Announcement     

Ashok Kauhsal 《Journal of the Indian Society of Remote Sensing》1999,27(2):xiii-xiii

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Simulation of Tropical Cyclone Circulation Over the Bay of Bengal Using the Arakawa-Schubert Cumulus Parameterization. Part II: Some Sensitivity Experiments     

D. V. Bhaskar Rao  K. Ashok 《Pure and Applied Geophysics》2001,158(5-6):1017-1046

—?The role of sea-surface temperature (SST) and Coriolis parameter in the evolution and intensification of tropical cyclones has been examined using the ten-level axi-symmetric primitive equation model described in the companion paper (Bhaskar Rao and Ashok, 1999). Two experiments have been conducted using the ten-level model to assess the role of Coriolis parameter “f” in tropical cyclone intensity and the size of the storm generated. Six experiments have been performed to assess the importance of Sea-Surface Temperature (SST) in tropical cyclogenesis and intensification. The initial thermodynamic field and the initial vortex are the same as that used to simulate the Bay of Bengal tropical cyclone discussed in the companion paper. Further sensitivity experiments indicated a strong dependency of the model on SSTs. The model initial vortex could not intensify with an SST of 299?K but could with an SST of 300?K. The increase of SST from 300?K to 300.5?K shows rapid intensification with a minimum central surface pressure of 910?hPa and a maximum tangential wind of 80?m/s. Further increase of SST only shows a marginal increase in intensity and a larger radius of maximum wind. Sensitivity experiments to assess the role of the Coriolis parameter suggest that tropical cyclones develop more intensity and are faster at relatively lower latitudes.  相似文献   

Effective strength eccentricity concept for inelastic analysis of asymmetric structures     

A. K. Mittal  Ashok K. Jain 《地震工程与结构动力学》1995,24(1):69-84

A large number of parameters affect the inelastic response of an eccentric system. The centre of resistance no longer remains constant due to continuous loading and unloading of various elements of the system in and out of the inelastic region. The objective of this study is to develop the concept of strength eccentricity for asymmetrical structures excited well into the inelastic region in the event of a severe earthquake. A single mass monosymmetric three-element system is selected. The torsional flexibility parameter is varied so as to obtain nine eccentric configurations covering the entire spectrum of such systems. These models were subjected to S00E component of the El Centro earthquake of 1940 which is considered to be a very severe earthquake. The concept of effective strength eccentricity is introduced which is defined as strength eccentricity at the point of intersection of ductility ratio curves of REE and FEE. It is proposed to provide additional strength in the elements of a torsionally unbalanced system independent of the design eccentricity. Empirical equations are proposed to account for design eccentricity and additional strength as well as distribution of the design strength. The proposed formulation is compared with the torsional provisions of UBC 1991, NBCC 1990 and NZC 1992. It is concluded that additional ductility demand on the REE and FEE designed based on the proposed formulation is almost nil as compared to that given by the three codes. The NZC and UBC require maximum ductility on the REE. The increase in overall strength of the system is least for the proposed formulation as compared to that given by the three codes. NBCC consistently requires the maximum total strength ratio.  相似文献   

Book reviews     

Juha J. Uitto  A. K. P. Mochtan  Ashok K. Dutt  Anindita Pari 《GeoJournal》1993,31(2):213-214

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An evaluation of national economic planning in the People's Republic of China     

Ashok K. Dutt  Frank J. Costa 《Geoforum》1980,11(1):1-15

The People's Republic of China has sought, since its inception in 1949, to develop through economic planning at the national level rather than rely on traditional free market mechanisms. This paper examines the changing characteristics of this economic planning over time, including the shifting balance between centralizing and decentralizing policies. The disruptive effects of the “Great Leap Forward” and the Cultural Revolution are also discussed and the general features of the contemporary situation are examined.  相似文献   

GIS assisted inverse geochemical modeling for plausible phase transfers in aquifers     

