The sponge silicatein-interacting protein silintaphin-2 blocks calcite formation of calcareous sponge spicules at the vaterite stage

2013

Ca-carbonate, the inorganic matrix of the spicules from the calcareous sponges, is formed as the result of an enzyme-catalyzed reaction with the carbonic anhydrase [CA] as a decisive component. The growth and the morphology of the spicules are genetically controlled, and are taxon-specific. In the present study it is shown that the silicatein-interacting protein silintaphin-2 is present at the surface of the siliceous spicules of the demosponge Suberites domuncula and prevents the association of calcareous crystals synthesized in vitro to these skeletal elements. Silintaphin-2 comprises a Ca2+-binding domain that is formed by a 22 amino acid-long peptide, N-DDDSQGEIQSDMAEEEDDDNVD-C. This ve…

The Understanding of the Metazoan Skeletal System, Based on the Initial Discoveries with Siliceous and Calcareous Sponges

2017

Initiated by studies on the mechanism of formation of the skeletons of the evolutionary oldest still extant multicellular animals, the sponges (phylum Porifera) have provided new insights into the mechanism of formation of the Ca-phosphate/hydroxyapatite skeleton of vertebrate bone. Studies on the formation of the biomineral skeleton of sponges revealed that both the formation of the inorganic siliceous skeletons (sponges of the class of Hexactinellida and Demospongiae) and of the calcareous skeletons (class of Calcarea) is mediated by enzymes (silicatein: polymerization of biosilica; and carbonic anhydrase: deposition of Ca-carbonate). Detailed studies of the initial mineralization steps i…

Double Laser LIBS and micro-XRF spectroscopy applied to characterize materials coming from the Greek-Roman theater of Taormina

2009

The laser-induced breakdown spectroscopy (LIBS) is an applied physical technique that has shown, in recent years, its great potential for rapid qualitative analysis of materials. The possibility to implement a portable instrument that perform LIBS analysis makes this technique particularly useful for in situ analysis in the field of cultural heritages. The aim of this work is to compare the results, obtained by LIBS measurements with X-Ray Fluorescence (XRF) ones, on calcareous and refractory materials coming from the Greek-Roman theater of Taormina. Calibration curves for LIBS and XRF were obtained by measuring certified reference materials and using them as standards. LIBS measurements we…

Phylogenetic Position of the Hexactinellida Within the Phylum Porifera Based on the Amino Acid Sequence of the Protein Kinase C from Rhabdocalyptus d…

1998

Recent analyses of genes encoding proteins typical for multicellularity, especially adhesion molecules and receptors, favor the conclusion that all metazoan phyla, including the phylum Porifera (sponges), are of monophyletic origin. However, none of these data includes cDNA encoding a protein from the sponge class Hexactinellida. We have now isolated and characterized the cDNA encoding a protein kinase C, belonging to the C subfamily (cPKC), from the hexactinellid sponge Rhabdocalyptus dawsoni. The two conserved regions, the regulatory part with the pseudosubstrate site, the two zinc fingers, and the C2 domain, as well as the catalytic domain were used for phylogenetic analyses. Sequence al…

Evolution of Early Metazoa: Phylogenetic Status of the Hexactinellida Within the Phylum of Porifera (Sponges)

1998

The evolution of the Metazoa from their protozoan ancestors is one of the greatest puzzles of phylogeny (Willmer 1994; Cavalier-Smith et al. 1996). The emergence of multicellular animals has been explained by two major theories: the syncytial theory (Hadzi 1963) - origin from a multinucleated ciliate - and the colonial theory (Haeckel 1868) - origin from a colonial flagellate - both of which assume a di(poly)phyletic origin of the Metazoa. Numerous attempts to resolve whether the Metazoa are of mono- or polyphyletic origin have sought evidence from a wide variety of developmental and morphological data such as body symmetry, type of development (protostome vs. deuterostome), type of body ca…

Calcar avis…rara avis: A Flash Through Its History and Terminology

2018

Mechanical behaviour of Palermo and Marsala calcarenites (Sicily), Italy

2016

Abstract This paper aims at finding a framework for the Sicilian Calcarenites relating the strength and the deformability of these materials to their geological and structural features: fabric, bonding, initial and actual specific volume. In particular, this study sets out to separate the effects of fabric and of bonding on the mechanical response. The investigated lithotypes, Calcarenites from Palermo and Marsala, outcropping in many areas of southwestern Sicily, are characterized by sudden changes in their deformability, strength and permeability characteristics. The geotechnical identification, by means of computerized axial tomography and thin section petrographic analysis suggested a s…

Strontium isotopes as tracers of water-rocks interactions, mixing processes and residence time indicator of groundwater within the granite-carbonate …

2016

This study aims at identifying the water-rock interactions and mixing rates within a complex granite-carbonate coastal aquifer under high touristic pressure. Investigations have been carried out within the coastal aquifer of Bonifacio (southern Corsica, France) mainly composed of continental granitic weathering products and marine calcarenite sediments filling a granitic depression. A multi-tracer approach combining physico-chemical parameters, major ions, selected trace elements, stable isotopes of the water molecule and 87Sr/86Sr ratios measurements is undertaken for 20 groundwater samples during the low water period in November 2014. 5 rock samples of the sedimentary deposits and surroun…

An anatomical fetal brain structure and a normal variant mimicking anomalies on routine neurosonographic imaging: report of two cases

2004

We present two cases in which an anatomical structure, the calcar avis, and a normal variant, a bifid choroid plexus, mimicked abnormalities on routine prenatal ultrasound examination. To the best of our knowledge these pitfalls have only been described in neonates. A familiarity with these false images is important to avoid erroneous diagnoses.

Destructuration of typical Sicilian calcarenites

2010

The paper discusses some interesting features of Sicilian fine grain calcarenites. Uniaxial, triaxial, oedometer and isotropic compression tests were undertaken on intact specimens of two types of calcarenite in order to investigate their mechanical characteristics. It was found that the strength and deformability is significantly influenced by the structure (fabric and bonding) and by the destructuration processes. A better understanding of fracture development behavior is gained through a combination of acoustic emission and photographic monitoring on non-homogeneous samples with natural pre-existing heterogeneities due to cementation or to density. The results show that the destructurati…