We consider only P-invariants that are nonnegative integer vectors in this paper. An P-invariant of a Petri net N=(P,T,E,α,β) is a |P|-dimensional vector Y with Yt A = for the place-transition incidence matrix A of N. The support of an invariant is the set of elements having nonzero values in the vector. Since any invariant is expressed as a linear combination of minimal-support invariants (ms-invariants for short) with nonnegative rational coefficients, it is usual to try to obtain either several invariants or the set of all ms-invariants. The Fourier-Motzkin method (FM) is well-known for computing a set of invariants including all ms-invariants. It has, however, critical deficiencies such that, even if invariants exist, none of them may be computed because of memory overflow caused by storing candidate vectors for invariants and such that, even when a set of invariants are produced, many non-ms invariants may be included. We are going to propose the following two methods: (1) FM1_M2 that finds a smallest possible set of invariants including all ms-invariants; (2) STFM that necessarily produces one or more invariants if they exist. Experimental results are given to show their superiority over existing ones.

This paper describes a design scheme of generalized minimum variance controllers (GMVC) using a group method of data handling (GMDH) network for nonlinear systems. Concretely, the predictive value of the output required in the GMVC is obtained by using the GMDH which is a kind of multilayered networks. Since the predictive value of the output in GMVC is calculated by a nonlinear model which is generated by the GMDH network, one can expect to obtain the better control performance than that by the conventional scheme. The behavior of the newly proposed control scheme is evaluated on numerical examples.

This paper proposes a non-linear adaptive algorithm, the amplitude banded RLS (ABRLS) algorithm, as an adaptation procedure for time variant channel equalizers. In the ABRLS algorithm, a coefficient matrix is updated based on the amplitude level of the received sequence. To enhance the capability of tracking for the ABRLS algorithm, a parallel adaptation scheme is utilized which involves the structures of decision feedback equalizer (DFE). Computer simulations demonstrate that the novel ABRLS based equalizer provides a significant improvement relative to the conventional RLS DFE on a rapidly time variant communication channel.

We proposed a simple technique for measuring the effective zero-dispersion wavelength. In this study, we measured the effective zero-dispersion wavelength of a 25-km-long dispersion-shifted fiber (DSF) using the four-wave mixing (FWM) of a spectrum-sliced fiber amplifier light source, and then compared our results with other conventional techniques to confirm the validity of our method.

Due to the advancements in Information Technology, such as the Internet and the presence of fierce competition in the market, the business environment is changing rapidly. To cope with these dynamic changes, heterogeneous systems are now required to integrate in order to form alliances with different business units or within individual business units. Since business operations can not be stopped to carry out these changes in the existing systems, the systems are required to integrate flexibly, preserving each constituent's individual characteristics. By implementing Atomic Action through a gateway and across constituent systems in a Heterogeneous Autonomous Decentralized System (HADS), higher degrees of assurance can be achieved through cooperation. However, if all the transactions are passed through a gateway, the response time worsens and the result cannot be obtained within an appropriate timeframe. Hence, a new technique of suppressing the flow passing through the gateway, while achieving a maximum number of successful transaction within the appropriate timeframe, is required.

This paper proposes a vector quantization scheme which makes it possible to consider the dynamics of input vectors. In the proposed scheme, a linear transformation is applied to the consecutive input vectors and the resulting vector is quantized with a distortion measure defined by the statistics. At the decoder side, the output vector sequence is determined using the statistics associated with the transmitted indices in such a way that a likelihood is maximized. To solve the maximization problem, a computationally efficient algorithm is derived. The performance of the proposed method is evaluated in LSP parameter quantization. It is found that the LSP trajectories and the corresponding spectra change quite smoothly in the proposed method. It is also shown that the use of the proposed method results in a significant improvement of subjective quality.

We present a novel kind of integrate-and-fire circuit (IFC) with two periodic inputs: a pulse-train stimulation input and a base input. We clarify that the system state is quantized by the pulse-train stimulation input. Then the system dynamics is described by a return map with quantized state (Qmap). By changing the shape of the base input, various Qmaps can be obtained. The Qmap exhibits co-existence state of various super-stable periodic orbits, and the IFC outputs one of corresponding super-stable periodic pulse-trains depending on the initial state. For a typical case, we clarify the number of co-existing periodic pulse-trains theoretically for the stimulation frequencies. Constructing a simple test circuit, typical phenomena can be verified in the laboratory.

System needs of growing systems including heterogeneous functions and operations are increased. High assurance system that achieves high reliability and high availability is very important for such systems. In order to realize high assurance system, we developed the assurance technology based on ADS (Autonomous Decentralized System). When a growing system changes or grows, its reliability may be lowered. In this paper, we clarify the risk factors which lower the reliability and quality of a growing system when the system is modified. We will then examine the technology to eliminate or mitigate those risk factors, and propose adaptive assurance technology that can minimize the risk. We also applied this technology to ATOS for Tokyo Metropolitan Railway Network as an example of really changing and growing system and mention its effectiveness. ATOS; Autonomous Decentralized Transport Operation Control System.

