We describe elements of a fast integral equation solver for large periodic and partly periodic finite array systems. A key element of the algorithm is utilization (in a rigorous way) of a block-Toeplitz structure of the impedance matrix in conjunction with either conventional Method of Moments (MoM), Fast Multipole Method (FMM), or Fast Fourier Transform (FFT)-based Adaptive Integral Method (AIM) compression techniques. We refer to the resulting algorithms as the (block-)Toeplitz-MoM, (block-)Toeplitz-AIM, or (block-)Toeplitz-FMM algorithms. While the computational complexity of the Toeplitz-AIM and Toeplitz-FMM algorithms is comparable to that of their non-Toeplitz counterparts, they offer a very significant (about two orders of magnitude for problems of the order of five million unknowns) storage reduction. In particular, our comparisons demonstrate, that the Toeplitz-AIM algorithm offers significant advantages in problems of practical interest involving arrays with complex antenna elements. This result follows from the more favorable scaling of the Toeplitz-AIM algorithm for arrays characterized by large number of unknowns in a single array element and applicability of the AIM algorithm to problems requiring strongly sub-wavelength resolution.

Active replication is a common approach to building highly available and reliable distributed software applications. The redundant nested invocation (RNI) problem arises when servers in a replicated group issues nested invocations to other server groups in response to a client invocation. Automatic suppression of RNI is always a desirable solution, yet it is usually a difficult design issue. If the system has multithreading support, the difficulties of implementation increase dramatically. Intuitively, to design a deterministic thread execution control mechanism is a possible approach. Unfortunately, some modern operating systems implement thread on kernel level for execution fairness. For the kernel thread case, modification on thread control implies modifying the operating system kernel. This approach loses system portability which is one of the important requirements of CORBA or middleware. In this work, we propose a mechanism to perform the auto-suppression of redundant nested invocation in an active replication fault-tolerant (FT) CORBA system. Besides the mechanism design, we discuss the design correctness semantic and the correctness proof of our design.

By using distributed database systems, many advantages can be obtained such as database management cost, efficiency, and high integrity of systems through allocating fragments to many distributed sites with horizontal/vertical fragmentation of global database schema. To minimize costs, distributed algorithms must be applied so that database fragments are allocated to optimal sites. It is useful to replicate fragments, such as allocating many copies in many sites including load balancing. But there are too many possible combinations of each site and fragment, making it impossible to find a solution in real time, i.e., it is an NP-complete problem. This paper proposes near optimal heuristic algorithms for minimizing cost by defining a cost model based on read and update queries that are requested in many sites. Various factors are applied to the proposed algorithms for sizing efficient network resources that compute database transactions as remote query or update requests for consistency in replicated database systems. For network load balancing, incoming network traffic table is defined in each site. A request transaction from unallocated sites to allocated sites can be accessed properly at any other replicated sites by using the network traffic table. Finally, some experimental results verified the proposed algorithms by comparing actual cases of database allocation.

In CC-NUMA multiprocessor systems, it is important to reduce the remote memory access time. Based upon the fact that increasing the size of the LRU second-level (L2) cache more than a certain value does not reduce the cache miss rate significantly, in this paper, we propose two split L2 caches to utilize the surplus of the L2 cache. The split L2 caches are composed of a traditional LRU cache and another cache to reduce the remote memory access time. Both work together to reduce total L2 cache miss time by keeping remote (or long-distance) blocks as well as recently used blocks. For another cache, we propose two alternatives: an L2-RVC (Level 2 - Remote Victim Cache) and an L2-DAVC (Level 2 - Distance-Aware Victim Cache). The proposed split L2 caches reduce total execution time by up to 27%. It is also found that the proposed split L2 caches outperform the traditional single LRU cache of double size.

Data Replication can be used to improve the system availability of distributed systems. In such a system, a mechanism is required to maintain the consistency of the replicated data. The grid structure technique based on quorum is one of the solutions to perform this while providing a high availability of the system. It was shown in the study that, it still requires a bigger number of copies be made available to construct a quorum. So it is not suitable for large systems. In this paper, we propose a technique called the neighbor replication on grid (NRG) technique by considering only neighbors to have the replicated data. In comparison to the grid structure technique, NRG requires a lower communication cost for an operation, while providing a higher system availability, which is preferred for large systems.

