南极海洋动物粪土源N2O稳定同位素实验研究

N₂O是一种重要的温室气体,土壤是全球N₂O的重要排放源。通过测定土壤源N₂O中N、O同位素值,可以有效识别N₂O的来源途径。本文采集了南极法尔兹半岛两个地点的海豹粪土（HS和GS）、阿德雷岛两个地点的企鹅粪土(AB和AF)以及东南极的帝企鹅粪土(DQ和DQT),在室内对所采集的样品分别在有氧和厌氧条件下进行冻融培养实验。结果表明：土壤在厌氧条件下比有氧条件下排放了更多的N₂O。土壤排放的N₂O与当地大气N₂O相比普遍贫15N和18O。除DQT和HS外, δ15N和δ18O在有氧和厌氧培养下均呈现很好的正相关性。N₂O排放量下降的同时伴随着培养瓶内剩余N₂O中δ15N和δ18O 值的增加,证实N₂O还原为N2的过程会引起重同位素富集。高的水分含量有利于土壤反硝化作用的进行,使释放的N₂O气体富集重同位素;pH值也会影响N₂O的同位素组成,低pH会引起δ15N值增加。     

Migration and enrichment of trace elements of Lower Palaeozoic carbonate rock strata in Beijing

Analyses of trace elements of the Lower Palaeozoic carbonate rock strata in Beijing show that the contents of As, Hg, F increase from primary carbonate rocks to weathered carbonate rocks and from primary carbonate rocks to the soil coexisting with carbonate rocks, but the distribution regularity of S is not obvious. In the whole weathered stages, the sorption of As is mainly affected by Fe2O3. In soil Fe2O3 is also the main affecting factor of Hg enrichment. The main existing forms of Hg in primary carbonate rocks should simply be physical adsorption, coprecipitation and false isomorphous form between surface of carbonate rock and Hg. In soil the enrichment of F has little relationship with sul-fides and Fe2O3. In primary carbonate rocks, F is mainly absorbed by sulfides and clay minerals, etc. Weathered samples have closer genetic relationships with primary carbonate rocks. This also implies that weathered carbonate rocks have the close existing forms to that of primary carbonate rocks. In primary carbonate rocks FeS2 and FeS are the main forms of S, and sulfides have fixation effect on some heavy metals, whereas in weathered carbonate rocks and soil the fixation effect is weakened.     

南极威德尔海周边雪冰和大气气溶胶中的MSA,nssSO_4~(2-)浓度及其比率研究

分析了威德尔海周边雪冰和大气中ＭＳＡ和ｎｓｓＳＯ２－４浓度资料。结果表明,威德尔海是造成这一地区大气中高含量生物硫化物的“源”,其周边岛屿及冰架表层雪冰记载和反映了大气中生物硫化物的空间分布和季节变化特点。源区产出硫化物的强度存在显著差异：靠近南极半岛一侧高于靠近Ｆｉｌｃｈｎｅｒ－Ｒｏｎｎｅ冰架一侧。尽管诸多因素对输运和沉降过程发生影响,表层积雪ＭＳＡ和ｎｓＳＯ２－４浓度仍呈现出很有规律性的空间分布：随沉降地点离海距离和海拔高度的增加,浓度值递减;但在一定海拔之下,“高程效应”不显著。冰芯中ＭＳＡ浓度垂向分布显示出季节分配“滞后”现象,在表层表现为受天气条件制约的输运过程造成的相位差,在深层则归因于有待验证的“迁移”机制作用的结果。大气和雪冰样品对比研究结果表明,在类似威德尔海这样的高纬地区,大气中的ＳＯ２－４和ＭＳＡ“信号”在雪冰样品中会遭到不同程度的减弱。但就空间变化趋势和季节分布而言,表层雪冰仍是大气中组分（在本文是ＳＯ２－４和ＭＳＡ）的良好载体。十分接近的大气和雪冰ＭＳＡ对ｎｓｓＳＯ２－４（或ＳＯ２－４）比率证实,这两种大气组分在由大气洗净和沉降到冰雪过程中只发生微弱的分离作用。这也就是大气和雪冰中     

