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991.
P. Roy 《Pure and Applied Geophysics》1970,82(1):29-33
Summary The propagation of longitudinal disturbances in a viscoelastic solid of Reiss type subjected to a magnetic field has been obtained in the present note. 相似文献
992.
Ajoy Roy Choudhury 《Pure and Applied Geophysics》1972,97(1):70-75
Summary The present note seeks to investigate the axisymmetric vibration in a transversely isotropic finite cylindrical shell in presence of axial magnetic field by making use of the electromagnetic equations of Maxwell and the equations of elasticity. The frequency with its minimum value is obtained. 相似文献
993.
Eastern North American and Western European paleomagnetic data indicate that, during most of the Upper Paleozoic, these regions and their adjacent continental shelves were parts of a single block situated near the paleoequator. With respect to a stationary paleopole, a north-north-west movement of the block during the Carboniferous can be detected. Comparison with polar displacement relative to other continents indicates that continental drift and possibly a pole displacement of about 15° occurred at that time. The Mesozoic results indicate that the rupture of the block and the opening of the North Atlantic did not follow each other closely in time. A latitudinal displacement of Eastern North America with respect to Western Europe places the time of rupture during Lower or Middle Triassic. A slight separation of the blocks may have occurred at that time. It is suggested that the rupture of the initial block occurred by strike slip with Eastern North America and Western Europe slipping one against the other in a north-south direction (by about 20° in latitude) but without pulling apart by any considerable distance. While this event took place before the Upper Triassic, it is probable that a substantial opening of the North Atlantic did not occur until after the Triassic. It appears that, in Cretaceous time, the longitudinal separation was considerable and that the North Atlantic Ocean was then partially open. Some of the relevant geological features and ocean floor spreading studies are discussed. A rupture by strike-slip in latitude mainly can be supported geologically and a post-Triassic time of opening of the North Atlantic is in agreement with the opening time obtained from certain interpretations of magnetic anomaly lineations. 相似文献
994.
Ajoy Roy Choudhury 《Pure and Applied Geophysics》1973,104(1):453-459
Summary The dynamical response due to the interaction of viscoelastic field and magnetic field in a layer ofVito Volterra's hereditary model is analysed by making use of Laplace-transform. 相似文献
995.
996.
Amiya Bhusan Roy 《Pure and Applied Geophysics》1964,59(1):21-26
Summary The disturbances in a viscoelastic medium by a twist of finite duration applied on the inner surface of a spherical cavity inside the medium have been considered. 相似文献
997.
Part I: Chemical and structural effects of cation-exchange
Attempts were made to prepare, by appropriate exchange methods, homoionic samples of phillipsite, gismondite, harmotome, chabazite
and gmelinite containing Ba, Ca, K, Na or Li-ions. Powdered natural samples were used as starting material. All samples were
analysed chemically before and after the cation exchange. The results of the analyses demonstrated clearly that the „exchange
capacity“ depends on the method used, the structure of the zeolite and the nature of the cation involved in the exchange.
The analyses also disclosed the important fact that the ratio in Mole % of the sum of exchangeable cations: Al2O3 of the natural and of the exchanged samples is generally <1, and can be as low as 0.74. Examples are presented where cation
exchange results in a substantial change in the framework structure.
Part II: Dehydration behavior and structural changes at elevated temperatures
Samples of the natural zeolites mentioned above, and of some of their cation exchange products were dehydrated in air of controlled
humidity up to 600° C. The slopes of the weight loss curves of chabazite and gmelinite are continuous, whereas those of phillipsite,
gismondite, and harmotome show a discontinuity between 90–190° C, indicating the existence of two discrete hydrated phases
for each of these zeolites. High temperature x-ray studies of powdered samples confirmed this result. The high temperature
hydrates of phillipsite, gismondite, and harmotome persist reversibly up to approximately 230° C. At higher temperatures,
new probably anhydrous phases form. Gmelinite, at 240° C, transforms irreversibly to anhydrous gmelinite which is stable up
to >700° C. The transition was studied by single crystal techniques. The chabazite structure remains intact up to >700° C.
