Mesoscale moisture transport effects on forest edges in a fragmented landscape in Amazonia     

Somnath Baidya Roy 《Climatic change》2011,108(3):609-617

This work explores the dry season micrometeorology of fragmented forests in Amazonia. Numerical simulations with a coupled atmosphere-vegetation model show that mesoscale moisture transport leads to a significant drying and vegetation stress at the forest edges. Increased evaporation cannot fully compensate for the drying. Typical convective precipitation events that occur in the dry season have a localized impact and do not affect the drying trend in the long term. Availability of soil moisture can partially mitigate the drying effect and consequent vegetation stress. Edge effects can dominate the vegetation dynamics and fire susceptibility of forest fragments as a whole. Hence, understanding the dynamics and drivers of edge effects is crucial for understanding the ecology and future of tropical forests in a changing climate.  相似文献   

Critical Investigation of Wear Behaviour of WC Drill Bit Buttons     

Anurag Gupta  Somnath Chattopadhyaya  Sergej Hloch 《Rock Mechanics and Rock Engineering》2013,46(1):169-177

Mining and petroleum drill bits are subjected to highly abrasive rock and high-velocity fluids that cause severe wear and erosion in service. To augment the rate of penetration and minimize the cost per foot, such drill bits are subjected to increasing rotary speeds and weight. A rotary/percussive drill typically hits the rock 50 times per second with hydraulic impact pressure of about 170–200 bar and feed pressure of about 90–100 bar, while rotating at 75–200 rpm. The drill rig delivers a high-velocity flow of drilling fluid onto the rock surface to dislodge cuttings and cool the bit. The impingement of high-velocity drilling fluid with entrained cuttings accelerates the erosion rate of the bit. Also, high service temperature contributes to softening of the rock for increased penetration. Hence, there is a need to optimize the drilling process and balance the wear rate and penetration rate simultaneously. This paper presents an experimental scanning electron microscopy (SEM) study of electroplated (nickel-bonded) diamond drills for different wear modes.  相似文献   

Exploring star formation using the filaments in the Sloan Digital Sky Survey Data Release Five     

Biswajit Pandey  Somnath Bharadwaj 《Monthly notices of the Royal Astronomical Society》2008,387(2):767-771

We have quantified the average filamentarity of the galaxy distribution in seven nearly two-dimensional strips from the Sloan Digital Sky Survey Data Release Five (SDSS DR5) using a volume-limited sample in the absolute magnitude range  −21 ≤ M _r ≤−20  . The average filamentarity of star-forming (SF) galaxies, which are predominantly blue, is found to be more than that of other galaxies which are predominantly red. This difference is possibly an outcome of the fact that blue galaxies have a more filamentary distribution. Comparing the SF galaxies with only the other blue galaxies, we find that the two show nearly equal filamentarity. Separately analyzing the galaxies with high star formation rates (SFR) and low SFR, we find that the latter has a more filamentary distribution. We interpret this in terms of two effects. (i) A correlation between the SFR and individual galaxy properties like luminosity with the high-SFR galaxies being more luminous. (ii) A relation between the SFR and environmental effects like the density with the high-SFR galaxies preferentially occurring in high-density regions. These two effects are possibly not independent and are operating simultaneously. We do not find any difference in the filamentarity of SF galaxies and active galactic nuclei.  相似文献   

31 IGC in Rio de Janeiro, 2000     

Somnath Dasgupta 《Gondwana Research》2001,4(2):251

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Mid-crustal contact metamorphism around the Chimakurthy mafic-ultramafic complex, Eastern Ghats Belt, India     

Somnath Dasgupta  Jürgen Ehl  Michael M. Raith  Pulak Sengupta  Pranesh Sengupta 《Contributions to Mineralogy and Petrology》1997,129(2-3):182-197

