Enhanced Activity in Close T Tauri Binaries

The number of confirmed and suspected close T Tauri binaries (period days) is increasing. We discuss some systems with enhanced emission line activity and periodic line profile changes. Non-axisymmetric flows of plasma in the region between the circumbinary disk and the stars can be generated through the influence of the secondary component. Such enhanced activity is found around binaries with eccentric as well as circular orbits. We discuss our observations of the T Tauri stars RW Aurigae A and RU Lupi, which may host very close brown dwarf companions. Model simulations indicate that non-axisymmetric flows are generated around close binaries with circumbinary disks, also in systems with circular orbits.     

陆地生态系统氮状态对碳循环的限制作用研究进展

陆地生态系统碳循环和氮循环密切相关, 碳贮量与碳通量在很大程度上受氮循环的影响 和限制。由于氮循环的复杂性, 在以往的大多数碳循环研究中, 更多考虑水分、温度和大气CO2 浓 度等因子的影响, 考虑碳氮相互作用的研究较少。氮素可限制植物光合、有机质分解、同化产物的 分配以及生态系统对大气CO2 浓度升高的响应。根据目前有关碳氮模型的发展状况可将碳氮耦 合循环模型分为三大类: 一是静态模型, 它的土壤养分水平或者叶氮含量不变, 是常数, 这类模型 适合于在站点或氮素浓度变化不大的区域应用; 二是土壤氮限制模型, 能够保持稳定的生态系统 氮收支, 在NPP(Net Primary Productivity, 净初级生产力)的模拟中考虑土壤氮有效性的动态变化 的影响, 使模拟结果更为合理; 三是叶氮限制模型, 在NPP 的模拟中考虑叶片氮浓度的动态变化 的影响。这三类模型虽然都考虑了氮对碳循环的限制作用, 但在氮碳循环机理方面尚有不少欠 缺, 所以在研究中可能会带来很大的不确定性。在以后的研究中, 应通过加强碳氮相互作用的实 验研究, 增进对碳氮过程的深入了解, 进而建立综合动态的碳氮耦合模型, 以减少目前碳循环研 究中的不确定性。     

Mobility of Al, Co, Cr, Cu, Fe, Mn, Ni and V in sulphide-bearing fine-grained sediments exposed to atmospheric O2: an experimental study

 The major aim was to increase our knowledge on the behaviour of Al, Co, Cr, Cu, Fe, Mn, Ni and V in sulphide-bearing fine-grained sediments exposed to atmospheric oxygen. Samples of this type of sediment collected in a previous investigation at eight sites in western Finland were digested in HClO₄-HNO₃-HCl-HF at 200  °C and in HCl:HNO₃:H₂O at 95  °C (aqua regia), and subjected to extractions with ammonium acetate and hydrogen peroxide. Metals and S in the leachates were determined with ICP-AES. The results of the chemical analyses are compared with previously reported experimental data. The concentrations of Al and Fe in the sulphide-bearing fine-grained sediments are about 7% and 5%, respectively. Of the trace metals studied, Mn is most abundant followed in decreasing order by V>Cr>Ni>Cu>Co. On oxidation of the sediments, high proportions of Co, Mn and Ni, intermediate proportions of Cu but low proportions of Fe, Al, Cr and V are released. The extent of the release of a metal on oxidation is controlled either by (1) the level to which the pH of the sediments drops on oxidation (Al, Cu, Cr, V), (2) the amount of the metal associated with easily reduced phases (metal sulphides) in the sediments (Ni, Co) or (3) the sum of the amount associated with reduced phases and adsorbed on soil compounds (Mn). No control of the release of Fe on oxidation of the sediments was identified. Based on the results of the study it is argued that artificial drainage and the subsequent oxidation of sulphide-bearing sediments will result in extensive leaching of Co, Mn and Ni, moderate leaching of Cu and limited leaching of Cr and V into drainages. The major elements, Fe and Al, have the potential to be mobilised and leached in large amounts, though the proportions mobilised/leached will remain low. It is suggested that the identification of sulphide-bearing sediments with a high potential of metal release should be based on determination of metals in easily mobilised reduced compounds (dissolved e.g. in H₂O₂) and of the level to which the pH of the sediments drops on oxidation. Received: 16 October 1997 · Accepted: 9 March 1998     

