According to the simulation of nitrogen sorption process in porous media with three-dimensional network model, and the analysis for such a process with percolation theory, a new method is proposed to determine a pore ...According to the simulation of nitrogen sorption process in porous media with three-dimensional network model, and the analysis for such a process with percolation theory, a new method is proposed to determine a pore structure parameter--mean coordination number of pore network, which represents the connectivity among a great number of pores. Here the 'chamber-throat' model and the Weibull distribution are used to describe the pore geometry and the pore size distribution respectively. This method is based on the scaling law of percolation theory after both effects of sorption thermodynamics and pore size on the sorption hysteresis loops are considered. The results show that it is an effective procedure to calculate the mean coordination number for micro- and meso-porous media.展开更多
Top-k ranking of websites according to traffic volume is important for Internet Service Providers(ISPs) to understand network status and optimize network resources. However, the ranking result always has a big deviati...Top-k ranking of websites according to traffic volume is important for Internet Service Providers(ISPs) to understand network status and optimize network resources. However, the ranking result always has a big deviation with actual rank for the existence of unknown web traffic, which cannot be identified accurately under current techniques. In this paper, we introduce a novel method to approximate the actual rank. This method associates unknown web traffic with websites according to statistical probabilities. Then, we construct a probabilistic top-k query model to rank websites. We conduct several experiments by using real HTTP traffic traces collected from a commercial ISP covering an entire city in northern China. Experimental results show that the proposed techniques can reduce the deviation existing between the ground truth and the ranking results vastly. In addition, we find that the websites providing video service have higher ratio of unknown IP as well as higher ratio of unknown traffic than the websites providing text web page service. Specifically, we find that the top-3 video websites have more than 90% of unknown web traffic. All these findings are helpful for ISPs understanding network status and deploying Content Distributed Network(CDN).展开更多
For business service workflow,QoS-based services selection can't guarantee whether the composite service satisfies user' s requirement after delivery,because once any service interrupts or quality of service(Q...For business service workflow,QoS-based services selection can't guarantee whether the composite service satisfies user' s requirement after delivery,because once any service interrupts or quality of service(QoS) maliciously reduces,the quality of workflow will be reduced.Trustworthy services can provide reliable QoS,so trustworthiness research could improve the efficiency of services selection.This paper investigates trust assessment in the perspective of workflow.Firstly,trust network of business service workflow(TN-BSW) is proposed to analyze trust attributes;then,the trust measurement system of TN-BSW is investigated to assess the trust value quantitatively;and then,a trust-aware service recommendation model(TaSRM) is proposed to enhance the efficiency of QoS-basedservices selection;finally,experiment shows the feasibility of TN-BSWand the performance of TaSRM.展开更多
Pattern matching is a fundamental approach to detect malicious behaviors and information over Internet, which has been gradually used in high-speed network traffic analysis. However, there is a performance bottleneck ...Pattern matching is a fundamental approach to detect malicious behaviors and information over Internet, which has been gradually used in high-speed network traffic analysis. However, there is a performance bottleneck for multi-pattern matching on online compressed network traffic(CNT), this is because malicious and intrusion codes are often embedded into compressed network traffic. In this paper, we propose an online fast and multi-pattern matching algorithm on compressed network traffic(FMMCN). FMMCN employs two types of jumping, i.e. jumping during sliding window and a string jump scanning strategy to skip unnecessary compressed bytes. Moreover, FMMCN has the ability to efficiently process multiple large volume of networks such as HTTP traffic, vehicles traffic, and other Internet-based services. The experimental results show that FMMCN can ignore more than 89.5% of bytes, and its maximum speed reaches 176.470MB/s in a midrange switches device, which is faster than the current fastest algorithm ACCH by almost 73.15 MB/s.展开更多
ransport network in the paper is defined as follows: (1) Connected and directed network without self loop;(2) There is only one source vertex with zero in degree; (3) There is only one sink vertex with zero out de...ransport network in the paper is defined as follows: (1) Connected and directed network without self loop;(2) There is only one source vertex with zero in degree; (3) There is only one sink vertex with zero out degree;(4) The capacity of every arc is non negative integer Blocking flow is a kind of flow commonly happened in a transport network . Its formation is due to the existance of a blocking cutset in the network. In this paper the fundamental concepts and theorems of the blocking flow and the blocking cutset are introduced and a linear programming model for determining the blocking cutset in a network is set up. In order to solve the problem by graph theoretical approach a method called 'two way flow augmenting algorithm' is developed. With this method an iterative procedure of forward and backward flow augmenting process is used to determine whether a given cutset is a blocking one.展开更多