In recent years, not only functionality but also usability have come to be required in software. In order to develop a highly usable GUI (Graphical User Interface) application, it is effective that end users evaluate their GUI and the results of the evaluation are reflected on the original GUI. In these cases, it is necessary to replace a widget with another widget, and to reconnect the new GUI part with the original body part. When widgets are replaced, the operations are usually changed, but the roles of the GUI are seldom changed. In this research, we propose a development method for GUI applications with easy operations and also a method of automatic reconnection between GUI parts and new body parts. This reconnection is realized by classifying widgets according to their roles and by replacing methods of widgets with abstract methods categorized by common roles.

Speech quality of VoIP (Voice over Internet Protocol) may potentially be degraded by transmission errors such as packet loss and delay which are basically inevitable in best-effort communications. This study investigates an error concealment technique for such degradation by using a receiver-based technique called pitch waveform replication. For enhancing the conventional technique, this study proposes a waveform reconstruction technique that also takes account of the pitch variation between the backward and forward frames of gap frames. From experimental results of objective evaluation, it is indicated that the proposed technique may potentially be useful for improving the speech quality, compared with the conventional technique.

The deployment of server replicas of a service across an asynchronous distributed system (e.g., Internet) is a real practical challenge. This target cannot be indeed achieved by classical software replication techniques (e.g., passive and active replication) as these techniques usually rely on group communication toolkits that require server replicas to run over a partially synchronous distributed system to solve the underlying agreement problem. This paper proposes a three-tier architecture for software replication that encapsulates the need of partial synchrony in a specific software component of a mid-tier to free replicas and clients from the need of underlying partial synchrony assumptions. Then we propose how to specialize the mid-tier in order to manage active replication of server replicas.

Fault-tolerant execution of a mobile agent is an important design issue to build a reliable mobile agent system. Several fault-tolerant schemes for a single agent system have been proposed, however, there has been little research result on the multi-agent system. For the cooperating mobile agents, fault-tolerant schemes should consider the inter-agent dependency as well as the mobility; and try to localize the effect of a failure. In this paper, we investigate properties of inter-agent dependency and agent mobility; and then characterize rollback propagation caused by the dependency and the mobility. We then suggest some schemes to localize rollback propagation.

It is expected that per-user customized services are widely used in next generation Personal Communication Network. To provide personalized services for each call, per-user service profiles are frequently referenced, so efficient service profile management is essentially required. To provide service profile based services, typically two schemes can be employed: One is Intelligent Network based Central scheme and the other is IMT-2000 based full replication scheme, we refer to as Follow-Me Replication Unconditional (FMRU). Since the Central scheme only depends on the service call rate and the FMRU is merely dependent on the movement rate, it is apparent that the FMRU scheme outperforms the Central scheme if the call-to-mobility ratio (CMR) is large, and vice versa. In this paper, we propose a new service profile replication schemes, Adaptive Follow-Me Replication Conditional (AFMRC) that determine replication automatically according to the user's varying CMR in real-time. We compared the performance of the AFMRC with the previous non-adaptive Follow-Me Replication Conditional (FMRC) scheme. Performance results indicate that as the CMR of a user changes, AFMRC adapts well compared to the existing schemes.

Speech quality of VoIP (Voice over Internet Protocol) may potentially be degraded by transmission errors such as packet loss and delay that are basically inevitable in best-effort communications. This study newly proposes an error concealment technique for such degradation by taking account of both sender-based and receiver-based techniques. In the proposed technique, sender-based side information, which is required by the receiver-based technique, is transmitted by using steganography, so that its datagram is completely compatible with the conventional format of VoIP. From experimental results of objective evaluation, it is indicated that the proposed technique may potentially be useful for improvement of speech quality, compared with the conventional technique.

The technique of replica placement has been extensively employed to improve client perceived performance and disperse server workload. In this paper, we study some well-known algorithms of replica placement on the network and observe the logarithmic relationship between replica number and total access cost. Numerous simulations are done and it is found that some replica algorithms obey the logarithmic relationship with high correlation coefficients. A logrithmic function is proposed about replica number and total access cost. The logarithmic relationship is applied to the minimum facility problem and a function is deduced to get the optimal replica number.

Multicast communications have been expected as an effective way to disseminate information to potentially large number of receivers. IP multicast is a well- known multicast protocol for the Internet. However, IP multicast has several technical problems to be resolved until it is widely deployed in the Internet. These includes service-model of multicast group, reliable transport protocol, congestion control and security. A lot of researches trying to resolve these technical problems make multicast communications a hot research area in these couple of decades. This paper overviews the present style of IP multicast and clearlify technical issues of the present multicast communications. The paper also surveys important approaches to these problems and discuss about future directions of multicast communications.