Hydrochemical variation in the springs water between Jerusalem–Ramallah Mountains and Jericho Fault,Palestine

The spatial and temporal changes of the composition of the groundwater from the springs along the Wadi Qilt stream running from the Jerusalem–Ramallah Mountains towards the Jericho Plain is studied during the hydrological year 2006/2007. The residence time and the intensity of recharge play an important role in controlling the chemical composition of spring water which mainly depends on distance from the main recharge area. A very important factor is the oxidation of organics derived from sewage and garbage resulting in variable dissolved CO₂ and associated HCO₃ ⁻ concentration. High CO₂ yields lower pH values and thus under-saturation with respect to calcite and dolomite. Low CO₂ concentrations result in over-saturation. Only at the beginning and at the end of the rainy season calcite saturation is achieved. The degradation of dissolved organic matter is a major source for increasing water hardness. Besides dissolution of carbonates dissolved species such as nitrate, chloride, and sulfate are leached from soil and aquifer rocks together with only small amounts of Mg. Mg not only originates from carbonates but also from Mg–Cl waters are leached from aquifer rocks. Leaching of Mg–Cl brines is particularly high at the beginning of the winter season and lowest at its end. Two zones of recharge are distinguishable. Zone 1 represented by Ein Fara and Ein Qilt is fed directly through the infiltration of meteoric water and surface runoff from the mountains along the eastern mountain slopes with little groundwater residence time and high flow rate. The second zone is near the western border of Jericho at the foothills, which is mainly fed by the under-groundwater flow from the eastern slopes with low surface infiltration rate. This zone shows higher groundwater residence time and slower flow rate than zone 1. Groundwater residence time and the flow rate within the aquifer systems are controlled by the geological structure of the aquifer, the amount of active recharge to the aquifer, and the recharge mechanism. The results of this study may be useful in increasing the efficiency of freshwater exploitation in the region. Some precautions, however, should be taken in future plans of artificial recharge of the aquifers or surface-water harvesting in the Wadi. Because of evaporation and associated groundwater deterioration, the runoff water should be artificially infiltrated in zones of Wadis with high storage capacity of aquifers. Natural infiltration along the Wadis lead to evaporation losses and less quality of groundwater.     

Atmospheric response to soil-frost and snow in Alaska in March

Summary A hydro-thermodynamic soil-vegetation model including soil freezing/thawing (soil-frost) and snow-metamorphism has been integrated into the PennState/NCAR Mesoscale Meteorological Model MM5 in a two-way coupled mode. A hierarchy of simulations with and without the soil-frost module, each combined with and without the snow module, shows the influence of snow-cover and soil-frost on weather in Alaska. Herein the landscape is featured as it is typically by mesoscale models.Theoretical considerations suggest that organic soil types should be considered in mesoscale modeling because of their different thermal and hydrological behavior as compared to mineral soils. The Ludwig-Soret and Dufour effects are small, but increase appreciably during freezing/thawing and snow-melt.The snow and soil-frost processes have a demonstrable impact on the surface thermal and hydrological regimes and on the near-surface atmospheric conditions even on the short (synoptic) timescales. The presence of snow-cover results in a highly stable stratification. In cloud-free areas, the enhanced loss of radiant energy and cooling of the air over snow-cover lead to a positive feedback to relatively colder, drier conditions. In cloudy areas, a positive feedback to warmer, moister conditions develops over snow-cover. As the changes in atmospheric humidity and temperature caused by snow-cover propagate into the pressure field, sea level pressure is lower by more than 1hPa in the simulations with snow-cover. Although the effect of soil-frost alone is an order of magnitude smaller, the soil-frost snow system leads to an increase of the pressure difference to 1.2hPa. The changes in the pressure field alter wind speed and direction slightly.Soil-frost results in soil temperature differences of 2–5K in the upper soil layers, while snow results in differences of 3–10K. Soil-frost has a notably greater impact in cloud-free than cloudy areas. When a snow-cover is present, frozen soil enhances the insulating effect of a snow-cover in cloudy areas, but reduces it in cloud-free areas. In cloudy areas, soil-frost without snow-cover leads to cooler, drier atmospheric conditions relative to no frost. In cloudy areas, soil-frost under a snow-cover reduces the water supply to the atmosphere as compared to snow-covered conditions without soil-frost. The combined effects of soil-frost and snow increase precipitation locally by as much as 12.2mm/ 48h. If mesoscale modeling does not consider the soil-frost snow system, predicted water vapor fluxes will be too high in cloud-free areas, and too low in cloudy areas.     