In order to identify any traces of suspicious activities for the networks security, Network Traffic Analysis has been the basis of network security and network management. With the continued emergence of new applicati...In order to identify any traces of suspicious activities for the networks security, Network Traffic Analysis has been the basis of network security and network management. With the continued emergence of new applications and encrypted traffic, the currently available approaches can not perform well for all kinds of network data. In this paper, we propose a novel stream pattern matching technique which is not only easily deployed but also includes the advantages of different methods. The main idea is： first, defining a formal description specification, by which any series of data stream can be unambiguously descrbed by a special stream pattern; then a tree representation is constructed by parsing the stream pattern; at last, a stream pattern engine is constructed with the Non-t-mite automata （S-CG-NFA） and Bit-parallel searching algorithms. Our stream pattern analysis system has been fully prototyped on C programming language and Xilinx Vn-tex2 FPGA. The experimental results show the method could provides a high level of recognition efficiency and accuracy.展开更多
A new superstructure model of heat exchanger networks (HEN) with streamsplits based on rangers of streams supply temperatures and heat capacity flow rates is presented.The simultaneous optimal mathematical model of fl...A new superstructure model of heat exchanger networks (HEN) with streamsplits based on rangers of streams supply temperatures and heat capacity flow rates is presented.The simultaneous optimal mathematical model of flexible HEN synthesis is established too. Firstly,the streams with rangers of supply temperatures and/or the streams with the rangers of heat capacityflow rates are pretreated; Secondly, several rules are proposed to establish the superstructuremodel of HEN with splits and the simultaneous optimal mathematical model of flexible HEN; Thirdly,the improving genetic algorithm is applied to solve the mathematical model established at the secondstep effectively, and the original optimal structure of HEN based on the maximum operation limitingcondition can be obtained easily; Finally, the rules of heat exchange unit merged and the heat loadof heat exchanger relaxed are presented, the flexible configuration of HEN satisfied the operationcondition between the upper and down bounds of supply temperature and heat capacity flow rates canbe obtained based on the original optimal structure of HEN by means of these rules. A case studydemonstrates the method presented in this paper is effective展开更多
In order to understand how a network is being used or whether it is being abused, an administrator needs to inspect the flow of the traffic and ＂infers＂ the intent of the users and applications. So the network traff...In order to understand how a network is being used or whether it is being abused, an administrator needs to inspect the flow of the traffic and ＂infers＂ the intent of the users and applications. So the network traffic measurement and analysis are crucial to network monitoring, reliable DDoS detecting and attack source locating as well. In this paper, we discuss the principle of real-time network traffic measurement and analysis through embedding a traffic measurement and analysis engine into IP packet-decoding module, and emphasize the implementation of visualizing the real-time network traffic, which are helpful to network monitoring and network traffic modeling.展开更多
In this paper, data streams are classified into four types conforming to a standardized infrastructure of communication networks for a substation automation system （SAS） based on IEC61850 system. The data exchanged ...In this paper, data streams are classified into four types conforming to a standardized infrastructure of communication networks for a substation automation system （SAS） based on IEC61850 system. The data exchanged on the net are demonstrated to be stochastic according to investigation on the Ethemet communication principles. Four generalized stochastic Petri nets （GSPN） based models for performance analysis of communication networks of IEC61850 system are developed based on the three-level structure of SAS, different time requirements of the four data streams and different networks topology for different voltage level. The GSPN-based model associated with immediate and exponential transitions is proven to be theoretically isomorphic with Markov chain; hence we apply the mathematic methods of performance evaluation contained in Markov chain to the GSPN models proposed. The computer simulation of the model including only sample value data streams shows that it can meet performance evaluation needs of communication networks of IEC61850 system. Further researches should be focused on the pe^ormance of the other three models to explain clear how those different data streams are interrelated to and interact on each other.展开更多
