Three-dimensional convection simulations of the outer layers of the Sun using realistic physics     

F. J. Robinson  P. Demarque  L. H. Li  S. Sofia  Y.-C. Kim  K. L. Chan  D. B. Guenther 《Monthly notices of the Royal Astronomical Society》2003,340(3):923-936

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The power of low‐resolution spectroscopy: On the spectral classification of planet candidates in the ground‐based CoRoT follow‐up     

M. Ammler‐von Eiff  D. Sebastian  E. W. Guenther  B. Stecklum  J. Cabrera 《Astronomische Nachrichten》2015,336(2):134-144

Planetary transits detected by the CoRoT mission can be mimicked by a low‐mass star in orbit around a giant star. Spectral classification helps to identify the giant stars and also early‐type stars which are often excluded from further follow‐up. We study the potential and the limitations of low‐resolution spectroscopy to improve the photometric spectral types of CoRoT candidates. In particular, we want to study the influence of the signal‐to‐noise ratio (SNR) of the target spectrum in a quantitative way. We built an own template library and investigate whether a template library from the literature is able to reproduce the classifications. Including previous photometric estimates, we show how the additional spectroscopic information improves the constraints on spectral type. Low‐resolution spectroscopy (R ≈ 1000) of 42 CoRoT targets covering a wide range in SNR (1–437) and of 149 templates was obtained in 2012–2013 with the Nasmyth spectrograph at the Tautenburg 2 m telescope. Spectral types have been derived automatically by comparing with the observed template spectra. The classification has been repeated with the external CFLIB library. The spectral class obtained with the external library agrees within a few sub‐classes when the target spectrum has a SNR of about 100 at least. While the photometric spectral type can deviate by an entire spectral class, the photometric luminosity classification is as close as a spectroscopic classification with the external library. A low SNR of the target spectrum limits the attainable accuracy of classification more strongly than the use of external templates or photometry. Furthermore we found that low‐resolution reconnaissance spectroscopy ensures that good planet candidates are kept that would otherwise be discarded based on photometric spectral type alone. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Modeling the impacts of climate change on China’s agriculture     

LIU Hui  LI Xiu-bin  Guenther Fischer  SUN Lai-xiang 《地理学报》2001,11(2):149-160

The impacts of climate change on China’s agriculture are measured based on Ricardian model. By using county-level cross-sectional data on agricultural net revenue, climate, and other economic and geographical data for 1275 agriculture-dominated counties in the period of 1985-1991, we find that both higher temperature and more precipitation will have overall positive impact on China’s agriculture. However, the impacts vary seasonally and regionally. Higher temperature in all seasons except spring increases agricultural net revenue while more precipitation is beneficial in winter but is harmful in summer. Applying the model to five climate scenarios in the 2020s and 2050s shows that the North, the Northeast, the Northwest, and the Qinghai-Tibet Plateau would always benefit from climate change while the South and the Southwest may be negatively affected. For the East and the Central China, most scenarios show that they may benefit from climate change. In conclusion, climate change would be beneficial to the whole China.  相似文献   

A GIS FOR THE ANTARCTIC SPECIALLY MANAGED AREA OF ADMIRALTY BAY,KING GEORGE ISLAND,ANTARCTICA   总被引：1，自引：0，他引：1  

Jefferson Cardia Sim“非汉字符号”es  F.A.Ferron  Matthias Braun  J.Arigony Neto  F.E.Aquino 《地球空间信息科学学报》2001,4(2):8-14

1　ＩｎｔｒｏｄｕｃｔｉｏｎＫｉｎｇＧｅｏｒｇｅＩｓｌａｎｄ’ｓ (ＫＧＩ)ｅｃｏｓｙｓｔｅｍｓｈａｖｅｂｅｅｎｓｕｂｊｅｃｔｅｄｔｏｖａｒｉｏｕｓｔｙｐｅｓｏｆｅｘｐｌｏｉｔａｔｉｏｎａｎｄｏｂｊｅｃｔｏｆｓｅｖｅｒａｌｓｃｉｅｎｔｉｆｉｃｅｘｐｅｄｉｔｉｏｎｓ,ｓｉｎｃｅｉｔｗａｓｄｉｓｃｏｖｅｒｅｄｊｕｓｔａｆｔｅｒｔｈｅｆｉｒｓｔｓｉｇｈｔｉｎｇｏｆＡｎｔａｒｃｔｉｌａｎｄｂｙＷｉｌｌｉａｍＳｍｉｔｈｉｎ1 81 9.ＫＧＩｗａｓｎａｍｅｄａｆ ｔｅｒｔｈｅＢｒｉｔｉｓｈｋｉｎｇｏｆｔｈａｔｔｉｍｅ …  相似文献   

