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Extracting 21 cm signal by frequency and angular filtering

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Research in Astronomy and Astrophysics 2018年第9期18卷 101-112页

作者： Qi-Zhi Huang feng-quan wu Reza Ansari Xuelei Chen Key Laboratory of Computational Astrophysics National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China School of Astronomy and Space Science University of Chinese Academy of SciencesBeijing 100049China Universite Paris-Sud LALUMR 8607F-91898 Orsay CedexFrance&CNRS/IN2P3F-91405 OrsayFrance Center for High Energy Physics Peking UniversityBeijing 100871China

Extracting the neutral hydrogen （HI） signal is a great challenge for cosmological 21 cm experiments; both the astrophysical foregrounds and receiver noise are typically several orders of magnitude greater than the 21 cm signal. However, the different properties of the 21 cm signal, foreground and noise can be exploited to separate these components. The foregrounds are generally smooth or correlated over the frequency space along a line of sight （LOS）, while both the 21 cm signal and noise vary stochastically along the same LoS. The foreground can be removed by filtering out the smooth component in frequency space. The receiver noise is basically uncorrelated for observations at different times, hence for surveys it is also uncorrelated in different directions, while the 21 cm signal, which traces the large scale structure, is correlated up to certain scales. In this exercise, we apply Wiener filters in frequency and angular space to extract the 21 cm signals. We found that the method works well. Inaccurate knowl- edge about the beam could degrade the reconstruction, but the overall result is still good, showing that the method is fairly robust.

关键词： methods: data analysis - (cosmology:) dark ages reionization first stars - cosmology:observations

Cosmological constraint on Brans-Dicke Model

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Research in Astronomy and Astrophysics 2015年第12期15卷 2151-2163页

作者： Ji-Xia Li feng-quan wu Yi-Chao Li Yan Gong Xue-Lei Chen National Astronomical Observatories Chinese Academy of Sciences University of Chinese Academy of Sciences Center of High Energy Physics Peking University

We combine new Cosmic Microwave Background （CMB） data from Planck with Baryon Acoustic Oscillation （BAO） data to constrain the Brans-Dicke （BD） the- ory, in which the gravitational constant G evolves with time. Observations of type Ia supernovae （SNela） provide another important set of cosmological data, as they may be regarded as standard candles after some empirical corrections. However, in theories that include modified gravity like the BD theory, there is some risk and complication when using the SNIa data because their luminosity may depend on G. In this paper, we assume a power law relation between the SNIa luminosity and G, but treat the power index as a free parameter. We then test whether the differ- ence in distances measured with SNIa data and BAO data can be reduced in such a model. We also constrain the BD theory and cosmological parameters by making a global fit with the CMB, BAO and SNIa data set. For the CMB＋BAO＋SNIa data set, we find 0.08 × 10-2 〈 ζ 〈 0.33 ×10-2 at the 68% confidence level （CL） and -0.01 × 10-2 〈 ζ〈 0.43 × 10-2 at the 95% CL, where ζ is related to the BD parameter w by ζ = In（1 ＋ 1/w）.

关键词： cosmology: supernovae -- Brans-Dicke -- standard-candle -- BAO

Sky reconstruction for the Tianlai cylinder array

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Research in Astronomy and Astrophysics 2016年第10期16卷 71-80页

作者： Jiao Zhang Shi-Fan Zuo Reza Ansari Xuelei Chen Yi-Chao Li feng-quan wu Jean-Eric Campagne Christophe Magneville Key Laboratory of Computational Astrophysics National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100012China Universite Paris-Sud LALUMR 8607F-91898 Orsay CedexFrance&CNRS/IN2P3F-91405 OrsayFrance University of Chinese Academy of Sciences Beijing 100049China Center for High Energy Physics Peking UniversityBeijing 100871China CEA DSM/IRFUCentre d'Etudes de SaclayF-91191 Gif-sur-YvetteFrance

We apply our sky map reconstruction method for transit type interferometers to the Tianlai cylin- der array. The method is based on spherical harmonic decomposition, and can be applied to a cylindrical array as well as dish arrays and we can compute the instrument response, synthesized beam, transfer func- tion and noise power spectrum. We consider cylinder arrays with feed spacing larger than half a wavelength and, as expected, we find that the arrays with regular spacing have grating lobes which produce spurious images in the reconstructed maps. We show that this problem can be overcome using arrays with a different feed spacing on each cylinder. We present the reconstructed maps, and study the performance in terms of noise power spectrum, transfer function and beams for both regular and irregular feed spacing configura- tions.