The structure and working principle of a self-deigned high pressure electronic pneumatic pressure reducing valve (EPPRV) with slide pilot are introduced.The resistance value formulas and the relationship between the r...The structure and working principle of a self-deigned high pressure electronic pneumatic pressure reducing valve (EPPRV) with slide pilot are introduced.The resistance value formulas and the relationship between the resistance and pressure of three typical pneumatic resistances are obtained.Then,the method of static characteristics analysis only considering pneumatic resistances is proposed,the resistance network from gas supply to load is built up,and the mathematical model is derived from the flow rate formulas and flow conservation equations,with the compressibility of high pressure gas and temperature drop during the expansion considered in the model.Finally,the pilot spool displacement of 1.5 mm at an output pressure of 15MPa and the enlarging operating stroke of the pilot spool are taken as optimization targets,and the optimization is carried out based on genetic algorithm and the model mentioned above.The results show that the static characteristics of the EPPRV are significantly improved.The idea of static characteristics analysis and optimization based on pneumatic resistance network is valuable for the design of pneumatic components or system.展开更多
It is often required to know which roadway （adjustment roadway） resistances and how much values of the resis- tances should be changed to make the airflow rates in roadways （target roadways） to certain required va...It is often required to know which roadway （adjustment roadway） resistances and how much values of the resis- tances should be changed to make the airflow rates in roadways （target roadways） to certain required values in the practice of mine ventilation. In this case, the airflow rates of the target roadways and the resistances of the roadways other than the ad- justment roadways are the given conditions and the resistances of the adjustment roadways are the solutions to be found. No straightforward method to solve the problem has been found up to now. Therefore, trial and error method using the ventilation network analysis program is utilized to solve the problem so far. The method takes long calculation time and the best answer is not necessarily obtained. The authors newly defined ＂airflow element＂ as an element of the ventilation network analysis. The resistances that satisfy the airflow requirements can be calculated straight forwardly by putting the function of the airflow element into the ventilation network analysis. The air power required for the ventilation can be minimized while meeting the airflow requirements by the advanced application of the method. The authors made the computer program fulfill the method. The program was applied to actual ventilation network and it was found that the method is very practical and the time required for the analysis is short.展开更多
Based on patent cooperation data,this study used a range of city network analysis approaches in order to explore the structure of the Chinese city network which is driven by technological knowledge flows.The results r...Based on patent cooperation data,this study used a range of city network analysis approaches in order to explore the structure of the Chinese city network which is driven by technological knowledge flows.The results revealed the spatial structure,composition structure,hierarchical structure,group structure,and control structure of Chinese city network,as well as its dynamic factors.The major findings are:1) the spatial pattern presents a diamond structure,in which Wuhan is the central city;2) although the invention patent knowledge network is the main part of the broader inter-city innovative cooperation network,it is weaker than the utility model patent;3) as the senior level cities,Beijing,Shanghai and the cities in the Zhujiang(Pearl) River Delta Region show a strong capability of both spreading and controlling technological knowledge;4) whilst a national technology alliance has preliminarily formed,regional alliances have not been adequately established;5) even though the cooperation level amongst weak connection cities is not high,such cities still play an important role in the network as a result of their location within ′structural holes′ in the network;and 6) the major driving forces facilitating inter-city technological cooperation are geographical proximity,hierarchical proximity and technological proximity.展开更多
Debris flow is one of the most destructive phenomena of natural hazards. Recently, major natural hazard, claiming human lives and assets, is due to debris flow in the world. Several practical methods for forecasting d...Debris flow is one of the most destructive phenomena of natural hazards. Recently, major natural hazard, claiming human lives and assets, is due to debris flow in the world. Several practical methods for forecasting debris flow have been proposed, however, the accuracy of these methods is not high enough for practical use because of the stochastic and non-linear characteristics of debris flow. Artificial neural network has proven to be feasible and useful in developing models for nonlinear systems. On the other hand, predicting the future behavior based on a time series of collected historical data is also an important tool in many scientific applications. In this study we present a three-layer feed-forward neural network model to forecast surge of debris flow according to the time series data collected in the Jiangjia Ravine, situated in north part of Yunnan Province of China. The simulation and prediction of debris flow using the proposed approach shows this model is feasible, however, further studies are needed.展开更多
