Chemical Composition Of Shell Research Articles

Cluster Self-Organization of Intermetallic Systems: K66 and K130 Clusters for the Self-Assembly of the K78In160-hP238 Crystal Structure and K17 Clusters for the Self-Assembly of the K8In11-hR114 Crystal Structure

The combinatorial topological analysis and modeling of self-assembly of the K78In160-hP238 (space group P-3m1, a = b = 17.211, c = 28.888 A, V = 7410 A3) and K8In11-hR114 (space group R-3c, a = b = 10.021 A, c = 50.891 A, V = 4426 A3) crystal structures are performed by computer methods (the ToposPro software package). Icosahedra In12 (with the -3m symmetry) are the templates on which three-layer clusters K130 = 0@12(In12)@30(In12K18)@86(K20In66) with the diameter of 17 A are formed. The two-layer cluster K66 formed on Friauf polyhedra K(K4In12) (with 3m symmetry) has a chemical composition of shells K@16(K4In12)@49(K16In33) and a diameter of 14 A. The K130 and K66 nanoclusters are framework-forming and involved in the formation of 2D layers A and B, respectively, thus forming a three-layer B–A–B package. The In12 clusters (with the -3m symmetry), In8 hexagonal bipyramids (with the 3m symmetry), and K spacer atoms are located in the voids of the layer of the K66 clusters. The three-layer package thickness corresponds to the value of the translation vector modulus c = 28.888 A. The framework structure is formed by linking the three-layer B–A–B packages in the [001] direction. The cluster precursor K17 = 0@In11K6 is installed for K8In11-hR114 in the form of a triangular In5 bipyramid on six faces of which In atoms are located with six bound potassium atoms. The microlayer is formed when the primary chains are bound in the (001) plane with a shift. The localization of the K spacer atoms takes place in the layer. The microframework of the structure is formed when the microlayers are bound with a shift.

Ecological Composites Materials for Brake Pads Using Shells as Filler Material

The brake pads are one of the basic components for the development an ecological transport. The main objective of the paper is to produce green brake pads used shells as filler material capable to reducing the emission of fine and ultrafine particles resulting from vehicle braking systems. The stages in the development of this goal were: establishing the chemical composition of shells, formulating the recipes of composite materials, selecting parameters of technology, obtaining in laboratory and characterization of new materials in terms of physico-mechanical and tribological characteristics, evaluating their performance compared to similar materials presented in the scientific literature.

Cluster Self-Organization of Intermetallic Systems: 0@12(Ga12)@24(Na12Ga12)@72(Rb4Na8Ga60) 108-Atom Three-Layer Icosahedral Cluster and 0@12(Ga12)@32(Na20Ga12) 44-Atom Two-Layer Icosahedral Cluster for Rb24Na200Ga696-oF920 Crystal Structure Self-Assembly

The combinatorial-topological analysis and simulation of the self-assembly of the Rb24Na200Ga696-oF920 (space group Fmmm, V = 17 837 A3) crystal structure are conducted by the computer-based methods (TOPOS program package). The number of options for the cluster representation of the 3D atomic framework with the number of structural units ranging from 4 to 12 came to 9565 variants. Two framework-forming icosahedral clusters—ico-K108 and ico-K44—are determined. The ico-K108 three-layer 108-atom nanocluster has the 0@12(Ga12)@24(Na12Ga12)@72(Rb4Na8Ga60) chemical composition of shells, a diameter of 17 A, and symmetry g = mmm. The ico-K44 two-layer 44-atom nanocluster has the 0@12(Ga12)@32(Na20Ga12) chemical composition of shells, a diameter of 11 A, and symmetry g = 2/m. The symmetry and topological codes of the Rb24Na200Ga696–oF920 3D structure’s self-assembly processes from the iсo-K108 and ico-K44 nanocluster precursors are reconstructed in the form primary chain → microlayer → microframework. The Rb spacer atoms and related groups of Ga atoms in the form of chains are located in the large voids of the 3D framework.

Freshwater mollusks from Neogene-Quaternary Dniester and Prut riverine deposits as indicator paleoenvironments: chemical composition of shells and its palaeoecological interpretation

The respective environments in two ancient rivers were studied using geochemical methods with paleogeographic reconstructions of fossil material represented by shells of freshwater bivalve mollusks. The studied outcrops are located in the basins of the Dniester and Prut rivers. Materials were collected from two Pliocene (Brînza, Giurgiuleşti) outcrops and the ages of the second group of localities (Sucleia, Slobozia Mare, Gura Bîcului) are from Middle to Late Pleistocene. The determination of the taxonomic position was carried out using standard malacological methods. Geochemical data were used for the environmental reconstruction and included stable isotope ratio and trace element compositions in subfossil freshwater bivalve shell (Bivalvia: Unionoida). Key indicators of paleoenvironments show changes in water temperature. Changes in the taxonomic composition of bivalve mollusk assemblages also occurred. In the present study, increasing the water temperature caused a change of stenobiont species of bivalve mollusks to eurybiont species. Eutrophication of watercourses, caused by anthropogenic pollution and climate change in the direction of warming, has led to the replacement of pearl mussels of the family Margaritiferidae by more eurybiont species of the family Unionidae in the benthic communities of European oligotrophic rivers. These processes are similar to those deduced for the Neogene-Quaternary watercourses of the Prut and Dniester basins, but they proceed at a much faster pace. They are processes of eutrophication of watercourses – the main factor leading to the catastrophically rapid modern reduction of the ranges of pearl mussel.

