长期以来,疏散星团成员星的证认问题一直是天文学领域的一个挑战,由于疏散星团形成及演化的复杂性,没有统一的方法能准确地确定疏散星团中的成员星.目标是以3种不同空间分布类型的疏散星团为样本,选取恒星的位置和运动的五维参数,通过DB...长期以来,疏散星团成员星的证认问题一直是天文学领域的一个挑战,由于疏散星团形成及演化的复杂性,没有统一的方法能准确地确定疏散星团中的成员星.目标是以3种不同空间分布类型的疏散星团为样本,选取恒星的位置和运动的五维参数,通过DBSCAN(Density-Based Spatial Clustering of Applications with Noise)、FOF(Friend of Friend)和STAR GO(Star's Galactic Origin)3种聚类方法,对疏散星团进行聚类检测,量化不同算法的绩效.研究结果表明,FOF与STAR GO算法对有特殊结构的星团更为适用,能识别出星团的潮汐或延展结构,而DBSCAN对星团核心区域成员星的识别更为完整.旨在星团结构细节与提高成员星识别的完整性之间找到更均衡的算法策略.展开更多
We investigate the relationships between infrared excess(IRX = LIR/LUV) and Balmer decrement(Hα/Hβ) as indicators of dust attenuation for 609 H II regions at scales of ~50–200 pc in NGC 628, utilizing data from Ast...We investigate the relationships between infrared excess(IRX = LIR/LUV) and Balmer decrement(Hα/Hβ) as indicators of dust attenuation for 609 H II regions at scales of ~50–200 pc in NGC 628, utilizing data from AstroSat, the James Webb Space Telescope(JWST) and Multi Unit Spectroscopic Explorer. Our findings indicate that about three-fifths of the sample H II regions reside within the regime occupied by local star-forming galaxies(SFGs) along the dust attenuation correlation described by their corresponding color excess parameters E(B-V)IRX= 0.51 E(B-V)Hα/Hβ. Nearly 27% of the sample exhibits E(B-V)IRX> E(B-V)Hα/Hβ, while a small fraction(~13%) displays significantly lower E(B-V)IRXcompared to E(B-V)Hα/Hβ. These results suggest that the correlation between the two dust attenuation indicators no longer holds for spatially resolved H II regions. Furthermore, the ratio of E(B-V)IRXto E(B-V)Hα/Hβremains unaffected by various physical parameters of the H II regions, including star formation rate(SFR), SFR surface density, infrared luminosity(LIR),LIRsurface density, stellar mass, gas-phase metallicity, circularized radius, and the distance to the galactic center.We argue that the ratio is primarily influenced by the evolution of the surrounding interstellar medium of the starforming regions, transitioning from an early dense and thick phase to the late blown-away stage.展开更多
The inner Milky Way disk globular cluster NGC 6362 appears to exhibit tidal tails composed of stars that have proper motions and positions in the color–magnitude diagram similar to those of cluster stars. Because rec...The inner Milky Way disk globular cluster NGC 6362 appears to exhibit tidal tails composed of stars that have proper motions and positions in the color–magnitude diagram similar to those of cluster stars. Because recent results seem also to show that these stars are distributed across the regions least affected by interstellar absorption and reproduce the observed composite star field density map, we carried out a detailed spectroscopic analysis of a number of chemical element