海王星特洛伊小天体动力学

特洛伊小天体与行星同享一个轨道,并与太阳、行星在空间构成等边三角形,最早为人们所知的特洛伊小天体是位于木星轨道上并位于木星前(后)方60°的两群小天体.而海王星特洛伊小天体则是近20年来太阳系内最重要的发现之一.观测证据表明海王星特洛伊小天体的总数量和总质量远超过木星特洛伊小天体和主带小行星,是太阳系内仅次于柯伊伯带的第二大小天体集群.它们一方面具有独特的轨道特征,另一方面又联系着海王星轨道内、外的空间,自然而然地成为检验太阳系起源与演化的试金石.我们简要介绍了对海王星特洛伊小天体的观测结果、对它们的轨道动力学和起源研究的进展.     

Earth's Trojan asteroid

It was realized in 1772 that small bodies can stably share the same orbit as a planet if they remain near 'triangular points' 60° ahead of or behind it in the orbit. Such 'Trojan asteroids' have been found co-orbiting with Jupiter, Mars and Neptune. They have not hitherto been found associated with Earth, where the viewing geometry poses difficulties for their detection, although other kinds of co-orbital asteroid (horseshoe orbiters and quasi-satellites) have been observed. Here we report an archival search of infrared data for possible Earth Trojans, producing the candidate 2010 TK(7). We subsequently made optical observations which established that 2010 TK(7) is a Trojan companion of Earth, librating around the leading Lagrange triangular point, L(4). Its orbit is stable over at least ten thousand years.     

Origin of the orbital architecture of the giant planets of the Solar System

Planetary formation theories suggest that the giant planets formed on circular and coplanar orbits. The eccentricities of Jupiter, Saturn and Uranus, however, reach values of 6 per cent, 9 per cent and 8 per cent, respectively. In addition, the inclinations of the orbital planes of Saturn, Uranus and Neptune take maximum values of approximately 2 degrees with respect to the mean orbital plane of Jupiter. Existing models for the excitation of the eccentricity of extrasolar giant planets have not been successfully applied to the Solar System. Here we show that a planetary system with initial quasi-circular, coplanar orbits would have evolved to the current orbital configuration, provided that Jupiter and Saturn crossed their 1:2 orbital resonance. We show that this resonance crossing could have occurred as the giant planets migrated owing to their interaction with a disk of planetesimals. Our model reproduces all the important characteristics of the giant planets' orbits, namely their final semimajor axes, eccentricities and mutual inclinations.     

Discovery of 12 satellites of Saturn exhibiting orbital clustering.

The giant planets in the Solar System each have two groups of satellites. The regular satellites move along nearly circular orbits in the planet's orbital plane, revolving about it in the same sense as the planet spins. In contrast, the so-called irregular satellites are generally smaller in size and are characterized by large orbits with significant eccentricity, inclination or both. The differences in their characteristics suggest that the regular and irregular satellites formed by different mechanisms: the regular satellites are believed to have formed in an accretion disk around the planet, like a miniature Solar System, whereas the irregulars are generally thought to be captured planetesimals. Here we report the discovery of 12 irregular satellites of Saturn, along with the determinations of their orbits. These orbits, along with the orbits of irregular satellites of Jupiter and Uranus, fall into groups on the basis of their orbital inclinations. We interpret this result as indicating that most of the irregular moons are collisional remnants of larger satellites that were fragmented after capture, rather than being captured independently.     

A low density of 0.8 g cm(-3) for the Trojan binary asteroid 617 Patroclus

The Trojan population consists of two swarms of asteroids following the same orbit as Jupiter and located at the L4 and L5 stable Lagrange points of the Jupiter-Sun system (leading and following Jupiter by 60 degrees ). The asteroid 617 Patroclus is the only known binary Trojan. The orbit of this double system was hitherto unknown. Here we report that the components, separated by 680 km, move around the system's centre of mass, describing a roughly circular orbit. Using this orbital information, combined with thermal measurements to estimate the size of the components, we derive a very low density of 0.8(- 0.1)+0.2 g cm(-3). The components of 617 Patroclus are therefore very porous or composed mostly of water ice, suggesting that they could have been formed in the outer part of the Solar System.     

