Wireless sensor networks represent a new data collection paradigm in which expandability plays an important role. In a practical monitoring environment, for example, food factory monitoring system, sensor relocations and reorganizations are necessary with reorganization of production lines and starting of new production lines. These relocations sometime make congestion in some area of the network. In this dynamic changing environment online expansion is a challenging problem for resource constraint network. This paper proposes a two-tier autonomous decentralized community architecture for wireless sensor network to solve the problem. The first layer consists of sensors and second layer consists of routers. In the architecture routers make community (a group of nodes mutually cooperate for a common goal is a community). The goal of this paper is to introduce the concept of sharing information among routers of the community to decrease sensor connection time for the network especially for the dynamic changing environment. Results show that our proposed technologies can reduce sensor connection time to achieve online expansion.

We have investigated the bottleneck in web-based MORPG system and proposed a load-distribution method using multiple web servers. This technique uses a dynamic data allocation method, called the moving home. This paper describes the evaluation of our method using 4, 8, 16 web servers. We evaluated it on both the single-server system and multi-server system. And we confirm that the effect of the moving home through the comparison between the multi-server system without the moving home and that with the moving home. Our experimental result shows that the upper bound of the number of avatars in the eight-server system with the moving home becomes 380 by contrast that in the single-server system is 200.

Wireless Sensor and Actor Networks (WSAN) are commonly used to monitor physical parameters and execute opportune actions in response to specific events. In order to achieve this goal it is necessary to implement efficient coordination and cooperation among the network nodes (i.e. sensors and actors) with the aim of reducing the energy consumption and improving the response time of the system. This work propose a clustering mechanism that organizes the sensor nodes to form clusters where the mobile actors nodes in the WSAN perform the cluster head role. The proposal considers the mobility aspect of the actor nodes and implements a mechanism to dynamically change the geographical location of the actors while trying to reduce the load in terms of the number of sensors within each cluster, all this with the aim of extending the network lifetime.

This paper presents the forcible resonant characteristics of a cutoff cavity-backed slot radiator. It has a feed post and a parasitic post inserted parallel to the slot width, done by adding a single external reactance to the top or the bottom side of the parasitic post. The basic radiator characteristics for a perfect matching to a 50-Ω coaxial line due to the connecting position of the external reactance are discussed. Comparisons show that the bandwidth of the top side loading is narrower than the bottom side loading case. The theoretical analysis is verified by the measured return loss.

Internet computing is proposed to exploit personal computing resources across the Internet in order to build large-scale Web applications at lower cost. In this paper, a DHT-based distributed Web crawling model based on the concept of Internet computing is proposed. Also, we propose two optimizations to reduce the download time and waiting time of the Web crawling tasks in order to increase the system's throughput and update rate. Based on our contributor-friendly download scheme, the improvement on the download time is achieved by shortening the crawler-crawlee RTTs. In order to accurately estimate the RTTs, a network coordinate system is combined with the underlying DHT. The improvement on the waiting time is achieved by redirecting the incoming crawling tasks to light-loaded crawlers in order to keep the queue on each crawler equally sized. We also propose a simple Web site partition method to split a large Web site into smaller pieces in order to reduce the task granularity. All the methods proposed are evaluated through real Internet tests and simulations showing satisfactory results.

The aim of this research is to study the power energy cost reduction of the mobile telecom industry through the supervisor control and data acquisition (SCADA) system application during globalization and liberalization competition. Yet this management system can be proposed functions: operating monitors, the analysis on load characteristics and dropping the cost of management.

The phenomena of retrograde motion of arc in the atmosphere under transverse magnetic field were studied. AgSnO2 contacts were set in DC resistive and inductive circuits, respectively. The break voltage was 28 V, the current ranged from 1 to 5 A, and the magnetic flux density changed from 0 to 100 mT. A high speed camera and an oscilloscope were used to record time variations of arc images, voltages and currents, simultaneously. Different from previous experiment results, the arc motion showed three stages which was more obvious under larger magnetic flux density in inductive circuit. It was also found that the arc movement was closely related with the arc voltage. Explanation to the retrograde motion under such conditions was given.

We present a session initiation protocol (SIP) network design for a voice-over-IP network to prevent congestion caused by people calling friends and family after a disaster. The design increases the capacity of SIP servers in a network by using all of the SIP servers equally. It takes advantage of the fact that equipment for voice data packets is different from equipment for signaling packets in SIP networks. Furthermore, the design achieves simple routing on the basis of telephone numbers. We evaluated the performance of our design in preventing congestion through simulation. We showed that the proposed design has roughly 20 times more capacity, which is 57 times the normal load, than the conventional design if a disaster were to occur in Niigata Prefecture struck by the Chuetsu earthquake in 2004.

