A comparative study of the sunrise and sunset effects on the integrated field intensity of VLF atmospherics     

A. B. Bhattacharya  B. K. Datta  R. Bhattacharya 《Annales Geophysicae》1995,13(9):976-980

A comparative study is made of the stepped structure of atmospherics during sunrise and sunset hours at three harmonically related frequencies in the VLF band, observed at the coast of the Bay of Bengal. The occurrences of the steps, their duration, time sequence and amplitudes are critically examined. Our analysis reveals that the start times of the third and second steps of the sunrise effect are always before ground sunrise, while the start of the main step is distributed on both sides of it. During sunset hours, the onset time of the main step is before the local ground sunset, but for the second and third steps, the onset times are after that. The results are interpreted by considering the multi-hop propagation as well as the distributed noise sources surrounding the observing site.  相似文献   

Genetic reinterpretation of crystallographicintergrowths of jacobsite andhausmannite from natural assemblages     

Dr. Somnath Dasgupta  P. K. Bhattacharya  G. Chattopadhyay  M. Fukuoka  H. Banerjee  Supriya Roy 《Mineralogy and Petrology》1987,37(2):109-116

Summary Crystallographic intergrowths of jacobsite and hausmannite (vredenburgite) occur in association with braunite in the Precambrian Sausar Group of rocks, India, that were metamorphosed under 600-700°C and P 6 kb. Quartz, hematite, rhodochrosite and a later hausmannite may occasionally occur as minor associates. Detailed characterization of the intergrown phases reveals that hausmannite lamellae, oriented in 4 or 5 crystallographic directions in the jacobsite host, show a wide variation in thickness and tapered intersections at low angles. The lamellae may be locally deformed. Analytical data reveal that the composition of natural hausmannite and jacobsite in the intergrowths cannot be approximated within the system Fe₃O₄ -Mn₃O₄, as has been conventionally done. These really belong to the Fe₂O₃-Mn₃O₄ subsystem. In the two phase intergrowths, hausmannite is depleted and the jacobsite is enriched in Fe in higher grade rocks. Mineral associations and petrographic considerations suggest that the jacobsite-hausmannite intergrowth originated through prograde decarbonation-oxidation reactions of a carbonatic precursor in an unbuffered X CO₂ situation, but f O₂ was held between hematite-magnetite and bixbyite-hausmannite buffers at the ambient physical conditions of metamorphism. Subsequent oxidation yielded a strong oxygenbuffering assemblage jacobsite, hausmannite, braunite, hematite and quartz. This study negates the commonly held idea that hausmannite jacobsite crystallographic intergrowth (vredenburgite) originates through unmixing of a high ([ldvredenburgite) originates through unmixing of a high temperature spinel_ss temperature spinel_ss during cooling.

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Genetische Reinterpretation der kristallographischen Verwachsungen von Jakobsit und Hausmannit in natürlichen Vorkommen

Zusammenfassung Kristallographische Verwachsungen von Jakobsit und Hausmannit (Vredenburgit) treten in Verbindung mit Braunit in Gesteinen der präkambrischen Sausargruppe in Indien auf. Die Gesteine wurden bei Drucken von ca. 6 kbar und Termperaturen von 600–700°C metamorphosiert. Quarz, Hämatit, Rhodochrosit, und Hausmannit als Spätphase treten gelegentlich als untergeordnete Gemengteile auf. Hausmannit-Lamellen, die in vier oder fünf kristallographischen Richtungen in Jakobsit orientiert sind, haben sehr unterschiedliche Durchmesser und bilden versetzte Zwickel in kleinem Winkel mit dem Jakobsit. Die Lamellen können lokal deformiert sein. Analytische Daten zeigen, daß die Zusammensetzung von natürlichem Hausmannit und Jakobsit in Verwachsungen nicht, wie bisher angenommen, in dem System Fe₃O₄-Mn₃O₄ dargestellt werden kann. Diese Verwachsungen gehören vielmehr in das Fe₂O₃-Mn₃O₄ System. In höher-gradigen metamorphen Gesteinen ist Fe in zwei-phasigen Verwachsungen im Hausmannit ab- und im Jakobsit angereichert. Die Mineralzusammensetzung und petrographische Gesichtspunkte lassen darauf schließen, daß die Jakobsit/Hausmannit Verwachsung durch prograde Dekarbonatisierung/Oxydationsreaktion eines karbonatischen Vorläufers in einem nicht gepufferten X CO₂ Milieu entstanden ist. F O₂ wurde durch Hämatit-Magnetit und Bixbyit-Hausmannit Puffer unter den gegebenen physikalischen Bedingungen der Metamorphose stabil gehalten. Eine nachfolgende Oxydation führte zu einer starken Sauerstoff-puffernden Assoziation von Jakobsit, Hausmannit, Braunit, Hämatit und Quarz. Diese Untersuchungen widerlegen die allgemein verbreitete Ansicht, daß die kristallographische Verwachsung von Hausmannit und Jakobsit (Vredenburgit) durch Entmischung eines Hochtemperatur-Spinells während der Abkühlung entstanden ist.

