A chaotic neural network consisting of chaotic neurons exhibits such rich dynamical behaviors as nonperiodic associative memory. But it is difficult to distinguish the stored patterns from others, since the chaotic neural network shows chaotic wandering around the stored patterns. In order to apply the nonperiodic associative memory to information search or pattern identification, it is necessary to control chaotic dynamics. In this paper, we propose a delay feedback control method for the chaotic neural network. Computer simulation shows that, by means of the control method, the chaotic dynamics in the chaotic neural network are changed. The output sequence of the controlled network wanders around one stored pattern and its reverse pattern.

In 1987, Ito, Saito and Nishizeki proposed a secret sharing scheme realizing general access structures, called the multiple assignment secret sharing scheme (MASSS). In this paper, we propose new MASSS's which are perfect secret sharing schemes and include Shamir's (k,n)-threshold schemes as a special case. Furthermore, the proposed schemes are more efficient than the original MASSS from the viewpoint of the number of shares distributed to each participant.

In this paper, Message Passing Interface (MPI) techniques are used to implement high-order full 3-D Navier-Stokes equations in multi-domain applications. A two-domain interface with five-point overlapping used previously is expanded to a multi-domain computation. There are normally two approaches for this expansion. One is to break up the domain into two parts through domain decomposition (say, one overlapping), then using MPI directives to further break up each domain into n parts. Another is to break the domain up into 2n parts with (2n-1) overlappings. In our present effort, the latter approach is used and finite-size overlappings are employed to exchange data between adjacent multi-dimensional sub-domains. It is an alternative way to parallelize the high-order full 3-D Navier-Stokes equations into multi-domain applications without adding much complexity. Results with high-order boundary treatments show consistency among multi-domain calculations and single-domain results.

For network computing on desktop machines, fast execution of Java bytecode programs is essential because these machines are expected to run substantial application programs written in Java. We believe higher Java performance can be achieved by exploiting instruction-level parallelism (ILP) in the context of Java JIT compilation. This paper introduces VLaTTe, a Java JIT compiler for VLIW machines that performs efficient scheduling while doing fast register allocation. It is an extended version of our previous JIT compiler for RISC machines called LaTTe whose translation overhead is low (i.e., consistently taking one or two seconds for SPECJVM98 benchmarks) due to its fast register allocation. VLaTTe adds the scheduling capability onto the same framework of register allocation, with a constraint for precise in-order exception handling which guarantees the same Java exception behavior with the original bytecode program. Our experimental results on the SPECJVM98 benchmarks show that VLaTTe achieves a geometric mean of useful IPC 1.7 (2-ALU), 2.1 (4-ALU), and 2.3 (8-ALU), while the scheduling/allocation overhead is 3.6 times longer than LaTTe's on average, which appears to be reasonable.

DualFS is a next-generation journaling file system which has the same consistency guaranties as traditional journaling file systems but better performance. This paper introduces three new enhancements which significantly improve DualFS performance during normal operation, and presents different experimental results which compare DualFS and other traditional file systems, namely, Ext2, Ext3, XFS, JFS, and ReiserFS. The experiments carried out prove, for the first time, that a new file system design based on separation of data and metadata can significantly improve file systems' performance without requiring several storage devices.

In policy-based management, in addition to deliver and enforce policies in managed systems, it is inevitable to manage the policy life-cycle. We mean the policy life-cycle as cyclic iteration of processes involving monitoring to see if the enforced policies actually work at operators' will and their adaptation based on monitoring. Enabling such policy life-cycle management by the current centralized management paradigm such as SNMP may, however, result in poor scalability and reliability. This is typically due to much bandwidth consumption for monitoring and communication failure between a management system and a managed system. It may also impose a heavy burden on the operators in analyzing management information for the policy adaptation. For a solution to that, we propose a scalable and reliable policy-based management scheme enabling the policy life-cycle management based on distributed management paradigm. In the scheme, we provide a new management script describing policies and how their life-cycle should be managed, and execute the script on the managed system with enough computation resources. The scheme can make the current policy-based management more scalable by reducing management traffic, more reliable by distributing management tasks to the managed systems, and more promising by relieving of the operators' burden. We implement a prototype system based on the scheme taking Differentiated Services as a policy enforcement mechanism, and evaluate the scheme from the following viewpoints: 1) the reliability, 2) relievability, and 3) scalability. The first two will be shown with a policy adaptation scenario in an operational network. The last one will be investigated in terms of the management traffic reduction by a management script, the management traffic required for the management of a management script, and the load on a managed system to execute management scripts. As deployment consideration of the proposed scheme besides technical aspects, we also discuss how the prototype system could be integrated with managed systems compliant to the standards emerging in the marketplace.

