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Improving performance by creating a native join-index for OLAP

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Frontiers of Computer Science 2011年第2期5卷 236-249页

作者： Yansong ZHANG Shan WANG jiaheng lu National Survey Research Center at Renmin University of China Beijing 100872 China Key Laboratory of the Ministry of Education for Data Engineering and Knowledge Engineering Renmin University of China Beijing 100872 China School of Information Renmin University of China Beijing 100872 China

The performance of online analytical processing （OLAP） is critical for meeting the increasing requirements of massive volume analytical applications. Typical techniques, such as in-memory processing, column-storage, and join indexes focus on high perfor- mance storage media, efficient storage models, and reduced query processing. While they effectively perform OLAP applications, there is a vital limitation： main- memory database based OLAP （MMOLAP） cannot provide high performance for a large size data set. In this paper, we propose a novel memory dimension table model, in which the primary keys of the dimension table can be directly mapped to dimensional tuple addresses. To achieve higher performance of dimensional tuple access, we optimize our storage model for dimension tables based on OLAP query workload features. We present directly dimensional tuple accessing （DDTA） based join （DDTA- JOIN）, a technique to optimize query processing on the memory dimension table by direct dimensional tuple access. We also contribute by proposing an optimization of the predicate tree to shorten predicate operation length by pruning useless predicate processing. Our experimental results show that the DDTA-JOIN algorithm is superior to both simulated row-store main memory query processing and the open-source column-store main memory database MonetDB, thanks to the reduced join cost and simple yet efficient query processing.

关键词： directly dimensional tuple accessing (DDTA) – DDTA JOIN – native join index – predicate tree

Big data challenge： a data management perspective

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Frontiers of Computer Science 2013年第2期7卷 157-164页

作者： Jinchuan CHEN Yueguo CHEN Xiaoyong DU Cuiping LI jiaheng lu Suyun ZHAO Xuan ZHOU Key Laboratory of Data Engineering and Knowledge Engineering School of Information Renmin University of China China Beijing 100872

There is a trend that, virtually everyone, rang- ing from big Web companies to traditional enterprisers to physical science researchers to social scientists, is either al- ready experiencing or anticipating unprecedented growth in the amount of data available in their world, as well as new op- portunities and great untapped value. This paper reviews big data challenges from a data management respective. In partic- ular, we discuss big data diversity, big data reduction, big data integration and cleaning, big data indexing and query, and fi- nally big data analysis and mining. Our survey gives a brief overview about big-data-oriented research and problems.

关键词： big data performance databases

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高效的XML关键字查询改写和结果生成技术

计算机研究与发展 2010年第5期47卷 841-848页

作者：黄静陆嘉恒孟小峰中国人民大学信息学院北京100872

用户使用关键字查询时可能不能准确地表达他们的意图,即使用户正确地表达了查询意图,查询引擎也可能不能准确地返回查询结果.针对这一问题,重点研究了在XML关键字查询中如何进行有效的查询改写并生成有意义的结果.提出4种查询改写操作... 详细信息

用户使用关键字查询时可能不能准确地表达他们的意图,即使用户正确地表达了查询意图,查询引擎也可能不能准确地返回查询结果.针对这一问题,重点研究了在XML关键字查询中如何进行有效的查询改写并生成有意义的结果.提出4种查询改写操作和查询改写代价的概念,给出了动态规划的方法计算查询改写代价.为了找出最优的查询改写,给出了基于栈的查询改写和结果生成算法,并提出了基于划分的优化算法.最后通过丰富的实验对提出的方法进行了验证.

关键词： XML 查询查询改写查询重写查询推荐 SLCA

The P_(5)-saturation Game

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Acta Mathematicae Applicatae Sinica 2025年第1期41卷 295-304页

作者： Zhen HE Mei lu School of Mathematics and Statistics Beijing Jiaotong UniversityBeijing 100044China Department of Mathematical Sciences Tsinghua UniversityBeijing 100084China

Let F,G and H be three graphs with G■*** call G an F-saturated graph relative to H,if there is no copy of F in G but there is a copy of F in G+e for any e∈E(H)\E(G).The F-saturation game on host graph H consists of two players,named Max and Min,who alternately add edges of H to G such that each chosen edge avoids creating a copy of F in G,and the players continue to choose edges until G becomes F-saturated relative to *** wishes to maximize the length of the game,while Min wishes to minimize the *** sat_(g)(F,H)(***_(g)'(F,H))denote the number of edges chosen when Max(*** Min)starts the game and both players play *** this article,we show that sat_(g)(P_(5),K_(n))=sat_(g)'(P_(5),K_(n))=n+2 for n≥15,and satg(P_(5),K_(m,n)),sat_(g)'(P_(5),K_(m,n))lie in{m+n-[m+2/4];m+n-[m-3/4]}if n≥5/2m and m≥4,respectively.