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With 1 figure  相似文献   

landslide due to mass sinking phenomenon: Sunil-Joshimath of U.P. Himalaya example     

A. Bhattacharya  D. K. Jugran 《Journal of the Indian Society of Remote Sensing》1982,10(1):53-55

Mass sinking associated with soil creep and debris displacement is mainly responsible for landslide in Sunil area of Joshimath hill complex. Seepage plays the important role in soil subsidence. The area representing moderate to high relief denudational hills, shows rarely any insitu rock exposures. Gneissic boulders are embedded in loose sandy soil where due to presence of many springs excess seepage occurs, causing a soil creep and displacement of the bou.ders giving rise to local sinking.  相似文献   

Geologic and geomorphic controls in land use patterns — examples using remote sensing techniques     

A. Bhattacharya 《Journal of the Indian Society of Remote Sensing》1983,11(3):57-64

Land use on earth’s landscape primarily indicates the degree of human activity which in turn reflects the man’s life style. Though land use is controlled by several factors like soil, hydrologic, climatic, socio-economic and political yet geology and gecmorphology play an important role. The basic lanscape formation depends mainly on the inherent lithology and sturcture. Certain landforms in the present landscape are such that they are suitable to a particular land use, and the human being from the very beginning without knowing this natural relationship between the landform and landuse, have been using that part of land for that particular use only. Remote sensing techniques are used effectively to map the landforms, to find out the land use pattern and to delineate the lithology and structure. Some examples from east coast deltaic plains and sedimentary terrain of Tripura state have been given here to show the influence of geology and geomorphology on broad land use pattern.  相似文献   

Analysis of a vertical dike,infinitely deep,striking north by fourier transform     

Bireswar Bhattacharya 《Pure and Applied Geophysics》1971,89(1):134-138

Summary The present work deals with the analysis of the frequency spectrum of a vertical magnetic dike like body, infinitely deep, striking north to determine its width and depth from the surface. Fourier transform of the functional representative of the theoretical magnetic anomaly for such a body has been obtained. By framing amplitude response curves, the parameters were estimated.  相似文献   

Hydraulic Effects of Shales in Fluvial-Deltaic Deposits: Ground-Penetrating Radar, Outcrop Observations, Geostatistics, and Three-Dimensional Flow Modeling for the Ferron Sandstone, Utah   总被引：1，自引：0，他引：1  

Djuro Novakovic  Christopher D. White  Rucsandra M. Corbeanu  William S. Hammon III  Janok P. Bhattacharya  George A. McMechan 《Mathematical Geology》2002,34(7):857-893

Ground-penetrating radar (GPR) surveys, outcrop measurements, and cores provide a high-resolution 3D geologic model to investigate the hydraulic effects of shales in marine-influenced lower delta-plain distributary channel deposits within the Cretaceous-age Ferron Sandstone at Corbula Gulch in central Utah, USA. Shale statistics are computed from outcrop observations. Although slight anisotropy was observed in mean length and variogram ranges parallel and perpendicular to pale of low , the anisotropy is not statistically significant and the estimated mean length is 5.4 m. Truncated Gaussian simulation was used to create maps of shales that are placed on variably dipping stratigraphic surfaces interpreted from high-resolution 3D GPR surveys, outcrop interpretations, and boreholes. Sandstone permeability is estimated from radar responses calibrated to permeability measurements from core samples. Experimentally designed flow simulations examine the effects of variogram range, shale coverage fraction, and trends in shale coverage on predicted upscaled permeability, breakthrough time, and sweep efficiency. Approximately 1500 flow simulations examine three different geologic models, flow in the 3 coordinate directions, 16 geostatistical parameter combinations, and 10 realizations for each model. ANOVA and response models computed from the flow simulations demonstrate that shales decrease sweep, recovery, and permeability, especially in the vertical direction. The effect on horizontal flow is smaller. Flow predictions for ideal tracer displacements at Corbula Gulch are sensitive to shale-coverage fraction, but are relatively insensitive to twofold variations in variogram range or to vertical trends in shale coverage. Although the hydraulic effects of shale are statistically significant, the changes in flow responses rarely exceed 20%. As a result, it may be reasonable to use simple models when incorporating analogous shales into models of reservoirs or aquifers.  相似文献   

Palaeomonsoon and palaeoproductivity records of δ18O, δ{13}C and CaCO3 variations in the northern Indian Ocean sedimentsC and CaCO3 variations in the northern Indian Ocean sediments     

A. Sarkar  R. Ramesh  S. K. Bhattacharya  N. B. Price 《Journal of Earth System Science》2000,109(1):157-169

δ¹⁸ O and δ¹³C of G.sacculifer have been measured in five cores from the northern Indian Ocean. In addition, high resolution analysis (1 to 2 cm) was performed on one core (SK-20-185) for both δ¹⁸O and gd¹³C in five species of planktonic foraminifera. CaCO₃ variation was measured in two cores. The results, presented here, show that

