Revisit the calibration errors on experimental slant total electron content (TEC) determined with GPS

The calibration errors on experimental slant total electron content (TEC) determined with global positioning system (GPS) observations is revisited. Instead of the analysis of the calibration errors on the carrier phase leveled to code ionospheric observable, we focus on the accuracy analysis of the undifferenced ambiguity-fixed carrier phase ionospheric observable determined from a global distribution of permanent receivers. The results achieved are: (1) using data from an entire month within the last solar cycle maximum, the undifferenced ambiguity-fixed carrier phase ionospheric observable is found to be over one order of magnitude more accurate than the carrier phase leveled to code ionospheric observable and the raw code ionospheric observable. The observation error of the undifferenced ambiguity-fixed carrier phase ionospheric observable ranges from 0.05 to 0.11 total electron content unit (TECU) while that of the carrier phase leveled to code and the raw code ionospheric observable is from 0.65 to 1.65 and 3.14 to 7.48 TECU, respectively. (2) The time-varying receiver differential code bias (DCB), which presents clear day boundary discontinuity and intra-day variability pattern, contributes the most part of the observation error. This contribution is assessed by the short-term stability of the between-receiver DCB, which ranges from 0.06 to 0.17 TECU in a single day. (3) The remaining part of the observation errors presents a sidereal time cycle pattern, indicating the effects of the multipath. Further, the magnitude of the remaining part implies that the code multipath effects are much reduced. (4) The intra-day variation of the between-receiver DCB of the collocated stations suggests that estimating DCBs as a daily constant can have a mis-modeling error of at least several tenths of 1 TECU.     

漠河盆地西部二十二站组碎屑锆石U-Pb年龄、地球化学特征及其物源意义

大兴安岭北部漠河盆地内广泛发育二十二站组,其形成时代及物质来源一直以来备受争议.本文在野外地质调查及岩相学的基础上,利用碎屑锆石LA-ICP-MS U-Pb法测年,并结合岩石地球化学等方法,探讨了二十二站组形成时代、物源区大地构造环境及沉积物来源.测年结果显示132个测点年龄主要分布在4个群落,分别为508.3～492.3 Ma;486.9～435.5 Ma;278.3～254.2 Ma;209.5～178.1 Ma.本次获得二十二站组最小碎屑锆石年龄为178.1 Ma,并结合漠河盆地东西部碎屑锆石的年龄,综合认为二十二站组形成时代应为中晚侏罗世.地球化学分析结果显示,二十二站组砂岩的稀土元素与活动大陆边缘的稀土元素曲线吻合较好,且相对亏损高场强元素(Nb和Ta)和大离子亲石元素(Ba和Sr),相对富集高场强元素(La、Th、Zr、Hf),地球化学特征与活动大陆边缘相似.综合古流向、源区母岩分析、碎屑锆石测年分析、微量元素特征等诸多因素,本次研究认为本区二十二站组砂岩的母岩主要来源于盆地南缘广泛分布的前中生代沉积-变质基底(兴华渡口岩群、佳疙瘩组、额尔古纳河组等)及各期中酸性火成岩.     

Monotonic and cyclic characteristics of K0-Consolidated saturated soft clay under a stress path involving a variable confining pressure

In certain field conditions such as offshore projects under wave loads or embankments under traffic loads, both the vertical and horizontal stresses are variable. However, previous investigations rarely considered the variation in horizontal stress. To better understand the characteristics of natural saturated soft clay, a series of monotonic and cyclic triaxial tests with a K₀-consolidation state were carried out under a variable confining pressure (VCP) stress path. The development of axial strain, pore water pressure and effective stress path is analysed. The results show that with the increase in η (the ratio of the variation in the mean effective principal stress to that of the deviatoric stress), the undrained shear strength (q_f) decreases continuously. The pore water pressure generation is slightly improved under a stress path with increasing confining pressure. Based on the test results, a unified formula was established to predict the pore water pressure under VCP stress paths. The unique p–q–e relationship of normally consolidated clay in monotonic VCP triaxial tests was also demonstrated. Under VCP stress paths, the amplitude of the pore pressure increases, and the effective stress path tilts more sharply to the right. Moreover, a unified formula was established that can provide a good reference for predicting effective stress paths under cyclic VCP triaxial tests.