The absolute water content and the dehydration behavoir of the zeolites investigated are primarily dependent on the nature
of the exchange cation. The structural changes at elevated temperatures are determined by the silica alumina framework.
Part III: Hydrothermal stability* and interconversions
The stability of phillipsite, gismondite, harmotome, chabazite, gmelinite, their exchange products, and of the synthetic Linde
zeolites Faujasite and Type A was studied in the temperature range between 150° and 350° C at a constant pressure of 1000
atm of H2O. Between 180° and 260° C all examined Sodium and Calcium zeolites were metastable with respect to analcite (wairakite**).
Phillipsite and sodium-rich zeolites generally converted to analcite (wairakite) directly. Caex-chabazite and Caex-gmelinite formed phillipsite, whereas Ca-gismondite and Ca-Type A formed natrolite as intermediate phases. Li-gmelinite converted
to bikitaite***. (This represents the first successful preparation of natrolite and bikitaite. Attempts starting from gels
or glasses have been unsuccessful so far.) Ba-gmelinite converted to harmotome at 250° C. This transformation was studied
microscopically and by single crystal x-ray techniques.
The transformations that take place on hydrothermal treatment as well as on low temperature cation exchange of zeolites (see
Part I) indicate that, unlike the conditions prevailing in clays, the type of cation and the ratio of cations in the exchange
positions have an important influence on the structure of the silicaalumina-oxygen framework. This explains two phenomena:
The lack of solid solution between two potential end members of a solid solution series (for instance phillipsite-gismondite),
and the large number of different zeolites in nature, where a great variety in the ratios of available alkali and alkaline
earths ions must be expected.
Any classification of zeolites becomes still more difficult in view of the fact that conversions among different groups (chabazite
→ phillipsite) and different structures (three-dimensional framework → fibre) take place relatively easily.
Contribution No. 59–92, College of Mineral Industries, The Pennsylvania State University, University Park, Pennsylvania. 相似文献
998.
Fugacity and free-energy values have been calculated from p-v-t data for CO2 in the temperature range from 50 to 1000°C, at pressures from 25 to 1400 bars. 相似文献
999.
Somnath Dasgupta Pulak Sengupta M. Fukuoka Supriya Roy 《Contributions to Mineralogy and Petrology》1993,114(4):533-538
Mn silicate-carbonate rocks at Parseoni occur as conformable lenses within metapelites and calc-silicate rocks of the Precambrian Sausar Group, India. The host rocks are estimated to have been metamorphosed at uppermost P-T conditions of 500–550°C and 3–4 kbar. The Mn-rich rocks contain appreciable Fe, reflected in the occurrence of magnetite(1) (MnO 1%), magnetite(2) (MnO 15%) and magnetite(3) (MnO 10%). Two contrasting associations of pyroxmangite, with and without tephroite, developed in the Mn silicate-carbonate rocks under isothermal-isobaric conditions. The former assemblage formed in relatively Fe-rich bulk compositions and equilibrated with a metamorphic fluid having a low X
CO
2 (<0.2), and the latter equilibrated with a CO2-rich fluid. Rhodochrosite+magnetite(1)+quartz protoliths produced the observed mineral assemblages on metamorphism. Partitioning of major elements between coexisting phases is somewhat variable. Fe shows preference for tephroite over pyroxmangite at the ambient physical conditions of metamorphism. Oxygen fugacity during metamorphism was monitored at or near the QFM buffer in tephroite bearing domains, and the fluid composition was buffered by mineral reactions in respective domains. As compared to other metamorphosed Mn deposits of the Sausar Group, the Mn silicate-carbonate rocks at Parseoni were, therefore, metamorphosed at much lower f
O
2 through complex mineral-fluid interactions. 相似文献
1000.