–	• the summer monsoon was weaker during 18 ka and was stronger during 9 ka, relative to modern conditions;
–	• δ13C variations are consistent with independent evidence that shows that during the last glacial maximum (LGM; 18 ka) the upwelling was reduced while during 9 ka it was vigorous;
–	• calculation of CaCO3 flux shows that the LGM was characterized by low biogenic productivity in the Arabian Sea while during the Holocene productivity increased by ∼65%, as a direct consequence of the changes in upwelling. Similar changes (of lesser magnitude) are also seen in the equatorial Indian Ocean. The amount of terrigenous input into the Arabian Sea doubled during LGM possibly due to the higher erosion rate along the west coast.
–	• δ18O values indicate that the Arabian Sea was saltier by 1 to 2%o during LGM. The northern part was dominated by evaporation while in the equatorial part there was an increased precipitation.

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Implications of trace fossil assemblages from Late Paleozoic Glaciomarine Talchir Formation, Raniganj Basin, India     

Biplab Bhattacharya  H.N. Bhattacharya   《Gondwana Research》2007,12(4):509-524

The trace fossil assemblages of the ice-marginal shallow marine sediments of the Talchir Formation (Permo-Carboniferous), Raniganj Basin, India, record the adverse effect of extreme climatic conditions on biota. The glaciomarine Talchir succession starts with glacial sediments near the base and gradually passes to storm-laid shallow marine sediments up-section. The fine-grained storm sediments host abundant trace fossils. Although the studied ichnites characteristically show marginal marine affinity, the ichnodiversity and bioturbation intensity suggest a lower than normal shallow marine trace fossil population. Further, endobenthic annelids, worms and crustaceans are identified as dominant trace-makers.

Sediment reworking near the ice-grounding line, extremely cold climate, high-energy storm sedimentation and anomalous water chemistry hindered organic colonization during the early phases of Talchir sedimentation. Later, climatic amelioration ushered in a favourable ambience for the benthic community to colonize within or beyond the storm weather wave-base in the outer shoreface–shelf environment. Fluctuating storm energy dominantly controlled the availability and influence of other environmental stimuli in the environment, and thus, governed the distribution, abundance and association of the studied ichnites. However, impoverished ichnodiversity, sporadic distribution of the traces, overall smaller burrow dimensions, absence of body fossils, dominance of worms and annelids as trace-makers all indicate a stressed environmental condition, induced by cold climate and lowered marine salinity due to influx of glacier melt-out freshwater during climatic amelioration, in the Permo-Carboniferous ice-marginal sea.  相似文献   

Hydromorphology of a part of Azamgarh and Ghazipur districts,Uttar Pradesh     

Asis Bhattacharya  H. R. Mankhand 《Journal of the Indian Society of Remote Sensing》1979,7(2):1-10

Hydrogeological studies in the Quaternary alluvial plain of a part of Azamgarh and Ghazipur districts, using air photos on scale 1:60,000 indicate the presence of five hydromorphic units namely, Alluvial upland, older alluvial plain of Mangat-Besu, older flood plain of Ganga—Gomti, youngest terrace of Ganga—Gomti and present flood plain of Ganga-Gomti. From the groundwater point of view older flood plain of Ganga—Gomti is the most promising hydromorphic unit. Abandoned channel of river Ganga offers favourable site for deep groundwater exploration with high potentiality. Chemical quality of shallow and deep aquifers is suitable for irrigation and other purposes.  相似文献   

The role of multispectral imagery in elucidation of recent channel pattern changes in middle ganga plain     

S. K. Pal  A. K. Bhattacharya 《Journal of the Indian Society of Remote Sensing》1979,7(1):11-20

The mapability of Landsat images has opened up a new potentiality for study of channel pattern changes which was earlier not so easy due to nonavailability of suitable evidences at different timespans. Middle Ganga plain covering largely the northern part of Bihar and parts of eastern Uttar Pradesh is in a slate of perpetual flux due to large scale channel migration and avulsion resulting in devastating floods. Mosaic of three Landsat images has helped to study the channel changes which have occurred since 1935. The course of the river Ganga has beeh digitised along a basal line and two dimensional coordinates are taken at as many as more than fifty sample points for studying the magnitude and direction of channel changes during 1935–1975 period. The analysis shows that the main multiple channel river Ganga is under the huge hydrostatic thrust to be shifted towards south of its basin annually at a very high rate of 100 Meter per year all along the course except at its upstream near Ghazipur and at Monghyr where the shifting is towards north. The northward bend at Monghyr may be due to the presence of the Precambrian outliers here. For the multi-and single channelld tributaries of Ganga in channel behaviour is mainly in three directions—the lower water channels in the floodplain of Ganga are shifting to the south in conformity with that of their parent stream, the tributaries in Gogra-Gandak doab are shifting towards east but the shifting of the Kosi-Mahananda group of tributaries in the eastern part of the basin is towards west These channel pattern changes thus known at the interregional scale from the Landsat images may further be integrated with the study in hydrogeomorphology and their pertinent environmental impact.  相似文献