VSOP Space VLBI observations of Pearson-Readhead survey sources

The VSOP Space VLBI mission uses the HALCA spacecraft, launched from Japan in February 1997, in conjunction with ground radio observatories around the world to create a high resolution radio-wavelength imaging facility. We are using this unique facility to observe a sub-sample of Pearson-Readhead Survey sources at 4.8 GHz to determine core brightness temperatures and pc-scale jet properties. We will highlight one of the sources that has been observed using a combination of the HALCA spacecraft and the EVN, 1642+690, and describe the preliminary brightness temperature distribution for the sub-sample, based on all data analyzed to date.     

椭球的倾斜像面空间透视投影正反解变换

利用矢量方法推出椭球的倾斜像面空间透视投影正解公式, 计算出此正解公式与球体的相应正解公式之间的误差, 并且利用矢量方法导出其相应反解公式。     

Atmospheric modelling in GPS analysis and its effect on the estimated geodetic parameters

Permanently operating Global Positioning System (GPS) receivers are used today, for example, in precise positioning and determination of atmospheric water vapour content. The GPS signals are delayed by various gases when traversing the atmosphere. The delay due to water vapour, the wet delay, is difficult to model using ground surface data and is thus often estimated from the GPS data. In order to obtain the most accurate results from the GPS processing, a modelling of the horizontal distribution of the wet delay may be necessary. Through simulations, three such models are evaluated, one of which is developed in this paper. In the first model the water vapour is assumed to be horizontally stratified, thus the wet delay can be described by only one zenith parameter. The second model gives the wet delay with one zenith and two horizontal gradient parameters. The third model uses the correlation between the wet-delay values in different directions. It is found that for large gradients and strong turbulence the two latter models yield lower errors in the estimated vertical coordinate and wet-delay parameters. For large gradients this improvement is up to 7 mm in the zenith wet-delay parameter, from 9 mm down to 2 and 4 mm for the second and third models, respectively. Received: 7 May 1998 / Accepted: 1 March 1999     

Overview and current status of the VSOP mission

An overview and status report of the VLBI Space Observatory Programme is presented.     

The Exo-Zodiacal Disk Mapper: A Space Interferometer to Detect and Map Zodiacal Dust Disks Around Nearby Stars

We present a concept for a space mission designed to make a mid-IR survey of potential zodiacal dust disks around nearby stars. We show that a two-aperture (0.6 m diameter), 10-m baseline, nulling interferometer located in a 1 × 4 AU, 4-yr solar orbit would allow for the survey of 400 stars in the solar neighborhood and permit a first-order determination of the disk inclination and radial dependences of density and temperature. The high dynamic range of the instrument may also be used to study additional astrophysical phenomena. Beyond its own scientific merit, such a mission would serve as a technological precursor to a larger interferometer of the type being considered for the detection of earth-like planets.     

Strategy and Scenario for Radioastron Space VLBI Observations

Space VLBI's highly dynamic geometry, ability to access the space radio telescope (SRT) only via distant communication links, very expensive mission cost, and scientific goals define the basic strategy and scenario for mission control and radio source observations. These are very different from those for ground-based VLBI. Space VLBI strategy must be based on the limitation of SRT repointings, periodic orbit determination before astronomical observations, preliminary preparation and checking of space and ground facilities, and recommended observing sequences and modes. A control and observation scenario is considered for an in-orbit-checkout period, and also for short (1-orbit – 1 week) and long (1 week and more) observation sessions. Examples and illustrations are given for the Radioastron space VLBI Project.     

Long-term experimental study on gravitational sedimentation of water aluminum oxide nanofluid at different volumetric concentrations

The stability of nanofluids is critical in engineering applications. The sedimentation of the nanoparticles in the base fluid limits the stability of the nanofluid. By measuring the absorbance of a visible laser through water aluminum oxide nanofluids it is possible to observe the evolution of the sedimentation process. A simple experimental setup consisting of a thin closed test cavity(0.8 mm or 1.5 mm thickness)filled with nanofluid and a set of laser diodes-photodiodes pairs was used in the e...     

海域使用权立体分层确权及管理配套制度探讨

由于社会经济的不断发展和科技的快速进步,我国对海域空间资源的开发利用已从二维平面转向三维立体空间开发,但随之也对我国海域空间范围界定和权属管理提出了更高的要求。文章从海域立体空间分层特性出发,对我国海域使用权立体分层确权的内涵、基本原则、考虑因素进行了深入剖析,并对我国海域三维立体开发利用中面临的困境和管理配套制度的设计进行了综合探讨。研究结果表明：海域空间可以分为水面上方、水面、水体、海床和底土5个部分,海域使用权立体分层确权则是在同一海域多层次利用中,对基于特定功能用途所占用的特定海域空间开展使用权确权的过程,在海域使用权管理的过程中,必须构建和完善海域空间三维产权法律制度体系,以确保海域使用权立体分层确权的实施。     

SGP4/SDP4模型精度分析

本文基于最新发布的SGP4/SDP4(Simplified General Perturbation Version 4/Simplified Deep-space Perturbation Version 4)模型设计了一套定轨方案,从空间目标库中挑选出不同类型和轨道参数的1120个目标进行计算,定量给出了SGP4/SDP4模型处理不同类型空间目标的定轨预报精度.结果表明:近地目标定轨精度为百米量级;半同步和同步轨道定轨精度平均为0.7和1.9km.椭圆轨道目标的定轨精度与偏心率有关,除少数e>0.8的椭圆轨道目标,绝大多数椭圆轨道目标定轨误差均小于10km.用SGP4/SDP4模型对近地目标预报3天,半同步轨道预报30天,同步轨道预报15天,椭圆轨道预报1天,预报误差一般不超过40km.     

A Model Evaluation of Biological Effects on Seasonal Variation of Air–Sea CO2 Flux in the Yellow and East China Seas

Based on a coupled physical-biogeochemical model of the Yellow and East China Seas (YECS), the influence of biological activity on the seasonal variation of the air–sea CO₂ flux is evaluated. The solution of a sensitivity experiment that excludes biological activity is compared with that of a reference experiment that includes the full processes. The comparison reveals that biological activity results in a much stronger seasonal variation of surface dissolved inorganic carbon (DIC) and, hence, the ratio of total alkalinity to DIC in the northern parts of the YECS. The increased ratio resulting from biological DIC consumption contributes to the undersaturated partial pressure of CO₂ at the sea surface with respect to the atmosphere, causing the central Yellow Sea in summer and autumn to shift from being a CO₂ source to a sink; this same shift also occurs over the Changjiang Bank in summer. In the southern YECS, the biological effect is relatively weak. The comparison further reveals that low water temperature, instead of biological activity, is the dominant factor causing the YECS to become a carbon sink in spring. The biological effect on the variation of DIC (both at the surface and in the water column) differs greatly among the three representative regions of the YECS because of differences in primary production and hydrodynamic conditions. Particle-tracking simulations quantify the regional difference in horizontal advection. In the northern region, weaker horizontal advection causes the longer residence time of low DIC water induced by biological consumption. Over the entire YECS, biological activity contributes to about one-third of the total annual absorption of atmospheric CO₂.