Rotation and strain of linear and planar structures in three-dimensional progressive deformation     

Hans Ramberg  Subir Kumar Ghosh 《Tectonophysics》1977,40(3-4):309-337

Rotation and progressive strain have been studied for a sheet embedded in a matrix which undergoes rotational three-dimensional strain under constant volume conditions. The mathematics gives explicit information on the following features:

1. (1) The length and position (relative to a defined coordinate system) of the principal axes of the strain ellipsoid at any stage of the progressive deformation.

2. (2) The position and length of the principal axes in any plane intersecting the strain ellipsoid, also at any stage of the deformation.

3. (3) The position and length of passive markers which initially coincided with the principal axes in an intersecting plane. This is of consequence for the distinction between passively rotating structures and actively forming structures.

4. (4) The shear strain parallel to an intersecting plane or sheet, as indicated by the angular difference between the normal to an intersecting plane at any time and the marker at the same time which initially, however, was parallel to the normal. This layer-parallel shear causes boudins to rotate and the axial plane of buckles to tilt.

The relationships have been expressed quantitatively in the bulk of the paper and illustrated in diagrams. The analysis presented is basic for the study of the deformational behavior of competent sheets of rocks embedded in less competent ones.  相似文献   

Patterns of deformed early lineations over later folds formed by buckling and flattening     

S.K Ghosh  A Chatterjee 《Journal of Structural Geology》1985,7(6):651-666

The patterns of deformed early lineations (L₁) over later folds (F₂) can be classified into several morphological types depending on the nature of variation of L₁ F₂ over the folds. The field relations indicate that the folds under consideration are neither shear folds nor parallel folds modified by flattening. The lineation patterns are therefore interpreted in terms of an empirical model of simultaneous buckling and flattening in which it is assumed that (i) the central surface of the folded layer remains a sine curve in transverse profile, (ii) the ratio of rates of buckle shortening to homogeneous strain is proportional to sin 2a, with a as the dip angle and (iii) the progressive deformation is coaxial with the Z-axis of bulk strain parallel to the planar segments of the early folds. The model gives an insight into the relative importance of different physical factors which control the development of dissimilar lineation patterns. Not all lineation patterns are explicable by this simplified model. Thus complex patterns with variable L₁ F₂ along the fold axis may develop by a progressive rotation of the geometrically defined fold hinge through successive material lines. The theoretical results have been applied to interpret the lineation patterns in Central Rajasthan, India. It is concluded that L₁ was initially very close to the E-ESE trending subhorizontal Z-axis of bulk deformation during F₂-folding and that the X-axis was subhorizontal or gently plunging with a N-NNE trend.  相似文献   

Unsteady flow of a viscoelastic Maxwell fluid in a channel bounded by two concentric circular arcs under a radial magnetic field     

Arun Kumar Ghosh 《Pure and Applied Geophysics》1974,112(1):162-171

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Effect of couple-stresses on the propagation of waves in an elastic layer     

P. R. Sengupta  Bhabanicharan Ghosh 《Pure and Applied Geophysics》1974,112(2):331-338

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Retrieval of vertical wind profiles during monsoon from satellite observed winds over the Indian ocean using complex EOF analysis     

C. M. Kishtawal  Sujit Basu  S. Karthikeyan 《Journal of Earth System Science》2001,110(1):77-86

The aim of this paper is to study the feasibility of deriving vertical wind profiles from current satellite observations. With this aim, we carried out complex empirical orthogonal function (CEOF) analysis of a large number of radiosonde observations of wind profiles over the Indian Ocean during the monsoon months. It has been found that the first two CEOFs explain 67% of the total variance in wind fields. While the first principal component is well correlated with the winds at 850 mb (r = 0:80), the second one is highly correlated with winds at 200 mb (r = 0:89). This analysis formed the basis of a retrieval algorithm which ensures the retrieval of vertical profiles of winds using satellite tracked cloud motion vector winds. Under the assumption that accurate measurements of wind are available at the above mentioned levels, the r.m.s. error of retrieval of each component of wind is estimated to range between 2 ms^-1 and 6 ms^-1 at different levels, which is much less than the natural variance of winds at these levels. For a better visualization of retrieval, we have provided retrieved and true wind profiles side by side for four typical synoptic conditions during the monsoon season.  相似文献   

