Distributed Control Software for the Active Surface System of Tian-ma Radio Telescope

The Tian-ma Radio Telescope(TMRT) applies an Active Surface System(ASFS), which corrects for large-scale deformations due to gravity and thermal on the primary reflector. The centralized and automated management of the ASFS using software has become a challenge, for which we have developed the TMRT Active Surface System Control Software(TASCS). This paper describes the design and implementation of TASCS for device control,status monitoring, human-computer interaction, and data management functionalities. TASCS adopts the opensource Tango Controls framework and distributes middleware technology to realize real-time automated adjustment of the primary reflector through remote centralized control of a large number of actuators. At present, it has been successfully deployed on the TMRT and has played an important role in Event Horizon Telescope observations.

East Asian VLBI Network observations of active galactic nuclei jets:imaging with KaVA+Tianma+Nanshan

The East Asian Very Long Baseline Interferometry(VLBI) Network(EAVN) is a rapidly evolving international VLBI array that is currently promoted under joint efforts among China,Japan and Korea.EAVN aims at forming a joint VLBI Network by combining a large number of radio telescopes distributed over East Asian regions.After the combination of the Korean VLBI Network(KVN) and the VLBI Exploration of Radio Astrometry(VERA) into Ka VA,further expansion with the joint array in East Asia is actively promoted.Here we report the first imaging results(at 22 and 43 GHz) of bright radio sources obtained with Ka VA connected to Tianma 65-m and Nanshan 26-m Radio Telescopes in China.To test the EAVN imaging performance for different sources,we observed four active galactic nuclei(AGN) having different brightness and morphology.As a result,we confirmed that the Tianma 65-m Radio Telescope(TMRT) significantly enhances the overall array sensitivity,a factor of 4 improvement in baseline sensitivity and 2 in image dynamic range compared to the case of Ka VA only.The addition of the Nanshan 26-m Radio Telescope(NSRT) further doubled the east-west angular resolution.With the resulting high-dynamic-range,high-resolution images with EAVN(Ka VA+TMRT+NSRT),various fine-scale structures in our targets,such as the counter-jet in M87,a kink-like morphology of the 3 C 273 jet and the weak emission in other sources are successfully detected.This demonstrates the powerful capability of EAVN to study AGN jets and to achieve other science goals in general.Ongoing expansion of EAVN will further enhance the angular resolution,detection sensitivity and frequency coverage of the network.

Thermal Analysis of the Backup Structure of the Tianma Telescope

Taking the Tianma Radio Telescope(TMRT)as an object,this paper focuses on the determination of temperature gradients and thermal deformations of the backup structure(BUS)with the finite element method.To this end,a modeling and analysis method,which consists of a simplified FEM and a four-component simulation process,is proposed.In the development,only solar radiation is considered and thermal convection is neglected.Based on the thermal time constant of the BUS,the simulations of temperature gradients are simplified as static analysis.The superposed temperature gradients agree well with the ones measured by thermometers with a 0.57℃ root mean square(rms)error.In addition,the illuminated-weighted rms errors of the primary reflector surface calculated by the simulation and measured by the extended out-of-focus holography are in good agreement.The rms error increases approximately 170μm when the Sun persistently illuminated the BUS for 3 hr.The optimized initial temperature of the antenna structure is 20℃ by comparing the results between the finite element analysis and the e-OOF measurement.The thermal deformation database can support the real-time compensation of the active surface system if the traces of the radio telescope are known in advance.

A Q-band two-beam cryogenic receiver for the Tianma Radio Telescope

A Q-band two-beam cryogenic receiver for the Tianma Radio Telescope（TMRT）has been developed,and it uses the independently-developed key microwave and millimeter-wave components operating from 35 to 50 GHz with a fractional bandwidth of 35%.The Q-band receiver consists of three parts：optics,cold unit assembly and warm unit assembly,and it can receive simultaneously the lefthanded and right-handed circularly polarized waves.The cold unit assembly of each beam is composed of a feed horn,a noise injection coupler,a differential phase shifter,an orthomode transducer and two low-noise amplifiers,and it works at a temperature range near 20 K to greatly improve the detection sensitivity of the receiving system.The warm unit assembly includes four radio-frequency amplifiers,four radio-frequency high-pass filters,four waveguide biased mixers,four 4–12 GHz intermediate-frequency amplifiers and one 31–38 GHz frequency synthesizer.The measured Q-band four-channel receiver noise temperatures are roughly 30–40 K.In addition,the single-dish spectral line and international very long baseline interferometry（VLBI）observations between the TMRT and East Asia VLBI Network at the Q-band have been successfully carried out,demonstrating the advantages of the TMRT equipped with the state-of-the-art Q-band receiver.

