Comparative Analysis of Phytoplankton Composition and Abundance over a Two-Decade Period at the Land–Ocean Boundary of a Tropical Mangrove Ecosystem     

Haimanti Biswas  Mitali Dey  Dipnarayan Ganguly  Tarun K. De  Sandip Ghosh  Tapan K. Jana 《Estuaries and Coasts》2010,33(2):384-394

Inter-annual variations of phytoplankton abundance and community organization were observed over a two-decade period along with the ancillary parameters at the land–ocean boundary associated with the Sundarban mangrove forest (21°32′ and 22°40′ N and 88°05′ and 89° E), along the NE Coast of the Bay of Bengal. The number of definable Bacillariophyceae species exceeded Dinophyceae taxa, and the total number of bloom-forming species declined from a maximum of ten in 2000 and a minimum of two in 2007. Blooms of the diatom Coscinodiscus radiatus were common in 2000 and 2007. Tide cycles and the onset of the monsoon season played important roles in diurnal and seasonal variability of phytoplankton. Phytoplankton biovolume showed seasonality, with the highest levels during post-monsoon periods and lowest levels during the monsoon period. Phytoplankton abundance was correlated to rainfall patterns, which may be altered by long-term changes in climate.  相似文献   

Interference effect of two nearby strip footings on layered soil: theory of elasticity approach     

Priyanka Ghosh  Anirudh Sharma 《Acta Geotechnica》2010,5(3):189-198

In recent times, rapid urbanisation coupled with scarcity of land forces several structures to come up ever closer to each other, which may sometime cause severe damage to the structures from both strength and serviceability point of view, and therefore, a need is felt to devise simplified methods to capture the effect of footing interference. In the present study, an attempt has been made to model the settlement behaviour of two strip footings placed in close spacing on layered soil deposit consisting of a strong top layer underlying a weak bottom layer. Theory of elasticity is employed to derive the governing differential equations and subsequently solved by the finite difference method. The perfectly rough strip footings are considered to be resting on the surface of two-layer soil system, and the soil is assumed to behave as linear elastic material under a range of static foundation load. The effect of various parameters such as the elastic moduli and thickness of two layers, clear spacing between the footings and footing load on the settlement behaviour of closely spaced footings has been determined. The variation of vertical normal stress at the interface of two different soil layers as well as at the base of the failure domain also forms an important part of this study. The results are presented in terms of settlement ratio (ξ_δ), and their variation is obtained with the change in clear spacing between two footings. The present theoretical investigation indicates that the settlement of closely spaced footings is found to be higher than that of single isolated footing, which further reduces with increase in the spacing between the footings.  相似文献   

On reflection and diffraction of pressure waves from floating ice     

M. L. Ghosh 《Pure and Applied Geophysics》1973,111(1):2163-2176

Summary The diffraction of a pressure wave arising from the edge of the floating ice due to an incident wave of the formH[t–(xcos/)+ (ysin/)], whereH(t) is the Heaviside step function, has been studied. The ice sheet has been taken to be moving with a velocity much less than the velocity of sound in the liquid. The problem has been solved using an approximate method of solving Wiener Hopf problems. Finally, the pressure field at a large distance from the edge has been derived in a closed form evaluating the integrals by the saddle point method.  相似文献   

A new method for estimating rate constants for trace gas reactions within stratospheric sulphuric acid aerosol droplets     

S. Ghosh 《Journal of Earth System Science》1993,102(1):265-270

Uptake of trace gases by (stratospheric aerosol can be significant particularly after large injections of volcanic sulphur. A theoretical scheme is presented to quantify the rate at which trace gases diffuse into these aerosol droplets. Rate constants for 19 trace gases are calculated and it is found that the rates vary from a value of 2.85 × 10^-7s^-1 for CC14 to 8.08 × 10^-7s^-1 for NO. The calculations are characterised by their ease of application and can be incorporated into stratospheric chemical models.  相似文献   

Trace element geochemistry and genesis of the copper ore deposits of the Singhbhum shear zone,Eastern India     

