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After a brief introduction to gravitational lensing theory, a rough overview of the types of gravitational lensing statistics that have been performed so far will be given. I shall then concentrate on recent results of galaxy-galaxy lensing, which indicate that galactic halos extend much further than can be probed via rotation of stars and gas. 相似文献
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Thomas H. Reiprich Kaustuv Basu Stefano Ettori Holger Israel Lorenzo Lovisari Silvano Molendi Etienne Pointecouteau Mauro Roncarelli 《Space Science Reviews》2013,177(1-4):195-245
Until recently, only about 10 % of the total intracluster gas volume had been studied with high accuracy, leaving a vast region essentially unexplored. This is now changing and a wide area of hot gas physics and chemistry awaits discovery in galaxy cluster outskirts. Also, robust large-scale total mass profiles and maps are within reach. First observational and theoretical results in this emerging field have been achieved in recent years with sometimes surprising findings. Here, we summarize and illustrate the relevant underlying physical and chemical processes and review the recent progress in X-ray, Sunyaev–Zel’dovich, and weak gravitational lensing observations of cluster outskirts, including also brief discussions of technical challenges and possible future improvements. 相似文献
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The Warm-Hot Intergalactic Medium (WHIM) is thought to contribute about 40–50% to the baryonic budget at the present evolution
stage of the universe. The observed large scale structure is likely to be due to gravitational growth of density fluctuations
in the post-inflation era. The evolving cosmic web is governed by non-linear gravitational growth of the initially weak density
fluctuations in the dark energy dominated cosmology. Non-linear structure formation, accretion and merging processes, star
forming and AGN activity produce gas shocks in the WHIM. Shock waves are converting a fraction of the gravitation power to
thermal and non-thermal emission of baryonic/leptonic matter. They provide the most likely way to power the luminous matter
in the WHIM. The plasma shocks in the WHIM are expected to be collisionless. Collisionless shocks produce a highly non-equilibrium
state with anisotropic temperatures and a large differences in ion and electron temperatures. We discuss the ion and electron
heating by the collisionless shocks and then review the plasma processes responsible for the Coulomb equilibration and collisional
ionisation equilibrium of oxygen ions in the WHIM. MHD-turbulence produced by the strong collisionless shocks could provide
a sizeable non-thermal contribution to the observed Doppler parameter of the UV line spectra of the WHIM. 相似文献
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Understanding of the planetary interiors depends upon our knowledge of the equations of state and of the transport properties of matter at high pressures and temperatures. The present status of this knowledge in relation to hydrogen and helium is discussed in detail including electrical and thermal conductivity, viscosity, diffusivity, etc. On this basis the various possible models of the internal structure of Jupiter and of Saturn are presented and their agreement with observational constraints such as the multipole gravitational coefficients analyzed. Relevance of planetary magnetic fields, basic atmospheric information and the Great Red Spot of Jupiter to the models of the interiors are discussed. 相似文献
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Terrestrial planets are accreted in a disk orbiting a central star. The basic challenge of their formation consists of assembling
micron-sized or smaller dust grains to bodies with over 104 km in diameter. This formation process, ultimately based on collisions, occurs in three very different physical regimes depending
upon the size of the bodies present: 1) Early on, micron- to mm-sized dust grains, chondrules and chondrites are strongly
coupled to the gas. 2) As they grow larger, gravity increases the collisional cross section allowing runaway growth to occur.
3) After this runaway phase stops from exhaustion of matter in the immediate surroundings of the protoplanets, further growth
occurs on timescales typical of mutual gravitational perturbations. The emphasis of this book is on the timescales corresponding
to these formation phases as well as the characteristic chemical and isotopic composition of the bodies involved.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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以任意相控阵天线式空间太阳能电站为研究对象,主要研究了其在轨运行过程中受到的重力姿轨耦合效应对其轨道运动的影响。首先,通过Hamilton原理建立起考虑重力姿轨耦合效应时的姿态运动和轨道运动的方程。其中,任意相控阵天线式空间太阳能电站被简化成刚体,它的重力势能以其结构尺寸和其轨道半径的比值为小量进行泰勒展开,并保留至二阶项。之后,采用解析的方法对方程进行分析,并发现当电站的姿态运动满足一定条件时,其轨道运动将会出现共振现象。此外,重力姿轨耦合效应还会引起空间太阳能电站轨道运动长期的漂移,通过选择合适的轨道运动初始条件可以消除漂移;而且,在一定条件下,重力姿轨耦合效应还会引起轨道运动的发散。最后,数值仿真结果验证了分析的正确性。 相似文献
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We consider the influence of the nonlinear stage of gravitational instability on the two-point correlation functions of gravitationally bound objects. Based on the theory of nonlinear gravitational contraction of a single density peak of dissipationless matter (Gurevich and Zybin, 1988a,b; 1990) we develop a method for calculating the two-point correlation functions of different objects of any mass. The method works good in the region of strong correlations and can be easily extended to calculate higher correlation functions. We show that the main contribution to the correlation function i in the region of strong correlations i 1 is made by pair systems located outside large clusters of objects. In this region the shape of i is determined only by the nonlinear dynamics of gravitational contraction of dissipationless matter and has the form i C
–, where 1.8 is a universal parameter. 相似文献
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摄动对编队飞行星座相对构型的影响分析 总被引:4,自引:0,他引:4
在近圆轨道编队飞行的假设条件下,根据动力学关系推导出了环绕卫星相对参考卫星的运动学简化模型,并以此简化模型为基础,分别研究了大气阻力摄动、日月引力摄动、太阳光压摄动和地球扁率摄动对编队飞行星座的构型影响,着重分析了地球扁率摄动周期项和长期项对构型的影响,并以此对编队轨道设计提出建议。 相似文献
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Certain meteoritical inclusions contain evidence for the existence of short-lived radioactivities such as 26Al and 41Ca at the time of their formation 4.566 billion years ago. Because the half-lives of these nuclides are so short, this evidence
requires that no more than about a million years elapsed between their nucleosynthesis and their inclusion in cm-sized solids
in the solar nebula. This abbreviated time span can be explained if these nuclides were synthesized in a stellar source such
