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A possible precessing nozzle and the Lense-Thirring effect in blazar 3C 454.3

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Research in Astronomy and Astrophysics 2014年第3期14卷 249-274页

作者： Shan-Jie qian S.Britzen A.Witzel T.P.Krichbaum heng-qian gan Long Gao National Astronomical Observatories Chinese Academy of Sciences Max-Planck Institt fr Radioastronomie

The kinematics of superluminal components in blazar 3C 454.3 are *** components are included： superluminal knots R1, R2, R3, R4, A, B, C and D（from Britzen et al. 2013） and C4 （from Pauliny-Toth 1998）. We find that their kine-matics derived from VLBI observations can be consistently interpreted in terms of ajet precession scenario with a period of about 14.5 yr. We discuss the model fits oftheir trajectory, distance from the core and apparent velocity. We show that the bulkLorentz factor （in the range 4 to 15） derived for these components does not have anydependence on the phase of the precession （or position angle for ejection）. The Lense-Thirring effect is assumed to interpret the precession of the jet nozzle. The resultsobtained for blazar 3C 454.3 are only suggestive. They are not unique and have yet tobe tested, but they might be useful for understanding the kinematics of superluminalcomponents in blazars and for disentangling different mechanisms and factors.

关键词： radio continuum: galaxies galaxies: jets galaxies: kinematics galaxies: individual (blazar 3C 454.3)

Simulation of FAST EM performance for both the axial and lateral feed defocusing

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Research in Astronomy and Astrophysics 2020年第5期20卷 127-131页

作者： heng-qian gan Peng Jiang Kai Zhu Jing-Hai Sun Rui Yao Dong-Jun Yu National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China

Five-hundred-meter Aperture Spherical radio Telescope(FAST)is the world’s largest single dish radio telescope,which is located in Guizhou Province,in southwest *** FAST feed cabin is supported and positioned by six steel *** deviation of the feed position and orientation would lead to loss in the telescope *** this paper,a series of electromagnetic(EM)simulations of the FAST facility with varying feed positions and orientation offsets was *** maximum gain of FAST is about 82.3 dBi and the sibelobe is–32 dB with respect to the main beam at 3 *** simulation results have demonstrated that the telescope efficiency loss is more sensitive to the lateral feed deviation compared with the axial *** telescope efficiency would decrease by 8.2%due to the FAST feed position deviation of 10 mm rms when the observing frequency is 3 *** FAST feed deviation basically has no effect on the sidelobes and cross polarization characteristic according to the simulations.

关键词： techniques:FAST Telescope telescope efficiency feed position error

EMC design for actuators in the FAST reflector

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Research in Astronomy and Astrophysics 2018年第4期18卷 123-128页

作者： Hai-Yan Zhang Ming-Chang Wu You-Ling Yue heng-qian gan Hao Hu Shi-Jie Huang National Astronomical Observatories Chinese Academy of Sciences Beijing 100101 China Key Laboratory of Radio Astronomy Chinese Academy of Sciences Nanjing 210034 China

An active reflector is one of the three main innovations incorporated in the Five-hundredmeter Aperture Spherical radio Telescope（FAST）.The deformation of such a huge spherically shaped reflector into different transient parabolic shapes is achieved by using 2225 hydraulic actuators which change the position of the 2225 nodes through the connected down tied *** each different tracking process of the telescope,more than 1/3 of these 2225 actuators must be in operation to tune the parabolic aperture accurately and meet the surface error *** means that some of these actuators are inevitably located within the main beam of the receiver,and Electromagnetic Interference（EMI）from the actuators must be mitigated to ensure the scientific output of the *** on the threshold level of interference detrimental to radio astronomy described in ITU-R Recommendation RA.769 and EMI measurements,the shielding efficiency（SE）requirement for each actuator is set to be 80 d B in the frequency range from 70 MHz to 3 ***,Electromagnetic Compatibility（EMC）was taken into account in the actuator design by measures such as power line filters,optical fibers,shielding enclosures and other structural *** 2015,all the actuators had been installed at the FAST *** now,no apparent EMI from the actuators has been detected by the receiver,which demonstrates the effectiveness of these EMC measures.