关键词： saturation number saturation game host graph

An embedded electron current layer observed at the edge of the plasma sheet in the Earth’s magnetotail

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Earth and Planetary Physics 2025年第1期9卷 148-158页

作者： ChenChen Zhan RongSheng Wang QuanMing lu San lu XinMin Li Deep Space Exploration Laboratory/School of Earth and Space Sciences University of Science and Technology of ChinaHefei 230026China Chinese Academy of Sciences(CAS)Center for Excellence in Comparative Planetology/CAS Key Laboratory of Geospace Environment/Anhui Mengcheng National Geophysical Observatory University of Science and Technology of ChinaHefei 230026China Collaborative Innovation Center of Astronautical Science and Technology Harbin 150001China

The formation of an embedded electron current sheet within the magnetotail plasma sheet has been poorly *** this article,we present an electron current layer detected at the edge of the magnetotail plasma *** ions were demagnetized inside the electron current layer,but the electrons were still frozen in with the magnetic field ***,this decoupling of ions and electrons gave rise to a strong Hall electric field,which could be the reason for the formation of the embedded thin current *** magnetized electrons,the absence of the nongyrotropic electron distribution,and negligible energy dissipation in the layer indicate that magnetic reconnection had not been triggered within the embedded thin current *** highly asymmetric plasma on the two sides of the current layer and low magnetic shear across it could suppress magnetic *** observations indicate that the embedded electric current layer,probably generated by the Hall electric field,even down to electron scale,is not a sufficient condition for magnetic reconnection.

关键词： magnetotail plasma sheet magnetic reconnection

Understanding the local structure and thermophysical behavior of Mg-La liquid alloys via machine learning potential

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International Journal of Minerals,Metallurgy and Materials 2025年第2期32卷 439-449页

作者： Jia Zhao Taixi Feng Guimin lu National Engineering Research Center for Integrated Utilization of Salt Lake Resource East China University of Science and TechnologyShanghai 200237China Joint International Laboratory for Potassium and Lithium Strategic Resources East China University of Science and TechnologyShanghai 200237China

The local structure and thermophysical behavior of Mg-La liquid alloys were in-depth understood using deep potential molecular dynamic(DPMD) simulation driven via machine learning to promote the development of Mg-La alloys. The robustness of the trained deep potential(DP) model was thoroughly evaluated through several aspects, including root-mean-square errors(RMSEs), energy and force data, and structural information comparison results;the results indicate the carefully trained DP model is reliable. The component and temperature dependence of the local structure in the Mg-La liquid alloy was analyzed. The effect of Mg content in the system on the first coordination shell of the atomic pairs is the same as that of temperature. The pre-peak demonstrated in the structure factor indicates the presence of a medium-range ordered structure in the Mg-La liquid alloy, which is particularly pronounced in the 80at% Mg system and disappears at elevated temperatures. The density, self-diffusion coefficient, and shear viscosity for the Mg-La liquid alloy were predicted via DPMD simulation, the evolution patterns with Mg content and temperature were subsequently discussed, and a database was established accordingly. Finally, the mixing enthalpy and elemental activity of the Mg-La liquid alloy at 1200 K were reliably evaluated,which provides new guidance for related studies.

关键词： magnesium-lanthanum liquid alloys local structure macroscopic properties thermodynamic behavior deep potential mo-lecular dynamic simulation

In-situ liquid-phase transmission electron microscopy for two-dimensional energy materials

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SCIENCE CHINA-CHEMISTRY 2025年第2期68卷 414-429页

作者： Zhang, Junyu Xiao, Liangping lu, Mi Xiamen Univ Technol Sch Mat Sci & Engn Xiamen 361024 Peoples R China Huaqiao Univ Instrumental Anal Ctr Lab & Equipment Management Dept Xiamen 361021 Peoples R China Xiamen Univ Res Inst Biomimet & Soft Matter Jiujiang Res Inst Dept PhysFujian Prov Key Lab Soft Funct Mat Xiamen 361005 Peoples R China

Two-dimensional (2D) materials are vital for the development of advanced materials in the next-generation energy conversion and storage devices. In-situ liquid-phase transmission electron microscopy (LP-TEM) acts as a powerful tool for characterizing the dynamic evolution of materials under work condition in real time and in operando. Herein, this mini-review highlights the considerable advances in the utilization of in-situ LP-TEM for studying the physical and chemical process dynamics of 2D materials, such as their nucleation growth and phase transformation. The electrocatalytic water splitting reactions and CO2 electroreduction of 2D energy materials are highlighted. The underlying electrochemical reaction mechanisms of the 2D electrode materials in rechargeable batteries are discussed and summarized. Finally, the current challenges and perspectives for future research are proposed. This min-review aims to inspire and stimulate further innovation and encourage the broader adoption of LP-TEM in exploring the fascinating dynamics of 2D energy materials.