Pelitic rocks were thermally metamorphosed at the contact of the Chimakurthy mafic-ultramafic igneous complex, Eastern Ghats Belt, India. The rocks show progressive change in mineralogy from biotite-sillimanite-quartz-garnet-K-feldspar (association I, 150 m from the intrusive contact) to garnet-spinel-cordierite-K-feldspar-sillimanite (association II, 20–30 m from the intrusive contact) to cordierite-K-feldspar-(cordierite-orthopyroxene-K-feldspar symplectite after osumilite)-spinel-FeTiAl oxides with/without garnet (associations III and IV, 5 m from the intrusive contact), and finally to spinel-orthopyroxene-cordierite-K-feldspar (association V, xenoliths). Oxide mineral clots in associations III and IV resemble emery-type rocks. Initial mineral reactions involved biotite-dehydration melting with partial segregation of the melt. Down-temperature mineral reactions were largely diffusion controlled and preservation of symplectitic and coronitic textures in microdomains is common. Interpretation of reaction textures in relevant petrogenetic grids for the sytems KFMASH and FMAS and combined with geothermobarometry suggest that the pelitic rocks were thermally metamorphosed at c. 6 kbar pressure along a heating-cooling trajectory within the temperature interval between c. 750 °C and c. 1000 °C. Received: 20 October 1996 / Accepted: 17 June 1997  相似文献   

Mixing behavior in quaternary garnet solid solution and an extended Ellis and Green garnet-clinopyroxene geothermometer   总被引：7，自引：0，他引：7  

Pulak Sengupta  Somnath Dasgupta  P. K. Bhattacharya  Y. Hariya 《Contributions to Mineralogy and Petrology》1989,103(2):223-227

Applications of the different formulations of garnet-clinopyroxene geothermometers to crustal granulites and particularly to metamorphosed manganese formations show a wide scatter of estimates. This is primarily related to the uncertainty associated with the formulation of the activity-composition relationship in garnet solid solution besides that in the clinopyroxene solid solution. The largest uncertainty appears to have resulted from the adopted Mg-Mn interaction parameter in garnet which is yet to be experimentally determined. A fresh statistical regression of eleven pairs of garnet and clinopyroxene equilibrated at identical P-T conditions from a manganese formation in India yields W _Mg-Mn ^Gt (=W_Mn-Mg) value of 1600±500 cal/mols. An extension of the Ellis and Green (1979) geothermometer, known to work well in normal granulites, incorporating terms associated with the activity coefficients of the exchangeable cations, now yields consistent temperature estimation from normal granulites as well as from metamorphosed manganese formations. The geothermometer, however, will not work well for garnet having X_Fe0.65 and clinopyroxenes containing appreciable Na, Al and/or Fe³⁺.  相似文献   

Geochemistry of braunite and associated phases in metamorphosed non-calcareous manganese ores of India     

P. K. Bhattacharyya  Somnath Dasgupta  M. Fukuoka  Supriya Roy 《Contributions to Mineralogy and Petrology》1984,87(1):65-71

In the metamorphosed manganese oxide ores of India, braunite is ubiquitous in all assemblages from chlorite to sillimanite grades. Chemical analyses of braunite from different prograde assemblages confirm the presence of a fixed R²⁺ (=Mn²⁺+Mg+Ca) SiO₃ molecule in the mineral. Element partitioning between coexisting braunite and bixbyite indicates a near-ideal mixing of Fe⁺³/ -Mn⁺³ in the phases. This also indicates that braunite became relatively ferrian while equilibrating with associated phases such as bixbyite, hollandite and jacobsite during prograde reactions. Petrogenetic studies show that as a general trend, prograde lower oxide phases appeared by deoxidation of higher oxide phases. But braunite, a more reduced phase than bixbyite, appeared early from deoxidation of pyrolusite in presence of quartz. Bixbyite could appear later from the reacting pyrolusite-braunite-quartz assemblage. Inferred mineral reaction paths and the general trend of pro-grade deoxidation reactions suggest that the composition of ambient fluid phase was internally buffered during metamorphism.  相似文献   

Multidimensional poverty in slums: an empirical study from urban India     

Kaibarta  Samyakami  Mandal  Somnath  Mandal  Pintu  Bhattacharya  Subhasis  Paul  Suman 《GeoJournal》2022,87(4):527-549

