Sub-arcsec 10 μm imaging of β pictoris and other star disk candidates     

P. O. Lagage  E. Pantin 《Experimental Astronomy》1994,3(1-4):57-60

We have used the ESO 10 m camera, TIMMI, to image with a very high angular resolution (PFoV: 0.3; FWHM:0.9) several main-sequence star disk candidates. Information on the -Pictoris dust disk has been obtained in a region largely inaccessible to previous observations: 0–80 AU, with a resolution of about 5 AU after deconvolution. Another promising target for 10 m imaging, 51 Ophiuchi, appears point-like.based on data collected at the European Southern Observatory (ESO), La Silla, Chile  相似文献   

Structure of the satellitary accretion disk of Saturn     

A. Coradini  G. Magni 《Icarus》1984,59(3):376-391

A detailed computation on the equilibrium structure of an accretion disk around Saturn from which the regular satellites presumably originated is reported. Such a disk is the predecessor of the self-dissipating disk that is formed when the mass infall stops (Cassen and Moosman, 1981, Icarus48, 353–376). When determining the disk structure local energy balance was assumed. Convention was taken into account by introducing local energy dissipation and, in an approximate manner, sonic convection. Changes in the disk structure were investigated by varying the free parameters, i.e., the external flux from both the protosun and the protoplanet, the abundance of dust and the strength of turbulence. It has been verified that the external energy flux does not play an important role in the evolution of the disk structure. Models characterized by either longer times (?3 10³ year) or a noticeable depletion of condensable elements (10^?2 times less than the solar value) have a total mass of the order of 0.34?0.1 times the mass of the regular satellites increased by the mass of the light elements. Low turbulence models (Reynolds critical number $\text{Re}{}^1\text{= 150}$) are characterized approximately by a total mass twice as large the mass of the regular satellites. All the studied models present a temperature distribution that allows the condensation of iron, silicate, and, in the outer regions, ice grains. All models but the one with 10^?2 of the solar value of condensable elements are characterized by a wide convective region that contains the formation zone of the regular satellites.  相似文献   

Distribution and mode of occurrences of radionuclides in phosphogypsum from the Aqaba and Eshidiya fertilizer plants, Jordan     

Mohammad S. Al-Hwaiti Robert A. Zielinski James R. Budahn James F. Ranville Philippe E. Ross 《中国地球化学学报》2006,25(B08):178-178

Phosphogypsum is a waste by-product of the phosphate fertilizer industry that has relatively high concentrations of some U decay-series radionuclides such as ^226Ra and ^210Pb. The distribution and environmental mobility of radionuclides in phosphogypsum are an important concern because this gypsum by-product is used for wallboard, in agriculture and as a soil amendment. This study determined the distribution of ^226Ra, ^210Pb, within phosphogypsum stacks of varying age and among three size fractions （coarse： 〈0.212 mm; medium： 0.212-0.053 mm; fine： 〈0.053 mm）, in phosphogypsum derived from Aqaba and Eshidiya fertilizer plants. The results indicated that ^226Ra and ^210Pb were generally uniformly distributed in phosphogypsum stacks and showed no significant difference in the concentration of these elements with the age of stack. In the Aqaba phosphogypsum ^226Ra was slightly 10% enriched in the coarse fraction, while ^210Pb was 10% enriched in the free size fraction. In the Eshidiya phosphogypsum ^226Ra and ^210Pb contents were both relatively enriched （10%） in the fine size fraction.  相似文献   

Oxydation expérimentale de Fe-tourmalines et corrélation avec une déprotonation des groupes hydroxyleAnnealing in oxidising conditions of Fe-tourmalines and correlated deprotonation of OH groups     

Yves Fuchs  Martine Lagache  Jorge Linares 《Comptes Rendus Geoscience》2002,334(4):245-249

Annealing at 400?T?600 °C (40?P?60 MPa and HM buffer-controlled f(O₂)) of tourmalines synthesised at the same T and P with NNO buffer induces an oxidation of Fe²⁺ into Fe³⁺ in some Y sites only (Mössbauer Spectroscopy data). Annealing in the same conditions of natural tourmalines is consistent with these results. FTIR spectroscopy shows that oxidation of Fe²⁺ into Fe³⁺ is charge-balanced by deprotonation of the external OH₍₃₎ groups. To cite this article: Y. Fuchs et al., C. R. Geoscience 334 (2002) 245–249.  相似文献   

长江口沉积物210Pb分布及沉积环境解释   总被引：19，自引：0，他引：19  

段凌云  王张华  李茂田  潘建明  陈中原  Yishiki Saito  Yutaka kanai 《沉积学报》2005,23(3):514-522

在长江河口潮滩、分流河道和水下三角洲共获得18个柱样,进行沉积学分析和210Pb测定,并对其中6根柱样进行137Cs测定。经研究发现,长江口外在水深25～30m,122°30′N,31°00′E附近存在一个泥质沉积中心,沉积速率达2.0～6.3cm/yr。另外,在潮滩和涨潮槽也获得较高沉积速率,其中南汇和横沙岛潮滩沉积速率(1.03～1.94cm/yr)高于崇明东滩(0.51～0.76cm/yr),涨潮槽沉积速率也达0.86cm/yr。此外,在石洞口、南汇、九段沙潮滩和三角洲前缘有部分柱样未获沉积速率,推测为沉积环境不稳定或沉积速率过快所致。  相似文献   

