Torsional vibration of a composite truncated conical bar     

A. K. Mitra  S. K. Chatterjee 《Pure and Applied Geophysics》1971,90(1):30-34

Summary Torsional vibration of a body composed of two conical bars, the upper one being made of non-homogeneous material and the lower of a homogeneous material, by the application of a shearing stress on the upper end has been considered in the problem. It is assumed that the lower end of the composite body is fixed and the lateral surface is free from shearing stress.  相似文献   

Crystal chemical and 57Fe Mössbauer study of chromite from the Nuggihalli schist belt (India)     

D. Lenaz  G. B. Andreozzi  S. Mitra  M. Bidyananda  F. Princivalle 《Mineralogy and Petrology》2004,80(1-2):45-57

Summary In the Nuggihalli schist belt (India), chromite bodies were affected by intense serpentinization followed by weathering. In spite of the strong oxidation of the chromite grains, some unaltered cores were preserved, and they were characterised using electron probe microanalysis, single-crystal X-ray diffraction and low temperature ⁵⁷Fe Mössbauer spectroscopy. Results of such investigations revealed that chromite cores from the Nuggihalli schist belt are effectively not oxidised, and their study revealed that chromite was not affected by greenschist-facies metamorphism. The apparently highly ordered cation distribution of the chromites, which would suggest low equilibration temperature, is just caused by the very high Cr contents, which prevent Mg–Al exchange between T and M sites. Using Fabries (1979) geothermometer a temperature of about 1180°C was retrieved (Mitra and Bidyananda, 2003), which therefore corresponds to the quenched-in igneous equilibrium.  相似文献   

Geomorphological study of sundarban deltaic estuary     

Dipnarayan Ganguly  Anirban Mukhopadhyay  Rahul Krishna Pandey  Debasish Mitra 《Journal of the Indian Society of Remote Sensing》2006,34(4):431-435

Study of landforms in Sundarbans deltaic estuary is necessary in regular basis due to its importance and impact on ecology, climate and economy. Remote sensing has proved as an important tool to study this. Multi-temporal satellite data helps to delineate the various geomorphic classes in different time domain and also provide inputs to study the coastal erosion and accretion. Finer spatial and better temporal resolution will be an added adventure for this kind of study.  相似文献   

Photogeologic mapping north of Khairwara,Udaipur district,Rajasthan     

Arupkumar Mitra  Supriya Brahma 《Journal of the Indian Society of Remote Sensing》1988,16(2):27-31

Photogeologic mapping of a sample area defined by latitudes 24° O to 6′N and longitudes 73° 30′ to 45′ E from a part of the Aravalli orogen, illustrates the advantages, as well as limitations, of photo-interpretation (PI) in terrains comprsing, highly deformed ancient rock formations. Discrimination between psammitic and pelitic metasediments is easy, using micro-relief and drainage parameters as PI elements; but that between pelites, ultra-basic schists and impure marbles is difficult and less reliable. Trends of foliations, several sets of joints and faults are distinct on the aerial photographs, but complete reconstruction of the superposed fold geometry is not possible. Within the area studied, dominantly pelitic, psammitic and a little clacareous metasediments, intruded by ultra-basics, exhibit a prominent and persistent NNE trend defined by lithologic contacts, bedding and foliations, with steep northwesterly dips. In its central part, bands of psammites within the pelites exhibit a hook shaped fold interference pattern (type 3 of Ramsay, 1967) with the later upright (Fleuty, 1964) fold axial trace trending northwesterly.  相似文献   

Significance of contrast in the early stages of the structural history of the Delhi and the pre-Delhi rock groups in the Proterozoic of Rajasthan, western India     

K. Naha  D.K. Mukhopadhyay  R. Mohanty  S.K. Mitra  T.K. Biswal 《Tectonophysics》1984,105(1-4)

Structures of four generations are decipherable both in the pre-Delhi rocks of central Rajasthan, and in the Delhi rocks of Khetri in northeastern Rajasthan and around Todgarh in central Rajasthan. There is a remarkable identity in the later phases of the deformational history of the two groups, with gravity-induced structures followed by conjugate folds due to longitudinal shortening (N-S in northeastern Rajasthan and NE-SW in central Rajasthan). The earlier stages of the structural history of the two groups are, however, significantly different. The E-W-trending reclined folds of the first generation in the pre-Delhi rocks are absent in the Delhi rocks throughout Rajasthan. The NNE- to NE-trending folds of the second generation in the pre-Delhi groups are upright, whereas these structures in the Delhi rocks are of two phases—recumbent folds, followed by coaxial upright folds. The folds of the first and the second phases in the Delhi rocks plunge gently NE or SW where they are not affected by subsequent deformations. But the NE-trending folds in the pre-Delhi rocks show an extreme variation in axial plunge from horizontal to vertical, even where they are unaffected by later movements. Evidence has been adduced to suggest that these differences in the earlier phases of the structural evolution of the two groups are due to an angular unconformity between the Delhi and the pre-Delhi rocks.  相似文献   

Chromitites of komatiitic affinity from the Archaean Nuggihalli greenstone belt in South India     

