期刊文献+
共找到8,683篇文章
< 1 2 250 >
每页显示 20 50 100
COMPLETE KAHLER METRICS WITH POSITIVE HOLOMORPHIC SECTIONAL CURVATURES ON CERTAIN LINE BUNDLES(RELATED TO A COHOMOGENEITY ONE POINT OF VIEW ON A YAU CONJECTURE) 被引量:1
1
作者 段晓曼 关庄丹 《Acta Mathematica Scientia》 SCIE CSCD 2024年第1期78-102,共25页
In this article,we study Kahler metrics on a certain line bundle over some compact Kahler manifolds to find complete Kahler metrics with positive holomorphic sectional(or bisectional)curvatures.Thus,we apply a strateg... In this article,we study Kahler metrics on a certain line bundle over some compact Kahler manifolds to find complete Kahler metrics with positive holomorphic sectional(or bisectional)curvatures.Thus,we apply a strategy to a famous Yau conjecture with a co-homogeneity one geometry. 展开更多
关键词 Kahler Metrics complete Riemannian metrics open complex manifolds holomorphic bisectional curvature C*bundle almost homogeneous manifolds
下载PDF
Navigation Finsler metrics on a gradient Ricci soliton
2
作者 LI Ying MO Xiao-huan WANG Xiao-yang 《Applied Mathematics(A Journal of Chinese Universities)》 SCIE CSCD 2024年第2期266-275,共10页
In this paper,we study a class of Finsler metrics defined by a vector field on a gradient Ricci soliton.We obtain a necessary and sufficient condition for these Finsler metrics on a compact gradient Ricci soliton to b... In this paper,we study a class of Finsler metrics defined by a vector field on a gradient Ricci soliton.We obtain a necessary and sufficient condition for these Finsler metrics on a compact gradient Ricci soliton to be of isotropic S-curvature by establishing a new integral inequality.Then we determine the Ricci curvature of navigation Finsler metrics of isotropic S-curvature on a gradient Ricci soliton generalizing result only known in the case when such soliton is of Einstein type.As its application,we obtain the Ricci curvature of all navigation Finsler metrics of isotropic S-curvature on Gaussian shrinking soliton. 展开更多
关键词 gradient Ricci soliton navigation Finsler metric isotropic S-curvature Ricci curvature Gaussian shrinking soliton
下载PDF
The Correct Reissner-Nordstrøm, Kerr and Kerr-Newman Metrics
3
作者 Carlo Maria Pace 《Journal of Modern Physics》 2024年第10期1502-1522,共21页
In a very recent article of mine I have corrected the traditional derivation of the Schwarzschild metric thus arriving to formulate a correct Schwarzschild metric different from the traditional Schwarzschild metric. I... In a very recent article of mine I have corrected the traditional derivation of the Schwarzschild metric thus arriving to formulate a correct Schwarzschild metric different from the traditional Schwarzschild metric. In this article, starting from this correct Schwarzschild metric, I also propose corrections to the other traditional Reissner-Nordstrøm, Kerr and Kerr-Newman metrics on the basis of the fact that these metrics should be equal to the correct Schwarzschild metric in the borderline case in which they reduce to the case described by this metric. In this way, we see that, like the correct Schwarzschild metric, also the correct Reissner-Nordstrøm, Kerr and Kerr-Newman metrics do not present any event horizon (and therefore do not present any black hole) unlike the traditional Reissner-Nordstrøm, Kerr and Kerr-Newman metrics. 展开更多
关键词 General Theory of Relativity SCHWARZSCHILD Reissner-Nordstrøm KERR Kerr-Newman Metric Event Horizon Black Hole
下载PDF
MAXWELL-EINSTEIN METRICS ON COMPLETIONS OF CERTAIN C* BUNDLES 被引量:2
4
作者 关庄丹 《Acta Mathematica Scientia》 SCIE CSCD 2023年第1期363-372,共10页
In this paper,we prove that for some completions of certain fiber bundles there is a Maxwell-Einstein metric conformally related to any given Kahler class.