Poverty is the most important metric for determining the nature and sense of wellbeing in a given area. Most economists consider poverty to be an economic criterion for assessing many aspects of human development as well as overall social development; yet, society is multi-faceted in its many forms. To address this pressing societal issue, the current study used the Multidimensional poverty index (MPI). To analyse urban poverty among slum communities, the researchers used the Global MPI of the Oxford Poverty and Human Development Initiative and UNDP (following Alkire and Foster) techniques. Researchers attempted to create a Multidimensional poverty index (MPI) for impoverished households in Purulia's designated slums in this study. In the second phase, the multidimensional poverty of Purulia's urban poor households was assessed based on (a) location, (b) social groupings, and (c) length of stay. Finally, researchers have attempted to identify the factors that contribute to multidimensional poverty. Two indicators, the Head Count Ratio (H) and Intensity of Poverty, have been offered to better explain the nature of MPI (A). Based on slum population density and areal density, eight urban slum areas with 320 households has been taken from 8 selected slums based on Yamane’s methodology from Purulia Municipality's wards. A structured questionnaire, an oral history interview, and a focus group discussion were used as primary data sources, with secondary data acquired from several officially published sources. The study displays a decomposed multidimensional poverty picture in terms of overall condition, socioeconomic groups, and household age, with a quantitative methodology that is transparent. When the locations have been considered, a qualitative approach has been used to determine that the slums closest to the railway track are the most multidimensionally disadvantaged of the eight slums. Furthermore, the schedule caste population has been found to be more deprived across many socioeconomic groups, with Scheduled tribe (ST) households being the most deprived in terms of health on one hand (applied quantitative methodology) and multi-nominal regression (applied qualitative methodology) indicating a mix mode approach. This form of analysis, which combines quantitative and qualitative approaches, can aid stakeholders and policymakers in developing specific poverty-reduction policies at the regional level.

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Evidence of Superposed Metamorphism from the Gokavaram Area, Eastern Ghats Belt, and its Relation with the Kemp Land Coast, East Antarctica     

Somnath Dasgupta  Pulak Sengupta  Supratim Pal  Masato Fukuoka 《Gondwana Research》1999,2(2):227

In this paper, we compare the petrological histories of the Kemp Land Coast (east Antarctica), and Gokavaram area (Eastern Ghats), that were supposed to have been juxtaposed. The area around Gokavaram is dominated by different varieties of paragneisses (pelitic, quartzofeldspathic, and calcareous composition) with relatively minor amounts of orthogneisses (mafic, enderbitic, and granitic composition). The rocks were involved in three major phases of deformation, and were finally affected by localised shear movement. On the basis of reaction textures, well preserved in high Mg-Al granulites, and calc-silicate granulites, and geothermobarometric data we deduce a polymetamorphic evolution of the rocks. Following an early M₁ metamorphism culminating at 9.2–9.4 kbar, > 950°C, the rocks cooled nearly isobarically down to 850°C. During a subsequent M₂ metamorphism, near isothermal decompression to 5–6 kbar occurred. This was followed by near isobaric cooling down to 600–650°C. M₃ is a weak amphibolite facies overprint, largely restricted to late shears, which involved hydration as well. Available radiometric data from this area can be interpreted in terms of partial resetting of U-Pb systematics in older sphenes due to M₃ metamorphism at ca. 550 Ma. Despite the absence of sufficient isotopic data on the Eastern Ghats granulites, we document a remarkable similarity in the petrological history of the two supposedly erstwhile neighbours.  相似文献   

Efficacy of Fine-Grained Soil as Landfill Liner Material for Containment of Chrome Tannery Sludge     

Sudipta Ghosh  Somnath Mukherjee  Ashraf Z. Al-Hamdan  Krishna R. Reddy 《Geotechnical and Geological Engineering》2013,31(2):493-500

This paper evaluates the potential use of a fine-grained soil obtained from a site in West Bengal, India, as a suitable landfill liner material for the containment of hexavalent chromium from tanning waste sludge. The physico-chemical properties of the soil were determined. The soil adsorption affinity for hexavalent chromium was also assessed through adsorption batch and breakthrough column tests. The zero point charge (pH_zpc) of the soil was found to be 7.3. The batch kinetics and column tests results indicated that the soil liner possesses a relatively good hexavalent chromium adsorption capacity at natural or slightly alkaline condition. The adsorption results showed that the hexavalent chromium uptake by the soil follows both Langmuir and Freundlich adsorption isotherms. This study also illustrated that the hexavalent chromium breakthrough curve in the column experiment reached equilibrium concentration after 3.5 pore volumes (900 h). Overall, this study showed that the fine-grained soil has the potential for usage as a landfill liner or as a component of a landfill barrier system to prevent chromium contamination from the tannery waste disposal.  相似文献