S. D. Dhiman  Ashok K. Keshari 《Environmental Geology》2006,50(8):1211-1219

A geographical information system (GIS) assisted approach that couples a groundwater flow model and an inverse geochemical model is presented to quantify the phase mole transfers between two points on the flow path within a groundwater system. It is used to investigate the plausible phase transfers in the unconfined aquifer of Mehsana district of Gujarat State, India. X-ray diffraction analysis of soil samples is carried out for mineral characterization. The groundwater flow field is simulated using MODFLOW and flow paths used for inverse geochemical modeling are traced using PMPATH, a particle tracking algorithm. The plausible phase mole transfers in the flow path are quantified using PHREEQC geochemical code. The different scenarios generated by inverse modeling routine are used as input to the geochemical model and simulation runs are taken as forward models. The obtained results are compared to the target solution chemistry by using the square of the Pearson product moment correlation coefficient. Results reveal that the groundwater is undersaturated with anhydrite, carbon dioxide (gas), fluorite, gypsum, halite, jarosite-K, and siderite. It is oversaturated with aragonite, calcite, dolomite, ferrihydrite, goethite, and hematite. Results further reveal that calcite is precipitating, while dolomite, gypsum, carbon dioxide, and fluorite are dissolving together with ion exchange in the flow path.  相似文献   

Extraction of geomorphological features using radarsat data     

Ashok Kaushal  Yogesh Singh 《Journal of the Indian Society of Remote Sensing》2006,34(3):299-307

A study was undertaken to evaluate the potential of RADARSAT SAR data (Standard-7 and Wide-2 beam positions) for delineating the geomophological units in Itanagar Capital Complex of Arunachal Pradesh, India. Principal Component Analysis (PCA) has been applied to Standard-7 and Wide-2 data with incidence angle 45° – 49° and 31 ° – 39° respectively. The resulting components yield imagery that highlights the Geomorphological units. The area of investigation has been classified into five geomophological units’ viz., High relief structural hills, low relief structural hills, low relief rugged hills, piedmont and intermontane valley. The surface roughness can be observed by studying the difference of the responses from different incidence angles. Wide-2 beam position was found to be more useful for identifying features in flat terrain, and Standard-7 beam position data for features of high relief.  相似文献   

Groundwater assessment through hydrogeomorphological and geophysical survey — A case study in Godavari sub-watershed, Giridih, Bihar     

Ashok Kumar  Savita Tomar 《Journal of the Indian Society of Remote Sensing》1998,26(4):177-183

Groundwater assessment has been carried out through hydrogeomorphological and geophysical survey. Remotely sensed data has been used to delineate the hydrogeomorphological units. Each hydrogeomorphological unit has been further sub-divided based on the tone, texture and pattern. These units its have been categorised based on depth of weathering, local geomorphological association, recharge characteristics etc. The top layer resistivity of hydrogeomorphological units has been analysed by electrical resistivity method. Correlation between different sub-units of same hydrogeomorphic unit and top soil resistivity has been attempted. The correlation and integration of resistivity map with geomorphological map were carried out through. ‘GRAM’ Geographic information System, This has helped in better understanding the surface resistivity pattern. These sub divisions have different geohydrological and recharge characteristics. Resistivity zonation map prepared on the basis of limited field data anfd through interpolation/extrapolation can be modified/corrected with the help of information derived from remotely sensed data to obtain more realistic picture.  相似文献   

Dynamics of Helically Twisted Prominence of January 22, 1979     

Nandita Srivastava  Ashok Ambastha 《Astrophysics and Space Science》1998,262(1):29-38

We have studied the dynamics of a macroscopically twisted helical prominence observed in H line on January 22, 1979 from Udaipur Solar Observatory. The analysis carried out is similar to that of March 11, 1979 event (Srivastava et al., 1991) wherein we had studied the role of twisted force-free magnetic fields in the prominence system. In the present study, it is found that of the two helically braided prominence tubes, one was dynamically more active. We have examined the temporal evolution of force-free parameter , and the axial currents associated with the prominence system that decreased with time. We find that the magnitude of the electric currents and also the rate of energy release during the untwisting of the prominence was of comparatively higher order 10³⁰ ergs s^-1 than that of March 11, 1979 event, in agreement with the physical dimensions of the two prominences.  相似文献   

Solar Photospheric and Chromospheric Observations using a Lithium Niobate Fabry-Perot Etalon     

C. Debi Prasad  Shibu K. Mathew  Arvind Bhatnagar  Ashok Ambastha 《Experimental Astronomy》1998,8(2):125-133

We have made a narrow band tunable filter for solar observations using a Lithium Niobate Fabry-Perot etalon. The 60 mm aperture etalon with a free spectral range of 4.22 Å and finesse of 26 at = 6122 Å has been procured from CSIRO, Australia. The wavelength tuning is achieved by applying high voltage to the etalon substrate at the rate of 0.45 Å per 1000 Volts. The filter is being used for imaging the sun in H line and obtaining Doppler- and Magnetogram in CaI 6122 Å line. In this paper, we present some initial observations carried out with this filter at Udaipur Solar Observatory.  相似文献