A nova outburst scenario for GX 1+4 spin-down episode     

R. K. Manchanda 《Astrophysics and Space Science》1988,150(1):31-41

X-ray spectral data of the source during 1982–1987 suggest that the observed low state of the source intensity could have arisen due to additional absorption of the X-ray flux by material surrounding the X-ray source, which could have come from the companion star during a nova outburst. The accretion models can not explain the rapid spin-down of the pulsar. If the spin-down is caused by the nova outburst, it is suggested that period slow down can occur due to mechanical braking of the pulsar generated by the increased moment of inertia.  相似文献   

Soft X-ray emission from the high galactic latitude X-ray source MX 2140-60     

K. P. Singh  R. K. Manchanda  S. Naranan  B. V. Sreekantan 《Astrophysics and Space Science》1981,77(1):215-220

Soft X-rays (0.2–1.0 keV) have been detected from the high galactic latitude source MX 2140-60 in a rocket experiment. The measured flux of 10^–10 erg cm^–2 s^–1 combined with OSO-7 measurements in 2–40 keV X-rays, are best fit by a power law photon spectrum with spectral index 2.3 and a neutral hydrogen column densityN _H=(3–7) 10²⁰ atoms cm^–2. The observations support the source identification with the cluster of galaxies SC 2146-594, as suggested by Lugger.  相似文献   

Flood risk modeling for optimal rice planning for delta region of Mahanadi river basin in India     

Dibyendu Samantaray  Chandranath Chatterjee  Rajendra Singh  Praveen Kumar Gupta  Sushma Panigrahy 《Natural Hazards》2015,76(1):347-372

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The 8.2 ka event: Evidence for seasonal differences and the rate of climate change in western Europe     

Sushma Prasad  Annette Witt  Ulrike Kienel  Peter Dulski  Eva Bauer  Gergana Yancheva 《Global and Planetary Change》2009,67(3-4):218-226

Recent studies have drawn attention to differences in the seasonal impact of the 8.2 ka event, with longer cooler summers and shorter cooler/drier winters. However, there are no data available on the simultaneity or the rate of onset of the seasonal changes in Europe. Based on the microfacies and geochemical analyses of seasonally laminated varved sediments from Holzmaar, we present evidence of differences in duration and onset time of changes in summer temperature and winter rainfall during the 8.2 ka event. Since both summer and winter climate signals are co-registered within a single varve, there can be no ambiguity about the phasing and duration of the signals. Our data show that the onset and withdrawal of the 8.2 ka summer cooling occurred within a year, and that summer rains were reduced or absent during the investigated period. The onset of cooler summers preceded the onset of winter dryness by ca. 28 years. In view of the differences in nature and duration of the impact of the 8.2 ka event we suggest that a clearer definition of the 8.2 ka event (summer cooling or winter cooling/dryness) needs to be developed. Based on regional comparison and available modelling studies we also discuss the roles of solar variability, changes in North Atlantic Thermohaline circulation, and North Atlantic Circulation (NAO) during the period under consideration. Wavelet analyses of seasonal laminae indicates that the longer NAO cycles, linked to changes in the N. Atlantic temperatures, were more frequent during the drier periods.  相似文献   

Varve counting reveals high resolution radiocarbon reservoir age variations in palaeolake Lisan     

Sushma Prasad  J. F. W. Negendank  Mordechai Stein 《第四纪科学杂志》2009,24(7):690-696

The laminated lacustrine sediments deposited in the last glacial Lake Lisan represent annual deposits of primary aragonite and silty detritus that reflect the annual supply of bicarbonate‐bearing freshwater to the lake. A varve‐counting curve was constructed for the time interval of ca. 17.4–22 cal. ka BP based on aragonite U/Th, and atmospheric radiocarbon ages of organic debris recovered from the studied section. Radiocarbon in the primary (evaporitic) aragonite comprises both atmospheric and old carbon (reflecting the reservoir age). The aragonite reservoir ages were determined by comparing the aragonite radiocarbon dates to the varve counting curve, and are found to lie in the range 1900–600 a and display a continuous decline. This opens the possibility for high (annual) resolution monitoring of the reservoir age, similar in quality to tree ring counting, during the upper part of Marine Isotope Stage (MIS) 2. Our work also demonstrates that a ‘uniform’ reservoir age correction is inappropriate when determining the chronology of short‐term climate events in lacustrine environments. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Accuracy assessment in cotton acreage estimation using Indian remote sensing satellite data     

Sujay Dutta  S.A. Sharma  A.P. Khera  Ajai  M. Yadav  R.S. Hooda  K.E. Mothikumar  M.L. Manchanda 《ISPRS Journal of Photogrammetry and Remote Sensing》1994,49(6)

The accuracy of cotton crop classification using satellite data has been assessed with respect to a detailed land cover map prepared by field survey. The effect of spatial resolution on classification accuracy was studied using LISS-I (spatial resolution 72.6 m) and LISS-II data (spatial resolution 36.25 m) of the Indian remote sensing satellite IRS-1B. The performances of the maximum likelihood and the minimum distance to mean as classifiers have also been assessed. LISS-II data have been found to give a higher classification accuracy. The estimate of cotton acreage using LISS-II data was closer to that obtained from the base map. The maximum likelihood classifier (MXL) and the minimum distance to mean (MDM) classifier performed equally well.  相似文献   

Analysis of cropping pattern changes in Bathinda district,Punjab     

Sushma Panigrahy  S. S. Ray  Anil Sood  L. B. Patel  P. K. Sharma  J. S. Parihar 《Journal of the Indian Society of Remote Sensing》2004,32(2):209-216