A. K. Ghosh 《Mineralium Deposita》1972,7(3):292-313

The genesis of the copper ore deposits of the Singhbhum shear zone, India, has been worked out through a detailed geochemical examination of the ores and the country rocks. Following different techniques of atomic absorption, the abundances of Cu, Co, Ni, Pb, Zn, Cd, Ag, Mn and Hg were determined and the trace element characteristics of the principal rock units in and outside the shear zone have been compiled and critically evaluated. The data suggest that the ore deposits are the result of a sequence of long-continued and over-lapping geological processes culminating in intense shearing, syntectonic granitization and considerable mobilization of the ore elements. The Precambrian metasedimentary and metavolcanic rocks of the shear zone, as well as those enclosing it, served as the source, while diffusion of the ore constituents and their precipitation in physicochemically favourable structural traps, formed in response to shearing, resulted in the formation of the deposits.

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Zusammenfassung Als Beitrag zur Klärung der Genese der Kupferlagerstätten in der Singhbhum Shear Zone, Indien, wurden geochemische Untersuchungen an Erzen und Nebengestein durchgeführt. Spurengehalte von Cu, Co, Ni, Pb, Zn, Cd, Ag, Mn, Hg wurden mit Hilfe der AAS bestimmt, ihre Verteilung innerhalb der Zone und der angrenzenden Gesteinstypen wird diskutiert. Auf Grund der vorliegenden geochemischen Daten wird folgende Deutung zur Entstehung der Erzlagerstätten gegeben: Die Bildung der Singhbhum-Erzvorkommen ist das Ergebnis einer Folge langandauernder und sich überschneidender geologischer Prozesse, wie intensiver Scherung, syntektonischer Granitisation und damit verbundener Mobilisierung der oben genannten Elemente. Die präkambrischen Metasedimente und Metavulkanite innerhalb der Scherzone und ihrer näheren Umgebung sind als Muttergesteine der erzbildenden Elemente anzusehen. Die Bildung der Lagerstätte ist das Resultat der Diffusion von Lösungen und ihres Absatzes in physikalisch-chemisch günstigen Struktur-Fallen, gebildet im Anschluß an die Scherung.

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Comparison of two forest types using adeos 1-polder data over west coast of India     

Anjum Mahtab  V. N. Sridhar  Ranendu Ghosh 《Journal of the Indian Society of Remote Sensing》2004,32(3):261-268

Parametric kernel-based models for Bi-directional Reflectance Distribution Function (BRDF) of vegetated land surfaces attempt to describe the BRDF as a linear superposition of a set of kernels describing basic angular shapes. The kernels and associated model coefficients are derived as approximations to the underlying theories of radiative transfer as well as geometric-optical scattering within vegetation canopies. In the present study, five kernels viz. Ross-Thick, Li-Sparse, Ross-Thin, Li-Dense and Roujean geometric-optical (GO) kernels along with a purely empirical model were examined for their suitability in describing the angular characteristics of two forest types (semi-evergreen and deciduous) during November 1996-March 1997 using ADEOS-1 POLDER data. The statistically significant kernels and their combinations with respect to red and NIR (near infra-red) wavelengths were determined using correlation analysis. Atmospherically corrected POLDER measured reflectances at red and NIR wavelengths were regressed with different kernels and their combinations. It is found that the best fitting volume and GO kernel combinations depend on forest type, wavelength and date.  相似文献   

Morphology, mineralogy and magnetic susceptibility of epikarst-Terra Rossa developed in late Quaternary aeolianite deposits of southeastern Saurashtra, India     

Aniruddha S. Khadkikar  Nathani Basavaiah 《Geomorphology》2004,58(1-4):339-355

The nature and development of epikarst and soil development in aeolianites under a monsoonal climatic regime has not yet been described. Late Quaternary aeolianites of the southeastern coast of Saurashtra in western India show a wide array of epikarst and red-soil formation, and serve to typify the character of aeolianite weathering under a monsoonal climate. Three varieties of epikarst are identified that represent down-profile increase in groundwater flow. Five types of Terra Rossae represent a transition from the karstified limestone to soil development. Terra Rossae differ in the content of residual aeolianite and show both simple and complex profiles. The latter at places shows ped development. The results show that an ontogenetic (growth) sequence exists from incipient epikarst to complex palaeosols. This ontogenetic sequence represents an incremental increase in the groundwater budget of the region in response to changing intensification of the Indian monsoon rainfall. Magnetic properties of the Terra Rossae formed under a monsoonal climate are described for the first time. The magnetic susceptibility together with its frequency-dependent and anhysteretic remanent magnetization (ARM) represents both the concentration of single domain and ultrafine superparamagnetic (SP) magnetite. The formation of single domain and superparamagnetic magnetite and hematite are linked genetically to weathering of the aeolianite that leads to the formation of Terra Rossa.  相似文献   

