Bias estimation and correction for triangle-based surface area calculations

The calculation of surface area is meaningful for a variety of space-filling phenomena, e.g., the packing of plants or animals within an area of land. With Digital Elevation Model (DEM) data we can calculate the surface area by using a continuous surface model, such as by the Triangulated Irregular Network (TIN). However, just as the triangle-based surface area discussed in this paper, the surface area is generally biased because it is a nonlinear mapping about the DEM data which contain measurement errors. To reduce the bias in the surface area, we propose a second-order bias correction by applying nonlinear error propagation to the triangle-based surface area. This process reveals that the random errors in the DEM data result in a bias in the triangle-based surface area while the systematic errors in the DEM data can be reduced by using the height differences. The bias is theoretically given by a probability integral which can be approximated by numerical approaches including the numerical integral and the Monte Carlo method; but these approaches need a theoretical distribution assumption about the DEM measurement errors, and have a very high computational cost. In most cases, we only have variance information on the measurement errors; thus, a bias estimation based on nonlinear error propagation is proposed. Based on the second-order bias estimation proposed, the variance of the surface area can be improved immediately by removing the bias from the original variance estimation. The main results are verified by the Monte Carlo method and by the numerical integral. They show that an unbiased surface area can be obtained by removing the proposed bias estimation from the triangle-based surface area originally calculated from the DEM data.     

Effect of stocking density on water quality and (Growth,Body Composition and Plasma Cortisol Content) performance of pen-reared rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

The goal of the study was to examine the effect of stocking density on the water quality of culture area, as well as the growth, body composition and cortisol content of rainbow trout（Oncorhynchus mykiss）. Pen-reared trout were stocked in densities of 40, 60, 80 fish individuals m^-3(4.6, 6.6, 8.6 kg m^-3, SD1, SD2 and SD3 groups, respectively) for 300 days. Compared to the water from SD1 and SD2, that from SD3 exhibited significantly higher NH₄⁺-N content and COD（chemical-oxygen-demand）, and a significant reduction of dissolved oxygen in day 180(40.6 kg m^-3). Stocking density was significantly associated with body weight, standard length, VSI（viscerosomatic index）, CF（condition factor） and FC（food coefficient） in group SD3, particularly in day 240 and day 300(45 or 49.3 kg m^-3). Increased crude fat and decreased crude protein were displayed in high density group when the density reached to 36 kg m^-3. As a cumulative effect of density-related stress, VSI, CF, FC, moisture, and crude protein content varied over time in each density group（SD1, SD2, and SD3）. In summary, trout exhibited a better growth performance in low density(26.3 kg m^-3) than those reared in high densities(36 and 45 kg m^-3). The results indicate that rainbow trout（114.44 g ± 6.21 g, 19.69 cm ± 0.31 cm） initially stocked in 6.6 or 8.6 kg m^-3 should be lightened to less than 36 kg m^-3 after an intensive rearing for 240 days.     

Spatial and temporal analyses of air pollutants and meteorological driving forces in Beijing–Tianjin–Hebei region,China

Due to its negative impact on the living environment of human beings, ambient air pollution has become a global challenge to human health. In this study, surface observations of six criteria air pollutants, including PM_2.5, PM₁₀, SO₂, NO₂, CO and O₃, were collected to investigate the spatial and temporal variation in the Beijing–Tianjin–Hebei (BTH) region during 2013–2016 and to explore the relationships between atmospheric pollutants and meteorological variables using quantile regression model (QRM) and multiple linear regression model (MLRM). The results show that BTH region has experienced significant air pollution, and the southern part generally has more severe conditions. The annual average indicates clear decreasing trends of the particulate matters, SO₂ and CO concentrations over the last 4 years and slight increasing trends of NO₂ and O₃ in several cities. The seasonal and monthly characteristics indicate that the concentrations of five species reach their maxima in the winter and their minima in the summer, whereas O₃ has the opposite behaviour. Finally, the pseudo R² values show that the QRMs have the best performance in the winter, followed by spring, fall, and summer. Specifically, all the meteorological factors have significant impacts on air pollution but change with pollutants and seasons. The MLRM results are generally consistent with the QRM results in all seasons, and the inconsistencies are more common in the fall and winter. The results of this research provide foundational knowledge for predicting the response of air quality to climate change in the BTH region.     

