查看更多>>摘要：The theoretical model suggests that relativistic jets of active galactic nuclei(AGNs)rely on the black hole spin and/or accretion.We study the relationship between jet,accretion,and spin using supermassive black hole samples with reliable spin of black holes.Our results are as follows:(1)There is a weak correlation between radio luminosity and the spin of the black hole for our sample,which may imply that the jet of the supermassive black hole in our sample depends on the other physical parameters besides black hole spins,such as accretion disk luminosity.(2)The jet power of a supermassive black hole can be explained by the hybrid model with magnetic field of corona.(3)There is a significant correlation between radio-loudness and black hole spin for our sample.These sources with high radio-loudness tend to have high black hole spins.These results provide observational evidence that the black hole spin may explain the bimodal phenomena of radio-loud and radio-quiet AGNs.
查看更多>>摘要：In this paper,an effective active vibration control method was investigated to further improve the positioning accuracy of the Five-hundred-meter Aperture Spherical radio Telescope(FAST)feed cabin.The actual operation data of FAST was collected to analyze the vibration characteristics of the feed cabin in multiple directions.A simplified model of the cabin-cable system was established to evaluate the effects of a mass damper on different vibration frequencies and modes.On this basis,an active mass damper system and control system were designed for the cabin with multiple degrees of freedom and modal variation characteristics.Theoretical calculation and simulation proved that it has a significant effect on improving the damping of the cabin-cable system and suppressing the vibration of the FAST feed cabin.
查看更多>>摘要：The f(R)modified gravity theory can explain the accelerating expansion of the late Universe without introducing dark energy.In this study,we predict the constraint strength on the f(R)theory using the mock data generated from the Chinese Space Station Telescope(CSST)Ultra-Deep Field Type Ⅰa supernova(SN Ⅰa)survey and wide-field slitless spectroscopic baryon acoustic oscillation(BAO)survey.We explore three popular f(R)models and introduce a parameter b to characterize the deviation of the f(R)theory from the ACDM theory.The Markov Chain Monte Carlo method is employed to constrain the parameters in the f(R)models,and the nuisance parameters and systematic uncertainties are also considered in the model fitting process.Besides,we also perform model comparisons between the f(R)models and the ACDM model.We find that the constraint accuracy using the CSST SN Ⅰa+BAO data set alone is comparable to or even better than the result given by the combination of the current relevant observations,and the CSST SN Ⅰa+BAO survey can distinguish the f(R)models from the ACDM model.This indicates that the CSST SN Ⅰa and BAO surveys can effectively constrain and test the f(R)theory.
查看更多>>摘要：We analyzed the fractions of barred galaxies in the local Universe using a volume-limited sample of galaxies from the Sloan Digital Sky Survey Data Release 3.We examined 116 field galaxies with redshifts between 0.0207 and 0.030,using r and z-band images.Overall,the bar fraction was 26％in the r-band and 19％in the z-band.For distinct morphological groups,barred spiral galaxies had fractions of 33％in the r-band and 22％in the z-band,while barred lenticular galaxies had 25％in the r-band and 12％in the z-band.We observed that the bar fraction in spiral galaxies increases for stellar masses log(M*/M☉)＞10.5 and for galaxies with red colors(u-r)＞2.0.Additionally,most barred galaxies have a bulge-to-total ratio B/T≤ 0.2.Our results indicate that the bar fraction is more dependent on internal morphology than on the galaxy environment.
查看更多>>摘要：Our Portable Adaptive Optics(PAO)system designed for high-contrast imaging of exoplanets with current 2-4 m class telescopes achieves a correction speed of nearly 1000 Hz,utilizing a Shack-Hartmann Wave Front Sensor(WFS)in a 9 x 9 sub-aperture configuration.As we look towards adapting the PAO system for larger telescopes,an increase in the number of sub-apertures in the WFS and enhanced precision in wave front detection are imperative.Originally programmed in Lab VIEW,our initial PAO software is based on a traditional centroid calculation module for nighttime wave front sensing and lacks adaptive processing of background noise.To address these limitations and to boost the PAO system's performance and accuracy in wave front detection,we propose a compressive neural network(Th-Net)combined with a specialized hybrid parallel programming approach for wave front detection.Our experimental results indicate that this hybrid parallel technique and Th-Net significantly enhance the PAO system's operational speed and wave front detection precision under uneven background noise.This work paves the way so that a duplicable and low-cost PAO system can be used for direct imaging of exoplanets with large telescopes.
查看更多>>摘要：We propose a multi-source radio frequency interference(RFI)mitigation method based on a reference antenna array to address the challenge of RFI from multiple directions in radio observation equipment.It introduces a sampling point correction technique using a multi-channel parallel cross-correlation computation method,enhancing the effectiveness of frequency domain adaptive RFI fast mitigation algorithms.The design implements an RFI component detection method based on cross-correlation coefficient thresholds to effectively reduce new interference frequency components introduced by the reference antenna array.Simulated RFI signals and baseband signals of pulsar J0332+5434 observed by the Nanshan 26 m Radio Telescope(NSRT)were used to test the algorithm proposed in this paper.Simulation results demonstrate that the simulated radio telescope signals after RFI mitigation closely match the original pulsar data in profile and phase,confirming the effectiveness of the proposed method.
