检索结果-南通市图书馆

TIME-EXTRAPOLATION ALGORITHM （TEA） FOR LINEAR PARABOLIC PROBLEMS

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 2014年第2期32卷 183-194页

作者： Hongling hu Chuanmiao Chen kejia Pan College of Mathematics and Computer Science Key Laboratory of High Performance Computing and Stochastic Information Processing (HPCSIP) (Ministry of Education of China) Hunan Normal University Changsha 410081 China School of Mathematics and Statistics Central South University Changsha 410083 China

The fast solutions of Crank-Nicolson scheme on quasi-uniform mesh for parabolic prob- lems are discussed. First, to decrease regularity requirements of solutions, some new error estimates are proved. Second, we analyze the two characteristics of parabolic discrete scheme, and find that the efficiency of Multigrid Method （MG） is greatly reduced. Nu- merical experiments compare the efficiency of Direct Conjugate Gradient Method （DCG） and Extrapolation Cascadic Multigrid Method （EXCMG）. Last, we propose a Time- Extrapolation Algorithm （TEA）, which takes a linear combination of previous several level solutions as good initial values to accelerate the rate of convergence. Some typical extrapolation formulas are compared numerically. And we find that under certain accuracy requirement, the CG iteration count for the 3-order and 7-level extrapolation formula is about 1/3 of that of DCG＇s. Since the TEA algorithm is independent of the space dimension, it is still valid for quasi-uniform meshes. As only the finest grid is needed, the proposed method is regarded very effective for nonlinear parabolic problems.

关键词： Parabolic problem Crank-Nicolson scheme Error estimates Time-extrapolationalgorithm CG-iteration.

Three-dimensional temperature prediction in cylindrical turning with large-chamfer insert based on a modified slip-line field approach

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2021年第10期34卷 265-281页

作者： Cheng hu kejia ZhuANG Yuanwei TANG Jian WENG Xiaoming ZHANG Han DING hubei Digital Manufacturing Key Laboratory School of Mechanical and Electronic EngineeringWuhan University of TechnologyWuhan 430070China Institute of Advanced Materials and Manufacturing Technology Wuhan University of TechnologyWuhan 430070China AECC Guizhou Liyang Aviation Power CO.LTD Guiyang 550000China State Key Laboratory of Digital Manufacturing Equipment and Technology Huazhong University of Science and TechnologyWuhan 430074China

Chamfered inserts have found broader applications in metal cutting process especially in high-performance machining of hard-to-cut materials for their excellent edge resistance and cutting toughness.However,excessive heat generation and resulting high cutting temperature eventually cause severe tool wear and poor surface integrity,which simultaneously limits the optimal selection of machining parameters.In the present study,an analytical thermal–mechanical model is proposed for the prediction of the three-dimensional(3-D)temperature field in cylindrical turning with chamfered round insert based on a modified slip-line field approach.First,an innovative discretization method is introduced in a general 3-D coordinate system to provide a comprehensive demonstration of the irregular cutting geometry and heat generation zones.Then,a plasticity-theory-based slip-line field model is developed and employed to determine the intensities and geometries of every elementary heat sources in Primary Deformation Zones(PDZ),Secondary Deformation Zones(SDZ)and Dead Metal Zones(DMZ).At last,a 3-D analytical model is suggested to calculate the temperature increases caused by the entire heat sources and associated images.The maximum cutting temperature region predicted is found existing upon the chip-tool contact area rather than the tool edge.Moreover,the rationalities of cutting parameters employed are analyzed along with theoretical material removal rates and ensuing maximum cutting temperatures.The results indicate that the cutting conditions with large depth of cut and high cutting speed are more desirable than those with high feed rates.The proposed models are respectively verified through a series of 3-D Finite Element(FE)simulations and dry cutting experiments of Inconel 718 with chamfered round insert.Satisfactory agreement has been reached between the predictions and simulations as well as the measurements,which confirms the correctness and effectiveness of the presented analytical model.