Contrasting metamorphic conditions in the Neoproterozoic collision-related Nappes south of São Francisco Craton, SE Brazil     

Maria da Glria Motta Garcia  Mrio da Costa Campos Neto 《Journal of South American Earth Sciences》2003,15(8):853-870

Metamorphic conditions are described for three major tectonic entities on the basis of geothermobarometry in a huge Neoproterozoic nappe complex that verges toward the southern border of the São Francisco craton. The uppermost Socorro-Guaxupé Nappe, represented by its granulite facies basal portion, yields a maximum temperature and pressure of 890 °C and 11 kbar. Its metamorphic evolution is consistent with heating at the base of the crust as a result of an abnormally high geothermal gradient, probably due to underplating by the lithospheric mantle. The underlying Três Pontas-Varginha Nappe yields two somewhat distinct P–T paths, both characterized by peak assemblages in the kyanite stability field. The basal kyanite-bearing granulites show higher peak pressure values (15 kbar at 840 °C) and a trajectory that continues in the kyanite stability field, whereas the upper sillimanite granulites show higher temperatures (880 °C at 13 kbar) and a steeper path toward the sillimanite stability field. Data for the Carmo da Cachoeira nappe reveal a steep trajectory, in which the elevated maximum pressure (18.5 kbar at 820 °C) was obtained from a garnet amphibolite that lies along its basal contact. The inverted metamorphic pattern previously observed across these sequences is confirmed by our thermobarometric data, which reveal that the highest temperatures were attained toward the top of the pile.  相似文献   

植物挥发性有机物的分析方法   总被引：6，自引：0，他引：6  

Bai Jianhui  Wang Mingxing  Hu Fei  James P. Greenberg  Alex B. Guenther 《大气科学进展》2002,19(1):64-72

为了分析植物排放到大气中的挥发性有机物，在2000年1-6月期间，与美国国家大气研究中心（NCAR）的科学家共同发展和研究了一套自动的气相色谱系统和分析方法。该系统引入一个小型冰箱以除去空气样品进样时的水分，得到了对挥发性有机物样品进行分析时比较好的准确度。在5℃以及稳定的进样速率的条件下，可以得到比较好的除水效果。对NCAR附近的大气进行了采样，并利用此系统做了分析。本简单介绍此自动系统以及样品分析结果。实验结果表明，此套系统具有良好的重复性和稳定性，主要的挥发性有机物的成分如异戊二烯和单萜烯等具有明显的日变化。  相似文献   

Genetic and metamorphic conditions constrained by fluid inclusions from Paleoproterozoic (c. 1.8 Ga) magnesite ore deposits, NE Brazil     

Luiz Henrique Ronchi  Clvis Vaz Parente  Kazuo Fuzikawa  Artur Bastos Neto 《Journal of South American Earth Sciences》2008,25(4):492-500

Precambrian magnesite occurrences hosted by metadolomites from the Orós belt, Ceará, Brazil, are part of a greenschist–amphibolite, metavolcano-sedimentary terrain, dated at 1.8 Ga, cut by Meso- to Neoproterozoic Brasiliano granites and Neoproterozoic basic sills. These rocks were affected by a shear zone between 580 and 500 Ma. The magnesite-bearing marbles can be grouped as medium-grained (1–9 mm) at the Riacho Fundo ore deposit or sparry magnesite (1–15 cm) at the Cabeça de Negro ore deposit. The sparry magnesite shows textural characteristics related to original sedimentary structures. Both types of magnesite-bearing marbles contain aqueous and aqueous-carbonic fluid inclusions that yield homogenization temperatures between 170 and 370 °C. Applying a pressure correction, these temperatures are compatible with the evolution from greenschist to amphibolite facies metamorphic conditions, as described in previous work on the Orós region. It also agrees with data in specialized literature on the metamorphism of carbonate rocks. Fluid inclusion distribution, composition, and physical-chemical characteristics suggest temperature increase, probably related to metamorphism on these rocks. The medium-grained magnesite records partial contamination of CO₂-rich inclusions by relict carbonaceous material (bitumen, hydrocarbons?) that favors, but does not confirm, a syngenetic sedimentary origin and could have caused the lowering of CO₂ melting point in these inclusions. Therefore, though textural evidence points to a sedimentary-diagenetic model, fluid inclusions record conditions of a metamorphic event.  相似文献   