The purpose of this paper is to propose an efficient and effective design scheme to implement compact, high-performance wideband bandpass filters based on a novel compound three-line unit consisting of a stub-loaded short-circuited parallel-coupled three-line structure and two lead lines. Firstly, a simulative investigation is conducted on the transmission characteristics of the proposed coupling unit. The results show that the bandwidth of such structure can be predicted by a symmetric parallel-coupled short-circuited three-line unit, whereas the transmission zeros by a three-section stub composed of the loaded stub, one of the parallel-coupled three lines and the lead line. Accordingly, given specifications, a pseudo-elliptical filter can be designed in an novel three-coupled-line based two-step design scheme: 1. after the derivation of the new closed-form synthesis formulae, a Chebyshev ultra-wideband (UWB) filter is synthesized on a desired passband using symmetric three-line coupling units. 2. By designing the stubs and choosing the proper lengths of the lead lines, multiple transmission zeros are then introduced to improve the skirt and stopband characteristics, whereas the equiripple characteristics are kept in passband. As an example, a UWB bandpass filter covering the Japan's lower UWB band (BW: 3.1-4.8 GHz, FBW: 43%) is designed to describe the proposed design procedure. The measured filtering characteristics agree very well with the theoretical predictions, which validate the effectiveness of the proposed new coupling structure and corresponding filter design technique. In addition, the designed filters exhibit good characteristics, such as steep skirt selectivity, very wide stopbands, a compact size compared with the filter based on short-circuited three-line structure, etc.

Spin-torque transfer magnetic random access memory (STT-MRAM) is a promising technology for next generation nonvolatile universal memory because it reduces the high write current required by conventional MRAM and enables write current scaling as technology becomes smaller in size. However, the sensing margin is not improved in STT-MRAM and tends to decrease with technology scaling due to the lowered supply voltage and increased process variation. Moreover, read disturbance, which is an unwanted write in a read operation, can occur in STT-MRAM because its read and write operations use the same path. To overcome these problems, we present a load-line analysis method, which is useful for systematically analyzing the impacts of transistor size and gate voltage of MOSFETs on the sensing margin, and also propose an optimization procedure for the commonly applicable MRAM sensing circuits. This methodology constitutes an effective means to optimize the transistor size and gate voltage of MOSFETs and thus maximizes the sensing margin without causing read disturbance.

We propose a call admission control scheme in cellular and wireless local area networks (WLANs) integration: integrated service-based admission control with load-balancing capability (ISACL). The novel aspects of the ISACL scheme include that load transfer in the cellular/WLAN overlapping areas is allowed for the admission of originating data calls from the area with cellular access only and vertical handoff requests to the cellular network. Packet-level quality of service (QoS) constraints in the WLANs and other-cell interference in the code division multiple access (CDMA) cellular network are taken into account to derive the WLANs and cellular capacity. We model the integrated networks using a multi-dimensional Markov chain and the important performance measures are derived for effective optimization of the admission parameters. The analytical model is validated by a computer simulation. The variation of admission parameters with traffic load and the dependence of resource utilization on admission parameters are investigated. It is shown that optimal balancing of the traffic load between the cellular network and WLANs results in the maximum resource utilization. Numerical results demonstrate that substantial performance improvements can be achieved by applying the proposed ISACL scheme.

In this paper, we propose a file replication method to achieve load balancing in terms of write access to storage device ("write storage access load balancing" for short) in unstructured peer-to-peer (P2P) file-sharing networks in which the popularity trend of queried files varies dynamically. The proposed method uses a write storage access ratio as a load balance index value in order to stabilize dynamic P2P file-sharing environments adaptively. In the proposed method, each peer autonomously controls the file replication ratio, which is defined as a probability to create the replica of the file in order to uniform write storage access loads in the similar way to thermal diffusion phenomena. Theoretical analysis results show that the behavior of the proposed method actually has an analogy to a thermal diffusion equation. In addition, simulation results reveal that the proposed method has an ability to realize write storage access load balancing in the dynamic P2P file-sharing environments.

ISO/IEC 18000-7 Active RFID standard, a single channel system operating at 433 MHz, faces technical difficulties in supporting some recently introduced application demands because of its low transmission rates and vulnerability to radio interference between the readers. We propose a new multi-channel active RFID system operating at the 2.4 GHz band. The special feature of the proposed system is that a reader makes use of multiple interfaces to improve its performance. However, if only a small part of the interfaces is actually used, the performance improvement would not meet expectations. To overcome this problem, a multi-channel multi-interface active RFID protocol that balances the loads among all available interfaces is necessary. Three protocols, "Aggregated," "LP-Combined" and "AP-Balanced" are proposed in this paper. We carry out simulations to compare them under various conditions by changing numbers of tags, numbers of interfaces and tag data size. The AP-Balanced shows the best and the most stable performance and its performance increases almost linearly in proportion to the number of interfaces, which meets our expectation.

Output voltage regulation problem of DC-DC boost power converters is studied based on an averaged model with a practical inductor. This paper exploits the effect of inductor's parasitic resistance on the performance of an existing parallel-damped (PD) passivity-based controller (PBC) under load variations. As an attempt to apply the passivity-based framework to the converter with parasitic resistance we have combined a new proportional-integral (PI) controller with the PBC. Simulation results show that the combined (PBC and PI) dynamic output feedback controller successfully achieves the performance improvement under reference step changes and load variations.

