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IPS observation system for the Miyun 50m radio telescope and its commissioning observation

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Research in Astronomy and Astrophysics 2012年第7期12卷 857-864页

作者： xin-Ying Zhu xi-zhen zhang Hong-Bo zhang De-Qing Kong Hui-Peng Qu National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Beijing Institute of Tracking and Telecommunications Technology Beijing 100094 China

Ground-based observation of Interplanetary Scintillation （IPS） is an impor- tant approach for monitoring solar wind. A ground-based IPS observation system has been newly implemented on a 50 m radio telescope at Miyun station, managed by the National Astronomical Observatories, Chinese Academy of Sciences. This observa- tion system has been constructed for the purpose of observing solar wind speed and the associated scintillation index by using the normalized cross-spectrum of a simul- taneous dual-frequency IPS measurement. The system consists of a universal dual- frequency front-end and a dual-channel multi-function back-end specially designed for IPS. After careful calibration and testing, IPS observations on source 3C 273B and 3C 279 have been successfully carried out. The preliminary observation results show that this newly-developed observation system is capable of performing IPS observa- tion. The system＇s sensitivity for IPS observation can reach over 0.3 Jy in terms of an IPS polarization correlator with 4 MHz bandwidth and 2 s integration time.

关键词： instrument - interplanetary scintillation -- telescope -- radio astron-omy

A state-of-the-art review of the development of self-healing concrete for resilient infrastructure

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Frontiers of Structural and Civil Engineering 2024年第2期18卷 151-169页

作者： Dong LU xi JIANG Yao zhang Shaowei zhang Guoyang LU zhen LENG Department of Civil and Environmental Engineering The Hong Kong Polytechnic UniversityHong Kong 999077China Laboratory of Fire Safety School of Safety Engineering and Emergency ManagementShijiazhuang Tiedao UniversityShijiazhuang 050043China Department of Architecture and Civil Engineering City University of Hong KongHong Kong 999077China

The brittleness of cement composites makes cracks almost inevitable,producing a serious limitation on the lifespan,resilience,and safety of concrete *** address this brittleness,self-healing concrete has been developed for regaining its mechanical and durability properties after becoming cracked,thereby promising sustainable development of concrete *** paper provides a comprehensive review of the latest developments in self-healing *** begins by summarizing the methods used to evaluate the self-healing efficiency of ***,it compares strategies for achieving healing *** then discusses the typical approaches for developing self-healing ***,critical insights are proposed to guide future studies on the development of novel self-healing *** review will be useful for researchers and practitioners interested in the field of self-healing concrete and its potential to improve the durability,resilience,and safety of concrete infrastructure.

关键词： resilient infrastructure sustainable concrete self-healing cracks

New radio observations of the Moon at L band

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维普期刊数据库

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Research in Astronomy and Astrophysics 2012年第9期12卷 1297-1312页

作者： xi-zhen zhang Andrew Gray Yan Su Jun-Duo Li Tom Landecker Hong-Bo zhang Chun-Lai Li National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China zxz @ nao. cas. cn Dominion Radio Astrophysical Observatory Penticton BC V2A 6K3 Canada

We present results of new radio observations of the Moon at L band with the synthesis telescope of the Dominion Radio Astrophysical Observatory Synthesis Telescope. The resolution and temperature sensitivity of the observations are 159 × 87 and 1.7K, respectively. The main results are: (1) the lunar brightness temperature averaged over the whole disk is about 233K while the average brightness temperature for the four quadrants are 228.1K (NE), 239.7K (NW), 233.9K (SW) and 228.8K (SE). The observations reveal large temperature and spatial variations on the Moon for the first time. The highest brightness temperature is about 257 K and it is located along the lunar equator, to the west. The total uncertainty is about 5% due to the absolute accuracy of the fluxes of the primary calibrators; (2) the total degree of po- larization is about 6%. Both polarization intensity and degree of polarization increase from the disk’s center to the limb, and the distribution of the degree of polarization along the limb is not uniform; (3) the new data are used to study the properties of regolith, such as dielectric constant and thickness distribution. The results show that the lunar regolith’s thickness increases from the NW (mare area) to the SE (highland area) regions on the lunar surface.

