A new approximation for spectral velocity ordinates at short periods     

Vinay K. Gupta 《地震工程与结构动力学》2009,38(7):941-949

Response spectrum methods in earthquake‐resistant design sometimes require information on the spectral velocity (SV) for a given single‐degree‐of‐freedom oscillator and specified seismic hazard. SV has been conventionally approximated as pseudo spectral velocity (PSV) in the case of lightly damped structures that are not too flexible. This study shows that the PSV approximation may lead to large overestimation errors when the structure is stiffer to the ground motion and the ground motion is a long‐period motion. It is also shown that a new approximation requiring the use of peak ground acceleration of the motion may significantly reduce these errors. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Climate and vegetation water use efficiency at catchment scales   总被引：1，自引：0，他引：1  

Peter A. Troch  Guillermo F. Martinez  Valentijn R. N. Pauwels  Matej Durcik  Murugesu Sivapalan  Ciaran Harman  Paul D. Brooks  Hoshin Gupta  Travis Huxman 《水文研究》2009,23(16):2409-2414

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Interplanetary structures and solar wind behaviour during major geomagnetic perturbations     

Vivek Gupta 《Journal of Atmospheric and Solar》2009,71(8-9):885-896

We consider five different solar wind structures to study their relative geo-effectiveness in producing major geomagnetic perturbations. Geomagnetic indices and solar wind parameters during major storms have been utilized to understand the physical mechanism(s) during the passage of structures with distinct structural and dynamical properties. Attempt has been made to find distinct features of the structures responsible for large-intensity and/or long-duration geomagnetic storms. We search for precursors of major storms that may be useful for space-weather predictions. Average recovery characteristics of storms and the influence of solar wind speed on the recovery have been discussed.  相似文献   

Benthic foraminiferal assemblages of the South Brazil: Relationship to water masses and nutrient distributions     

P.P.B. Eichler  B.K. Sen Gupta  B.B. Eichler  E.S. Braga  E.J. Campos 《Continental Shelf Research》2008

Using distributions of benthic Foraminifera and bottom-water variables (depth, salinity, temperature, oxygen, suspended matter, organic matter, phosphate, silicate, nitrite, and nitrate), we investigated movements of water masses on the South Brazilian Shelf (27–30°S) and assessed the seasonality of continental runoff on the distribution of shelf water masses. The data were obtained from water and sediment samples collected in the austral winter of 2003 and austral summer of 2004 in three transects. The terrestrial nutrient input was significantly reduced at stations away from the coast, but high values of nutrients were maintained in subsurface waters due the presence of South Atlantic Central Water (SACW) at greater depths. At shallow sampling stations the influence of freshwater runoff was related to (1) the dominance of calcareous benthic Foraminifera, such as lagoon-related Pseudononion atlanticum, Hanzawaia boueana, Bulimina marginata, Bolivina striatula, Elphidium poeyanum, together with several agglutinated species, including Arenoparrella mexicana, Gaudryina exilis, and Trochammina spp., common in coastal environments subject to wide salinity fluctuations. In contrast, smaller forms and higher species diversity characterized the assemblage at offshore stations. In winter, the presence of Buccella peruviana and Uvigerina peregrina at Santa Marta Cape suggest the possible transport of those species of Subantarctic Shelf Waters (SASW) origin. Foraminifera associated to Subtropical Shelf Water (STSW) were dominated by Globocassidulina subglobosa in both seasons. In summer, the occurrence of U. peregrina in the shallower stations suggested the influence of SACW nutrients brought up by upwelling of deeper waters.  相似文献   

Water resource accounting for an iron-ore mining area in India     

S. K. Chaulya  M. K. Chakraborty  M. Ahmad  K. K. K. Singh  R. S. Singh  B. K. Tewary  P. K. Gupta 《Environmental Geology》2000,39(10):1155-1162

A study has been conducted at the Bicholim iron-ore mine, North Goa, India to investigate the hydrogeological continuity between the mine's open pit and surrounding villages. Water resource accounting by demarcating different watersheds has also been carried out to analyse the major causes of groundwater scarcity in the region during dry periods. A resistivity survey and a ground penetrating radar survey were completed around the periphery of open pits, the surrounding village areas and Mayem Lake. The results of the two independent surveys and other related data confirm that there is no observable hydrogeological continuity between the pits, nearby villages and Mayem Lake. Hence, there may not be any significant effect on surrounding water resources due to mining or mine dewatering. Water resource accounting has revealed that only 15–20% of 3500 mm precipitation per annum becomes part of the groundwater resource. The remainder of the annual precipitation is lost as heavy runoff, evapotranspiration and subsurface capillary moisture. Closely spaced wells in the region have also aggravated the groundwater scarcity problem due to draw down effects. Therefore, an effective water resource conservation plan is required for the region to overcome the problem. Received: 18 January 1999 · Accepted: 17 May 1999  相似文献   

Mass transport modelling to assess contamination of a water supply well in Sabarmati river bed aquifer, Ahmedabad City, India     