关键词 Hermitian metrics Maxwell-Einstein metrics complex manifolds scalar curvature fiber bundle almost homogeneous manifolds
下载PDF
Novel Metrics for Mutation Analysis
5
作者 Savas Takan Gokmen Katipoglu 《Computer Systems Science & Engineering》 SCIE EI 2023年第8期2075-2089,共15页
A measure of the“goodness”or efficiency of the test suite is used to determine the proficiency of a test suite.The appropriateness of the test suite is determined through mutation analysis.Several Finite State Machi... A measure of the“goodness”or efficiency of the test suite is used to determine the proficiency of a test suite.The appropriateness of the test suite is determined through mutation analysis.Several Finite State Machine(FSM)mutants are produced in mutation analysis by injecting errors against hypotheses.These mutants serve as test subjects for the test suite(TS).The effectiveness of the test suite is proportional to the number of eliminated mutants.The most effective test suite is the one that removes the most significant number of mutants at the optimal time.It is difficult to determine the fault detection ratio of the system.Because it is difficult to identify the system’s potential flaws precisely.In mutation testing,the Fault Detection Ratio(FDR)metric is currently used to express the adequacy of a test suite.However,there are some issues with this metric.If both test suites have the same defect detection rate,the smaller of the two tests is preferred.The test case(TC)is affected by the same issue.The smaller two test cases with identical performance are assumed to have superior performance.Another difficulty involves time.The performance of numerous vehicles claiming to have a perfect mutant capture time is problematic.Our study developed three metrics to address these issues:FDR/|TS|,FDR/|TC|,and FDR/|Time|;In this context,most used test generation tools were examined and tested using the developed metrics.Thanks to the metrics we have developed,the research contributes to eliminating the problems related to performance measurement by integrating the missing parameters into the system. 展开更多
关键词 Software engineering TESTING mutation analysis fault detection ratio metrics TIME
下载PDF
Characterisation of Meteorological Drought in Northern Nigeria Using Comparative Rainfall-Based Drought Metrics
6
作者 Onemayin David Jimoh Martins Yusuf Otache +2 位作者 Adeolu Richard Adesiji Rotimi Saka Olaleye James Agajo 《Journal of Water Resource and Protection》 CAS 2023年第2期51-70,共20页
Meteorological droughts occur when there is deficiency in rainfall;i.e. rainfall availability is below some acclaimed normal values. Hence, the greater challenge is to be able to obtain suitable methods for assessing ... Meteorological droughts occur when there is deficiency in rainfall;i.e. rainfall availability is below some acclaimed normal values. Hence, the greater challenge is to be able to obtain suitable methods for assessing drought occurrence, its onset or initiation and termination. Thus, an attempt was made in this paper to evaluate the performance of Standardised Precipitation Index (SPI) and Standardised Precipitation Anomaly Index (SPAI) to characterise drought in Northern Nigeria for purposes of comparison and eventual adoption of probable candidate index for the development of an Early Warning System. The findings indicated that despite the fact that the annual timescale may be long, it can be employed to obtain information on the temporal evolution of drought especially, regional behaviour. However, monthly timescale can be more appropriate if emphasis is on evaluating the effects of drought in situations relating to water supply, agriculture and groundwater abstractions. The SPAI can be employed for periodic rainfall time series though;it accentuates drought signatures and may not necessarily dampen high fluctuations due to implications of high climatic variability considering the stochastic nature and state transition of drought phenomena. On