abundances of tidal tail star candidates in order to investigate the relationship between them and NGC 6362. From European Southern Observatory's VLT@FLAMES spectra we found that the red giant branch stars selected as the cluster's tidal tail stars neither have overall metallicities nor abundances of Mg, Ca, Sc, Ti, Cr, Ni and Ba similar to the cluster's ones. Moreover, they are mainly alike to stars that belong to the Milky Way thick disk, some of them could be part of the thin disk and a minor percentage could belong to the Milky Way halo star population. On the other hand, since the resulting radial velocities do not exhibit a distribution function similar to that of the cluster's stars, we concluded that looking for kinematic properties similar to those of the cluster would not seem to be as suitable of an approach for selecting the cluster's tidal tail stars as previously thought.展开更多
学术背景:长期以来,医疗相关部门和管理机构制定指南都是通过收集不全面的临床试验和(或)专家意见而完成,在医疗资源有限的情况下,如何满足人们日益增长的健康需求刻不容缓。循证医学的出现为解决这一矛盾开辟了新的思路,尤其是循证医...学术背景:长期以来,医疗相关部门和管理机构制定指南都是通过收集不全面的临床试验和(或)专家意见而完成,在医疗资源有限的情况下,如何满足人们日益增长的健康需求刻不容缓。循证医学的出现为解决这一矛盾开辟了新的思路,尤其是循证医学临床实践指南能更合理地制定临床决策,并减轻患者的医疗负担。好的指南必须使用循证医学的原则和方法加以制定和完善,而临床医生工作繁忙、时间有限,详细了解循证临床实践指南的产生、制作过程几乎不太可能,如何快速有效的查找和利用循证临床实践指南少见报道。目的:为使众多的医务工作者了解循证医学临床实践指南,详细阐述临床实践指南的意义及产生过程、网络资源及检索方法。检索策略:由四川大学华西医院图书信息中心的图书馆员应用计算机检索PubMed、NGC及Cochrane Library数据库1990-01/2007-05的相关文献,检索词"evidence based medicine,clinical practice,guideline,search",并限定文章语言种类为English。同时计算机检索CBMdisc、CNKI、VIP中文数据库1999-01/2007-05的相关文献,检索词"循证医学,临床实践,指南,检索",并限定文章语言种类为中文。共检索到109篇文献,对资料进行初审,纳入标准:①临床实践指南研究。②采用循证医学原理与方法。③阐述内容完整,结论真实可靠。排除标准:重复性研究。文献评价:对符合纳入标准的内容进行循证医学系统评价,文献的筛选由两位作者独立完成,不同意见协商解决,协商不成咨询第3方。所选用的35篇文献中,9篇为综述,12篇为应用研究(包括临床循证治疗),其余均为临床或基础实验研究。资料综合:制定临床实践指南过程复杂,通过搜索现有的临床实践指南信息资源,可以有效提高指南的质量和制定效率。目前国内循证医学指南还没有整合的网站,但有一些专业循证医学指南杂志或网站提供检索服务。检索方式主要为计算机检索,不同的数据库和系统有各自的检索途径和界面,灵活使用检索技术与掌握多种检索方法是提高查全率和查准率的关键。循证临床实践逐渐受到医疗、管理、保险等相关行业的重视,借此系统评价希望达到以下目标:①在有限的医疗卫生资源下,医生能更好的做出医疗决策,避免或减少医疗差错的发生。②患者能得到更有效、及时的治疗,同时能更节省医疗费用。③管理和保险等相关职能部门在制定决策时能采用循证决策。④医生在诊治患者的过程中懂得正确查找和有效利用循证临床实践指南。结论:通过对循证临床实践指南的检索研究,能够让更多的医务工作者了解和掌握一些重要的临床实践指南信息资源,在临床实践过程中快速查找并加以有效利用。有关循证临床实践指南的制作未详细阐述,需要参阅更多的专门研究。展开更多
成员判定是疏散星团研究中最关键的一步,成员判定的好坏直接影响对星团基本参数的估计.首次利用数据挖掘技术中的DBSCAN(Density-Based Spatial Clustering of Applications with Noise)聚类算法对疏散星团NGC 6791和M67(NGC 2682)分别...成员判定是疏散星团研究中最关键的一步,成员判定的好坏直接影响对星团基本参数的估计.首次利用数据挖掘技术中的DBSCAN(Density-Based Spatial Clustering of Applications with Noise)聚类算法对疏散星团NGC 6791和M67(NGC 2682)分别进行了成员判定,结果表明DBSCAN聚类算法能很有效地剔除场星污染.得到的NGC6791成员星的颜色-星等图上主序清晰并呈现明显的双重主序结构,这表明NGC 6791可能有更复杂的恒星形成与演化历史.对M67的分析表明出现了质量分层现象,并且星团的核心和外围两部分有明显的相对运动.对NGC 6791和M67的分析均表明DBSCAN聚类算法是一种有效的成员判定方法,有传统成员判定方法不具备的一些优点.展开更多