基于航空客流的中国城市对外联系网络结构与演化

改革开放以来,经济全球化和快速城市化促进了中国城市外向型联系的发展,改变了中国城市对外联系的空间格局。越来越复杂化的城市空间分布和组织规律需要一个全新的、综合的网络视角来考察。航空运输是当前城市间相互联系的重要物质基础,体现了城市间的直接关系,是研究城市网络的合适工具。本文以中国城市对外的航空客运联系作为衡量城市关系的指标,借鉴社会网络分析中的2-模网络概念构建了中国城市对外联系网络,并对网络的结构特征和演化规律进行了分析。研究结果表明,中国城市对外联系网络存在北京-上海-广州的三中心结构。中心城市以外,西部城市上升势头迅猛,体现了网络多元化发展的趋势。此外,中国城市对外联系的主要对象逐渐从东南亚向东亚转移,并呈现出以首尔为核心的网络结构。同时,中国城市对外联系扩张以强化区域内部联系为主,洲际联系发展滞后。     

Al掺杂对尖晶石型LiMn2O4结构及循环性能的影响

用柠檬酸作为螯合物的载体,采用溶胶-凝胶法合成了Al3+掺杂的锂离子电池正极材料LiAlxMn2-xO4,并用XRD、SEM等多种测试手段研究了不同掺杂铝量对粉体形貌、晶体结构的影响。结果表明,800℃烧结可获得单一尖晶石结构的物相。随着Al3+掺入量的增加,LiAlxMn2-xO4的晶格常数变小,晶格更趋于完整,有利于抑制因锂的反复脱嵌而造成结构的破坏。实验表明,当掺Al量为0.05时,首次放电容量为103.8 mAh/g,25次循环后容量还有100.6 mAh/g,容量衰减仅为3.08%。该正极材料具备高的容量和优异的循环性能。     

Flow and form in rehabilitation of large-river ecosystems: An example from the Lower Missouri River

On large, intensively engineered rivers like the Lower Missouri, the template of the physical habitat is determined by the nearly independent interaction of channel form and flow regime. We evaluated the interaction between flow and form by modeling four combinations of modern and historical channel form and modern and historical flow regimes. The analysis used shallow, slow water (shallow-water habitat, SWH, defined as depths between 0 and 1.5 m, and current velocities between 0 and 0.75 m/s) as an indicator of habitat that has been lost on many intensively engineered rivers and one that is thought to be especially important in rearing of young fishes. Two-dimensional hydrodynamic models for modern and historical channels of the Lower Missouri River at Hermann, Missouri, indicate substantial differences between the two channels in total availability and spatial characteristics of SWH. In the modern channel, SWH is maximized at extremely low flows and in overbank flows, whereas the historical channel had substantially more SWH at all discharges and SWH increased with increasing discharge. The historical channel form produced 3–7 times the SWH area of the modern channel regardless of flow regime. The effect of flow regime is evident in increased within-year SWH variability with the natural flow regime, including significant seasonal peaks of SWH associated with spring flooding. Comparison with other reaches along the Lower Missouri River indicates that a) channel form is the dominant control of the availability of habitat even in reaches where the hydrograph is more intensively altered, and b) rehabilitation projects that move toward the historical condition can be successful in increasing topographic diversity and thereby decreasing sensitivity of the availability of habitat to flow regime. The relative efficacy of managing flow and form in creating SWH is useful information toward achieving socially acceptable rehabilitation of the ecosystem in large river systems.     

电离层等离子体漂移的振荡

根据中纬Ｗａｋｋａｎａｉ站与低纬Ｏｋｉｎａｗａ站的垂测数据,得出电离层峰区垂直漂移的频谱结构．结果表明,漂移除具有周期在２４ｈ之内的潮汐分量外,低纬站还呈现出值得特别注意的２．１ｄ的周期振荡．作者认为,低纬垂直漂移的振荡行为,主要是电场的波动分量引起;这种波动电场包含潮汐振荡与行星波两日振荡的成分．峰值电子浓度的振荡最直接地是由中性大气温度控制;而峰高的波动起伏,则主要是电场振荡的结果．