关键词： Analytical model Chamfered round insert Dead metal zone Prediction of temperature Slip-line field

在线全文

学校读者我要写书评

暂无评论

青岛市博物馆藏越州祗园寺西塔基记砖拓本考

中国国家博物馆馆刊 2021年第4期 88-93页

作者：胡可佳青岛市博物馆青岛266061

青岛市博物馆藏越州祗园寺西塔基记砖拓为六舟亲手所拓,并附有题跋,具有较高的历史文化价值。本文对六舟交游及拓本所承载信息进行考证,对比存世的西塔基记砖拓其他版本发现,六舟曾于道光二十六年(1846年)于汤氏私处捶拓祗园寺西塔基记... 详细信息

青岛市博物馆藏越州祗园寺西塔基记砖拓为六舟亲手所拓,并附有题跋,具有较高的历史文化价值。本文对六舟交游及拓本所承载信息进行考证,对比存世的西塔基记砖拓其他版本发现,六舟曾于道光二十六年(1846年)于汤氏私处捶拓祗园寺西塔基记砖,订正了以往塔砖自道光十六年至咸丰十一年(1836-1861)藏于西塔的认识,为西塔基记砖递藏与流传研究提供了新见。

关键词：释六舟祗园寺西塔基记拓片

地方博物馆原创展览策划的思考——基于观众评估研究

在线全文

学校读者我要写书评

暂无评论

博物院 2022年第5期 95-102页

作者：胡可佳青岛市博物馆青岛266061

科学深入的观众调查研究是评估展览和博物馆最有效的方法,也是了解观众需求最直接的方式。采用交叉分析、卡方检验等统计学方法对青岛市博物馆原创展览“从清爱堂走来——刘墉和他的书法艺术展”观众调查数据进行分析研究,通过反思策展... 详细信息

科学深入的观众调查研究是评估展览和博物馆最有效的方法,也是了解观众需求最直接的方式。采用交叉分析、卡方检验等统计学方法对青岛市博物馆原创展览“从清爱堂走来——刘墉和他的书法艺术展”观众调查数据进行分析研究,通过反思策展过程的得与失,以窥观众评估对地方博物馆原创展览策划的积极作用,结合其他博物馆相关实践研究,探讨地方博物馆原创展览评估的必要性及应用对策。

关键词：观众评估地方博物馆原创展览策展

Trend Analysis and Intervention Effect Starting Point Detection of COVID-19 Epidemics Using Recalibrated Time Series Models—Worldwide,2020

在线全文

学校读者我要写书评

暂无评论

China CDC weekly 2021年第20期3卷 417-422页

作者： Shu Li Chen Chen Shuyin Cao Kejia Hu Hao Lei Xiaolin Xu Qinchuan Wang Changzheng Yuan Sicong Wang Sisi Wang Junlin Jia Yuanqing Ye Xifeng Wu Center of Clinical Big Data and Analytics Second Affiliated Hospital and Department of Big Data Health Science School of Public HealthZhejiang University School of MedicineHangzhouZhejiangChina National Institute for Data Science in Health and Medicine HangzhouZhejiang UniversityZhejiangChina Department of Surgical Oncology Affiliated Sir Run Run Shaw HospitalZhejiang University School of MedicineHangzhouZhejiangChina.

Objective:This study aimed to identify a model for short-term coronavirus disease 2019(COVID-19)trend prediction and intervention evaluation.Methods:We compared the autoregressive integrated moving average(ARIMA)model and Holt exponential smoothing(Holt)model on predicting the number of cumulative COVID-19 cases in China.Based on the mean absolute percentage error(MAPE)value,the optimal model was selected and further tested using data from the United States,Italy and Republic of Korea.The intervention effect starting time points and abnormal trend changes were detected by observing the pattern of differences between the predicted and real trends.Results:The recalibrated ARIMA model with a 5-day prediction time span has the best model performance with MAPEs ranged between 2%and 5%.The intervention effects started to show on February 7 in the mainland of China,March 5 in Republic of Korea and April 27 in Italy,but have not been detected in the US as of May 19.Temporary abnormal trends were detected in Korea and Italy,but the overall epidemic trends were stable since the effect starting points.Conclusion:The recalibrated ARIMA model can detect the intervention effects starting points and abnormal trend changes;thus to provide valuable information support for epidemic trend analysis and intervention evaluation.

