No abstract

As an inexpensive, flexible, and scalable Internet-access wireless network, we have studied the architecture, protocols, and design optimizations of the Wireless Internet-access Mesh NETwork (WIMNET) that adopts multiple access-points (APs) connected through wireless links. WIMNET can improve the dependability to failures of APs and/or their links by allocating APs redundantly in the network field. Because redundant APs may increase the operational cost and degrade the throughput due to increasing radio interferences, only the necessary APs for connectivity between the hosts and the Internet gateway should be activated in communications. In this paper, we first define the active AP selection problem of selecting the minimum number of active APs, and prove the NP-completeness of its decision version through reduction from the known minimum set cover problem. Then, we propose an active AP selection algorithm of deactivating APs one by one until no more AP can be deactivated. Due to the limited transmission capacity in WIMNET, we further present an algorithm extension for throughput maximization. We verify the effectiveness of our proposal through simulations in three instances, where the number of active APs is reduced by more than 40% and the throughput is improved by more than 10% from the original in any instance.

No abstract

In order to offer an inexpensive, scalable Internetaccess wireless network, we have studied the architecture, protocols, and design optimizations of the wireless Internet-access mesh network (WIMNET) that adopts multiple access-points (APs) connected by wireless links. WIMNET can improve the dependability to failures of links and/or APs by allocating APs redundantly in the network field. Because redundant APs may increase the operational cost and degrade the throughput due to increasing radio interferences, only the necessary APs for the connectivity between the hosts and the Internet gateway should be activated in communications. Previously, we have defined the active AP selection problem of selecting the minimum number of active APs, and proposed its heuristic algorithm. However, the throughput should be maximized in WIMNET as a bandlimited wireless network, even if the number of active APs is slightly increased. In this paper, we propose the extension of the active AP selection algorithm for the throughput maximization using the average hop count. We confirm the effectiveness of our algorithm extension through simulations in three instances, where the throughput is improved by about 10% with 7 − 14 additional active APs on average.

A burr is most commonly created after machining operations, such as drilling. Drilling burrs, for example, are common when drilling almost any material. When burrs are broken during the operation of a machine including the parts with the created burrs, the broken piece is in fear of disturbing normal operation or damaging the parts of the machine, so that the sufficient deburring is requested because it can affect equipment performance, reliability, and durability. Several deburring method have been developed up to date. In the present report, we proposed a deburring method by means of applying underwater shock wave. The method is as follows: after all entrance of holes is closed with seal tape, the equipment is submerged, so that all passages for running fluid are filled with air. The explosive is set under water near the entrance of the main hole. As soon as the explosive is detonated, the underwater shock wave generated at the detonation point arrives at the entrance of the hole and breaks through the tape. The water flows into the hole with a high speed. The burr is broken by water hummer action of high speed. In the present investigation, the experiments of deburring are performed under some setting conditions of explosive. It is found by experimental results, that the burr is sufficiently removed with the newly proposed method. When the shock pressure is sufficiently high at the entrance of hole, the burr is broken surface is smooth as polished one. When the shock pressure is not sufficiently high, the broken surface of the burr is notched.