The impact of resolution on the accuracy of hydrologic data derived from DEMs

Hydrologic data derived from digital elevation models (DEM) has been regarded as an effective method in the spatial analysis of geographical information systems (GIS). However, both DEM resolution and terrain complexity has impacts on the accuracy of hydrologic derivatives. In this study, a multi-resolution and multi-relief comparative approach was used as a major methodology to investigate the accuracy of hydrologic data derived from DEMs. The experiment reveals that DEM terrain representation error affects the accuracy of DEM hydrological derivatives (drainage networks and watershed etc.). Coarser DEM resolutions can usually cause worse results. However, uncertain result commonly exists in this calculation. The derivative errors can be found closely related with DEM vertical resolution and terrain roughness. DEM vertical resolution can be found closely related with the accuracy of DEM hydrological derivatives, especially in the smooth plain area. If the mean slope is less than 4 degrees, the derived hydrologic data are usually unreliable. This result may be helpful in estimating the accuracy of the hydrologic derivatives and determining the DEM resolution that is appropriate to the accuracy requirement of a particular user. By applying a threshold value to subset the cells of a higher accumulation flow, a stream network of a specific network density can be extracted. Some very important geomorphologic characteristics, e.g., shallow and deep gullies, can be separately extracted by means of adjusting the threshold value. However, such a flow accumulationbased processing method can not correctly derive those streams that pass through the working area because it is hard to accumulate enough flow direction values to express the stream channels at the stream's entrance area. Consequently, errors will definitely occur at the stream’s entrance area. In addition, erroneous derivatives can also be found in deriving some particular rivers, e.g., perched (hanging up) rivers, anastomosing rivers and braided rivers. Therefore, more work should be done to develop and perfect the algorithms.     

新疆哈密市图拉尔根①号杂岩体成矿远景探讨

从区域铜镍矿成矿地质背景、矿区地球物理、地球化学特征等方面入手,对图拉尔根①号杂岩体进行岩相、岩石化学特征及矿化蚀变分析,与黄山、香山成型矿床进行对比.证实①号杂岩体岩石组合类型与香山、黄山闪长岩-辉长岩-辉石岩-橄榄岩型岩石组合相当,并具有相似的m/f、Ni/Co及较高的S值含量.矿化主要赋存在角闪橄辉岩相中,主要受杂岩体岩相带及岩相接触带间脆-韧性构造破碎带控制,认为该岩体具有形成岩浆型铜镍矿的成矿远景.     

铜同位素的分馏机制及其在矿床学研究中的应用

作为一种重要的成矿元素,铜广泛分布于不同地质体中,并广泛参与成岩成矿作用。近年来,由于同位素分析方法的改进和新一代多接收等离子质谱仪(MC-ICPMS)的应用,使得铜同位素的高精度测试成为现实,并已成为国际地学领域的一个前沿研究方向。铜同位素在自然界中具有较大的变化范围,δ65Cu值介于-3.03‰～5.74‰之间。本文介绍和评述了铜同位素的分析方法和可能的分馏机制,并根据已发表数据,重点讨论了铜同位素组成与成矿温度、矿化阶段和成矿物质来源的关系。认为铜同位素有可能作为一种灵敏的地球化学示踪剂,对指示成矿物质来源、成矿作用过程和矿床形成机理具有重要作用。     

Numerical simulation of spatial-temporal evolution characteristics of subsurface fluid based on strong body seismogenic model

Using finite element technique of the plane-strain problem in solid-liquid two-phase medium, we studied the characteristics of "field precursors" and "focus precursors" of subsurface fluid and their spatial-temporal evolution in case of dip-slip earthquake. The results show that: ① the change of ground fluid is slow and the anomaly is not prominent in the early period which is of elastic accumulation and non-linear; ②dilatancy emerges and anomaly focus mainly in the source region in the moderate period which is hardening and of local dilatancy. In the period the focus precursors emerge earlier than the field precursors; ③anomalies spread continuously in the source area and new regions with big anomaly emerge out of the source region in the middle-short period which is of large-scale dilatancy.     

大地电磁测深法在铜镍矿勘查中的应用

文章介绍了大地电磁勘探的基本原理,结合在新疆哈密地区图拉尔根铜镍矿区的实际应用,从野外数据采集到资料处理和地质解释对该方法的实际效果进行了剖析,所获异常得到钻探证实为厚大矿体。文章还对该方法的适用条件进行了分析,并给出了在荒漠戈壁地区进行大地电磁勘探的一些可以借鉴的经验。     

俯冲增生杂岩带变形特征、成因机制及与后期变形的区别

俯冲增生杂岩带是造山带重要的组成单元,它记录了从俯冲到碰撞以及碰撞后陆内的演化历史,具有重要的研究价值。由于增生楔形成过程复杂,而后期的碰撞以及陆内变形又会强烈改造俯冲期的变形,因此如何区分增生杂岩中俯冲期间和碰撞阶段的变形就非常重要,但明确的区分两者又是非常困难的工作。我国几乎所有地区发育的俯冲-增生杂岩都经历了后期强烈的改造,因而正确合理地筛分俯冲阶段和碰撞阶段的变形,在我国的造山带研究中日益突出。本文在详细介绍俯冲期间相关变形及其机制的基础上,从不同构造要素的分布、发育特征、形成环境、成因机制等方面综合对比了俯冲阶段和碰撞阶段以及之后构造变形的异同,提出了区别不同阶段变形的主要原则。相比碰撞阶段变形,俯冲阶段的变形主要集中在俯冲隧道中,以简单剪切或一般剪切为主(逆冲断层多见),底板垫托以及双冲构造是变形的重要特征,变形呈弥散性,断层和面理以及褶皱等具有优势的构造极性,但缺少区域尺度的大型褶皱;纯剪变形少见,主要发育在俯冲隧道上方的增生楔中。流体作用以及水岩反应强烈,直接控制变形行为,发育有从显微尺度到区域尺度的变形分解现象。而碰撞阶段主要是在陆上环境进行,主要变形集中在接触带以及大型断裂/剪切带附近。断层和面理的构造极性不明显,增生楔整体变形,出现区域尺度的大型褶皱;流体作用虽有,但不如俯冲阶段明显和强烈,以逆冲和走滑断层多见。然而很多指标和依据并不是某种环境下唯一的,因此在实际工作中需要综合各方面信息和要素进行判断,合理区分不同阶段的变形。     

