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1.
Sky models have been used in the past to calibrate individual low radio frequency telescopes. In this article we generalize this approach from a single antenna to a two element interferometer, and formulate the problem in a way that allows us to estimate the flux density of the Sun using the normalized cross-correlations (visibilities) measured on a low resolution interferometric baseline. For wide field-of-view instruments, typically the case at low radio frequencies, this approach can provide robust absolute solar flux calibration for well characterized antennas and receiver systems. It can provide a reliable and computationally lean method for extracting parameters of physical interest using a small fraction of the voluminous interferometric data, which can be computationally prohibitively expensive to calibrate and image using conventional approaches. We demonstrate this technique by applying it to data from the Murchison Widefield Array and assess its reliability. 相似文献
2.
Fractional crystallization of primitive,hydrous arc magmas: an experimental study at 0.7 GPa 总被引：4，自引：2，他引：2
Rohit H. Nandedkar Peter Ulmer Othmar Müntener 《Contributions to Mineralogy and Petrology》2014,167(6):1-27
Differentiation of mantle-derived, hydrous, basaltic magmas is a fundamental process to produce evolved intermediate to SiO2-rich magmas that form the bulk of the middle to shallow continental and island arc crust. This study reports the results of fractional crystallization experiments conducted in a piston cylinder apparatus at 0.7 GPa for hydrous, calc-alkaline to arc tholeiitic magmas. Fractional crystallization was approached by synthesis of starting materials representing the liquid composition of the previous, higher temperature experiment. Temperatures ranged from near-liquidus at 1,170 °C to near-solidus conditions at 700 °C. H2O contents varied from 3.0 to more than 10 wt%. The liquid line of descent covers the entire compositional range from olivine–tholeiite (1,170 °C) to high-silica rhyolite (700 °C) and evolves from metaluminous to peraluminous compositions. The following crystallization sequence has been established: olivine → clinopyroxene → plagioclase, spinel → orthopyroxene, amphibole, titanomagnetite → apatite → quartz, biotite. Anorthite-rich plagioclase and spinel are responsible for a marked increase in SiO2-content (from 51 to 53 wt%) at 1,040 °C. At lower temperatures, fractionation of amphibole, plagioclase and Fe–Ti oxide over a temperature interval of 280 °C drives the SiO2 content continuously from 53 to 78 wt%. Largest crystallization steps were recorded around 1,040 °C and at 700 °C. About 40 % of ultramafic plutonic rocks have to crystallize to generate basaltic–andesitic liquids, and an additional 40 % of amphibole–gabbroic cumulate to produce granitic melts. Andesitic liquids with a liquidus temperature of 1,010 °C only crystallize 50 % over an 280 °C wide range to 730 °C implying that such liquids form mobile crystal mushes (<50 % crystals) in long-lived magmatic systems in the middle crust, allowing for extensive fractionation, assimilation and hybridization with periodic replenishment of more mafic magmas from deeper magma reservoirs. 相似文献
3.
Over a period of 12 months, soil moisture content and potential was monitored in an annual‐grass‐dominated 20 ha catchment in order to determine flow paths leading to exfiltration at the catchment outlet. Water was found to enter the catchment valley either through flow originating in the slopes or through surface infiltration during rainfall events. Although subsurface flow from the slopes to the catchment outlet occurred throughout the year, surface recharge was restricted to a few events during the wet season. In the deeper saturated profile of the valley, flow was directed upwards along the valley edges and gradually became horizontal towards the central axis of the valley. During the peak of the rainfall season, horizontal flow close to the catchment outlet intercepted the gradually sloping surface, resulting in exfiltration. Plants influenced the hydrology of the catchment by removing moisture from the root zone during spring and early summer, resulting in evapotranspiration losses from the vadose zone. Heterogeneities within the valley soil were evident as variable‐permeability layers that resulted in a seasonally confined water table within the valley. This investigation shows that the vadose zone plays an important role in redistributing surface recharge and emphasizes the importance of accounting for effective moisture in low‐yielding catchments with ephemeral surface runoff. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
4.