the other hand, the temporal evolution of SPI and SPAI were not coherent at different temporal accumulations with differences in fluctuations. However, despite the differences between the SPI and SPAI, generally at some timescales, for instance, 6-month accumulation, both spatial and temporal distributions of drought characteristics were seemingly consistent. In view of the observed shortcomings of both indices, especially the SPI, the Standardised Nonstationary Precipitation Index (SnsPI) should be looked into and too, other indexes that take into consideration the implications of global warming by incorporating potential evapotranspiration may be deemed more suitable for drought studies in Northern Nigeria. 展开更多
关键词 Characterisation TIMESCALE METEOROLOGICAL DROUGHT Metrics
下载PDF
A Component Selection Framework of Cohesion and Coupling Metrics
7
作者 M.Iyyappan Arvind Kumar +3 位作者 Sultan Ahmad Sudan Jha Bader Alouffi Abdullah Alharbi 《Computer Systems Science & Engineering》 SCIE EI 2023年第1期351-365,共15页
Component-based software engineering is concerned with the develop-ment of software that can satisfy the customer prerequisites through reuse or inde-pendent development.Coupling and cohesion measurements are primaril... Component-based software engineering is concerned with the develop-ment of software that can satisfy the customer prerequisites through reuse or inde-pendent development.Coupling and cohesion measurements are primarily used to analyse the better software design quality,increase the reliability and reduced system software complexity.The complexity measurement of cohesion and coupling component to analyze the relationship between the component module.In this paper,proposed the component selection framework of Hexa-oval optimization algorithm for selecting the suitable components from the repository.It measures the interface density modules of coupling and cohesion in a modular software sys-tem.This cohesion measurement has been taken into two parameters for analyz-ing the result of complexity,with the help of low cohesion and high cohesion.In coupling measures between the component of inside parameters and outside parameters.Thefinal process of coupling and cohesion,the measured values were used for the average calculation of components parameter.This paper measures the complexity of direct and indirect interaction among the component as well as the proposed algorithm selecting the optimal component for the repository.The better result is observed for high cohesion and low coupling in compo-nent-based software engineering. 展开更多
关键词 Component-based software system coupling metric cohesion metric complexity component interface module density
下载PDF
Evaluating grant proposals:lessons from using metrics as screening device
8
作者 Katerina Guba Alexey Zheleznov Elena Chechik 《Journal of Data and Information Science》 CSCD 2023年第2期66-92,共27页
Purpose:This study examines the effects of using publication-based metrics for the initial screening in the application process for a project leader.The key questions are whether formal policy affects the allocation o... Purpose:This study examines the effects of using publication-based metrics for the initial screening in the application process for a project leader.The key questions are whether formal policy affects the allocation of funds to researchers with a better publication record and how the previous academic performance of principal investigators is related to future project results.Design/methodology/approach:We compared two competitions,before and after the policy raised the publication threshold for the principal investigators.We analyzed 9,167 papers published by 332 winners in physics and the social sciences and humanities(SSH),and 11,253 publications resulting from each funded project.Findings:We found that among physicists,even in the first period,grants tended to be allocated to prolific authors publishing in high-quality journals.In contrast,the