白令海盆pCO2分布特征及其对北极碳汇的影响

利用中国首次北极科学考察期间所观测到的白令海及楚克奇海表层海水CO₂分压(pCO₂)的变化及其异常, 研究了白令海盆pCO₂的分布特征及与周围水文环流的相关关系. 结果表明, 与具有高生产力的白令海陆架区不同, 在白令海盆观测区内, 叶绿素整体水平较低, 生物作用不是pCO₂空间分布的主要调控因子, 而水文环流要素呈现出重要影响, 是典型的高营养盐低叶绿素(HNLC)海区. 研究表明, 白令陆坡流(Bering Slope Current; 后变性为阿纳德尔流, Anadyr Current)对白令海盆pCO₂空间分布也产生了重要影响. 从HNLC的白令海盆流过来的白令海亚北极水, 将补充西北冰洋夏季几乎耗尽的表层营养盐, 有利于浮游植物的生长, 增强对大气CO₂的吸收能力, 形成有机碳汇; 另一方面, 注入白令海的淡水来源的无机碳在白令海没有向深海输出, 多数会通过阿拉斯加沿岸流注入北冰洋, 形成一个重要的无机碳汇, 这两大碳汇都在北极对全球变化的响应中起着十分重要的反馈作用.     

半城市化地区不透水面遥感提取优化方法研究北大核心CSCD

快速、准确获取不透水面的空间分布信息对加快城市化进程及城市规划具有重要意义。目前多数研究注重提取大城市不透水面,忽略了不透水面占比较低的半城市化地区,而传统不透水面提取方法在半城市化地区适用性差,存在大量不透水面与裸土混分。该文在BAEM(Built-up Area Extraction Method)指数的基础上,针对半城市化地区存在大量裸土以及建筑密度低的特点,选取Sentinel-2A作为数据源,分别从指数选取和阈值方法两方面展开优化,提出一种适用于半城市化地区的不透水面提取指数MBAEM(Modified BAEM),并在江苏省淮安市盱眙县和淮阴区开展实证研究。结果表明:1)基于MBAEM指数和OTSU阈值法的优化方法提取效果最好,盱眙县和淮阴区的总体精度分别为89.50%和89.73%,Kappa系数分别为0.7907和0.7950;2)相较于传统BAEM指数提取方法,MBAEM指数较好解决了部分不透水面与水体、裸土混分的问题;3)相较于归一化建筑指数、遥感建筑用地指数、组合建筑区指数,MBAEM指数的总体精度和Kappa系数均有不同程度的提升,且优化方法的提取结果在空间分布上更接近真实结果。     

一种VLBI数字基带转换器的阈值计算方法及其FPGA实现

随着电子技术的进步,数字化的设备成为发展的趋势.在VLBI2010中定义了新型VLBI数据终端,新的系统使用数字逻辑电路完成VLBI的数据采集.数字基带转换器(Digital Base Band Converter,DBBC)是VLBI数据终端的核心部件,其功能是将射频接收机输出的宽带模拟中频信号数字化处理后,选取若干频道转换为基频信号.与模拟设备相比,其在带通特性、长基线条纹信噪比性能等方面有很大优势.其中经过基带转换后的信号需要通过自动增益控制(Auto Gain Control,AGC)模块进行阈值比较,得到2 bits量化信号作为输出.目前2 bits数字自动增益控制模块设置阈值的方法是基于传统的自动增益控制方法,即信号通过平方、累加和开方,计算出信号的平均功率,再通过平均功率得到阈值.提出了一种量化闽值计算的新方法,该方法通过统计数字信号各比特位的状态分布,并与原阈值进行比较,从而确定新阈值的相应比特位的值,使经阈值比较后的量化输出符合预定的比例.阈值随每N个输入信号的统计情况进行更新,从而实现2 bits动态量化.这种方法可以避免多位数据的平方、累加和开方的复杂计算,从而减少数字自动增益控制模块的资源占用.通过对其FPGA设计的仿真结果分析,验证了该方法的可行性.对2 bits量化原理及其量化误差分析的关键部分作了论述,并通过MATLAB计算出最佳量化门限和量化状态.     

