This paper describes how to use medium access control (MAC) isolation to enhance management performance in public wireless LAN (PWLAN). To comply with the IEEE 802.11 standards, a scheme to implement MAC isolation in ...This paper describes how to use medium access control (MAC) isolation to enhance management performance in public wireless LAN (PWLAN). To comply with the IEEE 802.11 standards, a scheme to implement MAC isolation in WLAN access points by re-designing the Distribution_Service component of the MAC state machine is proposed. A variable named dotl 1 Isolation is defined to determine whether the MAC level communication between wireless stations in the same BSS is permitted or not. Finally, a design solution based on MPC860 hardware and embedded Linux software for PWLAN access point is specified. The simulation results of MAC isolation for PWLAN show that the proposed scheme is feasible and effective.展开更多
In order to resolve the conflict between the limited resources of embedded devices and the growing amount of massive image data to be shown, a solution for fast images rendering in embedded devices is proposed and imp...In order to resolve the conflict between the limited resources of embedded devices and the growing amount of massive image data to be shown, a solution for fast images rendering in embedded devices is proposed and implemented. First, an improved algorithm of a multi-resolution file-pyramid construction which is used for the organization of massive image data is presented. Then, a strategy, adopting technologies such as view-dependent levels of detail, target-tiles quick search and tiles seamless connection, is presented for fast scheduling and viewing of images. The results show that compared with the solution of multi-scale image representations based on wavelet, the proposed solution can improve the rendering speed, and the rendering speed does not depend on the image size, though it increases some data storage space. And the proposed solution is suitable for embedded devices and friendly experience.展开更多
The effects of Ni coating on the mechanical behaviors of single graphene sheet and their embedded Al matrix composites under axial tension are investigated using molecular dynamics （MD） simulation method. The result...The effects of Ni coating on the mechanical behaviors of single graphene sheet and their embedded Al matrix composites under axial tension are investigated using molecular dynamics （MD） simulation method. The results show that the Young＇s moduli and tensile strength of graphene obviously decrease after Ni coating. The results also show that the mechanical properties of Al matrix can be obviously increased by embedding a single graphene sheet. From the simulation, we also find that the Young＇s modulus and tensile strength of the Ni-coated graphene/Al composite is obviously larger than those of the uncoated graphene/Al composite. The increased magnitude of the Young＇s modulus and tensile strength of graphene/Al composite are 52.27% and 32.32% at 0.01 K, respectively, due to Ni coating. By exploring the effects of temperature on the mechanical properties of single graphene sheet and their embedded Al matrix composites, it is found that the higher temperature leads to the lower critical strain and tensile strength.展开更多
Although convection embedded in stratiform cloud is often disordered, it is ordered under certain weather conditions. In particular, there are two forms of ordered convection: embedded convection with a ladder-like pa...Although convection embedded in stratiform cloud is often disordered, it is ordered under certain weather conditions. In particular, there are two forms of ordered convection: embedded convection with a ladder-like pattern and that with a parallel pattern. However, there is little literature regarding these patterns. Because stratiform clouds with embedded convection are major objects for weather-modification studies, it is important to explore the formation/development and characteristic precipitation of embedded convection from the perspective of cloud and precipitation physics. In this paper, using observation data, we simulate a large-scale precipitation event in China for July 19-21, 2007, employing the mesoscale Weather Research and Forecasting (WRF) model (V2.2). The rainfall-related clouds are analyzed through simulation, with particular focus being given to the genesis of embedded convection, the precipitation and microphysical properties. The results show that the WRF model can simulate features of this kind of nephsystem, indicating a close relationship between convection genesis and the 500 hPa trough and low-level convergence line. In such a favorable weather situation, there are two ordered patterns of embedded con- vection in the nephsystem, one being a group of convection centers arranged at different altitudes in a ladder-like manner and the other being a group of convection centers with a parallel pattern. In the first case, rainfall also has a ladder feature, with precipitation being highest for the top convection and reducing to the base convection. This implies that the higher the convection develops, the more active the microphysics in warmand cold-cloud processes is, leading to greater precipitation; i.e. rainfall in a ladder-like distribution. In the second case, rainfall decreases step by step from south to north, with the precipitation depending strongly on the cloud-water content therein. The two patterns of embedded convection and their precipitation features and microphysics are intensively studied from a new point of view.展开更多
文摘This paper describes how to use medium access control (MAC) isolation to enhance management performance in public wireless LAN (PWLAN). To comply with the IEEE 802.11 standards, a scheme to implement MAC isolation in WLAN access points by re-designing the Distribution_Service component of the MAC state machine is proposed. A variable named dotl 1 Isolation is defined to determine whether the MAC level communication between wireless stations in the same BSS is permitted or not. Finally, a design solution based on MPC860 hardware and embedded Linux software for PWLAN access point is specified. The simulation results of MAC isolation for PWLAN show that the proposed scheme is feasible and effective.
