In the procedure of the steady-state hierarchical optimization with feedback for large-scale industrial processes, a sequence of set-point changes with different magnitudes is carried out on the optimization layer. To...In the procedure of the steady-state hierarchical optimization with feedback for large-scale industrial processes, a sequence of set-point changes with different magnitudes is carried out on the optimization layer. To improve the dynamic performance of transient response driven by the set-point changes, a filter-based iterative learning control strategy is proposed. In the proposed updating law, a local-symmetric-integral operator is adopted for eliminating the measurement noise of output information,a set of desired trajectories are specified according to the set-point changes sequence, the current control input is iteratively achieved by utilizing smoothed output error to modify its control input at previous iteration, to which the amplified coefficients related to the different magnitudes of set-point changes are introduced. The convergence of the algorithm is conducted by incorporating frequency-domain technique into time-domain analysis. Numerical simulation demonstrates the effectiveness of the proposed strategy,展开更多
In recent years,the usage,management and benefit of large-scale scientific research instruments and equipment in scientific research institutes have been a leading issue in the management of scientific research instit...In recent years,the usage,management and benefit of large-scale scientific research instruments and equipment in scientific research institutes have been a leading issue in the management of scientific research institutes.Within the scope of equipment budget,it is necessary for each equipment acquisition team to conduct a round of communication,coordination and negotiation with suppliers in order to improve the cost performance of equipment procurement and maximize the performance index to meet the needs of scientific research.By introducing the practical experience of the State Key Laboratory in purchasing imported equipment and managing large-scale instruments,this paper probes into the management process of the imported large-scale scientific research tax-free equipment of scientific research institutes,and explores the system and methods to guarantee and improve the efficiency of large-scale instruments in scientific research institutes from the aspects of policy,funds and technology.展开更多
The key-value store can provide flexibility of data types because it does not need to specify the data types to be stored in advance and can store any types of data as the value of the key-value pair.Various types of ...The key-value store can provide flexibility of data types because it does not need to specify the data types to be stored in advance and can store any types of data as the value of the key-value pair.Various types of studies have been conducted to improve the performance of the key-value store while maintaining its flexibility.However,the research efforts storing the large-scale values such as multimedia data files(e.g.,images or videos)in the key-value store were limited.In this study,we propose a new key-value store,WR-Store++aiming to store the large-scale values stably.Specifically,it provides a new design of separating data and index by working with the built-in data structure of the Windows operating system and the file system.The utilization of the built-in data structure of the Windows operating system achieves the efficiency of the key-value store and that of the file system extends the limited space of the storage significantly.We also present chunk-based memory management and parallel processing of WR-Store++to further improve its performance in the GET operation.Through the experiments,we show that WR-Store++can store at least 32.74 times larger datasets than the existing baseline key-value store,WR-Store,which has the limitation in storing large-scale data sets.Furthermore,in terms of processing efficiency,we show that WR-Store++outperforms not only WR-Store but also the other state-ofthe-art key-value stores,LevelDB,RocksDB,and BerkeleyDB,for individual key-value operations and mixed workloads.展开更多
Large-scale magnetic structures are the main carrier of major eruptions in the solar atmosphere. These structures are rooted in the photosphere and are driven by the unceasing motion of the photospheric material throu...Large-scale magnetic structures are the main carrier of major eruptions in the solar atmosphere. These structures are rooted in the photosphere and are driven by the unceasing motion of the photospheric material through a series of equilibrium configurations. The motion brings energy into the coronal magnetic field until the system ceases to be in equilibrium. The catastrophe theory for solar eruptions indicates that loss of mechanical equilibrium constitutes the main trigger mechanism of major eruptions, usually shown up as solar flares, eruptive prominences, and coronal mass ejections （CMEs）. Magnetic reconnection which takes place at the very beginning of the eruption as a result of plasma instabilities/turbulence inside the current sheet, converts magnetic energy into heating and kinetic energy that are responsible for solar flares, and for accelerating both plasma ejecta （flows and CMEs） and energetic particles. Various manifestations are thus related to one another, and the physics behind these relationships is catastrophe and magnetic reconnection. This work reports on recent progress in both theoretical research and observations on eruptive phenomena showing the above manifestations. We start by displaying the properties of large-scale structures in the corona and the related magnetic fields prior to an eruption, and show various morphological features of the disrupting magnetic fields. Then, in the framework of the catastrophe theory, we look into the physics behind those features investigated in a succession of previous works, and discuss the approaches they used.展开更多