Decentralized XML databases are often used in Electronic Commerce (EC) business models such as e-brokers on the Web. To flexibly model such applications, we need a modeling language for EC business processes. To this end, we have adopted a query language approach and have designed a query language, called XBML, for decentralized XML databases used in EC businesses. In this paper, we explain and validate the functionality of XBML by specifying e-broker business models and describe the implementation of the XBML server, focusing on the distributed query processing.

The heterogeneous autonomous decentralized system technology offers a way to integrate different types of context-related autonomous decentralized (sub) systems into a coherent system. The aim of this research is to model and evaluate the communication capacity among the subsystems connected by communication gateways of a heterogeneous autonomous decentralized system. Failures of subsystems and communication gateways in the system are taken into account. We use graphs to represent the topologies of heterogeneous autonomous decentralized systems and use the residual connectedness reliability (RCR) to characterize the communication capacity among its subsystems connected by its gateways. This model enables us to share research results obtained in residual connectedness reliability study in graph theory. Not to our surprise, we learnt soon that computing RCR of general graphs is NP-hard. But to our surprise, there exist no efficient approximation algorithms that can give a good estimation of RCR for an arbitrary graph when both vertices and edges may fail. We proposed in this paper a simulation scheme that gave us good results for small to large graphs but failed for very large graphs. Then we applied a theoretical bounding approach. We obtained expressions for upper and lower bounds of RCR for arbitrary graphs. Both upper and lower bound expressions can be computed in polynomial time. We applied these expressions to several typical graphs and showed that the differences between the upper and lower bounds tend to zero as the sizes of graphs tend to infinite. The contributions of this research are twofold, we find an efficient way to model and evaluate the communication capacity of heterogeneous autonomous decentralized systems; we contribute an efficient algorithm to estimate RCR in general graph theory.

A new architecture and methods for an enhanced autonomous decentralized production system (EADPS) are described. This EADPS was developed to ensure high flexibility of production systems consisting of intelligent devices based on the autonomous decentralized system model and to guarantee the time used for communication to simultaneously maintain high productivity. The system architecture of the EADPS guarantees the time by managing groups of nodes and the priorities in these groups. A bit-arbitration method is used to prevent collision of messages. The nodes autonomously check the waveforms in the network and terminate transmission when the nodes with a higher priority are transmitting. A parallel-filtering method is used to speed up message acceptance. The nodes check the identifiers of the messages using parallel-filtering circuits and each node determines autonomously where a message should be accepted or not. Implementing the system architecture and these methods as circuits and integrating the circuits into a chip using system LSI technologies resulted in low-cost implementation of the system. Experimental evaluation demonstrated the effectiveness of this system.

This paper introduces a new digital ATC (Automatic Train Control device) system. In the current ATC, the central ATC logic device calculates permissive speed of each blocking section and controls speed of all trains. On the other hand, in the new digital ATC, the central logic controller calculates each position to which a train can move safely, and sends the information on positions to all trains. On each train, the on-board equipment calculates an appropriate braking pattern with the information, and controls velocity of the train. That is, in the new system, the device on each train autonomously calculates permissive speed of that train. These special features realize ideal speed control of each train making full use of its performance for acceleration and deceleration, which in turns allows high-density train operations.

Before we gave a fast generalized minimum distance (GMD) decoding algorithm for one-point algebraic-geometry (AG) codes. In this paper, we propose another fast GMD decoding algorithm for these codes, where the present method includes an erasure deletion procedure while the past one uses an erasure addition procedure. Both methods find a minimal polynomial set of a given syndrome array, which is a candidate for an erasure-and-error locator polynomial set constrained with an erasure locator set of each size. Although both erasure addition and deletion GMD decoding algorithms have been established for one-dimensional algebraic codes such as RS codes, nothing but the erasure addition GMD decoding algorithm for multidimensional algebraic codes such as one-point AG codes have been given. The present erasure deletion GMD decoding algorithm is based on the Berlekamp-Massey-Sakata (BMS) algorithm from the standpoint of constrained multidimensional shift register synthesis. It is expected that both our past and present methods play a joint role in decoding for one-point AG codes up to the error correction bound.

A new algorithm for the maximum a posteriori (MAP) decoding of linear block codes is presented. The proposed algorithm can be regarded as a conventional BCJR algorithm for a section trellis diagram, where branch metrics of the trellis are computed by the recursive MAP algorithm proposed by the authors. The decoding complexity of the proposed algorithm depends on the sectionalization of the trellis. A systematic way to find the optimum sectionalization which minimizes the complexity is also presented. Since the algorithm can be regarded as a generalization of both of the BCJR and the recursive MAP algorithms, the complexity of the proposed algorithm cannot be larger than those algorithms, as far as the sectionalization is chosen appropriately.

