北京主城区伪基站时空规律分析     

汪伟  陶海燕  卓莉  李敏  李旭亮  汪珂丽  史清丽 《地球信息科学学报》2018,20(7):978-987

随着公众移动通信的快速发展,伪基站的泛滥不仅破坏正常电信秩序,危害公共安全,而且严重损害群众财产权益,侵犯公民个人隐私,已成为社会一大公害。如何从垃圾短信大数据中挖掘出伪基站活动的时空规律,寻找有效的防控方案,从源头上进行打击和治理成为管理部门和研究者共同关注的焦点。本文基于北京市垃圾短信数据,利用非负矩阵分解的方法分析伪基站的时空分布规律;并利用TF-IDF构建垃圾短信分类模型,对垃圾短信进行分类,结合土地利用数据,分析伪基站在发送不同类型垃圾短信时的时空分布规律。结果显示：北京市垃圾短信多分布于路网和中心城区;白天垃圾短信数量远远多于晚上;垃圾短信的分布随时间的推移沿着路网逐渐向内收缩;发送不同类型垃圾短信的伪基站的时空分布具有一定的差异;通过非负矩阵分解得到的结果,与垃圾短信分类后得到的结果有很好的匹配。研究表明,非负矩阵分解具有实现上的简便性、分解形式和分解结果上的可解释性等优点,可以有针对性的为有关部门建言打击伪基站的有效方案,对于伪基站违法行为的治理具有一定的意义。  相似文献   

Structural Variation Analysis of Mutated Nannochloropsis oceanica Caused by Zeocin Through Genome Re-Sequencing     

LIN Genmei  ZHANG Zhongyi  GUO Li  DING Haiyan  YANG Guanpin 《中国海洋大学学报(英文版)》2018,(5)

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Study of the flood control scheduling scheme for the Three Gorges Reservoir in a catastrophic flood          下载免费PDF全文

Shanghong Zhang  Zhu Jing  Wenda Li  Yujun Yi  Yong Zhao 《水文研究》2018,32(11):1625-1634

The Three Gorges Project is the world's largest water conservancy project. According to the design standards for the 1,000‐year flood, flood diversion areas in the Jingjiang reach of the Yangtze River must be utilized to ensure the safety of the Jingjiang area and the city of Wuhan. However, once these areas are used, the economic and life loss in these areas may be very great. Therefore, it is vital to reduce this loss by developing a scheme that reduces the use of the flood diversion areas through flood regulation by the Three Gorges Reservoir (TGR), under the premise of ensuring the safety of the Three Gorges Dam. For a 1,000‐year flood on the basis of a highly destructive flood in 1954, this paper evaluates scheduling schemes in which flood diversion areas are or are not used. The schemes are simulated based on 2.5‐m resolution reservoir topography and an optimized model of dynamic capacity flood regulation. The simulation results show the following. (a) In accord with the normal flood‐control regulation discharge, the maximum water level above the dam should be not more than 175 m, which ensures the safety of the dam and reservoir area. However, it is necessary to utilize the flood diversion areas within the Jingjiang area, and flood discharge can reach 2.81 billion m³. (b) In the case of relying on the TGR to impound floodwaters independently rather than using the flood diversion areas, the maximum water level above the dam reaches 177.35 m, which is less than the flood check level of 180.4 m to ensure the safety of the Three Gorges Dam. The average increase of the TGR water level in the Chongqing area is not more than 0.11 m, which indicates no significant effect on the upstream reservoir area. Comparing the various scheduling schemes, when the flood diversion areas are not used, it is believed that the TGR can execute safe flood control for a 1,000‐year flood, thereby greatly reducing flood damage.  相似文献   

海水中铯-137的γ能谱测量不确定度评估     

魏计房  邓春梅  王荣元  王伟  张馨星  姚海燕  张蒙蒙  丁凯 《海洋学报》2018,40(8):20-28

为科学评价测量结果的可靠性，对海水中137Cs γ能谱分析方法的不确定度进行了评估。根据《化学分析中不确定度的评估指南》，分析不确定度的来源并逐一对各不确定度分量进行了量化，最终计算了合成相对标准不确定度。结果表明，影响海水中137Cs γ能谱测量不确定度的因素分别为样品源137Cs峰区计数、标准源活度、取样体积、化学回收率、本底137Cs峰区计数及标准源137Cs峰区计数，其中样品源137Cs峰区计数的不确定度贡献最为突出。对于137Cs活度浓度为1.28 mBq/L的海水样品，其合成相对标准不确定度为9.78%。  相似文献   

Transcriptome assembly of Modiolus modiolus and comparative analysis with Bathymodiolus platifrons     

MENG Jie  YANG Mei  XU Fei  LI Xinzheng  LI Li 《海洋学报(英文版)》2018,(8)

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机载条纹管成像激光雷达在拍岸区探测水雷          下载免费PDF全文

王力  刘峡  王玥  吴中平 《数字海洋与水下攻防》2018,1(1):30-33

为了解决拍岸区水雷探测的问题，以无人机为载体的条纹管成像蓝绿激光雷达可以用来扫描、识别水雷，蓝绿激光成像雷达白天和夜晚均可以稳定成像，机载探测方式相对于水下、水面等传统探测方式效率也可以提高，机载激光雷达可由小型船舶、小型汽车等多平台携带使用。  相似文献   