SSH project grantees had been less prolific in publishing internationally in both periods;however,in the second period,the selection of grant recipients yielded better results regarding awarding grants to more productive authors in terms of the quantity and quality of publications.There was no evidence that this better selection of grant recipients resulted in better publication records during grant realization.Originality:This study contributes to the discussion of formal policies that rely on metrics for the evaluation of grant proposals.The Russian case shows that such policy may have a profound effect on changing the supply side of applicants,especially in disciplines that are less suitable for metric-based evaluations.In spite of the criticism given to metrics,they might be a useful additional instrument in academic systems where professional expertise is corrupted and prevents allocation of funds to prolific researchers. 展开更多
关键词 Grant funding Research evaluation Publication-based metrics Funding allocation
下载PDF
NATURALLY REDUCTIVE(α_(1),α_(2))METRICS
9
作者 谭举 许明 《Acta Mathematica Scientia》 SCIE CSCD 2023年第4期1547-1560,共14页
Letting F be a homogeneous(α_(1),α_(2))metric on the reductive homogeneous manifold G/H,we first characterize the natural reductiveness of F as a local f-product between naturally reductive Riemannian metrics.Second... Letting F be a homogeneous(α_(1),α_(2))metric on the reductive homogeneous manifold G/H,we first characterize the natural reductiveness of F as a local f-product between naturally reductive Riemannian metrics.Second,we prove the equivalence among several properties of F for its mean Berwald curvature and S-curvature.Finally,we find an explicit flag curvature formula for G/H when F is naturally reductive. 展开更多
关键词 (α_1 α_2)metric homogeneous Finsler space naturally reductive S-CURVATURE
下载PDF
ISO25000-Related Metrics for Evaluating the Quality of Complex Information Systems
10
作者 Antonia Stefani Bill Vassiliadis 《Journal of Computer and Communications》 2023年第9期18-43,共26页
Evaluating complex information systems necessitates deep contextual knowledge of technology, user needs, and quality. The quality evaluation challenges increase with the system’s complexity, especially when multiple ... Evaluating complex information systems necessitates deep contextual knowledge of technology, user needs, and quality. The quality evaluation challenges increase with the system’s complexity, especially when multiple services supported by varied technological modules, are offered. Existing standards for software quality, such as the ISO25000 series, provide a broad framework for evaluation. Broadness offers initial implementation ease albeit, it often lacks specificity to cater to individual system modules. This paper maps 48 data metrics and 175 software metrics on specific system modules while aligning them with ISO standard quality traits. Using the ISO25000 series as a foundation, especially ISO25010 and 25012, this research seeks to augment the applicability of these standards to multi-faceted systems, exemplified by five distinct software modules prevalent in modern information ecosystems. 展开更多
关键词 Software Quality Information Systems Quality Standards Quality Metrics ISO25000
下载PDF
MultiDMet: Designing a Hybrid Multidimensional Metrics Framework to Predictive Modeling for Performance Evaluation and Feature Selection
11
作者 Tesfay Gidey Hailu Taye Abdulkadir Edris 《Intelligent Information Management》 2023年第6期391-425,共35页