利用疏散星团NGC 188所在天区的1046颗恒星样本的高精度3维(3D)运动学数据(自行和视向速度)测试了DBSCAN(Density-Based Spatial Clustering of Applications with Noise)聚类算法的成员判定效果.为了避免自行和视向速度的单位不一致带...利用疏散星团NGC 188所在天区的1046颗恒星样本的高精度3维(3D)运动学数据(自行和视向速度)测试了DBSCAN(Density-Based Spatial Clustering of Applications with Noise)聚类算法的成员判定效果.为了避免自行和视向速度的单位不一致带来的影响,在数据预处理阶段将3个分量的数据统一标准化至[0,1]区间.利用第k个最近邻点距离方法分析了1046颗恒星样本在标准化无量纲3D速度空间的分布特征,再根据第k个最近邻点距离随k值的变化趋势确定了DBSCAN聚类算法的输入参数(Eps,MinPts),最后利用DBSCAN聚类算法分离出497颗3D运动学成员星.分析结果表明得到的3D运动学成员星是可靠的.展开更多
文摘长期以来,疏散星团成员星的证认问题一直是天文学领域的一个挑战,由于疏散星团形成及演化的复杂性,没有统一的方法能准确地确定疏散星团中的成员星.目标是以3种不同空间分布类型的疏散星团为样本,选取恒星的位置和运动的五维参数,通过DBSCAN(Density-Based Spatial Clustering of Applications with Noise)、FOF(Friend of Friend)和STAR GO(Star's Galactic Origin)3种聚类方法,对疏散星团进行聚类检测,量化不同算法的绩效.研究结果表明,FOF与STAR GO算法对有特殊结构的星团更为适用,能识别出星团的潮汐或延展结构,而DBSCAN对星团核心区域成员星的识别更为完整.旨在星团结构细节与提高成员星识别的完整性之间找到更均衡的算法策略.
基金supported by the National Key Research and Development Program of China (2023YFA1608100)the National Science Foundation of China (NSFC, Grant Nos.12233005, 12073078, 12173088, and 12303015)+3 种基金the China Manned Space Program with grants nos. CMS-CSST-2025-A20 and CMS-CSST-2025-A08the support from the Scientific Research Foundation for High-level Talents of Anhui University of Science and Technology(2024yjrc104)the National Science Foundation of Jiangsu Province (BK20231106)the science research grants from the China Manned Space Project
文摘We investigate the relationships between infrared excess(IRX = LIR/LUV) and Balmer decrement(Hα/Hβ) as indicators of dust attenuation for 609 H II regions at scales of ~50–200 pc in NGC 628, utilizing data from AstroSat, the James Webb Space Telescope(JWST) and Multi Unit Spectroscopic Explorer. Our findings indicate that about three-fifths of the sample H II regions reside within the regime occupied by local star-forming galaxies(SFGs) along the dust attenuation correlation described by their corresponding color excess parameters E(B-V)IRX= 0.51 E(B-V)Hα/Hβ. Nearly 27% of the sample exhibits E(B-V)IRX> E(B-V)Hα/Hβ, while a small fraction(~13%) displays significantly lower E(B-V)IRXcompared to E(B-V)Hα/Hβ. These results suggest that the correlation between the two dust attenuation indicators no longer holds for spatially resolved H II regions. Furthermore, the ratio of E(B-V)IRXto E(B-V)Hα/Hβremains unaffected by various physical parameters of the H II regions, including star formation rate(SFR), SFR surface density, infrared luminosity(LIR),LIRsurface density, stellar mass, gas-phase metallicity, circularized radius, and the distance to the galactic center.We argue that the ratio is primarily influenced by the evolution of the surrounding interstellar medium of the starforming regions, transitioning from an early dense and thick phase to the late blown-away stage.
基金Based on observations collected at the European Southern Observatory under ESO program(s)113.2661.001.
