分类： 医学、药学 >> 预防医学与公共卫生学 提交时间： 2023-03-29
William J. Liu
Peipei Liu
Wenwen Lei
Zhiyuan Jia
Xiaozhou He
Weifeng Shi
Yun Tan
Shumei Zou
Gary Wong
Ji Wang
Feng Wang
Gang Wang
Kun Qin
Rongbao Gao
Jie Zhang
Min Li
Wenling Xiao
Yuanyuan Guo
Ziqian Xu
Yingze Zhao
摘要： Emerging in December 2019, coronavirus disease 2019 (COVID-19) eventually became a pandemic and posed a tremendous threat to global public health. However, the origins of SARS-CoV-2, the causative agent of COVID-19, remain to be determined. It has been reported that a certain number of the early case clusters had a contact history with the Huanan Seafood Market. Therefore, surveillance of SARS-CoV-2 within the market is of vital importance. Herein, we presented the SARS-CoV-2 detection results of 1380 samples collected from the environment since 1st Jan and animals since 18th Jan within the market in early 2020. By SARS-CoV-2-specific RT-qPCR, 73 environmental samples tested positive for SARS-CoV-2 and three live viruses were successfully isolated. The viruses from the market shared nucleotide identity of 99.99% to 100% with the human isolate HCoV-19/Wuhan/IVDC-HB-01/2019. The A lineage (8782T and 28144C), as the likely ancestral SARS-CoV-2 lineage, was found in an environmental sample. No virus was detected in the animal swabs covering 18 species of animals in the market. The RNA-seq analysis of SARS-CoV-2 positive/negative environmental samples showed the abundance of different vertebrata genera. In summary, this study provided convincing evidence of the prevalence of SARS-CoV-2 in the Huanan Seafood Market during the early stage of COVID-19 outbreak.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ying Mei
Shoulin Wei
Feng Wang
Chen Wu
Rodrigo Tobar
Mohsim Shaikh
Hui Deng
Wei Dai
Bo Liang
Andreas Wicenec
摘要： The Square Kilometre Array (SKA) project is an international cooperation project to build the largest radio telescope worldwide. Data processing is one of the biggest challenges of building the SKA telescope. As a distributed execution framework, the Data Activated Liu Graph Engine (DALiuGE) was proposed to be one of the candidates for addressing the massive data of the SKA. DALiuGE has many distinctive features, but its actual ability to handle scientific data is still not evident. In this paper, we perform an objective evaluation of the usability of DALiuGE concerning the execution performance, developer workload, and implementation difficulty of porting the SAGECal to DALiuGE. The evaluation results showed that the DALiuGE enables fast integration of astronomical software, but there are significant differences in the efficiency of different parallel granularities. Even with the deep optimization of the program, there is still a gap between the current DALiuGE and the traditional MPI in execution performance. Therefore, we come to a preliminary conclusion that the DALiuGE has no performance advantage in batch processing of massive data, while it may be more suitable for application scenarios with more customized computational tasks, such as SKA science regional centers.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： As groups of coeval stars born from the same molecular cloud, an Open cluster (OC) is an ideal laboratory for studying the structure and dynamical evolution of the Milky Way. The release of High-Precision Gaia Early Data Release 3 (Gaia EDR3) and modern machine-learning methods offer unprecedented opportunities to identify OCs. In this study, we extended conventional HDBSCAN (e-HDBSCAN) for searching for new OCs in Gaia EDR3. A pipeline was developed based on the parallel computing technique to blindly search for open clusters from Gaia EDR3 within Galactic latitudes $\left| b \right|$ $<$25 $^\circ$. As a result, we obtained 3787 star clusters, of which 83 new OCs were reported after cross-match and visual inspection. At the same time, the main star cluster parameters are estimated by colour-magnitude diagram fitting. The study significantly increases the sample size and physical parameters of open clusters in the catalogue of OCs. It shows the incompleteness of the census of OCs across our Galaxy.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Open clusters (OCs) are regarded as tracers to understand stellar evolution theory and validate stellar models. In this study, we presented a robust approach to identifying OCs. A hybrid method of pyUPMASK and RF is first used to remove field stars and determine more reliable members. An identification model based on the RF algorithm built based on 3714 OC samples from Gaia DR2 and EDR3 is then applied to identify OC candidates. The OC candidates are obtained after isochrone fitting, the advanced stellar population synthesis (ASPS) model fitting, and visual inspection. Using the proposed approach, we revisited 868 candidates and preliminarily clustered them by the friends-of-friends algorithm in Gaia EDR3. Excluding the open clusters that have already been reported, we focused on the remaining 300 unknown candidates. From high to low fitting quality, these unrevealed candidates were further classified into Class A (59), Class B (21), and Class C (220), respectively. As a result, 46 new reliable open cluster candidates among classes A and B are identified after visual inspection.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yangfan Xie
