Exploring Magnetic Activity from The Sun to the Stars     

Dibyendu Nandy 《Solar physics》2004,224(1-2):161-169

Sun-like stars are known to display a wide variety of magnetic activity which is likely to be the signature of a hydromagnetic dynamo mechanism working in stellar interiors. This dynamo mechanism has been studied extensively in the context of the Sun. Here we take ideas and experiences gained from solar dynamo modeling and build upon it to study the inferred scaling laws, involving stellar parameters, from observations of stellar magnetic activity. We also discuss how such a synthesis of theoretical dynamo modeling of Sun-like stars and stellar cycle observations may help us reconstruct the long-term variability of the Sun – an important ingredient for understanding the effects of solar forcing on space and global climate.  相似文献   

Experimental studies to constrain parental magma of Malangtoli volcanics from Singhbhum craton of the eastern Indian shield     

Mousumi Banerjee  Jyotisankar Ray  Nupur Adhikary  Sandip Nandy  C. Manikyamba  Madhuparna Paul  Dola Chakraborty  Alireza Eslami 《Journal of the Geological Society of India》2016,88(2):245-255

Malangtoli volcanics of the Singhbhum craton of the eastern Indian shield is one of the important Proterozoic lava suites. Experimental studies on 1 atmosphere pressure constrain the parental magma type and temperature range of crystallization of the parent magma (deduced to be in the range of 1500°C to 1200°C). The experimental studies show that at 1500°C, plagioclase is the first phase to crystallize, followed by few opaques which join along with plagioclase at 1450°C. At subsequent lower temperature (1400°C-1300°C), plagioclase and opaque continue to crystallize. At 1250°C plagioclase and opaque still persist while pyroxene appears first and liquid (glass) still remains. Appearance of opaque minerals (magnetite and illmenite) at both ~1400°C and ~1300°C indicate oscillation of oxygen fugacity in the parent magma, petrographically documented by coarser phenocrysts as well as finer or peripheral tiny grains. Use of tectonic discrimination diagrams (based on discrimination factors F₁-F₂ and FeO^t/MgO vs. TiO₂) shows an island arc tholeiitic affinity for Malangtoli volcanic, suggests that the role of proto-plate convergence in Singhbhum architecture played an important role to build up Malangtoli volcanics during Proterozoic.  相似文献   

Texture Measurement Through Local Pattern Quantization for SAR Image Classification     

Debasish Chakraborty  Dibyendu Dutta  Jaswant Raj Sharma 《Journal of the Indian Society of Remote Sensing》2016,44(3):471-477

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Land use indicators of a watershed in arid region, western Rajasthan using Remote Sensing and GIS     

Debashis Chakraborty  Dibyendu Dutta  H Chandrasekharan 《Journal of the Indian Society of Remote Sensing》2001,29(3):115-128

The vegetation dynamics and land use/land cover types of Birantiya Kalan watershed located in the arid tracts of western Rajasthan have been characterized and evaluated using Remote Sensing and Geographical Information System (GIS). The watershed under study falls in the transitional plain of Luni Basin and is characterized by Aravali ranges in the eastern half and vast alluvial plains in the west. The land use/land cover types, as identified are cropland, fallow, forest, land with scrub, land without scrub, sandy area and the water body. Land with scrub occupied maximum area (39% area of the watershed) in 1996 in place of crop land which was dominant (43% of total area) in the year 1988. During eight years period, seasonal fallow land increased significantly and the areal extent of water body decreased to almost half. Vegetation vigour types have been classified into very poor, poor. moderate, good and very good categories. Moderate vigour type reduced from 62 to 27% and poor type increased from 34 to 68% during the period 1988 to 1996. Other vegetation vigour types have not shown any significant changes. To quantify the changes over the years in both vegetation and land use/land cover, weightages have been given to each type and composite values of both vegetation vigour and land use types for 1996 and 1988 have been calculated. It has been observed that the ratio for vegetation vigour has been found to be 0.85 showing that the overall vegetation have not improved after the treatment. The ratio for land use is found to be 1.01, which indicates negligible change in land use.  相似文献   

The ratio of total to selective absorption in the galaxy     

J. G. Ireland  K. Nandy 《Astrophysics and Space Science》1969,5(4):438-443

Values for the ratio of total to selective absorption are estimated from optical measurements on Cepheids, their radial velocities, and an assumed rotational velocity model of the Galaxy. It is shown that there is no systematic variation ofR with galactic longitude on the basis of these measurements.  相似文献   

A new method of photometric calibration of photographic plats by a doubly refracting crystal filter     