关键词： radio telescope — active reflector actuator — electromagnetic compatibility

Development of wideband orthomode transducers for FAST cryogenic receiver system

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Research in Astronomy and Astrophysics 2020年第5期20卷 137-147页

作者： Jin Fan Kai Zhu heng-qian gan Peng Jiang Jian Yang Yang Cao Hong-Fei Liu Hang Zhang Ming-Lei Guo Xiang-Wei Shi CAS Key Laboratory of FAST the National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China Chalmers University of TechnologyGothenburgSweden

This paper describes the design,construction,and performance of the wideband orthomode transducers(OMTs)for the L-(1.2–1.8 GHz),the S-(2–3 GHz)and the P-(0.56–1.12 GHz)band receiver systems of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).These OMTs operate at the cryogenic temperature of 70 K to reduce their thermal noise contribution to the receiver *** development on the FAST L-and S-band quad-ridged waveguide(QRWG)OMTs is carried out based on the theoretical mode *** view of the miniaturization of FAST cryogenic receiver system at P-band,a novel wideband compact bowtie dipole OMT is designed with an octave bandwidth as well as a length of only quarter *** proposed L-,S-and P-band OMTs are designed and optimized by using Ansys High Frequency Structure Simulator(HFSS),and then manufactured,tested at room *** of FAST cryogenic receiver system noise is also performed with the L-,S-and P-band OMTs *** measured results fully comply with the design specifications.

关键词： FAST instruments telescopes

RFI measurements and mitigation for FAST

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Research in Astronomy and Astrophysics 2020年第5期20卷 171-174页

作者： Hai-Yan Zhang Ming-Chang Wu You-Ling Yue heng-qian gan Hao Hu Shi-Jie Huang Xin-Xin Zhang Jin-Hai Sun Bo Peng Ren-Dong Nan FAST Collaboration National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China CAS Key Laboratory of FAST National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China

Radio Frequency Interference(RFI)mitigation is essential for supporting the science output of Five-hundred-meter Aperture Spherical radio Telescope(FAST)due to its high *** order to protect FAST from RFI,an Electromagnetic Compatibility(EMC)study has been carried out and the operation of a Radio Quiet Zone(RQZ)is *** measurements of the telescope instruments and monitoring of the active radio services outside the site have revealed the radiation properties of the RFI *** on the measurement results and theoretical analysis,various EMC methods have been implemented for the telescope to decrease the ***,the main RFI sources in the FAST RQZ,such as mobile stations,broadcast stations and navigation instruments,have been identified,and the technical measures have been adopted to protect the quiet radio environment around the *** early science outputs of FAST have demonstrated the efficiency of RFI mitigation methods.

关键词： radio telescope:FAST radio frequency interference measurement mitigation

The time and frequency standard system for FAST receivers

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Research in Astronomy and Astrophysics 2020年第5期20卷 148-154页

作者： Kai Zhu Jin Fan Kun Liang Wei Tang Zhi-Sheng Gao Yan Zhu Yi Feng Wei-Wei Zhu Lei qian You-Ling Yue Jin-You Song Xiang-Wei Shi Xing-Yi Wang Ming-Lei Guo Hang Zhang heng-qian gan Hong-Fei Liu Cheng-Jin Jin Peng Jiang National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China National Institute of Metrology Beijing 100013China

This paper reports on the time and frequency standard system for the Five-hundred meter Aperture Spherical radio Telescope(FAST),including the system design,stability measurements and pulsar timing *** stability and drift rate of the frequency standard are calculated using 1-year monitoring *** UTC-NIM Disciplined Oscillator(NIMDO)system improves the system time accuracy and stability to the level of 5 *** timing observations were carried out for several *** weighted RMS of timing residuals reaches the level of less than 3.0μs.

关键词： FAST:radio telescope time frequency standard NIMDO:UTC-NIM

Pilot HI survey of Planck Galactic Cold Clumps with FAST

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Research in Astronomy and Astrophysics 2020年第5期20卷 181-192页

作者： Ning-Yu Tang Pei Zuo Di Li Lei qian Tie Liu Yue-Fang Wu Marko Krco Meng-Ting Liu You-Ling Yue Yan Zhu Hong-Fei Liu Dong-Jun Yu Jing-Hai Sun Peng Jiang Gao-Feng Pan Hui Li heng-qian gan Rui Yao Shu Liu FAST Collaboration National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China CAS Key Laboratory of FAST National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China Kavli Institute for Astronomy and Astrophysics Peking UniversityBeijing 100871China School of Astronomy and Space Science University of Chinese Academy of SciencesBeijing 100049China Shanghai Astronomical Observatory Chinese Academy of SciencesShanghai 200030ChinaShanghai 200030China East Asian Observatory HI 96720USA Department of Astronomy School of PhysicsPeking UniversityBeijing 100871China

