排序方式： 共有37条查询结果，搜索用时 156 毫秒
21.
We study the relationship between full-disk solar radiative flux at different wavelengths and average solar photospheric magnetic-flux
density, using daily measurements from the Kitt Peak magnetograph and other instruments extending over one or more solar cycles.
We use two different statistical methods to determine the underlying nature of these flux – flux relationships. First, we
use statistical correlation and regression analysis and show that the relationships are not monotonic for total solar irradiance
and for continuum radiation from the photosphere, but are approximately linear for chromospheric and coronal radiation. Second,
we use signal theory to examine the flux – flux relationships for a temporal component. We find that a well-defined temporal
component exists and accounts for some of the variance in the data. This temporal component arises because active regions
with high magnetic-field strength evolve, breaking up into small-scale magnetic elements with low field strength, and radiative
and magnetic fluxes are sensitive to different active-region components. We generate empirical models that relate radiative
flux to magnetic flux, allowing us to predict spectral-irradiance variations from observations of disk-averaged magnetic-flux
density. In most cases, the model reconstructions can account for 85 – 90% of the variability of the radiative flux from the
chromosphere and corona. Our results are important for understanding the relationship between magnetic and radiative measures
of solar and stellar variability. 相似文献
22.
Dibyendu Nandy 《Astrophysics and Space Science》2002,282(1):209-219
We report here results from a dynamo model developed on the lines of the Babcock-Leighton idea that the poloidal field is
generated at the surface of the Sun from the decay of active regions. In this model magnetic buoyancy is handled with a realistic
recipe – wherein toroidal flux is made to erupt from the overshoot layer wherever it exceeds a specified critical field B
c (105 G). The erupted toroidal field is then acted upon by the α-effect near the surface to give rise to the poloidal field. In
this paper we study the effect of buoyancy on the dynamo generated magnetic fields. Specifically, we show that the mechanism
of buoyant eruption and the subsequent depletion of the toroidal field inside the overshoot layer, is capable of constraining
the magnitude and distribution of the magnetic field there. We also believe that a critical study of this mechanism may give
us new information regarding the solar interior and end with an example, where we propose a method for estimating an upper
limit of the difusivity within the overshoot layer.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
23.
24.
Sejuti Naha Biswas Dibyendu Rakshit Santosh Kumar Sarkar Ranjit Kumar Sarangi Kamala Kanta Satpathy 《Marine pollution bulletin》2014
A multispecies bloom caused by the centric diatoms, viz. Coscinodiscus radiatus, Chaetoceros lorenzianus and the pennate diatom Thalassiothrix frauenfeldii was investigated in the context of its impact on phytoplankton and microzooplankton (the loricate ciliate tintinnids) in the coastal regions of Sagar Island, the western part of Sundarban mangrove wetland, India. Both number (15–18 species) and cell densities (12.3 × 103 cells l−1 to 11.4 × 105 cells l−1) of phytoplankton species increased during peak bloom phase, exhibiting moderately high species diversity (H′ = 2.86), richness (R′ = 6.38) and evenness (E′ = 0.80). The diatom bloom, which existed for a week, had a negative impact on the tintinnid community in terms of drastic changes in species diversity index (1.09–0.004) and population density (582.5 × 103 to 50 × 103 ind m−3). The bloom is suggested to have been driven by the aquaculture activities and river effluents resulting high nutrient concentrations in this region. An attempt has been made to correlate the satellite remote sensing-derived information to the bloom conditions. MODIS-Aqua derived chlorophyll maps have been interpreted. 相似文献
25.
Dibyendu?Ghosh Debashish?ChakravartyEmail author 《Journal of the Indian Society of Remote Sensing》2012,40(2):179-190
Any underground excavation or depletion of either solid minerals or liquids may lead to deformation of the surface profile
for areas present above these underground zones. The awareness of deformation rate or rate of change of the natural surface
is very important for proper planning and utilization of the geo-resources. These often suffer from the limitations of proper
methods of data capture in such areas, accessible or in-accessible to the human beings; in terms of the data density, the
time involved in the data capturing process and the associated risks in doing so. Once a proper data is captured, it may easily
be used to generate the models of the geo-structures present in and around the region of interest. Till date, the conventional
methods of surveying, like precise leveling or GPS, were used for the data capture, which are point observations and suffer
from disadvantages like limited spatial resolution, large data capture time, easy manipulability of the collected data, high
risk for the operators involved, high cost for large areas etc. With the advent of newer and advanced techniques of data capture
in geo-information; use of high precision satellite imagery, especially the synthetic aperture radar (SAR) data having the
complex information (i.e. the phase as well as amplitude), has been found to provide adequate data for such purposes. Interferometric
synthetic aperture radar (InSAR) is a technique used to reconstruct the digital elevation models (DEM) of the observed scenes.
Determination of the surface deformation profiles, integrating the surface displacements using the GIS tool (GRASS) and verification
of the surface displacement rates become the main objectives of the present paper. It has been observed that the values of
the displacement rates computed using the new method match closely with those obtained using the conventional methods of surface
data capture techniques. It has also been found that the new method has several advantages over the conventional methods,
as discussed later in this paper. 相似文献
26.