In a competitive digital age where data volumes are increasing with time, the ability to extract meaningful knowledge from high-dimensional data using machine learning (ML) and data mining (DM) techniques and making d... In a competitive digital age where data volumes are increasing with time, the ability to extract meaningful knowledge from high-dimensional data using machine learning (ML) and data mining (DM) techniques and making decisions based on the extracted knowledge is becoming increasingly important in all business domains. Nevertheless, high-dimensional data remains a major challenge for classification algorithms due to its high computational cost and storage requirements. The 2016 Demographic and Health Survey of Ethiopia (EDHS 2016) used as the data source for this study which is publicly available contains several features that may not be relevant to the prediction task. In this paper, we developed a hybrid multidimensional metrics framework for predictive modeling for both model performance evaluation and feature selection to overcome the feature selection challenges and select the best model among the available models in DM and ML. The proposed hybrid metrics were used to measure the efficiency of the predictive models. Experimental results show that the decision tree algorithm is the most efficient model. The higher score of HMM (m, r) = 0.47 illustrates the overall significant model that encompasses almost all the user’s requirements, unlike the classical metrics that use a criterion to select the most appropriate model. On the other hand, the ANNs were found to be the most computationally intensive for our prediction task. Moreover, the type of data and the class size of the dataset (unbalanced data) have a significant impact on the efficiency of the model, especially on the computational cost, and the interpretability of the parameters of the model would be hampered. And the efficiency of the predictive model could be improved with other feature selection algorithms (especially hybrid metrics) considering the experts of the knowledge domain, as the understanding of the business domain has a significant impact. 展开更多
关键词 Predictive Modeling Hybrid Metrics Feature Selection Model Selection Algorithm Analysis Machine Learning
下载PDF
科学活动理论视角下的Altmetrics主题演化研究
12
作者 杨岳 《情报理论与实践》 北大核心 2023年第11期73-80,共8页
[目标/意义]通过构建中观层面的网络和社交媒体时代科学活动理论模型,探索科学活动视角下的Altmetrics的主题演化特征。[方法/过程]使用解释性内容分析法对Altmetrics相关文献进行梳理,进行聚类分析和时间序列分析,以了解Altmetrics研... [目标/意义]通过构建中观层面的网络和社交媒体时代科学活动理论模型,探索科学活动视角下的Altmetrics的主题演化特征。[方法/过程]使用解释性内容分析法对Altmetrics相关文献进行梳理,进行聚类分析和时间序列分析,以了解Altmetrics研究主题的演变规律,并进一步比较国内外Altmetrics研究的差异。[结果/结论]时间序列分析揭示了Altmetrics研究的细分领域存在不同程度的相似性和差异性。研究结果表明,科学活动理论框架有助于描述Altmetrics数据和指标背后的社会现象和行为机制。这一框架能更好地体现科学界的“以人为本”的本质和趋势,从社会学的研究视角弥补Altmetrics作为定量研究方法的局限性,探索网络和社交媒体时代科学计量学的社会学转向。 展开更多
关键词 Altmetrics 科学社会学 活动理论 科学活动理论 科学活动计量
下载PDF
Adapted Metrics for a Modified Coulomb/Newton’s Potential
13
作者 Lucian M. Ionescu Cristina-Liliana Pripoae Gabriel Pripoae 《Journal of High Energy Physics, Gravitation and Cosmology》 2023年第4期1311-1355,共45页
Modified Theories of Gravity include spin dependence in General Relativity, to account for additional sources of gravity instead of dark matter/energy approach. The spin-spin interaction is already included in the eff... Modified Theories of Gravity include spin dependence in General Relativity, to account for additional sources of gravity instead of dark matter/energy approach. The spin-spin interaction is already included in the effective nuclear force potential, and theoretical considerations and experimental evidence hint to the hypothesis that Gravity originates from such an interaction, under an averaging process over spin directions. This invites to continue the line of theory initiated by Einstein and Cartan, based on tetrads and spin effects modeled by connections with torsion. As a first step in this direction, the article considers a new modified Coulomb/Newton Law accounting for the spin-spin interaction. The physical potential is geometrized through specific affine connections and specific semi-Riemannian metrics, canonically associated to it, acting on a manifold or at the level of its tangent bundle. Freely falling particles in these “toy Universes” are determined, showing an interesting behavior and unexpected patterns. 展开更多
关键词 Modified Gravity Theory SPIN Coulomb’s Law Newton’s Law Modified Coulomb’s Law Nuclear Force Adapted Connection Adapted Metric
