M型恒星周围系外行星统计研究          下载免费PDF全文

潘梦睿  季江徽  王素 《天文学报》2021,62(4):38

M型恒星(M dwarf)是主序星中质量较小的恒星,也是银河系中数量最多的恒星类型,在其周围形成的行星通常距离主星较近,宜居带也比F、G、K型恒星更靠近主星,更有利于发现系外宜居行星.研究表明, M型恒星周围平均存在2.5颗小质量行星,约为F、 G、 K型恒星的3.5倍,但M型恒星周围巨行星的出现率(occurrence rate)则比F、 G、K型小一个量级.基于M型恒星周围发现的401颗行星的参数开展了统计研究,发现质量越大的行星平均轨道半长径越大.类地行星约占行星总数的74%,且轨道半长径均小于1 au,其中28颗行星具有潜在宜居性.根据行星质量-半径关系,在质量等于4倍地球质量(M⊕)处存在一拐点,除少数几颗行星外,大部分小于该质量的行星可能都是由约65%的硅酸盐和约35%的铁组成,大于该质量的行星半径则随质量增加而迅速增大.约60%的M型恒星周围的行星位于多行星系统且轨道分布紧密,相邻行星轨道在3:2、5:3及2:1等平运动共振位置处存在峰值. M型恒星的多行星系统形成与演化等问题对现今的行星形成理论提出了新挑战.  相似文献   

Discovery of Four New Clusters in the Cygnus Cloud     

秦松梅  李静  陈力  钟靖 《天文和天体物理学研究(英文版)》2021,(2)

We report the discovery of four new open clusters(named QC 1,QC 2,QC 3 and QC 4)in the direction of Cygnus Cloud and select their members based on five astrometric parameters(l,b,ω,μα*,μδ)of Gaia DR2.We also derive their astrophysical parameters for each new cluster.Structure parameters are generated by fitting the radial density distribution with a King’s profile.Using solar metallicity,we performed isochrone-fitting on their purified color-magnitude diagrams(CMDs)to derive the age of the clusters.The known cluster NGC 7062 in an adjacent area is chosen to verify our identification process.The estimated distance,reddening and age of NGC 7062 are in good agreement with the literature.  相似文献   

太平洋深海沉积物来源的菌株Tenacibaculum sp.HMG1对孔雀石绿降解特性的研究     

曲武  洪国粦  赵晶 《海洋学报(英文版)》2018,37(6):104-111

本文在太平洋深海沉积物中分离得到一株孔雀石绿降解菌株，鉴定命名为Tenacibaculum sp.HMG1。通过菌株生长实验和高效液相色谱的研究表明， HMG1菌株可以在20 mg/L的孔雀石绿中维持较快的生长速率，并且在12 h内可降解98.8%的孔雀石绿，这证明该菌株具有很高的孔雀石绿耐受能力和降解活性。通过基因组测序在HMG1菌株发现一条过氧化物酶基因可能参与了孔雀石绿的降解，随后利用原核表达获得了相应的重组蛋白。实验表明，该重组过氧化物酶具有极强的活性，可在1000 mg/L的孔雀石绿中发挥降解功能。本文利用液相色谱-质谱联用（LC-MS）技术对孔雀石绿的菌株降解产物和重组酶降解产物进行鉴定，并基于鉴定结果推测了两种降解途径。结果发现两种降解方式存在共同的降解途径。此外，孔雀石绿降解条件的实验结果证明重组过氧化物酶可以在低温（20℃）、复杂的pH值（6.0–9.0）、高盐度（100 mmol/L）、金属离子和EDTA等反应条件下依旧维持很高的孔雀石绿降解活性。以上实验结果表明，HMG1菌株和重组过氧化物酶均在孔雀石绿污染生物修复方面具有很大潜力。  相似文献   

Study of the flood control scheduling scheme for the Three Gorges Reservoir in a catastrophic flood          下载免费PDF全文

Shanghong Zhang  Zhu Jing  Wenda Li  Yujun Yi  Yong Zhao 《水文研究》2018,32(11):1625-1634

