Autoencoder-based identification of predictors of Indian monsoon     

Moumita Saha  Pabitra Mitra  Ravi S. Nanjundiah 《Meteorology and Atmospheric Physics》2016,128(5):613-628

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Exact solution of the source problem for a finite threedimensional source     

M. Mitra 《Pure and Applied Geophysics》1963,56(1):31-38

Summary In this note the surface displacement for an elastic half-space due to a finite cylindrical source has been calculated in exact terms. The source consists of outward body forces acting on the surface of the right circular cylinder, one end of which is parallel to the free surface of the half-space.  相似文献   

Relative Radiometric Normalisation - performance testing of selected techniques and impact analysis on vegetation and water bodies     

Abhisek Santra  Shreyashi Santra Mitra  Debashis Mitra  Ashis Sarkar 《国际地球制图》2019,34(1):98-113

In this paper, six image-based Relative Radiometric Normalization (RRN) techniques were applied to normalize the bi-temporal Landsat 5 TM data-set. RRN techniques do not require any atmospheric and ground information at the time of image acquisition. The target image for the year 2009 was normalized in such a way that it resembled the atmospheric and sensor conditions similar to those under which the reference image of the same season for the year 1990 was acquired. Among the selected methods applied, it was found that the Iteratively Reweighted Multivariate Alteration Detection (IR-MAD) method performed better, based on the error statistic. The IR-MAD technique was found to be advantageous as it identified a large set of true time-invariant pixels automatically from the change background using iterative canonical component analysis. The technique also stretches the values of Normalized Difference Vegetation Index and Normalized Difference Water Index and may help to distinguish different vegetation and water bodies better.  相似文献   

Capillary hysteresis and gravity segregation in two phase flow through porous media     

Mitra  K.  van Duijn  C. J. 《Computational Geosciences》2022,26(1):101-114

We study the gravity driven flow of two fluid phases in a one dimensional homogeneous porous column when history dependence of the pressure difference between the phases (capillary pressure) is taken into account. In the hyperbolic limit, solutions of such systems satisfy the Buckley-Leverett equation with a non-monotone flux function. However, solutions for the hysteretic case do not converge to the classical solutions in the hyperbolic limit in a wide range of situations. In particular, with Riemann data as initial condition, stationary shocks become possible in addition to classical components such as shocks, rarefaction waves and constant states. We derive an admissibility criterion for the stationary shocks and outline all admissible shocks. Depending on the capillary pressure functions, flux function and the Riemann data, two cases are identified a priori for which the solution consists of a stationary shock. In the first case, the shock remains at the point where the initial condition is discontinuous. In the second case, the solution is frozen in time in at least one semi-infinite half. The predictions are verified using numerical results.

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Homogeneous freezing of single sulfuric and nitric acid solution drops levitated in an acoustic trap     

Karoline Diehl  Matthias Ettner-Mahl  Anke Hannemann  Subir K. Mitra   《Atmospheric Research》2009,94(2):356-361

The freezing temperatures of single supercooled drops of binary and ternary sulfuric and nitric acid solutions were measured while varying the acid concentration. An acoustic levitator was used which allows to freely suspend single solution drops in air without electrical charges thereby avoiding any electrical influences which may affect the freezing process. The drops of typically 500 µm in radius were monitored by a video camera during cooling cycles down to − 85 °C to simulate the upper tropospheric and stratospheric temperature range. The present data confirm that liquid solution droplets can be supercooled far below the equilibrium melting point by approximately 35 °C. They follow the general trend of the expected freezing temperatures for homogeneous ice nucleation.  相似文献   

Study of drainage pattern of Raniganj Coalfield (Burdwan district) as observed on Landsat-TM/IRS LISS II imagery   总被引：1，自引：0，他引：1  