关键词： starting absolute smoothing

A Spatio-Temporal Heterogeneity Data Accuracy Detection Method Fused by GCN and TCN

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Computer Systems Science & Engineering 2023年第11期47卷 2563-2582页

作者： Tao Liu kejia Zhang Jingsong Yin Yan Zhang Zihao Mu Chunsheng Li Yanan hu School of Computer&Information Technology Northeast Petroleum UniversityDaqing163318China School of Qinhuangdao Northeast Petroleum UniversityQinhuangdao066004China

Spatio-temporal heterogeneous data is the database for decisionmaking in many fields,and checking its accuracy can provide data support for making decisions.Due to the randomness,complexity,global and local correlation of spatiotemporal heterogeneous data in the temporal and spatial dimensions,traditional detection methods can not guarantee both detection speed and accuracy.Therefore,this article proposes a method for detecting the accuracy of spatiotemporal heterogeneous data by fusing graph convolution and temporal convolution networks.Firstly,the geographic weighting function is introduced and improved to quantify the degree of association between nodes and calculate the weighted adjacency value to simplify the complex topology.Secondly,design spatiotemporal convolutional units based on graph convolutional neural networks and temporal convolutional networks to improve detection speed and accuracy.Finally,the proposed method is compared with three methods,ARIMA,T-GCN,and STGCN,in real scenarios to verify its effectiveness in terms of detection speed,detection accuracy and stability.The experimental results show that the RMSE,MAE,and MAPE of this method are the smallest in the cases of simple connectivity and complex connectivity degree,which are 13.82/12.08,2.77/2.41,and 16.70/14.73,respectively.Also,it detects the shortest time of 672.31/887.36,respectively.In addition,the evaluation results are the same under different time periods of processing and complex topology environment,which indicates that the detection accuracy of this method is the highest and has good research value and application prospects.

关键词： Spatiotemporal heterogeneity data data accuracy complex topology structure graph convolutional networks temporal convolutional networks

Risk Factors for Gestational Diabetes Mellitus(GDM)in Subsequent Pregnancy Among Women Without GDM History in China:A Multicenter Retrospective Study

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Maternal-Fetal Medicine 2023年第1期5卷 9-15页

作者： Geng Song Yumei Wei Juan Juan Rina Su Jianying Yan Mei Xiao Xianlan Zhao Meihua Zhang Yuyan Ma Haiwei Liu Jingxia Sun Kejia Hu huixia Yang Department of Obstetrics and Gynecology Peking University First HospitalBeijing 100034China Beijing Key Laboratory of Maternal Fetal Medicine of Gestational Diabetes Mellitus Beijing 100034China Department of Obstetrics and Gynecology Fujian Province Maternal and Child Health HospitalFuzhou 350005China Department of Obstetrics and Gynecology Maternal and Child Health Hospital of Hubei ProvinceWuhan 430064China Department of Obstetrics and Gynecology Zhengzhou University First Affiliated HospitalZhengzhou 450052China Department ofObstetrics and Gynecology Taiyuan Maternal and Child Health HospitalTaiyuan 030012China Department of Obstetrics and Gynecology Shandong University Qilu HospitalJinan 250063China Department of Obstetrics and Gynecology Hainan General HospitalHaikou 570311China Department of Obstetrics and Gynecology First Affiliated Hospital of Harbin Medical UniversityHarbin 150007China Department of Obstetrics and Gynecology Beijing Shunyi District HospitalBeijing 101312China

Objective:This study aimed to determine the likelihood of gestational diabetes mellitus(GDM)in subsequent pregnancy among women without GDM history and to identify risk factors for GDM in subsequent pregnancy.Methods:This retrospective cohort study involved participants who delivered twice in same hospital of 18 research centers when delivered the second baby from January 2018 to December 2018.Finally 6204 women were enrolled and 5180 women without GDM history were analyzed further.Women were categorized as non-GDM or GDM based on the blood glucose values of the subsequent pregnancy,and the characteristics and GDM risk of these groups were compared.A univariate analysis of potential risk factors was performed using the Chi-squared test and/ort-test for qualitative or quantitative variables,respectively.Associations withP values<0.1 were chosen to be included in the multivariate binary logistic regression model.Results:In primary analysis of 6204 women,the incidence of GDM in subsequent pregnancy is 48.9%(490/1002)in women with GDM history and 16.1%(835/5202)in women without GDM history.In a further analysis for 5180 women without GDM at index pregnancy,compared with the non-GDM group,the GDM group had a significantly higher age,prepregnancy body mass index,and blood glucose value at each oral glucose tolerance test(OGTT)timepoint(fasting,1 h and 2 h)during the index and subsequent pregnancies,as well as higher weight retention during the interval between the two pregnancies(P<0.001).Age above 35 years in subsequent pregnancy(odds ratio(OR)=1.540,95%confidence interval(CI)=1.257-1.886,P<0.001),macrosomia in index pregnancy(OR=1.749,95%CI=1.277-2.395,P=0.001),OGTT blood glucose values in index pregnancy(fasting,OR=2.487,95%CI=1.883-3.285,P<0.001;1 h,OR=1.142,95%CI=1.051-1.241,P=0.002;2 h,OR=1.290,95%CI=1.162-1.432,P<0.001)and weight retention(OR=1.052,95%CI=1.035-1.068,P<0.001)were independent risk factors for GDM in subsequent pregnancy.Conclusion:For women without GDM history,GDM risk factors including age,macros