A novel high precision Doppler frequency estimation method based on the third-order phase-locked loop

In deep space exploration,many engineering and scientific requirements require the accuracy of the measured Doppler frequency to be as high as possible.In our paper,we analyze the possible frequency measurement points of the third-order phase-locked loop(PLL)and find a new Doppler measurement strategy.Based on this finding,a Doppler frequency measurement algorithm with significantly higher measurement accuracy is obtained.In the actual data processing,compared with the existing engineering software,the accuracy of frequency of 1 second integration is about 5.5 times higher when using the new algorithm.The improved algorithm is simple and easy to implement.This improvement can be easily combined with other improvement methods of PLL,so that the performance of PLL can be further improved.

Photoluminescence Characteristics of ZnCuInS-ZnS Core-Shell Semiconductor Nanocrystals

The photoluminescence （PL） characteristics of ZnCuInS quantum dots （Q, Ds） with varying ZnS shell thicknesses of O, 0.5, and 1.5 layers are investigated systemically by time-correlated single-photon counting measurements and temperature-dependent PL measurements. The results show that a ZnS shell thickness of 1.5 layers can effectively improve the PL quantum yield in one order of magnitude by depressing the surface trapping states of the core ZnCuInS QDs at room temperature. However, the PL measurements at the elevated temperature reveal that the core-shell nanocrystals remain temperature-sensitive with respect to their relatively thin shells. The temperature sensitivity of these small-sized single-layered core-shell nanocrystals may find applications as effective thermometers for the in vivo detection of biological reactions within cells.

Solving Surface Deformation of Radio Telescope Antenna by Artificial Neural Network

Recent investigations have derived the relation between the near-field plane amplitude and the surface deformation of reflector antenna,namely deformation-amplitude equation(DAE),which could be used as a mathematical foundation of antenna surface measurement if an effective numerical algorithm is employed.Traditional algorithms are hard to work directly due to the complex mathematical model.This paper presents a local approximation algorithm based on artificial neural network to solve DAE.The length factor method is used to construct a trial solution for the deformation,which ensures the final solution always satisfies the boundary conditions.To improve the algorithm efficiency,Adam optimizer is employed to train the network parameters.Combining the application of the data normalization method proposed in this paper and a step-based learning rate,a further optimized loss function could be converged quickly.The algorithm proposed in this paper could effectively solve partial differential equations without boundary conditions such as DAE,which at the same time contains the first-order and the second-order partial derivatives,and constant terms.Simulation results show that compared with the original algorithm by Fast Fourier transform,this algorithm is more stable and accurate,which is significant for the antenna measurement method based on DAE.

Deformation measurement by single spherical near-field intensity measurement for large reflector antenna

This paper presents a new method to obtain the deformation distribution on the main reflector of an antenna only by measuring the electric intensity on a spherical surface with the focal point as the center of the sphere,regardless of phase.Combining the differential geometry theory with geometric optics method,this paper has derived a deformation-intensity equation to relate the surface deformation to the intensity distribution of a spherical near-field directly.Based on the finite difference method(FDM)and GaussSeidel iteration,deformation has been calculated from intensity simulated by geometrical optics(GO)and physical optics(PO)methods,respectively,with relatively small errors,which prove the effectiveness of the equation proposed in this paper.By means of this method,it is possible to measure the deformation only by scanning the electric intensity of a single hemispherical near-field whose area is only about 1/15 of the aperture.The measurement only needs a plane wave at any frequency as the incident wave,which means that both the signals from the outer space satellite and the far-field artificial beacon could be used as the sources.The scanning can be realized no matter what attitude and elevation angle the antenna is in because the size and angle of the hemisphere are changeable.

A novel Doppler frequency measurement method based on the closed-loop signal correlation for deep space exploration

In deep space exploration,it is necessary to improve the accuracy of frequency measurement to meet the requirements of precise orbit determination and various scientific studies.A phase detector is one of the key modules that restricts the tracking performance of phase-locked loop(PLL).Based on the phase relationship between adjacent signals in the time domain,a novel phase detector is presented to replace the arctangent phase detector.The new PLL,which is a closed loop signal correlation algorithm,shows good performance in tracking signals with high precision and the tracking accuracy of frequency of1 second integration is close to Cramer-Rao lower bound(CRLB)when setting proper parameters.Actual data processing results further illustrate the excellent performance of the novel PLL.

A multi-responsive luminescent sensor towards Fe_(3+) and acetone based on a Cd-containing metal–organic framework

A Cd-containing metal–organic framework（Cd L）, formula as {[Cd_3（L）_2（H_2O）_6] 1.5DMF}, has been synthesized under solvothermal condition by the reaction of 4,40,400-（methylsilanetriyl）tribenzoic acid（H_3L） and Cd^（2＋）ion. Single-crystal X-ray diffraction reveals that Cd L displays a three-dimensional framework with 2-fold interpenetration and DMF molecules locate in the void space of the channels. A topological analysis of the framework indicates Cd Lisa 3,4-connected pto net. The photoluminescence properties of Cd L are systematically studied in detail. Impressively, Cd L shows excellent detection performance towards Fe^（3＋）ion and acetone in the sensing experiments, which undoubtedly demonstrates the great potential of Cd L as a highly selective multi-responsive luminescent sensor for the detection of organic solvents and metal ions.