Satyendra Bhandari Rohit Srivastava Vikram Mehta 《Journal of Earth System Science》2016,125(7):1313-1319
This paper presents results of a study of long term trends in the characteristics of the within-season temporal profile of southwest monsoon rainfall over western India during the last five decades in relation to global warming induced regional climate change. In contrast to recent climate change analyses and projections, no significant long-term trends have been observed in this study. Slow decadal scale variations observed are analysed in relation to Pacific Decadal Oscillations (PDO). Daily variations in rainfall anomaly show opposite characteristics during negative and positive phases of PDO. The above-normal rainfall (>25%) is found during the starting phase of monsoon in negative PDO. Over the last decade, i.e., during 2000–2007, the seasonal rainfall amount, as well as seasonal span of southwest monsoon over western India is indicative of a gradual increase. 相似文献
5.
Vikas Duggal Asha Rani Rohit Mehra V. Balaram 《Journal of the Geological Society of India》2017,89(1):77-81
In Shear strength reduction (SSR) technique, the factor of safety (FOS) is defined as the ratio of the material’s actual shear strength to the minimum shear strength required to prevent failure. Failure surface is found automatically through the zones within the material, where applied shear stresses cross the shear strength of the material. In this paper, a review of the technique is discussed in reference to FLAC. A brief background of the approach together with detailed procedure is presented.An attempt is made to exhibit the shear strength dependency of the strain. As stability of the slope is a function of the shear strength, the development of failure strain reflects the potential failure zone of slope. The shear strain developed in the slope increases with reduction in the shear strength and is reflected in the analysis. The concept of failure ratio (Rf) is incorporated in shear strength reduction technique and is demonstrated. Relationships between the critical shear strength reduction ratio and the safety factor are examined. 相似文献
6.
Sudhir Mittal Asha Rani Rohit Mehra V. Balaram M. Satyanarayanan S. S. Sawant 《Journal of the Geological Society of India》2017,90(2):233-238
In the present study, analysis of 238U concentration in 40 drinking water samples collected from different locations of Jodhpur, Nagaur, Bikaner and Jhunjhunu districts of Rajasthan, India has been carried out by using high resolution inductively coupled plasma mass spectroscopy (HR-ICP-MS) technique. The water samples were taken from hand pumps and tube wells having depths ranging from 50 to 800 feet. The measured uranium concentration lies in the range from 0.89 to 166.89 μg l-1 with the mean value of 31.72 μg l-1. The measured uranium content in twelve water samples was found to be higher than the safe limit of 30 μg l-1 as recommended by World Health Organization (WHO, 2011) and US Environmental Protection Agency (USEPA, 2011). Radiological risk calculated in the form of annual effective dose estimated from annual uranium intake ranges from 0.66 to 138.63 μSv y-1 with the mean value of 26.28 μSv y-1. The annual effective dose in two drinking water samples was found to be greater than WHO (2004) recommended level of 100 μSv y-1. Chemical risk calculated in the form of lifetime average daily dose (LAAD) estimated from the water samples varies from 0.02 to 4.57 μg kg-1 d-1 with the mean value of 0.87 μg kg-1 d-1. The lifetime average daily dose (LAAD) of ten drinking water samples was found to be greater than WHO (2011) recommended level of 1 μg kg-1 d-1. The corresponding values of hazard quotient of 48% water samples were found to be greater than unity.A good positive correlation of uranium concentration with total dissolved solids (TDS) and conductance has been observed. However no correlation of uranium concentration with pH was observed. The results revels that uranium concentration in drinking water samples of the study area can cause radiological and chemical threat to the inhabitants. 相似文献
7.