On climate reconstruction using bivalves: Three methods to interpret the chemical signature of a shell

To improve our understanding of the climate process and to assess the human impact on current global warming, past climate reconstruction is essential. The chemical composition of a bivalve shell is strongly coupled to environmental variations and therefore ancient shells are potential climate archives. The nonlinear nature of the relation between environmental condition (e.g. the seawater temperature) and proxy composition makes it hard to predict the former from the latter, however. In this paper we compare the ability of three nonlinear system identification methods to reconstruct the ambient temperature from the chemical composition of a shell. The comparison shows that nonlinear multi-proxy approaches are potentially useful tools for climate reconstructions and that manifold based methods result in smoother and more precise temperature reconstruction.

On Climate Reconstruction using Bivalve Shells: Three Methods to Interpret the Chemical Signature of a Shell

The chemical composition of a bivalve shell is strongly coupled to the seasonal variations in the environment. The nonlinear nature of this relation however makes it hard to predict, e.g. the temperature, from the chemical composition of a shell. In this paper we compare the ability of three nonlinear system identification methods to reconstruct the temperature from the chemical composition of a shell. The comparison shows that nonlinear multi-proxy approaches are potential tools for climate reconstructions with a preference for manifold based methods that results in smoother and a more precise temperature reconstruction.

Chemical composition of shell and flesh of three prawn samples from Lagos lagoon

AbstractThe protein, ash, fibre and individual mineral ion contents of three species of prawn taken from the Lagos lagoon were determined. The median liveweights of Macrobrachium vollenhovenii (Herklots), Palaemon species A (Powell) and Penaeus notialis were respectively, 25.52 g (shell + head 16.76 g; flesh 9.26 g), 3.15 g (shell + head 1.71 g; flesh 1.44 g) and 5.11 g (shell + head 2.14 g; flesh 2.96 g). All (shell + head) samples had high protein, ash and fibre contents but only the protein content was high in the flesh, which had low or undetectable quantities of fibre. The fat and carbohydrates contents were generally low. In M vollenhovenii the (shell + head) was a better source of Mg, Zn, Cu and K than the flesh, which was a better source of Ca, Ni, P, Fe, Co and Na. In P species A the (shell + head) was a better source of Ca, Mg, P, Cu, Co, Na and K than the flesh (higher in Zn and Ni). In P notialis the (shell + head) was the better source of Ca, Zn, P, Fe and Co and the flesh the better source of Mg, Ni, Fe, Na and K. Copyright © 2004 Society of Chemical Industry

An exploratory study with the proton microprobe of the ontogenetic distribution of 16 elements in the shell of living oysters (Crassostrea virginica)

Study of the chemical composition of shell of exoskeletonous organisms in the past has required the sacrifice of the organism. Because the beam of the proton microprobe is relatively nondestructive and analyzes the surface layer of the shell, organisms do not have to be killed. The present paper presents results of a preliminary experiment in which distribution of elements (Na to Sr) in shell of living juvenile oysters, Crassostrea virginica (Gmelin), was studied in situ with a proton microprobe at monthly intervals for four months. The relative concentration of 16 elements was measured in the newly deposited prismatic edge of the right valve of three oysters reared in controlled laboratory conditions. Na, Mg, Al, Si, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Cu, Zn, Br, and Sr were detected in concentrations as low as a few parts per million relative to the concentration of standards added to pure CaCO3. Concentration of elements varied nominally among shells of the three individual oysters and in their successive ontogenetic stages. Fluctuations in concentration of Na, Mg, S, Cl, Ca, Mn, Fe, Cu, and Zn were generally similar in the two normally growing oysters, but differed from those in the oyster that stopped growing. Trends in concentration of Al, Si, and Sr were similar in the three oysters: those of Br were variable. Relative concentrations of Na, Cl, S, Mn, Fe, and Zn increased slightly with age of oysters, that of the other elements stayed relatively constant. Concentration of most elements was higher in shell than in seawater. Variable concentrations, especially of Na, Cl, and Si in valve edges, tend to support the hypothesis of earlier workers that separate mineral phases are present as impurities entrapped within the shell during calcification.