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排序方式: 共有112条查询结果,搜索用时 15 毫秒
1.
We present a photometric analysis of the eclipsing binary systemGSC4832.400 based on 732 photometric observations obtained on sixteen clear nights during 1999–2000 in the V-Johnson and yb-Strömgren filters. The observed times of the minima yielded a linear ephemeris showing that the system has a constant period of 0.313150 ± 0.000002days. The light curve corresponds to a circular orbit for the system and clearly shows that GSC4832.400 has the defining characteristics of a W UMa-type eclipsing binary. It also shows a small O'Connell effect, which could be due to the presence of a hot spot in the primary star. A preliminary photometric solution based on the assumption of an over contact systemsatis factorily reproduced the observed light curve. 相似文献
2.
María Luisa García Vargas Angeles Díaz Roberto Terlevich Elena Terlevich 《Astrophysics and Space Science》1993,205(1):77-84
In the frame of the Starburst Model, we show that the evolution of a massive stellar cluster in a high metallicity environment can reproduce the observed emission-line spectrum and the UV-optical Spectral Energy Distribution of the Seyfert 2 galaxies and LINERs. We apply the results of our models to three objects: NGC 5506, NGC 5643 and Mk 348. 相似文献
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4.
Summary The existence of low-frequency variability in climatic-hydrological-oceanic variables may be useful for long-term forecasting
and climate modelling. By using long time series this paper attempts to identify large-scale quasi-cycles in the precipitation
regimes of Northern Argentina, moisture advection from the Atlantic Ocean and the streamflow of the Paraná River. This work
also shows the presence of coherent waves with long periodicity between the three series. As the three variables are estimated
over different time intervals, the presence of waves in each variable is studied separately, to show they respond to the same
process. The three variables show significant interdecadal variability at low frequency (22–26 years), which might be related
to the ENSO cycle modulation and to the intensification or weakening of the South American Low Level Jet (SALLJ) and South
Atlantic Convergence Zone (SACZ). 相似文献
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Till Czypionka Cristian A. Vargas Nelson Silva Giovanni Daneri Humberto E. González José Luis Iriarte 《Continental Shelf Research》2011,31(3-4):216-224
Mixotrophy, the combination of autotrophic and heterotrophic nutrition in the same organism, is widespread in planktonic algae. Several reports from temperate and high-latitude fjords in Scandinavia suggest the occurrence of a niche in late summer and autumn during post-bloom conditions in which mixotrophic algae can become important grazers in pelagic ecosystems, accessing the nutrients bound in their prey to overcome nutrient limitation. Here, we experimentally determined the trophic modes and bacterivory rates for the nanoplankton community (2–20 μm) in Aysén Fjord located in the Chilean Northern Patagonia during two contrasting seasons: winter and spring. While mixotrophic nanoplankton was virtually absent from the system in spring, in winter at occasions it even constituted the dominant trophic group of the nanoplankton with abundances of >900 cells mL?1. This indicates a second niche for mixotrophs in winter, when mixotrophy allows overcoming light limitation. 相似文献
7.
José Tasso Felix Guimarães Prafulla Kumar Sahoo Mariana Maha Jana Costa De Figueiredo Karen da Silva Lopes Markus Gastauer Silvio Junio Ramos Cecilio Frois Caldeira Pedro Walfir M. Souza-Filho Luiza Santos Reis Marcio Sousa Da Silva Paulo Rogenes Pontes Renato Oliveira Da Silva Junior Tarcísio Magevski Rodrigues 《第四纪科学杂志》2021,36(2):255-272
This study addresses paleoclimate influences in a southern Amazonia ecotone based on multiproxy records from lakes of the Carajás region during the last 45k cal a bp. Wet and cool environmental conditions marked the initial deposition in shallow depressions with detrital sediments and high weathering rates until 40k cal a bp. Concomitantly, forest and C3 canga plants, along with cool-adapted taxa, developed; however, short drier episodes enabled expansion of C4 plants and diagenetic formation of siderite. A massive event of siderite formation occurred approximately 30k cal a bp under strong drier conditions. Afterwards, wet and cool environmental conditions returned and persisted until the Last Glacial Maximum (LGM). The LGM was marked by lake-level lowstands and subaerial exposure. The transition from the LGM to the Holocene is marked by the onset of oscillations in temperature and humidity, with an expansion of forest and canga plants. Cool taxa were present for the last time in the Carajás region ~ 9.5–9k cal a bp. After 10k cal a bp , shallow lakes became upland swamps due to natural infilling processes, but the current vegetation types and structures of the plateaus were acquired only after 3k cal a bp under wetter climatic conditions. 相似文献
8.
Marine Geophysical Research - We have estimated empirical relationships that associate the age of the Pacific oceanic lithosphere with the seismic energy released on both flanks of the East Pacific... 相似文献
9.
Po-Hung Yeh Kuang-An Chang John Henriksen Billy Edge Peter Chang Andrew Silver Abel Vargas 《Ocean Engineering》2009,36(3-4):248-255
This study investigates the topographic deformation due to the erosion of a sand bed impinged by a moving submerged turbulent round jet in a large-scale laboratory. The test conditions represent the case of discharges beneath a vessel while operating in water with a limited clearance such as a shallow navigation channel. The jet moves horizontally and discharges water vertically downward towards the bed. The distance between the jet nozzle and the bed equals six times the jet diameter so the jet flow is in the potential core region. The speed of the jet horizontal motion was varied to examine its effect on the scour profile. The characteristic lengths of the scour profile in the asymptotic state were determined by modifying the empirical formulas in Aderibigbe and Rajaratnam [1996. Erosion of loose beds by submerged circular impinging vertical turbulent jets. Journal of Hydraulic Research 34(1), 19–33]. The maximum scour depth, the scour hole radius, and the ridge height were found to be a function of the ratio of the jet exit to jet translation velocities and were modeled using a hyperbolic function. Empirical equations describing the scour profile were developed and the scour profile was found to be self-similar when normalized by appropriate length scales. 相似文献
10.
Summary Monthly and annual climatic variabilities of precipitation were analyzed from a 60 years record of rainfall data at 10 measuring stations in the humid region of Argentina.Different statistical techniques were used to analyze the regional homogeneity of precipitation fields. Special structures and monthly trends were studied. Simple correlations of yearly precipitation at different locations were computed. Exponential functions relating cross-correlations and distances were determined through regression analysis.Monthly and annual rainfall show no evident signs of trends; aleatory processes are predominant in the whole region; and, correlation functions are independent of the direction of the vector connecting the stations.With 3 Figures 相似文献