Feng Wang
Hui Deng
Ying Mei
Ying-He Celeste Lu
Gabriella Hodosan
Vladislav Stolyarov
Oleg Smirnov
Xiaofeng Li
Tim Cornwell
摘要： The Square Kilometre Array (SKA) is the largest radio interferometer under construction in the world. The high accuracy, wide-field and large size imaging significantly challenge the construction of the Science Data Processor (SDP) of SKA. We propose a hybrid imaging method based on improved W-Stacking and snapshots. The w range is reduced by fitting the snapshot $uv$ plane, thus effectively enhancing the performance of the improved W-Stacking algorithm. We present a detailed implementation of WS-Snapshot. With full-scale SKA1-LOW simulations, we present the imaging performance and imaging quality results for different parameter cases. The results show that the WS-Snapshot method enables more efficient distributed processing and significantly reduces the computational time overhead within an acceptable accuracy range, which would be crucial for subsequent SKA science studies.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Improving the performance of solar flare forecasting is a hot topic in solar physics research field. Deep learning has been considered a promising approach to perform solar flare forecasting in recent years. We first used the Generative Adversarial Networks (GAN) technique augmenting sample data to balance samples with different flare classes. We then proposed a hybrid convolutional neural network (CNN) model M for forecasting flare eruption in a solar cycle. Based on this model, we further investigated the effects of the rising and declining phases for flare forecasting. Two CNN models, i.e., Mrp and Mdp, were presented to forecast solar flare eruptions in the rising phase and declining phase of solar cycle 24, respectively. A series of testing results proved: 1) Sample balance is critical for the stability of the CNN model. The augmented data generated by GAN effectively improved the stability of the forecast model. 2) For C-class, M-class, and X-class flare forecasting using Solar Dynamics Observatory (SDO) line-of-sight (LOS) magnetograms, the means of true skill statistics (TSS) score of M are 0.646, 0.653 and 0.762, which improved by 20.1%, 22.3%, 38.0% compared with previous studies. 3) It is valuable to separately model the flare forecasts in the rising and declining phases of a solar cycle. Compared with model M, the means of TSS score for No-flare, C-class, M-class, X-class flare forecasting of the Mrp improved by 5.9%, 9.4%, 17.9% and 13.1%, and the Mdp improved by 1.5%, 2.6%, 11.5% and 12.2%.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Cong-Ming Shi
Hui Deng
Feng Wang
Ying Mei
Shao-Guang Guo
Chen Yang
Chen Wu
Shou-Lin Wei
Andreas Wicenec
摘要： Data archiving is one of the most critical issues for modern astronomical observations. With the development of a new generation of radio telescopes, the transfer and archiving of massive remote data have become urgent problems to be solved. Herein, we present a practical and robust file-level flow-control approach, called the Unlimited Sliding-Window (USW), by referring to the classic flow-control method in TCP protocol. Basing on the USW and the Next Generation Archive System (NGAS) developed for the Murchison Widefield Array telescope, we further implemented an enhanced archive system (ENGAS) using ZeroMQ middleware. The ENGAS substantially improves the transfer performance and ensures the integrity of transferred files. In the tests, the ENGAS is approximately three to twelve times faster than the NGAS and can fully utilize the bandwidth of network links. Thus, for archiving radio observation data, the ENGAS reduces the communication time, improves the bandwidth utilization, and solves the remote synchronous archiving of data from observatories such as Mingantu spectral radioheliograph. It also provides a better reference for the future construction of the Square Kilometer Array (SKA) Science Regional Center.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The Square Kilometre Array (SKA) is the largest radio interferometer under construction in the world. Its immense amount of visibility data poses a considerable challenge to the subsequent processing by the science data processor (SDP). Baseline dependent averaging (BDA), which reduces the amount of visibility data based on the baseline distribution of the radio interferometer, has become a focus of SKA SDP development. This paper developed and implemented a full-featured BDA module based on Radio Astronomy Simulation, Calibration and Imaging Library (RASCIL). Simulated observations were then performed with RASCIL based on a full-scale SKA1-LOW configuration. The performance of the BDA was systematically investigated and evaluated based on the simulated data. The experimental results presented that the amount of visibility data is reduced by about 50\% to 85\% for different time intervals ($\Delta t_{max}$). In addition, different $\Delta t_{max}$ have a significant effect on the imaging quality. The smaller the $\Delta t_{max}$, the smaller the degradation of the imaging quality.