Origin of the obliquities of the giant planets in mutual interactions in the early Solar System

The origin of the spin-axis orientations (obliquities) of the giant planets is a fundamental issue because if the obliquities resulted from tangential collisions with primordial Earth-sized protoplanets, then they are related to the masses of the largest planetesimals out of which the planets form. A problem with this mechanism, however, is that the orbital planes of regular satellites would probably be uncorrelated with the obliquities, contrary to observations. Alternatively, they could have come from an external twist that affected the orientation of the Solar System plane; but in this model, the outer planets must have formed too rapidly, before the event that produced the twist. Moreover, the model cannot be quantitatively tested. Here I show that the present obliquities of the giant planets were probably achieved when Jupiter and Saturn crossed the 1:2 orbital resonance during a specific migration process: different migration scenarios cannot account for the large observed obliquities. The existence of the regular satellites of the giant planets does not represent a problem in this model because, although they formed soon after the planetary formation, they can follow the slow evolution of the equatorial plane it produces.     

一种基于网络行为分析的HTTP木马检测模型

基于HTTP协议进行网络通信的木马能够躲避部分网络安全监控系统的检测,是互联网安全的一个重大威胁。通过对该类木马样本和普通程序样本网络行为的对比分析,得到该类木马的6个网络行为特征,综合利用层级聚类、Davies-Bouldin指数和k-means聚类方法提出了一种木马检测模型,实现了HTTP木马检测。结果表明,该HTTP木马检测模型准确率较高,误报率较低。     

基于有限状态机的硬件木马设计和插入

针对集成电路设计和制造中存在的硬件木马问题, 提出一种新的模型来提高木马检测能力。该模型基于有限状态机, 比组合电路型木马难于触发和检测。同时, 木马电路插入位置的选择也可以有效规避路径延时检测方法。实验选择ISCAS’89基准电路中的S349作为目标电路, 对功能和延时信息进行仿真。实验结果表明, 这种类型的木马难于激活, 并且选择合适的插入位置可以有效隐藏延时信息。     

基于行为特征库的木马检测模型设计

目前木马检测的主流技术主要是特征码检测技术,而该技术提取特征码滞后,无法检测未知新型木马.为了更好的检测新型木马,详细归纳总结木马的行为特征,同时在此基础上提取木马通适性行为特征,构建木马行为特征库,设计了基于行为特征库的木马检测模型,并应用模糊模式识别方法判断木马程序.通过实验证明此模型可以对可疑程序的行为特征进行分析判断,较准确地识别木马程序.该检测模型是对基于特征码检测技术的强有力补充,在新型木马不断涌现的今天,基于木马行为特征检测技术具有重要的应用意义.     

基于SVM的木马流量特征检测方法

针对木马能以隐蔽的方式盗取用户敏感信息、文件资源或远程监控用户行为,对网络安全构成极大威胁,提出一种基于流量特征的木马检测方法,通过统计分析服务器端口有序性、服务器使用客户端端口号、客户端发包数、服务器端发包数等特征,使用支持向量机(support vector machine,SVM)算法进行分类训练并建立基于流量的木马监测模型;基于流量特征的普遍性和通用性,该方法对于未知木马也比较有效.仿真测试结果表明,所提出方法具备对常见木马或未知木马的良好检测能力,实验条件下盲检测准确率可达96.61%.     

HTDet:A Clustering Method Using Information Entropy for Hardware Trojan Detection

Hardware Trojans(HTs) have drawn increasing attention in both academia and industry because of their significant potential threat.In this paper,we propose HTDet,a novel HT detection method using information entropybased clustering.To maintain high concealment,HTs are usually inserted in the regions with low controllability and low observability,which will result in that Trojan logics have extremely low transitions during the simulation.This implies that the regions with the low transitions will provide much more abundant and more important information for HT detection.The HTDet applies information theory technology and a density-based clustering algorithm called Density-Based Spatial Clustering of Applications with Noise(DBSCAN) to detect all suspicious Trojan logics in the circuit under detection.The DBSCAN is an unsupervised learning algorithm,that can improve the applicability of HTDet.In addition,we develop a heuristic test pattern generation method using mutual information to increase the transitions of suspicious Trojan logics.Experiments on circuit benchmarks demonstrate the effectiveness of HTDet.     