Indoor radon is considered as one of the potential dangerous radioactive elements. Common building materials and soil are the major source of this radon gas in the indoor environment. In the present study, the measurement of radon exhalation rate in the soil and building material samples of Una and Hamirpur districts of Himachal Pradesh has been done with solid state alpha track detectors, LR-115 type-II plastic track detectors. The radon exhalation rate for the soil samples varies from 39.1 to 91.2 mBq kg?1 h?1 with a mean value 59.7 mBq kg?1 h?1. Also the radium concentration of the studied area is found and it varies from 30.6 to 51.9 Bq kg?1 with a mean value 41.6 Bq kg?1. The exhalation rate for the building material samples varies from 40.72 (sandstone) to 81.40 mBq kg?1 h?1 (granite) with a mean value of 59.94 mBq kg?1 h?1. 相似文献
8.
Rohit Mehra Sandeep Kumar Rajendra Sonkawade N. P. Singh Komal Badhan 《Environmental Earth Sciences》2010,59(5):1159-1164
The activity concentration and the gamma-absorbed dose rates of the terrestrial naturally occurring radionuclides (232Th, 226Ra and 40K) were determined in soil samples collected from ten different locations of Sirsa district of Haryana, using HPGe detector
based on high-resolution gamma spectrometry system. The range of activity concentrations of 226Ra, 232Th and 40K in the soil samples from the studied areas varies from 19.18 Bq kg−1 (Moriwala) to 40.31 Bq kg−1 (Rori), 59.43 Bq kg−1 (Pipli) to 89.54 Bq kg−1 (Fatehpur) and 223.22 Bq kg−1 (Moriwala) to 313.32 Bq kg−1 (SamatKhera) with overall mean values of 27.94, 72.75 and 286.73 Bq kg−1 respectively. The absorbed dose rate calculated from activity concentration of 226Ra, 232Th and 40K ranges between 8.84 and 18.58, 37.02 and 55.78, and 9.24 and 12.97 nGy h−1, respectively. The total absorbed dose in the study area ranges from 60.40 to 82.15 nGy h−1 with an average value of 70.12 nGy h−1. The calculated values of external hazard index (H
ex) for the soil samples of the study area range from 0.36 to 0.49 with an average value of 0.42. 相似文献
9.
Jonathan J. Liberda Jeroen W. Thompson W. Jack Rink Federico Bernaldo de Quirs Rohit Jayaraman Kailash Selvaretinam Kerry Chancellor‐Maddison Vito Volterra 《Geoarchaeology》2010,25(4):467-474
Nine faunal teeth from layer 20 of El Castillo cave in Cantabrian Spain were dated using electron spin resonance (ESR). Two teeth were rejected due to inconsistent subsample ages, while the remaining teeth yielded a mean age that is consistent with the stratigraphic expectations: 42.7±3.5. Uncertainty in the external γ dose rate results in a potential systematic uncertainty of±6.4ka that should affect all samples equally. The results provide independent confirmation of previously reported 14C ages for layer 20. © 2010 Wiley Periodicals, Inc. 相似文献
10.
We carried out simultaneous measurements of drop size distribution (DSD) and stable oxygen and hydrogen isotopic compositions (??18O and ??D) of rain at the National Atmospheric Research Laboratory (NARL), Gadanki (13.5°N, 79.2°E), southern India, during September?COctober 2006, with the aim of understanding microphysical processes leading to rain formation. The MST radar at NARL was operated continuously during rain events, while rain samples were collected at very short time intervals (<1?h), to capture small changes (>0.2?? and >2??) in their ??18O and ??D. The slope of the local meteoric water line (??D?C??18O line), was 8.07?±?0.47, similar to that of global meteoric water line, confirming that the precipitation occurred under isotopic equilibrium, and was unaffected by some anomalous process; further, the evaporation of rain drops at the cloud base was insignificant. Whenever the isotopic variations were larger during a rain event (>2??) there was a significant negative correlation between the ??18O and DSD. The possible explanation is that larger drops are mostly associated with convective rather than stratiform rain, and 18O (and D) depletion in convective rain is relatively more. Bin-resolved microphysical models incorporating water isotopologues could benefit by considering drop size spectra, which could improve the match with stable isotope observations of precipitation. 相似文献