Evolutionary status of T Tauri stars     

Olga Eretnova  Alexander Dudorov 《天文和天体物理学研究(英文版)》2018,(8)

The problem of determining the masses and ages of T Tauri star(TTS) using their evolutionary status is discussed. We test four pre-main sequence evolutionary models using well determined observational parameters of 12 binary TTSs and two binary red dwarfs. It is shown that the masses derived using the tracks of all models are in good agreement with the masses obtained from the observations of TTSs with masses M 0.7 M_⊙(mean error ε ~ 10%). Low-mass stars with M ≤ 0.7 M_⊙have significantly greater mean error: ε ~ 50% for the tracks of Bressan et al. and Chen et al., and ε ~ 30% for the other tracks. The isochrones of all tested evolutionary models diverge for stars with masses M ≤ 0.7 M_⊙. The difference increases with the mass decrease and can reach 10% of KelvinHelmholtz time for stars with mass M = 0.2 M_⊙. The ages of most of the considered TTSs are smaller than the Kelvin-Helmholtz time. This confirms their evolutionary status of being pre-main sequence stars.  相似文献   

Magnetotactic bacteria from the human gut microbiome associated with orientation and navigation regions of the brain     

Simon  Rozalyn A.  Ranasinghe  Purnika Damindi  Barazanji  Nawroz  Jungeström  Malin Bergman  Xu  Jie  Bednarska  Olga  Serrander  Lena  Engström  Maria  Bazylinski  Dennis A.  Keita  Åsa V.  Walter  Susanna 《中国海洋湖沼学报》2021,39(6):2044-2052

Journal of Oceanology and Limnology - Magnetotactic bacteria (MTB), ubiquitous in soil and fresh and saltwater sources have been identified in the microbiome of humans and many animals. MTB...  相似文献   

Intertidal meiofauna of Jeju Island,Korea     

Olga N. Pavlyuk  Yulia A. Trebukhova 《Ocean Science Journal》2011,46(1):1-11

For the first time, the structure of the meiobenthos community and marine nematodes in particular was investigated in the different intertidal zones of Jeju Island (South Sea of Korea). A relationship was found between the density of meiobenthic communities and the type of the bottom sediment. In addition, in the silty sediments, nematodes were dominant, while in the sandy sediments harpacticoids and ostracods were dominant groups. Sixty eight species belonging to 60 genera and 19 families of nematodes were found in the whole area. Four different nematode taxocenosis were distinguished using a cluster analysis. Dominant feeding groups were omnivores (2B) and epistratum-feeders (2A). The highest number of non-selective deposit-feeders (1B) was detected in the lagoon with the bottom silty sediments.  相似文献   

An assessment of the climate change impacts on groundwater recharge at a continental scale using a probabilistic approach with an ensemble of GCMs   总被引：1，自引：0，他引：1  

Russell S. Crosbie  Trevor Pickett  Freddie S. Mpelasoka  Geoff Hodgson  Stephen P. Charles  Olga V. Barron 《Climatic change》2013,117(1-2):41-53

This study used 16 Global Climate Models and three global warming scenarios to make projections of recharge under a 2050 climate for the entire Australian continent at a 0.05° grid resolution. The results from these 48 future climate variants have been fitted to a probability distribution to enable the results to be summarised and uncertainty quantified. The median results project a reduction in recharge across the west, centre and south of Australia and an increase in recharge across the north and a small area in the east of the continent. The range of results is quite large and for large parts of the continent encompasses both increases and decreases in recharge. This makes it difficult to utilise for water resources management so the results have been analysed with a risk analysis framework; this enables the future projections for groundwater recharge to be communicated to water managers in terms of likelihood and consequence of a reduction in recharge. This highlights an important message for water resource managers that in most areas of Australia they will be making decisions on water allocations under considerable uncertainty as to the direction and magnitude of recharge change under a future climate and that this uncertainty may be irreducible.  相似文献   

The finest white-light coronal features     

Serge Koutchmy  Olivier Bouchard  Jean Mouette  Olga Koutchmy 《Solar physics》1993,148(1):169-172

An attempt to detect the finest white-light coronal features observed with a large optical telescope was made at the July 11, 1991 Solar Total Eclipse. A few selected results taken from the video-CCD high speed observations obtained at the prime focus of the Canada-France-Hawaï-Telescope (CFHT) with a red coronal interference filter are presented. The smallest (sub-arsec) detected and/or resolved coronal features are shown. The methods that were used to extract them from the noisy and seeing-limited images taken from video frames are described.  相似文献   

Rest-frame optical continua of L∼L*, z > 3 quasars: probing the faint end of the high-z quasar luminosity function     

Olga P. Kuhn 《Monthly notices of the Royal Astronomical Society》2004,348(2):647-660

  相似文献   

Nitrogen and argon release profiles in Luna 16 and Luna 24 regolith samples: The effects of regolith reworking     

S. S. Assonov  I. A. Franchi  C. T. Pillinger  A. S. Semenova  Yu. A. Shukolyukov  A. B. Verchovsky  A. N. Iassevitch 《Meteoritics & planetary science》2002,37(1):27-48