The Unified Power Flow Controller （UPFC） is one of the most versatile Flexible AC Transmission Systems （FACTS） devices that has unique capability of independently controlling the real and reactive power flows, in ...The Unified Power Flow Controller （UPFC） is one of the most versatile Flexible AC Transmission Systems （FACTS） devices that has unique capability of independently controlling the real and reactive power flows, in addition to regulate the system bus voltage. This paper presents performance analysis of Unified Power Flow Controller based on two axis theory. Based on this analysis, a new Artificial Neural Network （ANN） based controller has been proposed to improve the system performance. The controller rules are structured depending upon the relationship between series inserted voltage and the desired changes in real/reactive power flow in the power system. The effects of different controllers along with parameters of series transformer and transmission line have been investigated through developed control block model in SIMULINK tool box of MATLAB. The effectiveness of the proposed scheme is demonstrated by case studies.展开更多
Electrifying the on-board subsystems of aircraft becomes an inevitable process as being faced with the environmental pollution,along with the proposed concept called more electric aircraft(MEA).With the increasing num...Electrifying the on-board subsystems of aircraft becomes an inevitable process as being faced with the environmental pollution,along with the proposed concept called more electric aircraft(MEA).With the increasing number of on-board power electronic based devices,the distribution system of the aircraft can be regarded as an onboard microgrid.As it is known that the load power electronic converters can exhibit constant power load(CPL)characteristics and reduce the system stability,it is necessary to accurately predict and enhance the system stability in designing process.This paper firstly analyzes the stability of an on-board DC microgrid with the presence of CPL.Then,discusses the reasons behind instability and proposes a control strategy to enhance system stability.Finally,the simulation results are worked out to validate the analysis and the effect of the proposed control strategy.展开更多
Thermal performance of a loop heat pipe with two evaporators and two condensers was examined using a lumped network model analysis. Thermosyphon-type vertical loop heat pipe and capillary-pump-type horizontal loop hea...Thermal performance of a loop heat pipe with two evaporators and two condensers was examined using a lumped network model analysis. Thermosyphon-type vertical loop heat pipe and capillary-pump-type horizontal loop heat pipe were calculated by examining the change of heating rate of two evaporators. Calculation results showed that the vapor and liquid flow rates in the loop heat pipe and the thermal conductance of the heat pipe changed significantly depending on the distribution ratio of the heating rate of the multiple evaporators. The thermal performance of the vertical loop heat pipe with two evaporators was also examined and experimental results of flow direction and thermal conductance of the heat pipe agreed with the analytical results. The lumped network model analysis is therefore considered accurate and preferable for the practical design of a loop heat pipe with multiple evaporators.展开更多
The Deep Packet Inspection(DPI)method is a popular method that can accurately identify the flow data and its corresponding application.Currently,the DPI method is widely used in common network management systems.Howev...The Deep Packet Inspection(DPI)method is a popular method that can accurately identify the flow data and its corresponding application.Currently,the DPI method is widely used in common network management systems.However,the major limitation of DPI systems is that their signature library is mainly extracted manually,which makes it hard to efficiently obtain the signature of new applications.Hence,in this paper,we propose an automatic signature extraction mechanism using Principal Component Analysis(PCA)technology,which is able to extract the signature automatically.In the proposed method,the signatures are expressed in the form of serial consistent sequences constructed by principal components instead of normally separated substrings in the original data extracted from the traditional methods.Extensive experiments based on numerous sets of data have been carried out to evaluate the performance of the proposed scheme,and the results prove that the newly proposed method can achieve good performance in terms of accuracy and efficiency.展开更多
In this paper, a new lattice hydrodynamic model is proposed by incorporating the driver anticipation effect of next-nearest-neighbor site. The linear stability analysis and nonlinear analysis show that the driver anti...In this paper, a new lattice hydrodynamic model is proposed by incorporating the driver anticipation effect of next-nearest-neighbor site. The linear stability analysis and nonlinear analysis show that the driver anticipation effect of next-nearest-neighbor site can enlarge the stable area of traffic flow. The space can be divided into three regions： stab/e, metastable, and unstable. Numerical simulation further illuminates that the driver anticipation effect of the next-neaxest-neighbor site can stabilize tramc flow in our modified lattice model, which is consistent with the analytical results.展开更多
基金Supported by the National Natural Science Foundation of China(No.29776038).