关键词： cosmology: observation -- HI intensity mapping -- method: transit telescope -- map making

Reflections and standing waves on the Tianlai cylinder array

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Research in Astronomy and Astrophysics 2021年第3期21卷 73-85页

作者： Ji-Xia Li feng-quan wu Shi-Jie Sun Zi-Jie Yu Shi-Fan Zuo Ying-feng Liu You-Gang Wang Cong Zhang Reza Ansari Peter Timbie Xuelei Chen National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China School of Astronomy and Space Science University of Chinese Academy of SciencesBeijing 100049China Center for Astrophysics and Department of Astronomy Tsinghua UniversityBeijing 100084China IJC Lab CNRS/IN2P3&Universite Paris-Saclay15 rue Georges Cl´emenceau91405 OrsayFrance´ Department of Physics University of Wisconsin Madison1150 University AveMadison WI 53703USA Center of High Energy Physics Peking UniversityBeijing 100871China

In 21 cm intensity mapping,the spectral smoothness of the foreground is exploited to separate it from the much weaker 21 cm ***,the non-smooth frequency response of the instrument complicates this *** and standing waves generate modulations on the frequency *** we report the analysis of the standing waves in the bandpass of the signal channels of the Tianlai Cylinder *** Fourier transforming the bandpass into the delay time domain,we find various standing waves generated on the telescope.A standing wave with time delay at~142 ns is most clearly identified which is produced in the 15-meter feed *** also identify a strong peak at a shorter delay ofτ<50 ns,which may be a mix of the standing wave between the reflector and feed,and the standing wave on the 4 m intermediate frequency(IF)*** also show that a smoother frequency response could be partially recovered by removing the reflection-inducted ***,the standing wave on the antenna is direction-dependent,which poses a more difficult challenge for high precision calibration.

关键词： techniques:interferometric methods:data analysis

The design and implementation of a ROACH2+GPU based correlator on the Tianlai dish array

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Research in Astronomy and Astrophysics 2019年第7期19卷 133-142页

作者： Chen-Hui Niu Qun-Xiong Wang David MacMahon feng-quan wu Xue-Lei Chen Ji-Xia Li Hai-Jun Tian Guillaume Shippee Dan Werthimer Xiao-Ping Zheng College of Physical Science and Technology Central China Normal UniversityWuhan 430079China Key Laboratory for Computational Astrophysics National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China University of California Berkeley Campbell Hall 339Berkeley CA 94720USA College of Science China Three Gorges UniversityYichang 443002China School of Astronomy and Space Sciences University of Chinese Academy of SciencesBeijing 100049China Center of High Energy Physics Peking UniversityBeijing 100871China

A digital correlator is a crucial element in a modern radio *** this paper,we describe a scalable design for the correlator system of the Tianlai pathfinder array,which is an experiment dedicated to testing key technologies for conducting a 21cm intensity mapping *** correlator implements the FX design,which firstly performs a fast Fourier transform(FFT) including polyphase filter bank(PFB) computation using a Collaboration for Astronomy Signal Processing and Electronics Research(CASPER) Reconfigurable Open Architecture Computing Hardware-2(ROACH2) board,then computes cross-correlations by employing Graphics Processing Units(GPUs).The design has been tested both in laboratory and in actual observation.

关键词： instrumentation interferometers

Observation of acoustic hybrid topological phases induced by the p-d orbital interactions

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Science China(Physics,Mechanics & Astronomy) 2025年第1期Mechanics & Astronomy) .卷 132-139页

作者： Xiao Xiang feng Gao Yu-Gui Peng Peng wu Zong-Lin Li Xue-feng Zhu School of Physics and Innovation Institute Huazhong University of Science and Technology

In spinless systems,growing attention has recently been attracted to synthetic gauge fields,which redefine the fundamental crystal symmetries by utilizing the projective algebraic ***,synthetic gauge fields have been commonly investigated in single orbital systems,and explorations on hybrid orbitals remain elusive in ***,we report the experimental observation of hybrid topological phases induced by hybrid synthetic gauge flux,which is formed by the interaction between p and d orbitals embedded in acoustic *** breaking the translation symmetries of Lxand/or Ly,we unambiguously demonstrate the first-order M?bius edge states and higher-order corner *** work establishes a platform for seeking exotic topological phases induced by hybrid-orbitals interactions and initializing the framework of hybrid-orbitalsrelated topological *** applications can be anticipated in scenarios such as high-quality sensing and robust wave trapping due to the stepwise energy distribution of the hybrid topological phase.