Perovskite solar cells(PSCs) have emerged as one of the most promising candidates for photovoltaic applications. Low-cost, low-temperature solution processes including coating and printing techniques makes PSCs promis...Perovskite solar cells(PSCs) have emerged as one of the most promising candidates for photovoltaic applications. Low-cost, low-temperature solution processes including coating and printing techniques makes PSCs promising for the greatly potential commercialization due to the scalability and compatibility with large-scale, roll-to-roll manufacturing processes. In this review, we focus on the solution deposition of charge transport layers and perovskite absorption layer in both mesoporous and planar structural PSC devices. Furthermore, the most recent design strategies via solution deposition are presented as well, which have been explored to enlarge the active area, enhance the crystallization and passivate the defects, leading to the performance improvement of PSC devices.展开更多
Two types of persistent heavy rainfall events （PHREs） over the Yangtze River-Huaihe River Basin were determined in a recent statistical study： type A, whose precipitation is mainly located to the south of the Yangt...Two types of persistent heavy rainfall events （PHREs） over the Yangtze River-Huaihe River Basin were determined in a recent statistical study： type A, whose precipitation is mainly located to the south of the Yangtze River; and type B, whose precipitation is mainly located to the north of the river. The present study investigated these two PHRE types using a newly derived set of energy equations to show the scale interaction and main energy paths contributing to the persistence of the precipitation. The main results were as follows. The available potential energy （APE） and kinetic energy （KE） associated with both PHRE types generally increased upward in the troposphere, with the energy of the type-A PHREs stronger than that of the type-B PHREs （except for in the middle troposphere）. There were two main common and universal energy paths of the two PHRE types： （1） the baroclinic energy conversion from APE to KE was the dominant energy source for the evolution of large-scale background circulations; and （2） the downscaled energy cascade processes of KE and APE were vital for sustaining the eddy flow, which directly caused the PHREs. The significant differences between the two PHRE types mainly appeared in the lower troposphere, where the baroclinic energy conversion associated with the eddy flow in type-A PHREs was from KE to APE, which reduced the intensity of the precipitation-related eddy flow; whereas, the conversion in type-B PHREs was from APE to KE, which enhanced the eddy flow.展开更多
The isothermal local loading forming technology provides a feasible way to form Ti-alloy large-scale rib-web components in aerospace and aviation fields.However,the local loading process forming limit is restricted by...The isothermal local loading forming technology provides a feasible way to form Ti-alloy large-scale rib-web components in aerospace and aviation fields.However,the local loading process forming limit is restricted by forming defects in the transitional region.In this work,the feasibility of controlling forming defects and improving the process forming limit by adjusting die parameters is explored through finite element（FE） simulation.It is found that the common cavum and folding defects in the transitional region are significantly influenced by the fillet radii of left rib and middle rib,respectively.The cavum and folding defects can be effectively controlled by increasing the fillet radii of left rib and middle rib,respectively.The process forming limits considering forming defects in the transitional region are determined by the stepwise searching method under various die parameters.Moreover,the relationship between the process forming limit and die parameters is developed through the response surface methodology（RSM）.The developed RSM models suggest that increasing the fillet radii of left and middle ribs is effective to improve the process forming limit during local loading forming of rib-web components.The results will provide technical basis for the design of die parameters and the reduction amount,which is of great importance to control forming defects and improve the process forming limit in local loading forming of Ti-alloy large-scale rib-web components.展开更多