文摘According to the simulation of nitrogen sorption process in porous media with three-dimensional network model, and the analysis for such a process with percolation theory, a new method is proposed to determine a pore structure parameter--mean coordination number of pore network, which represents the connectivity among a great number of pores. Here the 'chamber-throat' model and the Weibull distribution are used to describe the pore geometry and the pore size distribution respectively. This method is based on the scaling law of percolation theory after both effects of sorption thermodynamics and pore size on the sorption hysteresis loops are considered. The results show that it is an effective procedure to calculate the mean coordination number for micro- and meso-porous media.
基金supported by 111 Project of China under Grant No.B08004
文摘Top-k ranking of websites according to traffic volume is important for Internet Service Providers(ISPs) to understand network status and optimize network resources. However, the ranking result always has a big deviation with actual rank for the existence of unknown web traffic, which cannot be identified accurately under current techniques. In this paper, we introduce a novel method to approximate the actual rank. This method associates unknown web traffic with websites according to statistical probabilities. Then, we construct a probabilistic top-k query model to rank websites. We conduct several experiments by using real HTTP traffic traces collected from a commercial ISP covering an entire city in northern China. Experimental results show that the proposed techniques can reduce the deviation existing between the ground truth and the ranking results vastly. In addition, we find that the websites providing video service have higher ratio of unknown IP as well as higher ratio of unknown traffic than the websites providing text web page service. Specifically, we find that the top-3 video websites have more than 90% of unknown web traffic. All these findings are helpful for ISPs understanding network status and deploying Content Distributed Network(CDN).
基金Supported by the Research Fund for the Doctoral Program of Higher Education of China(No.20120002110034)Initiative Scientific Research Program of Tsinghua University(No.20111080998)
文摘For business service workflow,QoS-based services selection can't guarantee whether the composite service satisfies user' s requirement after delivery,because once any service interrupts or quality of service(QoS) maliciously reduces,the quality of workflow will be reduced.Trustworthy services can provide reliable QoS,so trustworthiness research could improve the efficiency of services selection.This paper investigates trust assessment in the perspective of workflow.Firstly,trust network of business service workflow(TN-BSW) is proposed to analyze trust attributes;then,the trust measurement system of TN-BSW is investigated to assess the trust value quantitatively;and then,a trust-aware service recommendation model(TaSRM) is proposed to enhance the efficiency of QoS-basedservices selection;finally,experiment shows the feasibility of TN-BSWand the performance of TaSRM.
基金supported by China MOST project (No.2012BAH46B04)
文摘Pattern matching is a fundamental approach to detect malicious behaviors and information over Internet, which has been gradually used in high-speed network traffic analysis. However, there is a performance bottleneck for multi-pattern matching on online compressed network traffic(CNT), this is because malicious and intrusion codes are often embedded into compressed network traffic. In this paper, we propose an online fast and multi-pattern matching algorithm on compressed network traffic(FMMCN). FMMCN employs two types of jumping, i.e. jumping during sliding window and a string jump scanning strategy to skip unnecessary compressed bytes. Moreover, FMMCN has the ability to efficiently process multiple large volume of networks such as HTTP traffic, vehicles traffic, and other Internet-based services. The experimental results show that FMMCN can ignore more than 89.5% of bytes, and its maximum speed reaches 176.470MB/s in a midrange switches device, which is faster than the current fastest algorithm ACCH by almost 73.15 MB/s.