as a supernova, and were then transported across the interstellar medium by the resulting shock wave, which then triggered
the gravitational collapse of the presolar molecular cloud core. Detailed 2D and 3D numerical hydrodynamical models are reviewed
and show that such a scenario is consistent with the time scale constraint, and with the need to both trigger collapse and
to inject shock-wave matter into the collapsing protostellar cloud and onto the protoplanetary disk formed by the collapse.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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López-Valverde Miguel A. Gerard Jean-Claude González-Galindo Francisco Vandaele Ann-Carine Thomas Ian Korablev Oleg Ignatiev Nikolai Fedorova Anna Montmessin Franck Määttänen Anni Guilbon Sabrina Lefevre Franck Patel Manish R. Jiménez-Monferrer Sergio García-Comas Maya Cardesin Alejandro Wilson Colin F. Clancy R. T. Kleinböhl Armin McCleese Daniel J. Kass David M. Schneider Nick M. Chaffin Michael S. López-Moreno José Juan Rodríguez Julio 《Space Science Reviews》2018,214(1):1-31
Space Science Reviews - Time measured by an ideal clock crucially depends on the gravitational potential and velocity of the clock according to general relativity. Technological advances in... 相似文献
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Pulsars are natural cosmic clocks. On long timescales they rival the precision of terrestrial atomic clocks. Using a technique called pulsar timing, the exact measurement of pulse arrival times allows a number of applications, ranging from testing theories of gravity to detecting gravitational waves. Also an external reference system suitable for autonomous space navigation can be defined by pulsars, using them as natural navigation beacons, not unlike the use of GPS satellites for navigation on Earth. By comparing pulse arrival times measured on-board a spacecraft with predicted pulse arrivals at a reference location (e.g. the solar system barycenter), the spacecraft position can be determined autonomously and with high accuracy everywhere in the solar system and beyond. We describe the unique properties of pulsars that suggest that such a navigation system will certainly have its application in future astronautics. We also describe the on-going experiments to use the clock-like nature of pulsars to “construct” a galactic-sized gravitational wave detector for low-frequency (\(f_{GW}\sim 10^{-9} \text{--} 10^{-7}\) Hz) gravitational waves. We present the current status and provide an outlook for the future. 相似文献
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For the navigation algorithm of the strapdown inertial navigation system, by comparing to the equations of the dual quaternion and quaternion, the superiority of the attitude algorithm based on dual quaternion over the ones based on rotation vector in accuracy is analyzed in the case of the rotation of navigation frame. By comparing the update algorithm of the gravitational velocity in dual quaternion solution with the compensation algorithm of the harmful acceleration in traditional velocity solution, the accuracy advantage of the gravitational velocity based on dual quaternion is addressed. In view of the idea of the attitude and velocity algorithm based on dual quaternion, an improved navigation algorithm is proposed, which is as much as the rotation vector algorithm in computational complexity. According to this method, the attitude quaternion does not require compensating as the navigation frame rotates. In order to verify the correctness of the theoretical analysis, simulations are carried out utilizing the software, and the simulation results show that the accuracy of the improved algorithm is approximately equal to the dual quaternion algorithm. 相似文献
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Recent works on the determination of the earth gravitational potential by its dynamical effects to the motion of artificial satellite are reviewed. Future programs to improve the results and to detect from observations effects due to earth tide and any other time variations of the potential to the satellite motions are discussed. 相似文献
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The tensor characteristics of the inertial fields created by acceleration and rotation, and the gravitational fields created by masses are discussed. Although it is sometimes thought that it is impossible to distinguish between gravitational and inertial effects because of Einstein's principle of equivalence, these effects do have different, detectable tensor characteristics. The principle of equivalence is only strictly applicable at a point, while the instruments to measure these tensor fields exist over a finite region. The inertial field created by acceleration is a uniform vector field and has no gradients, while the inertial field created by rotation has a uniform cylindrically symmetric tensor gradient but none of higher order. The gravitational field created by a mass is highly nonuniform with essentially no limit to the number of higher order gradients. These differences make it theoretically possible to independently measure gravitation, rotation, and acceleration effects; to do so, some form of differential force sensor with tensor response characteristics must be used. The standard technique is static, using differential accelerometers to sense the spatial gradient characteristics of the fields. A more promising technique is dynamic; by rotation of the differential sensor, the static spatial variations are transformed into temporal variations with various frequency components. It is then possible to distinguish between the various fields by frequency filtering. 相似文献
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Matthias Maat 《Space Science Reviews》2010,151(1-3):149-157
Satellites in low Earth orbits are influenced by the Earth’s atmosphere. The interactions between the molecules and the spacecraft cause the highest non-gravitational force, which in magnitude is comparable to planetary disturbances. Therefore the modelling of atmospheric drag effects is important for many missions with a scientific background like STEP (Satellite Test of Equivalence Principle). With the STEP mission variations between gravitational and inertial mass shall be measured with an accuracy of 10?18. The results are of great interest for cosmological and gravitational theories. To achieve the aimed accuracy, a precise model of external disturbances is necessary. In this article the method of Ray-Tracing is used to quantify the atmospheric drag forces and torques for spacecrafts of arbitrary shape. 相似文献