This paper proposes an efficient query evaluation scheme for a mediator system intended to integrate heterogeneous computing environment in terms of operating systems, database management systems, and other software. Most of mediator systems transform a global query into a set of sub-queries based on their target remote servers. Each sub-query is evaluated by the query modification method to evaluate a global query. However, it is possible to reduce the evaluation cost of a global query when the results of frequently requested sub-queries are materialized in a mediator. In a mediator, its integrating schema can be incrementally modified and the evaluation frequency of a global query can also be continuously varied. In order to select the optimized set of materialized sub-queries with respect to their current evaluation frequencies, the proposed method applies a decay factor for modeling the recent access behavior of each sub-query. In other words, the latest access of a sub-query gets the highest attention in the selection process of materialized sub-queries. As a result, it is possible to adjust the optimized set of materialized sub-queries adaptively according to the recent changes in the evaluation frequencies of sub-queries. Since finding the optimum solution of this problem is NP-hard, it takes too long to be used in practice when the number of sub-queries is large. Consequently, given the size of mediator storage, the rank-based selection algorithm proposed in this paper finds the set of materialized sub-queries which minimizes the total evaluation cost of global queries in linear search complexity.

Many parallel applications involve different independent tasks with their own data. Using the MPMD model, programmers can have a modular view and simplified structure of the parallel programs. Although MPI supports both SPMD and MPMD models for programming, MPI libraries do not provide an efficient way for task communication for the MPMD model. We have developed a programming environment, called ClusterGOP, for building and developing parallel applications. Based on the graph-oriented programming (GOP) model, ClusterGOP provides higher-level abstractions for message-passing parallel programming with the support of software tools for developing and running parallel applications. In this paper, we describe how ClusterGOP supports programming of MPMD parallel applications on top of MPI. We discuss the issues of implementing the MPMD model in ClusterGOP using MPI and evaluate the performance by using example applications.

An all-optical switch based on a single photonic crystal defect with an air-bridge configuration and two-photon absorption was proposed, fabricated and characterized. In optical measurements, we obtained a sharp defect mode with a quality factor higher than 600 at 1.55 µm. More importantly, we observed its nonlinear response to the excitation of ultrashort pulses by utilizing two-photon absorption. Nonliner refractive index change of about -410-3 was achieved at a pumping power density of 3.6109 W/cm2.

The availability of a low cost hardware has increased the development of distributed systems, by making then more and more accessible. In order to optimize the resources allocation on the distributed systems, some load balancing algorithms have been proposed. These algorithms distribute the application loads over the environment computers, make homogeneous the occupation of the whole environment and increase the application performance. This equal distribution prevents certain computers to get overloaded, to the detriment of the idleness of the other ones. This article proposes and analyzes the TLBAGrid, a load balancing algorithm for Grid computing environments.

Timing noise of 160 GHz optical pulses has been evaluated over nine decades of Fourier frequency using the optoelectronic harmonic mixing technique. For down-converting the 160 GHz pulse intensity into a low-frequency IF signal, the fourth order modulation sidebands produced by a Mach-Zehnder intensity modulator have been employed. Phase noise power spectral density and timing jitter for 155.552-GHz optical time-division multiplexed pulses and 160.640-GHz passively mode-locked pulses are measured using the time domain demodulation and time interval analysis techniques, respectively.

All optical regenerations or wavelength conversions using SOA-based polarization discriminated switch injected by an assist light were investigated. First of all, cross gain modulation (XGM) and cross phase modulation (XPM) in a SOA injected by an external assist light were quantitatively analyzed. A simple measurement technique of XGM and XPM was shown to confirm that the injection of assist light could reduce a gain recovery time with some sacrifice for XGM and XPM efficiency. All-optical 3R regeneration using two-stage SOA-based polarization discriminated switch at 40 Gbit/s and its tolerances for some degradation against intensity deviation and optical signal-to-noise ratio (OSNR) were also shown. Finally, regeneration capability was evaluated through a dispersion shifted fiber (DSF)-based re-circulating loop transmission experiment. Those results indicate that the SOA-based polarization discriminated switch is a promising candidate for all-optical regenerator from the practical point of view.

The oscillation characteristics of a 40 GHz, 1-3 ps regeneratively and harmonically mode-locked erbium-doped fiber laser have been investigated in detail with respect to stability, linewidth, and mode hopping. We show that because the Q value of the microwave filter in the feedback loop is limited to around 1000, which is almost the same as that in a 10 GHz laser, the cavity length should not be greatly increased as this would result in as much as a fourfold increase in the number of longitudinal beat signals. We undertook a detailed stability analysis by using three cavity lengths, 60, 80, and 230 m. The 80 m long cavity greatly improved the long-term stability of the laser because the supermode noise was suppressed and there were not too many longitudinal modes. We measured the linewidth of the longitudinal mode of the laser using a heterodyne method, and it was less than 1 kHz. We also point out that there is a longitudinal mode hopping effect with time that is induced by very small changes in temperature.