文摘ransport network in the paper is defined as follows: (1) Connected and directed network without self loop;(2) There is only one source vertex with zero in degree; (3) There is only one sink vertex with zero out degree;(4) The capacity of every arc is non negative integer Blocking flow is a kind of flow commonly happened in a transport network . Its formation is due to the existance of a blocking cutset in the network. In this paper the fundamental concepts and theorems of the blocking flow and the blocking cutset are introduced and a linear programming model for determining the blocking cutset in a network is set up. In order to solve the problem by graph theoretical approach a method called 'two way flow augmenting algorithm' is developed. With this method an iterative procedure of forward and backward flow augmenting process is used to determine whether a given cutset is a blocking one.
基金This work is supported by the following projects： National Natural Science Foundation of China grant 60772136, 111 Development Program of China NO.B08038, National Science ＆ Technology Pillar Program of China NO.2008BAH22B03 and NO. 2007BAH08B01.
文摘In order to identify any traces of suspicious activities for the networks security, Network Traffic Analysis has been the basis of network security and network management. With the continued emergence of new applications and encrypted traffic, the currently available approaches can not perform well for all kinds of network data. In this paper, we propose a novel stream pattern matching technique which is not only easily deployed but also includes the advantages of different methods. The main idea is： first, defining a formal description specification, by which any series of data stream can be unambiguously descrbed by a special stream pattern; then a tree representation is constructed by parsing the stream pattern; at last, a stream pattern engine is constructed with the Non-t-mite automata （S-CG-NFA） and Bit-parallel searching algorithms. Our stream pattern analysis system has been fully prototyped on C programming language and Xilinx Vn-tex2 FPGA. The experimental results show the method could provides a high level of recognition efficiency and accuracy.
基金Supported by the State Major Basic Research Department Program of China (No. G20000263) and the Deutsche Forschungs- gemeinschaft(DFG)(No. RO294/9).
文摘A new superstructure model of heat exchanger networks (HEN) with streamsplits based on rangers of streams supply temperatures and heat capacity flow rates is presented.The simultaneous optimal mathematical model of flexible HEN synthesis is established too. Firstly,the streams with rangers of supply temperatures and/or the streams with the rangers of heat capacityflow rates are pretreated; Secondly, several rules are proposed to establish the superstructuremodel of HEN with splits and the simultaneous optimal mathematical model of flexible HEN; Thirdly,the improving genetic algorithm is applied to solve the mathematical model established at the secondstep effectively, and the original optimal structure of HEN based on the maximum operation limitingcondition can be obtained easily; Finally, the rules of heat exchange unit merged and the heat loadof heat exchanger relaxed are presented, the flexible configuration of HEN satisfied the operationcondition between the upper and down bounds of supply temperature and heat capacity flow rates canbe obtained based on the original optimal structure of HEN by means of these rules. A case studydemonstrates the method presented in this paper is effective
文摘In order to understand how a network is being used or whether it is being abused, an administrator needs to inspect the flow of the traffic and ＂infers＂ the intent of the users and applications. So the network traffic measurement and analysis are crucial to network monitoring, reliable DDoS detecting and attack source locating as well. In this paper, we discuss the principle of real-time network traffic measurement and analysis through embedding a traffic measurement and analysis engine into IP packet-decoding module, and emphasize the implementation of visualizing the real-time network traffic, which are helpful to network monitoring and network traffic modeling.
文摘In this paper, data streams are classified into four types conforming to a standardized infrastructure of communication networks for a substation automation system （SAS） based on IEC61850 system. The data exchanged on the net are demonstrated to be stochastic according to investigation on the Ethemet communication principles. Four generalized stochastic Petri nets （GSPN） based models for performance analysis of communication networks of IEC61850 system are developed based on the three-level structure of SAS, different time requirements of the four data streams and different networks topology for different voltage level. The GSPN-based model associated with immediate and exponential transitions is proven to be theoretically isomorphic with Markov chain; hence we apply the mathematic methods of performance evaluation contained in Markov chain to the GSPN models proposed. The computer simulation of the model including only sample value data streams shows that it can meet performance evaluation needs of communication networks of IEC61850 system. Further researches should be focused on the pe^ormance of the other three models to explain clear how those different data streams are interrelated to and interact on each other.