关键词： Diabetes gestational Without GDM history Risk factors Subsequent pregnancy.

Excess mortality associated with high ozone exposure:A national cohort study in China

在线全文

学校读者我要写书评

暂无评论

Environmental Science and Ecotechnology 2023年第3期15卷 98-105页

作者： Yang Yuan Kai Wang Haitong Zhe Sun Yu Zhan Zhiming Yang Kejia Hu Yunquan Zhang Institute of Social Development and Health Management Hubei Province Key Laboratory of Occupational Hazard Identification and ControlSchool of Public HealthWuhan University of Science and TechnologyWuhan430065China Centre for Atmospheric Science Yusuf Hamied Department of ChemistryUniversity of CambridgeCambridgeCB21EWUK Department of Earth Sciences University of CambridgeCambridgeCB23EQUK Department of Environmental Science and Engineering Sichuan UniversityChengduSichuan610065China School of Economics and Management University of Science and Technology BeijingBeijing100083China Department of Big Data in Health Science School of Public HealthZhejiang UniversityHangzhou310058China

Emerging epidemiological studies suggest that long-term ozone(O_(3))exposure may increase the risk of mortality,while pre-existing evidence is mixed and has been generated predominantly in North America and Europe.In this study,we investigated the impact of long-term O_(3)exposure on all-cause mortality in a national cohort in China.A dynamic cohort of 20882 participants aged40 years was recruited between 2011 and 2018 from four waves of the China Health and Retirement Longitudinal Study.A Cox proportional hazard regression model with time-varying exposures on an annual scale was used to estimate the mortality risk associated with warm-season(Aprile September)O_(3)exposure.The annual average level of participant exposure to warm-season O_(3)concentrations was 100 mg m^(-3)(range:61 e142 mg m^(-3)).An increase of 10 mg m^(-3)in O_(3)was associated with a hazard ratio(HR)of 1.18(95%confidence interval[CI]:1.13e1.23)for all-cause mortality.Compared with the first exposure quartile of O_(3),HRs of mortality associated with the second,third,and highest exposure quartiles were 1.09(95%CI:0.95e1.25),1.02(95%CI:0.88e1.19),and 1.56(95%CI:1.34e1.82),respectively.A J-shaped concentration eresponse associationwas observed,revealing a non-significant increase in risk below a concentration of approximately 110 mg m^(-3).Low-temperature-exposure residents had a higher risk of mortality associated with long-term O_(3)exposure.This study expands current epidemiological evidence from China and reveals that high-concentration O_(3)exposure curtails the long-term survival of middle-aged and older adults.

关键词： Ozone Long-term exposure All-cause mortality Cohort study

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

燃料污垢对DNBR的影响分析

核科学与工程 2022年第5期42卷 994-997页

作者：胡艺嵩李可嘉中广核研究院有限公司广东深圳518000

在压水堆中,一回路腐蚀产物会在燃料表面沉积产生污垢造成的局部位置冷却剂流通面积减小,在一定情况下可能会对偏离泡核沸腾比(DNBR)产生影响。本研究采用子通道程序LINDEN,基于通道轴向变形的方法,评估分析了各类典型工况下不同污垢位... 详细信息

在压水堆中,一回路腐蚀产物会在燃料表面沉积产生污垢造成的局部位置冷却剂流通面积减小,在一定情况下可能会对偏离泡核沸腾比(DNBR)产生影响。本研究采用子通道程序LINDEN,基于通道轴向变形的方法,评估分析了各类典型工况下不同污垢位置和不同污垢厚度对DNBR的影响。研究结果表明,污垢产生在DNBR最小的通道附近时会使DNBR减小,引起安全裕量降低。本研究结果为评估燃料污垢对DNBR的影响提供了数据支撑和参考依据。

关键词：压水堆燃料污垢子通道 DNBR