On combined operational method for transfer problems in homogeneous,spherical media     

T. H. Kho  K. K. Sen 《Astrophysics and Space Science》1971,14(1):223-242

In this paper, the Combined Operational Method developed by Busbridge (1961) in connection with the radiative transfer problems in plane-parallel atmospheres has been extended to similar problems in isotropic scattering, homogeneous spherical media. The relevant auxiliary equation has been formulated, the scattering function defined and the integro-differential equation for such function deduced. For a medium having radial distribution of source in addition to the incident flux at the outer surface, the integro-differential equations for source function and emergent intensity have been established.  相似文献   

Effects of E-region electric fields on F-region parameters at the magnetic equator     

K.Sen Gupta  B.V.Krishna Murthy 《Planetary and Space Science》1973,21(12):2227-2232

The effects of E-region electric fields on F-region parameters like height of constant electron density contours (h_N) and semi-thickness, at an equatorial station, Trivandrum, are investigated. The E-region east-west electric field (E_y) has been deduced using the horizontal magnetic field values from the ground magnetograms. It is found that the semi-thickness parameter and h_N follow closely the E-region electric field (E_y) variations in the forenoon and noon periods. In the afternoon, it is shown that there is close association between h_N and E_y, when the electric field variations are large. On a day-to-day basis also, h_N and the E-region electric field show very good correlation in the forenoon and noon hours. It is also shown that higher levels are affected more than the lower levels in the F-region by E_y.  相似文献   

A water quality model for the Patuxent estuary: Current conditions and predictions under changing land-use scenarios   总被引：1，自引：0，他引：1  

Wu-Seng?LungEmail author  Sen?Bai 《Estuaries and Coasts》2003,26(2):267-279

A water quality model was developed for the Patuxent estuary using the modeling framework CE-QUAL-W2 (called W2) to address the impact of current and projected land-use changes (stress) on the water quality. The W2 code, supported by the Army Corps of Engineers Waterways Experiment Station, is a two-dimensional (longitudinalvertical) model designed for hydrodynamic and water quality simulations of reservoirs and estuaries. The code was configured for the Patuxent estuary using a finite-difference grid for the water column. Also incorporated into the model calculations are flow and nutrient load results from a watershed model. The integrated model was calibrated with data of 1 yr from 1997 to 1998 by matching results with measured temperature, dissolved oxygen, chlorophylla, and nutrient levels in the water column. The calibrated model was used to predict the water quality effects of different watershed land-use scenarios. Model projection results suggest that reductions of nutrient loads would lead to improvement of anoxic conditions in the bottom waters of the lower Patuxent estuary.  相似文献   

Enforcing smoothness and assessing uncertainty in non-linear one-dimensional prestack seismic inversion   总被引：1，自引：0，他引：1  

Omar J. Varela  Carlos Torres-Verdín  Mrinal K. Sen 《Geophysical Prospecting》2006,54(3):239-259

Estimation of elastic properties of rock formations from surface seismic amplitude measurements remains a subject of interest for the exploration and development of hydrocarbon reservoirs. This paper develops a global inversion technique to estimate and appraise 1D distributions of compressional‐wave velocity, shear‐wave velocity and bulk density, from normal‐moveout‐corrected PP prestack surface seismic amplitude measurements. Specific objectives are: (a) to evaluate the efficiency of the minimization algorithm (b) to appraise the impact of various data misfit functions, and (c) to assess the effect of the degree and type of smoothness criterion enforced by the inversion. Numerical experiments show that very fast simulated annealing is the most efficient minimization technique among alternative approaches considered for global inversion. It is also found that an adequate choice of data misfit function is necessary for a reliable and efficient match of noisy and sparse seismic amplitude measurements. Several procedures are considered to enforce smoothness of the estimated 1D distributions of elastic parameters, including predefined quadratic measures of length, flatness and roughness. Based on the general analysis of global inversion techniques, we introduce a new stochastic inversion algorithm that initializes the search for the minimum with constrained random distributions of elastic parameters and enforces predefined autocorrelation functions (semivariograms). This strategy readily lends itself to the assessment of model uncertainty. The new global inversion algorithm is successfully tested on noisy synthetic amplitude data. Moreover, we present a feasibility analysis of the resolution and uncertainty of prestack seismic amplitude data to infer 1D distributions of elastic parameters measured with wireline logs in the deepwater Gulf of Mexico. The new global inversion algorithm is computationally more efficient than the alternative global inversion procedures considered here.  相似文献   

Hypoxia in the northern Gulf of Mexico: Does the science support the Plan to Reduce,Mitigate, and Control Hypoxia?     

