Entity

Time filter

Source Type


Chen J.,University of Chinese Academy of Sciences | Chen M.,Xinjiang Astronomical Observatory
2013 IEEE 3rd International Conference on Information Science and Technology, ICIST 2013 | Year: 2013

The application of an LQG controller in antenna servo system is presented in this work, using Nanshan 25-m antenna of Xinjiang Astronomical Observatory. A linear quadratic optimal controller is designed, based on establishing controlled object model and according to the quadratic performance index. Meanwhile, taking into account the actual situation of the antenna work, the Gaussian noise signal is added to simulate the actual interference signal. Then a Kalman filter is designed for the noise. A traditional PI (Proportional and Integral) controller is joined in order to further improve control performance. The good simulation results are obtained by repeatedly optimizing the controller. The results indicate that the designed LQG controller achieves desired results in control performance (such as settling time and overshoot) and has good disturbance performance. Besides, the system is relatively stable. © 2013 IEEE. Source


Chen D.,CAS Center for Space Science and Applied Research | Zhu X.-Z.,Chinese Academy of Sciences | Zhu X.-Z.,University of Chinese Academy of Sciences | Wang N.,Xinjiang Astronomical Observatory
Chinese Astronomy and Astrophysics | Year: 2012

The applications of pulsar timing to several important aspects are introduced and a skeletal definition of the pulsar time scale is given. By taking advantage of the observational timing data of millisecond pulsars obtained at the Parkes Astronomical Observatory, Australia, the ensemble pulsar time based on 4 millisecond pulsars is built up, the comparison of its stability σ z, with that of the atomic time is made, and finally a few of important factors which affect the ensemble pulsar time, as well as their influences on the pulsar timing accuracy and application are analyzed. © 2012. Source


Chen J.L.,Xinjiang Astronomical Observatory | Chen J.L.,University of Chinese Academy of Sciences | Wang H.G.,Guangzhou University | Wang H.G.,Max Planck Institute for Radio Astronomy | And 6 more authors.
Astrophysical Journal | Year: 2011

The mode-switching phenomenon of PSR B0329+54 is investigated based on the long-term monitoring from 2003 September to 2009 April made with the Urumqi 25 m radio telescope at 1540 MHz. At that frequency, the change of relative intensity between the leading and trailing components is the predominant feature of mode switching. The intensity ratios between the leading and trailing components are measured for the individual profiles averaged over a few minutes. It is found that the ratios follow normal distributions, where the abnormal mode has a greater typical width than the normal mode, indicating that the abnormal mode is less stable than the normal mode. Our data show that 84.9% of the time for PSR B0329+54 was in the normal mode and 15.1% was in the abnormal mode. From the two passages of eight-day quasi-continuous observations in 2004, supplemented by the daily data observed with the 15 m telescope at 610 MHz at Jodrell Bank Observatory, the intrinsic distributions of mode timescales are constrained with the Bayesian inference method. It is found that the gamma distribution with the shape parameter slightly smaller than 1 is favored over the normal, log-normal, and Pareto distributions. The optimal scale parameters of the gamma distribution are 31.5 minutes for the abnormal mode and 154 minutes for the normal mode. The shape parameters have very similar values, i.e., 0.75+0.22 -0.17 for the normal mode and 0.84 +0.28 -0.22 for the abnormal mode, indicating that the physical mechanisms in both modes may be the same. No long-term modulation of the relative intensity ratios was found for either mode, suggesting that the mode switching was stable. The intrinsic timescale distributions, constrained for this pulsar for the first time, provide valuable information to understand the physics of mode switching. © 2011 The American Astronomical Society. All rights reserved. Source


Chen J.L.,Xinjiang Astronomical Observatory | Chen J.L.,University of Chinese Academy of Sciences | Wang H.G.,Guangzhou University | Wang N.,Xinjiang Astronomical Observatory
Journal of Astrophysics and Astronomy | Year: 2011

Using the published data of multi-frequency time-aligned pulse profiles from Kuzmin et al. (1998), we calculate the phase-resolved spectra of PSRs B0525+21 and B2020+28. The results reveal that conal-double pulsars have common 'M'-shaped phase-resolved spectra. © 2011 Indian Academy of Sciences. Source

Discover hidden collaborations