Subjects: Astronomy submitted time 2024-04-12 Cooperative journals: 《天文学报》
Abstract： The characteristics of Low Surface Brightness Galaxies (LSBGs) are very important for understanding the overall characteristics of galaxies. It is of great significance to search and expand the samples of low surface brightness galaxies by modern machine learning, especially deep learning algorithm. LSBGs are difficult to discern automatically and accurately with traditional methods because of their obscure features. However, deep learning does have the advantage of automatically identifying complex and effective features. To solve this problem, an algorithm named You Only Look Once version X-CS (YOLOX-CS) is proposed to search LSBG in large sample sky survey. Firstly, five classical target detection algorithms are compared through experiments and the optimal YOLOX algorithm is selected as the basic algorithm. Then, the YOLOX-CS framework is constructed by combining different attention mechanisms and different optimizers. The data set uses images from the Sloan Digital Sky Survey (SDSS), labelled from LSBG in the $\alpha$.40-SDSS DR7 (the cross coverage area of 40\% HI Arecibo Legacy Fast ALFA Survey and SDSS Data Release7) survey. Due to the small number of samples in this data set, Deep Convolutional Generative Adversarial Networks (DCGAN) model is used to expand the experimental test data. After comparing with a series of target detection algorithms, YOLOX-CS has a good test result in searching LSBG recall rate and Average Precision (AP) value in two data sets before and after expansion. The recall rate and AP value in the test set without expansion data set reach 97.75\% and 97.83\%, respectively. In the expanded data set of DCGAN model, under the same test set, the recall rate reaches 99.10\% and the AP value reaches 98.94\%, which proves that the algorithm has excellent performance in LSBG search. Finally, the algorithm is applied to SDSS photometric data, and 765 LSBG candidates are obtained.
Subjects: Astronomy submitted time 2024-04-12 Cooperative journals: 《天文学报》
Abstract： With the rapid development of astronomical detection technology, there will be a huge torrent of incoming galaxy images in the coming years, making the automatic galaxy morphology classification a challenging task. To solve the problem of feature selection, the low speed and low accuracy of traditional galaxy morphology classification models, a galaxy morphology classification model based on Inception-v3 neural network with SE (Squeeze and Excitation Network) channel attention mechanism is introduced. We select galaxy images from Sloan Digital Sky Survey (SDSS) for the SE-Inception-v3 model. The test results show that the accuracy of SE-Inception-v3 model is as high as 99.37\%, and the F1 scores of spiral galaxy, completely round smooth galaxy, in-between smooth galaxy, cigar-shaped smooth galaxy and edge-on galaxy are 99.33\%, 99.58\%, 99.33\%, 99.41\% and 99.16\%, respectively. Compared with the MobileNet (Mobile Neural Network) and ResNet (Residual Neural Network) models, the width and depth advantages of SE-Inception-v3 make the classification model have stronger feature extraction capabilities, which provides a new galaxy morphology classification approach for future large-scale sky survey programs.
Subjects: Astronomy submitted time 2024-04-12 Cooperative journals: 《天文学报》
KANG Zhe
NIU Bing-li
LI Zhen-wei
SUN Jian-nan
LV You
ZHU Cheng-wei
DENG Shi-yu
LIU De-long
YANG Wen-bo
ZHANG Nan
LIU Ming
SUN Ming-guo
LIU Cheng-zhi
Abstract： Ground-based optical astronomical telescopes are one of the most important instruments for human exploration and research of the universe. Monitoring and analysis of the optical observation environment of the existing ground-based optical station can provide a reference for the targeted modification of equipment and the adjustment of observation strategies of observers, which is of great significance for improving the observation efficiency of ground-based optical equipment. Jilin Astronomical Observatory (hereinafter referred to as the ``Base'') is located about 5 kilometers (126.3$^{\circ}$ E, 43.8$^{\circ}$ N, 313 meters above sea level) in Nangou, Xiaosuihe Village, Dasuihe Town, Jilin City, Jilin Province, which is affiliated to the Changchun Observatory, National Astronomical Observatories, Chinese Academy of Sciences. The mean value of seeing of the base is about 1.3$''$--1.4$''$, the night sky brightness in the V band near the zenith is 20.64\;mag\,$\cdot$\,arcsec$^{-2}$, and the maximum number of clear nights is better than 270 days per year, which shows the good astronomical observation conditions. Jilin Astronomical Observatory, which was put into operation in 2016, has several photoelectric telescopes, including the 1.2-meter photoelectric telescope, the Mini Optoelectronic Telescope Array, the large field of view photoelectric telescope array, and the advanced multi-functional array-structured photoelectric detector. With the equipments mentioned above, we have carried out relevant research mainly on space target detection and recognition, precision orbit determination, new photoelectric detection methods and multicolor photometry of variables, and so forth. We have maintained a good cooperative relationship with a number of domestic universities and scientific research institutes.
