Determination of the area and mass distribution of orbital debris fragments   总被引：1，自引：0，他引：1  

Gautam D. Badhwar  Phillip D. Anz-Meador 《Earth, Moon, and Planets》1989,45(1):29-51

An important factor in modeling the orbital debris environment is the loss rate of debris due to atmospheric drag and luni/solar perturbations. An accurate knowledge of the area-to-mass ratio of debris fragments is required for the calculation of the effect of atmospheric drag. In general, this factor is unknown and assumed values are used. However, this ratio can be calculated for fragments for which changes in the orbital elements due to atmospheric drag as a function of time are known. This is the inverse of the technique used to determine the atmospheric density from the decay of satellites with accurately known area-to-mass ratios. These kinds of propagation programs are routinely used in predicting the decay of an orbiting vehicle. In this work the area-to-mass ratio of about 2600 fragments arising from the breakup of 24 artificial satellites have been determined. An analysis of the data on about 200 objects (rocket bodies, scientific satellites, etc.) with known mass, size, and shape has also been made. The value of the radar cross-section (RCS), as measured by the Eglin radar operating at 70 cm wavelength, has been correlated to the effective area of these objects. The measurements of the area-to-mass ratio of these objects then provide a calibration of the actual to the calculated mass. It has been shown that the debris mean mass, m, is related to the mean effective area, A, by a power law relation, m = k A ^1.86. However, for a given effective area the mass distribution is very broad. Moreover, the cumulative mass distribution, N(>m), can be expressed as N(>m) = D(m + b), where D, b, and c are constants. The asymptotic slope, c, of low intensity explosions is on the average lower than the slope for high intensity explosions, but there is considerable spread of this slope in each class. Part of the flattening, as indicated by the finite value of the parameter, b, can be understood as arising out of the spread in the RCS values due to the tumbling motion of the fragments and effects related to the detectability of the fragment by the Eglin radar. It has been established that the mass in a given breakup calculated using this technique is in good agreement with the expected mass value. These results can be used in modeling the breakups of other artificial earth satellites and safety analysis.  相似文献   

Folding by cataclastic flow: evolution of controlling factors during deformation   总被引：3，自引：1，他引：3  

Zeshan Ismat  Gautam Mitra 《Journal of Structural Geology》2005,27(12):2181-2203

Folding at upper crustal levels occurs by bending of beds and flexural slip between beds. As a fold's interlimb angle decreases, changes in bed thickness and limb rotation are accommodated by various mechanisms, depending on deformation conditions. In the elastico-frictional (EF) regime, cataclastic flow may be the dominant mechanism for fold tightening. The Canyon Range (CR) syncline, located in the Sevier belt of central Utah, shows this type of deformation. The fold involves three thick quartzite units, with slight lithological variations between them. Fold tightening took place in the EF regime (<2 km overburden) by cataclastic flow, involving collective movement on a distributed network of fractures and deformation zones (DZs) from the micro- to the outcrop-scale. In detail, the degree of cataclastic deformation varies significantly across the fold due to minor variations in initial bedding thickness, grain size, matrix composition, etc. A cooperative relationship exists across different scales, and the fracture networks result in a fracture shape fabric that is relatively homogeneous at the outcrop-scale.The initial outcrop scale fracture/DZ network geometry is a product of the growth and linking of micro-scale cataclasite zones, which in turn is controlled by primary lithological variations. Once a fracture network forms, the material behavior of the fractured rock is unlike that of the original rock, with sliding of fracture-bound blocks accomplishing ‘block-controlled’ cataclastic flow. Thus, initial lithological variations at the micro-scale largely control the final deformation behavior at the largest scale. During progressive fold tightening, additional factors regulate cataclastic flow, such as fracture/DZ reactivation or healing, during folding. Although initial lithological variations in different units may produce unique network geometries, each unit's behavior may also depend upon the behavior of adjacent units. In the CR syncline, during the initial stages of cataclastic flow, the inherent nature of each quartzite unit results in unit-specific fracture network geometries. As deformation progresses, unit-specific networks begin to interact with those in surrounding units, resulting in feedback mechanisms regulating the later stages of network development. Thus, the nature of cataclastic flow changes dramatically from the initial to the final stages of folding.  相似文献   

