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The 61 cm Lowell telescope at Perth Observatory has been automated by the Perth Astronomy Research Group (PARG) for the detection, confirmation and follow-up studies of supernovae and other transient events. This search program complements similar searches operating in the Northern Hemisphere, such as the Berkeley Supernova Search. The first supernova found by our search program, SN 1993k, was discovered on March 28, 1993 (IAUC 5733). The discovery has been made with the telescope in fully automated mode, including automated image analysis. We are currently imaging some 80 galaxies per night. Photometric methods for the analysis of lightcurves are at present being implemented. 相似文献
944.
Martin J. Siegert Martyn Tranter J. Cynan Ellis‐Evans John C. Priscu W. Berry Lyons 《水文研究》2003,17(4):795-814
Our understanding of Lake Vostok, the huge subglacial lake beneath the East Antarctic Ice Sheet, has improved recently through the identification of key physical and chemical interactions between the ice sheet and the lake. The north of the lake, where the overlying ice sheet is thickest, is characterized by subglacial melting, whereas freezing of lake water occurs in the south, resulting in ~210 m of ice accretion to the underside of the ice sheet. The accreted ice contains lower concentrations of the impurities normally found in glacier ice, suggesting a net transfer of material from meltwater into the lake. The small numbers of microbes found so far within the accreted ice have DNA profiles similar to those of contemporary surface microbes. Microbiologists expect, however, that Lake Vostok, and other subglacial lakes, will harbour unique species, particularly within the deeper waters and associated sediments. The extreme environments of subglacial lakes are characterized by high pressures, low temperatures, permanent darkness, limited nutrient availability, and oxygen concentrations that are derived from the ice that provides the meltwater. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
945.
Global Magnetic Patterns of Chirality 总被引:1,自引:0,他引:1
During the past five years at least six manifestations of a global organization of solar magnetic fields have been recognized. The magnetic chirality (handedness) of the following features shows a hemispheric preference: filament channels, quiescent filaments, sunspot whorls, superpenumbral fibrils, coronal arcades, and interplanetary clouds associated with CMEs. Although the patterns are clear in the data, their interpretation and their possible connection to the dynamo is open to question. This paper reviews the observations of the patterns, corrects some misinterpretations, and offers a scenario for the origin of the most marked pattern, the chirality of filaments. We suggest the pattern arises from the reconnection of coronal loops, under the influence of supergranulation and differential rotation. Unlike alternative scenarios, ours relies only on observable surface motions and fields. 相似文献
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Martin Novak Jitka Mikova Jan Kosler Eva Prechova Daniela Fottova 《Geochimica et cosmochimica acta》2010,74(15):4207-4218
Annual growth rings of a common hardwood species, Picea abies L., were investigated as a potential archive of past atmospheric Pb pollution. Wide distribution of trees in terrestrial settings and straightforward chronology are two advantages of this potential geochemical archive, but several processes described in the literature may obscure the trends in past Pb deposition. These confounding factors include, e.g., radial post-depositional mobility of Pb in xylem, and ecosystem acidification leading to higher bioavailability of Pb. One- to five-year annual wood increments were analyzed for Pb concentrations and 206Pb/207Pb ratios at Jezeri (JEZ), Uhlirska (UHL) and Na Lizu (LIZ), three sites in the Czech Republic, differing in atmospheric Pb loads. Three to four trees per site were included in the study. Distinct Pb concentration maxima between 1960 and 1990 at the two heavily polluted sites (JEZ and UHL) coincided with historical Pb emissions known from inventories of industrial production. No Pb concentration maxima were found at one site, LIZ, situated in a national park 150 km from major pollution sources. Spruce tree rings from JEZ, located just 5 km from coal-burning power stations, contained a large proportion of coal-derived Pb (a high-206Pb/207Pb ratio of 1.19). A coal-related maximum in 206Pb/207Pb in JEZ tree rings was found using two different analytical techniques, laser-ablation multi-collector ICP MS, and single-collector sector-field ICP MS. In a three-isotope graph (206Pb/207Pb vs. 208Pb/207Pb), tree-ring data plotted into the field of ombrotrophic (i.e., rain-fed) peat bogs, suggesting negligible contribution of bedrock-derived Pb in the xylem. We concluded that none of the potential confounding factors played a major role at our sites. Annual growth rings of P. abies in Central Europe faithfully recorded historical changes in atmospheric Pb depositions. 相似文献
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The Early-Middle Pleistocene Transition: characterization and proposed guide for the defining boundary 总被引:1,自引:0,他引:1
Martin J. Head Brad Pillans Sarah A. Farquhar 《《幕》》2008,31(2):255-259
The mid-Pleistocene transition (MPT, c. 1.2 to 0.5 Ma) records fundamental changes in Earth's climate state, where low-amplitude 41-kyr obliquity-dominated cycles gave way progressively to the high-amplitude, quasiperiodic (c. 100-kyr) fluctuations that characterize the later Pleistocene and Holocene. We use wavelet analysis on the LR04 δ^l8O benthic foraminiferal stack to confirm low-frequency power as early as 1.25-1.20 Ma, determine the persistence of obliquity-dominated cyclicity through and beyond the MPT, and reveal new levels of complexity in climate evolution. 相似文献