Subjects: Geosciences >> Geography submitted time 2024-03-01 Cooperative journals: 《干旱区研究》
Abstract： Based on hourly precipitation observation data from 340 meteorological stations in Gansu Province from April to October 2013 to 2022, the refined evolution characteristics of warm season precipitation in Gansu Province on a diurnal variation scale were revealed. Discussions and analyses were conducted in different regions, providing a scientific reference for the study of extreme precipitation events in Gansu. The results show the following: (1) the daily peak of precipitation and precipitation intensity in the warm season in Gansu mainly occurs between 10:00 and 13:00, the daily peak of precipitation frequency primarily occurs between 22:00 and 01:00 at night, and the daily precipitation variation has obvious seasonal differences. There is a relatively concentrated distribution of autumn rain in the central and southern parts of Gansu. (2) The diurnal variation of precipitation has distinct regional characteristics. Precipitation in the Qilian Mountains and the plateau slopes of central Gansu mainly occurs during the day, with intense precipitation dominating around noon, marking the peak of daytime precipitation. Conversely, in western Hexi, the peak and frequency of daily precipitation generally occur at night, with occasional sudden heavy rainfall between 18:00 and 21:00. In southeast and eastern Gansu, the precipitation is nonuniformly distributed; nighttime rain is common due to the frequency of precipitation peaks during the night, but strong precipitation periods tend to occur in the afternoon and morning, respectively. (3) The precipitation characteristics of different durations are different. For short-term precipitation events with a duration of 6 h and below, the daily variation of precipitation is mostly“bimodal type.”Long-term precipitation events lasting more than 6 h are“unimodal type”and primarily begin in the evening, reach their peak at night, and end at noon.
Subjects: Astronomy submitted time 2024-01-31 Cooperative journals: 《天文学报》
Abstract： The features of upper atmospheric midnight density maximum (MDM) around low geographic latitudes are studied based on neutral mass densities data at altitudes 360--480\;km, derived from the accelerometer measurements aboard on the three polar orbiting satellites CHAMP (CHAllenging Minisatellite Payload), GRACE-A (Gravity Recovery and Climate Experiment-A) and SWARM-C (The Earth's Magnetic Field and Environment Explorers-C). The MDM appears during the local times from 23:00 to 02:00\;LT, whose peak locates at the low latitudes within ${15}^\circ$ and two valleys locate at the middle latitudes between ${35}^\circ$ and ${45}^\circ$ on both hemispheres separately. The structure of MDM drifts toward the southern hemisphere overall. The MDM's amplitude decreases with increases in altitude and solar radiation level. The seasonal effect weakens the MDM's amplitudes around the summer and winter solstices, while the amplitudes around the spring and autumn equinoxes are extremely significant due to the slight seasonal difference between both hemispheres. Three atmospheric density models DTM2000 (Drag Temperature Model 2000), NRLMSISE00 (Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar Extended atmosphere model) and JB2008 (Jacchia-Bowman 2008 model) are used to simulate the MDM along these three satellites' orbits, and compared with the observations. It is found that the JB2008 model is failed to describe the MDM, and the other two models underestimate the MDM's amplitudes at altitudes 360 km and 480 km: the simulated amplitudes by the DTM2000 model are 46\% and 53\% of the observed amplitudes respectively, and only 33\% and 26\% for the NRLMSISE00 model. These three models are also failed to depict the MDM's variation with altitude, solar radiation level and seasonal effects. In order to correct the model prediction, a 6th-order Legendre polynomial of geographic latitude, coupled with arguments of local time and altitude, is designed to fit the MDM signals from the three satellites' observations. In terms of amplitude and phase of the MDM, the fitting results agree with the observations very well, and the correlation coefficient is 0.923. It indicates that this empirical polynomial could be helpful to the density model correction and high accuracy prediction of spacecrafts in low Earth orbits.}
Subjects: Astronomy submitted time 2024-01-31 Cooperative journals: 《天文学报》
Abstract： CK (Karoonda-like) carbonaceous chondrites (CCs) are highly oxidized meteorites, with metal/magnetite ratio close to zero. Unlike other CCs (petrologic type: 1--3), most CK chondrites have suffered intense thermal process (550--1270 K) on their parent body with a petrologic type 4 or above. Lines of evidence indicate that CK chondrites could be genetically related to CV (Vigarano-like) chondrites which are mostly type 3 meteorites. However, there are still slight differences in petrographic texture and chemical composition between these two meteorites. Therefore, it is crucial to distinguish their geochemical characteristics for testing the CK-CV single parent body hypothesis. Northwest Africa (NWA) 13943, a newly found meteorite which has undergone intense thermal metamorphism, was classified using scanning electron microscopy and electron microprobe. The whole-rock oxygen and chromium isotope composition of NWA 13943 meteorite were also determined by mass spectrometer. Integrating petrology, mineralogy, oxygen isotope anomaly ($\Delta^{17}$O, where $\Delta$ represents isotopic fractionation value), and chromium isotope anomaly ($\varepsilon^{54}$Cr, where $\varepsilon$ expresses parts per ten thousand mass-independent isotope deviation) data, it is legitimated to infer that CK and CV chondrites may derive from two similar but distinct isotopic reservoirs within the protoplanetary disk.
