A digital signal pre-processor for pulsar search     

P. S. Ramkumar  T. Prabu  Madhu Girimaji  G. Marker leyulu 《Journal of Astrophysics and Astronomy》1994,15(3):343-353

A fast digital signal processor has been designed and built for survey and some observations of pulsars. The processor obtains spectral information over a bandwidth of 16 MHz (256 channels) every 25μsecs Wedescribethe design ofthisprocessor and present some test observations made with the Ooty Radio Telescope.  相似文献   

A Long Term Study on Chemical Composition of Rainwater at Dayalbagh, a Suburban Site of Semiarid Region     

Ranjit Kumar  Abha Rani  S. P. Singh  K. Maharaj Kumari  S. S. Srivastava 《Journal of Atmospheric Chemistry》2002,41(3):265-279

Rainwater samples were collected for the monsoon period of 1988 and 1991–1996 at Dayalbagh (Agra), a suburban site situated in semiaridregion. The mean pH was 7.01 ±1.03 well above 5.6, which is the reference pH. Concentration of Ca²⁺ was observed to be highest followed by Mg²⁺, NH₄ ⁺,SO₄ ^2–, Cl^–,NO₃ ^–, Na⁺, F^– and K⁺. The ratios of SO₄ ^2– + NO₃ ^– andCa²⁺ + Mg²⁺ (TA/TC) have been considered as indicatorfor acidity. In the Agra region ratio of TA/TC is quite below 1.0 indicating alkaline nature of rainwater. The lowest value of 0.24 was observed in 1991 likely due to the lowest rain depth of the decade. The highest value of 0.54 was observed in 1996, a year with a large rain depth and increase in line (vehicular traffic) and area sources (population growth). Good correlation between Ca²⁺ and NO₃ ^–,Ca²⁺ and SO₄ ^2– andSO₄ ^2– and NO₃ ^–,indicates that wind carried dust and soil play a significant role in neutralization of precipitation acidity.  相似文献   

Formate and acetate levels compared in monsoon and winter rainwater at Dayalbagh, Agra (India)     

Nandini Kumar  U. C. Kulshrestha  A. Saxena  P. Khare  K. M. Kumari  S. S. Srivastava 《Journal of Atmospheric Chemistry》1996,23(1):81-87

A total of 59 rainwater samples were collected during the winter and monsoon (1991–92) at Dayalbagh, Agra. This site is relatively free from the influence of anthropogenic emissions and the volume-weighted average concentrations (VWA) of formate in the winter and monsoon were 22.5±6, 16.1±3 while acetate VWAs were 17.1±5 and 13.8±3 mol l^-1, respectively. Although the VWAs varied between seasons, it was not statistically different. Total deposition (in mmol m^-2) varied between season (winter formate, 1.4; acetate, 1.1; monsoon formate, 7.4; acetate, 6.4). A difference in VWA values may have occurred as a result of the dilution factor; the total rain depth from collected samples in the monsoon was 46 cm while that in winter was 6.3 cm. Sources at this site may be anthropogenic and natural; scavenging from the vapour phase, washout of soil particles and emissions from vegetative sources are probably important sources for formate and acetate.  相似文献   

Impact of freshwater influx on microzooplankton mediated food web in a tropical estuary (Cochin backwaters – India)     

R. Jyothibabu  N.V. Madhu  K.V. Jayalakshmi  K.K. Balachandran  C.A. Shiyas  G.D. Martin  K.K.C. Nair 《Estuarine, Coastal and Shelf Science》2006,69(3-4):505

The diversity, abundance and biomass of microzooplankton in Cochin backwaters were studied for the first time during pre-summer monsoon to peak of summer monsoon (April–July 2003) to understand the impact of large freshwater influx. Microzooplankton abundance and biomass were highest during pre-summer monsoon (av. 3817 ind. L⁻¹ and 146 μg C L⁻¹) that declined with the onset (av. 2052 ind. L⁻¹ and 45 μg C L⁻¹) and peak (av. 409 ind. L⁻¹ and 10 μg C L⁻¹) summer monsoon. Species diversity, richness and evenness of microzooplankton also showed similar trends as that of abundance and biomass. Grazing experiment showed that microzooplankton consumes 43 ± 1% of the daily phytoplankton standing stock during the high saline condition (27.5). Low abundance of microzooplankton during summer monsoon period (1/8 of the pre-summer monsoon value) along with the concomitant occurrence of low mesozooplankton (1/8 times of pre-summer monsoon value) suggests that there could be a general lack of planktonic grazers. This would result in a weak transfer of primary and bacterial carbon to higher trophic levels, eventually leaving behind much unconsumed basic food in the estuary during summer monsoon. Thus a major portion of the primary carbon either settles down or gets transported to the coastal regions during monsoon. High flushing of Cochin backwaters also facilitates faster removal of primary producers to the coastal regions during monsoon.  相似文献   