In the Anyue Gasfield,Sichuan Basin,the Lower Cambrian Longwangmiao Fm gas reservoir in Moxi Block has enormous natural gas reserves,and it is a typical three-high(high temperature,high pressure,and high flow rate)sou...In the Anyue Gasfield,Sichuan Basin,the Lower Cambrian Longwangmiao Fm gas reservoir in Moxi Block has enormous natural gas reserves,and it is a typical three-high(high temperature,high pressure,and high flow rate)sour gas field.Its ground engineering project(with the designed gas processing capacity of 60×10^(8)m^(2)/a)is characterized by high processing rate of each unit,complex process control,large construction load,restricted construction site and tight schedule.Based on the traditional engineering construction mode,however,it is difficult to complete the project design and construction within 16 months.In view of this,the design concept of unit large-scale modularization was introduced to implement“normalized design,scale purchase,factory-like prefabrication and modularized construction”and develop the modularization technology of large-scale surface engineering construction.This modularizationtechnology is performed as follows.First,the modularized units are laid out reasonably according to the technological process.Second,the layout of modularized units is usually super-imposed in the multi-layer framework.Third,those equipments with the same or similar operational modes,medium properties,functional characteristics and installation requirements are concentrated in the pattem of a module.Fourth,escape passageway is specially set up.Fifth,room for installation,maintenance and repair of large equipments is reserved.And sixth,transportation and hoisting requirements of modules are taken into consideration sufficiently.This technology is contributive to the improvement of design quality,effective shortening of design period,reduction of field working load,decrease of safety management risk of on-site installation,increase of production efficiency,conservation of land occupation and diminishment of construction investment.It plays a reference role in the modularized construction of surface engineering of similar large projects.展开更多
Renewable energy,such as solar energy,wind energy,and hydraulic energy,mostly belongs to process energy,which is hard to store,while fossil energy belongs to energy-carrier energy,which can achieve long-term storage.C...Renewable energy,such as solar energy,wind energy,and hydraulic energy,mostly belongs to process energy,which is hard to store,while fossil energy belongs to energy-carrier energy,which can achieve long-term storage.Current conversion and utilization technologies for all types of energy mainly focus on power generation.Fossil energy is convenient to store,but its conversion and utilization technologies mainly rely on the combustion of fossil fuels for power and thermal energy generation,emitting huge amounts of pollutants and CO_(2).Power and thermal energy are still process energy which is hard to be stored,and the problem of the low-cost,efficient and long-term storage of energy is difficult to solve,which is the fundamental deficiencies of the current energy production and supply system.H2as an energy-carrier energy enables both clean and efficient use and storage.Therefore,the development of efficient,low-cost,large-scale green H2/power generation is imperative.It is recommended that:(1)new renewable energy units be developed based on integrating H2,thermal energy and power energy poly-generation technology on demand.The already built“sole power generation”renewable energy units should be transformed into H2,thermal energy and power energy poly-generation model,to build a comprehensive energy multi-link supply system that achieves energy storage,transportation and utilization,as well as the full-time,high-efficiency,low-cost conversion and utilization of renewable energy.(2)Developing low-carbon and clean technologies for green H2and power from carbonbased energy sources,achieving efficient energy conversion and full utilization of resources.(3)Building a new industry for high-value conversion and high-quality utilization of fossil fuels to produce the high-value chemical products instead of pollutants which also provides the best solution for large-capacity and long-term energy storage.展开更多
Fe3 O4 has attracted tremendous interest in vast areas of biomedicine and catalysis as well as environment engineering.However,it is highly desired to fully understand the chemical kinetic process and propose a genera...Fe3 O4 has attracted tremendous interest in vast areas of biomedicine and catalysis as well as environment engineering.However,it is highly desired to fully understand the chemical kinetic process and propose a general,surfactantfree,large-scale synthesis approach for Fe3 O4 spheres.Herein,we developed a facile scalable solvothermal method in the absence of surfactants to produce Fe3 O4 spheres with the yield of 5.1 g,which present tunable sizes from 107 to 450 nm by modulated molar ratio of Fe3+/COO-in the solution.Particularly,it is observed that the reactants undergo a redox process,composed of a precipitation-dissolution equilibrium combined with a coordination reaction(termed as RPC),to the final product based on the LaMer model.It is worth noting that the generation of di-carboxyl group and its coordination with iron cations determine the formation of Fe3 O4 spheres.This work not only offers a strategy to precisely tailor the particle size in scalable synthesis process,but also gives the insight on the role of dihydric alcohol in the formation mechanism of Fe3 O4 spheres in the absence of surfactants.展开更多
