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GPS Solutions - Recently, 3D building models have become an important aid to many positioning methods such as LiDAR and GPS positioning. Creating an accurate 3D building model requires accurate 2D... 相似文献
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Far-infrared properties of metallic particle are reinvestigated in detail. In the far-infrared region, absorption due to the eddy current generally dominates over that obtained by using the Rayleigh approximation erroneusly. The wavelength dependence of the eddy current term is examined carefully and shown to be less steep than that predicted by the Rayleigh approximation for dust grains larger than 100 nm in radius. It also depends more sensitively on the grain size. A wider temperature distribution is expected corresponding to a given size distribution and hence the emission spectrum becomes less steep than the preductions by the Rayleigh approximation. Iron and graphite particles are investigated as typical interstellar metallic grains. Effects of coating of dielectric materials are also examined. Comparisons with experimental results and with observations are discussed. 相似文献
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The current low-cost global navigation satellite systems (GNSS) receiver cannot calculate satisfactory positioning results for pedestrian applications in urban areas with dense buildings due to multipath and non-line-of-sight effects. We develop a rectified positioning method using a basic three-dimensional city building model and ray-tracing simulation to mitigate the signal reflection effects. This proposed method is achieved by implementing a particle filter to distribute possible position candidates. The likelihood of each candidate is evaluated based on the similarity between the pseudorange measurement and simulated pseudorange of the candidate. Finally, the expectation of all the candidates is the rectified positioning of the proposed map method. The proposed method will serve as one sensor of an integrated system in the future. For this purpose, we successfully define a positioning accuracy based on the distribution of the candidates and their pseudorange similarity. The real data are recorded at an urban canyon environment in the Chiyoda district of Tokyo using a commercial grade u-blox GNSS receiver. Both static and dynamic tests were performed. With the aid of GLONASS and QZSS, it is shown that the proposed method can achieve a 4.4-m 1σ positioning error in the tested urban canyon area. 相似文献
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Fine particles of various chemical substances—carbon, iron, iron oxide and silica—which are expected to exist in interstellar space are prepared in argon gas. The size, shape, and crystal structure of the powder particles are studied by electron microscopy and electron diffraction, and may have some bearing on models of comets and of the solar nebula.The largest size we have obtained is about 0.1 μm and the smallest about 40Å. Generally the size becomes smaller for lower temperature and also for lower pressure. This tendency is discussed in connection with nucleation theories. Except for iron and iron oxide the powder particles have no crystal structure. 相似文献
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Fumio Kamijo 《Astrophysics and Space Science》1991,181(1):147-152
This Letter reviews the results by computer simulations on the three-body problem carried out at Leningrad University Astronomical Observatory (Anosova, 1986, 1988, 1989). The intensive systematic studies of triple systems with negative and positive total energies have yielded the general features of the evolution of these systems. The processes of formation of the wide and hard binaries have been studied in details. The scenario of the general class of the final motions of the triple systems with negative total energy is considered, the necessary conditions of disruption of these systems are formulated. 相似文献
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The clustering of fine particles by mutual thermal collisions is investigated experimentally. Fine particles are prepared in an argon gas atmosphere by the gas evaporation technique. Mass distributions of clusters of the particles are obtained from micrographs of specimen grids placed at different heights above the evaporating source. The cluster growth is clearly seen in the change of mass distribution with height. A comparison of the experimental results with a theoretical model indicates that the cluster of fine particles does not grow in the spherical manner usually assumed, but in a planar manner. As an important consequence of the conclusion to the primordial solar nebula, the sedimentation time of the grains sinking towards the equatorial plane of the solar disk becomes longer than the value previously adopted because of the large ratio of surface to volume of a planar cluster. This longer time should alter the scenario of the evolution of the solar system after sedimentation.Invited contribution to the Proceedings of a Workshop onThermodynamics and Kinetics of Dust Formation in the Space medium held at the Lunar and Planetary Institute, Houston, 6–8 September, 1978. 相似文献
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Vibration of a two-component disordered chain of 500 atoms is investigated. The mass ratio is 28:16. Squared frequency-spectra are obtained for several cases with different degrees of disorder. For a simple case eigenvectors are also calculated to show that there exists a local vibration mode at disorder. If there is an additional impurity atom in the chain, there appear localized vibration modes at the impurity atom above the optical branch and between the optical and the acoustical branches. Vibration of the chain with variable force constants, which are governed by a probability distribution, is studied as a model for a glassy substance.Invited contribution to the Proceedings of a Workshop onThermodynamics and Kinetics of Dust Formation in the Space Medium held at the Lunar and lanetary Institute, Houston, 6–8 September, 1978. 相似文献
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