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Coronal mass ejections (CMEs) are energetic expulsions of organized magnetic features from the Sun. The study of CME quasi-periodicity helps establish a possible relationship between CMEs, solar flares, and geomagnetic disturbances. We used the angular width of CMEs as a criterion for classifying the CMEs in the study. Based on 25 years of observational data, we systematically analyzed the quasi-periodic variations corresponding to the CME occurrence rate of different angular widths in the northern and southern hemispheres, using frequency and time-frequency analysis methods. There are various periods for CMEs of different angular widths: 9 months, 1.7 years, and 3.3-4.3 years. Compared with previous studies based on the occurrence rate of CMEs, we obtained the same periods of 1.2(+-0.01) months, 3.1(+-0.04) months, ~6.1(+-0.4) months, 1.2(+-0.1) years, and 2.4(+-0.4) years. We also found additional periods of all CMEs that appear only in one hemisphere or during a specific solar cycle. For example, 7.1(+-0.2) months and 4.1(+-0.2) years in the northern hemisphere, 1(+-0.004) months, 5.9(+-0.2) months, 1(+-0.1) years, 1.4(+-0.1) years, and 2.4(+-0.4) years in the southern hemisphere, 6.1(+-0.4) months in solar cycle 23 (SC23) and 6.1(+-0.4) months, 1.2(+-0.1) years, and 3.7(+-0.2) years in solar cycle 24 (SC24). The analysis shows that quasi-periodic variations of the CMEs are a link among oscillations in coronal magnetic activity, solar flare eruptions, and interplanetary space.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： As a dedicated solar radioheliograph, the MingantU SpEctral RadioHeliograph (MUSER) has a maximum baseline of more than 3000 meters and a frequency range of 400 MHz -- 15 GHz. According to the classical radio interferometry theory, the non-coplanar baseline effect (i.e., w-term effect) would be considered and calibrated for such a radio instrument. However, little previous literature made the qualitative or quantitative analyses on w-term effects of solar radioheliograph in-depth. This study proposes a complete quantitative analysis of w-term effects for the MUSER. After a brief introduction of the MUSER, we systematically investigate the baseline variations over a year and analyze the corresponding variations of w-term. We further studied the effects of the w-term in the imaging for the specified extended source, i.e., the Sun. We discussed the possible effects of the w-term, such as image distortion and so on. The simulated results show that the w-term is an essential and unavoidable issue for solar radio imaging with high spatial resolution.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Hot subdwarf star is a particular type of star that is crucial for studying binary evolution and atmospheric diffusion processes. In recent years, identifying Hot subdwarfs by machine learning methods has become a hot topic, but there are still limitations in automation and accuracy. In this paper, we proposed a robust identification method based on the convolutional neural network (CNN). We first constructed the dataset using the spectral data of LAMOS DR7-V1. We then constructed a hybrid recognition model including an 8-class classification model and a binary classification model. The model achieved an accuracy of 96.17% on the testing set. To further validate the accuracy of the model, we selected 835 Hot subdwarfs that were not involved in the training process from the identified LAMOST catalog (2428, including repeated observations) as the validation set. An accuracy of 96.05% was achieved. On this basis, we used the model to filter and classify all 10,640,255 spectra of LAMOST DR7-V1, and obtained a catalog of 2393 Hot subdwarf candidates, of which 2067 have been confirmed. We found 25 new Hot subdwarfs among the remaining candidates by manual validation. The overall accuracy of the model is 87.42%. Overall, the model presented in this study can effectively identify specific spectra with robust results and high accuracy, and can be further applied to the classification of large-scale spectra and the search of specific targets.