Characterization of shale matrix pore structure via experiment and model

Shale gas reservoirs develop multi-scale pores ranging in size from nanometer to micrometer, the characteristics of gas transport involve the multi-scale pore space which divided into organic and inorganic matrix pores. This paper reveals the shale pore structure with large amounts of organic mesoporous based on the techniques of focused ion beam scanning electron microscopes (FIB-SEM), high-pressure mercury intrusion (MICP), and low-pressure adsorption (LPA), which also shows the size and distribution of these pores. Then the research characterizes effective pore scale via circular tube bundle model with due regard for gas adsorption layer thickness on the walls of organic pores and water film thickness on the walls of inorganic pores, and the investigation of shale pore geometry is significant for designing and developing shale gas reservoirs. This work shows that the widely existing shale mesoporous volume with diameter of 2~50 nm accounts for 81% based on experimental testing, then it reduces to about 76% via effective diameter model calculation.     

Middle Jurassic–Early Cretaceous tectonic evolution of the Bayanhushuo area,southern Great Xing’an Range,NE China: constraints from zircon U–Pb geochronological and geochemical data of volcanic and subvolcanic rocks

This study presents new zircon U–Pb geochronology, geochemistry, and zircon Hf isotopic data of volcanic and subvolcanic rocks that crop out in the Bayanhushuo area of the southern Great Xing’an Range (GXR) of NE China. These data provide insights into the tectonic evolution of this area during the late Mesozoic and constrain the evolution of the Mongol–Okhotsk Ocean. Combining these new ages with previously published data suggests that the late Mesozoic volcanism occurred in two distinct episodes: Early–Middle Jurassic (176–173 Ma) and Late Jurassic–Early Cretaceous (151–138 Ma). The Early–Middle Jurassic dacite porphyry belongs to high-K calc-alkaline series, showing the features of I-type igneous rock. This unit has zircon ε_Hf(t) values from +4.06 to +11.62 that yield two-stage model ages (T_DM2) from 959 to 481 Ma. The geochemistry of the dacite porphyry is indicative of formation in a volcanic arc tectonic setting, and it is derived from a primary magma generated by the partial melting of juvenile mafic crustal material. The Late Jurassic–Early Cretaceous volcanic rocks belong to high-K calc-alkaline or shoshonite series and have A₂-type affinities. These volcanics have ε_Hf(t) and T_DM2 values from +5.00 to +8.93 and from 879 to 627 Ma, respectively. The geochemistry of these Late Jurassic–Early Cretaceous volcanic rocks is indicative of formation in a post-collisional extensional environment, and they formed from primary magmas generated by the partial melting of juvenile mafic lower crust. The discovery of late Mesozoic volcanic and subvolcanic rocks within the southern GXR indicates that this region was in volcanic arc and extensional tectonic settings during the Early–Middle Jurassic and the Late Jurassic–Early Cretaceous, respectively. This indicates that the Mongol–Okhotsk oceanic plate was undergoing subduction during the Early–Middle Jurassic, and this ocean adjacent to the GXR may have closed by the Late Middle Jurassic–Early Late Jurassic.     

青藏铁路对西藏各经济部门发展影响的定量评估

青藏铁路对西藏经济发展影响重大,定量评估其对各经济部门发展的影响程度,是全面评价铁路交通基础设施效益、分析未来冰冻圈变化对线性工程及经济社会重大影响的基础。将灰色关联分析法与投入产出法相结合,既填补了关联度分析的黑箱式缺陷,又弥补了西藏投入产出调查缺乏长时间序列数据的问题,以此来认识青藏铁路对西藏经济发展的影响机理与路径。以2006-2016年统计数据为基础,采用灰色关联度模型计算青藏铁路与西藏各经济部门发展的灰色关联度值,表明铁路运输水平与西藏地区生产总值（GDP）、第三产业高度相关,其中与货运邮电业、住宿餐饮业两个部门关联度达到了0.9以上。在灰色关联度结果的基础上,运用西藏2012年投入产出表及投入产出模型计算铁路的直接作用,以及对各经济部门的间接波及作用,研究发现：青藏铁路建设及运营的劳动密集程度高,且通过灰色关联度较高行业的产品及服务影响其他行业,以直接作用、后向和前向波及作用、消费波及作用三种路径对区域经济的发展产生重要影响,扣除消费波及作用的总体贡献达到41.7亿元,相当于2012年西藏GDP的5.95%。由于铁路交通基础设施重要的直接作用及间接波及作用,建议在工程条件适宜地区加快铁路运输网络建设,同时,将工程设施的社会经济效益纳入冰冻圈服务功能核算中。     