Wave induced forces around buried pipelines   总被引：1，自引：0，他引：1  

Ch. Madhu Sudhan  V. Sundar  S. Narasimha Rao   《Ocean Engineering》2002,29(5):533-544

This work refers to an experimental investigation carried out to analyze wave induced pressures on a pipeline buried in a permeable seabed. In this investigation, the model tests were performed on a pipeline buried in the soil test bed. The wave flume used was 30 m long, 2 m wide and 1.7 m deep, 96 number of tests were conducted with waves generated for different wave heights. A pipeline 200 mm in diameter was buried in the sandy bed at different burial depth ratios. The pipeline was laid perpendicular to the wave direction, pressure was measured with 12 transducers along the outer circumference of the pipeline. The results show that wave induced pressures are significantly controlled by the wave period analyzed in terms of the scattering parameter (ka). Higher pressures were recorded at the top and the lower pressures were recorded at the bottom.  相似文献   

Trace ambient levels of particulate mercury and its sources at a rural site near Delhi     

Anita Kumari  Umesh Kulshrestha 《Journal of Atmospheric Chemistry》2018,75(4):335-355

Atmospheric particle-bound mercury levels were measured in PM₁₀ aerosols (HgP) at a rural site (Mahasar, Haryana) during winter 2014–15 and summer 2015. The PM₁₀ HgP was determined by using Differential Pulse Anodic Stripping Voltammetry through standard addition methods while the trace metals were determined by using an Atomic Absorption Spectroscopy. The mass concentrations of HgP varied from 591 to 1533 pg/m³ with an average of 1009?±?306 pg/m³ during the winter, while the mass concentrations of HgP varied from 43 to 826 pg/m³ with an average of 320?±?228 pg/m³ during the summer. However, it is difficult to assess whether these levels are harmful or not because there is no standard value available as National Ambient Air Quality Standard. The higher concentrations of HgP during winters were possibly due to favourable local meteorological conditions for the stagnation of particulate matter in the lower atmosphere and the increased emissions from existing natural or anthropogenic sources, regional sources and long-range transportation. Relatively low concentrations of HgP during summer might be due to increased mixing heights as well as scavenging effect because some light to heavy rain events were observed during summer time sampling. However, among other metals determined, the concentration of HgP was the lowest during both the seasons. The study may be useful in assessing the health impacts of PM₁₀ HgP and other metals.  相似文献   

Bridging the gap or broadening the problem?     

Harinarayan Tiwari  Subash Pd. Rai  Kumari Shivangi 《Natural Hazards》2016,80(1):351-365

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Glacial lake outburst flood risk in Himachal Pradesh,India: an integrative and anticipatory approach considering current and future threats   总被引：1，自引：0，他引：1  

S. K. Allen  A. Linsbauer  S. S. Randhawa  C. Huggel  P. Rana  A. Kumari 《Natural Hazards》2016,84(3):1741-1763

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Characterization of Organic Acids in Dew Collected on Surrogate Surfaces     

Puja Khare  S. P. Singh  K. Maharaj Kumari  Ashok Kumar  S. S. Srivastava 《Journal of Atmospheric Chemistry》2000,37(3):231-244

Levels of formate and acetate in dew were measured at Dayalbagh, India, usingsurrogate surfaces. The dew formed per night ranged between 0.06 lm^–2 and 1.38 l m^–2, with an average of 0.59l m^–2. pH ranged between 6.7 and 7.4. Mean concentrations offormate and acetate in dew were 10.2 ± 10.2 eql^–1 and 7.5 ± 4.5 eq l^–1,respectively. The correlation coefficient between the two ions was 0.80 (p =0.001), which suggested that concentrations of these species in dew are linkedtogether. They have either common or different sources with fairly constantstrengths or products of same reaction. Good correlation of formate andacetate with Ca (r = 0.82 and r = 0.70, respectively) and Mg (r = 0.74 and r= 0.71, respectively) suggested that these ions may be associated with Ca andMg after the neutralization process. Deposition rates for formate and acetatein dew per night were 10.2 ± 7.22 mol m^–2 pernight and 4.6 ± 2.2 mol m^–2 per night,respectively. The theoretical Henry's law constant (K^* _H)and the field-observed Henry's law coefficient (K^* _H) ascalculated from concurrent measurements of gas phase and dew for both acidsshowed large discrepancies of three orders of magnitude.  相似文献   

Surface waves in a heterogeneous liquid half-space     

Santosh Kumari 《Pure and Applied Geophysics》1970,83(1):62-73

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