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71.
Natural Hazards - Using a high-resolution daily gridded rainfall data set for the period 1951–2015, new objective criteria were developed to determine rainstorms over the Indian region during... 相似文献
72.
Torrentfish Cheimarrichthys fosteri Haast were collected at 4‐hour intervals over a full day in winter and summer, 1984–85, from the Ashley and Rakaia Rivers in Canterbury, New Zealand, to determine their diel feeding periodicity. Both populations fed, almost exclusively, from dusk to dawn in both seasons, with the quantity of food in their stomachs accumulating to peak levels by early morning. However, Ashley females had significantly less food in their stomachs than did males in summer, the season with a high incidence (91%) of females in spawning condition. Aquatic stages of Deleatidium spp. (Ephemeroptera: Leptophle‐biidae) and Chironomidae constituted from 85 to 98% by number and 63 to 80% by dry weight of all foods eaten. Chironomids (small prey) comprised up to 85% of the total foods eaten by number but only 17% by dry weight, while Deleatidium (large prey) comprised up to 69% of the prey by number and 63% by dry weight. Numerically, chironomids were an important component in the torrentfish diet in both seasons in the Rakaia (71 to 75%), but only so in winter in the Ashley (85%). The reported daily feeding cycle is consistent with observations in a simulated stream, that torrentfish largely remain inactive during the day and come out to feed at night. 相似文献
73.
74.
Macroinvertebrate benthos and drift and the diet of juvenile brown trout (Salmo trutta) were investigated in willowed and non‐willowed sections of three New Zealand streams during summer. The abundance and biomass of the principal macroinvertebrate taxa in the benthos and daytime drift differed in relation to riparian willow (Salix spp.) density, but the trends were not consistent across all three streams. Crustacea, Ephemeroptera, Trichoptera, and Diptera comprised a major proportion of the diet of juvenile trout. Diets of trout from non‐willowed and willowed sections were dissimilar in three of five pair‐wise comparisons. In all three streams, juvenile trout fed selectively, with the amphipod Paracalliope fluviatilis, ephemeropteran Deleatidium, and trichopterans Aoteapsyche and Hydrobiosidae being the preferred prey. Their avoidance of the gastropod Potamopyrgus antipodarum, trichopteran Oxye‐thira albiceps, coleopteran Hydora, and drift of terrestrial origin appeared to occur in all streams. Total abundance and biomass of invertebrates drifting during the day described the potential prey available to juvenile brown trout better than did the abundance and biomass of benthic invertebrates. 相似文献
75.
Benthic macroinvertebrates were collected and the diets of shortfinned eels (Anguilla australis) and longfinned eels (Anguilla dieffenbachii) inhabiting a small coastal New Zealand stream were examined to investigate intraspecific and interspecific trophic partitioning and prey selection. Our results showed intraspecific segregation of preferred prey among three size classes of juvenile shortfinned eels, but there was significant overlap between different size classes of longfinned eels. All size classes of both species of eel fed nocturnally on similar prey, and so there was no indication of temporal or trophic segregation. Therefore, habitat separation is assumed to be the main mechanism to reduce interspecific competition in these two co‐occurring species of eels. 相似文献
76.
Ramanpreet Kaur Biswajit Paul Brijesh Kumar Ram Sagar 《Monthly notices of the Royal Astronomical Society》2008,386(4):2253-2261
We have investigated multiband optical photometric variability and stability of the Hα line profile of the transient X-ray binary IGR J01583+6713. We set an upper limit of 0.05 mag on photometric variations in the V band over a time-scale of three months. The Hα line is found to consist of non-Gaussian profile and quite stable for a duration of two months. We have identified the spectral type of the companion star to be B2 IVe while the distance to the source is estimated to be ∼4.0 kpc. Along with the optical observations, we have also carried out analysis of X-ray data from three short observations of the source, two with the Swift –XRT and one with the RXTE –PCA. We have detected a variation in the absorption column density, from a value of 22.0 × 1022 cm−2 immediately after the outburst down to 2.6 × 1022 cm−2 four months afterwards. In the quiescent state, the X-ray absorption is consistent with the optical reddening measurement of E ( B − V ) = 1.46 mag. From one of the Swift observations, during which the X-ray intensity was higher, we have a possible pulse detection with a period of 469.2 s. For a Be X-ray binary, this indicates an orbital period in the range of 216–561 d for this binary system. 相似文献
77.
