In this paper, a specisl purpose NDT (non-destructive testing) computer system has been proposed,with which dynamic NDT can be taken for a monitored subject during its practical operation. It has more .dvantages than ...In this paper, a specisl purpose NDT (non-destructive testing) computer system has been proposed,with which dynamic NDT can be taken for a monitored subject during its practical operation. It has more .dvantages than the static NDT, which can only be taken after the monitored subject stopped ed unloaded. At the same time several experiments, applying this system, kave been studied, such as weld real-time monitoring of Austenitic steel, exploding experiments of pressure containers and realtime monitoring of splitting full-process of rock. All of experiments achieve ideal results.展开更多
The standardized IEEE ,802. II distributed coordination function （ DCF） provides a contention-based distributed channel access mechanism for mobile stations to share the wireless medium. However, when stations are m...The standardized IEEE ,802. II distributed coordination function （ DCF） provides a contention-based distributed channel access mechanism for mobile stations to share the wireless medium. However, when stations are mobile or portable units, power consumption becomes a primary issue since terminals are usually battery driven. This paper proposes an analytical model that calculates the energy efficiency of both the basic and the RTS/CTS access mechanisms of the IEEE 802. II protocol. The model is validated with simulation results using NS-2 simulation package. The effects of the network size, the average packet length, the initial contention window and maximum backoff stages on the energy efficiency of both access mechanisms are also investigated. Results show that the basic scheme has low energy efficiency at large packet length and large network size, and depends strongly on the number of stations and the backoff procedure parameters. Conversely, the RTS/CTS mechanism provides higher energy efficiency when the network size is large, and is more robust to variations in the backoff procedure parameters.展开更多
文摘In this paper, a specisl purpose NDT (non-destructive testing) computer system has been proposed,with which dynamic NDT can be taken for a monitored subject during its practical operation. It has more .dvantages than the static NDT, which can only be taken after the monitored subject stopped ed unloaded. At the same time several experiments, applying this system, kave been studied, such as weld real-time monitoring of Austenitic steel, exploding experiments of pressure containers and realtime monitoring of splitting full-process of rock. All of experiments achieve ideal results.
文摘The standardized IEEE ,802. II distributed coordination function （ DCF） provides a contention-based distributed channel access mechanism for mobile stations to share the wireless medium. However, when stations are mobile or portable units, power consumption becomes a primary issue since terminals are usually battery driven. This paper proposes an analytical model that calculates the energy efficiency of both the basic and the RTS/CTS access mechanisms of the IEEE 802. II protocol. The model is validated with simulation results using NS-2 simulation package. The effects of the network size, the average packet length, the initial contention window and maximum backoff stages on the energy efficiency of both access mechanisms are also investigated. Results show that the basic scheme has low energy efficiency at large packet length and large network size, and depends strongly on the number of stations and the backoff procedure parameters. Conversely, the RTS/CTS mechanism provides higher energy efficiency when the network size is large, and is more robust to variations in the backoff procedure parameters.
