A rigorous modal approach based on the transmission-line description has developed to explore effectively the filtering characteristics of planar optical DFB guiding structures. Using the modal transmission-line theory, the leakage and filtering characteristics of metal-strip gratings and dielectric gratings with gain or loss are first evaluated in details at the first- and third-order Bragg regimes. It can thus serve as a powerful template for computational algorithms to determine systematically and rigorously the optical effects of multilayered periodic guiding structures, which are not readily obtained by other methods.

There are two distinct types of maintenance action, namely preventive one and corrective one. Preventive maintenance is performed at regular intervals and can contribute significantly towards the increase of reliability and availability. It must be scheduled carefully in order that the availability is maximized through optimizing regular interval. On the other hand, corrective maintenance is performed when the system fails, and so the occurrence of corrective maintenance action is a random variable that cannot be predicted beforehand. From these considerations, it is clear that time is the most important factor in maintainability, and therefore, we classify maintenance data into two groups, that is, scheduled maintenance data and unscheduled maintenance one. Next, based on these classified data, we propose the new availability model which modifies Policy II proposed by R. Barlow and L. Hunter. Finally, we show the usefulness of the new model proposed here by applying these theoretical results to real data of some power plant.

The SDP (Sum of Disjoint Products) approach is a well-known technique for computing network reliability measures. So far several algorithms have been developed based on this approach. In this letter, we present a general framework for parallelization of these SDP algorithms. Based on the framework, we implemented a parallel version of an SDP algorithm called CAREL on a network of workstations. Experimental results show that it works fairly well with almost linear speedups.

In this paper, we construct a software availability model considering the number of restoration actions. We correlate the failure and restoration characteristics of the software system with the cumulative number of corrected faults. Furthermore, we consider an imperfect debugging environment where the detected faults are not always corrected and removed from the system. The time-dependent behavior of the system alternating between up and down states is described by a Markov process. From this model, we can derive quantitative measures for software availability assessment considering the number of restoration actions. Finally, we show numerical examples of software availability analysis.

Migration transparency is considered in the context of multi-agent systems. A mobile agent architecture is proposed with an Availability service and a Transparency interface. We define mobility as explicit (or proactive) when the agent decides when and where to move and define mobility as implicit (i. e. , transparent or reactive) when it is a consequence of changes in the environment. Implicit mobility of agents is explored in addition to the usual explicit mobility. The search for a target agent (or agency) follows a transparent location and selection. The client agent preferably moves towards the target agent. If not possible, the target agent will move towards the client agent when calling back. If both agents can not move then the execution takes place remotely or is abandoned. Transparency is goal oriented.

Recently, because of the expansion of TCP/IP networks, the evaluation of IP networks is being considered as a major task for network operators and administrators. As a result, many IP evaluation tools have appeared, but almost all of them can only be applied to a limited purpose. The authors have already developed an IP evaluation tool, called KITS (KDD Internet Test System) that can generate flexible load traffic. Based on KITS, the authors have now developed a new IP measurement tool. This paper describes the flexible and general IP evaluation tool, STAGE (Simulated Traffic Analyzer/generator for General Evaluation).

This paper proposes a novel cache architecture suitable for merged DRAM/logic LSIs, which is called "dynamically variable line-size cache (D-VLS cache). " The D-VLS cache can optimize its line-size according to the characteristic of programs, and attempts to improve the performance by exploiting the high on-chip memory bandwidth on merged DRAM/logic LSIs appropriately. In our evaluation, it is observed that an average memory-access time improvement achieved by a direct-mapped D-VLS cache is about 20% compared to a conventional direct-mapped cache with fixed 32-byte lines. This performance improvement is better than that of a doubled-size conventional direct-mapped cache.

For cluster systems consisting of multiple processing nodes and shared servers which consist of an on-line and a backup shared server, we propose a hot-standby scheme for shared servers. In this scheme for shared servers, when the on-line shared server receives a command from a node, it sends only an update command and its data identifier to the backup shared server. Both the on-line and the backup shared server execute the update command independently, and the command result of the on-line shared server is identical to that of the backup shared server. When the on-line shared server fails, the backup reconstructs the shared data by using its own shared data and the user data from each node. We evaluated the system recovery time and the performance overhead for this hot-standby scheme. It enables the performance overhead to be ignored, and the system recovery time to be shortened to 20 seconds in cluster systems.