查看更多>>摘要：High-precision ephemerides not only support space missions,but can also be used to study the origin and future of celestial bodies.In this paper,a coupled orbit-rotation dynamics model that fully takes into account the rotation of the Martian moons is developed.Phobos and Deimos'rotations are first described by Eulerian rotational equations,and integrated simultaneously with the orbital motion equations.Orbital and orientational parameters of Mars satellites were simultaneously obtained by numerical integration for the first time.In order to compare the differences between our newly developed model and the one now used in the ephemerides,we first reproduced and simulated the current model using our own parameters,and then fit it to the Institut de Mécanique Céleste et de Calcul des Éphémérides ephemerides using least-square procedures.The adjustment test simulations show Phobos and Deimos'orbital differences between the refined model and the current model are no more than 300 m and 125 m,respectively.The orientation parameters are confirmed and the results are in good agreement with the International Astronomical Union results.Moreover,we simulated two perturbations(main asteroids and mutual torques)which were not included in our refined model,and find that their effects on the orbits are completely negligible.As for the effect on rotation,we propose to take care of the role of mutual attraction in future models.
查看更多>>摘要：Structures in molecular ISM are observed to follow a power-law relation between the velocity dispersion and spatial size,known as Larson's first relation,which is often attributed to the turbulent nature of molecular ISM and imprints the dynamics of molecular cloud structures.Using the 13CO(J=1-0)data from the Milky Way Imaging Scroll Painting survey,we built a sample with 360 structures having relatively accurate distances obtained from either the reddened background stars with Gaia parallaxes or associated maser parallaxes,spanning from 0.4 to～15 kpc.Using this sample and about 0.3 million pixels,we analyzed the correlations between velocity dispersion,surface/column density,and spatial scales.Our structure-wise results show power-law indices smaller than 0.5 in both the σv-Reff and σv-Reff·Σ relations.In the pixel-wise results,the σpixv is statistically scaling with the beam physical size(Rs=ΘD/2)in form of σpixv ∝ Rs0.43±003.Meanwhile,σpixv in the inner Galaxy is statistically larger than the outer side.We also analyzed correlations between σpixv and the H2 column density N(H2),finding that σpixv stops increasing with N(H2)after ≳1022 cm-2.The structures with and without high-column-density(＞1022 cm-2)pixels show different σpixv ∝ N(H2)ξ relations,where the mean(std)ξ values are 0.38(0.14)and 0.62(0.27),respectively.
查看更多>>摘要：Stellar classification and radius estimation are crucial for understanding the structure of the Universe and stellar evolution.With the advent of the era of astronomical big data,multimodal data are available and theoretically effective for stellar classification and radius estimation.A problem is how to improve the performance of this task by jointly using the multimodal data.However,existing research primarily focuses on using single-modal data.To this end,this paper proposes a model,Multi-Modal SCNet,and its ensemble model Multimodal Ensemble for Stellar Classification and Regression(MESCR)for improving stellar classification and radius estimation performance by fusing two modality data.In this problem,a typical phenomenon is that the sample numbers of some types of stars are evidently more than others.This imbalance has negative effects on model performance.Therefore,this work utilizes a weighted sampling strategy to deal with the imbalance issues in MESCR.Some evaluation experiments are conducted on a test set for MESCR and the classification accuracy is 96.1％,and the radius estimation performance Mean of Absolute Error and σ are 0.084 dex and 0.149 R☉,respectively.Moreover,we assessed the uncertainty of model predictions,confirming good consistency within a reasonable deviation range.Finally,we applied our model to 50,871,534 SDSS stars without spectra and published a new catalog.
查看更多>>摘要：Using a uniform partitioning of cubic cells,we cover the total volume of a ACDM cosmological simulation based on particles.We define a visualization cell as a spatial extension of the cubic cell,so that we collect all simulation particles contained in this visualization cell to create a series of Cartesian plots in which the overdensity of matter is clearly visible.We then use these plots as input to a convolutional neural network(CNN)based on the Keras library and TensorFlow for image classification.To assign a class to each plot,we approximate the Hessian of the gravitational potential in the center of the cubic cells.Each selected cubic cell is then assigned a label of 1,2 or 3,depending on the number of positive eigenvalues obtained for the Householder reduction of the Hessian matrix.We apply the CNN to several models,including two models with different visualization volumes,one with a cell size of type L(large)and the other with a cell type S(small).A third model combines the plots of the previous L and S cell types.So far,we have mainly considered a slice parallel to the XY plane to make the plots.The last model is considered based on visualizations of cells that also include slices parallel to the ZX and ZY planes.We find that the accuracy in classification plots is acceptable,and the ability of the models to predict the class works well.These results allow us to demonstrate the aim of this paper,namely that the usual Cartesian plots contain enough information to identify the observed structures of the cosmic web.
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