Subjects: Astronomy submitted time 2024-01-31 Cooperative journals: 《天文学报》
Abstract： In this study, globular clusters NGC (New General Catalogue) 104, NGC 5139 and NGC 6121 were used as experimental areas, and 10 parameters such as parallax were selected. Then, we propose a geography-based research paradigm to quantitatively describe the spatial distribution characteristics of globular cluster members stars by introducing the spatial analysis theory and corresponding analysis framework in geography. Based on this, we obtain the spatial distribution characteristics of parameters of globular cluster member stars by calculating the global Moran's I index, and obtain the local spatial distribution characteristics of parameters according to Moran scatter diagram and LISA (Local Indicators of Spatial Association) agglomeration map. The research results show that the parameters of the member stars of the globular clusters NGC 104, NGC 5139 and NGC 6121 generally exhibit positive spatial correlation characteristics, show the characteristics of spatial aggregation, but there are differences between different parameters. The local spatial distribution also shows aggregation characteristics, and different member stars show different spatial distribution characteristics and trends. In general, this study starts from a new perspective of geo-spatial correlation analysis, systematically and quantitatively describes the spatial distribution characteristics of globular cluster member stars, deepens the understanding of the internal spatial structure and mechanism of globular clusters, and provides new ideas for the study of globular clusters
Subjects: Biology >> Ecology submitted time 2017-11-29 Cooperative journals: 《中国生态农业学报》
Abstract： Cultivated lands are among the most fundamental resources for national food security and sustainable social development. Scientific analysis of the spatial distribution patterns and evolutionary characteristics of cultivated land quality is significant for the protection and layout optimization of cultivated lands. Analysis of the spatial distribution of cultivated land quality at different scales is the basis of cultivated land quality improvement and strengthening cultivated land protection. This paper was based on cultivated land quality monitoring experimental unit in Lichuan County in Jiangxi Province and then used weighted average; variation coefficient; and spatial autocorrelation to analyze spatial disparity characteristics of cultivated land quality. Multi-scale spatial autocorrelation analysis of cultivated land quality research is a hot research area. The innovation in this paper was the introduction of natural land grade index; use of the grade index and economic grade index as the space variable to separately explore and discuss the degree of spatial correlation and spatial disparity of cultivated land quality at county-scale; township-scale and village-scale in GIS environment. The results of the research showed that: 1) Cultivated land quality index was high in the south and north and low in the west and east in Lichuan County. When the threshold distance was 400 m; there was a significant spatial autocorrelation in cultivated land quality. The Moran’s I value of natural land grade index was highest; followed by economical land grade index; and land use grade index was the lowest. The Moran’s I value of cultivated land quality from county to township and then to village scales decreased systematically. Multi-scale spatial autocorrelation analysis of cultivated land quality exhibited a significant aggregation of global spatial distribution in Lichuan County. 2) It was found that different types of cultivated land quality indexes had remarkably different spatial correlations at different spatial scales. For the influence degree of spatial scale; land use grade index was greatly affected by spatial scale; followed by natural land index; and the economic land grade index was the weakest. For the coefficient of variation of cultivated land quality index; fluctuation in Moran’s I value for cultivated land at village-scale was far greater than that at township scale. While at the same spatial scale; the coefficient of variation of natural land index was strongest; followed by economic land index and then land use index. 3) The results based on local indicators of spatial association (LISA) showed that positive spatial autocorrelation of cultivated land quality; included the high-high type and the low-low type; emerged as the shape of the cluster and in the form of group; while the negative spatial autocorrelation contained the high-low type and low-high type was fragmented in space. The results of the study showed that spatial disparity in cultivated land quality was sensitive to spatial scale. Therefore; for cultivated land quality improvement and protection; there was the need to pay more attention to spatial disparity of cultivated land quality at town scale and village scale. Also based on the difference in spatial correlation degree among the natural conditions; utilization conditions and economic benefits; it was possible to explore cultivated land quality improvement and protection measures that met actual ground situations in the study area. The results of the study provided the needed references for the construction of high-standard basic farmlands; land reclamation; regional cultivated land quality monitoring; cultivated land protection; partitioning and management of cultivated lands; cultivated land quality improvement and spatial optimization of cultivated land quality.
