Astrometric Science and Technology Roadmap for Astrophysics (ASTRA) is a bilateral cooperation between China and Italy with the goal of consolidating astrometric measurement concepts and technologies. In particular, the objectives include critical analysis of the Gaia methodology and performance, as well as principle demonstration experiments aimed at future innovative astrometric applications requiring high precision over large angular separations (one to 180 degrees). Such measurement technologies will be the building blocks for future instrumentation focused on the "great questions" of modern cosmology, like General Relativity validity (including Dark Matter and Dark Energy behavior), formation and evolution of structure like proto-galaxies, and planetary systems formation in bio compatibles environments. We describe three principle demonstration tests designed to address some of the potential showstoppers for high astrometric precision experiments. The three tests are focused on the key concepts of multiple fields telescopes, astrometric metrology and very fine sub-pixel precision (goal: < 1/2000 pixel) in white light.
Introduction: The Multi-Channel Imager (MCI), one of the back-end modules of the future China Space Station Telescope (CSST), is designed for high-precision spacebased astronomical observations. This paper evaluates the astrometric capability of the MCI based on simulated observational images and Gaia data: the M31 galaxy is selected as a representative case to validate the astrometric capability by calculating the proper motions (PMs) of the M31 member stars. Method: We analyze the stellar centroids of the simulated images in the R, I and G bands, positional uncertainty of 2.5 mas for brighter foreground reference stars from the Gaia DR3 catalog and of 7.5 mas for the fainter M31 member stars, are adopted respectively. The theoretical PMs are generated from the adopted velocity field model, rotation curve, and stellar surface density profile. And the simulated observed PMs are generated from the aforementioned position uncertainties and theoretical PMs. Result: We conclude that the precision of the MCI derived PMs strongly depends on the number of astrometric epochs per year. Specifically, uncertainty of 10 μas/yr is achievable with 10 epochs per year, and of 5 μas/yr with 50 epochs ignoring possible systematic effects. And symmetrically distributed observed fields yield better M31 kinematic parameters. Discussion: Unknown systematic errors, space environment effects on detectors, dithering strategies, and observation schedules can affect the PMs of M31, the above issues need further analysis and validation in future work.
Abstract Many state-of-the-art researches focus on predicting infection scale or threshold in infectious diseases or rumor and give the vaccination strategies correspondingly. In these works, most of them assume that the infected probability and initially infected individuals are known at the very beginning. Generally, infectious diseases or rumor has been spreading for some time when it is noticed. How to predict which individuals will be infected in the future only by knowing the current snapshot becomes a key issue in infectious diseases or rumor control. In this paper, a prediction model based on snapshot is presented to predict the potentially infected individuals in the future. Experimental results on synthetic and real networks demonstrate that the predicted infected individuals have rather consistency with the actual infected ones.
We present a study of transport on complex networks with routing based on local information. Particles hop from one node of the network to another according to a set of routing rules with different degrees of congestion awareness, ranging from random diffusion to rigid congestion-gradient driven flow. Each node can be either source or destination for particles and all nodes have the same routing capacity, which are features of ad hoc wireless networks. It is shown that the transport capacity increases when a small amount of congestion awareness is present in the routing rules, and that it then decreases as the routing rules become too rigid when the flow becomes strictly congestion-gradient driven. Therefore, an optimum value of the congestion awareness exists in the routing rules. It is also shown that, in the limit of a large number of nodes, networks using routing based on local information jam at any nonzero load. Finally, we study the correlation between congestion at node level and a betweenness centrality measure.
To address the problem of online measurement of the base vector angle of beacon light in satellite-ground quantum optical communication, a measurement scheme is proposed to decouple the spatial base vector angle by using RGB tri-color combined beam as the beacon light with different light intensity values after beam splitting. The RGB combined beam with three different polarization angles carries the optical basis vector angle information of the carrier platform. After transmitted in free space, the RGB combined beam is decoupled from the basis vector angle by the ground receiving system. The receiving system reflects the RGB tri-color light in a split beam, uses photo detectors to obtain the intensity values of different wavelengths. According to the differential and ratio operation of the intensity values of the tri-color wavelengths, the receiving system obtains the characteristic parameter β and establishes the θ-β curve. With this curve, it is possible to inverse perform the spatial base vector angle θ information of the beacon light carrier platform in real time. The corresponding values of σ are inverted by analyzing the results of different operations on β. The verification of the experimental system shows that the accuracy of the beacon base vector angle θ obtained by the inversion of the real-time parameter β can reach ±0.05°, the standard deviation value of 3σ for random fluctuations is less than 0.1°, and the value of 3σ in the case of complex outdoor interference is less than 0.5°.
Tactical Internet environment is quite different to that of the civil mobile ad hoc network, due to the special connectivity, mobility and traffic mode, which has great impact on the performance of routing protocol in ad hoc networks. The simulation and performance analysis of routing protocol in the tactical environment was provided. in this paper. The conclusion is drawn from simulation work. In tactical environment, the traffic load has far more great impact on the performance of routing protocol than mobility. And the proactive routing protocol in the mobile ad hoc network is more suitable than reactive routing protocol in the heavy network traffic scenario in tactical Internet.
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