The research on the form and control method of impact load arresting buffer has been an active topic in the field of buffer arresting system(BAS).It becomes significant on reducing the weight of arresting system,impro...The research on the form and control method of impact load arresting buffer has been an active topic in the field of buffer arresting system(BAS).It becomes significant on reducing the weight of arresting system,improving the hindered efficiency,and guaranteeing the security of BAS.The hydraulic hindered device of impact load is currently used in BAS.There are some problems.For example,the system needs large power sources.However,once the power of active hydraulic control system is turned off,there arise unpredictable security risks.An arresting form of semi-active control based on magneto-rheological damper(MRD) is proposed,and the mechanical model of the BAS is established.Meanwhile,the state equation of impact load BAS is established according to the characteristics of impact load buffer arresting,and its sliding model buffer control is achieved.Due to the chattering characteristic of the output signal of sliding mode controller,the method to prevent chattering is designed based on short-term energy and zero-crossing rate detection.For the model and chattering suppression of sliding model buffer control algorithms,simulation results show that the proposed state equation and the arresting model are reasonable,and the design of semi-active control algorithm is effective.On the condition of the buffer control system requirement and the accuracy,the proposed algorithms effectively control the chattering of sliding mode control algorithms,and improve the security of the BAS.展开更多
Compared with wheeled or tracked robots,legged robots exhibit advantages on agile locomotion and higher survival chance for deadly impacts. A buffering strategy is proposed for quadruped robots with non-extreme initia...Compared with wheeled or tracked robots,legged robots exhibit advantages on agile locomotion and higher survival chance for deadly impacts. A buffering strategy is proposed for quadruped robots with non-extreme initial attitudes from the end of air-righting to the steady standing on the ground.This approach consists of landing phase,buffering phase and recovering phase. The variable stiffness control,proportional-derivative( PD) force control and foot trajectory planning are applied to the joints of quadruped robots until the end of the recovering phase. The PD parameters are tuned according to the desired performance of each phase. The above approach is verified on a virtual platform.展开更多
Available Bit Rate (ABR) service has been developed to support data applications to asynchronous transfer mode (ATM) networks.Since a ratebased feedback flow control mechanism has been selected as a standard by ATM Fo...Available Bit Rate (ABR) service has been developed to support data applications to asynchronous transfer mode (ATM) networks.Since a ratebased feedback flow control mechanism has been selected as a standard by ATM Forum,buffering becomes an issue that needs intensive study.In this paper,the queuing performance in a switch is studied in detail.It is theoretically proven that the goals of no cell loss and full utilization of link capacity can be achieved by choosing an appropriate buffersize and threshold of the switch buffer which is supported by our simulation results of a complex network.展开更多
Transmission Control Protocol (TCP) is the most important transport layer protocol being used nowadays. It suffers from many problems over mobile networks especially over Cognitive Radio (CR). CR is one of the latest ...Transmission Control Protocol (TCP) is the most important transport layer protocol being used nowadays. It suffers from many problems over mobile networks especially over Cognitive Radio (CR). CR is one of the latest mobile technologies that brings its own share of problems for TCP. The buffer overflow for CR secondary network relay node can affect the performance of TCP. The contribution of this paper is the novel cross-layer model being used to evaluate the effect of the TCP congestion control on the secondary relay node buffer size in Cognitive Radio Network (CRN). The performance has been assessed by buffer overflow probability.展开更多
The dynamic math model of shift clutch in engagement process was determined on the basis of hydraulic buffering valve and shift clutch of a power shift steering transmission. The influence of buffering pressure chara...The dynamic math model of shift clutch in engagement process was determined on the basis of hydraulic buffering valve and shift clutch of a power shift steering transmission. The influence of buffering pressure characteristic on shift clutch engagement process was analyzed. The study results could be used to the characteristics match of the shift clutch with the hydraulic system of the high speed tracked vehicle power shift steering transmission and the performance prediction.展开更多