The establishment of inter-domain traffic engineered paths is a requisite to accomplishing an end-to-end bandwidth guarantee and end-to-end resource optimization. Though the inter-domain paths must be reliable, it is difficult to compute suitable backup inter-domain paths in advance when the traffic engineering information is not disclosed outside of each domain. This means that the inter-domain path computation must satisfy the severe requirement of path establishment delay, since all inter-domain paths traversing the links in failure need to be computed after the failure occurs. Though several inter-domain path computation schemes have been proposed, their relative characteristics remain unknown. First, this paper classifies the conventional inter-domain path computation schemes into two types, i.e. end-to-end and per-domain schemes, and compares their performances under various traffic loads. Based on results of the comparisons, this paper proposes an adaptive inter-domain path computation scheme that can satisfy the severe requirement of the path establishment delay. In this scheme, the domain sequence from the source node to the destination node is divided into multiple sub-domain sequences according to the traffic load in each domain. The end-to-end path computation scheme is applied to the sub-domain sequences under heavy traffic loads, while the per-domain path computation scheme is applied to those under normal traffic loads. The simulation results show that the proposed scheme can adaptively satisfy the requirement for the path establishment delay while it maintains the optimality of path computation, even if the traffic load applied to each domain changes.

Electrical contacts are an important part of electrical circuits and many reliability problems are related to electrical contact failure. It is important to investigate the relationship between load and contact resistance which is an important factor of contact reliability. In this study, the effect of plated material and plated thickness on contact resistance was examined. The samples were constructed of a copper alloy with tin or silver plating. Contact configuration was hemispherical-flat contact. The contact resistance was measured by using a four-probe method with a load up to 40 N. The relation between indentation contact area (i.e. apparent contact area) and contact resistance was determined. As experimental results, the contact resistance depends on the indentation of the contact area. In the same contact area, tin-plated samples have higher resistance than those that are silver-plated due to their own resistivity. The constriction resistance of a plated layer, which depends on contact area, plated material and plated thickness, is analyzed by a theoretical solution, which is shown by R=Φρ /2a, using a surface resistance coefficient Φ . The theoretical results show almost good agreement with the experimental results. Thus, the indentation contact area (i.e. apparent contact area) is almost the same as the real contact area in this study.

P2P (Peer-to-Peer) file sharing architectures have scalable and cost-effective features. Hence, the application of P2P architectures to media streaming is attractive and expected to be an alternative to the current video streaming using IP multicast or content delivery systems because the current systems require expensive network infrastructures and large scale centralized cache storage systems. In this paper, we investigate the P2P progressive download enabling Internet video streaming services. We demonstrated the capability of the P2P progressive download in both laboratory test network as well as in the Internet. Through the experiments, we clarified the contribution of the FTTH links to the P2P progressive download in the heterogeneous access networks consisting of FTTH and ADSL links. We analyzed the cause of some download performance degradation occurred in the experiment and discussed about the effective methods to provide the video streaming service using P2P progressive download in the current heterogeneous networks.

In this letter, we propose a distributed channel assignment where each basestation selects a set of channels shared by multiple users through time domain scheduling for best effort services. The proposed scheme distributedly assigns the channels considering a cochannel interference from neighboring basestations and its own traffic load condition. The computer simulation demonstrates that the proposed scheme appropriately assigns the channels to the basestations taking into account these requirements.

In this paper we propose a file replication scheme inspired by a thermal diffusion phenomenon for storage load balancing in unstructured peer-to-peer (P2P) file sharing networks. The proposed scheme is designed such that the storage utilization ratios of peers will be uniform, in the same way that the temperature in a field becomes uniform in a thermal diffusion phenomenon. The proposed scheme creates replicas of files in peers probabilistically, where the probability is controlled by using parameters that can be used to find the trade-off between storage load balancing and search performance in unstructured P2P file sharing networks. First, we show through theoretical analysis that the statistical behavior of the storage load balancing controlled by the proposed scheme has an analogy with the thermal diffusion phenomenon. We then show through simulation that the proposed scheme not only has superior performance with respect to balancing the storage load among peers (the primary objective of the present proposal) but also allows the performance trade-off to be widely found. Finally, we qualitatively discuss a guideline for setting the parameter values in order to widely find the performance trade-off from the simulation results.

Wireless mesh networks have been attracting many users in recent years. By connecting base stations (mesh nodes) with wireless connections, these network can achieve a wide-area wireless environment with flexible configuration and low cost at the risk of radio interference between wireless links. When we utilize wireless mesh networks as infrastructures for Internet access, all network traffic from mobile nodes goes through a gateway node that is directly connected to the wired network. Therefore, it is necessary to distribute the traffic load by deploying multiple gateway nodes. In this paper, we propose a spanning tree construction algorithm for TDMA-based wireless mesh networks with multiple gateway nodes so as to maximize the traffic volume transferred between the mesh network and the Internet (system throughput) by taking account of the traffic load on the gateway nodes, the access link capacity and radio interference. Through a performance evaluation, we show that the proposed algorithm increases the system throughput regardless of the bottleneck position and achieves up to 3.1 times higher system throughput than a conventional algorithm.