There are several indexing techniques that can optimize system performances. The choice of the right index type in a schema can improve the DB performances by up to 80%. Unfortunately the illustrations of the various ...There are several indexing techniques that can optimize system performances. The choice of the right index type in a schema can improve the DB performances by up to 80%. Unfortunately the illustrations of the various techniques are scattered over a number of texts and manuals, and the courses for database designers are often somewhat incomplete. The present paper shows a didactical experience which tackles this kind of limitations. In particular, the authors have prepared a textbook that includes twenty-one different index formats; it discusses advantages and disadvantages of each indexing technique, and has been positively validated during advanced courses on relational database design.展开更多
The prevalence of smart phone and improvement of wireless net promote the usage of crowdsourced live streaming,where individual users act as live streaming sources to broadcast themselves online. Characterizing the pe...The prevalence of smart phone and improvement of wireless net promote the usage of crowdsourced live streaming,where individual users act as live streaming sources to broadcast themselves online. Characterizing the performance and identifying its bottleneck in such systems can shed light on the system design and performance optimization. TCP performance of a commercial crowdsourced live streaming system is examined by analyzing packet-level traces collected at streaming servers. TCP stalls that heavily hurt the Qo E of user have been identified. In particular,the TCP stalls account for as much as 31. 6% of the flow completion time for upload flows and result in abandonment of upload on the corresponding channels. Stalls caused by timeout retransmissions are further dissected and timeout retransmission characteristics are revealed to be dependent on the video encoding methods. These findings provide new insights in crowdsourced live streaming systems and can guide designers to improve the TCP efficiency.展开更多
In the era of Web2.0, AJAX as one of the core technology to provide asynchronous communication with the server＇s ability to solve most of the Web site to force the user to enter the ＂submit, wait for redisplay proce...In the era of Web2.0, AJAX as one of the core technology to provide asynchronous communication with the server＇s ability to solve most of the Web site to force the user to enter the ＂submit, wait for redisplay process, so that user from requestfreed response cycle, ultimately allows developers and designers to use standard HTML / CSS / JavaScript to create a ＂desktop style Web applications. According AJAX principles and characteristics, and the combination of educational administration and educational management system based on AJAX technology solutions.展开更多
The braking behavior of drivers when a pedestrian comes out from the sidewalk to the road was analyzed using a driving simulator. Based on drivers＇ braking behavior, the braking control timing of the system for avoid...The braking behavior of drivers when a pedestrian comes out from the sidewalk to the road was analyzed using a driving simulator. Based on drivers＇ braking behavior, the braking control timing of the system for avoiding the collision with pedestrians was proposed. In this study, the subject drivers started braking at almost the same time in terms of TTC （Time to Collision）, regardless of the velocity of a subject vehicle and crossing velocity of pedestrians. This experimental result showed that brake timing of the system which can minimize the interference for braking between drivers and the system is 1.3 s of TTC. Next, the drivers＇ braking behavior was investigated when the system controlled braking to avoid collision at this timing. As a result, drivers did not show any change of braking behavior with no excessive interference between braking control by the system and braking operation by drivers for avoiding collisions with pedestrians which is equivalent to the excessive dependence on the system.展开更多
The controller design for hypersonic vehicle is critical and challenging because of the inherent couplings between the propulsion system and the airframe dynamics,as well as the presence of strong flexibility effects....The controller design for hypersonic vehicle is critical and challenging because of the inherent couplings between the propulsion system and the airframe dynamics,as well as the presence of strong flexibility effects.Many researchers have investigated various strategies to mitigate the coupling by means of robust design methods.This paper reviews the recent research efforts to promote the capability of control design for hypersonic vehicle.Methodologies such as robust control,adaptive control,sliding mode control and other hybrid methods have made significant progresses in hypersonic control.Then,the main challenges of control approaches for hypersonic vehicle are systematically analyzed in detail.展开更多
文摘There are several indexing techniques that can optimize system performances. The choice of the right index type in a schema can improve the DB performances by up to 80%. Unfortunately the illustrations of the various techniques are scattered over a number of texts and manuals, and the courses for database designers are often somewhat incomplete. The present paper shows a didactical experience which tackles this kind of limitations. In particular, the authors have prepared a textbook that includes twenty-one different index formats; it discusses advantages and disadvantages of each indexing technique, and has been positively validated during advanced courses on relational database design.
基金Supported by the National Basic Research Program of China(2012CB315801)the National Natural Science Foundation of China(No.6157060397)
文摘The prevalence of smart phone and improvement of wireless net promote the usage of crowdsourced live streaming,where individual users act as live streaming sources to broadcast themselves online. Characterizing the performance and identifying its bottleneck in such systems can shed light on the system design and performance optimization. TCP performance of a commercial crowdsourced live streaming system is examined by analyzing packet-level traces collected at streaming servers. TCP stalls that heavily hurt the Qo E of user have been identified. In particular,the TCP stalls account for as much as 31. 6% of the flow completion time for upload flows and result in abandonment of upload on the corresponding channels. Stalls caused by timeout retransmissions are further dissected and timeout retransmission characteristics are revealed to be dependent on the video encoding methods. These findings provide new insights in crowdsourced live streaming systems and can guide designers to improve the TCP efficiency.
文摘In the era of Web2.0, AJAX as one of the core technology to provide asynchronous communication with the server＇s ability to solve most of the Web site to force the user to enter the ＂submit, wait for redisplay process, so that user from requestfreed response cycle, ultimately allows developers and designers to use standard HTML / CSS / JavaScript to create a ＂desktop style Web applications. According AJAX principles and characteristics, and the combination of educational administration and educational management system based on AJAX technology solutions.
文摘The braking behavior of drivers when a pedestrian comes out from the sidewalk to the road was analyzed using a driving simulator. Based on drivers＇ braking behavior, the braking control timing of the system for avoiding the collision with pedestrians was proposed. In this study, the subject drivers started braking at almost the same time in terms of TTC （Time to Collision）, regardless of the velocity of a subject vehicle and crossing velocity of pedestrians. This experimental result showed that brake timing of the system which can minimize the interference for braking between drivers and the system is 1.3 s of TTC. Next, the drivers＇ braking behavior was investigated when the system controlled braking to avoid collision at this timing. As a result, drivers did not show any change of braking behavior with no excessive interference between braking control by the system and braking operation by drivers for avoiding collisions with pedestrians which is equivalent to the excessive dependence on the system.
基金supported by the National Natural Science Foundation of China (Grant Nos. 61273054,60975072,60604009)the Program for New Century Excellent Talents in University of China (Grant No. NCET-10-0021)+1 种基金the Aeronautical Foundation of China (Grant No. 20115151019)the Open Fund of the State Key Laboratory of Virtual Reality Technology and Systems (Grant No. VR-2011-ZZ-01)
文摘The controller design for hypersonic vehicle is critical and challenging because of the inherent couplings between the propulsion system and the airframe dynamics,as well as the presence of strong flexibility effects.Many researchers have investigated various strategies to mitigate the coupling by means of robust design methods.This paper reviews the recent research efforts to promote the capability of control design for hypersonic vehicle.Methodologies such as robust control,adaptive control,sliding mode control and other hybrid methods have made significant progresses in hypersonic control.Then,the main challenges of control approaches for hypersonic vehicle are systematically analyzed in detail.