Core formation in planetesimals triggered by permeable flow

The tungsten isotope composition of meteorites indicates that core formation in planetesimals occurred within a few million years of Solar System formation. But core formation requires a mechanism for segregating metal, and the 'wetting' properties of molten iron alloy in an olivine-rich matrix is thought to preclude segregation by permeable flow unless the silicate itself is partially molten. Excess liquid metal over a percolation threshold, however, can potentially create permeability in a solid matrix, thereby permitting segregation. Here we report the percolation threshold for molten iron-sulphur compounds of approximately 5 vol.% in solid olivine, based on electrical conductivity measurements made in situ at high pressure and temperature. We conclude that heating within planetesimals by decay of short-lived radionuclides can increase temperature sufficiently above the iron-sulphur melting point (approximately 1,000 degrees C) to trigger segregation of iron alloy by permeable flow within the short timeframe indicated by tungsten isotopes. We infer that planetesimals with radii greater than about 30 km and larger planetary embryos are expected to have formed cores very early, and these objects would have contained much of the mass in the terrestrial region of the protoplanetary nebula. The Earth and other terrestrial planets are likely therefore to have formed by accretion of previously differentiated planetesimals, and Earth's core may accordingly be viewed as a blended composite of pre-formed cores.     

Chaos-assisted capture of irregular moons

It has been thought that the capture of irregular moons--with non-circular orbits--by giant planets occurs by a process in which they are first temporarily trapped by gravity inside the planet's Hill sphere (the region where planetary gravity dominates over solar tides). The capture of the moons is then made permanent by dissipative energy loss (for example, gas drag) or planetary growth. But the observed distributions of orbital inclinations, which now include numerous newly discovered moons, cannot be explained using current models. Here we show that irregular satellites are captured in a thin spatial region where orbits are chaotic, and that the resulting orbit is either prograde or retrograde depending on the initial energy. Dissipation then switches these long-lived chaotic orbits into nearby regular (non-chaotic) zones from which escape is impossible. The chaotic layer therefore dictates the final inclinations of the captured moons. We confirm this with three-dimensional Monte Carlo simulations that include nebular drag, and find good agreement with the observed inclination distributions of irregular moons at Jupiter and Saturn. In particular, Saturn has more prograde irregular moons than Jupiter, which we can explain as a result of the chaotic prograde progenitors being more efficiently swept away from Jupiter by its galilean moons.     

Origin of the Moon's orbital inclination from resonant disk interactions

The Moon is generally believed to have formed from the debris disk created by a large body colliding with the early Earth. Recent models of this process predict that the orbit of the newly formed Moon should be in, or very near, the Earth's equatorial plane. This prediction, however, is at odds with the known history of the lunar orbit: the orbit is currently expanding, but can be traced back in time to reveal that, when the Moon formed, its orbital inclination relative to the Earth's equator was I approximately = 10 degrees. The cause of this initial inclination has been a mystery for over 30 years, as most dynamical processes (such as those that act to flatten Saturn's rings) will tend to decrease orbital inclinations. Here we show that the Moon's substantial orbital inclination is probably a natural result of its formation from an impact-generated disk. The mechanism involves a gravitational resonance between the Moon and accretion-disk material, which can increase orbital inclinations up to approximately 15 degrees.     