关键词： techniques: high angular resolution-imaging processing — radio contin- uum: Moon

The OH Maser Line Receiving System for the Urumqi 25m Radio Telescope

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Chinese Journal of Astronomy and Astrophysics 2005年第5期5卷 557-562页

作者： Hong-Bo zhang Jarken Esimbek Jian-Jun Zhou xing-Wu zhen xi-zhen zhang Wen-Jie Yang National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 Urumqi Astronomical Observatory National Astronomical Observatories Chinese Academyof Sciences Urumqi 830011 Department of Astronomy Nanjing University 210093 Beijing Institute of Tracking and Telecommunication Technology Beijing 100094

A maser spectral line system is newly implemented on the Urumqi 25m Radio Telescope. The system consists mainly of a cooling receiver and a 4096 channels digital correlation spectrometer. The frequency resolution of the spectrometer at the maximum signal bandwidth of 80MHz is 19.5kHz. After careful calibrations observation at the 1665 MHz OH maser emission was made towards a number of sources, including W49N and W75N. The observed results demonstrate that the digital correlation spectrometer is suitable for astronomical spectral line observations.

关键词： instrumentation: spectrometer - OH maser

High Brightness Temperatures in IDV Sources

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Chinese Journal of Astronomy and Astrophysics 2006年第5期6卷 530-542页

作者： Shan-Jie Qian T.P. Krichbaum A. Witzel J. A. Zensus xi-zhen zhang National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 Max-Planck-Institut for Radio astronomie Auf dem Htige169 53121 Bonn Germany

High brightness temperatures are a characteristic feature of IntraDay Variability （IDV） of extragalactic radio sources. Recent studies of the polarization properties of some IDV sources （e.g., 1150＋812, PKS 0405-385 and 0716＋714） have shown that these sources harbor several compact IDV components with angular sizes of -10-30μas and very high polarizations （of up to -50%-70%）. These results indicate the possibility of the existence of uniform magnetic fields in the IDV components. We investigate the incoherent synchrotron and self- Compton radiation of an anisotropic distribution of relativistic electrons which spin around the magnetic field lines at small pitch angles. The brightness temperature limit caused by second-order Compton losses is discussed and compared to the brightness temperatures derived from energy equipartition arguments. It is found that anisotropic distributions of electrons moving in ordered magnetic fields can raise the equipartition and Compton brightness temperatures by a factor of up to -3-5. This would remove some of the difficulties in the interpretation of extremely high intrinsic brightness temperatures of 〉 1012 K （or apparent brightness temperatures of - 10^14 K with a Doppler factor of -30）.

关键词： radio continuum galaxies - Quasars individual PKS 0405-385

Annual Modulation in Intraday Variability Timescales of Extragalactic Radio Sources

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Chinese Journal of Astronomy and Astrophysics 2001年第2期1卷 133-143页

作者： Shan-Jie Qian and xi-zhen zhang (Beijing Astronomical Observatory, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012) Beijing Astronomical Observatory National Astronomical Observatories Chinese Academy of Sciences Beijing 100012

Annual modulations in timescales of intraday variability (IDV hereafter) are discussed for six extragalactic sources: 0716+714, 0917+624, 0954+65, 1749+70, 1803+78 and 2007+77. The timescales calculated from scintillation theory are compared with the observational data . It is emphasized that systematic observations are required to identify the phenomenon and to determine the motion of the interstellar medium with respect to the Local Standard of Rest. In addition, significant deviations from the annual modulation could be due to intrinsic variations.