基于RTS2的RAO管理系统二次开发

程控自主天文台(Robotic Autonomous Observatory,RAO)是一架能够执行各种远程观测并且能够在任务执行过程中在没有任何人为协助的情况下自主适应各种变化的望远镜.使用程控自主天文台进行自主化观测,是近些年天文学观测模式新的重要发展方向.首先对程控自主天文台历史、现状、应用领域等做了回顾;然后重点介绍了一套程控自主天文台软件管理系统——RTS2;在此基础上对其代码结构进行详细分析,并且以一种小型赤道仪为实例,实现了在RTS2系统下驱动程序的设计.二次开发试验的成功为自行建设基于RTS2的程控自主天文台系统奠定了基础.     

银川隐伏断层带土壤气中H2的地球化学特征

在银川隐伏断层带已知断层位置的区段布设了两条土壤气H2测线,发现土壤气H2异常最高浓度位于银川隐伏主断层新渠稍探槽附近,含量达73.6×10-6,初步分析认为土壤气H2异常可能主要受断层活动性和倾角控制,说明土壤气H2测量对隐伏断层具有一定的指示意义.     

The generation kinetics of natural gases in the Kela-2 gas field from the Kuqa Depression, Tarim Basin, northwestern China

The Kela-2 gas field, found in the Kuqa Depression of the Tarim Basin, northwestern China, is a large-sized dry gas field (C1 /C1-5 =0.992 0.999) and characterized by ultra-high pressure (pressure factor up to 2.0 2.2). The pyrolysis experiment was carried out under isothermal gold-tube closed system, with samples collected from the Jurassic coal, Jurassic mudstone and Triassic mudstone in the Kuqa Depression. The result of gas yield showed that the Middle and Lower Jurassic source rocks have higher gas generation potential than the Triassic source rocks. The kinetic modeling of gas generation and methane carbon isotope fractionation suggested that the Kela-2 gases belong to the products of high-over mature stages and were mainly derived from the Middle and Lower Jurassic coal-bearing strata. The Triassic source rocks made a minor contribution to the Kela-2 gases. The Kela-2 gases chiefly generated from coal-bearing source rocks with R o values from 1.3% to 2.5%, and thus primarily accumulated after 5 Ma.     

Nitrous oxide emissions from different land use patterns in a typical karst region, Southwest China

Fluxes of nitrous oxide (N2O) from different land use patterns (matured forest, secondary forest, grassland and cropland) in a subtropical karst region of Guizhou Province, Southwest China, were measured for one year with a closed static chamber technique and by gas chromatography. The results showed that soil under different land uses was a source of atmospheric N2O. The cropland was a source with relatively high N2O as compared to forest and grassland, but no significant differences were observed. N2O emissions from soils varied with land use change and fertilizer application. There were two peaks of N2O flux occurred following the combination of two obvious precipitation and fertilizer events in the cultivated land. Converting from the matured forest to secondary forest tended to increase annual emissions of N2O (from 1.40 to 1.65 kg N ha -1 a -1 ), while changing land use from secondary forest to scattered grassland tended to decrease annual emissions of N2O slightly (from 1.65 to 1.45 kg N ha -1 a -1 ). Our range of cumulative annual N2O emission across different land uses (1.40-1.91 kg N ha -1 a -1 ) in a karst region is in general agreement with previously published data in a non-karst region. However, in the maize field, N2O emission factor (EF) was 0.34% for fertilizer application, which is about 71.2% lower than the IPCC default value. It is suggested that current IPCC (Intergovernmental Panel on Climate Change) EF methodology could overestimate N2O emission from the karstic cropland. Anyway, the N2O emission from cropland in the karst region would contribute significantly to the global N2O budget, so reducing fertilization frequency during the crop growing season could lead to a decrease in N2O emission in the whole year.     

Mg(OH)2热分解动力学机理研究

采用Satava法对Mg(OH)2热分解动力学机理进行了分析,借助扫描电子显微镜对其煅烧过程结构、形貌变化进行了分析,认为Mg(OH)2的热分解是一较为复杂的过程,用单一的热分解机理函数描述是不合理的。这一过程可分为两个部分,分界点为397℃,在此温度之前,热分解控制机理为成核和随后生长,动力学机理函数为A3;而在这一温度之后,热分解控制机理为扩散控制,动力学机理函数为D4。     

293 K时KCl在混合溶剂(DMF-H2O)中无限稀释摩尔电导率的测定

293 K时测定了KCl在混合溶剂(DMF-H2O)中的电导率,根据公式求得KCl的摩尔电导率λ值;应用Kohlrausch经验规则,使用Origin软件进行线性拟合,作图外推求得KCl在混合溶剂(DMF-H2O)中的无限稀释摩尔电导率λ0=138.44(S.cm2.mol-1)。