     

国家数字地震台数据处理研究

为了突显被淹没在噪声背景下的有用信息,对国家数字地震台的数据处理方法进行了研究,并用Matlab程序给出了详细的设计过程。     

2005年云南会泽、文山5.3级地震短临预报及再认识

2005年8月5日、8月13日云南会泽、文山分别发生5．3级地震。震前,前兆各学科出现不同程度的异常变化,异常台项达30多项,并呈现非线性上升趋势。据此,震前对这两次地震做出了短临预报。震后对两次地震的震前异常做了进一步分析研究,认为异常主要分布在距离震中20～180km范围内,集中出现在震前2个月。水温异常对发震地点有一定的指示意义。     

新疆S214公路台特玛湖干涸湖盆段风沙危害及防治

新疆S214（考干-米兰,考米线）公路位于库鲁克塔格沙漠东南缘,穿越台特玛湖干涸湖盆。由于该区气候干旱,风力强劲,沙源丰富,流动沙丘广布且快速移动,风沙危害对公路运输构成严重威胁。通过对风沙环境和风沙危害定位观测和土壤水盐特征系统调查,确定了风沙危害极为严重的公路区段,提出了合理的风沙防护措施及防沙体系结构。结果表明：该区具有明显的单风向风况,主要盛行ENE和NE风,偶有反向风沙活动,起沙风频率、输沙势、输沙率极高,属于高能-大比率风能环境;受土壤水分、盐分含量影响,地表紧实度差异较大,部分地段为极疏松的沙层,部分地段为紧实的盐壳;S214公路风沙危害防护区段为K4+900~K18+200,设计建造的阻-固-输相结合的机械-植物复合防沙体系,防沙效果明显,保障了道路安全运营。这一强风沙、高盐区公路防沙体系建设模式可为类似环境地区工程防沙提供借鉴。     

Application of flocculation combined with vacuum preloading to reduce river-dredged sludge

Abstract

To achieve the rapid dewatering of dredged sludge, the flocculation–vacuum-preloading method was tested indoors. In this study, the optimal mixing ratio of six flocculants was determined through the settling column test, and then the proposed method was tested. The water drainage and settlement were monitored during the test, while the soil moisture content and shear strength were measured after the test. The results show that all the flocculants had an optimal mixing ratio, and the addition of 0.8% FeCl₃ or 0.08% anionic polyacrylamide (APAM) in the sludge can better accelerate solid–liquid separation of the sludge. After the test, the water content in the sludge decreased from 140% to 60%. Compared with general vacuum preloading, the use of the proposed method increased the water drainage by 46.5% and 56.8% and decreased the soil volumes by 60.5% and 82.4% for FeCl₃ and APAM, respectively. Moreover, the corresponding shear strength was increased from 10 to 14 and 17?kPa. In addition, the use of APAM increased the solidification rate of heavy metals in the sludge to more than 80%, effectively inhibiting the migration of heavy metals.     

A Thermo–Hydro–Mechanical Model: Capturing the Effects of Initial Permeability and Gas Pressure on Outburst-Prone Indicators

Natural Resources Research - Coal and gas outbursts often result in a large number of casualties and economic losses. Its complex processes involve the multi-field coupling of gas flow, coal...     

Spatiotemporal characteristics of Qinghai Lake ice phenology between 2000 and 2016

Journal of Geographical Sciences - Lake ice phenology is considered a sensitive indicator of regional climate change. We utilized time series information of this kind extracted from a series of...     

Numerical Simulation on Flow Past Two Side-by-Side Inclined Circular Cylinders at Low Reynolds Number

A series of three-dimensional numerical simulations is carried out to investigate the effect of inclined angle on flow behavior behind two side-by-side inclined cylinders at low Reynolds number Re=100 and small spacing ratio T/D=1.5 (T is the center-to-center distance between two side-by-side cylinders, D is the diameter of cylinder). The instantaneous and time-averaged flow fields, force coefficients and Strouhal numbers are analyzed. Special attention is focused on the axial flow characteristics with variation of the inclined angle. The results show that the inclined angle has a significant effect on the gap flow behaviors behind two inclined cylinders. The vortex shedding behind two cylinders is suppressed with the increase of the inclined angle as well as the flip-flop gap flow. Moreover, the mean drag coefficient, root-mean-square lift coefficient and Strouhal numbers decrease monotonously with the increase of the inclined angle, which follows the independent principle at small inclined angles.