Ellipsoids, material points and material segments

Simple models of potential based on material points and material segments are confronted with a homogeneous ellipsoid potential. A spheroid is approximated with a pair of material points or with one material segment. The segment model proves to be more accurate. For a triaxial ellipsoid, two models are considered: one with five material points and one with two material segments and a point. When their parameters are determined with the fourth sectorial harmonic ignored, both simple models have a similar approximation error. Numerical tests indicate that the approximate models of a triaxial ellipsoid are 5 to 10 times faster than exact formulation, whereas for a spheroid the approximate models are at most twice as fast as the exact formulae.     

Ceres,a wet planet: The view after Dawn

Ceres, a nearly 1000-km diameter body located in the Solar System’s main asteroid belt, has been classified under many categories: planet, comet, asteroid, minor planet and, presently, dwarf planet. No matter what the designation, Ceres has experienced major planetary processes. Its evolution has been controlled by water, making it a most unusual, interesting and accessible inner Solar System object that can inform the evolution of outer Solar System moons and other dwarf planets. Early telescopic observations suggested a hydroxylated mineralogy similar to carbonaceous chondrite meteorites and a size and mass indicating a bulk density that implied a water content of 17?27 wt%. Thermodynamic modeling of Ceres’ evolution indicated that thermal aqueous evolution likely occurred. The Dawn Mission produced a huge increase in our understanding of Ceres, confirming but vastly extending the early knowledge. Dawn, carrying multispectral cameras, a visible-infrared imaging spectrometer and a nuclear spectrometer, orbited Ceres between 2015–2018 (after orbiting Vesta) at a number of different altitudes, ultimately reaching 35 km from the surface at periapsis. Observations of almost the entire surface and gravity field mapping revealed multiple geological and internal features attributed to the effects of water. The surface displays cryovolcanic-like and flow structures, exposed phyllosilicates, carbonates, evaporites and water ice. The subsurface shows partial differentiation, decreasing viscosity with depth, and lateral density heterogeneity. Ceres appears to be geologically active today and possesses liquid water/brine pockets or even an extended liquid layer in the interior, confirming an “Ocean World” designation in today’s vernacular.     

北京地区小震精定位结果初步探讨

利用双差重定位方法对北京地区(39.2°N～41.2°N,115.2°E～117.6°E)2008年10月至2020年3月期间共6463个地震事件进行重新定位,得到4776个高质量地震事件的空间位置分布。定位结果均方根走时残差显著降低,震源间的相对位置精度明显提高,地震活动的成丛性与活动断层之间的关系更加密切。根据重定位结果探讨了小震活动与活动断裂及深浅构造的关系,得到以下结论:夏垫断裂小震活动强烈,重定位后震中分布明显向断裂靠拢,呈现沿断裂走向延伸的NE向线状分布。结合人工剖面探测结果推测,该区域深度剖面上小震集中带10km深度附近较宽的丛集区主要是浅部铲形断裂活动所致,14～22km深度附近相对较窄近直立的小震丛集为深部断裂活动产生。怀—涿次级盆地北缘断裂现今小震活动活跃,该区域小震深度剖面揭示该断裂为倾向南东、上陡下缓的铲形断层。结合人工剖面探测结果,分析认为该区域深浅断裂共存和非均匀的地壳结构为中强地震发生的深部构造背景。平原区内部小震分布与第四纪断陷盆地和地层厚度分布存在较强的相关性,研究区域内部昌平—海淀小震集中区、顺义小震集中区、夏垫小震丛集区和廊坊小震丛集区分别位于马池口—沙河断陷盆地、顺义断陷盆地、大厂断陷盆地和固安—廊坊—永清断陷盆地。根据小震空间密集成带分布特征来推测未知断裂,推测怀柔南部山区小震集中区下方存在隐伏断层,宝坻至夏垫断裂段之间NW向的小震集中分布区下方存在一条走向NW或者NWW的隐伏断层。     

小基线集合成孔径雷达干涉测量算法及其应用

针对地理国情监测中地表形变监测研究不足的现状,文章在分析常规DInSAR特点及趋势性发展的基础上,结合地理国情监测的尺度特征与实际需求,给出了小基线集(SBAS-InSAR)算法原理;并比较了与永久散射体(PS-InSAR)算法的异同点;在此基础上,选取试验区,获取了COSMO-SkyMed雷达卫星数据,采用SBAS-InSAR算法,提取了试验区时间序列地表形变量与形变速率。结果表明:SBAS-InSAR算法可以利用比较适中的数据量获取到较高精度的反演结果,能够满足地理国情监测的实际需要,在地理国情监测中具有很好的适用性和可行性。     

