Triple-frequency GPS precise point positioning with rapid ambiguity resolution

At present, reliable ambiguity resolution in real-time GPS precise point positioning (PPP) can only be achieved after an initial observation period of a few tens of minutes. In this study, we propose a method where the incoming triple-frequency GPS signals are exploited to enable rapid convergences to ambiguity-fixed solutions in real-time PPP. Specifically, extra-wide-lane ambiguity resolution can be first achieved almost instantaneously with the Melbourne-Wübbena combination observable on L2 and L5. Then the resultant unambiguous extra-wide-lane carrier-phase is combined with the wide-lane carrier-phase on L1 and L2 to form an ionosphere-free observable with a wavelength of about 3.4 m. Although the noise of this observable is around 100 times the raw carrier-phase noise, its wide-lane ambiguity can still be resolved very efficiently, and the resultant ambiguity-fixed observable can assist much better than pseudorange in speeding up succeeding narrow-lane ambiguity resolution. To validate this method, we use an advanced hardware simulator to generate triple-frequency signals and a high-grade receiver to collect 1-Hz data. When the carrier-phase precisions on L1, L2 and L5 are as poor as 1.5, 6.3 and 1.5 mm, respectively, wide-lane ambiguity resolution can still reach a correctness rate of over 99 % within 20 s. As a result, the correctness rate of narrow-lane ambiguity resolution achieves 99 % within 65 s, in contrast to only 64 % within 150 s in dual-frequency PPP. In addition, we also simulate a multipath-contaminated data set and introduce new ambiguities for all satellites every 120 s. We find that when multipath effects are strong, ambiguity-fixed solutions are achieved at 78 % of all epochs in triple-frequency PPP whilst almost no ambiguities are resolved in dual-frequency PPP. Therefore, we demonstrate that triple-frequency PPP has the potential to achieve ambiguity-fixed solutions within a few minutes, or even shorter if raw carrier-phase precisions are around 1 mm. In either case, we conclude that the efficiency of ambiguity resolution in triple-frequency PPP is much higher than that in dual-frequency PPP.     

A site selection method of DNS using the particle swarm optimization algorithm

The Domain Name System (DNS) is an essential component of the functionality of the Internet. With the growing number of domain names and Internet users, the growing rate and number of visit quantity and analytic capacity of DNS are also proportional to the Internet users' size. This study (based on the analysis of access popularity and the distribution of massive DNS log data) aims to optimize the configuration of the DNS sites, which has become an important problem. The ArcGIS software is used to show the temporal and spatial distributions of visit source of DNS logs. This study also analyzes the influence of different sites and the dependence on DNS service in different regions of the world. This information is important to further decision‐making on new DNS site selection. This article proposes new DNS site selection solutions, using particle swarm and multi‐objective particle swarm optimization algorithms for one new site and multiple sites, respectively. The results from particle swarm optimization, genetic, and simulated annealing algorithms were compared and experimental results confirmed the correctness and effectiveness of the proposed methods. The proposed methods could also be extended to solve other layout related issues, such as onsite facility layout and road network optimization.     

运用信息技术 提高管理水平

本文针对目前我国勘察设计企业管理现状，指出信息技术的应用在勘察设计企业管理中的促进作用；它可使管理者树立规范化、制度化的工作方法，并在许多方面为勘察设计企业创造价值和效益。     

北半球对流层上层遥相关型的涡度源、能量源与能量传播

基于ECMWF 1980～1988年的全球资料,研究了北半球对流层上层两个主要遥相关型（大西洋/欧亚型与太平洋/北美型）的涡度源、能量源及能量传播路径。结果表明,这两个遥相关型的涡度源和能量源分别主要位于北大西洋和北太平洋地区。遥相关型在北大西洋和北太平洋通过正压能量转换从气候平均流中吸收能量,然后从这两个地区将能量向外传播,以维持其水平遥相关结构。     

Quantitative correction of influence of rain on well water level

In this paper a new method of the quantitative correction of influence of the rain on the water level in a well is given. Using the faltung filtering and polynary regression, considering the effect of the rain on the well water level with the lag “memory”, the correction of the influence of the rain on the well water level is made. The result of correction of the water level in the well Lu-08 by the rain shows that the correction result of this method is better. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 202–207, 1993. This study was supported by the Chinese Joint Seismological Science Foundation. Thank The Seismic Office of Victory Oil Field for their help in gathering data of the well Lu-08.     