Relation of Velocity Distribution and Mass for DA White Dwarfstwo     

Xiao-bo Gong  Li-fang Li 《Chinese Astronomy and Astrophysics》2018,42(2):202-212

White dwarfs are the evolutionary endpoint of the low-and-medium mass stars. In the studies of white dwarfs, the mass of white dwarf is an important physical parameter. In this paper, we give an analysis about the velocity distribution of DA white dwarfs in the Sloan Digital Sky Survey (SDSS), and hope to find the relation between mass and velocity distribution of white dwarfs. We get the radial velocity and tangential velocity of every DA white dwarf according to their proper motion and spectral shift. Through analyzing the velocity distribution of DA white dwarfs, we find that the small-mass white dwarfs, which are produced from the single-star evolution channel, have a relatively large velocity dispersion.  相似文献   

The nature of the L chondrite parent body's disruption as deduced from high-pressure phases in the Sixiangkou L6 chondrite          下载免费PDF全文

Shaolin Li  Weibiao Hsu 《Meteoritics & planetary science》2018,53(10):2107-2122

The disruption of the L chondrite parent body (LCPB) at ~470 Ma is currently the best-documented catastrophic celestial impact event, based on the large number of L chondritic materials associated with this event. Uranium-lead (U-Pb) dating of apatite and its high-pressure decomposition product, tuite, in the Sixiangkou L6 chondrite provides a temporal link to this event. The U-Pb system of phosphates adjacent to shock melt veins was altered to varying degrees and the discordance of the U-Pb system correlates closely with the extent of apatite decomposition. This suggests that the U-Pb system of apatite could be substantially disturbed by high-temperature pulse during shock compression from natural impacts, at least on the scale of mineral grains. Although many L chondrites can be temporally related to the catastrophic LCPB impact event, the shock conditions experienced by each individual meteorite vary. This could be due to the different geologic settings of these meteorites on their parent body. The shock pressure and duration derived from most meteorites may only reflect local shock features rather than the impact conditions, although they could provide lower limits to the impact conditions. The Sixiangkou shock duration (~4 s), estimated from high-pressure transformation kinetics, provides a lower limit to the high-pressure pulse of the LCPB disruption impact. Combined with available literature data of L chondrites associated with this impact event, our results suggest that the LCPB suffered a catastrophic collision with a large projectile (with a diameter of at least 18–22 km) at a low impact velocity (5–6 km s⁻¹). This is consistent with astronomical estimates based on the dynamical evolution of L chondritic asteroids.  相似文献   

Analytical study of ground motion caused by seismic wave propagation across faulted rock masses          下载免费PDF全文

J.C. Li  N.N. Li  S.B. Chai  H.B. Li 《国际地质力学数值与分析法杂志》2018,42(1):95-109

Studying seismic wave propagation across rock masses and the induced ground motion is an important topic, which receives considerable attention in design and construction of underground cavern/tunnel constructions and mining activities. The current study investigates wave propagation across a rock mass with one fault and the induced ground motion using a recursive approach. The rocks beside the fault are assumed as viscoelastic media with seismic quality factors, Q_p and Q_s. Two kinds of interactions between stress waves and a discontinuity and between stress waves and a free surface are analyzed, respectively. As the result of the wave superposition, the mathematical expressions for induced ground vibration are deduced. The proposed approach is then compared with the existing analysis for special cases. Finally, parametric studies are carried out, which includes the influences of fault stiffness, incident angle, and frequency of incident waves on the peak particle velocities of the ground motions.  相似文献   

An algorithm to resolve γ-rays from charged cosmic rays with DAMPE     

Zun-Lei Xu  Kai-Kai Duan  Zhao-Qiang Shen  Shi-Jun Lei  Tie-Kuang Dong  Fabio Gargano  Simone Garrappa  Dong-Ya Guo  Wei Jiang  Xiang Li  Yun-Feng Liang  Mario Nicola Mazziotta  Maria Fernanda Munoz Salinas  Meng Su  Valerio Vagelli  Qiang Yuan  Chuan Yue  Jing-Jing Zang  Ya-Peng Zhang  Yun-Long Zhang  Stephan Zimmer 《天文和天体物理学研究(英文版)》2018,(3)

The DArk Matter Particle Explorer(DAMPE),also known as Wukong in China,which was launched on 2015 December 17,is a new high energy cosmic ray and γ-ray satellite-borne observatory.One of the main scientific goals of DAMPE is to observe Ge V-Te V high energy γ-rays with accurate energy,angular and time resolution,to indirectly search for dark matter particles and for the study of high energy astrophysics. Due to the comparatively higher fluxes of charged cosmic rays with respect to γ-rays,it is challenging to identify γ-rays with sufficiently high efficiency,minimizing the amount of charged cosmic ray contamination. In this work we present a method to identify γ-rays in DAMPE data based on Monte Carlo simulations,using the powerful electromagnetic/hadronic shower discrimination provided by the calorimeter and the veto detection of charged particles provided by the plastic scintillation detector. Monte Carlo simulations show that after this selection the number of electrons and protons that contaminate the selected γ-ray events at～10 Ge V amounts to less than 1% of the selected sample.Finally,we use flight data to verify the effectiveness of the method by highlighting known γ-ray sources in the sky and by reconstructing preliminary light curves of the Geminga pulsar.  相似文献