关键词： scattering - ISM: kinematics - BL Lacertae objects: individual: 0716+71 - quasars: individual: 0917+62 - radiation mechanisms: non-thermal

Refractive Focusing of Interstellar Clouds and Intraday Polarization Angle Swings

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Chinese Journal of Astronomy and Astrophysics 2007年第2期7卷 215-223页

作者： Shan-Jie Qian T. E Krichbaum Long Gao xi-zhen zhang A. Witzel J. A. Zensus National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 Max-Planck-Institut fur Radioastronomie Auf dem Huge169 53121 Bonn Germany

Intraday variations of compact extragalactic radio sources in flux density and polarization are generally interpreted in terms of refractive scintillation from the continuous interstellar medium of our Galaxy. However, continuous polarization angle swings of - 180° （for example, the one observed in the QSO 0917＋624） could not be interpreted in this way. Qian et al. have shown that the polarization angle swing observed in the QSO 1150＋812 can be explained in terms of focusing-defocusing effect by an interstellar cloud, which occults two closely-placed polarized components. Here we further show that the polarization angle swing event observed in the QSO 0917＋624 can also be explained in this way. We also found evidence for the cloud eclipsing a non-polarized （core） component during a short period out- side the swing. A particular （and specific） plasma-lens model is proposed to model-fit the polarization swing event of 0917＋624. Some physical parameters related to the plasma-lens and the source components are estimated. The brightness temperatures of the two lensed components are estimated to be -1.6× 10^13 K. Thus bulk relativistic motion with a Lorentz factor less than -20 may be sufficient to avoid the inverse - Compton catastrophe.

关键词： radio continuum galaxies - polarization intraday variability - scattering refractive focusing - quasars Individual QSO 0917+624

Periodicity of the ejection of superluminal components in 3C345

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Chinese Journal of Astronomy and Astrophysics 2009年第2期9卷 137-150页

作者： Shan-Jie Qian A. Witzel J. A. Zensus T. R Krichbaum S. Britzen xi-zhen zhang National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Max-Planck-Institut für Radioastronomie Auf dem Hügel 69 53121 Bonn Germany

The search for periodic behavior in Blazars has been an important subject, which is helpful for providing significant clues to the structure and physical processes of their central energy engine. A binary black hole system has recently been suggested for causing precession of relativistic jets and rotation of the ejection position angle of VLBI knots in superluminal sources. It has been suggested that in QSO 3C345, the ejection direction of the superluminal knots rotates due to the precession of the central engine and thus the ejection position angle of the successive knots shows a periodic behavior. Some authors argue for a period of precession being ～5.6 yr （Abraham ＆ Caproni）, ～8-10 yr （Klare et al.） and ～9.5 yr （Lobanov ＆ Roland）. Applying the helical model proposed by Qian et al. and selecting appropriate parameters to fit the initial trajectories （within 0.3 mas） of all the components （C4 to C10）, we derive the relation between the ejection position angle of the components and their precession phase, and thus find a 6.9-year precession period （4.3 yr in the source frame）, which can fit the ejection position angle of all these superluminal knots well. Since the VLBI observations have covered more than two precession periods, confirmation in one or more future periods would be important. In addition, we emphasize that the initial parts of the trajectories of these knots can be fitted by a common helical pattern （channel） through a precessing of its initial phase. This scenario （or helical precessing model） is different from the usual ballistic precessing model in which the individual superluminal knots move along straight-lines after ejection （Tateyama ＆ Kingham）.

关键词： radio continuum galaxies -- quasars individual 3C345

Statistics of Galactic Supernova Remnants

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Chinese Journal of Astronomy and Astrophysics 2005年第2期5卷 165-174页

作者： Jian-WenXu xi-zhenzhang Jin-LinHan NationalAstronomicalObservatories ChineseAcademyofSciencesBeijing100012

We collected the basic parameters of 231 supernova remnants (SNRs) in ourGalaxy, namely, distances (d) from the Sun, linear diameters (D), Galactic heights (Z), estimatedages (t), luminosities (L), surface brightness (Σ) and flux densities (S_1) at 1-GHz frequency andspectral indices (α). We tried to find possible correlations between these parameters. As expected,the linear diameters were found to increase with ages for the shell-type remnants, and also to havea tendency to increase with the Galactic heights. Both the surface brightness and luminosity ofSNRs at 1-GHz tend to decrease with the linear diameter and with age. No other relations between theparameters were found.

关键词： methods: statistical (ISM:) supernova remnants