We present a pilot HI survey of 17 Planck Galactic Cold Clumps(PGCCs)with the Five-hundred-meter Aperture Spherical radio Telescope(FAST).HI Narrow Self-Absorption(HINSA)is an effective method to detect cold HI being mixed with molecular hydrogen H2 and improves our understanding of the atomic to molecular transition in the interstellar *** was found in 58%PGCCs that we *** column density of HINSA was found to have an intermediate correlation with that of 13CO,following log(N(HINSA))=(0.52±0.26)log(N13CO)+(10±4.1).HI abundance relative to total hydrogen[HI]/[H]has an average value of 4.4×10-3,which is about 2.8 times of the average value of previous HINSA surveys toward molecular *** clouds with total column density NH>5×1020 cm-2,an inverse correlation between HINSA abundance and total hydrogen column density is found,confirming the depletion of cold HI gas during molecular gas formation in more massive *** line width of 13CO is about 0-0.5 kms-1 larger than that of *** possible explanation of narrower non-thermal width of HINSA is that HINSA region is smaller than that of *** on an analytic model of H2 formation and H2 dissociation by cosmic ray,we found the cloud ages to be within 106.7-107.0 yr for five sources.

关键词： ISM:clouds ISM:evolution ISM:molecules

CNN-LSTM based incremental attention mechanism enabled phase-space reconstruction for chaotic time series prediction

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Journal of Electronic Science and Technology 2024年第2期22卷 77-90页

作者： Xiao-qian Lu Jun Tian qiang Liao Zheng-Wu Xu Lu gan Bidding and Purchasing Center University of Electronic Science and Technology of ChinaChengdu611731China Yibin Research Institute University of Electronic Science and Technology of ChinaYibin644000China School of Information and Communication Engineering University of Electronic Science and Technology of ChinaChengdu611731China

To improve the prediction accuracy of chaotic time series and reconstruct a more reasonable phase space structure of the prediction network,we propose a convolutional neural network-long short-term memory(CNN-LSTM)prediction model based on the incremental attention ***,a traversal search is conducted through the traversal layer for finite parameters in the phase ***,an incremental attention layer is utilized for parameter judgment based on the dimension weight criteria(DWC).The phase space parameters that best meet DWC are selected and fed into the input ***,the constructed CNN-LSTM network extracts spatio-temporal features and provides the final prediction *** model is verified using Logistic,Lorenz,and sunspot chaotic time series,and the performance is compared from the two dimensions of prediction accuracy and network phase space ***,the CNN-LSTM network based on incremental attention is compared with long short-term memory(LSTM),convolutional neural network(CNN),recurrent neural network(RNN),and support vector regression(SVR)for prediction *** experiment results indicate that the proposed composite network model possesses enhanced capability in extracting temporal features and achieves higher prediction ***,the algorithm to estimate the phase space parameter is compared with the traditional CAO,false nearest neighbor,and C-C,three typical methods for determining the chaotic phase space *** experiments reveal that the phase space parameter estimation algorithm based on the incremental attention mechanism is superior in prediction accuracy compared with the traditional phase space reconstruction method in five networks,including CNN-LSTM,LSTM,CNN,RNN,and SVR.

关键词： Chaotic time series Incremental attention mechanism Phase-space reconstruction

The fundamental performance of FAST with 19-beam receiver at L band

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Research in Astronomy and Astrophysics 2020年第5期20卷 65-92页

作者： Peng Jiang Ning-Yu Tang Li-gang Hou Meng-Ting Liu Marko Krco Lei qian Jing-Hai Sun Tao-Chung Ching Bin Liu Yan Duan You-Ling Yue heng-qian gan Rui Yao Hui Li Gao-Feng Pan Dong-Jun Yu Hong-Fei Liu Di Li Bo Peng Jun Yan FAST Collaboration National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China CAS Key Laboratory of FAST National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China School of Astronomy and Space Science University of Chinese Academy of SciencesBeijing 100101China

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) has passed national acceptance and finished one pilot cycle of ‘Shared-Risk’ observations. It will start formal operation soon. In this context, this paper describes testing results of key fundamental parameters for FAST, aiming to provide basic support for observation and data reduction of FAST for scientific researchers. The 19-beam receiver covering 1.05–1.45 GHz was utilized for most of these observations. The fluctuation in electronic gain of the system is better than 1% over 3.5 hours, enabling enough stability for observations. Pointing accuracy,aperture efficiency and system temperature are three key parameters for FAST. The measured standard deviation of pointing accuracy is 7.9′′, which satisfies the initial design of FAST. When zenith angle is less than 26.4°, the aperture efficiency and system temperature around 1.4 GHz are ~0.63 and less than 24 K for central beam, respectively. The sensitivity and stability of the 19-beam backend are confirmed to satisfy expectation by spectral HI observations toward NGC 672 and polarization observations toward 3 C 286. The performance allows FAST to take sensitive observations for various scientific goals, from studies of pulsars to galaxy evolution.

关键词： instrumentation:detectors line:profiles