排序方式： 共有63条查询结果，搜索用时 31 毫秒
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Jayanta Kumar Pati Michael H. Poelchau Wolf Uwe Reimold Norihiro Nakamura Yutaro Kuriyama Anuj Kumar Singh 《Meteoritics & planetary science》2019,54(10):2312-2333
The fundamental approach for the confirmation of any terrestrial meteorite impact structure is the identification of diagnostic shock metamorphic features, together with the physical and chemical characterization of impactites and target lithologies. However, for many of the approximately 200 confirmed impact structures known on Earth to date, multiple scale‐independent tell‐tale impact signatures have not been recorded. Especially some of the pre‐Paleozoic impact structures reported so far have yielded limited shock diagnostic evidence. The rocks of the Dhala structure in India, a deeply eroded Paleoproterozoic impact structure, exhibit a range of diagnostic shock features, and there is even evidence for traces of the impactor. This study provides a detailed look at shocked samples from the Dhala structure, and the shock metamorphic evidence recorded within them. It also includes a first report of shatter cones that form in the shock pressure range from ~2 to 30 GPa, data on feather features (FFs), crystallographic indexing of planar deformation features, first‐ever electron backscatter diffraction data for ballen quartz, and further analysis of shocked zircon. The discovery of FFs in quartz from a sample of the MCB‐10 drill core (497.50 m depth) provides a comparatively lower estimate of shock pressure (~7–10 GPa), whereas melting of a basement granitoid infers at least 50–60 GPa shock pressure. Thus, the Dhala impactites register a strongly heterogeneous shock pressure distribution between <2 and >60 GPa. The present comprehensive review of impact effects should lay to rest the nonimpact genesis of the Dhala structure proposed by some earlier workers from India. 相似文献
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Ramiz Aktar Santabrata Das Anuj Nandi H. Sreehari 《Journal of Astrophysics and Astronomy》2018,39(1):17
We examine the properties of the viscous dissipative accretion flow around rotating black holes in the presence of mass loss. Considering the thin disc approximation, we self-consistently calculate the inflow-outflow solutions and observe that the mass outflow rates decrease with the increase in viscosity parameter (\(\alpha \)). Further, we carry out the model calculation of quasi-periodic oscillation frequency (\(\nu _{\mathrm{QPO}}\)) that is frequently observed in black hole sources and observe that \(\nu ^\mathrm{max}_{\mathrm{QPO}}\) increases with the increase of black hole spin (\(a_k\)). Then, we employ our model in order to explain the High Frequency Quasi-Periodic Oscillations (HFQPOs) observed in black hole source GRO J1655-40. While doing this, we attempt to constrain the range of \(a_k\) based on observed HFQPOs (\(\sim \)300 Hz and \(\sim \)450 Hz) for the black hole source GRO J1655-40. 相似文献
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M. C. Ramadevi B. T. Ravishankar N. Sitaramamurthy G. Meena Brajpal Singh Anand Jain Reena Yadav Anil Agarwal V. Chandra Babu Kumar Ankur Kushwaha S. Vaishali Nirmal Kumar Iyer Anuj Nandi Girish V. Vivek Kumar Agarwal S. Seetha Dipankar Bhattacharya K. Balaji Manoj Kumar Prashanth Kulshresta 《Journal of Astrophysics and Astronomy》2017,38(2):32
We report the in-orbit performance of Scanning Sky Monitor (SSM) onboard AstroSat. The SSM operates in the energy range 2.5 to 10 keV and scans the sky to detect and locate transient X-ray sources. This information of any interesting phenomenon in the X-ray sky as observed by SSM is provided to the astronomical community for follow-up observations. Following the launch of AstroSat on 28th September, 2015, SSM was commissioned on October 12th, 2015. The first power ON of the instrument was with the standard X-ray source, Crab in the field-of-view. The first orbit data revealed the basic expected performance of one of the detectors of SSM, SSM1. Following this in the subsequent orbits, the other detectors were also powered ON to find them perform in good health. Quick checks of the data from the first few orbits revealed that the instrument performed with the expected angular resolution of 12’ \(\times \) 2.5\(^\circ \) and effective area in the energy range of interest. This paper discusses the instrument aspects along with few on-board results immediately after power ON. 相似文献
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Tilak B. Kotoch Anuj Nandi D. Debnath J. P. Malkar A. R. Rao M. K. Hingar Vaibhav P. Madhav S. Sreekumar Sandip K. Chakrabarti 《Experimental Astronomy》2011,29(1-2):27-54
Cadmium Zinc Telluride (CZT) detectors are high sensitivity and high resolution devices for hard X-ray imaging and spectroscopic studies. The new series of CZT detector modules (OMS40G256) manufactured by Orbotech Medical Solutions (OMS), Israel, are used in the RT-2/CZT payload onboard the CORONAS-PHOTON satellite. The CZT detectors, sensitive in the energy range of 20 to 150 keV, are used to image solar flares in hard X-rays. Since these modules are essentially manufactured for commercial applications, we have carried out a series of comprehensive tests on these modules so that they can be confidently used in space-borne systems. These tests lead us to select the best three pieces of the ??Gold?? modules for the RT-2/CZT payload. This paper presents the characterization of CZT modules and the criteria followed for selecting the ones for the RT-2/CZT payload. The RT-2/CZT payload carries, along with three CZT modules, a high spatial resolution CMOS detector for high resolution imaging of transient X-ray events. Therefore, we discuss the characterization of the CMOS detector as well. 相似文献
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Simulation of the Arabian Sea Tsunami propagation generated due to 1945 Makran Earthquake and its effect on western parts of Gujarat (India) 总被引：1，自引：1，他引：0
The 1945 Tsunami generated due to Makran Earthquake in the Arabian Sea was the most devastating tsunami in the history of
the Arabian Sea and caused severe damage to property and loss of life. It occurred on 28th November 1945, 21:56 UTC (03:26
IST) with a magnitude of 8.0 (M
w), originating off the Makran Coast of Pakistan in the Arabian Sea. It has impacted as far as Mumbai in India and was noticed