The Three Gorges Project is the world's largest water conservancy project. According to the design standards for the 1,000‐year flood, flood diversion areas in the Jingjiang reach of the Yangtze River must be utilized to ensure the safety of the Jingjiang area and the city of Wuhan. However, once these areas are used, the economic and life loss in these areas may be very great. Therefore, it is vital to reduce this loss by developing a scheme that reduces the use of the flood diversion areas through flood regulation by the Three Gorges Reservoir (TGR), under the premise of ensuring the safety of the Three Gorges Dam. For a 1,000‐year flood on the basis of a highly destructive flood in 1954, this paper evaluates scheduling schemes in which flood diversion areas are or are not used. The schemes are simulated based on 2.5‐m resolution reservoir topography and an optimized model of dynamic capacity flood regulation. The simulation results show the following. (a) In accord with the normal flood‐control regulation discharge, the maximum water level above the dam should be not more than 175 m, which ensures the safety of the dam and reservoir area. However, it is necessary to utilize the flood diversion areas within the Jingjiang area, and flood discharge can reach 2.81 billion m³. (b) In the case of relying on the TGR to impound floodwaters independently rather than using the flood diversion areas, the maximum water level above the dam reaches 177.35 m, which is less than the flood check level of 180.4 m to ensure the safety of the Three Gorges Dam. The average increase of the TGR water level in the Chongqing area is not more than 0.11 m, which indicates no significant effect on the upstream reservoir area. Comparing the various scheduling schemes, when the flood diversion areas are not used, it is believed that the TGR can execute safe flood control for a 1,000‐year flood, thereby greatly reducing flood damage.  相似文献   

赤潮治理方法综述          下载免费PDF全文

韩锡锡  李琴  曹婧  于文涛  鞠莲 《海洋开发与管理》2018,35(4):76-80

文章综述目前赤潮治理的主要方法,其中物理法重点介绍机械搅动法、超声波法、吸附法和气浮法,化学法重点介绍无机药剂法、有机药剂法和胶体絮凝沉淀法,生物法主要介绍引入赤潮藻类生物天敌、微生物技术和化感技术,分析各自优势和不足,采用微生物技术和化感技术具有重要意义和发展前景。  相似文献   

OceanRoute: Vessel Mobility Data Processing and Analyzing Model Based on MapReduce     

Chao Liu  Yingjian Liu  Zhongwen Guo  Wei Jing 《中国海洋大学学报(英文版)》2018,17(3):594-602

The network coverage is a big problem in ocean communication, and there is no low-cost solution in the short term. Based on the knowledge of Mobile Delay Tolerant Network (MDTN), the mobility of vessels can create the chances of end-to-end communication. The mobility pattern of vessel is one of the key metrics on ocean MDTN network. Because of the high cost, few experiments have focused on research of vessel mobility pattern for the moment. In this paper, we study the traces of more than 4000 fishing and freight vessels. Firstly, to solve the data noise and sparsity problem, we design two algorithms to filter the noise and complement the missing data based on the vessel’s turning feature. Secondly, after studying the traces of vessels, we observe that the vessel’s traces are confined by invisible boundary. Thirdly, through defining the distance between traces, we design MR-Similarity algorithm to find the mobility pattern of vessels. Finally, we realize our algorithm on cluster and evaluate the performance and accuracy. Our results can provide the guidelines on design of data routing protocols on ocean MDTN.  相似文献   

Classification of stellar spectra with SVM based on within-class scatter and between-class scatter     

Zhong-bao Liu  Fang-xiao Zhou  Zhen-tao Qin  Xue-gang Luo  Jing Zhang 《Astrophysics and Space Science》2018,363(7):140

Support Vector Machine (SVM) is a popular data mining technique, and it has been widely applied in astronomical tasks, especially in stellar spectra classification. Since SVM doesn’t take the data distribution into consideration, and therefore, its classification efficiencies can’t be greatly improved. Meanwhile, SVM ignores the internal information of the training dataset, such as the within-class structure and between-class structure. In view of this, we propose a new classification algorithm-SVM based on Within-Class Scatter and Between-Class Scatter (WBS-SVM) in this paper. WBS-SVM tries to find an optimal hyperplane to separate two classes. The difference is that it incorporates minimum within-class scatter and maximum between-class scatter in Linear Discriminant Analysis (LDA) into SVM. These two scatters represent the distributions of the training dataset, and the optimization of WBS-SVM ensures the samples in the same class are as close as possible and the samples in different classes are as far as possible. Experiments on the K-, F-, G-type stellar spectra from Sloan Digital Sky Survey (SDSS), Data Release 8 show that our proposed WBS-SVM can greatly improve the classification accuracies.  相似文献   