Design of an effective congestion control scheme is a hot topic in the development of compute network. The flow control scheme can adjust the packet sending rate in source host, thus effectively avoiding the network c...Design of an effective congestion control scheme is a hot topic in the development of compute network. The flow control scheme can adjust the packet sending rate in source host, thus effectively avoiding the network congestion. This paper proposes a flow control scheme based on discrete control theory. The simulation results show that this method can adjust the sending rate and queue level in buffer rapidly and effectively. The method is easy to implement and applicable to high speed networks.展开更多
We present a nonlinear flow control scheme based on a buffer management model with physical constraints. It extends previous result of Pitsillides et al. in [6] by improving the queue length regulation for better serv...We present a nonlinear flow control scheme based on a buffer management model with physical constraints. It extends previous result of Pitsillides et al. in [6] by improving the queue length regulation for better service of network traffics. Besides a single node system, we also address the decentralized control of many cascaded nodes. The proposed discontinuous controller asymptotically regulates the buffer queue length at the output port of a router/switch to a constant reference value, under unknown time varying interfering traffics and saturation constraints on control input and states. Its continuous approximation achieves practical regulation with an ultimate bound on the regulation error tunable by a design parameter.展开更多
The Olkaria geothermal field is located in the Kenya Rift valley, about 120 km from Nairobi. Geothermal activity is widespread in this rift with 14 major geothermal prospects being identified. Structures in the Greate...The Olkaria geothermal field is located in the Kenya Rift valley, about 120 km from Nairobi. Geothermal activity is widespread in this rift with 14 major geothermal prospects being identified. Structures in the Greater Olkaria volcanic complex include: the ring structure, the Ol’Njorowa gorge, the ENE-WSW Olkaria fault and N-S, NNE-SSW, NW-SE and WNW-ESE trending faults. The faults are more prominent in the East, Northeast and West Olkaria fields but are scarce in the Olkaria Domes area, possibly due to the thick pyroclastics cover. The NW-SE and WNW- ESE faults are thought to be the oldest and are associated with the development of the rift. The most prominent of these faults is the Gorge Farm fault, which bounds the geothermal fields in the northeastern part and extends to the Olkaria Domes area. The most recent structures are the N-S and the NNE-SSW faults. The geochemistry and output of the wells cut by these faults have a distinct characteristic that is the N-S, NW-SE and WNW-ESE faults are characterized by wells that have high Cl contents, temperatures and are good producers whereas the NE-SW faults, the Ring Structure and the Ol’Njorowa gorge appear to carry cool dilute waters with less chloride concentration and thus low performing wells. Though the impacts of these faults are apparent, there exists a gap in knowledge on how wide is the impact of these faults on the chemistry and performance of the wells. This paper therefore seeks to bridge this gap by analysis of the chemical trends of both old wells and newly drilled ones to evaluate the impacts of individual faults and then using buffering technique of ArcGis estimate how far and wide the influence of the faults is. The data was obtained after the sampling and analysis of discharge fluids of wells located on six profiles along the structures cutting through the field. Steam samples were collected with a stainless steel Webre separator connected between the wellhead and an atmospheric silencer on the discharging wells whereas the analysis was done in house in the KenGen geochemistry laboratory. The results indicates that Olkaria field has three categories of faults that control fluid flow that is the NW-SE trending faults that bring in high temperature and Cl rich waters, and the NE-SW trending Olkaria fracture tend to carry cool temperature waters that have led to decline in enthalpies of the wells it cuts through. The faults within the Ol Njorowa gorge act to carry cool, less mineralized water. Though initially, these effects were thought to be in shallow depths, an indication in OW-901 which is a deeper at 2200 m compared to 1600 m of OW-23 well that proves otherwise. This is, however, to be proved later as much deeper wells have been sited.展开更多
随着高清电视和网络媒体的快速发展,音视频同步技术在广播电视节目制作中的重要性日益突出。通过对当前音视频同步系统的分析,深入研究节目时钟参考(Program Clock Reference,PCR)、显示时间戳(Presentation Time Stamp,PTS)/解码时间戳...随着高清电视和网络媒体的快速发展,音视频同步技术在广播电视节目制作中的重要性日益突出。通过对当前音视频同步系统的分析,深入研究节目时钟参考(Program Clock Reference,PCR)、显示时间戳(Presentation Time Stamp,PTS)/解码时间戳(Decoding Time Stamp,DTS)、音视频缓冲区控制等关键技术在实际制作环境中的应用。基于自适应缓冲区控制的音视频同步方案能将音视频延迟控制在±15 ms以内,满足广播级节目制作要求。展开更多
缓冲区溢出漏洞广泛存在于由不安全的高级语言所编写的程序中.利用缓冲区溢出漏洞,攻击者可以实现控制流劫持等危险攻击方式.基于Canary的栈保护技术是处理缓冲区溢出漏洞的一种简单有效且广泛部署的防御手段,然而位置固定和取值相同的...缓冲区溢出漏洞广泛存在于由不安全的高级语言所编写的程序中.利用缓冲区溢出漏洞,攻击者可以实现控制流劫持等危险攻击方式.基于Canary的栈保护技术是处理缓冲区溢出漏洞的一种简单有效且广泛部署的防御手段,然而位置固定和取值相同的特点使其容易被攻击者分析和破解.本文提出一种基于软件多样性的栈保护技术,它以拥有随机化大小和偏移的异构Canary为核心,不仅能直接抵御常规Canary无法处理的泄漏类和覆盖类攻击,而且能构造出各种更加安全的多样性软件系统.实验结果表明,异构Canary在有效提升安全性的同时仅为SPEC CPU 2017基准程序集额外引入了不高于2%的编译开销和平均3.22%的运行开销.展开更多