V. K. Srtvastava  D. Mitra 《Journal of the Indian Society of Remote Sensing》1995,23(4):225-235

Drainage pattern of Raniganj Coalfield basin has been mapped as observed on false colour composites of Landsat TM and IRS-LISS II imagery and their characteristics have been interpreted in terms of basin morphology, surface materials and underlying rock types. The drainage system of the region is composed of 3 perennial rivers with 15 ephemeral nalas and jhors which as a whole flows on recent peneplain basin. Although, on an average, nalas and jhors of the area have smaller stream length and with smaller basinal area but they hold sufficient amount of water during monsoon and therefore by effective planning and management, surface water resources could be enhanced in the region.  相似文献   

Impact of Farakka barrage on the hydrology and fishery of Hoogly estuary     

M. Sinha  M. K. Mukhopadhyay  P. M. Mitra  M. M. Bagchi  H. C. Karamkar 《Estuaries and Coasts》1996,19(3):710-722

Construction of the Farakka barrage on the Ganga River in April 1975 to augment water supply to the Calcutta port has brought about a significant increase in freshwater discharge in its distributary, the Hoogly estuary. This has naturally resulted in major changes in the ecology of this estuary, causing modifications in the structure of its fishery resources, fishing pattern, and fish production. This paper presents observations on salinity, plankton, bottom biota, fishery resource, and fish production of different zones of the Hooghly estuary during the period 1982–1992. Comparison with similar studies made before and immediately after commissioning of the Farakka barrage (1975–1977) has revealed that the increased freshwater discharge has resulted in considerable decrease in salinity throughout the estuary. The freshwater zone now extends toward the mouth of the estuary. The true estuarine zone has moved seaward and the marine zone has been restricted to the area near the mouth of the estuary. This has effected major changes in plankton dynamics, sharp decline in the fishery of marine and neritic species in the upper estuary, caused a significant increase in catch ofTenualosa ilisha and an over twofold increase in the average annual fish landings from the estuary as a whole. New zonations have been proposed based on the presently, observed salinity values, which are the most significant factor in determining the fishery of any estuary. An interdisciplinary study of the ecology of the new zones is needed to establish their correct biological characteristics.  相似文献   

The disturbance due to periodic surface traction in a semi-infinite medium of varying elasticity and density     

M. Mitra 《Pure and Applied Geophysics》1958,41(1):86-90

Summary In this paper, the shear displacement due to a transverse periodic surface traction on a semi-infinite elastic solid, in which the rigidity and density vary exponentially with the depth has been obtained. The normal modes are calculated for high frequencies and the surface displacement obtained numerically in a particular case for a low frequency.  相似文献   

A quantitative study of deformation mechanisms and finite strain in quartzites     

Shankar Mitra 《Contributions to Mineralogy and Petrology》1976,59(2):203-226

The Weverton quartzites in the Maryland Blue Ridge are deformed by one major period of greenschist-grade deformation. The components of finite strain due to different independent mechanisms have been measured for these rocks. The total strain is split up into two major components: $$\varepsilon ^t = \varepsilon ^p + \varepsilon ^d .$$ The finite natural strain caused by dislocation creep (? ^d ) is measured by a new technique using folded and stretched rutile needles which are good strain markers within the quartz crystals. Pressure solution strain (? ^p ) is measured from the ratio of the area of new crystals and fibers to the whole rock area in principal sections. Grain boundary sliding is a dependent process which accompanies both mechanisms. Pressure solution obeys a linear Newtonian flow law, \(\left| {\dot \gamma _0^p } \right| = A_p \left| {\tau _0 } \right|\) , while dislocation creep obeys a power law of the form \(\left| {\dot \gamma _0^d } \right| = A_d \left| {\tau _0 } \right|^n \) where \(\dot \gamma _0^p ,\dot \gamma _0^d \) are octahedral shear strain rates, τ₀ is the octahedral shear stress and A _p , A _p and n are constants. A direct correlation between finite strain measurements and the operating flow laws can be made. Application of these methods and principles to a few field examples indicates that the rocks obey a flow law partly governed by each mechanism. Any set of physical conditions defines a unique flow law and there is a transition in creep behavior from dominantly Newtonian to a power law with increasing strain rate.  相似文献   

SH-wave propagation in a composite elastic medium     

A. Dutta  M. Mitra 《Pure and Applied Geophysics》1974,112(2):339-351

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