文摘The inner Milky Way disk globular cluster NGC 6362 appears to exhibit tidal tails composed of stars that have proper motions and positions in the color–magnitude diagram similar to those of cluster stars. Because recent results seem also to show that these stars are distributed across the regions least affected by interstellar absorption and reproduce the observed composite star field density map, we carried out a detailed spectroscopic analysis of a number of chemical element abundances of tidal tail star candidates in order to investigate the relationship between them and NGC 6362. From European Southern Observatory's VLT@FLAMES spectra we found that the red giant branch stars selected as the cluster's tidal tail stars neither have overall metallicities nor abundances of Mg, Ca, Sc, Ti, Cr, Ni and Ba similar to the cluster's ones. Moreover, they are mainly alike to stars that belong to the Milky Way thick disk, some of them could be part of the thin disk and a minor percentage could belong to the Milky Way halo star population. On the other hand, since the resulting radial velocities do not exhibit a distribution function similar to that of the cluster's stars, we concluded that looking for kinematic properties similar to those of the cluster would not seem to be as suitable of an approach for selecting the cluster's tidal tail stars as previously thought.
文摘学术背景:长期以来,医疗相关部门和管理机构制定指南都是通过收集不全面的临床试验和(或)专家意见而完成,在医疗资源有限的情况下,如何满足人们日益增长的健康需求刻不容缓。循证医学的出现为解决这一矛盾开辟了新的思路,尤其是循证医学临床实践指南能更合理地制定临床决策,并减轻患者的医疗负担。好的指南必须使用循证医学的原则和方法加以制定和完善,而临床医生工作繁忙、时间有限,详细了解循证临床实践指南的产生、制作过程几乎不太可能,如何快速有效的查找和利用循证临床实践指南少见报道。目的:为使众多的医务工作者了解循证医学临床实践指南,详细阐述临床实践指南的意义及产生过程、网络资源及检索方法。检索策略:由四川大学华西医院图书信息中心的图书馆员应用计算机检索PubMed、NGC及Cochrane Library数据库1990-01/2007-05的相关文献,检索词"evidence based medicine,clinical practice,guideline,search",并限定文章语言种类为English。同时计算机检索CBMdisc、CNKI、VIP中文数据库1999-01/2007-05的相关文献,检索词"循证医学,临床实践,指南,检索",并限定文章语言种类为中文。共检索到109篇文献,对资料进行初审,纳入标准:①临床实践指南研究。②采用循证医学原理与方法。③阐述内容完整,结论真实可靠。排除标准:重复性研究。文献评价:对符合纳入标准的内容进行循证医学系统评价,文献的筛选由两位作者独立完成,不同意见协商解决,协商不成咨询第3方。所选用的35篇文献中,9篇为综述,12篇为应用研究(包括临床循证治疗),其余均为临床或基础实验研究。资料综合:制定临床实践指南过程复杂,通过搜索现有的临床实践指南信息资源,可以有效提高指南的质量和制定效率。目前国内循证医学指南还没有整合的网站,但有一些专业循证医学指南杂志或网站提供检索服务。检索方式主要为计算机检索,不同的数据库和系统有各自的检索途径和界面,灵活使用检索技术与掌握多种检索方法是提高查全率和查准率的关键。循证临床实践逐渐受到医疗、管理、保险等相关行业的重视,借此系统评价希望达到以下目标:①在有限的医疗卫生资源下,医生能更好的做出医疗决策,避免或减少医疗差错的发生。②患者能得到更有效、及时的治疗,同时能更节省医疗费用。③管理和保险等相关职能部门在制定决策时能采用循证决策。④医生在诊治患者的过程中懂得正确查找和有效利用循证临床实践指南。结论:通过对循证临床实践指南的检索研究,能够让更多的医务工作者了解和掌握一些重要的临床实践指南信息资源,在临床实践过程中快速查找并加以有效利用。有关循证临床实践指南的制作未详细阐述,需要参阅更多的专门研究。
文摘利用疏散星团NGC 188所在天区的1046颗恒星样本的高精度3维(3D)运动学数据(自行和视向速度)测试了DBSCAN(Density-Based Spatial Clustering of Applications with Noise)聚类算法的成员判定效果.为了避免自行和视向速度的单位不一致带来的影响,在数据预处理阶段将3个分量的数据统一标准化至[0,1]区间.利用第k个最近邻点距离方法分析了1046颗恒星样本在标准化无量纲3D速度空间的分布特征,再根据第k个最近邻点距离随k值的变化趋势确定了DBSCAN聚类算法的输入参数(Eps,MinPts),最后利用DBSCAN聚类算法分离出497颗3D运动学成员星.分析结果表明得到的3D运动学成员星是可靠的.