The low-frequency noise of InGaAs pseudomorphic HEMTs fabricated on GaAs substrate was studied. The dependence of the noise spectral density on the gate voltage indicates that the channel of the device dominates the low-frequency noise. Generation-recombination (G-R) noise was observed in the form of bulges superimposed on a background of 1/f. The activation energyof the G-R noise was 0.32-0.39 eV which is close to that of the DX center, suggesting that the origin of the G-R noise is the DX center in the AlGaAs barrier layer. Little bulge was observed in the gate current noise of the HEMTs with large InAs mole fractions of 0.4 and 0.5. Generation of the traps with different time constant can explain this behavior.

This paper presents methods of combining buffer insertion and transistor sizing into a single post-layout optimization. The proposed method considers the tradeoff between upsizing transistors and inserting buffers then chooses the solution with the lowest possible power and area cost. The proposed method is efficient and tunable in that optimality can be traded for compute time.

Theoretical and experimental aspects of GaN-based Gunn diodes are reviewed. Since the threshold field for Gunn effect in GaN (FTH>150 kV/cm) is reported to be much higher than in GaAs (FTH=3.5 kV/cm), the active layer of GaN-based devices can be made thinner (<3 µm) and doped higher (>1017 cm-3) than in conventional Gunn diodes. Consequently, GaN-based devices are expected to offer increased frequency and power capabilities. The advantages of GaN are demonstrated with the help of large-signal simulations of GaN and GaAs Gunn diodes. The simulations revealed that GaN diodes can be operated at a higher frequency (up to 760 GHz vs. 100 GHz) and with larger output power density (105 W/cm2 vs. 103 W/cm2) than GaAs diodes. Epitaxial layers of n+/n-/n+ GaN (1019 cm-3/1017 cm-3/1019 cm-3) designed for millimeter-wave operation were grown using MOCVD on SiC substrates. GaN Gunn diodes with 4 µm-thick active layers were fabricated using specially developed dry etching techniques. The RIE was optimized to allow deep low-damage etching and allowed reduction of contact resistivity of etched layers (RC10-6 Ωcm2). GaN diodes fabricated on SiC substrates with high thermal conductivity were tested on-wafer and demonstrated high voltage and current capability (60 V and 2.5 A). High frequency testing of these devices requires proper dicing, mounting on efficient heatsinks, and connection to appropriate oscillator cavities.

This paper describes the numerical analysis for terahertz electromagnetic-wave oscillation/detection properties of plasma-wave field-effect transistors (PW-FET's) and their applications to future smart photonic network systems. The PW-FET is a new type of the electron device that utilizes the plasma resonance effect of highly dense two-dimensional conduction electrons in the FET channel. By numerically solving the hydrodynamic equations for PW-FET's, the plasma resonance characteristics under terahertz electromagnetic-wave absorption are analyzed for three types of FET's; Si MOSFET's, GaAs MESFET's, and InP-based HEMT's. The results indicate that the InP-based sub-100-nm gate-length HEMT's exhibit the most promising oscillation/detection characteristics in the terahertz range with very wide frequency tunability. By introducing the PW-FET's as injection-locked terahertz-frequency-tunable oscillators and terahertz mixers, a new idea of coherent heterodyne detection utilizing terahertz IF (intermediate-frequency) bands is proposed for the future smart photonic network systems that enable real-time adaptive wavelength routing for add-drop multiplexing. The plasma resonance of PW-FET's by means of different frequency generation based on direct photomixing is also proposed as an alternative approach to injection-locked terahertz oscillation. To realize it, virtual carrier excitations by the polariton having photon energy lower than the bandgap of the channel is a possible mechanism.

We propose a three-dimensional structure on a planar substrate employing micromachining technology. A low-loss suspended structure incorporating a BCB membrane employing deep trench etching technology has been newly proposed. A micromachined suspended line structure using BCB membrane film enables us to realize a low loss planar resonator, which achieved an unloaded quality factor (Q-factor) of more than 280 at 60 GHz. We design low-loss filters and antennas built into silicon in a 60 GHz band. A low-loss filter realizes an insertion loss of 1.0 dB at 60 GHz and a patch antenna obtains a 3% bandwidth. In addition, we demonstrate a 60 GHz receiver front-end IC incorporating the planar filter and the antenna, and obtain good results. These techniques enable us to integrate various functions into a compact package even in millimeter-wave bands.

Rectangular/circular-to-radial waveguide tra-nsformers through a ring slot have been proposed for the feeder of radial line slot antennas (RLSAs) in millimeter wave application. Rotating electric modes are excited by a set of ring slot and perturbation dog bone slot. Basic operation is observed in 12 GHz band. Concentric array radial line slot antennas fed by these transformers are fabricated and the antenna gain of 26.9 dBi with the efficiency more than 60% is measured. The applicability for millimeter wave is verified for 38 GHz band RLSA fed by the rectangular waveguide. The measured gain of the antenna is 22.5 dBi with the efficiency of 53% with the diameter of 46mm and 26.4 dBi with 61% with the diameter of 66mm.