Preface     

Pitambar Gautam  Teiji Watanabe  Hiroshi Nishi  Tetsuzo Yasunari 《Island Arc》2005,14(4):295-296

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Reassembly of the Dharwar and Bastar cratons at ca. 1 Ga: Evidence from multiple tectonothermal events along the Karimnagar granulite belt and Khammam schist belt,southern India     

Sojen Joy  Gert Van Der Linde  Asru K Choudhury  Gautam K Deb  Sebastian Tappe 《Journal of Earth System Science》2018,127(6):76

The northern part of the Nellore–Khammam schist belt and the Karimnagar granulite belt, which are juxtaposed at high angle to each other have unique U–Pb zircon age records suggesting distinctive tectonothermal histories. Plate accretion and rifting in the eastern part of the Dharwar craton and between the Dharwar and Bastar craton indicate multiple and complex events from 2600 to 500 Ma. The Khammam schist belt, the Dharwar and the Bastar craton were joined together by the end of the Archaean. The Khammam schist belt had experienced additional tectonic events at \(\sim \)1900 and \(\sim \)1600 Ma. The Dharwar and Bastar cratons separated during development of the Pranhita–Godavari (P–G) valley basin at \(\sim \)1600 Ma, potentially linked to the breakup of the Columbia supercontinent and were reassembled during the Mesoproterozoic at about 1000 Ma. This amalgamation process in southern India could be associated with the formation of the Rodinia supercontinent. The Khammam schist belt and the Eastern Ghats mobile belt also show evidence for accretionary processes at around 500 Ma, which is interpreted as a record of Pan-African collisions during the Gondwana assembly. From then on, southern India, as is known today, formed an integral part of the Indian continent.  相似文献   

Evaluation of the SWAT model for water balance study of a mountainous snowfed river basin of Nepal     

Birsingh Dhami  Sushil Kumar Himanshu  Ashish Pandey  Amar Kant Gautam 《Environmental Earth Sciences》2018,77(1):21

In this study, a semi-distributed hydrologic model Soil and Water Assessment Tool (SWAT) has been employed for the Karnali River basin, Nepal to test its applicability for hydrological simulation. Further, model was evaluated to carry out the water balance study of the basin and to determine the snowmelt contribution in the river flow. Snowmelt Runoff Model (SRM) was also used to compare the snowmelt runoff simulated from the SWAT model. The statistical results show that performance of the SWAT model in the Karnali River basin is quite good (p-factor = 0.88 and 0.88, for daily calibration and validation, respectively; r-factor = 0.76 and 0.71, for daily calibration and validation, respectively). Baseflow alpha factor (ALPHA_BF) was found most sensitive parameter for the flow simulation. The study revealed that the average annual runoff volume available at the basin outlet is about 47.16 billion cubic metre out of which about 12% of runoff volume is contributed by the snowmelt runoff. About 25% of annual precipitation seems to be lost as evapotranspiration. The results revealed that both the models, SWAT and SRM, can be efficiently applied in the mountainous river basins of Nepal for planning and management of water resources.  相似文献   

An alternative interpretation for the map expression of “abrupt” changes in lateral stratigraphic level near transverse zones in fold-thrust belts     

Sanghoon Kwon  Gautam Mitra 《地学前缘(英文版)》2012,3(4):401-406

The map expression of "abrupt" changes in lateral stratigraphic level of a thrust fault has been traditionally interpreted to be a result of the presence of(1) a lateral(or oblique) thrust-ramp,or(2) a frontal ramp with displacement gradient、and/or(3) a combination of these geometries.These geometries have been used to interpret the structures near transverse /ones in fold-thrust belts(FTB).This contribution outlines an alternative explanation that can result in the same map pattern by lateral variations in stratigraphy along the strike of a low angle thrust fault.We describe the natural example of the Leamington transverse zone.which marks the southern margin of the Pennsy lvanian—Permian Oquirrh basin with genetically related lateral stratigraphic variations in the North American Sevier(TB.Thus.the observed map pattern at this zone is closely related to lateral stratigraphic variations along the strike of a horizontal fault.Even though the present-day erosional level shows the map pattern that could be interpreted as a lateral ramp.the observed structures along the Leamington zone most likely share the effects of the presence of a lateral(or oblique) ramp,lateral stratigraphic variations along the fault trace.and the displacement gradient.  相似文献