S. Rakshit C. J. Matocha M. S. Coyne D. Sarkar 《International Journal of Environmental Science and Technology》2016,13(5):1329-1334
Interactions of iron (Fe) with the nitrogen (N) cycle have emerged and contain elements of abiotic and biological reactions. One such abiotic reaction which has received little study is the reactivity of NO2 ? and Fe(II) associated with a major clay mineral, kaolinite. The main objective of this study was to evaluate the reactivity of NO2 ? with Fe(II) added to kaolinite under anoxic conditions. Stirred batch reactivity experiments were carried out with 10 g L?1 kaolinite spiked with 25 and 100 µM Fe(II) at pH 6.45 in an anaerobic chamber. Approximately 500 µM NO2 ? was added to initiate the reaction with Fe(II)-loaded kaolinite. The rate of nitrite removal from solution was 2.4-fold slower in the high Fe(II) treatment when compared with the low Fe(II) treatment. A large portion of the NO2 ? removed from solution was confirmed to be reduced to N2O(g) in the Fe(II)-kaolinite slurries. However, NO2 ? reduction was also noticed in the presence of kaolinite-alone and to somewhat lesser extent in the presence of dithionite-citrate-bicarbonate (DCB)-treated kaolinite. Chemical extractions coupled with infrared spectroscopy suggest that Fe(III) oxide mineral impurities and structural Fe(III) in kaolinite may participate in NO2 ? removal from solution. Furthermore, a magnetite mineral was identified based on X-ray diffraction analysis of untreated kaolinite and DCB-treated kaolinite. Our findings reveal a novel pathway of NO2 ? transformation in the environment in the presence of Fe(II) associated (sorbed and impurity) with kaolinite. 相似文献
27.
Ingestion of As – contaminated soil by children is a growing concern in former agricultural lands converted to residential or recreational land use areas. The mobility and bioavailability of As is controlled by its reactions with soil particles. The degree and strength of As retention by soil constituents may vary greatly with time. The present authors hypothesize that aging results in reduced mobility of As thereby decreasing As release and its bioavailability. The present study is aimed at evaluating the effect of aging on soil As fractionation and bioaccessibility in a temperature and humidity-controlled greenhouse setting. The design allowed the evaluation of dynamic interactions between soils, pesticides, water, and plants. Therefore, 4 soil types (Immokalee, Millhopper, Pahokee Muck, and Orelia) were selected based on their potential differences in As reactivity. The soils were amended with the pesticide Na arsenate at two rates. Rice was used as the test crop. Soil samples collected after different time periods (0, 6 months, 1 a and 3 a) were extracted for soil-As forms via a sequential extraction technique. Bioaccessible As was extracted via an in vitro gastrointestinal method. At time 0, most of the extractable As in soil was in the soluble form, resulting in high bioaccessibility. As expected, soluble and exchangeable fractions decreased with time for up to 6 months, but remained constant thereafter. After 3 a of soil–pesticide equilibration, As bioaccessibility was still high in all the soils except for the Pahokee Muck. No significant difference in As bioaccessibility was observed between the soils. Arsenic was present predominantly as As(V) with 5–10% of the total dissolved As being present as As(III). Data obtained suggest that although aging had an impact on the geochemical forms, gastric pH was the sole important factor effecting As bioaccessibility. 相似文献
28.
Syam S. Andra Rupali Datta Ramana Reddy Sumathi K. M. Saminathan Dibyendu Sarkar 《洁净——土壤、空气、水》2011,39(5):428-436
In a previous study we have demonstrated the suitability of using vetiver grass (Vetiveria zizanioides L.) for the phytostabilization of lead‐based paint contaminated residential soils. Vetiver did not show any growth retardation or toxicity symptoms despite high soil Pb levels. Antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) reportedly allow plants to combat metal stress. Thus, we hypothesized that in vetiver, these antioxidant enzymes can play an important role in combating Pb induced stress, and that chelant‐bound Pb is less toxic to vetiver compared to free Pb in soil. The response of antioxidant enzymes was studied in vetiver grass grown in Pb paint‐contaminated residential soils collected from San Antonio, Texas and Baltimore, Maryland. Chelating agents such as ethylenediaminetetraacetic acid (EDTA) and ethylenediaminedisuccinic acid (EDDS) were used to mobilize Pb from bound fractions to the labile pool, facilitating Pb uptake by vetiver. Although the Pb concentration in vetiver from these treatments was significantly higher than those grown in the absence of a chelant, the antioxidant enzymes activities were lower compared to the latter. Antioxidant enzymes activity of vetiver plants grown in the presence of chelants is lower compared to those in without chelant treatment, while they tended to increase with dose in treatments with varying chelant concentrations. Data obtained support the proposed hypothesis. 相似文献
29.
The problem of liquid sloshing has gained recent attention with the proliferation of liquefied natural gas (LNG) carriers transporting liquids in partially filled tanks. Impact pressures caused by sloshing depend on the tank fill level, period and amplitude of oscillation of the tank. In this paper, we first present the rudiments of a linear potential theory for sloshing motions in a two-dimensional rectangular tank, due to small amplitude sway motions. Although this topic is fundamental, we clarify inconsistencies in the published literature and texts.Numerical investigations were carried out on the sloshing motions in a two-dimensional tank in the sway excitation. The fluid domain was modeled using a finite volume approximation, and the air–water interface was tracked using a volume-of-fluid (VOF) technique. Computational results for free surface elevation and impact pressure are found to be in good agreement with theory and published data. The fill levels were varied from 10% to 95%, and the excitation time periods were varied from 0.8 to 2.8 s for a constant sway amplitude of 0.25 m (peak–peak) at 1:30 scale. The results of the parametric study are compared with theoretical predictions and suggestions are made on incorporating sloshing effects in standard seakeeping analysis for LNG carriers. 相似文献