青海湖1.8万年以来甲藻Dinoflagellate群落变化及其古气候环境的指示意义

近年来,有学者通过古DNA方法成功地重建了海洋沉积记录中古微生物群落变化,并借此反演了当地古环境—气候变化。然而,此种方法对于陆地湖泊沉积记录是否适用仍然有待研究。采用聚合酶链式反应(PCR,Polymerase Chain Reaction)、变性梯度凝胶电泳(DGGE,Denaturing Gradient Gel Electrophoresis)与实时荧光定量聚合酶链式反应(Q-PCR,Quantitative PCR)相结合的综合分析技术手段,系统研究青海湖5.8 m(时间跨度为~18 500 a)沉积柱中的甲藻(Dinoflagellate)多样性和丰度变化。研究结果显示,青海湖Dinoflagellate藻18S rRNA基因序列主要与海洋型藻类Woloszynskiahalophila和Scrippsiellahangoei相近(~98%序列相似性)。定量Q-PCR结果显示,每克沉积物含有dinoflagellate藻类18S rRNA基因丰度范围为2.27×10~3~8.55×10~6拷贝。另外,Dinoflagellate藻类18S rRNA基因丰度与总有机碳含量成显著正相关(R=0.408,p=0.0001)。对比分析揭示,较高的藻类丰度对应高总有机碳含量和较低的可溶解性盐电导率;反之,较低的藻类丰度对应较高的可溶解性盐电导率和较低的总有机碳含量。在青海湖区,总有机碳指示着季风降雨变化,并间接地指示着外源输入和湖泊营养状况变化,然而可溶性盐电导率则指示着湖泊盐度变化。综上所述,青海湖沉积柱Dinoflagellate藻类丰度可能反应了历史时期湖泊营养状况和盐度波动情况。     

新型冠状病毒肺炎的X线及CT表现

目的:总结新型冠状病毒肺炎(2019-nCoV)的X线、CT表现,为临床提供影像学诊断依据。材料与方法:收集2020年1月21日至2月25日我院发热门诊的1028例患者,均进行X线检查,其中18例核酸检测确诊为2019-nCoV,6例同日行CT检查,9例于1周内进行影像学复查。结果:18例确诊的2019-nCoV患者,4例X线表现为肺纹理增重,14例X线表现为肺内单发或多发病灶。好发部位为肺下叶,单侧肺下叶病灶9例,双肺下叶病灶3例,双下肺合并双肺上叶病灶2例。6例同日进行CT检查,1例CT正常,3例发现X线胸片未显示的小片状磨玻璃影,2例CT显示的病灶较X线片多,CT表现以双肺胸膜下分布为主,可伴空气支气管征且小叶间隔增厚。6例患者1周内复查X线片,3例复查CT,其中1例CT显示磨玻璃影吸收,8例显示病变进展,范围较前增大和病灶增多,以双下肺外带为著。结论:新冠肺炎胸部X线及CT表现具有一定的特征性,结合临床病史和实验室检查可作出明确诊断。     

断陷湖盆差异湖侵过程与层序格架下沉积体系特征响应: 以霸县凹陷古近系沙河街组为例*

断陷湖盆充填演化过程中发生的多期差异湖侵,控制了层序格架及其内部沉积体系类型和分布。基于霸县凹陷的三维地震资料,结合800口探井钻/测井、岩心及古生物等资料,在明确古近系湖盆演化过程的基础上,以沙河街组三段和一段为研究目标,分析差异湖侵作用过程中的层序结构及层序格架下的沉积差异特征。研究结果表明,沙三段沉积时期的缓慢湖侵过程中发育断坡—坡折层序结构,以多期退积型三角洲、扇三角洲沉积为主,形成厚层优质烃源岩。沙一段沉积时期的快速湖侵过程中,形成弯折—宽缓坡型层序结构样式,发育混积滩坝、小型近岸水下扇(扇三角洲)沉积。根据上述研究结果,认为断陷湖盆差异沉降控制了层序结构样式,古地貌和物源供给调节岩相的空间分布,湖盆不同演化阶段层序结构和沉积体系都存在显著的差异。在此基础上,建立差异湖侵作用下沉积体系特征的响应模型,可为同类型盆地中的油气勘探特别是岩性油气藏的勘探提供借鉴。     

冲击载荷作用下准脆性材料Ⅱ型裂纹扩展研究

冲击载荷作用下准脆性材料的动态断裂一直是关注的热点问题,Ⅱ型裂纹试样受冲击剪切时其裂纹扩展方向同材料力学性质和冲击速度等密切相关。应用岩石动态破裂过程动态分析系统软件,对单边平行双裂缝试样开展了冲击载荷作用下的裂纹动态扩展数值模拟,分别研究了不同材料力学性质、材料均质度、入射应力脉冲幅值和历时对II型裂纹动态扩展的影响。数值模拟结果表明,纯II型裂纹在动荷载作用下的扩展,不仅受到剪切损伤,而且还存在拉伸损伤;准脆性材料的非均匀性导致了主裂缝周围产生大量微裂纹的破坏,影响裂缝的分岔和内部的应力值;应力幅值和应力脉冲历时分别超过某一定值时,主裂缝将出现分叉现象,试样的破坏程度加剧,其研究结果对于深入揭示准脆性材料在动荷载作用下II型裂纹扩展的规律及准脆性材料的损伤断裂机制具有重要的参考价值。     

PRIMARY ANALYSIS OF DROUGHT AND WATERLOGGING LAW IN NORTH CHINA

According to the drought and waterlogging disaster statistics over the last 30 years (1950-1979), the annual average area suffering from drought was about 300 million mu (1 mu= 1/ 15 ha) in the whole country, among which about 100 million mu were disastrous areas where the output reduced more than 30%. and the annual lost grains totalled about 5 billion kg. The waterlogging disaster was less than drought disaster. The area suffering from waterlogging was about 100 million mu, among which 60 million mu were disastrous. Drought and waterlogging disasters affect directly the development of the national economy. So it is important to study drought and waterlogging variations, especially the drought and waterlogging variation laws of the areas where the disasters frequently occur.The historical literatures and recent observation data reveal the fact that there existed drought and waterlogging variations. For example, the occurrence frequency of the outstanding and severe drought years in north China is highe