Geochronology,Geochemistry and Petrogenesis of the Pungco Ophiolite,TibetEI北大核心CSCD

Although the middle section of the Bangong-Nujiang suture zone has been intensively investigated, its tectonic framework and evolution is still controversy. The Pungco ophiolite has a relative complete ophiolitic complex, which is an ideal specimen for studying this tricky problem. LA-ICP-MS U-Pb dating of zircons from the diabasic rock yielded an age of 159.0±2.1 Ma. This age suggests that the Pungco ophiolite was formed in the Late Jurassic, indicating the development of the Late Jurassic ophiolite in the third ophiolitic subzone. The whole-rock major and trace element compositions of diabasic and basaltic rocks exhibit mixed arc and N-MORB geochemical characteristics. Two diabasic samples have (87Sr/86Sr)i values of 0.7055 and 0.7063 and εNd(t) values of 11.28 and 11.84, respectively. The geochemical signatures and formation age of the Pungco ophiolite suggest that this ophiolite was probably produced in an active continental fore-arc setting. It originated from a N-MORB-like depleted mantle source with the involvement of subducted-slab fluids. Considering the regional geological background, the Pungco ophiolite was likely generated during the southward subduction of the Bangong-Nujiang Tethyan oceanic lithosphere beneath the Lhasa terrane, and belongs to a regional archipelagic arc-basin system together with the other Early Jurassic-Early Cretaceous ophiolites from the northern Tibet Lake district. © 2018, Science Press. All right reserved.     

路网距离约束的GTWR模型应用——以北京市房价为例

针对传统地理加权回归方法无法解决时空非平稳性的问题,该文提出了一种路网距离约束的时空地理加权回归方法。引入时间特性,进一步把握了不同因子在时空维度影响的分异性;以路网距离度量约束,提高模型解释力。以北京市城6区1980—2015年的1 632个住宅小区特征价格数据为例,通过与直线距离约束的常规地理加权回归方法等进行比较,采用各模型的AIC与拟合优度等指标对模型置信水平高低进行评价。实验结果表明,路网距离约束的地理加权回归模型不仅能够提高模型的拟合精度,还能更好地揭示房价在时间与空间方面的变化规律。     

2016年四川省PM2.5浓度时空分布研究

PM2.5导致大气能见度下降,造成雾霾天气.本文基于2016年四川省89个空气质量监测站的PM2.5数据,对2016年四川省PM2.5浓度时空分布特征进行研究分析.结果表明,2016年四川省PM2.5浓度空间分布呈现出西北部PM2.5浓度较低、空气质量较好,东南部PM2.5浓度较高、空气质量较差的趋势;时间分布呈现夏季PM2.5浓度较低、空气质量较好,冬季PM2.5浓度较高、空气质量较差的趋势,从而得出四川省PM2.5浓度时间和空间分布规律及分布图.     

东天山早中生代侵入体地球化学特征及其构造意义

东天山百灵山西辉长岩、似斑状花岗岩近年来才被发现,为了解其成因及相关大地构造背景,对其进行地质学、地球化学、锆石U-Pb定年及Sr-Nd同位素分析.LA-ICP-MS锆石U-Pb测年结果显示,百灵山西辉长岩、似斑状花岗岩分别形成于236 Ma和228 Ma.辉长岩具有较低的SiO₂（43.50%~46.03%）含量,较高的CaO（11.40%~13.24%）、Fe₂O₃T（9.62%~11.84%）和MgO（6.02%~10.58%;Mg#=53~69）含量以及Ce/Pb、Ti/Zr、Ti/Y及Ba/Th比值,且富集LREE、LILE,表明其形成于受板片脱水流体交代地幔楔的部分熔融.似斑状花岗岩表现出I型花岗岩的特征,且具有较高的SiO₂（71.14%~72.71%）,强富集LREE[（La/Yb）_N=12.61~28.45]和LILE（例如Rb,K和Pb）,表明其形成于下地壳的部分熔融.而较高的Mg#（39~41）值、Ti/Y（154.40~306.18）比值,显示其源区有地幔物质的加入.结合前人研究成果,可知东天山地区在240 Ma以后已经进入陆内演化阶段,百灵山西辉长岩及似斑状花岗岩均形成于陆内环境.