M. T. Brück  K. Nandy  G. Caprioli  F. Smriglio 《Astrophysics and Space Science》1969,4(2):213-217

A filter composed of a crossed pair of doubly refracting crystals and a polaroid, mounted at the focal plane of the telescope, divides each star image into two images of constant intensity ratio. It is shown that such a filter arrangement is capable of providing reliable photographic calibration for stellar photometry.  相似文献   

Preliminary assessment of the impacts of deep foundations and land reclamation on groundwater flow in a coastal area in Hong Kong, China   总被引：4，自引：2，他引：2  

Jiu J. Jiao  Xu-Sheng Wang  Subhas Nandy 《Hydrogeology Journal》2006,14(1-2):100-114

Many coastal areas have been intensively urbanized because people living and working on or near coastlines are increasing. Land reclamation from the sea and high-rise buildings are common approaches to satisfying the growing needs for more housing and other land use. Coastal areas are usually the ultimate discharge zones of groundwater systems. Using a coastal area in Hong Kong as a case study, this paper discusses the change in a groundwater system due to land reclamation and construction of building foundations in a coastal area. The upper part of the study area is in a nearly natural state, whereas the lower part is probably one of the most extensively developed areas in the world. It is evident that the groundwater flow system in this area has been changed over the last century. The piezometers in the transitional zone between the natural slopes and the urbanized areas indicate significant response to rainfall and obvious upward groundwater flow. To understand these piezometric responses to rainfall, a cross section is selected for detailed study using a two-dimensional multilayered numerical model. The parameters and structure of the aquifer system are calibrated by comparing the simulated and observed water levels. To reproduce the observed behavior of the groundwater system, the model has to include two important characteristics: a highly permeable zone at the rockhead and a reduction in hydraulic conductivity of 14–20 times in the urbanized area. The simulation demonstrates that both land reclamation along the coastline and deep foundations have contributed to the modification of the flow system, but the deep foundations have the most profound impact, especially when a high conductivity zone is present at the rockhead.

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Resumen Muchas áreas costeras han sido urbanizadas de manera intensiva, debido a la presión creciente de la gente que quiere vivir y trabajar en estos sitios. Los terrenos arrebatados al mar y los edificios de gran altura, son las respuestas comunes para satisfacer las necesidades de mas vivienda y usos nuevos para el suelo. Las áreas costeras son comúnmente las zonas de descarga final de los sistemas de agua subterránea. A través de un área costera en Hong Kong, tomada como estudio de caso, este artículo discute el cambio causado en un sistema de agua subterránea, debido a la recuperación de terrenos anteriormente cubiertos por el mar y a la construcción de cimientos de edificios en la zona costera. La parte más alta de la área de estudio está casi en su estado natural, mientras que la parte baja es probablemente una de las áreas más extensas en su tipo y más desarrolladas en el mundo. Es evidente que el sistema de flujo del agua subterránea en esta área ha sido cambiado a lo largo del último siglo. Los piezómetros en la zona transicional, entre los taludes naturales y las áreas urbanizadas, muestran una respuesta notable a la lluvia y un flujo evidente hacia arriba del agua subterránea. Para entender estas respuestas piezométricas a la lluvia, se seleccionó una sección vertical para estudio detallado, utilizando un modelo numérico bidimensional multicapa. Los parámetros y estructura del sistema acuífero son calibrados mediante la comparación de los niveles de agua observados y simulados. Para reproducir el comportamiento observado del sistema de agua subterránea, el modelo ha incluido dos características importantes: Una zona altamente permeable en la parte más elevada y una reducción de 14 a 20 veces en la conductividad hidráulica, dentro de la zona urbanizada. La simulación demuestra que tanto los terrenos recuperados del mar, como las cimentaciones profundas a lo largo de la línea de costa, han contribuido a la modificación del sistema de flujo, pero las cimentaciones profundas han causado el mayor impacto, especialmente cuando se presenta una zona de alta conductividad en la parte más elevada del área.