Surface inhomogeneities and line variability on DF Tau     

Y. C. Unruh  A. Collier Cameron  & E. Guenther 《Monthly notices of the Royal Astronomical Society》1998,295(4):781-798

We have mapped surface inhomogeneities on the classical T Tauri star DF Tau, using the Li  i doublet at 670.8 nm, the Ca  i lines at 612.2 nm and 643.9 nm and a calcium and iron blend at 646.3 nm. We find compelling evidence that there are hotspots with temperatures of more than 5000 K. Two of the hotspots produce line-profile deformations that can be traced as they move through the cross-correlated profiles. When one of the hotspots crosses the stellar disc, redshifted absorption components appear in the Na D lines. As these redshifted absorption features are usually tracers for mass-infall we interpret this hotspot as an accretion shock close to the stellar surface.   Parts of the surface of DF Tau are covered with a hot chromosphere that is visible in the Ca  ii infrared triplet lines and the narrow component of He  i . We find no correlation between the veiling and the lines that originate from the hot chromosphere, suggesting that the veiling and the chromospheric emission are produced in physically distinct regions.  相似文献   

DIGITAL PHOTOGRAMMETRIC SYSTEMS     

F. Neto   《The Photogrammetric Record》1992,14(79):130-132

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Chronologie et évolution des fluides hydrothermaux dans le district à fluorine de Santa Catarina,Brésil: Données de l'analyse des terres rares et de l'étude des inclusions fluides     

A. Bastos Neto  J.-C. Touray  M. Dardenne  J. Charvet 《Mineralium Deposita》1991,26(3):211-216

RésumRé Dans le district de Santa Catarina, la teneur en terres rares des fluorines filoniennes caractérise chacune des neuf générations successives mises en évidence (concentrations en Sm, rapports La/Sm ou La/Yb, anomalie en Europium). Deux cycles hydrothermaux majeurs, rapportés au rifting Sud-Atlantique (130-115 m.a.) ont été distingués à partir de l'évolution des rapports La/Sm et La/Yb et des températures d'homogénisation des inclusions aqueuses primaires. Dans cette évolution, une coupure brutale sépare les générations I–IV et V–VI. Les fluorines plus tardives sont rapportées à un évènement néocrétacé-éotertiaire. Une signature géochimique constante est notée pour les terres lourdes, quelle que soit la génération considérée (ex: Yb/Tb = 5; Gd/Yb = 1) suggérant l'existence d'une source unique pour les terres rares et probablement le fluor. A titre d'hypothèse, on pense qu'il s'agit de fluorine disséminée dans les granitoïdes altérés du socle.

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In the Santa Catarina district, REE contents of vein fluorites characterize each one of the nine successive generations (Sm concentrations, La/Sm or La/Yb ratio, Eu anomaly). Two main hydrothermal cycles, related to the South Atlantic rifting (130-115 m.y.), are distinguished through the evolutions of the La/Sm and La/Yb ratios and of the homogenization temperatures of primary aqueous inclusions. In this evolution, a sharp break separates generations I–IV and V–VI. Later fluorite deposits are related to a Neo-Cretaceous-to-Eo-Tertiary event. A constant geochemical signature for heavy REE is noticed, whatever the fluorite generation (e.g. Yb/ Tb = 5; Gd/Yb = 1) suggesting an unique source for REE and possibly fluorine. This source is tentatively determined as disseminated fluorite in altered granitoids from the basement.

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