Gopal-Krishna Alok C. Gupta Ram Sagar Paul J. Wiita U. S. Chaubey C. S. Stalin 《Monthly notices of the Royal Astronomical Society》2000,314(4):815-825
We report results of the observations at the Vainu Bappu Observatory and the Uttar Pradesh State Observatory of eight radio-quiet quasi-stellar objects (RQQSOs) during 1996–99. This is a part of our ongoing programme to search for intranight optical variability in RQQSOs. Additional evidence for very rapid variability in three of the five optically bright and very luminous RQQSOs we had observed earlier, 1049−006, 1444+408 and 1630+377, was found. Of the three newly observed RQQSOs, the data for 0043+039 are too noisy to allow conclusions about variability to be drawn, but 0748+294 and 0824+098 show strong hints of microvariability. We also present a summary of the results from our entire programme to date, which includes observations of 16 radio-quiet QSOs and one radio-weak QSO, and compare the general properties of rapid variability in radio-quiet versus radio-loud AGN as determined from our work and that of several other groups. Observations of this kind are likely to play a key role in understanding the relative contributions of accretion discs and relativistic plasma jets to rapid optical fluctuations of AGN. 相似文献
78.
Atish Kamble Kuntal Misra D. Bhattacharya Ram Sagar 《Monthly notices of the Royal Astronomical Society》2009,394(1):214-220
The afterglow of GRB 050401 presents several novel and interesting features. (i) An initially faster decay in optical band than in X-rays. (ii) A break in the X-ray light curve after ∼0.06 d with an unusual slope after the break. (iii)The X-ray afterglow does not show any spectral evolution across the break while the R -band light curve does not show any break. We have modelled the observed multiband evolution of the afterglow of GRB 050401 as originating in a two-component jet, and interpreting the break in X-ray light curve as due to lateral expansion of a narrow collimated outflow which dominates the X-ray emission. The optical emission is attributed to a wider jet component. Our model reproduces all the observed features of multiband afterglow of GRB 050401. We present optical observations of GRB 050401 using the 104-cm Sampurnanand Telescope at the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital. Results of the analysis of multiband data are presented and compared with GRB 030329, the first reported case of double jet. 相似文献
79.
The H-R diagram of the open cluster Tr-1 based on Oja-membership andU, B, V photoelectric photometry is presented. The colour excessE(B-V) is 0
.
m
52. The distance modulus to the cluster and its age are, respectively, estimated at 11
.
m
6 and 2.6×107 yr. 相似文献
80.
Himali Bhatt J. C. Pandey K. P. Singh Ram Sagar Brijesh Kumar 《Journal of Astrophysics and Astronomy》2013,34(4):393-429
We present a detailed investigation of X-ray source contents of eight young open clusters with ages between 4 to 46 Myr using archival X-ray data from XMM-Newton. The probable cluster memberships of the X-ray sources have been established on the basis of multi-wavelength archival data, and samples of 152 pre-main sequence (PMS) low mass (<2M ⊙), 36 intermediate mass (2–10M ⊙) and 16 massive (>10M ⊙) stars have been generated. X-ray spectral analyses of high mass stars reveal the presence of high temperature plasma with temperature <2 keV, and mean L X/L bol of 10???6.9. In the case of PMS low mass stars, the plasma temperatures have been found to be in the range of 0.2 keV to 3 keV with a median value of ~1.3 keV, with no significant difference in plasma temperatures during their evolution from 4 to 46 Myr. The X-ray luminosity distributions of the PMS low mass stars have been found to be similar in the young star clusters under study. This may suggest a nearly uniform X-ray activity in the PMS low mass stars of ages ~4–14 Myr. These observed values of L X/L bol are found to have a mean value of 10??3.6±0.4, which is below the X-ray saturation level. The L X/L bol values for the PMS low mass stars are well correlated with their bolometric luminosities, that implies its dependence on the internal structure of the low mass stars. The difference between the X-ray luminosity distributions of the intermediate mass stars and the PMS low mass stars has not been found to be statistically significant. Their L X/L bol values, however have been found to be significantly different from each other with a confidence level greater than 99.999% and the strength of X-ray activity in the intermediate mass stars is found to be lower compared to the low mass stars. However, the possibility of X-ray emission from the intermediate mass stars due to a low mass star in close proximity of the intermediate mass star can not be ruled out. 相似文献