Accounting for sparsely observed rainfall space—time variability in a rainfall—runoff model of a semiarid Tunisian basin/Prise en compte d'observations peu denses de la variabilité spatiotemporelle de la pluie dans une modélisation pluie—débit d'un bassin semi-aride Tunisien     

《水文科学杂志》2013,58(4)

Abstract

The management of water excesses and deficits is a major task in semiarid Mediterranean regions, where the variability of rainfall inputs is high at different time and space scales. Thus intense hydrometeorological events, which generate both potential resource and hazards, are of major interest. A simple method is proposed, with the example of the Skhira basin (192 km²) in central Tunisia, to account for the event space–time variability of rainfall in a rainfall–runoff model, in order to check its influence on the shape, magnitude and timing of resulting hydrographs. The transfer function used is a geomorphology-based unit hydrograph with an explicit territorial significance. Simulations made for highly variable events show the relevance of this method, seen as the first step of a downward approach, and its robustness with respect to the quality and the density of rainfall data.  相似文献   

岱海¹⁴ C测年的现代碳库效应研究^*   总被引：2，自引：0，他引：2  

吴艳宏  王苏民  周力平  孙照斌 《第四纪研究》2007,27(4):507-510

碳库效应的复杂性是影响建立湖泊沉积物高精度年代序列的一大障碍。本项研究通过我国内蒙古半干旱区封闭湖泊表层沉积物、湖水、现生沉水植物狐尾藻、现生鲤鱼鱼骨和湖岸表层土壤等一系列样品的¹⁴ C年代测定,表明现代岱海确实存在碳库效应。碳库效应年龄因湖水盐度在湖区的不均而有所变化,岱海西部湖区弓坝河径流补给量大,湖水盐度较东部稍低,碳库效应年龄也略小于东部湖区。表层沉积物中有机质包含浮游生物和沉水植物的混合信息,因而其碳库效应年龄较沉水植物年龄轻,岱海湖心表层沉积物碳库效应年龄在2000a左右。这一碳库效应年龄较通过沉积钻孔¹⁴ C年龄线性回归获得的年龄偏大,可能的原因是在时间序列上碳库效应并非恒定。  相似文献   

博斯腾湖湖泊沉积物光释光年代测量^*   总被引：2，自引：0，他引：2  

范育新  赵晖  陈发虎  黄小忠  杨美临 《第四纪研究》2007,27(4):568-575

使用光释光年代学的单片再生法测量了博斯腾湖沉积剖面中碳酸盐泥及粉砂质泥底部的浅湖相灰色粉细砂和风成沙的年龄,对剖面上部碳酸盐层中陆生植物残体进行了AMS ¹⁴ C测年。通过不同测片的等效剂量(D_e)值的分布状况评价了样品的晒褪程度,选择不随灵敏度校正后的自然释光信号变化的相对集中的等效剂量(D_e)值计算了样品的埋藏年龄。通过这些年龄结果的对比,发现石英矿物的OSL年龄和AMS ¹⁴ C年龄在地层上是一致的,表明尽管在浅湖相细砂中存在不完全晒褪,但根据相对较小而集中的D_e值计算得到的年龄结果是可靠的。这些年龄结果和地层资料揭示末次冰消期以来至早全新世,博斯腾湖处于无水干盆地向深水湖泊转化的浅水湖泊状态,现代深水博斯腾湖大约形成于距今8ka前后。  相似文献   

青藏高原崇测冰芯氯离子、硫酸根离子记录     

刘业祥  刘永建  韩建康 《云南地理环境研究》2007,19(3):11-14

通过对青藏高原崇测冰帽一支18．70m冰芯中Cl^-、SO4^2-离子含量变化的分析表明，20世纪90年来Cl^-、SO4^2-离子含量在波动中呈下降趋势，两种离子的周期性波动变化相似，20世纪晚期比早期和中期的波动幅度小，总体上离子含量逐渐减少与温度在波动中上升相一致，但每一次温度的升高与离子含量的下降并非一一对应。陆源物质和青藏高原上的盐湖是冰芯中Cl^-、SO4^2-离子的主要贡献者。揭示了研究地区大气成分和环境变化与气候变化的关系及亚洲粉尘在全球环境变化中的源区地位。  相似文献   

RS技术在实时区域土壤侵蚀评价中的应用--以福建省花山溪流域为例   总被引：6，自引：0，他引：6  

黄文义  陈刚  胡成 《中国地质灾害与防治学报》2003,14(2):116-118,124

传统数据采集方法严重制约了土壤侵蚀评价实时、快速的要求。文章以福建花山溪流域为例,基于“通用土壤侵蚀方程式”(USLE)为土壤侵蚀定量评价模型,利用多时效、多光谱的遥感数据,在ERDAS8．5软件平台上,研究提取流域动态最易变化的植被、土地利用类型等信息的技术方法。研究结果证实,这种方法可以快速、准确地提取影响土壤侵蚀的基本参数．进而实现对区域流域土壤侵蚀的实时评价。  相似文献