基于多源遥感数据的日本海内波特征研究   总被引：2，自引：1，他引：1  

孙丽娜  张杰  孟俊敏  王晶  张旭东 《海洋学报》2018,40(3):102-111

日本海特殊的地理位置和复杂的地形使得该海域内波表征极为复杂，遥感是大范围观测内波的有效手段，已被广泛应用于内波的探测研究。本文利用MODIS、GF-1和ENVISAT ASAR遥感影像，开展了日本海内波特征研究。通过提取内波波峰线，生成了日本海内波空间分布图；获取了内波的波峰线长度和传播速度，并基于非线性薛定谔方程反演了内波振幅。研究结果表明，日本海内波分布范围宽广，不仅大陆架沿海区内波分布密集，深海盆地也探测到了大量内波；日本海北部45°N附近海域有少量内波出现，利用高分影像探测到朝鲜陆架浅海区有大量小尺度内波，大和海盆、大和隆起的西南部海域没有发现内波。日本海内波波峰线长达100多千米，深海区的传播速度大于1 m/s；浅海区内波振幅约10 m左右，深海区可达60 m以上。  相似文献   

A Preliminary Genetic Linkage Map of Sinonovacula constricta(Lamarck, 1818) Based on Microsatellites Derived from RAD Sequencing     

WU Xueping  FENG Yanwei  JIANG Hailin  LIU Xiangquan  PAN Ying 《中国海洋大学学报(英文版)》2018,(4)

Sinonovacula constricta is one of the important economic aquaculture species in China. In this study, we constructed genetic linkage maps of S. constricta based on 300 microsatellite markers derived from RAD-seq using an F1 full-sib family. The female map contained 204 microsatellites assigned to 22 linkage groups, which covered 1529.5 cM with an average interval of 10.3 cM. The male consisted of 187 microsatellites in 19 linkage groups corresponding to the haploid chromosome number(n(28)19), which spanned 1429.3 cM with an average interval of 8.7 cM. The genome coverage was approximately 83.5% and 81.4%, respectively. An integrated map was constructed according to the common markers in parental linkage groups, which had a total length of 1683.8 cM with an average interval of 7.3 cM. The genome coverage of the integrated map was approximately 86.3%. The genetic linkage map would form the foundation for further studies on the quantitative trait loci(QTL), as well as accelerating the breeding process of this species.  相似文献   

Levels of Metabolic Enzymes and Nitrogenous Compounds in the Swimming Crab Portunus trituberculatus Exposed to Elevated Ambient Ammonia-N     

PAN Luqing  SI Lingjun  LIU Shengnan  LIU Maoqi  WANG Guohui 《中国海洋大学学报(英文版)》2018,(4)

This study investigated the effects of ammonia-N(control and 1 and 5 mg L~(-1)) on the changes of metabolic enzymes activities and nitrogenous compounds levels in the gills, hepatopancreas, muscles, and hemolymph of the swimming crab Portunus trituberculatus. Results showed that the levels of hemolymph ammonia increased significantly at 6 h and then decreased to control level at 12 h. The activities of key enzymes involved in biosynthesis pathways of glutamine(Gln) and urea, such as glutamate dehydrogenase(GDH), glutamine synthetase(GS), and arginase(ARG), increased remarkably in different tissues of P. trituberculatus. Gln level was the highest in muscles, while urea content was the largest in hepatopancreas. The m RNA expression level of xanthine dehydrogenase(XDH) was downregulated sharply in gills but upregulated in the hepatopancreas and muscles. A small amount of uric acid was detected in the hemolymph. This result suggests that Gln in muscles may be used as an intermediary nitrogen repository, while urea may be primarily synthesized in the hepatopancreas and then transferred to other tissues via the hemolymph. Uric acid could be synthesized by the anabolism of purine nucleotides, in additon to the inhibitory activities of gills. In addition, the levels of Gln, urea and uric acid exhibited dose-and time-dependent effects with ammonia content. Therefore, P. trituberculatus could possibly convert ammonia into Gln, urea, or uric acid to detoxify ammonia during high ambient ammonia-N stress.  相似文献