Abstract— Fines, microbreccias and agglutinates from the Luna 16 mature regolith 1635 and fines from the immature/submature Luna 24 regolith have been analysed for N and argon isotopes in order to understand the origin of isotopically distinct N released at different temperatures. All high‐resolution runs reveal a similarity in the release of ³⁶Ar, ⁴⁰Ar and N over a wide temperature interval. The similarity in the ⁴⁰Ar and ³⁶Ar releases and the near coincidence in the 1635 agglutinates implies that the implanted species were redistributed and homogenised during regolith processing such that, regardless of the huge difference in ion implantation energy between solar ³⁶Ar and non‐solar ⁴⁰Ar, their present distribution and their release temperatures are now essentially equal. A small amount of ⁴⁰Ar released in the lower temperature steps with elevated ⁴⁰Ar/³⁶Ar is considered to be trapped after reworking. While such mixing and homogenisation may also be expected for N components of different origins, to date all known stepped runs regularly demonstrate a reproducible variation in δ¹⁵N, suggesting no homogenisation. We consider regolith N to be a mixture of several components trapped at different times, and some nitrogen that was not involved in the reworking. Relatively heavy N released around 500 °C appears to be the most pure form of the component trapped after reworking, probably from accreted meteoritic matter. Middle‐temperature isotopically lighter N appears to be a mixture of solar and non‐solar N largely homogenised, and therefore solar N can not be seen in its pure form. Bulk δ¹⁵N as well as formally deconvoluted δ¹⁵N thermal profiles imply that the non‐solar N has a variable δ¹⁵N value. Several non‐solar N sources are considered with their input resulting in increasing regolith δ¹⁵N with time. Because N from meteorites and interplanetary dust particles appear to be dominant, a mechanism is required to reduce the C/N ratio typical of meteoritic matter to that approaching the low value observed in the lunar regolith. Preferential loss of methane appears to be a viable explanation, following generation either by proton sputtering or in reducing vapour plumes.  相似文献   

Factors and mechanisms of chemical composition formation of saline lakes in West Mongolia     

Marina KOLPAKOVA  Stepan SHVARTSEV  Vitalyi ISUPOV  Sodov ARIUNBILEG  Alexander VLADIMIROV  Olga GASKOVA 《《地质学报》英文版》2014,88(Z1):142-144

正All the lakes are accumulative systems for the various chemical elements.However,the ratios of the elements in different lake types are very different.It is generally accepted that the composition of lake water determined by  相似文献   

Multi-methodological investigation of kunzite, hiddenite, alexandrite, elbaite and topaz, based on laser-induced breakdown spectroscopy and conventional analytical techniques for supporting mineralogical characterization     

Manuela Rossi  Marcella Dell’Aglio  Alessandro De Giacomo  Rosalba Gaudiuso  Giorgio Saverio Senesi  Olga De Pascale  Francesco Capitelli  Fabrizio Nestola  Maria Rosaria Ghiara 《Physics and Chemistry of Minerals》2014,41(2):127-140

Gem-quality alexandrite, hiddenite and kunzite, elbaite and topaz minerals were characterized through a multi-methodological investigation based on EMPA-WDS, LA-ICP-MS, and laser-induced breakdown spectroscopy (LIBS). With respect to the others, the latter technique enables a simultaneous multi-elemental composition without any sample preparation and the detection of light elements, such as Li, Be and B. The criteria for the choice of minerals were: (a) the presence of chromophore elements in minor contents and/or as traces; (b) the presence of light lithophile elements (Li, Be and B); (c) different crystal chemistry complexity. The results show that LIBS can be employed in mineralogical studies for the identification and characterization of minerals, and as a fast screening method to determine the chemical composition, including the chromophore and light lithophile elements.  相似文献   

Wind-induced sediment resuspension as a potential factor sustaining eutrophication in large and shallow Lake Peipsi   总被引：1，自引：0，他引：1  

Olga Tammeorg  Juha Niemistö  Tõnu Möls  Reet Laugaste  Kristel Panksep  Külli Kangur 《Aquatic Sciences - Research Across Boundaries》2013,75(4):559-570

Using sediment traps, we aimed to elucidate the temporal and spatial variations in sediment fluxes in large and shallow Lake Peipsi, over the May to October 2011 period, and analyze the factors behind those variations. The effects of weather factors (mean and maximum wind velocity, water level and water temperature) on sediment resuspension and the concentrations of suspended solids (SS), total phosphorus (TP), soluble reactive phosphorus (SRP), and chlorophyll a (Chl a) were investigated. Moreover, the internal loading of TP due to sediment resuspension was determined. The sediment resuspension rates were significantly higher in the shallower waters than in the deeper parts of the lake. Resuspension was a major factor in sedimentation dynamics of the lake, which is presently subject to eutrophication. The rates of sediment resuspension followed the same pattern as gross sedimentation during the study period, and their respective values differed significantly between sampling dates. The highest resuspension rates were observed in September (mean 55.4 g dw m^?2 day^?1), when the impacts of wind events were particularly pronounced. Weather factors that were recorded approximately 2 weeks before water and sediment sampling affected the gross sedimentation and sediment resuspension. The water quality variables of SS, TP, SRP, Chl a were similarly affected. During the study, TP concentrations of the water were mainly determined by the resuspension of sediments containing a large pool of organic material. Although internal loading of TP due to resuspension was several times greater than external loading, external loading determines the amount of phosphorus that enters the lake and can be resuspended.  相似文献