Resource description framework(RDF)stream is useful to model spatio-temporal data.In this paper,we propose a framework for large-scale RDF stream processing,LRSP,to process general continuous queries over large-scale ...Resource description framework(RDF)stream is useful to model spatio-temporal data.In this paper,we propose a framework for large-scale RDF stream processing,LRSP,to process general continuous queries over large-scale RDF streams.Firstly,we propose a formalization(named CT-SPARQL)to represent the general continuous queries in a unified,unambiguous way.Secondly,based on our formalization we propose LRSP to process continuous queries in a common white-box way by separating RDF stream processing,query parsing,and query execution.Finally,we implement and evaluate LRSP with those popular continuous query engines on some benchmark datasets and real-world datasets.Due to the architecture of LRSP,many efficient query engines(including centralized and distributed engines)for RDF can be directly employed to process continuous queries.The experimental results show that LRSP has a higher performance,specially,in processing large-scale real-world data.展开更多
Kernel is a kind of data summary which is elaborately extracted from a large dataset.Given a problem,the solution obtained from the kernel is an approximate version of the solution obtained from the whole dataset with...Kernel is a kind of data summary which is elaborately extracted from a large dataset.Given a problem,the solution obtained from the kernel is an approximate version of the solution obtained from the whole dataset with a provable approximate ratio.It is widely used in geometric optimization,clustering,and approximate query processing,etc.,for scaling them up to massive data.In this paper,we focus on the minimumε-kernel(MK)computation that asks for a kernel of the smallest size for large-scale data processing.For the open problem presented by Wang et al.that whether the minimumε-coreset(MC)problem and the MK problem can be reduced to each other,we first formalize the MK problem and analyze its complexity.Due to the NP-hardness of the MK problem in three or higher dimensions,an approximate algorithm,namely Set Cover-Based Minimumε-Kernel algorithm(SCMK),is developed to solve it.We prove that the MC problem and the MK problem can be Turing-reduced to each other.Then,we discuss the update of MK under insertion and deletion operations,respectively.Finally,a randomized algorithm,called the Randomized Algorithm of Set Cover-Based Minimumε-Kernel algorithm(RA-SCMK),is utilized to further reduce the complexity of SCMK.The efficiency and effectiveness of SCMK and RA-SCMK are verified by experimental results on real-world and synthetic datasets.Experiments show that the kernel sizes of SCMK are 2x and 17.6x smaller than those of an ANN-based method on real-world and synthetic datasets,respectively.The speedup ratio of SCMK over the ANN-based method is 5.67 on synthetic datasets.RA-SCMK runs up to three times faster than SCMK on synthetic datasets.展开更多
基金This work was supported by the National Natural Science Foundation of China (No. 60274055)
文摘In the procedure of the steady-state hierarchical optimization with feedback for large-scale industrial processes, a sequence of set-point changes with different magnitudes is carried out on the optimization layer. To improve the dynamic performance of transient response driven by the set-point changes, a filter-based iterative learning control strategy is proposed. In the proposed updating law, a local-symmetric-integral operator is adopted for eliminating the measurement noise of output information,a set of desired trajectories are specified according to the set-point changes sequence, the current control input is iteratively achieved by utilizing smoothed output error to modify its control input at previous iteration, to which the amplified coefficients related to the different magnitudes of set-point changes are introduced. The convergence of the algorithm is conducted by incorporating frequency-domain technique into time-domain analysis. Numerical simulation demonstrates the effectiveness of the proposed strategy,
文摘In recent years,the usage,management and benefit of large-scale scientific research instruments and equipment in scientific research institutes have been a leading issue in the management of scientific research institutes.Within the scope of equipment budget,it is necessary for each equipment acquisition team to conduct a round of communication,coordination and negotiation with suppliers in order to improve the cost performance of equipment procurement and maximize the performance index to meet the needs of scientific research.By introducing the practical experience of the State Key Laboratory in purchasing imported equipment and managing large-scale instruments,this paper probes into the management process of the imported large-scale scientific research tax-free equipment of scientific research institutes,and explores the system and methods to guarantee and improve the efficiency of large-scale instruments in scientific research institutes from the aspects of policy,funds and technology.