Subjects: Biology >> Ecology submitted time 2017-11-29 Cooperative journals: 《中国生态农业学报》
Abstract： Parasitic root weed Orobanche has already severely constrained the development of agriculture in many areas around the world and it was therefore urgent to develop effective control measures of Orobanche. As the parasitic root weed had a specific life cycle and was highly intimate to its host plants; it has been difficult to develop an ideal control measure based on traditional practices. Up till now; there has been no measure to effectively control Orobanche to make it completely harmless to host plants and easily applicable at large field scale. Among the control measures available; the use of micro-organisms has increased concerns about other negative effects. In this paper; national and global efforts to control Orobanche by the use of micro-organisms and the mechanisms of the control measures were summarized. Until now; research on biocontrol by the use of micro-organisms has focused on pathogens of Orobanche; such as Fusarium spp. and symbiotic bacteria (such as rhizobia) of host plants. The mechanisms of the use of micro-organisms to control Orobanche have involved the production of metabolites that directly inhibited the germination and growth of Orobanche seeds. The indirect mechanisms have included the degradation of chemical compounds which stimulated the germination of Orobanche; indirectly affecting the parasitic behavior and growth of Orobanche by enhancing host plant resistance against the parasitic root plant. Furthermore; the possibility of research advances by the use of soil-borne antagonistic micro-organisms against soil-borne plant diseases in controlling weedy Orobanche has been tried. Both soil borne plant pathogens and Orobanche first infected plant roots underground and then damaged normal growth of the plants. Resistances of plants to soil-borne plant diseases were similar to those of Orobanche. Thus; micro-organisms that controlled soil-borne plant diseases have the potential to control parasitic root weed Orobanche. In a pot experiment; we screened out one actinomycete strain (Streptomyces enissocaesilis Sveshnikova) and one actinomycete strain (Streptomyces pactum Bhuyan B.K.) that effectively controlled Orobanche cumana Wallr. and Orobanche aegyptiaca Pers.; respectively. The application of Streptomyces pactum inoculum in the field reduced epigaeous number of O. aegyptiaca and increased yield of tomato. In conclusion; the use of micro-organisms to control parasitic root weed Orobanche was a promising effective measure to control the parasitic root weed.
Subjects: Physics >> Nuclear Physics submitted time 2016-09-14
D. R. Madison(1
2)
X.-J. Zhu(3
4)
G. Hobbs
W. Coles
R. M. Shannon(4
6)
J. Wang
C. Tiburzi(8
9
10
11)
R. N. Manchester
M. Bailes
N. D. R. Bhat
S. Burke-Spolaor
S.Dai
J. Dempsey
M. Keith
Abstract： By regularly monitoring the most stable millisecond pulsars over many years, pulsar timing arrays (PTAs) are positioned to detect and study correlations in the timing behaviour of those pulsars. Gravitational waves (GWs) from supermassive black hole binaries (SMBHBs) are an exciting potentially detectable source of such correlations. We describe a straight-forward technique by which a PTA can be "phased-up" to form time series of the two polarisation modes of GWs coming from a particular direction of the sky. Our technique requires no assumptions regarding the time-domain behaviour of a GW signal. This method has already been used to place stringent bounds on GWs from individual SMBHBs in circular orbits. Here, we describe the methodology and demonstrate the versatility of the technique in searches for a wide variety of GW signals including bursts with unmodeled waveforms. Using the first six years of data from the Parkes Pulsar Timing Array, we conduct an all-sky search for a detectable excess of GW power from any direction. For the lines of sight to several nearby massive galaxy clusters, we carry out a more detailed search for GW bursts with memory, which are distinct signatures of SMBHB mergers. In all cases, we find that the data are consistent with noise.
Peer Review Status:
Awaiting Review
Subjects: Physics >> Nuclear Physics submitted time 2016-09-14
Abstract： The theory and phenomenology of light sterile neutrinos at the eV mass scale is reviewed. The reactor, Gallium and LSND anomalies are briefly described and interpreted as indications of the existence of short-baseline oscillations which require the existence of light sterile neutrinos. The global fits of short-baseline oscillation data in 3+1 and 3+2 schemes are discussed, together with the implications for beta-decay and neutrinoless double-beta decay. The cosmological effects of light sterile neutrinos are briefly reviewed and the implications of existing cosmological data are discussed. The review concludes with a summary of future perspectives.
Peer Review Status:Awaiting Review
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