基金Project(50575202) supported by the National Natural Science Foundation of China
文摘The structure and working principle of a self-deigned high pressure electronic pneumatic pressure reducing valve (EPPRV) with slide pilot are introduced.The resistance value formulas and the relationship between the resistance and pressure of three typical pneumatic resistances are obtained.Then,the method of static characteristics analysis only considering pneumatic resistances is proposed,the resistance network from gas supply to load is built up,and the mathematical model is derived from the flow rate formulas and flow conservation equations,with the compressibility of high pressure gas and temperature drop during the expansion considered in the model.Finally,the pilot spool displacement of 1.5 mm at an output pressure of 15MPa and the enlarging operating stroke of the pilot spool are taken as optimization targets,and the optimization is carried out based on genetic algorithm and the model mentioned above.The results show that the static characteristics of the EPPRV are significantly improved.The idea of static characteristics analysis and optimization based on pneumatic resistance network is valuable for the design of pneumatic components or system.
文摘It is often required to know which roadway （adjustment roadway） resistances and how much values of the resis- tances should be changed to make the airflow rates in roadways （target roadways） to certain required values in the practice of mine ventilation. In this case, the airflow rates of the target roadways and the resistances of the roadways other than the ad- justment roadways are the given conditions and the resistances of the adjustment roadways are the solutions to be found. No straightforward method to solve the problem has been found up to now. Therefore, trial and error method using the ventilation network analysis program is utilized to solve the problem so far. The method takes long calculation time and the best answer is not necessarily obtained. The authors newly defined ＂airflow element＂ as an element of the ventilation network analysis. The resistances that satisfy the airflow requirements can be calculated straight forwardly by putting the function of the airflow element into the ventilation network analysis. The air power required for the ventilation can be minimized while meeting the airflow requirements by the advanced application of the method. The authors made the computer program fulfill the method. The program was applied to actual ventilation network and it was found that the method is very practical and the time required for the analysis is short.
基金Under the auspices of Major Project of National Social Science Foundation of China(No.13&ZD027)National Natural Science Foundation of China(No.41201128,71433008)
文摘Based on patent cooperation data,this study used a range of city network analysis approaches in order to explore the structure of the Chinese city network which is driven by technological knowledge flows.The results revealed the spatial structure,composition structure,hierarchical structure,group structure,and control structure of Chinese city network,as well as its dynamic factors.The major findings are:1) the spatial pattern presents a diamond structure,in which Wuhan is the central city;2) although the invention patent knowledge network is the main part of the broader inter-city innovative cooperation network,it is weaker than the utility model patent;3) as the senior level cities,Beijing,Shanghai and the cities in the Zhujiang(Pearl) River Delta Region show a strong capability of both spreading and controlling technological knowledge;4) whilst a national technology alliance has preliminarily formed,regional alliances have not been adequately established;5) even though the cooperation level amongst weak connection cities is not high,such cities still play an important role in the network as a result of their location within ′structural holes′ in the network;and 6) the major driving forces facilitating inter-city technological cooperation are geographical proximity,hierarchical proximity and technological proximity.
文摘Debris flow is one of the most destructive phenomena of natural hazards. Recently, major natural hazard, claiming human lives and assets, is due to debris flow in the world. Several practical methods for forecasting debris flow have been proposed, however, the accuracy of these methods is not high enough for practical use because of the stochastic and non-linear characteristics of debris flow. Artificial neural network has proven to be feasible and useful in developing models for nonlinear systems. On the other hand, predicting the future behavior based on a time series of collected historical data is also an important tool in many scientific applications. In this study we present a three-layer feed-forward neural network model to forecast surge of debris flow according to the time series data collected in the Jiangjia Ravine, situated in north part of Yunnan Province of China. The simulation and prediction of debris flow using the proposed approach shows this model is feasible, however, further studies are needed.
文摘The Unified Power Flow Controller （UPFC） is one of the most versatile Flexible AC Transmission Systems （FACTS） devices that has unique capability of independently controlling the real and reactive power flows, in addition to regulate the system bus voltage. This paper presents performance analysis of Unified Power Flow Controller based on two axis theory. Based on this analysis, a new Artificial Neural Network （ANN） based controller has been proposed to improve the system performance. The controller rules are structured depending upon the relationship between series inserted voltage and the desired changes in real/reactive power flow in the power system. The effects of different controllers along with parameters of series transformer and transmission line have been investigated through developed control block model in SIMULINK tool box of MATLAB. The effectiveness of the proposed scheme is demonstrated by case studies.