N. N. Rabalais  R. E. Turner  B. K Sen Gupta  D. F. Boesch  P. Chapman  M. C. Murrell 《Estuaries and Coasts》2007,30(5):753-772

We update and reevaluate the scientific information on the distribution, history, and causes of continental shelf hypoxia that supports the 2001 Action Plan for Reducing, Mitigating, and Controlling Hypoxia in the Northern Gulf of Mexico (Mississippi River/Gulf of Mexico Watershed Nutrient Task Force 2001), incorporating data, publications, and research results produced since the 1999 integrated assessment. The metric of mid-summer hypoxic area on the LouisianaTexas shelf is an adequate and suitable measure for continued efforts to reduce nutrients loads from the Mississippi River and hypoxia in the northern Gulf of Mexico as outlined in the Action Plan. More frequent measurements of simple metrics (e.g., area and volume) from late spring through late summer would ensure that the metric is representative of the system in any given year and useful in a public discourse of conditions and causes. The long-term data on hypoxia, sources of nutrients, associated biological parameters, and paleoindicators continue to verify and strengthen the relationship between the nitratenitrogen load of the Mississippi River, the extent of hypoxia, and changes in the coastal ecosystem (eutrophication and worsening hypoxia). Multiple lines of evidence, some of them representing independent data sources, are consistent with the big picture pattern of increased eutrophication as a result of long-term nutrient increases that result in excess carbon production and accumulation and, ultimately, bottom water hypoxia. The additional findings arising since 1999 strengthen the science supporting the Action Plan that focuses on reducing nutrient loads, primarily nitrogen, through multiple actions to reduce the size of the hypoxic zone in the northern Gulf of Mexico.  相似文献   

Geochemical approach to magmatic evolution of Mt. Erciyes stratovolcano Central Anatolia, Turkey   总被引：1，自引：0，他引：1  

Biltan Kürküoglu  Erdal Sen  Erkan Aydar  Alain Gourgaud  Niyazi Gündogdu 《Journal of Volcanology and Geothermal Research》1998,85(1-4)

Erciyes stratovolcano, culminating at 3917 m, is located in the Cappadocian region of central Anatolia. During its evolution, this Quaternary volcano produced pyroclastic deposits and lava flows. The great majority of these products are calc-alkaline in character and they constitute Kocdag and Erciyes sequences by repeated activities. Alkaline activity is mainly observed in the first stages of Kocdag and approximately first-middle stages of Erciyes sequences. Generally, Kocdag and Erciyes stages terminate by pyroclastic activities. The composition of lavas ranges from basalt to rhyolite (48.4–70.5 wt.% SiO₂). Calc-alkaline rocks are represented mostly by andesites and dacites. Some compositional differences between alkaline basaltic, basaltic and andesitic rocks were found; while the composition of dacites remain unchanged. All these volcanics are generally enriched in LIL and HFS elements relative to the orogenic values except Rb, Ba, Nb depleted alkaline basalt. ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd isotopic composition of the volcanics range between 0.703344–0.703964, 0.512920–0.512780 for alkaline basalts and change between 0.704322–0.705088, 0.512731–0.512630 for alkaline basaltic rocks whereas calc-alkaline rocks have relatively high Sr and Nd isotopic ratios (0.703434–0.705468, 0.512942–0.512600). Low Rb, Ba, Nb content with high Zr/Nb, low Ba/Nb, La/Yb ratio and low Sr isotopic composition suggest an depleted source component, while high Ba, Rb, Nb content with high La/Yb, Ba/Nb, low Zr/Nb and low ⁸⁷Sr/⁸⁶Sr ratios indicate an OIB-like mantle source for the generation of Erciyes alkaline magma. These elemental and ratio variations also indicate that the different mantle sources have undergone different degree of partial melting episodes. The depletion in Ba, Rb, Nb content may be explained by the removal of these elements from the source by slab-derived fluids which were released from pre-collisional subduction, modified the asthenospheric mantle. The chemically different mantle sources interacted with crustal materials to produce calc-alkaline magma. The Ba/Nb increase of calc-alkaline samples indicates the increasing input of crustal components to Erciyes volcanics. Sr and Nd isotopic compositions and elevated LIL and HFS element content imply that calc-alkaline magma may be derived from mixing of an OIB-like mantle melts with a subduction-modified asthenospheric mantle and involvement of crustal materials in intraplate environments.  相似文献   

Early tertiary deltaic sedimentation around Kalka and Nahan, Punjab Himalaya, India     

D.P. Sen 《Sedimentary Geology》1981,30(4):291-310

During the Early Tertiary epoch a basin of deposition covered almost all the present Himalayan foot hill zone. Large quantities of detrital sediments were transported from the northern source area to the depositional basin. The rivers carrying the sediment load formed large delta complexes. In the area studied at least two such delta complexes, one around Kalka and the other around Nahan, were formed; of these the one around Kalka contains the greatest volume of sediments.

The recognition of the deltas is based on: (a) greater abundance of stream deposits than deposits of other environments; (b) lithologic criteria, particularly sedimentary structures, repetitive lithologic associations; (c) the general coarsening-upward nature of the sediments; (d) strong unimodal current direction; (e) the typical lenticular lithogenetic model, common in recent deltas.

The rocks of the Nahan Group are divisible into three formations at Kalka and two formations at Nahan where central formation did not develop. Himalayan tectonism has largely controlled both delta formation and stratigraphy.