The purpose of this note is to carry out study on a 3-out-of-4:G warm standby system with nonidentical components. By using Markov model, the general form solution of stationary availability of the system is obtained. Examples are given to illustrate the solutions of transient and stationary availability of such system.

This paper considers two simulation models for simple unreliable file systems with checkpointing and rollback recovery. In Model 1, the checkpoint is generated at a pre-specified time and the information on the main memory since the last checkpoint is back-uped in a secondary medium. On the other hand, in Model 2, the checkpointing is executed at the time when the number of transactions completed for processing is achieved at a pre-determined level. However, it is difficult to treat such models analytically without employing any approximation method, if queueing effects related with arrival and processing of transactions can not be ignored. We apply the generalized stochastic Petri net (GSPN) to represent the stochastic behaviour of systems under two checkpointing schemes. Throughout GSPN simulation, we evaluate quantitatively the maintainability of checkpoint models under consideration and examine the dependence of model parameters in the optimal checkpoint policies and their associated system availabilities.

Efficient content-based retrieval of complex images is a challenging task since the detected object may appear in various scale, rotation and orientation with a wide variety of background colors and forms. In this paper, we propose a novel representation of objects with multiple colors, the spatial neighborhood-adjacency graph(SNAG), which can serve as a basis for detecting object by color contents from the candidate image. The SNAG consists of a set of main-vertices and two sets of edges. Each main-vertex represents a single color region of multi-colored object, and edges are divided into two classes: Neighborhood edges representing neighborhood relationship between two main-vertices with similar color, and adjacency edges representing adjacency relationship between a main-vertex and another vertex with different color. By investigating whether SNAG of object image is an isomorphic subgraph of SNAG of a candidate image, we can determine whether the similar object exists in the candidate image. In addition, we have also applied the proposed approach to a range of different object detection problems involving complex background, and effectiveness has been proved.

It is generally known that the autonomic nervous system regulates the pupil. In this study, we attempted to assess mental workload on the basis of the fluctuation rhythm in the pupil area. Controlling the respiration interval, we measured the pupil area during mental tasking for one minute. We simultaneously measured the respiration curve to monitor the respiration interval. We required the subject to perform two mental tasks. One was a mathematical division task, the difficulty of which was set to two, three, four, and five dividends. The other was a Sternberg memory search task, which had four work levels defined by the number of memory sets. In the Sternberg memory search, the number of memory set changed from five to eight. In such a way, we changed the mental workload induced by mental loading. As a result of calculating an autoregressive (AR) power spectrum, we could observe two peaks which corresponded to the blood pressure variation and respiratory sinus arrhythmia under a low workload. With an increased workload, the spectral peak related to the respiratory sinus arrhythmia disappeared. The ratio of the power at the low frequency band, from 0.05-0.15Hz, to the power at the respiration frequency band, from 0.35-0.4Hz, increased with the work level. In conclusion, the fluctuation of the pupil area is a promising means for the evaluation of mental workload or autonomic nervous function.

Mathematical proof for the equivalent edge currents for physical optics (POEECs) is given for plane wave incidence and the observer in far zone; the perfect accuracy of POEECs for plane wave incidence as well as the degradation for the dipole source closer to the scatterer is clearly explained for the first time. POEECs for perfectly conducting plates are extended to those for impedance plates.

This paper proposes and evaluates a character or symbol code system called EPICS for multilingual information processing. EPICS integrates a variable-length coding system using 16-bit units and a smart virtual machine. EPICS enhances the interchangeability of data. The variable-length coding system provides a huge code space. This huge space can include not only standardized code sets but also non-standardized codes of ancient symbols and user-specific symbols. The smart virtual machine executes inputs as instructions and is dynamically customizable. It allows us to define and modify instructions during runtime and provides us with customization facilities. Customization facilities can be used to specify a sorting order and normalization. Customization also makes it possible for an information producer (sender) to express his intentions or annotations in data and for an information consumer (receiver) to process the data depending on his needs. Moreover, customization enables one to send compressed data and decompression program fragments incrementally and efficiently without predefined decompression algorithms.