文摘The key-value store can provide flexibility of data types because it does not need to specify the data types to be stored in advance and can store any types of data as the value of the key-value pair.Various types of studies have been conducted to improve the performance of the key-value store while maintaining its flexibility.However,the research efforts storing the large-scale values such as multimedia data files(e.g.,images or videos)in the key-value store were limited.In this study,we propose a new key-value store,WR-Store++aiming to store the large-scale values stably.Specifically,it provides a new design of separating data and index by working with the built-in data structure of the Windows operating system and the file system.The utilization of the built-in data structure of the Windows operating system achieves the efficiency of the key-value store and that of the file system extends the limited space of the storage significantly.We also present chunk-based memory management and parallel processing of WR-Store++to further improve its performance in the GET operation.Through the experiments,we show that WR-Store++can store at least 32.74 times larger datasets than the existing baseline key-value store,WR-Store,which has the limitation in storing large-scale data sets.Furthermore,in terms of processing efficiency,we show that WR-Store++outperforms not only WR-Store but also the other state-ofthe-art key-value stores,LevelDB,RocksDB,and BerkeleyDB,for individual key-value operations and mixed workloads.
基金the National Natural Science Foundation of China.
文摘Large-scale magnetic structures are the main carrier of major eruptions in the solar atmosphere. These structures are rooted in the photosphere and are driven by the unceasing motion of the photospheric material through a series of equilibrium configurations. The motion brings energy into the coronal magnetic field until the system ceases to be in equilibrium. The catastrophe theory for solar eruptions indicates that loss of mechanical equilibrium constitutes the main trigger mechanism of major eruptions, usually shown up as solar flares, eruptive prominences, and coronal mass ejections （CMEs）. Magnetic reconnection which takes place at the very beginning of the eruption as a result of plasma instabilities/turbulence inside the current sheet, converts magnetic energy into heating and kinetic energy that are responsible for solar flares, and for accelerating both plasma ejecta （flows and CMEs） and energetic particles. Various manifestations are thus related to one another, and the physics behind these relationships is catastrophe and magnetic reconnection. This work reports on recent progress in both theoretical research and observations on eruptive phenomena showing the above manifestations. We start by displaying the properties of large-scale structures in the corona and the related magnetic fields prior to an eruption, and show various morphological features of the disrupting magnetic fields. Then, in the framework of the catastrophe theory, we look into the physics behind those features investigated in a succession of previous works, and discuss the approaches they used.
基金Projects(51673214,51673218,61774170)supported by the National Natural Science Foundation of ChinaProject(2017YFA0206600)supported by the National Key Research and Development Program of China。
文摘Perovskite solar cells(PSCs) have emerged as one of the most promising candidates for photovoltaic applications. Low-cost, low-temperature solution processes including coating and printing techniques makes PSCs promising for the greatly potential commercialization due to the scalability and compatibility with large-scale, roll-to-roll manufacturing processes. In this review, we focus on the solution deposition of charge transport layers and perovskite absorption layer in both mesoporous and planar structural PSC devices. Furthermore, the most recent design strategies via solution deposition are presented as well, which have been explored to enlarge the active area, enhance the crystallization and passivate the defects, leading to the performance improvement of PSC devices.
基金supported by the National Key Basic Research and Development Project of China(Grant No.2012CB417201)the National Natural Science Foundation of China(Grant Nos.41375053 and 41505038)
文摘Two types of persistent heavy rainfall events （PHREs） over the Yangtze River-Huaihe River Basin were determined in a recent statistical study： type A, whose precipitation is mainly located to the south of the Yangtze River; and type B, whose precipitation is mainly located to the north of the river. The present study investigated these two PHRE types using a newly derived set of energy equations to show the scale interaction and main energy paths contributing to the persistence of the precipitation. The main results were as follows. The available potential energy （APE） and kinetic energy （KE） associated with both PHRE types generally increased upward in the troposphere, with the energy of the type-A PHREs stronger than that of the type-B PHREs （except for in the middle troposphere）. There were two main common and universal energy paths of the two PHRE types： （1） the baroclinic energy conversion from APE to KE was the dominant energy source for the evolution of large-scale background circulations; and （2） the downscaled energy cascade processes of KE and APE were vital for sustaining the eddy flow, which directly caused the PHREs. The significant differences between the two PHRE types mainly appeared in the lower troposphere, where the baroclinic energy conversion associated with the eddy flow in type-A PHREs was from KE to APE, which reduced the intensity of the precipitation-related eddy flow; whereas, the conversion in type-B PHREs was from APE to KE, which enhanced the eddy flow.