基金supported by Ministry of Science&Technology under National Key R&D Program of China(No.2021YFE0108600)Ningbo Science and Technology Bureau under S&T Innovation 2025 Major Special Program(No.2019B10071)Key International Cooperation of National Natural Science Foundation of China(No.51920105011)。
文摘Electrifying the on-board subsystems of aircraft becomes an inevitable process as being faced with the environmental pollution,along with the proposed concept called more electric aircraft(MEA).With the increasing number of on-board power electronic based devices,the distribution system of the aircraft can be regarded as an onboard microgrid.As it is known that the load power electronic converters can exhibit constant power load(CPL)characteristics and reduce the system stability,it is necessary to accurately predict and enhance the system stability in designing process.This paper firstly analyzes the stability of an on-board DC microgrid with the presence of CPL.Then,discusses the reasons behind instability and proposes a control strategy to enhance system stability.Finally,the simulation results are worked out to validate the analysis and the effect of the proposed control strategy.
文摘Thermal performance of a loop heat pipe with two evaporators and two condensers was examined using a lumped network model analysis. Thermosyphon-type vertical loop heat pipe and capillary-pump-type horizontal loop heat pipe were calculated by examining the change of heating rate of two evaporators. Calculation results showed that the vapor and liquid flow rates in the loop heat pipe and the thermal conductance of the heat pipe changed significantly depending on the distribution ratio of the heating rate of the multiple evaporators. The thermal performance of the vertical loop heat pipe with two evaporators was also examined and experimental results of flow direction and thermal conductance of the heat pipe agreed with the analytical results. The lumped network model analysis is therefore considered accurate and preferable for the practical design of a loop heat pipe with multiple evaporators.
基金supported by the National Natural Science Foundation of China under Grant No.61003282Beijing Higher Education Young Elite Teacher Project+3 种基金China Next Generation Internet(CNGI)Project"Research and Trial on Evolving Next Generation Network Intelligence Capability Enhancement(NICE)"the National Basic Research Program(973 Program)under Grant No.2009CB320-505the National Science and Technology Major Project"Research about Architecture of Mobile Internet"under Grant No.2011ZX03-002-001-01the National High Technology Research and Development Program(863 Program)under Grant No.2011AA010704
文摘The Deep Packet Inspection(DPI)method is a popular method that can accurately identify the flow data and its corresponding application.Currently,the DPI method is widely used in common network management systems.However,the major limitation of DPI systems is that their signature library is mainly extracted manually,which makes it hard to efficiently obtain the signature of new applications.Hence,in this paper,we propose an automatic signature extraction mechanism using Principal Component Analysis(PCA)technology,which is able to extract the signature automatically.In the proposed method,the signatures are expressed in the form of serial consistent sequences constructed by principal components instead of normally separated substrings in the original data extracted from the traditional methods.Extensive experiments based on numerous sets of data have been carried out to evaluate the performance of the proposed scheme,and the results prove that the newly proposed method can achieve good performance in terms of accuracy and efficiency.
基金Supported by the Key Project of Chinese Ministry of Education under Grant No.211123the Scientific Research Fund of Hunan Provincial Education Department under Grant No.10B072+2 种基金Doctor Scientific Research Startup Project Foundation of Hunan University of Arts and Science under Grant No.BSQD1010the Fund of Key Construction Academic Subject of Hunan Provincethe Natural Science Foundation of Hunan Province under Grant No.14JJ2125
文摘In this paper, a new lattice hydrodynamic model is proposed by incorporating the driver anticipation effect of next-nearest-neighbor site. The linear stability analysis and nonlinear analysis show that the driver anticipation effect of next-nearest-neighbor site can enlarge the stable area of traffic flow. The space can be divided into three regions： stab/e, metastable, and unstable. Numerical simulation further illuminates that the driver anticipation effect of the next-neaxest-neighbor site can stabilize tramc flow in our modified lattice model, which is consistent with the analytical results.