基金The National Public Benefit Research Foundation of China (No. 201111013-02)
文摘In order to resolve the conflict between the limited resources of embedded devices and the growing amount of massive image data to be shown, a solution for fast images rendering in embedded devices is proposed and implemented. First, an improved algorithm of a multi-resolution file-pyramid construction which is used for the organization of massive image data is presented. Then, a strategy, adopting technologies such as view-dependent levels of detail, target-tiles quick search and tiles seamless connection, is presented for fast scheduling and viewing of images. The results show that compared with the solution of multi-scale image representations based on wavelet, the proposed solution can improve the rendering speed, and the rendering speed does not depend on the image size, though it increases some data storage space. And the proposed solution is suitable for embedded devices and friendly experience.
基金Supported by National Natural Science Foundation of China under Grant No.10902083the Natural Science Foundation of Shannxi Province under Grant No.2009GM1007
文摘The effects of Ni coating on the mechanical behaviors of single graphene sheet and their embedded Al matrix composites under axial tension are investigated using molecular dynamics （MD） simulation method. The results show that the Young＇s moduli and tensile strength of graphene obviously decrease after Ni coating. The results also show that the mechanical properties of Al matrix can be obviously increased by embedding a single graphene sheet. From the simulation, we also find that the Young＇s modulus and tensile strength of the Ni-coated graphene/Al composite is obviously larger than those of the uncoated graphene/Al composite. The increased magnitude of the Young＇s modulus and tensile strength of graphene/Al composite are 52.27% and 32.32% at 0.01 K, respectively, due to Ni coating. By exploring the effects of temperature on the mechanical properties of single graphene sheet and their embedded Al matrix composites, it is found that the higher temperature leads to the lower critical strain and tensile strength.
基金supported by National Natural Science Foundation of China (Grant Nos. 40975086 and 40537034)the National Research Project of the Scientific & Technical Support (Grant No. 2006BAC12B02)
文摘Although convection embedded in stratiform cloud is often disordered, it is ordered under certain weather conditions. In particular, there are two forms of ordered convection: embedded convection with a ladder-like pattern and that with a parallel pattern. However, there is little literature regarding these patterns. Because stratiform clouds with embedded convection are major objects for weather-modification studies, it is important to explore the formation/development and characteristic precipitation of embedded convection from the perspective of cloud and precipitation physics. In this paper, using observation data, we simulate a large-scale precipitation event in China for July 19-21, 2007, employing the mesoscale Weather Research and Forecasting (WRF) model (V2.2). The rainfall-related clouds are analyzed through simulation, with particular focus being given to the genesis of embedded convection, the precipitation and microphysical properties. The results show that the WRF model can simulate features of this kind of nephsystem, indicating a close relationship between convection genesis and the 500 hPa trough and low-level convergence line. In such a favorable weather situation, there are two ordered patterns of embedded con- vection in the nephsystem, one being a group of convection centers arranged at different altitudes in a ladder-like manner and the other being a group of convection centers with a parallel pattern. In the first case, rainfall also has a ladder feature, with precipitation being highest for the top convection and reducing to the base convection. This implies that the higher the convection develops, the more active the microphysics in warmand cold-cloud processes is, leading to greater precipitation; i.e. rainfall in a ladder-like distribution. In the second case, rainfall decreases step by step from south to north, with the precipitation depending strongly on the cloud-water content therein. The two patterns of embedded convection and their precipitation features and microphysics are intensively studied from a new point of view.