下载PDF
电子资源使用评估与E-Metrics 被引量:12
14
作者 张玲 孙坦 《图书馆杂志》 CSSCI 北大核心 2005年第3期24-27,共4页
E-Metrics 项目是美国研究图书馆协会新评估计划的5个子项目之一。本文对E-Metrics 项目的产生背景及发展历程进行较为详细的介绍,并对整个项目进行简要的评价。
关键词 E—Metrics项目 图书馆 电子资源 网络环境
下载PDF
模糊Credit Metrics模型及其在信用风险评估中的应用 被引量:7
15
作者 王珂 孟海丽 杨全 《金融理论与实践》 北大核心 2016年第2期59-64,共6页
在经典的Credit Metrics模型中,通常假设具有相同信用评级的债务人的贷款是同质的,即具有相同的信用等级转移概率,且在实际应用中这种概率难以精确估计。这些局限性大大限制了该方法在实际中的应用。为了更好地描述和处理关于信用等级... 在经典的Credit Metrics模型中,通常假设具有相同信用评级的债务人的贷款是同质的,即具有相同的信用等级转移概率,且在实际应用中这种概率难以精确估计。这些局限性大大限制了该方法在实际中的应用。为了更好地描述和处理关于信用等级转移的模糊信息,借鉴经典Credit Metrics模型的思想,提出了模糊Credit Metrics模型,通过将传统的确定的信用转移矩阵模糊化,从而利用二型模糊变量来对信贷资产的远期价值进行描述和刻画,在此基础上对信贷资产的期望值和在险价值等量化指标进行计算,为基于不确定信息或专家主观判断的信用风险评估提供了一种系统的有效方法。 展开更多
关键词 模糊Credit Metrics模型 信用风险 风险评估 在险价值 二型模糊变量
下载PDF
Effect of slice scope on data slice-based class cohesion metrics 被引量:3
16
作者 周毓明 徐宝文 《Journal of Southeast University(English Edition)》 EI CAS 2008年第2期174-177,共4页
This paper suggests that a single class rather than methods should be used as the slice scope to compute class cohesion. First, for a given attribute, the statements in all methods that last define the attribute are c... This paper suggests that a single class rather than methods should be used as the slice scope to compute class cohesion. First, for a given attribute, the statements in all methods that last define the attribute are computed. Then, the forward and backward data slices for this attribute are generated by using the class as the slice scope and are combined to compute the corresponding class data slice. Finally, the class cohesion is computed based on all class data slices for the attributes. Compared to traditional cohesion metrics that use methods as the slice scope, the proposed metrics that use a single class as slice scope take into account the possible interactions between the methods. The experimental results show that class cohesion can be more accurately measured when using the class as the slice scope. 展开更多
关键词 COHESION class data slice metrics OBJECT-ORIENTED
下载PDF
基于Credit Metrics的城投公司结构性风险评价研究 被引量:2
17
作者 孙慧 高磊 《兰州交通大学学报》 CAS 2014年第6期82-87,共6页
随着我国城市基础设施建设规模的快速扩大,城市基础设施建设投资公司项目类型多元化与融资方式多元化匹配造成的结构性风险已经成为影响其健康发展的主要问题.在分析了城投公司结构性风险的发生机理及传导机制的基础上,针对城投公司债... 随着我国城市基础设施建设规模的快速扩大,城市基础设施建设投资公司项目类型多元化与融资方式多元化匹配造成的结构性风险已经成为影响其健康发展的主要问题.在分析了城投公司结构性风险的发生机理及传导机制的基础上,针对城投公司债务的信用转移问题,运用Credit Metrics模型对城投公司结构性风险进行评价研究.结果表明,城投公司存在结构性风险且隐患巨大.一旦资金链出现问题,城投公司的债务将出现严重的违约情况. 展开更多
关键词 城投公司 结构性风险 CREDIT Metrics VAR
下载PDF
Google Scholar Metrics中文期刊H指数评价研究 被引量:3
18
作者 杨毓丽 陈陶 张苏 《情报杂志》 CSSCI 北大核心 2013年第4期68-72,57,共6页
Google在2012年4月1日推出了一项新功能———Google学术计量(Google Scholar Metrics),公布了从2007年4月1日至今包括中文在内10种语言期刊H指数前100的排名。用户可以搜索期刊标题,获取期刊H指数。以Google学术计量H指数排名前100名... Google在2012年4月1日推出了一项新功能———Google学术计量(Google Scholar Metrics),公布了从2007年4月1日至今包括中文在内10种语言期刊H指数前100的排名。用户可以搜索期刊标题,获取期刊H指数。以Google学术计量H指数排名前100名的中文期刊为来源数据库,通过测算Google学术计量和中文期刊引文数据库(CNKI)的期刊H指数,了解二者之间的差异和联系。统计结果表明,Google的期刊H指数和CNKI的H指数呈相关性,对于同一种期刊,90%的Google期刊H指数低于CNKI期刊H指数。 展开更多
关键词 Google学术计量 H指数 中文期刊引文数据库
下载PDF
Altmetrics工具的起源、质疑、改进与发展 被引量:4
19
作者 刘春丽 《图书馆杂志》 CSSCI 北大核心 2018年第3期84-91,共8页
对Altmetrics的发展过程及现状进行了较为系统的总结,主要包括Altmetrics工具的起源、危机和转型三方面,厘清Altmetrics工具的产生背景,系统阐释了其面对来自科学共同体内、外的质疑和挑战,采取的积极应答、改进和发展的具体策略。
关键词 Altmetrics Article-Level Metrics 开放科学 科研成果评价
下载PDF
国外Altmetrics理论研究与实践进展 被引量:7
20
作者 刘丽敏 王晴 《情报理论与实践》 CSSCI 北大核心 2017年第3期132-137,共6页
为了总结现状,启迪创新,将Altmetrics研究引向深入,利用文献调研和内容分析等方法解读国外Altmetrics理论研究及实践进展,提出未来展望。研究表明:开放存取事业发展、科学交流模式变革和计量研究范式转向是Altmetrics产生的背景;Altmetr... 为了总结现状,启迪创新,将Altmetrics研究引向深入,利用文献调研和内容分析等方法解读国外Altmetrics理论研究及实践进展,提出未来展望。研究表明:开放存取事业发展、科学交流模式变革和计量研究范式转向是Altmetrics产生的背景;Altmetrics是传统评价机制的合理补充而非全盘替代,论文层面的Altmetrics等同于ALMs,价值特征表现在广度、多样、速度和开放4个方面;Altmetrics对计量工具的依附性较强,目前国际上发展比较成熟的4款工具分别是PLo S,Altmetric,Impact Story和Plum Analytics;研究发现和评价是Altmetrics的两大核心功能,在图书馆和机构知识库领域具有广阔的应用空间;Altmetrics目前仍处于起步阶段,应深化基础理论体系建构研究和应用实践探索。 展开更多
关键词 补充计量学 计量指标 计量工具 理论研究 应用研究
下载PDF
上一页 1 2 250 下一页 到第
使用帮助 返回顶部