京津冀区域大气霾污染研究意义、现状及展望

频发的霾污染是目前京津冀最严重的环境问题。如何协调区域经济合理快速发展与防止大气环境恶化,已经成为公众关注的焦点,也是各级政府亟待解决的问题之一。对国内外典型大气污染事件的产生及治理历程进行了简要回顾;结合我国当前霾污染问题产生的特殊性,分析了京津冀区域霾污染研究对经济和社会发展、气候和环境变化、人体健康和区域和谐发展的现实意义;阐述了京津冀霾污染现象频发的主要客观要素和内在原因,并分析了当前研究工作中的不足。最后,在全球气候变化的大背景下,推测了京津冀及东亚地区未来大气污染的发展趋势。     

钨在矿物/熔体和溶液/熔体中的分配行为及其对成矿作用的影响

总结了钨(W)在地球不同圈层、不同相以及不同集合体之间的分配行为,并据此来探讨与花岗岩有关的热液型钨矿床的某些成因机制,并将W矿化所需的较高的浓集系数归因于这一系列不均匀分配行为的累积。同时强调了W在溶液/熔体体系,尤其是富F体系中的分配行为是理解其成矿机理的关键。热液中W主要以钨酸(根)和碱性钨酸盐离子存在,后因流经理化条件(温度、盐度、p H值)骤变而沉淀成矿。     

祁连山黑河山区土地适宜性评价

以黑河山区为研究区域,利用Logic回归模型和空间分析技术对山区土地利用进行适宜性评价.以2011年土地利用现状数据作为背景值,构建气温、降水、海拔、坡度、人口密度、水系、交通网、村镇分布8种因子的评价指标体系.采用多尺度训练的方法确定适宜性评价最佳模拟尺度,对土地利用数据和评价因子进行Logic回归分析,得到评价因子对土地利用适宜性的影响程度.利用Spatial Analyst模块对对黑河山区土地适宜性进行评价,为区域土地资源合理利用提供科学参考.结果表明：（1）适宜性评价最佳尺度为210 m（ROC=0.79）.（2）Logic回归结果显示,坡度、气温（β_Temp=1.11）、降水对林地、草地的影响程度较高,同时距道路距离、人口密度（β_Pop=-0.555）对其分布也有重要影响.（3）山区土地利用适宜性排序为：Max_林地=Max_耕地 > Max_建设用地 > Max_裸地 > Max_草地 > Max_水域,林地与耕地最高,适宜性达到0.99.     

混凝土材料基本力学性质的声弹性试验结果及分析

本文进行了不同级配的混凝土圆柱体试样的声弹性试验和单轴压缩试验。通过试验得出不同级配混凝土试样的纵波波速与其单轴抗压强度的关系。试验结果表明,混凝土弹性波幅的衰减与材料的密度和尺寸有关。     

小振幅海洋内波的演变、破碎和所致混合

利用基于谱方法和MPI并行运算的数值模式SpectralModel,直接数值模拟了三维小振幅海洋内波的演变、破碎和所致湍流混合,指出导致其不稳定而破碎的为PSI(parametric subharmonic instability)机制;对于内波破碎所致的湍流混合过程,分析了跨等密度面扩散系数kρ、混合效率γ、浮力通量谱、动能谱以及势能谱等统计性质:内波破碎前,kρ和γ保持低值水平,浮力通量谱值为负,且集中在低波数段;内波破碎后,kρ和γ迅速增大,最大值分别约为0.9×103m2/s和0.18,浮力通量谱值在低波数段为负值,在高波数段为正值,这是因为层化湍流中势能向小尺度运动传递和动能向小尺度运动传递相比更为有效。在内波破碎、强湍流混合阶段,势能谱存在一谱段满足kz3律,P(kz)=0.2N2kz3。此外,与二维模拟结果相比较,导致内波不稳定而破碎的均为PSI机制,kρ、浮力通量谱、势能谱变化趋势大体一致;但三维数值实验中,内波破碎时间提前,湍流衰减加快;KE谱在高波数部分下降速度相对减小,更接近于kz3。