Flume, which implements decentralized information flow control （DIFC）, allows a high security level process to ＂pre-create＂ secret files in a low security level directory. However, the pre-create mechanism makes s...Flume, which implements decentralized information flow control （DIFC）, allows a high security level process to ＂pre-create＂ secret files in a low security level directory. However, the pre-create mechanism makes some normal system calls unavailable, and moreover, it needs priori knowledge to create a large quantity of objects, which is difficult to estimate in practical operating systems. In this paper, we present an extended Flume file access control mechanism, named Effect, to substitute the mechanism of pre-create, which permits write operations （create, delete, and rename a file） on directories and creates a file access virtual layer that allocates operational views for each process with noninterference properties. In the end, we further present an analysis on the security of Effect. Our work makes it easier for multi-user to share confidential information in decentralized information flow control systems.展开更多
In this paper we investigate self-organized phenomena such as lane formation generated by pedestrian counter flow in a channel.The lattice gas model is extended to take the effect of walkers in the opposite direction ...In this paper we investigate self-organized phenomena such as lane formation generated by pedestrian counter flow in a channel.The lattice gas model is extended to take the effect of walkers in the opposite direction into account simultaneously when they are in the view field of a walker,i.e.,walkers tend to follow the leaders in the same direction and avoid conflicts with those walking towards them.The improved model is then used to mimic pedestrian counter flow in a channel under periodic boundary conditions.Numerical simulations show that lane formation is well reproduced,and this process is rather rapid which coincides with real pedestrian traffic.The average velocity and critical density are found to increase to some degree with the consideration of view field.展开更多
While driving a car at high speed cruising, the mirror surface of side-view mirrors happens to vibrate. The vibration often leads to image blurs of objects reflected in the mirror. Once the phenomena happen, drivers c...While driving a car at high speed cruising, the mirror surface of side-view mirrors happens to vibrate. The vibration often leads to image blurs of objects reflected in the mirror. Once the phenomena happen, drivers cannot clearly identify the approaching vehicles from the rear. The paper aims to clarify the vibration modes of side-view mirror experimentally and to capture forces on the mirror surface induced by separating vortices around the mirror numerically. Experimental study clarified two findings. One is that the mirror has the primary natural frequencies of 25, 30 and 33 Hz. The other is that vibrations of the mirror increase in proportion to flow velocity and their frequencies have peak values at 120 and 140 km/h. The frequencies of the mirror vibration coincide completely with the primary natural frequencies. In order to capture the external forces vibrating the mirror surface, numerical study was performed by unsteady air-flow analyses. Relationships between flow velocity fluctuations close to the mirror surface and pressure fluctuations on the mirror surface were investigated. It was found that the two power spectra have peak values at the same frequency of 24.4 Hz at 120 km/h. This shows that flow velocity fluctuations with the frequency of 24.4 Hz affect directly pressure fluctuations on the mirror surface. Numerical analyses clarify that the frequencies of shedding vortices are 24.4 Hz at 120 km/h and 28.3 Hz at 140 km/h. The frequencies of mirror vibration are very close to those of flow fluctuations. This shows that the frequencies of the mirror vibration have much to do with the frequencies of the forces induced aerodynamically by vortex shedding. Therefore it follows that image blurs at high speed cruising are caused by resonance phenomena that the mirror surface resonates with the frequencies of shedding vortices around the mirror.展开更多
基金Supported by the National Natural Science Foundation of China(61003268,61103220,91118003,61173138,61170022)Hubei Provincial Natural Science Foundation(2010CDB08601)The Fundamental ResearchFunds for the Central Universities (3101038,274629)
文摘Flume, which implements decentralized information flow control （DIFC）, allows a high security level process to ＂pre-create＂ secret files in a low security level directory. However, the pre-create mechanism makes some normal system calls unavailable, and moreover, it needs priori knowledge to create a large quantity of objects, which is difficult to estimate in practical operating systems. In this paper, we present an extended Flume file access control mechanism, named Effect, to substitute the mechanism of pre-create, which permits write operations （create, delete, and rename a file） on directories and creates a file access virtual layer that allocates operational views for each process with noninterference properties. In the end, we further present an analysis on the security of Effect. Our work makes it easier for multi-user to share confidential information in decentralized information flow control systems.
基金Project partially supported by the National Basic Research Program of China (Grant No. 2012CB725404)the National Natural Science Foundation of China (Grant Nos. 10972135 and 11172164)+2 种基金the Innovation Program of Shanghai Municipal Education Commission,China (Grant No. 11YZ12)the Shanghai Program for Innovative Research Team in Universitiesthe Program for Changjiang Scholars and Innovative Research Team in Universities,China (Grant No. IRT0844)
文摘In this paper we investigate self-organized phenomena such as lane formation generated by pedestrian counter flow in a channel.The lattice gas model is extended to take the effect of walkers in the opposite direction into account simultaneously when they are in the view field of a walker,i.e.,walkers tend to follow the leaders in the same direction and avoid conflicts with those walking towards them.The improved model is then used to mimic pedestrian counter flow in a channel under periodic boundary conditions.Numerical simulations show that lane formation is well reproduced,and this process is rather rapid which coincides with real pedestrian traffic.The average velocity and critical density are found to increase to some degree with the consideration of view field.
文摘While driving a car at high speed cruising, the mirror surface of side-view mirrors happens to vibrate. The vibration often leads to image blurs of objects reflected in the mirror. Once the phenomena happen, drivers cannot clearly identify the approaching vehicles from the rear. The paper aims to clarify the vibration modes of side-view mirror experimentally and to capture forces on the mirror surface induced by separating vortices around the mirror numerically. Experimental study clarified two findings. One is that the mirror has the primary natural frequencies of 25, 30 and 33 Hz. The other is that vibrations of the mirror increase in proportion to flow velocity and their frequencies have peak values at 120 and 140 km/h. The frequencies of the mirror vibration coincide completely with the primary natural frequencies. In order to capture the external forces vibrating the mirror surface, numerical study was performed by unsteady air-flow analyses. Relationships between flow velocity fluctuations close to the mirror surface and pressure fluctuations on the mirror surface were investigated. It was found that the two power spectra have peak values at the same frequency of 24.4 Hz at 120 km/h. This shows that flow velocity fluctuations with the frequency of 24.4 Hz affect directly pressure fluctuations on the mirror surface. Numerical analyses clarify that the frequencies of shedding vortices are 24.4 Hz at 120 km/h and 28.3 Hz at 140 km/h. The frequencies of mirror vibration are very close to those of flow fluctuations. This shows that the frequencies of the mirror vibration have much to do with the frequencies of the forces induced aerodynamically by vortex shedding. Therefore it follows that image blurs at high speed cruising are caused by resonance phenomena that the mirror surface resonates with the frequencies of shedding vortices around the mirror.