We consider vector channel estimation for differentially modulated systems with transmit diversity. We propose a blind estimation scheme to yield superior performance to that of the pilot-aided estimation. The proposed scheme utilizes the repeated transmission of space-time coded data symbols. We compare the performance of the proposed blind scheme with the pilot-based estimation scheme via computer simulations.

We demonstrate the wide-band (> 25-nm) long-distance (> 1000-km) chromatic dispersion compensation by midway spectral inversion (MSI) using a periodically-polled LiNbO3 device. In order to achieve a flat zero net dispersion, the fourth order dispersion of the single-mode fibers is canceled by MSI, while the third order dispersion is compensated for by the negative slope dispersion compensation fiber (NS-DCF). The second order dispersion is canceled out by both. The long distance propagation is realized by a double recirculation-loop system. A very flat zero dispersion is measured for the first time for over 1000-km single-mode fiber propagation with MSI dispersion compensation.

We have developed the tunable dispersion compensator based on two twin linearly chirped fiber Bragg gratings with various temperature gradients. Controlling the temperature gradient over one of the twin fiber Bragg gratings by Peltier elements, the dispersion and the dispersion slope were changed independently and continuously. The dispersion and dispersion slope compensator has a large bandwidth of 8 nm and low group-delay ripple of < 4 ps in its chirped fiber Bragg gratings. We experimentally demonstrated a precise controllability of the dispersion and the dispersion slope using linear and parabolic temperature gradient. The dispersion and the dispersion slope changes were achieved continuously with -0.67 ps/nm/ and -0.14 ps/nm2/. The transmission characteristics of the dispersion slope compensation were examined using ultra short pulses in the fiber link. When the total dispersion was zero, the distorted pulse was restored back and the tail was significantly suppressed. 160 Gbit/s signals were also demonstrated over 140 km within 1 dB power penalty by using the dispersion slope compensator.

In this letter we suggest sets of features to classify genres of web documents. Web documents are different from textual documents in that they contain URL and HTML tags within the pages. We introduce the features specific to web documents, which are extracted from URL and HTML tags. Experimental results enable us to evaluate their characteristics and performances. On the basis of the experimental results, we implement a user interface of a web search engine that presents documents grouped by genres.

Over the last twenty years, 3-D audio technologies have advanced significantly despite the difficulties in implementing them. However, their performance in providing information, especially about the distance of a sound source, remains imperfect. Therefore, more researches on distance cues are indispensable to achieve more effective technology. In this paper, we try to show how the conventional cues change as the distance of a sound source varies, by means of measured impulse responses using the swept-sine method and modeled impulse responses using CATT Acoustics. It is well known that the conventional cues comprise loudness, spectral information, reverberation and binaural information. Among these, we focus on the reverberation cue to describe the distance of a sound source. Some researches have shown that reverberation can give listeners absolute distance information, but the implementation using this cue is unfeasible because there are no well-defined parameters. In this paper, we also try to validate reverberation as a feasible distance cue by suggesting early decay time (EDT) and clarity index, C80, as the parameters for controlling the perceived distance with the reverberation cue.

This letter introduces a pre-rejection technique for wireless channel distorted speech with application to automatic speech recognition (ASR). Based on analysis of distorted speech signals over a wireless communication channel, we propose a method to reject the channel distorted speech with a small computational load. From a number of simulation results, we can discover that the pre-rejection algorithm enhances the robustness of speech recognition operation.

Interconnection networks play a crucial role in the performance of massively parallel computers. Hierarchical interconnection networks provide high performance at low cost by exploring the locality that exists in the communication patterns of massively parallel computers. A Hierarchical Torus Network (HTN) is a 2D-torus network of multiple basic modules, in which the basic modules are 3D-torus networks that are hierarchically interconnected for higher level networks. The static network performance of the HTN has already been studied and has been shown to be good. Dynamic communication performance has been evaluated under uniform traffic pattern but not under non-uniform traffic patterns. In this paper, we present a deadlock-free routing algorithm for the HTN using 3 virtual channels and evaluate the network's dynamic communication performance under three non-uniform traffic patterns, using the proposed routing algorithm. We evaluate the dynamic communication performance of HTN, H3D-mesh, H3D-torus, TESH, and mesh networks by computer simulation. We find that the dynamic communication performance of HTN is better than that of the H3D-mesh, H3D-torus, TESH, and mesh networks.