Recently, Hwang and Yeh demonstrated that Peyravian-Zunic's password authentication scheme is vulnerable to several attacks, and then proposed a modified version. In this letter, we show that Hwang-Yeh's scheme still has several weaknesses and drawbacks.

Buffer caching is an integral part of the operating system. In this paper, we propose a scheme that integrates buffer cache management and prefetching via cache partitioning. The scheme, which we call SA-W2R, is simple to implement, making it a feasible solution in real systems. In its basic form, for buffer replacement, it uses the LRU policy. However, its modular design allows for any replacement policy to be incorporated into the scheme. For prefetching, it uses the LRU-One Block Lookahead (LRU-OBL) approach, eliminating any extra burden that is generally necessary in other prefetching approaches. Implementation studies based on the GNU/Linux kernel version 2.2.14 show that the SA-W2R performs better than the scheme currently used, with a maximum increases of 23% for the workloads considered.

Recently, Lin et al. addressed two weaknesses of a new strong-password authentication scheme, the SAS protocol, and then proposed an improved one called the OSPA (Optimal Strong-Password Authentication) protocol. However, we find that both the OSPA protocol and the SAS protocol are vulnerable to the stolen-verifier attack.

Using the great one-time password concept, the widely utilized one-way authentication scheme S/Key provides well protection against replay attacks. In this paper, S/key is enhanced to secure transactions in a critical environment. The proposed scheme is free from any of server spoofing attacks, preplay attacks, and off-line dictionary attacks. A session key here is also established to provide confidentiality. Moreover, simplicity and efficiency are taken into consideration from the user's point of view. A smart card is applied to simplify the user login process and only the hash function is used to keep its efficiency. Therefore, the scheme proposed hereinafter is able to build a safer shield for sensitive transactions like on-line banking or on-line trading in bonds and securities.

A quasi-periodic signal is a periodic signal with period and amplitude variations. Several physiological signals, including the electrocardiogram (ECG), can be treated as quasi-periodic. Vector quantization (VQ) is a valuable and universal tool for signal compression. However, compressing quasi-periodic signals using VQ presents several problems. First, a pre-trained codebook has little adaptation to signal variations, resulting in no quality control of reconstructed signals. Secondly, the periodicity of the signal causes data redundancy in the codebook, where many codevectors are highly correlated. These two problems are solved by the proposed codebook replenishment VQ (CRVQ) scheme based on a bar-shaped (BS) codebook structure. In the CRVQ, codevectors can be updated online according to signal variations, and the quality of reconstructed signals can be specified. With the BS codebook structure, the codebook redundancy is reduced significantly and great codebook storage space is saved; moreover variable-dimension (VD) codevectors can be used to minimize the coding bit rate subject to a distortion constraint. The theoretic rationale and implementation scheme of the VD-CRVQ is given. The ECG data from the MIT/BIH arrhythmic database are tested, and the result is substantially better than that of using other VQ compression methods.

We developed a method for analysis of boron penetration and gate depletion using N+ and P+ dual-gate PMOSFETs. An N+ gate PMOSFETs, which is immune to boron penetration and gate depletion, exhibited the threshold voltage shifts and fluctuation in P+ gate PMOSFETs fabricated using identical N- substrates. We showed the importance of Vth fluctuation analysis and found that the Vth fluctuation in N+ gate PMOSFETs was negligible, but, the Vth fluctuation in P+ gate PMOSFETs was significant, indicating that the Vth fluctuation in P+ gate PMOSFETs was dominated by boron penetration. It was also shown, for the first time, that boron penetration occurred with gate depletion, and gate depletion must be very strong to suppress boron penetration. The dual-gate PMOSFET method makes it possible to select high-performance G-bit DRAM fabrication processes that are robust against Vth fluctuation.

Partially depleted SOI technology with body-tied hybrid trench isolation was developed in order to counteract floating body effects which offers negative impact on the drive current of transistors and the stability of circuit operation while maintaining SOI's specific merits such as high speed operation and low power consumption. The feasibility of this technology and its superior soft error effects were demonstrated by a fully functional 4M-bit SRAM. Its radio frequency characteristics were also evaluated and it was verified that high-performance transistors and passive elements can be realized by the combination of the SOI structure and a high-resistivity substrate. Moreover, its application to a 2.5 GHz digital IC for optical communication was also demonstrated. Thus it was proven that the body-tied SOI devices with the hybrid trench isolation is suitable to realize intelligent and reliable high-speed system-on-a chip integrating various IP's.