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Coronal mass ejections (CMEs) are energetic expulsions of organized magnetic features from the Sun. The study of CME quasi-periodicity helps establish a possible relationship between CMEs, solar flares, and geomagnetic disturbances. We used the angular width of CMEs as a criterion for classifying the CMEs in the study. Based on 25 years of observational data, we systematically analyzed the quasi-periodic variations corresponding to the CME occurrence rate of different angular widths in the northern and southern hemispheres, using frequency and time-frequency analysis methods. There are various periods for CMEs of different angular widths: 9 months, 1.7 years, and 3.3-4.3 years. Compared with previous studies based on the occurrence rate of CMEs, we obtained the same periods of 1.2(+-0.01) months, 3.1(+-0.04) months, ~6.1(+-0.4) months, 1.2(+-0.1) years, and 2.4(+-0.4) years. We also found additional periods of all CMEs that appear only in one hemisphere or during a specific solar cycle. For example, 7.1(+-0.2) months and 4.1(+-0.2) years in the northern hemisphere, 1(+-0.004) months, 5.9(+-0.2) months, 1(+-0.1) years, 1.4(+-0.1) years, and 2.4(+-0.4) years in the southern hemisphere, 6.1(+-0.4) months in solar cycle 23 (SC23) and 6.1(+-0.4) months, 1.2(+-0.1) years, and 3.7(+-0.2) years in solar cycle 24 (SC24). The analysis shows that quasi-periodic variations of the CMEs are a link among oscillations in coronal magnetic activity, solar flare eruptions, and interplanetary space.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： As groups of coeval stars born from the same molecular cloud, an Open cluster (OC) is an ideal laboratory for studying the structure and dynamical evolution of the Milky Way. The release of High-Precision Gaia Early Data Release 3 (Gaia EDR3) and modern machine-learning methods offer unprecedented opportunities to identify OCs. In this study, we extended conventional HDBSCAN (e-HDBSCAN) for searching for new OCs in Gaia EDR3. A pipeline was developed based on the parallel computing technique to blindly search for open clusters from Gaia EDR3 within Galactic latitudes $\left| b \right|$ $<$25 $^\circ$. As a result, we obtained 3787 star clusters, of which 83 new OCs were reported after cross-match and visual inspection. At the same time, the main star cluster parameters are estimated by colour-magnitude diagram fitting. The study significantly increases the sample size and physical parameters of open clusters in the catalogue of OCs. It shows the incompleteness of the census of OCs across our Galaxy.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The statistical study of the Coronal Mass Ejections (CMEs) is a hot topic in solar physics. To further reveal the temporal and spatial behaviors of the CMEs at different latitudes and heights, we analyzed the correlation and phase relationships between the occurrence rate of CMEs, the Coronal Brightness Index (CBI), and the 10.7-cm solar radio flux (F10.7). We found that the occurrence rate of the CMEs correlates with CBI relatively stronger at high latitudes (>=60) than at low latitudes (<=50). At low latitudes, the occurrence rate of the CMEs correlates relatively weaker with CBI than F10.7. There is a relatively stronger correlation relationship between CMEs, F10.7, and CBI during Solar Cycle 24(SC24) than Solar Cycle 23 (SC23). During SC23, the high-latitude CME occurrence rate lags behind F10.7 by three months, and during SC24, the low-latitude CME occurrence rate leads to the low-latitude CBI by one month. The correlation coefficient values turn out to be larger when the very faint CMEsare removed from the samples of the CDAW catalog. Based on our results, we may speculate that the source regions of the high/low-latitude CMEs may vary in height, and the process of magnetic energy accumulation and dissipation is from the lower to the upper atmosphere of the Sun. The temporal offsets between different indicators could help us better understand the physical processes responsible for the solar-terrestrial interactions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The identification and analysis of different variable sources is a hot issue in astrophysical research. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectroscopic survey has accumulated massive spectral data but contains no information about variable sources. Although a few related studies present variable source catalogs for the LAMOST, the studies still have a few deficiencies regarding the type and number of variable sources identified. In this study, we presented a statistical modeling approach to identify variable source candidates. We first crossed the Kepler, Sloan Digital Sky Survey (SDSS), and Zwicky Transient Facility (ZTF) catalogs to obtain light curves data of variable and non-variable sources. The data are then modeled statistically using commonly used variability parameters, respectively. And then, an optimal variable source identification model is determined using the Receiver Operating Characteristic (ROC) curve and four credible evaluation indices such as precision, accuracy, recall, and F1score. Based on this identification model, a catalog of LAMOST variable sources (including 631,769 variable source candidates with a probability greater than 95% and so on) is obtained. To validate the correctness of the catalog, we performed a two-by-two cross-comparison with the GAIA catalog and other published variable source catalogs. We achieved the correct rate ranging from 50% to 100%. Among the 123,756 sources cross-matched, our variable source catalog identifies 85,669 with a correct rate of 69%, which indicates that the variable source catalog presented in this study is credible.
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