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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
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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
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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
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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
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We have tried to determine the flux of the ultraviolet background radiation field from the column density ratios of various
ions in several absorption systems observed in the spectra of QSOs. We find that in most cases the flux is considerably higher
than what has been estimated to be contributed by the AGNs. The excess flux could originate locally in hot stars. In a few
cases we have been able to show that such galactic flux can only contribute a part of the total required flux. The results
suggest that the background gets a significant contribution from an unseen QSO population. 相似文献
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We study the effects of incorporating magnetic buoyancy in a model of the solar dynamo—which draws inspiration
from the Babcock-Leighton idea of surface processes generating the poloidal field. We present our main results here. 相似文献
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Pixel-based or texture-based classification technique individually does not yield an appropriate result in classifying the high spatial resolution remote sensing imagery since it comprises textured and non-textured regions. In this study, Hölder exponents (HE) and variance (VAR) are used together to transform the image for measuring texture. A threshold is derived to segment the transformed image into textured and non-textured regions. Subsequently, the original image is extracted into textured and non-textured regions using this segmented image mask. Afterward, extracted textured region is classified using ISODATA classification algorithm considering HE, VAR, and intensity values of individual pixel of textured region. And extracted non-textured region of the image is classified using ISODATA classification algorithm. In case of non-textured region, HE and VAR value of individual pixel is not considered for classification for significant textural variation is not found among different classes. Consequently, the classified outputs of non-textured and textured regions that are generated independently are merged together to get the final classified image. IKONOS 1 m PAN images are classified using the proposed algorithm, and the classification accuracy is more than 88%. 相似文献