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951.
We present the results of twenty-year observations of a complete sample of 68 flat-spectrum radio sources with flux densities S 3.9 GHz > 200 mJy carried out at centimeter wavelengths with the RATAN-600 radio telescope. Since 1995, we have observed simultaneously at six frequencies between 0.97 and 21.7 GHz. Of the 56 sources identified with optical objects, 41 are quasars with redshifts between 0.293 and 3.263. Based on our analysis of the spectral shapes, we divide the sources into four classes. Changes of spectral class for individual sources are fairly rare. Based on the light curves and spectra, in most cases, a flare’s evolution is in accordance with a model in which the variations result from the evolution of a shock in the radio jet. The main result of our study is that there is no redshift dependence for the true linear sizes of the radiating regions, the variability indices derived for all 20 years of data or for individual flares, or the peak frequencies of the spectra of the compact radio emission. We suggest that this testifies to an absence of cosmological evolution of the sample quasars, at least to z ≈ 3. 相似文献
952.
M. K. Abubekerov E. A. Antokhina A. M. Cherepashchuk V. V. Shimanskii 《Astronomy Reports》2008,52(5):379-389
We have obtained the first estimates of the masses of the components of the Her X-1/HZ Her X-ray binary system taking into account non-LTE effects in the formation of the H γ absorption line: m x = 1.8 M ⊙ and m v = 2.5 M ⊙. These mass estimates were made in a Roche model based on the observed radial-velocity curve of the optical star, HZ Her. The masses for the X-ray pulsar and optical star obtained for an LTE model lie are m x = 0.85 ± 0.15 M ⊙ and m v = 1.87 ± 0.13 M ⊙. These mass estimates for the components of Her X-1/HZ Her derived from the radial-velocity curve should be considered tentative. Further mass estimates from high-precision observations of the orbital variability of the absorption profiles in a non-LTE model for the atmosphere of the optical component should be made. 相似文献
953.
V. V. Shimanskii N. V. Borisov N. A. Sakhibullin D. V. Sheveleva 《Astronomy Reports》2008,52(6):479-486
We have classified and determined the parameters of the evolved close binary MT Ser. Our moderate-resolution spectra covering various phases of the orbital period were taken with the 6-m telescope of the Special Astrophysical Observatory. The spectra of MT Ser freed from the contribution of the surrounding nebula Abell 41 contained no emission lines due to the reflection effect. The radial velocities measured from lines of different elements showed them to be constant on a time scale corresponding to the orbital period. At the same time, we find effects of broadening for the HeII absorption lines, due to the orbital motion of two hot stars of similar types. As a result, we classify MT Ser as a system with two blue subdwarfs after the common-envelope stage. We estimate the component masses and the distance to the object from the Doppler broadening of the HeII lines. We demonstrate that the age of the ambient nebula, Abell 41, is about 35 000 years. 相似文献
954.
N. G. Patyk-Kara E. N. Levchenko A. I. Stekhin V. V. Barsegyan A. A. Bochneva I. A. Chizhova E. A. Andrianova V. T. Dubinchuk 《Geology of Ore Deposits》2008,50(3):218-239
The study of mineral assemblages at the Central deposit allowed us to substantially refine the evolutionary model of the deposit and reveal the two main factors that control the variability of its mineralic space: (1) heterogeneity of the ore layer, consisting of a sublittoral bottom placer (the lower part) and a subaerial dune complex partly reworked in the course of a new transgression (the upper part), and (2) postore epigenetic alteration of the ore constituent of sands, which affected the quality of ore concentrates. The results obtained will be used in geological and technological mapping and development of the production program. 相似文献
955.
It is shown that the centroid of the heliospheric equator undergoes quasi-periodic oscillations. During the minimum of the 11-year cycle, the centroid shifts southwards (the so-called bashful-ballerina effect). The direction of the shift reverses during the solar maximum. The solar quadrupole is responsible for this effect. The shift is compared with the tilt of the heliospheric current sheet. 相似文献
956.
Analyses of 72 samples from Upper Panjhara basin in the northern part of Deccan Plateau, India, indicate that geochemical
incongruity of groundwater is largely a function of mineral composition of the basaltic lithology. Higher proportion of alkaline
earth elements to total cations and HCO3>Cl + SO4 reflect weathering of primary silicates as chief source of ions. Inputs of Cl, SO4, and NO3 are related to rainfall and localized anthropogenic factors. Groundwater from recharge area representing Ca + Mg–HCO3 type progressively evolves to Ca + Na–HCO3 and Na–Ca–HCO3 class along flow direction replicates the role of cation exchange and precipitation processes. While the post-monsoon chemistry
is controlled by silicate mineral dissolution + cation exchange reactions, pre-monsoon variability is attributable chiefly
to precipitation reactions + anthropogenic factors. Positive correlations between Mg vs HCO3 and Ca + Mg vs HCO3 supports selective dissolution of olivine and pyroxene as dominant process in post-monsoon followed by dissolution of plagioclase
feldspar and secondary carbonates. The pre-monsoon data however, points toward the dissolution of plagioclase and precipitation
of CaCO3 supported by improved correlation coefficients between Na + Ca vs HCO3 and negative correlation of Ca vs HCO3, respectively. It is proposed that the eccentricity in the composition of groundwater from the Panjhara basin is a function
of selective dissolution of olivine > pyroxene followed by plagioclase feldspar.
