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611.
Barbara Paltrinieri Francesco R. Ferraro Flavio Fusi Pecci & Eugenio Carretta 《Monthly notices of the Royal Astronomical Society》1998,293(4):434-442
In this paper, we present a B − V CCD colour–magnitude diagram (CMD) of the globular cluster M13 (NGC 6205), reaching down about 2 mag below the main sequence turn-off, based on a new, independent photometric calibration.
The most notable features of the CMD, including about 5500 stars, are (i) the long extension of the blue tail of the horizontal branch (HB), which can be traced down to V ∼19 and (moreover) shows the presence of two gaps; and (ii) the so-called bump on the red giant branch which is well-detected at V =14.75±0.05, using both the differential and integral luminosity functions.
No similar features have ever been detected in any previous ground-based photometry of this cluster.
A direct comparison between the CMD of M13 and M3, calibrated during the same run with the same apparatus, sets an upper limit of about 1.5 Gyr on their age difference, too small to explain the striking differences between their HB morphologies. 相似文献
The most notable features of the CMD, including about 5500 stars, are (i) the long extension of the blue tail of the horizontal branch (HB), which can be traced down to V ∼19 and (moreover) shows the presence of two gaps; and (ii) the so-called bump on the red giant branch which is well-detected at V =14.75±0.05, using both the differential and integral luminosity functions.
No similar features have ever been detected in any previous ground-based photometry of this cluster.
A direct comparison between the CMD of M13 and M3, calibrated during the same run with the same apparatus, sets an upper limit of about 1.5 Gyr on their age difference, too small to explain the striking differences between their HB morphologies. 相似文献
612.
Hervé Cabot Christian Meynadier Dorota Sobczyńska Barbara Szabelska Jacek Szabelski Tadeusz Wibig 《Astroparticle Physics》1998,9(4):269-276
We describe the possible measurable difference in the Cherenkov light component of EAS induced by an electromagnetic particle (i.e., e+, e− or γ) and induced by a hadron (i.e., proton or heavier nuclei) in the TeV range. The method can be applied in experiments which use wave front sampling method of EAS Cherenkov light detection (e.g., THEMISTOCLE, ASGAT). 相似文献
613.
Scattering parameters of the lithosphere below the Massif Central, France, from teleseismic wavefield records 总被引:1,自引:0,他引:1
Joachim R. R. Ritter Sergei A. Shapiro & Barbara Schechinger 《Geophysical Journal International》1998,134(1):187-198
Teleseismic P -wave recordings are analysed in the frequency range 0.3–6 Hz to derive structural (statistical) parameters of the lithosphere underneath the French Massif Central. For this we analyse differences in frequency-dependent intensities of the mean wavefield and the fluctuation wavefield. It is possible to discriminate a weak fluctuation regime of the wavefield in the frequency range below 1 Hz and a strong fluctuation regime starting above 1 Hz and continuing to higher frequencies. The observed wavefield fluctuations in the frequency range 0.3–3 Hz can be explained by scattering of the teleseismic P wave front at elastic inhomogeneities in the lithosphere. A statistical distribution of the inhomogeneities is assumed and the concept of random media is applied. The lithospheric structure under the Massif Central can be described as a 70 km thick heterogeneous layer with velocity fluctuations of 3–7 per cent and correlation lengths of the heterogeneities of 1–16 km. 相似文献
614.
615.
Evelyn E. Gaiser Mark J. Brooks William F. Kenney Claire L. Schelske Barbara E. Taylor 《Journal of Paleolimnology》2004,31(1):63-76
The hydrological history of a temporary pond in South Carolina was inferred from a 5500-year record of siliceous microfossils, including diatoms, freshwater sponge spicules, chrysophyte cysts, plates of testate amoebae and plant phytoliths. Microfossil abundance was estimated by microscopic quantification of siliceous particles and by chemical extractions of silica. Diatom, sponge and mineral particle volumes were correlated with silica concentrations attributable to these fractions. Both techniques suggested a sequence of four distinct community types. Basal sediments (4630–5520 14C YBP) containing phytoliths and sponge spicules indicative of a wetland community were covered by sediments dominated by the remains of planktonic protists (3750–4630 14C YBP) suggesting a transition from a vegetated marsh to an open-water, permanently flooded pond. Microfossil assemblages above this zone indicate the return of a wetland community ca. 3750 YBP that persisted until recently, when pond water levels stabilized as a result of seepage from a reservoir constructed nearby in 1985. This study suggests that the suite of siliceous microfossils commonly found in pond sediments can be used to infer historical alternations between macrophyte and plankton-dominated states in shallow basins. Regional climate inferences from this record include a mid-Holocene hydrological maximum and the onset of the modern climate ca. 3500 YBP. 相似文献
616.
In two limno-corrals loaded with heavy metals the density of tubificid worms and chironomid larvae was higher than in the
control. The better oxygen conditions observed in the heavy metal loaded corrals might explain this discrepancy. The higher
oxygen concentration at the sediment-water interface was due to lower organic sedimentation, consequence of the primary production
reduced by heavy metals. In all limno-corrals, the tubificid populations consisted ofTubifex tubifex. The size structure of tubificid populations in the heavy metal loaded corrals indicated a delayed reproduction compared
to the control. 相似文献
617.
618.
Seven species of mojarras (Gerreidae) were collected from three stations in the Indian River lagoon near the Sebastian Inlet, Florida over an eighteen month period to study spatial and temporal variations in occurrence and feeding habits. Two major habitats common to this area were represented in the study; a sandy beach and a seagrass flat. Of the 2,899 gerreids collected,Eucinostomus gula represented 67% and was found primarily in theHalodule seagrass site. The next most abundant species,E. argenteus (11%),E. jonesi andE. lefroyi (each 10%), were found most frequently at the inlet site.Diapterus auratus, E. melanopterus, andGerres cinereus were captured infrequently and were considered incidental. Prey items found included amphipods, bivalves, copepods, fish eggs, foraminifera, isopods, nematodes, ostracods, polychaetes and crustacean parts. Significant amounts of sand and unidentifiable amorphous debris were also included in the gut content analysis. Little interspecific variation in diet was found among the four major species examined. The general shift seen from a diet composed primarily of copepods and other crustaceans to one of polychaetes suggests an intraspecific ontogenetic progression. Spatial variations in diet composition were also indicated between the two major habitats. Feeding analyses showed gerreids to be diurnal feeders with the greatest consumption (total gut content weight) occurring at dusk. 相似文献
619.
620.
Warren L. Prell William H. Hutson Douglas F. Williams Allan W. H. B Kurt Geitzenauer Barbara Molfino 《Quaternary Research》1980,14(3):309-336
A seasonal reconstruction of the Indian Ocean during the last glacial maximum (18,000 yr B.P.) reveals that its surface circulation and sea surface temperature patterns were significantly different from the modern Indian Ocean. This reconstruction is based on the planktonic foraminiferal biogeography and estimated sea surface temperatures in 42 Indian Ocean samples. Compared to modern conditions, the polar front was 5° to 10° latitude further north during the last glacial maximum; the Subtropical Convergence was 2° to 5° latitude further north. The West Australian Current was more intense as part of the West Wind Drift was deflected northward along the coast of Australia. The Agulhas Current was cooler and weaker during the summer and more saline and subtropical during the winter. In general, the low latitudes underwent little temperature change. The western Arabian Sea was warmer which implies less upwelling and a weaker Southwest Monsoon. On the average, the Indian Ocean was 1.9°C cooler in February and 1.7°C cooler in August during the last glacial maximum. 相似文献