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71.
Marine organisms must possess strategies enabling them to initiate calcite precipitation despite the unfavorable conditions for inorganic precipitation in surface seawater. These strategies are poorly understood. Here we compare two potential strategies of marine calcifyers to manipulate seawater chemistry in order to initiate calcite precipitation: Removal of Mg2+ and H+ ions from seawater solutions. An experimental setup was used to monitor the onset of inorganic precipitation on seed crystals as a function of the Mg2+ concentration and pH in artificial seawater. We focused on precipitation rates typical for biogenic calcification in planktonic foraminifera (∼10−3 mol m−2 h−1) and time scales typical for the initiation of calcification in these organisms (minutes to hours). We find that the carbonate ion concentration has to increase by a factor of ∼13 when [Mg2+] increases from 0 to 53 mmol kg−1 in order to maintain a typical biogenic precipitation rate. Model calculations for the energy requirement for various scenarios of Mg2+ and H+ removal including Ca2+ exchange and CO2 diffusion are presented. We conclude that the more cost-effective strategy to initiate calcite precipitation in foraminifera is H+ removal, rather than Mg2+ removal. 相似文献
72.
Nonlinear dust ion acoustic solitary waves (DIASW) in dusty plasma are studied incorporating kinematic viscosity, using Sagdeev’s pseudopotential approach. The effects of kinematic viscosity and the nonextensive parameter q on the features of DIASW are investigated in some detail. 相似文献
73.
For the critical values of the parameters q and V, the work (Samanta et al. in Phys. Plasma 20:022111, 2013b) is unable to describe the nonlinear wave features in magnetized dusty plasma with superthermal electrons. To describe the nonlinear wave features for critical values of the parameters q and V, we extend the work (Samanta et al. in Phys. Plasma 20:022111, 2013b). To extend the work, we derive the modified Kadomtsev-Petviashvili (MKP) equation for dust ion acoustic waves in a magnetized dusty plasma with q-nonextensive velocity distributed electrons by considering higher order coefficients of ?. By applying the bifurcation theory of planar dynamical systems to this MKP equation, the existence of solitary wave solutions of both types rarefactive and compressive, periodic travelling wave solutions and kink and anti-kink wave solutions is proved. Three exact solutions of these above waves are determined. The present study could be helpful for understanding the nonlinear travelling waves propagating in mercury, solar wind, Saturn and in magnetosphere of the Earth. 相似文献
74.
Bifurcations of nonlinear electron acoustic solitary waves and periodic waves in an unmagnetized quantum plasma with cold and hot electrons and ions has been investigated. The one dimensional quantum hydrodynamic model is used to study electron acoustic waves (EAWs) in quantum plasma. Applying the well known reductive perturbation technique (RPT), we have derived a Korteweg-de Vries (KdV) equation for EAWs in an unmagnetized quantum plasma. By using the bifurcation theory and methods of planar dynamical systems to this KdV equation, we have presented the existence of two types of traveling wave solutions which are solitary wave solutions and periodic traveling wave solutions. Under different parametric conditions, some exact explicit solutions of the above waves are obtained. 相似文献
75.
Kaushik Roy Prasanta Chatterjee S. S. Kausik C. S. Wong 《Astrophysics and Space Science》2014,350(2):599-605
The dust-acoustic shock waves have been theoretically investigated using reductive perturbation technique. An unmagnetized four-component dusty plasma system consisting of nonextensive q-distributed electrons, Boltzmann distributed ions, and negatively as well as positively charged dust particles has been considered. The solution of Burgers equation in planar geometry is numerically analyzed. It has been observed that the nonextensive q-distribution of electrons has a significant role in the formation of shock waves. The relevance of our results to astrophysics as well as laboratory plasmas are briefly discussed. 相似文献
76.
Shreya?KarmakarEmail author Subham?Mukherjee Sanjoy?Sanyal Pulak?Sengupta 《Contributions to Mineralogy and Petrology》2017,172(8):67
The highly calcic anorthosite (An>95) from the Sittampundi Layered Complex (SLC) develops corundum, spinel and sapphirine that are hitherto not reported from any anorthositic rocks in the world. Petrological observations indicate the following sequence of mineral growth: plagioclasematrix → corundum; clinopyroxene → amphibole; corundum + amphibole → plagioclasecorona + spinel; and spinel + corundum → coronitic sapphirine. Phase relations in the CaO–Na2O–Al2O3–SiO2–H2O (CNASH) system suggest that corundum was presumably developed through vapour present incongruent melting of the highly calcic plagioclase during ultra-high temperature (UHT) metamorphism (T ≥ 1000 °C, P ≥ 9 kbar). Topological constraints in parts of the Na2O–CaO–MgO–Al2O3–SiO2–H2O (NCMASH) system suggest that subsequent to the UHT metamorphism, aqueous fluid(s) permeated the rock and the assemblage corundum + amphibole + anorthite + clinozoisite was stabilized during high-pressure (HP) metamorphism (11 ± 2 kbar, 750 ± 50 °C). Constraints of the NCMASH topology and thermodynamic and textural modeling study suggest that coronitic plagioclase and spinel formed at the expense of corundum + amphibole during a steeply decompressive retrograde P–T path (7–8 kbar and 700–800 °C) in an open system. Textural modeling studies combined with chemical potential diagrams (μSiO2–μMgO) in the MASH system support the view that sapphirine also formed from due to silica and Mg metasomatism of the precursor spinel ± corundum, on the steeply decompressive retrograde P–T path, prior to onset of significant cooling of the SLC. Extremely channelized fluid flow and large positive solid volume change of the stoichiometrically balanced sapphirine forming reaction explains the localized growth of sapphirine. 相似文献
77.
Prasanta K. Patro Ujjal K. Borah G. Ashok Babu B. Veeraiah S. V. S. Sarma 《Journal of the Geological Society of India》2017,89(6):711-718
The geochemistry of the mafic xenoliths from Baspa valley of Himachal Pradesh, India has been investigated to characterize their protoliths on the basis of immobile elements, especially trace elements including REE. The mafic xenoliths occur within the Kinnaur Kailash granite (KKG) and their geochemistry show that they have tholeiitic nature with basaltic composition. Compositionally, they range from ‘depleted’ to ‘enriched’ MORB as observed on the binary diagrams of Ti vs V and Zr vs Ti and on ternary diagrams of Zr-Ti-Y and Th-Zr-N. Likewise, they match with various enriched or ‘transitional’ MORB types as evident from their Zr vs Nb binary plot. Their enriched character when compared with N-MORB, E-MORB and OIB rocks on chondrite and primordial mantle normalized plots reveals that it is intermediate to that of E-MORB and OIB. The geochemistry of the rocks suggest that the enriched components are probably derived by melting of a mantle source with E-MORB or OIB rather than due to the crustal contamination. The study carried out emphasize that the mafic xenoliths have developed in rift environment, and that they are not volcanic rocks of island arc related to subduction tectonics. It is visualized that the mafic xenoliths were formed as cumulate rocks from the tholeiitic magmas that were rising to lower crust levels in a rift environment, which at a later stage got entrapped as restitic material in the host Kinnaur Kailash granite formed in a collision environment, and propose a change of regime from rift related to collision environment prior to Palaeozoic period. 相似文献