关键词： two-dimensional (2D) materials liquid-phase transmission electron microscopy electrochemical reaction electrode materials

Development of Gravity Theories in the View of TRAPPIST-1e

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Research in Astronomy and Astrophysics 2025年第1期25卷 143-161页

作者： Nan Wang lu-Yao lu Hui-Gen Liu An-Dong Chen Tiger lu Ao-Ran Cui Jun-Kai Wang Marine Science and Technology College Zhejiang Ocean University Key Laboratory of Modern Astronomy and Astrophysics Ministry of Education Zhoushan Astronomical Society School of Astronomy and Space Science Nanjing University Department of Astronomy Yale University Kuang Yaming Honors School Nanjing University School of Physics Nanjing University

Contrary to the solar system, most exoplanet systems detected hitherto are close-in and compact. One typical system is TRAPPIST-1, which has seven nearly co-planar terrestrial planets all within the orbit of Mercury,including three in the habitable zone. To evaluate the differences in developing sophisticated gravity theories from the solar system, we use N-body integrations to simulate ephemeris and reproduce some important astronomy phenomena observed on the potentially habitable planet TRAPPIST-1e. Retrograde motions of other planets last1–2 orders of magnitude shorter than in the solar system, but occur much more frequently. Transit events of all inner planets can be observed steadily. Except for Kepler's first law, which is hard to notice for low eccentricities of planets, the other two laws can then be precisely verified in 102days, because the areas swept by planets vary by?0.01% and the observed semimajor axes and periods result in constants with theoretical and observation accuracies both ?2%. However, the mean motion correlation implies that the Great Inequality is not always apparent between one pair of planets like Jupiter and Saturn. Furthermore, general relativity can hardly be discovered because it gives rise to perihelion precession of inner planets only ～0.1% of gravity precession, dozens of times smaller than Mercury. Our results support the possibility of developing part of gravity theories by potential exo-civilizations in compact systems like TRAPPIST-1.

关键词： ephemerides extraterrestrial intelligence gravitation planets and satellites: terrestrial planets

Analyzing carbon emissions and influencing factors in Chengdu-Chongqing urban agglomeration counties

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Journal of Environmental Sciences 2025年第5期151卷 640-651页

作者： Zhang Heng lu Wenfu Peng Lindan Zhang Key Laboratory of the Evaluation and Monitoring of Southwest Land Resources(Ministry of Education) Sichuan Normal UniversityChengdu 610068China The Institute of Geography and Resources Science Sichuan Normal UniversityChengdu 610068China

Majority of carbon emissions originate from fossil energy consumption,thus necessitating calculation and monitoring of carbon emissions from energy *** this study,we utilized energy consumption data from Sichuan Province and Chongqing Municipality for the years 2000 to 2019 to estimate their statistical carbon *** then employed nighttime light data to downscale and infer the spatial distribution of carbon emissions at the county level within the Chengdu-Chongqing urban ***,we analyzed the spatial pattern of carbon emissions at the county level using the coefficient of variation and spatial autocorrelation,and we used the Geographically and Temporally Weighted Regression(GTWR)model to analyze the influencing factors of carbon emissions at this *** results of this study are as follows:(1)from 2000 to 2019,the overall carbon emissions in the Chengdu-Chongqing urban agglomeration showed an increasing trend followed by a decrease,with an average annual growth rate of 4.24%.However,in recent years,it has stabilized,and 2012 was the peak year for carbon emissions in the Chengdu-Chongqing urban agglomeration;(2)carbon emissions exhibited significant spatial clustering,with high-high clustering observed in the core urban areas of Chengdu and Chongqing and low-low clustering in the southern counties of the Chengdu-Chongqing urban agglomeration;(3)factors such as GDP,population(Pop),urbanization rate(Ur),and industrialization structure(Ic)all showed a significant influence on carbon emissions;(4)the spatial heterogeneity of each influencing factor was evident.

关键词： Carbon emissions Chengdu-Chongqing urban agglomeration Spatial autocorrelation Geographically and temporally weighted regression