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Résumé La plupart des zones côtières ont été intensivement urbanisé due à la croissance de la population qui travaille et vive sur les zones littorales. La récupération des terrains sur la mer ainsi que la construction des grandes immeubles sont les moyens usuels utilisés pour satisfaire les demandes accrues de logement. Dhabitude les zones côtières représentent lexutoire final des aquifères. En utilisant la zones côtière de Hong Kong comme un étude de cas cet article analyse les changements dans les systèmes aquifères produits par la récupération des terrains et par les fondations des grandes immeubles. Tendis que la partie supérieure de la zone étudiée se trouve presque à létat naturel, la partie inférieure représente une des zones les plus développée du monde. Il est donc évident que la circulation des eaux souterraines a été modifiée pendant le dernière siècle. Les piézomètres remplacés entre les versants et la zone urbanisée montrent une réponse significative aux précipitations ainsi quune hausse générale des niveaux. Pour mieux comprendre la réponse des niveaux aux plues on a modélisé lécoulement dans une coupe vericale en utilisant un modèle numérique multicouches. Les paramètres et la strucure du système aquifère ont été calés en comparant les niveaux calculés et mesurés. Affin de reproduire les niveaux mesurés le modèle doit considérer deux caratéristiques importantes: une zone périglaciaire à grande perméabilité et une diminution jusqu à vingt fois de la perméabilité dans les zone urbanisées. La simulation a mis en évidence que les récupération des terrains au long du littoral aussi bien que les fondations profondes ont modifié lécoulement mais que les dernières ont limpact le plus important surtout lorsquil sagit de la zone périglaciaire à grande perméabilité.

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Geochemical Fractionation of Trace Elements in Stream Sediments Contaminated by Mining Activity          下载免费PDF全文

Paulo J. C. Favas  Santosh Kumar Sarkar  Dibyendu Rakshit 《洁净——土壤、空气、水》2015,43(3):446-455

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Chelant‐assisted Phytostabilization of Paint‐contaminated Residential Sites     

Syam S. Andra  Dibyendu Sarkar  Sumathi K. M. Saminathan  Rupali Datta 《洁净——土壤、空气、水》2010,38(9):803-811

Following the basic incubation study, a greenhouse experiment was conducted to elucidate the efficiency of vetiver grass (Vetiveria zizanioides L.), with or without chelating agents, in remediating lead (Pb)‐contaminated soils from actual residential sites where Pb‐based paints were used. Because the primary factor affecting Pb phytoavailability in soils is soil pH, we used two soil types widely varying in pH that have total Pb concentrations above 1500 mg kg^?1 soil. Lead‐contaminated, low pH, acidic soils were collected from residential sites in Baltimore, MD and high pH, alkaline soils were collected from residential sites in San Antonio, TX. Based on the soil characterization results, two most appropriate soils (one from each city, having similar Pb levels but variable soil physico‐chemical properties) were selected for this study. Ethylenediaminetetraacetic acid (EDTA) and [S,S′]ethylenediaminedisuccinate (EDDS) were applied at 5, 10, and 15 mmol kg^?1 soil. Lead uptake and translocation in vetiver was determined on day 10 after chelants addition. Plant and soil analysis show that EDTA treated soils have maximum Pb uptake and lower total soil Pb levels. Prediction models developed for exchangeable Pb show a strong correlation for total Pb accumulated in vetiver grass. Results of the sequential chemical extraction of the soils at both initial and final time‐points, indicates a significant mobilization of Pb by the two chelants from carbonate‐bound fraction to exchangeable pool. Information on physico‐chemical properties of contaminated residential soils help in predicting Pb phytoextraction and thus further help in calibrating a successful chelant‐assisted phytoremediation model.  相似文献   

Morphometric analysis of the upper catchment of Kosi River using GIS techniques     

Hemant Balwant Wakode  Dibyendu Dutta  V. R. Desai  Klaus Baier  Rafig Azzam 《Arabian Journal of Geosciences》2013,6(2):395-408

Geographical Information System (GIS) have proved to be an efficient tool in the delineation of drainage pattern for water resources management and its planning. In this study, GIS and image processing techniques have been adopted for the identification of morphological features and analyzing the properties of the upper catchment of Kosi River. The basin area includes the high-altitude Himalayan Mountains, including Mount Everest and Kanchenjunga peaks. This basin is the main contributing area for devastating floods in 2008 in the Bihar state of India. The catchment can be divided into three sub-catchments, namely, Arun, Sunkosi, and Tamur. A morphometric analysis shows the nature of drainage in the upper catchment of Kosi River and some causes behind the high-intensity floods by comparing the properties of these three sub-catchments. It shows that the highest-order drains are present in both Arun and Sunkosi and the length of the first-order drains is very high (6,088 km) due to the absence of vegetation and also due to the barren/rocky surface which has tremendous potential to generate runoff. Due to highest mean channel gradient in Tamur sub-basin compared to others, it has the highest flow kinetic velocity. Also, the results show that the Arun sub-catchment has the highest potential to contribute runoff and sediment. One of the major causes behind the high intensity of floods is that the sub-catchments Arun and Sunkosi have a nearly equal time of concentration, so they contribute their peak floods at the same time and hence double the intensity of floods.  相似文献