A study was conducted in the Bathinda district of Punjab state for mapping the cropping pattern and crop rotation, monitoring long term changes in cropping pattern by using the satellite based remote sensing data along other spatial and non-spatial collateral data. Multi-date IRS LISS I and IRS WiFS sensor data have been used for this study. Cropping pattern maps and crop rotation maps were generated for the years 1988-89 and 1998-99. The present study has shown the increase of cropping intensity significantly, mainly due to increase in rice area. However, crop diversity has decreased mainly due to decline in the area under the minor crops like pearl millet, gram, rapeseed/ mustard. There is increase in area coverage of cotton-wheat and rice-wheat rotation, at the expense of the minor crops.  相似文献   

Use of GIS and remote sensing for crop diversification — a case study for Punjab state     

S. S. Ray  Anil Sood  Gargi Das  Sushma Panigrahy  P. K. Sharma  J. S. Parihar 《Journal of the Indian Society of Remote Sensing》2005,33(2):181-188

In this study, an attempt has been made to suggest crop diversification based on soil and weather requirements of different crops. State level spatial databases of various agro-physical parameters such as rainfall, soil texture, physiography and problem soil along with the agricultural area derived from remote sensing data were integrated using GIS. A raster based modelling approach was followed to arrive at suitable zones for practicing different cropping systems. The results showed that the south-western Punjab is suitable for low water requiring crops such as desi cotton, pearl millet, gram etc., where as north-eastern Punjab with high rainfall and excess drainage should practice maize based cropping system. Rice can be substituted by maize and other crops in Central Punjab, where water table is going down fast. Using this approach the area of rice based cropping system can be reduced from present 24.7 lakh ha to 19.6 lakh ha, thereby reducing the degradation of valuable land and water resources.  相似文献   

Monsoon driven changes in phytoplankton populations in the eastern Arabian Sea as revealed by microscopy and HPLC pigment analysis   总被引：1，自引：0，他引：1  

Sushma G. Parab  S.G. Prabhu Matondkar  H. do R. Gomes  J.I. Goes 《Continental Shelf Research》2006,26(20):2538-2558

Like the rest of the Arabian Sea, the west coast of India is subject to semi-annual wind reversals associated with the monsoon cycle that result in two periods of elevated phytoplankton productivity, one during the northeast (NE) monsoon (November–February) and the other during the southwest (SW) monsoon (June–September). Although the seasonality of phytoplankton biomass in these coastal waters is well known, the abundance and composition of phytoplankton populations associated with this distinct and predictable seasonal cycle is poorly known. Here we present for the first time, the results of a study on the community structure of phytoplankton for this region, derived from HPLC pigment analysis and microscopic cell counts. Our sampling strategy allowed for large spatial and temporal coverage over regions representative of the coastal and offshore waters, and over seasons that included the NE and the SW monsoon. Monthly observations at a fixed coastal station in particular, allowed us to follow changes in phytoplankton community structure associated with the development of anoxia. Together these measurements helped establish a pattern of seasonal change of three major groups of phytoplankton: diatoms, dinoflagellates and cyanobacteria that appeared to be tightly coupled with hydrographic and chemical changes associated with the monsoonal cycle. During the SW monsoon when nitrate concentrations were high, diatoms were dominant but prymnesiophytes were present as well. By October, as nitrate fell to below detection levels and anoxic conditions began to develop on the shelf below the shallow pycnocline, both diatom and prymensiophytes declined sharply giving way to dinoflagellates. In the well oxygenated surface waters, where both nitrate and ammonium were below detection limits, pico-cyanobacterial populations became dominant.During the NE monsoon, a mixed diatom-dinoflagellate population was quickly replaced by blooms of Trichodesmium erythraeum and Noctiluca miliaris with higher amounts of zeaxanthin, β-carotene, Chl b and prasinoxanthin. Trichodesmium trichomes were noticed in the water column as early as December when nitrate concentrations became limiting. The low phytoplankton biomass and high ammonium concentrations argue that active grazing populations may be responsible for preventing diatom-dinoflagellate populations from establishing themselves to bloom proportions in the eastern Arabian Sea during the early NE monsoon. Trichodesmium continued its dominance well into May, when nutrient enrichment associated with its death and decay helped simulate the growth of both diatoms and dinoflagellates. Given that anoxic conditions are becoming more pervasive in the eastern Arabian Sea, our observations in particular, those of a shift towards dinoflagellate dominance during the development of anoxia assume particular importance.  相似文献   

Soil and soil conservation survey for watershed management in parts of North cachar hills and karbi — Anglong districts of ASSAM     

M. L. Manchanda  Jitendra Prasad  H. S. Iyer  S. K. Deb  R. Pathak 《Journal of the Indian Society of Remote Sensing》1984,12(1):7-18

Soil and Soil Conservation surveys for watershed management were conducted using aerial photos of 1:60,000 scale in parts of North Cachar and Karbi-Anglong districts of Assam. The area was divided into different river catchments and sub-watersheds. The erosion, slope, landuse and soils in relation to physiogrphy were studied in each sub-watershed. The different physiographic units identified in the area were high, medium, low and very low hills; pediplains; alluvial plain and the valleys. These units were further subdivided based on slope, landuse and erosion etc. The soils were classified according to Soil Taxonomy. For priority determination, weightage was alloted to each of the sub-watersheds considering their physiography, slope, landuse, erosion,soil texture, depth and delivery ratio and sediment yield was calculated for each subwatershed. It has been found that out of 122875 ha, an area of 1745 ha had very high priority, 30590 ha high, 37290 ha medium, 51957 ha low and 1294 ha very low priority for soil conservation purposes.  相似文献