M. Bidyananda  S. Mitra 《Mineralogy and Petrology》2005,84(3-4):169-187

Summary Mineral chemistry and petrological data of chromites from chromitite bands in the N–S trending schist belt of Nuggihalli (southern Karnataka, India), belonging to the Dharwar craton of South India, are presented in this paper. Crystal chemical data indicate a komatiitic affinity of the chromitite. P–T calculations of the chromite-hosting peridotites yielded a pressure range of 13 to 28 kbar and temperatures ranging from 775 to 1080 °C; the oxygen fugacity (log fO₂) varies from +0.5 to +1.6 above the QFM buffer. The P, T and fO₂ data indicate that Nuggihalli chromitites crystallized in an environment akin to the upper mantle. The studied samples also show partial resetting; the lower temperatures ranging from 515 to 680 °C are ascribed to subsequent metamorphism of the area.  相似文献   

Laboratory studies about the interaction of ammonia with ice crystals at temperatures between 0 and −20°C     

Ines Hoog  Subir K. Mitra  Karoline Diehl  Stephan Borrmann 《Journal of Atmospheric Chemistry》2007,57(1):73-84

In laboratory experiments the interactions of ammonia with ice crystals were studied within the temperature range between 0 and −20°C. In a first series of experiments dendritic ice crystals were grown from water vapor in presence of ammonia gas in various concentrations between 4 and 400 ppbv. In a second series of experiments pure ice crystals were exposed to a humidified ammonia–air mixture inside a horizontal flow tube. The influence of temperature, ammonia gas concentration (0.6, 1.5, and 10 ppmv), exposure time, and the presence of impurities such as sulfate on the ammonia uptake by the ice surface was investigated by determining the ammonium content in the melt water of the ice crystals by ion chromatography. During the growth of ice crystals significant amounts of ammonia (around 200 μg/l) were taken up even at small gas concentrations. In contrast, even at high gas concentrations the uptake of ammonia by non-growing ice crystals was lower by approximately one order of magnitude. The presence of sulfate on the ice surface affected an enhanced uptake of ammonia by a factor of 5–10. A model is presented which describes the uptake of ammonia by ice considering the chemical processes occurring in the ice surface layer and simultaneous diffusion of ammonia into bulk ice. Even the increased uptake of ammonia by growing ice is rather small compared to the uptake by water droplets; thus, the major process for scavenging of ammonia from the atmosphere via the ice phase might not be the direct uptake by ice crystals but the riming involving super-cooled droplets containing ammonia.  相似文献   

SCL — A new nomenclature to denote the effect of a solar flare on longwave field intensity     

S. N. Mitra 《Solar physics》1970,15(1):249-252

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Filling factors and scale heights of the diffuse ionized gas in the Milky Way     

E. M. Berkhuijsen  D. Mitra  P. Müller 《Astronomische Nachrichten》2006,327(1):82-96

The combination of dispersion measures of pulsars, distances from the model of Cordes & Lazio (2002) and emission measures from the WHAM survey enabled a statistical study of electron densities and filling factors of the diffuse ionized gas (DIG) in the Milky Way. The emission measures were corrected for absorption and contributions from beyond the pulsar distance. For a sample of 157 pulsars at |b | > 5. and 60° < ℓ < 360°, located in mainly interarm regions within about 3 kpc from the Sun, we find that: (1) The average volume filling factor along the line of sight and the mean density in ionized clouds are inversely correlated: ( ) = (0.0184 ± 0.0011) ^{–1.07 ± 0.03} for the ranges 0.03 < < 2 cm^–3 and 0.8 > > 0.01. This relationship is very tight. The inverse correlation of and causes the well‐known constancy of the average electron density along the line of sight. As (z ) increases with distance from the Galactic plane |z |, the average size of the ionized clouds increases with |z |. (2) For |z| < 0.9 kpc the local density in clouds n _c(z ) and local filling factor f (z ) are inversely correlated because the local electron density n _e(z ) = f (z )n _c(z ) is constant. We suggest that f (z ) reaches a maximum value of >0.3 near |z | = 0.9 kpc, whereas n _c(z ) continues to decrease to higher |z |, thus causing the observed flattening in the distribution of dispersion measures perpendicular to the Galactic plane above this height. (3) For |z | < 0.9 kpc the local distributions n _c(z ), f (z ) and (z ) have the same scale height which is in the range 250 < h ≲ 500 pc. (4) The average degree of ionization of the warm atomic gas (z ) increases towards higher |z | similarly to (z ). Towards |z | = 1 kpc, (z ) = 0.24 ± 0.05 and (z ) = 0.24 ± 0.02. Near |z | = 1 kpc most of the warm, atomic hydrogen is ionized. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

An improved practical approach for estimating catchment-scale response functions through wavelet analysis     

Ravindra Dwivedi  Christopher Eastoe  John F. Knowles  Lejon Hamann  Thomas Meixner  Paul A. “Ty” Ferre  Christopher Castro  William E. Wright  Guo-Yue Niu  Rebecca Minor  Greg A. Barron-Gafford  Nathan Abramson  Bhaskar Mitra  Shirley A. Papuga  Michael Stanley  Jon Chorover 《水文研究》2021,35(3):e14082

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