Numerical experiment with modelled return echo of a satellite altimeter from a rough ocean surface and a simple iterative algorithm for the estimation of significant wave height     

Sujit Basu  P. C. Pandey 《Journal of Earth System Science》1991,100(2):155-163

We have simulated the return echo of a satellite altimeter from a rough ocean surface using an analytical formula and have studied its sensitivity with respect to various oceanic and altimeter parameters. Our numerical experiment shows that for normally observed significant wave heights (SWH) the effect of off-nadir angle (ONA) up to 0.5° on the leading edge is not severe. Also, small surface roughness skewness seems to have little effect on the overall shape of the echo. Newton’s iterative scheme has been used to retrieve SWH from the mean return waveform without noise and with additive Gaussian noise typical of Seasat and Geosat altimeters. It has been observed that SWH can be retrieved in the presence of noise with an accuracy of ±0.6 m for ONA less than 0.5°. For higher ONA, accurate retrieval requires the use of precomputed look-up table along with our scheme.  相似文献   

Estimation of critical convergence and rock load in coal mine roadways — an approach based on rock mass rating     

C. N. Ghosh  A. K. Ghose 《Geotechnical and Geological Engineering》1992,10(3):185-202

Summary Based on field instrumentation in eight different coal mines representing varying depths and strata conditions, a relation for obtaining the critical convergence value has been established. In development heading for bord and pillar workings this relation can be used successfully to control the premature collapse of the roof. An empirical relation for rock load has been established. This can be utilized for optimum design of support system. The roofs have been categorized as stable, short-term stable and unstable. Proper attention should be provided for an unstable roof and the support design is to be changed before the convergence reaches the critical value.  相似文献   

The variational technique of data assimilation using adjoint equations in a shallow water model     

Sujit Basu  V Subramanian  P C Pandey 《Journal of Earth System Science》1993,102(4):521-536

The variational technique of data assimilation using adjoint equations has been illustrated using a nonlinear oceanographic shallow water model. The technique consists of minimizing a cost function representing the misfit between the model and the data subject to the model equations acting as constraints. The problem has been transformed into an unconstrained one by the use of Lagrange multipliers. Particular emphasis has been laid on finite difference formulation of the algorithm. Several numerical experiments have been conducted using simulated data obtained from a control run of the model. Implications of this technique for assimilating asynoptic satellite altimeter data into ocean models have been discussed.  相似文献   

Reconnaissance report on geotechnical effects and structural damage caused by the 3 January 2017 Tripura earthquake,India     

Anbazhagan  P.  Mog  Kunjari  Rao  K. S. Nanjunda  Prabhu  N. Siddharth  Agarwal  Ayush  Reddy  G. R.  Ghosh  Sima  Deb  Malay Kr.  Baruah  Saurabh  Das  Sarat Kr. 《Natural Hazards》2019,98(2):425-450

Natural Hazards - An earthquake of moment magnitude Mw 5.7 shook the northeastern region of India on 3 January 2017 at 14 h:39 min:0.5 s local time. The duration of the...  相似文献   

Strange Quark Matter in Cosmic Ray Flux and Exotic Events     

Shibaji Banerjee  Sanjay K. Ghosh  Amal Mazumdar  Sibaji Raha  Debapriyo Syam 《Astrophysics and Space Science》2000,274(3):655-660

There have been several reports of exotic nuclear fragments, with highly unusual charge to mass ratio, in cosmic ray experiments. Although there exist experimental uncertainties which make them, at best, only candidate `exotic' events, it is important to understand what they could be, if they are eventually confirmed. Among other possible explanations, some authors have interpreted them to be lumps of strange quark matter (strangelets).A major problem with such an interpretation is that to reach the earth's surface, they must possess an unusually high penetrability through the terrestrial atmosphere. We show that a recently proposed mechanism for the propagation of strangelets through the earth's atmosphere, together with a proper account of charge capture and ionisation loss, would solve this problem. We also argue that this could lead to viable strategies for definitive detection of strange quark matter in cosmic ray flux using aground based large area array of passive detectors. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献