A method to measure enforcement effort in shipping with incomplete information

Current methods in the shipping industry to evaluate performance do not account for differences in fleet profiles of registries such as age, size or ship type and not for bad luck. This can lead to unfair evaluation of enforcement efforts of the international standards. Furthermore, incentives to improve performance are concentrated on decreasing detentions rather than incidents. This article proposes a new method to a longstanding problem to evaluate performance that rectifies shortcomings of the method currently used. The proposed method measures the enforcement effort by means of proxy variables and introduces incentives for improvement that go beyond the currently used 'detention'. The aim is to provide a fair and transparent way. The proposed method is applied and results are compared with methods currently used to demonstrate how the rankings change. The method can be adapted to other areas of the shipping industry such as classification societies or ship management companies.     

KAM tori for N-body problems: a brief history

We review analytical (rigorous) results about the existence of invariant tori for planetary many-body problems.     

对豫西小秦岭太华群的重新认识

太华群具明显的两分性特征，下亚群属下部基底岩系，原岩为拉斑玄武岩及ＴＴＧ岩系；上亚群属上部基底岩系，具孔达岩系特征的一套沉积变质岩。根据生物地层学、岩石地层学、构造地层学、同位素年代学，提出了小秦岭地区的太华群上下亚群是不同地质时期、不同构造环境下的产物，下亚群时代为晚太古代，上亚群时代为古元古代，故太华群应予以解体．或给以新的内涵。     

Improving livelihoods in fishing communities of West Sumatra: More than just boats and machines

Despite a raft of livelihood programs designed to help Indonesian small-scale fishers there are concerns that the needs of the poor are still not being addressed. This study examines this concern through a two-pronged approach. Firstly, through a broad-scale series of interviews with fishers, community leaders and government employees in 25 fishing villages in the province of West Sumatra to identify which sectors of the fishing industry the poor operate in and the types of livelihood initiatives targeted at helping them. Secondly, by using three case studies of livelihood development projects and identifying the social, economic and institutional lessons learned that point both to best and worst practice. Three groups of poor fishers were identified; a large group of non-boat owning “labourers”, a group of “small-scale boat owners” and a small group of “processors and sellers”. Empowerment programs by the Department for Fisheries between 2005 and 2009 emphasised improving physical capital through providing fishing gear, motorisation and processing equipment. These initiatives could potentially help small-boat owners but would not benefit non-boat owning labourers. The new livelihood improvement programme GPEMP had non-fishing alternative livelihoods that could help labourers, but still demonstrated an ongoing bias towards physical capital interventions. The three case studies demonstrated that aspects of leadership, trust, advocacy, administration, accountability and ongoing institutional support are key elements of empowering coastal communities towards livelihood improvement. Human and social capital components need prioritisation in future poverty alleviation policy and programs in Indonesia, particularly for the large marginalised group of labourers.     

由地震分布丛集性给出断层参数的一种新方法

由于大范围内地质构造的复杂性和介质的非均匀性,发震断层面的几何形态一般十分复杂.如果大地震的破裂过程涉及多个断层的活动,则发震断层并非是单一断层平面,而是多个断层面的组合.利用地震空间位置分布丛集性,即震源点成丛位于断层面附近的假设,结合稳健扩充算法和主成分分析给出一种可以重构活断层网络三维空间结构的新方法.该方法每次从震源点集中处开始,利用假设检验扩充子断层面,并得到多个子断层面.接着按震源点属于最近断层面的准则把各子断层面内的震源点进行竞争,并根据一定假设合并和删除一些子断层面,最后用主成分分析确定每个子断层面参数.于是可根据地震事件目录给出一组矩形区域来描述断层面网络结构,其中每个矩形断层面由其位置、走向和倾角确定.通过计算机模拟发现,新方法可成功地重建模拟地震目录的断层面,最后用于南加州1992年6月28日发生的Landers地震部分余震目录中,得到各个子断层面参数与已知地质破裂或隐伏断层相当一致.