四种土方量计算方法的对比研究与应用

为确保工程建设土方量计算的准确性,对比研究了DTM法、方格网法、断面法和等高线法四种土方量计算方法的原理、精度以及适用性,并在南方CASS软件中进行了实例验证,最后提出了在本次项目中应采用的最优方案和土方量精确计算中应注意的事项。     

基于CATIA的飞机曲面重建方法研究

介绍了逆向工程的基本知识,飞机曲面数据采集的一般流程;提出了点云数据预处理算法实现方法,包括点云滤波算法、点云数据精简算法和基于奇异值分解法的多视点云拼接算法,通过对数据的预处理,大部分数据噪声得以消除,数据量进一步简化,多视点云数据实现空间配准;研究了飞机曲面重建的数据处理流程,对飞机机体进行若干分区,按照点、线、面的建模处理流程对每个区进行独立建模;最后以Catia逆向建模模块对某型样机点云数据处理流程为例,详细探讨了飞机曲面重建的流程和精度验证等方法。实践证明,本文介绍的算法和处理方法切实有效,建模数据准确可靠。     

Biomolecular Preservation of Miocene Fossil Liquidambar from Tiantai, China and Clarkia, USA: Implications for Palaeoenvironmental Study

Biomolecular characteristics of fossil Liquidambar from the Miocene Shengxian Formation, Tiantai, Zhejiang province in eastern China and Miocene Clarkia sediment, Idaho, U.S.A., are obtained by means of Pyrolysis-Gas chromatography-Mass spectrometry analysis (Py-GC-MS). Their modern equivalent (Liquidambar formosana) collected from Nanjing, eastern China, is also analyzed for comparison. The total ion chromatograms (TIC) of modern L. formosana leaves shows abundant pyrolysates of lignin, polysaccharide, aliphatic acid, and amino acid. However, only one polysaccharide molecule, i.e., levoglucosan, is retained in fossil Liquidambar leaves from the two Miocene sites with the Tiantai specimen possessing higher intensity. As expected, some lignin pyrolysates including benzene, phenol, guaiacol, vinylphenol and their derivatives, are detected in Miocene Tiantai L. miosinica. However, the lignin components with large molecular weight other than benzene and phenol compounds, are absent in Miocene Clarkia L. pachyphyllum. Abundant pristene and homologous series of n-alk-1-ene/n-alkane pairs with a long retention time are shown in pyrograms of both Tiantai and Clarkia fossils. Based upon our Py-GC-MS data, the molecular preservation in these Liquidambar leaf samples can be ranked as the following (from high to low quality respectively): modern sample >Tiantai sample >Clarkia sample. Vinyl phenol, an important compound, is present in modern and Tiantai Liquidambar leaves, while absent in Clarkia sample, implying that vinyl phenol may be sourced from lignin for Liquidambar leaves. Our data support the hypothesis of in situ polymerization for the origin of long-chain homologous series of n-alk-1-ene/n-alkane pairs as leaf alteration products. Our data have implications of the impact of leaf degradation toward biases for palaeoenvironmental reconstruction using stable carbon isotope of fossil plants, and suggest the importance of evaluating molecular preservation of fossil leaf tissues prior to the application of carbon isotope compositions of fossil leaves.     

急冷与空气暴露联合胁迫对凡纳滨对虾生理代谢影响

【目的】探明无水保活流通过程中凡纳滨对虾(Litopenaeus vannamei)响应急冷(acute cold,AC)与空气暴露(waterless duration,WD)联合胁迫的生理代谢调节规律。【方法】研究模拟产业运输实际,分析联合胁迫(AC+WD)进程中凡纳滨对虾血液和肝胰腺典型生化指标,以及肝胰腺组织病理变化。【结果】AC胁迫后,凡纳滨对虾生理应激指标血清皮质醇含量由正常组(normal control,NC)的(326.90±4.61)pg/mL显著增加到AC组的(427.16±7.92)pg/mL(P<0.05),AC+WD组则随时间延长而逐渐降低。血清葡萄糖含量在联合胁迫6 h后达到最大值(26.31±1.05)mg/dL,乳酸在9 h达到峰值(7.90±0.11)mmol/L。AC及AC+WD组中血蓝蛋白、尿素氮和肌酐含量较NC组均发生不同程度的增加,而总蛋白含量先升后降,总胆固醇和甘油三酯含量呈胁迫时间依赖性下降。血清谷草转氨酶、谷丙转氨酶、酸性和碱性磷酸酶活力呈上升趋势,并在9 h达到峰值。以上生化指标在胁迫复苏组有所恢复,表明AC+WD双重胁迫引起凡纳滨对虾物质代谢紊乱,复苏后机体生理应激和代谢系统发生一系列代偿性调节,且胁迫进程中肝胰腺组织病理损伤特征进一步解释了凡纳滨对虾响应环境联合胁迫的结构基础。【结论】无水保活流通过程中双重胁迫时间依赖性改变凡纳滨对虾生理应激水平和物质代谢,在9 h时可明显造成肝胰腺组织结构损伤,进而影响机体存活。