关键词： topological insulator synthetic gauge field projective symmetry corner states

Sky location of massive black hole binaries in the foreground of Galactic white dwarf binaries

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Science China(Physics,Mechanics & Astronomy) 2025年第1期Mechanics & Astronomy) .卷 97-108页

作者： Pan Guo Hong-Bo Jin Cong-feng Qiao Yue-Liang wu The International Centre for Theoretical Physics Asia-Pacific University of Chinese Academy of Sciences The School of Physical Sciences University of Chinese Academy of Sciences Institute for Frontiers in Astronomy and Astrophysics Beijing Normal University National Astronomical Observatories Chinese Academy of Sciences Institute of Theoretical Physics Chinese Academy of Sciences

For space-based gravitational wave （GW） detection,the main noise source for massive black hole binaries （MBHBs） is attributed to approximately 10～7double white dwarf binaries in the *** a GW source,the amplitude of the detector response,recorded by a space-based gravitational wave detector,exhibits a modulation effect with a year period when observing the source from various orbital *** the adverse conditions mentioned above,where there is a strong foreground noise and annual modulation in the signals,we employed the wavelet transform and the strong-amplitude relevant orbital position search methods,which allows the weak MBHB sources to achieve higher locating *** detail,for two MBHB sources of lower intensity,the precision of luminosity distance,represented by the ratio ?DL/DLat the 95%confidence level,is enhanced by factors of ～*** angular resolutions,denoted by??s,are enhanced by a factor of ～*** improvements increase the number of detectable GW sources,facilitate multi-messenger follow-up observations and provide constraints on the cosmological constant.

关键词： space-based gravitational wave detection gravitational waves massive black hole binaries

Bioinspired Passive Tactile Sensors Enabled by Reversible Polarization of Conjugated Polymers

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Nano-Micro Letters 2025年第1期17卷 361-377页

作者： feng He Sitong Chen Ruili Zhou Hanyu Diao Yangyang Han Xiaodong wu School of Mechanical Engineering Sichuan UniversityChengdu 610065People’s Republic of China School of Software Engineering Chongqing University of Posts and TelecommunicationsChongqing 400065People’s Republic of China State Key Laboratory of Polymer Materials Engineering Sichuan UniversityChengdu 610065People’s Republic of China

Tactile perception plays a vital role for the human body and is also highly desired for smart prosthesis and advanced *** to active sensing devices,passive piezoelectric and triboelectric tactile sensors consume less power,but lack the capability to resolve static ***,we address this issue by utilizing the unique polarization chemistry of conjugated polymers for the first time and propose a new type of bioinspired,passive,and bio-friendly tactile sensors for resolving both static and dynamic ***,to emulate the polarization process of natural sensory cells,conjugated polymers(including poly(3,4-ethylenedioxythiophen e):poly(styrenesulfonate),polyaniline,or polypyrrole)are controllably polarized into two opposite states to create artificial potential *** controllable and reversible polarization process of the conjugated polymers is fully in situ ***,a micro-structured ionic electrolyte is employed to imitate the natural ion channels and to encode external touch stimulations into the variation in potential difference *** with the currently existing tactile sensing devices,the developed tactile sensors feature distinct characteristics including fully organic composition,high sensitivity(up to 773 mV N^(−1)),ultralow power consumption(nW),as well as superior *** demonstrations,both single point tactile perception(surface texture perception and material property perception)and two-dimensional tactile recognitions(shape or profile perception)with high accuracy are successfully realized using self-defined machine learning *** tactile sensing concept innovation based on the polarization chemistry of conjugated polymers opens up a new path to create robotic tactile sensors and prosthetic electronic skins.

关键词： Passive tactile sensors Reversible polarization of conjugated polymers Tactile perception Machine learning algorithm Object recognition

Bending Stiffness of Concrete-Filled Steel Tube and Its Influence on Concrete Placement Timing of Composite Beam-String Structure

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Structural Durability & Health Monitoring 2025年第1期19卷 55-75页

作者： Zhenyu Zhang quan Jin Haitao Zhang Zhao Liu Yuyang wu Longfei Zhang Renzhang Yan CCCC Third Highway Engineering Co. Ltd.Beijing101300China School of Civil Engineering Chongqing Jiaotong UniversityChongqing400074China

When the upper chord beam of the beam-string structure(BSS)is made of concrete-filled steel tube(CFST),its overall stiffness will change greatly with the construction of concrete placement,which will have an impact on the design of the tensioning plans and selection of control measures for the *** order to accurately obtain the bending stiffness of CFST beam and clarify its impact on the mechanical properties of composite BSS during construction,the influence of some factors such as height-width ratio,wall thickness of steel tube,elasticity modulus of concrete,and friction coefficient on the bending stiffness are analyzed parametrically by the numerical simulation technology based on an actual *** calculation formula of the equivalent bending stiffness of CFST is also established through mathematical statistical ***,the equivalent bending stiffness is introduced into the construction and use stages of the composite BSS,respectively,and the mechanical properties such as prestress-tensioning control value,structural deformation,and internal force of key members are comparatively analyzed when adopting two different construction ***,the optimal construction plan of concrete placement first and then prestress-tensioning is proposed.

关键词： Concrete panels freeze-thaw damage compression-shear crack tension-shear crack