基于系统调用的安卓寄生木马的检测

在基于安卓操作系统的手机中,很多安全检测软件对独立存在的木马有很好的防范能力,却很难检测出依附于正常程序的寄生木马,文中提出一种新的安卓寄生木马检测方法,通过检测手机发送的数据包实时确定发送包的端口,再根据已确定的端口和系统提供的信息,将会发现通过该端口发送包的进程,接着追踪到创建该进程的应用程序,最后通过分析程序的系统调用序列判断其是否有寄生木马,仿真实验显示该方法可以有效地检测出安卓寄生木马。     

基于旁路分析的硬件木马检测方法

集成电路芯片在不受控的制造过程中可能会被嵌入恶意电路结构,形成硬件木马,这给集成电路芯片的可靠性和可信度带来了极大的隐患,而利用传统的测试技术很难发现这些硬件木马.针对这一问题,文中提出了一种非破坏性的、基于旁路分析的硬件木马检测方法,它通过对芯片功耗瞬态变化情况的分析,采用奇异值分解算法对功耗进行统计处理来检测芯片中的硬件木马.在FPGA芯片上的硬件验证结果表明,即使在测量噪声和工艺扰动较大的环境中,文中方法也能检测出面积比原始电路小2个数量级的硬件木马.     

钱德勒极移的激发机制研究

根据宋晓东等的地球内核差异旋转研究成果,提出“月球轨道运动改变地球各圈层角动量”的物理模型。太阳系星球（尤其是木星）在轨道运行过程中对月球的摄动会影响月球的轨道运动,月球轨道运动会改变地球各圈层角动量,在形成地核差异旋转的同时,也使地球液核远月半球的角动量与近月半球的角动量存在巨大落差,造成地轴的晃动,激发地球的钱德勒极移。     

Iron meteorites as remnants of planetesimals formed in the terrestrial planet region

Iron meteorites are core fragments from differentiated and subsequently disrupted planetesimals. The parent bodies are usually assumed to have formed in the main asteroid belt, which is the source of most meteorites. Observational evidence, however, does not indicate that differentiated bodies or their fragments were ever common there. This view is also difficult to reconcile with the fact that the parent bodies of iron meteorites were as small as 20 km in diameter and that they formed 1-2 Myr earlier than the parent bodies of the ordinary chondrites. Here we show that the iron-meteorite parent bodies most probably formed in the terrestrial planet region. Fast accretion times there allowed small planetesimals to melt early in Solar System history by the decay of short-lived radionuclides (such as 26Al, 60Fe). The protoplanets emerging from this population not only induced collisional evolution among the remaining planetesimals but also scattered some of the survivors into the main belt, where they stayed for billions of years before escaping via a combination of collisions, Yarkovsky thermal forces, and resonances. We predict that some asteroids are main-belt interlopers (such as (4) Vesta). A select few may even be remnants of the long-lost precursor material that formed the Earth.     

Rookit木马的隐藏机理与检测技术剖析

随着网络技术的发展，基于传统隐藏技术的木马已经很难生存，木马隐藏技术开始由Ring 3级转入Ring 0级．运行在Ring 0级的木马，拥有与系统核心同等级的权限，隐藏与伪装更为容易．笔者讨论了Windows内核系统服务调用机制，分析了删除进程双向链表中的进程对象、SSDT内核挂钩注册表隐藏、端口隐藏等Rootkit木马的隐藏机理，最后对Rookit木马的几种检测技术作了详细的剖析．研究内容对增强人们防患意识、更好地维护计算机系统的安全有一定的参考价值．     

An extrasolar giant planet in a close triple-star system

Hot Jupiters are gas-giant planets orbiting with periods of 3-9 days around Sun-like stars. They are believed to form in a disk of gas and condensed matter at or beyond approximately 2.7 astronomical units (au-the Sun-Earth distance) from their parent star. At such distances, there exists a sufficient amount of solid material to produce a core capable of capturing enough gas to form a giant planet. Subsequently, they migrate inward to their present close orbits. Here I report the detection of an unusual hot Jupiter orbiting the primary star of a triple stellar system, HD 188753. The planet has an orbital period of 3.35 days and a minimum mass of 1.14 times that of Jupiter. The primary star's mass is 1.06 times that of the Sun, 1.06 M(\circ). The secondary star, itself a binary stellar system, orbits the primary at an average distance of 12.3 au with an eccentricity of 0.50. The mass of the secondary pair is 1.63 M(\circ). Such a close and massive secondary would have truncated a disk around the primary to a radius of only approximately 1.3 AU (ref. 4) and might have heated it up to temperatures high enough to prohibit giant-planet formation, leaving the origin of this planet unclear.