This work presents a scalable and high performance prediction protocol for optical networks. In the proposed protocol, we develop a mathematical model to maintain the stability of a network system by prediction based on the traffic temporal locality property. All the critical factors, including transceiver tuning time, propagation delay, and processing time for dealing with control packets, are considered in the proposed prediction protocol. Furthermore, our protocol can resolve the bottlenecks attributed to control signaling and electronics processing. The performance evaluation reveals that the proposed scheme can yield the higher bandwidth efficiency and incur a lower packet delay than those of the TDM and conventional reservation schemes. Also, the proposed protocol can flexibly support any scaled network system such as MANs or LANs.

The problem we consider in this paper is whether the Menezes-Okamoto-Vanstone (MOV) reduction for attacking elliptic curve cryptosystems can be realized for genera elliptic curves. In realizing the MOV reduction, the base field Fq is extended so that the reduction to the discrete logarithm problem in a finite field is possible. Recent results by Balasubramanian and Koblitz suggest that, if l q-1, such a minimum extension degree is the minimum k such that l|qk-1, which is equivalent to the condition under which the Frey-Ruck (FR) reduction can be applied, where l is the order of the group in the elliptic curve discrete logarithm problem. Our point is that the problem of finding an l-torsion point required in evaluating the Weil pairing should be considered as well from an algorithmic point of view. In this paper, we actually propose a method which leads to a solution of the problem. In addition, our contribution allows us to draw the conclusion that the MOV reduction is indeed as powerful as the FR reduction under l q-1 not only from the viewpoint of the minimum extension degrees but also from that of the effectiveness of algorithms.

We present an architecture of a VOD system employing proxy servers. The proposed VOD system provides efficient and reliable VOD services and solves the problems caused by traditional VOD systems of centralized, hierarchical or distributed architecture. The proxy servers are placed between video servers and user systems. The proxy server is a small size video server that has not only caching function but also intelligence such as VCR-like video stream control or navigation of other proxy/video servers to search for a selected video program. Using a VOD system of the proposed architecture, the VOD services can be provided to more users because it reduces the workload of video servers and network traffic. We provide the performance model of the system. Service availability is also analyzed. The proposed architecture shows better performance and availability than the traditional VOD architectures.

This paper describes the architecture to implement an application in network environments, which adapts to unexpected change in the development phase. In this architecture, an application is expressed as an agent which consists of two layers: base level and meta level. The base level program is an application program and the meta level program is the program that controls the execution of the base level and changes the base level program. Virtual places are also provided in the network. They are used for the release of programs and information which agents retrieve to change their own base level program. An application (or an agent), when a change is required, moves from places to places for the retrieval of programs to adapt to the change. A program search strategy is introduced to adapt to changes by using distributed thesauri of released programs, which realizes an agent's program retrieval method in network environments.

The epitaxial lateral overgrowth (ELO) of GaN with a stripe tungsten (W) mask pattern is performed by hydride vapor phase epitaxy (HVPE) and the crystalline and optical properties are investigated compared with ELO GaN using SiO2 mask by characterizations of X-ray rocking curve (XRC), transmission electron microscopy (TEM) and low temperature cathodoluminescence (CL). A buried ELO structure of the W mask with a smooth surface is successfully obtained. The tilt of c-axis on the W mask in the ELO GaN is not observed, but in the case of the SiO2 mask, c-axis tilts on the mask region at 1 to 10 together with small angle grain boundaries. Half the way from the ELO interface to the surface, the luminescence becomes excitonic over the whole lateral extension region, which indicates the optically high crystalline quality of the material. On the other hand, different kinds of luminescence are observed depending on the position. The difference of these luminescence is caused by the defects and/or impurity incorporation on the mask region due to the tilting of c-axis.

PID control schemes have been widely used in most of process control systems. Most of these processes are often treated as first-order systems with dead times. And also, in many cases, PID parameters are usually tuned based on the process parameters, i. e. , the time constant, the dead time and the process gain. However, since these process parameters can not be obtained exactly, it is well known that it is difficult to find the suitable PID parameters in practice. In this paper, we propose a genetic tuning scheme of PID parameters for first-order systems with large dead times. The authors have already proposed a tuning method of PID parameters using a genetic algorithm (GA), which was based on the relationship between PID control and generalized minimum variance control(GMVC) laws. In practice, for large dead time systems, first-order low pass pre-filters are often used. The proposed method is an extended version of the previously proposed method mentioned above to the system with a pre-filter due to the large dead time, i. e. , a tuning method of both PID parameters and the pre-filter using a GA. The proposed control scheme is numerically evaluated on some simulation examples.