Pull-apart origin of the Satpura Gondwana basin, central India     

Chandan Chakraborty  Sanjoy Kumar Ghosh 《Journal of Earth System Science》2005,114(3):259-273

The Gondwana basins of peninsular India are traditionally considered as extensional-rift basins due to the overwhelming evidence of fault-controlled synsedimentary subsidence. These basins indeed originated under a bulk extensional tectonic regime, due to failure of the attenuated crust along pre-existing zones of weakness inherited from Precambrian structural fabrics. However, disposition of the basins and their structural architecture indicate that the kinematics of all the basins cannot be extensional. To maintain kinematic compatibility with other basins as well as the bulk lateral extension, some basins ought to be of strike-slip origin. The disposition, shape and structural architecture of the Satpura basin, central India suggest that the basin could be a pull-apart basin that developed above a releasing jog of a left-stepping strike-slip fault system defined by the Son-Narmada south fault and Tapti north fault in consequence to sinistral displacement along WSW-ENE. Development of a sedimentary basin under the above-mentioned kinematic condition was simulated in model experiments with sandpack. The shape, relative size, stratigraphic and structural architecture of the experimental basin tally with that of the Satpura basin. The experimental results also provide insights into the tectono-sedimentary evolution of the Satpura basin in particular and pull-apart basins in general.  相似文献   

Kinematics of large scale asymmetric folds and associated smaller scale brittle — Ductile structures in the proterozoic somnur formation, pranhita — Godavari Valley, South India     

Gautam Ghosh  Dilip Saha 《Journal of Earth System Science》2005,114(2):125-142

The development of structural elements and finite strain data are analysed to constrain kinematics of folds and faults at various scales within a Proterozoic fold-and-thrust belt in Pranhita-Godavari basin, south India. The first order structures in this belt are interpreted as large scale buckle folds above a subsurface decollement emphasizing the importance of detachment folding in thin skinned deformation of a sedimentary prism lying above a gneissic basement. That the folds have developed through fixed-hinge buckling is constrained by the nature of variation of mesoscopic fabric over large folds and finite strain data. Relatively low, irrotational flattening strain (X:Z-3.1-4.8, k<1) are associated with zones of near upright early mesoscopic folds and cleavage, whereas large flattening strain (X:Z-3.9-7.3, k<1) involving noncoaxiality are linked to domains of asymmetric, later inclined folds, faults and intense cleavage on the hanging wall of thrusts on the flanks of large folds. In the latter case, the bulk strain can be factorized to components of pure shear and simple shear with a maximum shearing strain of 3. The present work reiterates the importance of analysis of minor structures in conjunction with strain data to unravel the kinematic history of fold-and-thrust belts developed at shallow crustal level.  相似文献   

Effect of Mothers' Exposure to Electronic Mass Media on Knowledge and Use of Prenatal Care Services: A Comparative Analysis of Indian States*     

Debarchana Ghosh 《The Professional geographer》2006,58(3):278-293

The Government of India considers prenatal care programs as a priority activity for promoting safe motherhood and child survival. It relies heavily on electronic mass media, including radio, television, and cinema to educate mothers—two‐thirds of whom are illiterate—about prenatal check‐ups and timing, iron prophylaxis, and tetanus toxoid injections. This study evaluated the effect of mothers' exposure to electronic mass media on knowledge and use of prenatal care services, using data from India's 1998–1999 National Family Health Survey. Multivariate logistic regressions were used to estimate the effects of media exposure by calculating odds ratios of each of the four response variables (complete prenatal care services, prenatal check‐ups, tetanus toxoid injections, and iron prophylaxes) for exposure to mass media. The results indicated that exposure to mass media is related to the use of prenatal care services even when other likely causes of the relationships are statistically controlled at their mean. The effect also showed a north‐south divide among the Indian States, being stronger in northern states as compared with southern states.  相似文献