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501.
Elena Pavlenko Kirill Antoniuk Sergei Yu. Shugarov Nataly A. Katysheva Lenie Muzhdabaeva Vyacheslav Mikhajlov 《Astrophysics and Space Science》2005,296(1-4):461-464
We present results of multicolour photometry of the nova-like binary MV Lyr in the years 2002–2003, corresponding to the transition
of the star from its low (V = 17.8) to high (V = 12.3) brightness state. The transition lasted at most 200 days. During the first ∼50 days MV Lyr brightened at the rate
0.06 mag/day, and during the next ∼150 days at the rate 0.01 mag/day. The brightening was accompanied by a blue shift from
0.45 to 0.05 in V−R, interpreted as an increase of the accretion disk contribution to the total light. During the transition MV Lyr displayed
well-known ‘quasi-orbital’ light variations and fast quasi-periodic oscillations with a typical time scale of tens of minutes. 相似文献
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We introduce a novel technique, called the double wavelet analysis (DWA), for the determination of stellar rotation periods from time serial data. This first paper aims narrowly at the discussion, introduction and application of the DWA technique to records of surface magnetism in solar-type (relatively old) lower main sequence stars that are obtained by the Mount Wilson Observatory (MWO) HK Project. The technique takes a series of careful steps that seek to optimize wavelet parameters and normalization schemes, ultimately allowing fine-tuned, arguably more accurate, estimates of rotation-modulated signals (with, e.g., periods of days to months) in records that contain longer periodicities such as stellar magnetic activity cycles (with, e.g., period of years). The apparent rotation periods estimated from the DWA technique are generally consistent with results from both “first-pass” (i.e., ordinary) global wavelet spectrum and earlier classical periodogram analyses. But there are surprises as well. For example, the rotation period of the ancient subdwarf Goombridge 1830 (HD 103095), previously identified as ≈31 days, suggests under the DWA technique a significantly slower period of 60 days. DWA spectra also generally reveal a shift in the cycle period toward high frequencies (hence shorter periods) compared to the first-pass wavelet spectrum. For solar-type stars analyzed here, the character of the DWA spectrum and slope of the first-pass global wavelet spectrum produce a classification scheme that allows a star's record to be placed into one of three categories. 相似文献
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507.
Flooding mine tailings to limit the oxidation of sulfides provides a habitat for aquatic organisms, such as plants, plankton,
insects, and fish, which can uptake metals and, thus, threats for local ecosystems and influence the cycling of elements in
biogeocenosis. An aquatic ecosystem developed naturally in sulphide tailing ponds containing cyanidation wastes of the Salair
ore-refining plant (SORP), Russia, was studied. The objectives of this research were to: (i) reveal the level of contamination
of living organisms in the tailing ponds compared to a natural control site and (ii) calculate the weight of metals in aquatic
biomass to estimate the amount of metals transferring from the tailing ponds into the biogechemical cycle. The concentration
of Cu, Zn, Cd, and Pb in the sediments of the tailing ponds is significantly higher than from the control site. Concentrations
of Cu, Zn, Cd, and Pb in plant shoots were significantly higher than in the control and accumulated mainly in cell envelopes
and membranes. The concentration of Pb in fish liver and eggs were 41 and 7.5 times higher, respectively, than maximum allowable
concentrations.
The biomass distribution between producers and consumers of the tailing pond ecosystem is similar to those of natural pond
ecosystems. However, the weights of Cu, Zn, Cd, and Pb in all trophic levels per hectare of the tailing pond are orders of
magnitude higher than those for Lake Baikal. The largest portion of metal circulates within the ecosystem of the Dyukov Ravine
Pond with a maximum of 5 to 13% of this amount transferred into the surrounding environment through the food chains. 相似文献
508.
Giovanni Scicchitano Fabrizio Antonioli Elena Flavia Castagnino Berlinghieri Andrea Dutton Carmelo Monaco 《Quaternary Research》2008,70(1):26-39
Precise measurements of submerged archaeological markers in the Siracusa coast (Southeastern Sicily, Italy) provide new data on relative sea-level change during the late Holocene. Four submerged archaeological sites have been studied and investigated through direct observations. Two of them are Greek archaic in age (2.5–2.7 ka) and are now 0.98–1.48 m below sea level; the other two developed during the Bronze age (3.2–3.8 ka) and are now 1.03–1.97 m below sea level. These archaeological data have been integrated with information derived from a submerged speleothem collected in a cave located along the Siracusa coast at − 20 m depth. The positions of the archaeological markers have been measured with respect to present sea level, corrected for tide and pressure at the time of surveys. These data were compared with predicted sea-level rise curves for the Holocene using a glacio-hydro-isostatic model. The comparison with the curve for the southeastern Sicily coast yields a tectonic component of relative sea-level change related to regional uplift. Uplift rates between 0.3 and 0.8 mm/yr have been estimated. 相似文献
509.
The Tree Shelter site dates to the Early to Mid-Holocene (8000 to 4900 14C yr BP). Present conditions around the site are hyperarid, but charcoal remains indicate less severe aridity at the time of its occupation. The environment around the site then supported a rich wadi vegetation, which allowed hunting during the Epipaleolithic and herding during the Neolithic occupation. Although more favorable than today, the environmental conditions also displayed a desert character and seem to have limited the range of domestic herbivores introduced in the area. 相似文献
510.
Laurence R. Bentley Masaki Hayashi Elena P. Zimmerman Chris Holmden Lynn I. Kelley 《Hydrogeology Journal》2016,24(4):877-892
Hypersaline lakes occur in hydrologically closed basins due to evaporitic enrichment of dissolved salts transported to the lakes by surface water and groundwater. At the hypersaline Lydden Lake in Saskatchewan, Canada, groundwater/lake-water interaction is strongly influenced by the geological heterogeneity of glacial deposits, whereby a highly permeable glaciofluvial sand/gravel deposit is underlain by glaciolacustrine deposits consisting of dense clay interspersed with silt/sand lenses. Pressure head distribution in a near shore area indicates a bi-directional flow system. It consists of topographically driven flow of fresh groundwater towards the lake in the sand/gravel aquifer and density-driven, landward flow of saline groundwater in the underlying glaciolacustrine deposits. Electrical resistivity tomography, and chemical and isotopic composition of groundwater clearly show the landward intrusion of saline water in the heterogeneous unit. The feasibility of bi-directional flow and transport is supported by numerical simulations of density-coupled groundwater flow and transport. The results suggest that the geologically controlled groundwater exchange processes have substantial influences on both inputs and outputs of dissolved minerals in hypersaline lakes in closed basins. 相似文献