The data suggest siallitization (L < R and R
k) as dominant mechanism of chemical weathering of basalts, stimulating monosiallitic (kaolinite) and bisiallitic (montmorillonite)
products. The chemical denudation rates for Panjhara basin worked out separately for the ground and surface water component
range from 6.98 to 36.65 tons/km2/yr, respectively. The values of the CO2 consumption rates range between 0.18 × 106 mol//km2/yr (groundwater) and 0.9 × 106 mol/km2/yr (surface water), which indicates that the groundwater forms a considerable fraction of CO2 consumption, an inference, that is, not taken into contemplation in most of the studies. 相似文献
957.
Chandrani Singh D.V. Ramana R.K. Chadha M. Shekar 《Journal of Asian Earth Sciences》2008,31(4-6):499-503
An earthquake of Mw 5.1 occurred on March 14, 2005, in the seismically active Koyna–Warna region in western India, the site known for the largest reservoir triggered seismicity (RTS) in the world. For more than four decades, earthquakes with M 4.0 have occurred in this region at regular intervals. Impoundment of reservoirs and changes in lake levels can trigger earthquakes by two processes of stress modifications, namely direct loading effect of the reservoir and diffusion through various faults and fractures. In this paper we analysed the reservoir water level data at Koyna and Warna reservoirs prior to the occurrence of the March 14, 2005 earthquake, to explain the dominant mechanism behind its occurrence and its correlation with the observed coseismic changes. We conclude that the diffusion process, not the reservoir load effect, is the dominating mechanism triggering earthquakes in the region. The coseismic changes in deep well water levels sensitive to earth tides are found to be to the order of 1–12 cm. 相似文献
958.
Estimating groundwater evapotranspiration rates using diurnal water-table fluctuations in a semi-arid riparian zone 总被引:2,自引:1,他引:1
Laura K. Lautz 《Hydrogeology Journal》2008,16(3):483-497
In semi-arid climates, phreatophytes draw on shallow aquifers, and groundwater evapotranspiration (ETG) is a principal component of groundwater budgets. Diurnal water table fluctuations, which often are a product of ETG, were monitored in the riparian zone of Red Canyon Creek, Wyoming, USA. These fluctuations were higher in a riparian wetland (2–36 mm) than a grass-covered meadow (1–6 mm). The onset and cessation of water-table fluctuations correspond to daily temperatures relative to freezing. Spatial differences were due to vegetation type and specific yield, while temporal changes were due to vegetation dormancy. Ratios of ETG to potential evapotranspiration (PET), K c,GW, were similar to ratios of actual evapotranspiration (ET) to PET, K c, in semi-arid rangelands. Before vegetation senescence, K c,GW increased between precipitation events, suggesting phreatophytes pull more water from the saturated zone as soil moisture decreases. In contrast, K c decreases with soil moisture following precipitation events as ET becomes increasingly water-limited. Error in ETG is primarily from estimates of specific yield (S y), which is difficult to quantify in heterogeneous sediments. ETG values may be more reliable because the range of acceptable S y is smaller than K c and S y does not change with vegetation type or soil moisture. 相似文献
959.
Evaluation of distributed recharge in an upland semi-arid karst system: the West Bank Mountain Aquifer,Middle East 总被引:2,自引:0,他引:2
Assessment of recharge in a structurally complex upland karst limestone aquifer situated in a semi-arid environment is difficult. Resort to surrogate indicators such as measurement of spring outflow and borehole discharge, is a common alternative, and attempts to apply conventional soil moisture deficit analysis may not adequately account for the intermittent spate conditions that arise in such environments. A modelling approach has been made using the West Bank Mountain Aquifer system in the Middle East as a trial. The model uses object oriented software which allows various objects to be switched on and off. Each of the main recharge processes identified in the West Bank is incorporated. The model allows either conventional soil moisture deficit analysis calculations or wetting threshold calculations to be made as appropriate, and accommodates both direct recharge and secondary recharge. Daily time steps enable recharge and runoff routing to be calculated for each node. Model runs have enabled a series of simulations for each of the three aquifer basins in the West Bank and for the whole of the West Bank. These provide recharge estimates comparable to those prepared by earlier workers by conventional means. The model is adaptable and has been successfully used in other environments. 相似文献
960.
Artificial neural network and liquefaction susceptibility assessment: a case study using the 2001 Bhuj earthquake data,Gujarat, India 总被引:2,自引:0,他引:2
D. Ramakrishnan T. N. Singh N. Purwar K. S. Barde Akshay. Gulati S. Gupta 《Computational Geosciences》2008,12(4):491-501
This study pertains to prediction of liquefaction susceptibility of unconsolidated sediments using artificial neural network
(ANN) as a prediction model. The backpropagation neural network was trained, tested, and validated with 23 datasets comprising
parameters such as cyclic resistance ratio (CRR), cyclic stress ratio (CSR), liquefaction severity index (LSI), and liquefaction
sensitivity index (LSeI). The network was also trained to predict the CRR values from LSI, LSeI, and CSR values. The predicted
results were comparable with the field data on CRR and liquefaction severity. Thus, this study indicates the potentiality
of the ANN technique in mapping the liquefaction susceptibility of the area. 相似文献