V. V. S. Gurunadha Rao  S. K. Gupta 《Environmental Geology》2000,39(8):893-900

 Drinking water supply wells were constructed in the Sabarmati river bed aquifer of Ahmedabad city using radial pipes and are known as French Collector wells. Contamination of groundwater from one of the French wells near Sabarmati railway bridge was noticed in 1992. The suspected pollution sources are Duff-nala of Shahibaug and two other sources from slum dwellings on either side of Sabarmati river. A combined groundwater flow, pathlines and a mass transport model was constructed covering an area of 9 km² to analyse the capture zone of the French well under two different scenarios. Aquifer parameters of the river bed aquifer were available. Dry river bed condition was simulated under scenario I and controlled flow in the river bed was simulated under scenario II. The groundwater velocity and migration of contaminant particles from sources was analysed in the pathline model. Total dissolved solids (TDS) concentration contours originating from sources in the mass transport model (MT3D) were computed by solving an advection-dispersion equation. The computed pathlines and TDS concentration contours indicate likely migration of contaminant plume from pollutant sources to the French well during 365 days under two scenarios. The model results confirm the tracer injection studies carried out to know the likely migration of contaminants towards the French well. The modelling study emphasised the necessity of controlled release of surface water in Sabarmati river bed from Dharoi reservoir throughout the year. Received: 28 October 1998 · Accepted: 17 June 1999  相似文献   

On most general exact solution for Vaidya-Tikekar isentropicsuperdense star     

Y.K. Gupta  M.K. Jasim 《Astrophysics and Space Science》2000,272(4):403-415

The energy density of Vaidya-Tikekar isentropic superdense star is found to be decreasing away from the center, only if the parameter K is negative. The most general exact solution for the star is derived for all negative values of K in terms of circular and inverse circular functions. Which can further be expressed in terms of algebraic functions for K = 2-(n/δ)² < 0 (n being integer andδ = 1,2,3 4). The energy conditions 0 ≤ p ≤ αρc ², (α = 1 or 1/3) and adiabatic sound speed conditiondp dρ ≤ c ², when applied at the center and at the boundary, restricted the parameters K and α such that .18 < −K −2287 and.004 ≤ α ≤ .86. The maximum mass of the star satisfying the strong energy condition (SEC), (α = 1/3) is found to be3.82 Mq_· at K=−2/3, while the same for the weak energy condition (WEC), (α =1) is 4.57 M_ _⊙ atK=−>5/2. In each case the surface density is assumed to be 2 × 10¹⁴ gm cm^-3. The solutions corresponding to K>0 (in fact K>1) are also made meaningful by considering the hypersurfaces t= constant as 3-hyperboloid by replacing the parameter R ² by −R² in Vaidya-Tikekar formalism. The solutions for the later case are also expressible in terms of algebraic functions for K=2-(n/δ² > 1 (n being integer or zero and δ =1,2,3 4). The cases for which 0 < K < 1 do not possess negative energy density gradient and therefore are incapable of representing any physically plausible star model. In totality the article provides all the physically plausible exact solutions for the Buchdahl static perfect fluid spheres. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

MEASUREMENT OF KODAIKANAL WHITE-LIGHT IMAGES – V. Tilt-Angle and Size Variations of Sunspot Groups     

Howard  Robert F.  Sivaraman  K.R.  Gupta  S.S. 《Solar physics》2000,196(2):333-348

We examine here the variations of tilt angle and polarity separation (as defined in this paper) of multi-spot sunspot groups from the Kodaikanal and Mount Wilson data sets covering many decades. We confirm the tilt-angle change vs tilt-angle result found earlier from the Mount Wilson data alone. Sunspot groups tend on average to rotate their axes toward the average tilt angle. We point out that if we separate groups into those with tilt angles greater than and less than the average value, they show tilt-angle variations that vary systematically with the growth or decay rates of the groups. This result emphasizes again the finding that growing (presumably younger) sunspot groups rotate their magnetic axes more rapidly than do decaying (presumably older) groups. The tilt-angle variation as a function of tilt angle differs for those groups whose leading spots have greater area than their following spots and vice versa. Tilt-angle changes and polarity separation changes show a clear relationship, which has the correct direction and magnitude predicted by the Coriolis force, and this strongly suggests that the Coriolis force is largely responsible for the axial tilts observed in sunspot groups. The distribution of polarity separations shows a double peak. These peaks are perhaps related to super- and meso-granulation dimensions. Groups with polarity separations less than 43 Mm expand on average, while those groups with separations more than this value contract on average. We present evidence that the rotation of the magnetic axes of sunspot groups is about a location closer to the following than to the leading sunspots.  相似文献   

Microflares as possible sources for coronal heating     

Meera Gupta  Rajmal Jain  Jayshree Trivedi  A. P. Mishra 《Journal of Astrophysics and Astronomy》2008,29(1-2):171-177

We present a preliminary study of 27 microflares observed by Solar X-ray Spectrometer (SOXS) mission during July 2003 to August 2006. We found that all 27 microflares show the Fe-line feature peaking around 6.7 keV, which is an indicator of the presence of coronal plasma temperature ≥ 9 MK. On the other hand, the spectra of microflares show hybrid model of thermal and non-thermal emission, which further supports them as possible sources of coronal heating. Our results based on the analysis show that the energy relapsed by the microflares is good enough for heating of the active corona. We discuss our results in the light of the hybrid model of microflares production.  相似文献   

Biodegradation of Simazine and Diuron Herbicides under Aerobic and Anoxic Conditions Relevant to Managed Aquifer Recharge of Storm Water          下载免费PDF全文

Ali Shareef  Declan Page  Joanne Vanderzalm  Mike Williams  V. V. S. R. Gupta  Peter Dillon  Rai Kookana 《洁净——土壤、空气、水》2014,42(6):745-752

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