基金the support of the National Natural Science Foundation of China(Nos.51605388,51675433)111 Project(B08040)+2 种基金the Research Fund of the State Key Laboratory of Solidification Processing(NWPU)in China(Grant No.131-QP-2015)the Fundamental Research Funds for the Central Universitiesthe Open Research Fund of State Key Laboratory of Materials Processing and Die&Mold Technology at Huazhong University of Science and Technology
文摘The isothermal local loading forming technology provides a feasible way to form Ti-alloy large-scale rib-web components in aerospace and aviation fields.However,the local loading process forming limit is restricted by forming defects in the transitional region.In this work,the feasibility of controlling forming defects and improving the process forming limit by adjusting die parameters is explored through finite element（FE） simulation.It is found that the common cavum and folding defects in the transitional region are significantly influenced by the fillet radii of left rib and middle rib,respectively.The cavum and folding defects can be effectively controlled by increasing the fillet radii of left rib and middle rib,respectively.The process forming limits considering forming defects in the transitional region are determined by the stepwise searching method under various die parameters.Moreover,the relationship between the process forming limit and die parameters is developed through the response surface methodology（RSM）.The developed RSM models suggest that increasing the fillet radii of left and middle ribs is effective to improve the process forming limit during local loading forming of rib-web components.The results will provide technical basis for the design of die parameters and the reduction amount,which is of great importance to control forming defects and improve the process forming limit in local loading forming of Ti-alloy large-scale rib-web components.
文摘In the Anyue Gasfield,Sichuan Basin,the Lower Cambrian Longwangmiao Fm gas reservoir in Moxi Block has enormous natural gas reserves,and it is a typical three-high(high temperature,high pressure,and high flow rate)sour gas field.Its ground engineering project(with the designed gas processing capacity of 60×10^(8)m^(2)/a)is characterized by high processing rate of each unit,complex process control,large construction load,restricted construction site and tight schedule.Based on the traditional engineering construction mode,however,it is difficult to complete the project design and construction within 16 months.In view of this,the design concept of unit large-scale modularization was introduced to implement“normalized design,scale purchase,factory-like prefabrication and modularized construction”and develop the modularization technology of large-scale surface engineering construction.This modularizationtechnology is performed as follows.First,the modularized units are laid out reasonably according to the technological process.Second,the layout of modularized units is usually super-imposed in the multi-layer framework.Third,those equipments with the same or similar operational modes,medium properties,functional characteristics and installation requirements are concentrated in the pattem of a module.Fourth,escape passageway is specially set up.Fifth,room for installation,maintenance and repair of large equipments is reserved.And sixth,transportation and hoisting requirements of modules are taken into consideration sufficiently.This technology is contributive to the improvement of design quality,effective shortening of design period,reduction of field working load,decrease of safety management risk of on-site installation,increase of production efficiency,conservation of land occupation and diminishment of construction investment.It plays a reference role in the modularized construction of surface engineering of similar large projects.
基金supported by the Basic Science Center Program for Ordered Energy Conversion of the National Natural Science Foundation of China(Grant No.52488201)the National Key R&D Program of China(Grant No.2020YFA0714400)。
文摘Renewable energy,such as solar energy,wind energy,and hydraulic energy,mostly belongs to process energy,which is hard to store,while fossil energy belongs to energy-carrier energy,which can achieve long-term storage.Current conversion and utilization technologies for all types of energy mainly focus on power generation.Fossil energy is convenient to store,but its conversion and utilization technologies mainly rely on the combustion of fossil fuels for power and thermal energy generation,emitting huge amounts of pollutants and CO_(2).Power and thermal energy are still process energy which is hard to be stored,and the problem of the low-cost,efficient and long-term storage of energy is difficult to solve,which is the fundamental deficiencies of the current energy production and supply system.H2as an energy-carrier energy enables both clean and efficient use and storage.Therefore,the development of efficient,low-cost,large-scale green H2/power generation is imperative.It is recommended that:(1)new renewable energy units be developed based on integrating H2,thermal energy and power energy poly-generation technology on demand.The already built“sole power generation”renewable energy units should be transformed into H2,thermal energy and power energy poly-generation model,to build a comprehensive energy multi-link supply system that achieves energy storage,transportation and utilization,as well as the full-time,high-efficiency,low-cost conversion and utilization of renewable energy.(2)Developing low-carbon and clean technologies for green H2and power from carbonbased energy sources,achieving efficient energy conversion and full utilization of resources.(3)Building a new industry for high-value conversion and high-quality utilization of fossil fuels to produce the high-value chemical products instead of pollutants which also provides the best solution for large-capacity and long-term energy storage.
