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排序方式: 共有445条查询结果,搜索用时 31 毫秒
361.
Michael A. Dopita Daniela Calzetti Jesús Maíz Apellániz William P. Blair Knox S. Long Max Mutchler Bradley C. Whitmore Howard E. Bond John MacKenty Bruce Balick Marcella Carollo Michael Disney Jay A. Frogel Robert O’Connell Donald Hall Jon A. Holtzman Randy A. Kimble Patrick McCarthy Francesco Paresce Abhijit Saha Alistair R. Walker Joe Silk Marco Sirianni John Trauger Rogier Windhorst Erick Young 《Astrophysics and Space Science》2010,330(1):123-131
We present narrow band, continuum subtracted Hα, [S ii], Hβ, [O iii] and [O ii] data taken with the Wide Field Camera 3 on the Hubble Space Telescope in the nearby dwarf starburst galaxy NGC 4214. From these images, we identify seventeen new planetary nebula candidates, and seven supernova remnant candidates. We use the observed emission line luminosity function of the planetary nebulae to establish a new velocity-independent distance to NGC 4214. We conclude that the PNLF technique gives a reddening independent distance to NGC 4214 of 3.19±0.36 Mpc, and that our current best-estimate of the distance to this galaxy ids 2.98±0.13 Mpc. 相似文献
362.
Nidhi Nagabhatla Sonali S. Sellamuttu A. Ghosh Bobba Max Finlayson Rohan Wickramasuriya Martin Van Brakel S. Narendra Prasad Chiranjibi Pattanaik 《Journal of the Indian Society of Remote Sensing》2012,40(1):47-64
Ecosystem based approach (EBA) for resource management is a concerted, environmentally tuned and an integrated framework that
holistically addresses the ecological character of the natural resource, its societal benefit spectrum and its environmental
functions. In this paper, the EBA concept is closely linked with the emerging concept of multiple use systems (MUS) while
taking account of environmental, economic, and social factors that govern the ecosystems services and benefits. We elucidate
a multi-scalar approach and multiple case studies to understand EBA particularly in context of a wetlandscape. At the global
scale, Ramsar sites of international importance are geospatially analyzed with reference to their agro-ecology and biodiversity.
At regional scale, the agrarian use of inland wetlands in India was re-evaluated taking account of database from a recent
inland wetland inventory. At the local scale, drawing on the landscape characterization and the ecological economics for fresh
water Lake Kolleru in India and the Muthurajawela Marsh-Negombo Lagoon coastal marsh in Sri Lanka, we illustrate some of the
practical challenges in balancing wetland conservation, development needs and the overall well-being of local people. We also
discuss how variability in the scale, geophysical characteristics of the site and the data availability confines the ability
to simplify a single complete approach to address issues in complex ecosystem such as wetlands. All levels of the study are
supported by a variety of earth observation data and the geographical information system (GIS) tools. The site level analysis
also draws on socio-economic assessment tools. 相似文献
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The larger and most energetic cratering events from comet and asteroid collisions with the Earth are probably associated with ejection of solid material faster than escape speeds every 100 Myr or so. Metre-sized boulders, we estimate, may have been ejected directly into Venus-crossing and perhaps Mars-crossing orbits from comet impacts at higher speeds and of larger mass, at least on 10 occasions in the last 3.5 Ga. Subsequent close encounters with Earth can also enable slower boulders to reach Mars-crossing orbits. Orbit perturbations from Mars and Jupiter would then have sent a fraction of the boulders to the outer planets and their icy satellite systems. In the so-called late bombardment epoch at 3.9 Ga, when primitive life was developing, ejection-causing impacts were much more frequent, at 30 per 0.1 Ga, yielding an increased probability of distributing seeds of terrestrial biology to the outer regions of the solar system. 相似文献
365.
Precursory seismic quiescence 总被引:14,自引:0,他引:14
Seventeen cases of precursory seismic quiescence to mainshocks with magnitudes fromM
L=4.7 toM
S=8.0 are summarized. The amount of rate decrease ranges from 45% to 90%. The significance of these changes varies between 90% and 99.99%. The assumption that the background rate is approximately constant is fulfilled in most crustal volumes studied. All quiescence anomalies seem to have abrupt beginnings, and the rate during the anomalous period is fairly constant. The duration of the precursors ranges from 15 to 75 months, and it is not clear what factors determine that time. At least three successful predictions have been based on seismic quiescence. These cases have shown that mainshocks can be predicted based on quiescence, but they have also shown that the interpretation of the data in real time is difficult and nonunique. If a false alarm is defined as a period of quiescence with a significance level larger than a precursory quiescence in the same tectonic area, then we estimate, based on searches in four areas, that the false alarm rate may be on the order of 50%. Failure to predict may be expected in perhaps 50% of mainshocks, even in carefully monitored areas. Quiescence cannot be used as a precursor in tectonic environments with low seismic activity. Most characteristics of the phenomenon are still poorly defined, but data exist which probably permit at least a doubling of the presently available data on case histories. 相似文献
366.
Emma L. Yates Angela M. Detweiler Laura T. Iraci Brad M. Bebout Christopher P. McKay Kathleen Schiro Edwin J. Sheffner Cheryl A. Kelley Jovan M. Tadić Max Loewenstein 《Environmental Earth Sciences》2013,70(3):1047-1056
Alkaline soils occupy approximately 5 % of the Earth’s land surface (7 million km), and this may increase due to the global trend towards increasing desertification, yet the extent to which these soils modulate carbon dynamics on regional and global scales is inadequately studied and poorly understood. Railroad Valley (RRV) playa (Nevada, USA) is a semi-arid playa with highly alkaline soils (pH > 10) and no vegetation. The extreme, alkaline environment and absence of vascular vegetation make RRV an ideal site to investigate the role of physiochemical processes of soil-atmosphere CO2 exchange. Both field and laboratory investigations were conducted. This work shows how the atmospheric CO2 mixing ratio decreases at nighttime at RRV playa to a value well below the average global background CO2 concentration. Laboratory investigations using soil samples collected at RRV playa confirmed that CO2 uptake by RRV playa soils occurs when temperatures are decreased. Both field and laboratory studies suggest that the alkaline RRV soil acts as a CO2 reservoir during colder periods, such as at nighttime. These results highlight the importance of investigating carbon dynamics in previously understudied environments. Given how little information is available on the CO2 flux in desert and semi-arid alkaline ecosystems lacking vegetation, our findings draw attention to these environments as becoming increasingly important for carbon fluxes on regional and global scales. 相似文献
367.
Max D. Woodworth 《The Professional geographer》2013,65(4):630-638
China's coal industry has been plagued by fragmentation among thousands of producers, low productivity, environmental damage, and high accident rates. Coal-industry reforms have sought a “strategic westward movement” through which to achieve resource consolidation under larger firms and upgraded production in northern and western China. This article examines Ordos Municipality and Yulin Municipality to assess the role of differently scaled political and economic processes that have driven a regional coal boom. It finds that the regional coal boom in north-central China discloses persistent difficulties in controlling producers and modernizing the sector. 相似文献
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