The differential rates of sedimentation greatly influenced the rates of subsidence within the Nahan basin. The sediments of the Nahan Group are roughly bounded between two major phases of Himalayan uplift, namely Eocene and middle Miocene tectonic movements. The effects of intermittent tectonic pulses are well depicted in rocks of the Nahan Group. The intensity of the tectonism that controlled both the source-area rise and basin subsidence during deposition of the Nahan Group of sediments was nonuniform, both in vertical and lateral directions. Because of a generally higher rate of deposition compared to the rate of subsidence, the rocks of the Nahan group represent a normal regressive basin-filling sedimentation, forming thick detrital deposits due to progradation of younger deltas beyond the distal end of older deltas.  相似文献   

Total mercury content in some marine fish from the Indian Ocean     

Tariq W. Kureishy  M. D. George  R. Sen Gupta 《Marine pollution bulletin》1979,10(12):357-360

Total mercury was estimated in liver, gonads and muscle of some of the marine fishes from the Indian Ocean. The highest mercury concentration was observed in the muscle of sharks while the total mercury concentration was practically non-detectable in the liver and gonads. The range of all the values was 0.09–0.21 ppm (wet weight basis) and is quite low to reflect any possible mercury contamination.  相似文献   

Mineralogical variations in the Delakhari sill,Deccan trap intrusion,central India     

Gautam Sen 《Contributions to Mineralogy and Petrology》1980,75(1):71-78

The Delakhari sill (maximum thickness cf. 200 m) is the most extensive Deccan Trap instrusion which occurs in central India, between longitutdes 78°3835 to 78°2240 and latitudes 22°26 and 22°2230. Based on petrographic examination, the sill is divided, from bottom to top, into (1) the Lower Chilled Zone (LCZ), up to 8 m thick, marked by abundant interstitial glass and an overall fine grain size, (2) the Olivine-Rich Zone (ORZ), 27 m thick, enriched in olivine (relative to the other zones in the sill), (3) the Central Zone (CZ), 70 m thick, marked by depletion in olivine and overall coarse grain size, (4) the Upper Zone (UZ), 55 m thick, marked by the presence of two chemically and morphologically distinct olivine types and abundant interstitial granophyre, and (5) the Upper Chilled Zone (UCZ), 10–25m thick, marked by abundant interstitial glass.Compositions of the pyroxenes and olivines show an overall increase in Fe/Mg with crystallization, but extensive interzonal and intrazonal variations and overlaps exist. Olivine ranges from Fa₂₄ (ORZ) to Fa₉₅ (UZ). In the UZ and inner UCZ, an equant (Fa_44–50, called type-A olivine) and interstitial skeletal olivine (Fa_70–95, called type-B olivine) occur together. Compositions of the Ca-rich and Ca-poor pyroxenes fall in the range Wo₃₈En₃₄Fs₂₈ to Wo₃₃En₈Fs₅₉ and Wo₁₄En₄₁Fs₄₅ to Wo₁₆En₁₉Fs₆₅, respectively. Overall, the two pyroxene trends converge with Fe-enrichment except for one anomalous sample from the UZ which contains a Ca-rich (Wo₃₄En₈Fs₅₈) and a Ca-poor (Wo₁₀En₁₈Fs₇₂) pyroxene well within the Forbidden Zone of Smith (1972).Compositions of coexisting oxide minerals indicate that the sill crystallized at oxygen fugacities from 10^–10 atm (ORZ) to 10^–13 (UZ). The magma prior to intrusion appears to have been derived from a more primitive melt from which a considerable amount of olivine and plagioclase have fractionated out. A model of open, interrupted fractional crystallization in the sill is proposed to explain the compositional variations exhibited by the major mineral phases.A previous study (Crookshank 1936) concluded that the sill is actually a multiple intrusion and has given rise to the lowermost (flow I) and the topmost (flow III) lava flows in the neighboring area around Tamia (78°4015, 22°2035). The olivines of flows I and III have compositions Fo₈₇ and Fo₈₈ respectively, and are much more Mg-rich than the maximum Mg-rich olivine (Fo₇₆) of the Delakhari sill, refuting the possibility of the sill being the feeder of the lava flows I and III.Geosciences Department, University of Texas at Dallas Contribution No. 338  相似文献   

Dynamical Initialization of Boundary-Layer Data     

G. K. Sen  M. Chatterjee  D. K. Sinha 《Boundary-Layer Meteorology》1998,87(3):509-514

A procedure for the dynamic initialization of wind and temperature fields within the atmospheric boundary layer (ABL) is presented. The procedure uses transilient turbulence theory to assess the turbulent fluxes from observed wind and temperature data, which are used to estimate the eddy transfer coefficients, so enabling a local closure ABL model to be integrated forward in time to a new steady state. The method has been applied to initialize kytoon data taken at Kharagpur (22.3° N, 87.2° E) during the MONTBLEX field programme. Results of a case study for 17 June 1990 are discussed.  相似文献