基金financially supported by the National Natural Science Foundation of China(51631001,51672010 and81421004)the National Key R&D Program of China(2017YFA0206301 and 2016YFA0200102)
文摘Fe3 O4 has attracted tremendous interest in vast areas of biomedicine and catalysis as well as environment engineering.However,it is highly desired to fully understand the chemical kinetic process and propose a general,surfactantfree,large-scale synthesis approach for Fe3 O4 spheres.Herein,we developed a facile scalable solvothermal method in the absence of surfactants to produce Fe3 O4 spheres with the yield of 5.1 g,which present tunable sizes from 107 to 450 nm by modulated molar ratio of Fe3+/COO-in the solution.Particularly,it is observed that the reactants undergo a redox process,composed of a precipitation-dissolution equilibrium combined with a coordination reaction(termed as RPC),to the final product based on the LaMer model.It is worth noting that the generation of di-carboxyl group and its coordination with iron cations determine the formation of Fe3 O4 spheres.This work not only offers a strategy to precisely tailor the particle size in scalable synthesis process,but also gives the insight on the role of dihydric alcohol in the formation mechanism of Fe3 O4 spheres in the absence of surfactants.
基金the National Key Research and Development Program of China under Grant No.2017YFC0908401the National Natural Science Foundation of China under Grant No.61672377the program of Peiyang Young Scholars of China under Grant No.2019XRX-0032.
文摘Resource description framework(RDF)stream is useful to model spatio-temporal data.In this paper,we propose a framework for large-scale RDF stream processing,LRSP,to process general continuous queries over large-scale RDF streams.Firstly,we propose a formalization(named CT-SPARQL)to represent the general continuous queries in a unified,unambiguous way.Secondly,based on our formalization we propose LRSP to process continuous queries in a common white-box way by separating RDF stream processing,query parsing,and query execution.Finally,we implement and evaluate LRSP with those popular continuous query engines on some benchmark datasets and real-world datasets.Due to the architecture of LRSP,many efficient query engines(including centralized and distributed engines)for RDF can be directly employed to process continuous queries.The experimental results show that LRSP has a higher performance,specially,in processing large-scale real-world data.
基金the National Natural Science Foundation of China under Grant Nos.61732003,61832003,61972110 and U19A2059the National Key Research and Development Program of China under Grant No.2019YFB2101902the CCF-Baidu Open Fund CCF-BAIDU under Grant No.OF2021011.
文摘Kernel is a kind of data summary which is elaborately extracted from a large dataset.Given a problem,the solution obtained from the kernel is an approximate version of the solution obtained from the whole dataset with a provable approximate ratio.It is widely used in geometric optimization,clustering,and approximate query processing,etc.,for scaling them up to massive data.In this paper,we focus on the minimumε-kernel(MK)computation that asks for a kernel of the smallest size for large-scale data processing.For the open problem presented by Wang et al.that whether the minimumε-coreset(MC)problem and the MK problem can be reduced to each other,we first formalize the MK problem and analyze its complexity.Due to the NP-hardness of the MK problem in three or higher dimensions,an approximate algorithm,namely Set Cover-Based Minimumε-Kernel algorithm(SCMK),is developed to solve it.We prove that the MC problem and the MK problem can be Turing-reduced to each other.Then,we discuss the update of MK under insertion and deletion operations,respectively.Finally,a randomized algorithm,called the Randomized Algorithm of Set Cover-Based Minimumε-Kernel algorithm(RA-SCMK),is utilized to further reduce the complexity of SCMK.The efficiency and effectiveness of SCMK and RA-SCMK are verified by experimental results on real-world and synthetic datasets.Experiments show that the kernel sizes of SCMK are 2x and 17.6x smaller than those of an ANN-based method on real-world and synthetic datasets,respectively.The speedup ratio of SCMK over the ANN-based method is 5.67 on synthetic datasets.RA-SCMK runs up to three times faster than SCMK on synthetic datasets.