基金the National Natural Science Foundation of China(Nos.61074090 and 60804025)the Innovation Funds of Aviation Industry Corporation of China(No.cxy2013SH16)the Natural Science Foundation of Liaoning(Nos.2015020061 and 2015020069)
文摘The research on the form and control method of impact load arresting buffer has been an active topic in the field of buffer arresting system(BAS).It becomes significant on reducing the weight of arresting system,improving the hindered efficiency,and guaranteeing the security of BAS.The hydraulic hindered device of impact load is currently used in BAS.There are some problems.For example,the system needs large power sources.However,once the power of active hydraulic control system is turned off,there arise unpredictable security risks.An arresting form of semi-active control based on magneto-rheological damper(MRD) is proposed,and the mechanical model of the BAS is established.Meanwhile,the state equation of impact load BAS is established according to the characteristics of impact load buffer arresting,and its sliding model buffer control is achieved.Due to the chattering characteristic of the output signal of sliding mode controller,the method to prevent chattering is designed based on short-term energy and zero-crossing rate detection.For the model and chattering suppression of sliding model buffer control algorithms,simulation results show that the proposed state equation and the arresting model are reasonable,and the design of semi-active control algorithm is effective.On the condition of the buffer control system requirement and the accuracy,the proposed algorithms effectively control the chattering of sliding mode control algorithms,and improve the security of the BAS.
基金Supported by the National High Technology Research and Development Program of China(No.2015AA042201)the National Natural Science Foundation of China(No.61233014,61305130)+1 种基金the Shandong Provincial Natural Science Foundation(No.ZR2013FQ003,ZR2013EEM027)China Postdoctoral Science Foundation(No.2013M541912)
文摘Compared with wheeled or tracked robots,legged robots exhibit advantages on agile locomotion and higher survival chance for deadly impacts. A buffering strategy is proposed for quadruped robots with non-extreme initial attitudes from the end of air-righting to the steady standing on the ground.This approach consists of landing phase,buffering phase and recovering phase. The variable stiffness control,proportional-derivative( PD) force control and foot trajectory planning are applied to the joints of quadruped robots until the end of the recovering phase. The PD parameters are tuned according to the desired performance of each phase. The above approach is verified on a virtual platform.
文摘Available Bit Rate (ABR) service has been developed to support data applications to asynchronous transfer mode (ATM) networks.Since a ratebased feedback flow control mechanism has been selected as a standard by ATM Forum,buffering becomes an issue that needs intensive study.In this paper,the queuing performance in a switch is studied in detail.It is theoretically proven that the goals of no cell loss and full utilization of link capacity can be achieved by choosing an appropriate buffersize and threshold of the switch buffer which is supported by our simulation results of a complex network.
文摘Transmission Control Protocol (TCP) is the most important transport layer protocol being used nowadays. It suffers from many problems over mobile networks especially over Cognitive Radio (CR). CR is one of the latest mobile technologies that brings its own share of problems for TCP. The buffer overflow for CR secondary network relay node can affect the performance of TCP. The contribution of this paper is the novel cross-layer model being used to evaluate the effect of the TCP congestion control on the secondary relay node buffer size in Cognitive Radio Network (CRN). The performance has been assessed by buffer overflow probability.
文摘The dynamic math model of shift clutch in engagement process was determined on the basis of hydraulic buffering valve and shift clutch of a power shift steering transmission. The influence of buffering pressure characteristic on shift clutch engagement process was analyzed. The study results could be used to the characteristics match of the shift clutch with the hydraulic system of the high speed tracked vehicle power shift steering transmission and the performance prediction.
基金This paper was supported by the National Natural Science Foundation of China (No. 69874025).
文摘Design of an effective congestion control scheme is a hot topic in the development of compute network. The flow control scheme can adjust the packet sending rate in source host, thus effectively avoiding the network congestion. This paper proposes a flow control scheme based on discrete control theory. The simulation results show that this method can adjust the sending rate and queue level in buffer rapidly and effectively. The method is easy to implement and applicable to high speed networks.