up to Karvar Coast, Karnataka. More than 4,000 people were killed as a result of the earthquake and the tsunami. In this paper
an attempt is made for a numerical simulation of the tsunami generation from the source, its propagation into the Arabian
Sea and its effect on the western coast of India through the use of a numerical model, referred to as Tunami-N2. The present
simulation is carried out for a duration of 300 min. It is observed from the results that the simulated arrival time of tsunami
waves at the western coast of India is in good agreement with the available data sources. The paper also presents run-up elevation
maps prepared using Shuttle Radar Topographic Mission (SRTM) data, showing the possible area of inundation due to various
wave heights along different parts of the Gujarat Coast. Thus, these results will be useful in planning the protection measures
against inundation due to tsunami and in the implementation of a warning system. 相似文献
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We present the seismic energy, strain energy, frequency–magnitude relation (b-value) and decay rate of aftershocks (p-value) for the aftershock sequences of the Andaman–Sumatra earthquakes of December 26, 2004 (M
w 9.3) and March 28, 2005 (M
w 8.7). The energy released in aftershocks of 2004 and 2005 earthquake was 0.135 and 0.365% of the energy of the respective
mainshocks, while the strain release in aftershocks was 39 and 71% for the two earthquakes, respectively. The b-value and p-value indicate normal value of about 1. All these parameters are in normal range and indicate normal stress patterns and
mechanical properties of the medium. Only the strain release in aftershocks was considerable. The fourth largest earthquake
in this region since 2004 occurred in September 2007 off the southern coast of Island of Sumatra, generating a relatively
minor tsunami as indicated by sea level gauges. The maximum wave amplitude as registered by the Padang, tide gauge, north
of the earthquake epicenter was about 60 cm. TUNAMI-N2 model was used to investigate ability of the model to capture the minor
tsunami and its effect on the eastern Indian Coast. A close comparison of the observed and simulated tsunami generation, propagation
and wave height at tide gauge locations showed that the model was able to capture the minor tsunami phases. The directivity
map shows that the maximum tsunami energy was in the southwest direction from the strike of the fault. Since the path of the
tsunami for Indian coastlines is oblique, there were no impacts along the Indian coastlines except near the coast of epicentral
region. 相似文献
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Quantitative assessment of landslide hazard along transportation lines using historical records 总被引：2，自引：1，他引：1
In this paper, a quantitative landslide hazard model is presented for transportation lines, with an example for a road and
railroad alignment, in parts of Nilgiri hills in southern India. The data required for the hazard assessment were obtained
from historical records available for a 21-year period from 1987 to 2007. A total of 901 landslides from cut slopes along
the railroad and road alignment were included in the inventory. The landslides were grouped into three magnitude classes based
on the landslide type, volume, scar depth, and run-out distance. To calculate landslide hazard, we estimated the total number
of individual landslides per kilometer of the (rail) road for different return periods, based on the relationship between
past landslides (recorded in our database) and triggering events. These were multiplied by the probability that the landslides
belong to a given magnitude class. This gives the hazard for a given return period expressed as the number of landslides of
a given magnitude class per kilometer of (rail) road. The relationship between the total number of landslides and the return
period was established using a Gumbel distribution model, and the probability of landslide magnitude was obtained from frequency–volume
statistics. The results of the analysis indicate that the total number of landslides, from 1- to 50-year return period, varies
from 56 to 197 along the railroad and from 14 to 82 along the road. In total, 18 hazard scenarios were generated using the
three magnitude classes and six return periods (1, 3, 5, 15, 25, and 50 years). The hazard scenarios derived from the model
form the basis for future direct and indirect landslide risk analysis along the transportation lines. The model was validated
with landslides that occurred in the year 2009. 相似文献
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The objective of analyzing hazard and risk in an area is to utilize the result in selecting appropriate landslide risk reduction strategies. However, this does not happen always, and most often results of the hazard and risk analysis remain at an academic level. The under or non-utilization of results in pre-disaster planning could be due to several reasons, including difficulties in understanding the scientific content/meaning of the models, and lack of information on the practical significance and utility of the models. In this study, an attempt is made to highlight the uses of hazard and risk information in different landslide risk reduction strategies along a transportation corridor in Nilgiri, India. At first, a quantitative analysis of landslide hazard and risk was made. The obtained information was then incorporated in risk reduction options such as land use zoning, engineering solutions, and emergency preparedness. For emergency preparedness, the perception of the local Nilgiri communities toward landslide risk was evaluated and simplified maps were generated for the benefit and understanding of end users. A rainfall threshold-based early warning system was presented, which could be used in risk awareness programs involving public participation. The use of quantitative risk information in the cost-benefit analysis for the planning of structural measures to protect the road and railway alignments was also highlighted, and examples were shown how the transport organizations could implement these measures. Finally, the study provided examples of the utility of hazard and risk information for spatial planning and zoning, indicating areas where the landslide hazard is too high for planning future developments. 相似文献