基金Supported in part by the National Science Foundation under grants ANI-0081527 and ECS-0093176
文摘We present a nonlinear flow control scheme based on a buffer management model with physical constraints. It extends previous result of Pitsillides et al. in [6] by improving the queue length regulation for better service of network traffics. Besides a single node system, we also address the decentralized control of many cascaded nodes. The proposed discontinuous controller asymptotically regulates the buffer queue length at the output port of a router/switch to a constant reference value, under unknown time varying interfering traffics and saturation constraints on control input and states. Its continuous approximation achieves practical regulation with an ultimate bound on the regulation error tunable by a design parameter.
基金Supported by National Natural Science Foundation of China（60434030,60673178,and 60472076） and National Basic Research Program of China（973 Program）（2007CB307106）
文摘The Olkaria geothermal field is located in the Kenya Rift valley, about 120 km from Nairobi. Geothermal activity is widespread in this rift with 14 major geothermal prospects being identified. Structures in the Greater Olkaria volcanic complex include: the ring structure, the Ol’Njorowa gorge, the ENE-WSW Olkaria fault and N-S, NNE-SSW, NW-SE and WNW-ESE trending faults. The faults are more prominent in the East, Northeast and West Olkaria fields but are scarce in the Olkaria Domes area, possibly due to the thick pyroclastics cover. The NW-SE and WNW- ESE faults are thought to be the oldest and are associated with the development of the rift. The most prominent of these faults is the Gorge Farm fault, which bounds the geothermal fields in the northeastern part and extends to the Olkaria Domes area. The most recent structures are the N-S and the NNE-SSW faults. The geochemistry and output of the wells cut by these faults have a distinct characteristic that is the N-S, NW-SE and WNW-ESE faults are characterized by wells that have high Cl contents, temperatures and are good producers whereas the NE-SW faults, the Ring Structure and the Ol’Njorowa gorge appear to carry cool dilute waters with less chloride concentration and thus low performing wells. Though the impacts of these faults are apparent, there exists a gap in knowledge on how wide is the impact of these faults on the chemistry and performance of the wells. This paper therefore seeks to bridge this gap by analysis of the chemical trends of both old wells and newly drilled ones to evaluate the impacts of individual faults and then using buffering technique of ArcGis estimate how far and wide the influence of the faults is. The data was obtained after the sampling and analysis of discharge fluids of wells located on six profiles along the structures cutting through the field. Steam samples were collected with a stainless steel Webre separator connected between the wellhead and an atmospheric silencer on the discharging wells whereas the analysis was done in house in the KenGen geochemistry laboratory. The results indicates that Olkaria field has three categories of faults that control fluid flow that is the NW-SE trending faults that bring in high temperature and Cl rich waters, and the NE-SW trending Olkaria fracture tend to carry cool temperature waters that have led to decline in enthalpies of the wells it cuts through. The faults within the Ol Njorowa gorge act to carry cool, less mineralized water. Though initially, these effects were thought to be in shallow depths, an indication in OW-901 which is a deeper at 2200 m compared to 1600 m of OW-23 well that proves otherwise. This is, however, to be proved later as much deeper wells have been sited.
文摘随着高清电视和网络媒体的快速发展,音视频同步技术在广播电视节目制作中的重要性日益突出。通过对当前音视频同步系统的分析,深入研究节目时钟参考(Program Clock Reference,PCR)、显示时间戳(Presentation Time Stamp,PTS)/解码时间戳(Decoding Time Stamp,DTS)、音视频缓冲区控制等关键技术在实际制作环境中的应用。基于自适应缓冲区控制的音视频同步方案能将音视频延迟控制在±15 ms以内,满足广播级节目制作要求。
文摘缓冲区溢出漏洞广泛存在于由不安全的高级语言所编写的程序中.利用缓冲区溢出漏洞,攻击者可以实现控制流劫持等危险攻击方式.基于Canary的栈保护技术是处理缓冲区溢出漏洞的一种简单有效且广泛部署的防御手段,然而位置固定和取值相同的特点使其容易被攻击者分析和破解.本文提出一种基于软件多样性的栈保护技术,它以拥有随机化大小和偏移的异构Canary为核心,不仅能直接抵御常规Canary无法处理的泄漏类和覆盖类攻击,而且能构造出各种更加安全的多样性软件系统.实验结果表明,异构Canary在有效提升安全性的同时仅为SPEC CPU 2017基准程序集额外引入了不高于2%的编译开销和平均3.22%的运行开销.
