In this letter, a new output feedback tracking control using a fuzzy disturbance observer (FDO) is proposed and its application to control of a nonlinear system in the presence of the internal parameter perturbation and external disturbance is presented. An FDO using a filtered signal is developed and the high gain observer (HGO) is employed to implement the output feedback tracking control. It is shown in a rigorous manner that all the errors involved can be kept arbitrarily small. Finally, the effectiveness and the feasibility of the suggested method is demonstrated by computer simulation.

The Earth Simulator (ES), developed by the Japanese government's initiative "Earth Simulator project," is a highly parallel vector supercomputer system. In May 2002, the ES was proven to be the most powerful computer in the world by achieving 35.86 teraflops on the LINPACK benchmark and 26.58 teraflops for a global atmospheric circulation model with the spectral method. Three architectural features enabled these great achievements; vector processor, shared-memory and high-bandwidth non-blocking interconnection crossbar network. In this paper, an overview of the ES, the three architectural features and the result of performance evaluation are described particularly with its hardware realization of the interconnection among 640 processor nodes.

We propose and describe a free-space optical interconnection device with a photorefractive semi-linear resonator. The hologram in the photorefractive crystal is, in general, volatile and the erasing of it coincides with the diffraction of the signal beam. Therefore we have to reform the hologram again after several transmissions of the data or use some fixing techniques such as thermal fixing and electrical fixing. In our interconnection device, the hologram is enhanced by the feedback beam that is a part of the input signal divided by the beam splitter within semi-linear resonator, therefore the sustentation time of the connection can be extended. We explain the sustentation mechanism and investigate the optimum reflectivity of the beam splitters, which determine the feedback rate of the input signal, within feedback circuit for the high output conversion efficiency. We also analyze the coupling strength threshold for sustentation of the connection. We give a basic experiment on 33 interconnection by using BaTiO3 crystal and Ar+ laser whose wavelength is 514 [nm]. We show that the connections are held for long time without the continuous illumination of the control beam.

In this paper, we proposed the doubly tapered electromagnetic periodic structure (DT-EPS) bandstop filters in coplanar waveguide (CPW) and cylindrical coplanar waveguide (CCPW). The DT-EPS bandstop filter not only can effectively improve the stopband rejection but also increase its bandwidth. In addition, this technique can significantly reduce the passband ripples compared with conventional case.

We propose an analysis method for Franz-Keldysh (FK) oscillations appearing in photoreflectance (PR) spectra of heterojunction device structures, which enables precise and simultaneous evaluation of the built-in electric field strength and band-gap energy. Samples for PR measurements were n+-GaAs/n-Al0.3 Ga0.7 As/i-GaAs heterostructures with different Al0.3Ga0.7As-layer thickness. We have found that the phase of the FK oscillations originating from the i-GaAs buffer layer depends on the Al0.3 Ga0.7 As-layer thickness. We have derived a calculation model for FK oscillations that includes the interference of probe light. From the comparison of the calculated spectra with the measured spectra, we conclude that mixing of the real and imaginary parts of a modulated dielectric function, which is caused by the probe-light interference, gives rise to the phase shift of the FK oscillations. Our FK-oscillation analysis method reduces ambiguity in the estimation of band-gap energy that is considerable in a conventional analysis.

DC and RF performances of AlGaN/GaN HEMTs are simulated using a two-dimensional device simulator with the material parameters of GaN and AlGaN. The cut-off frequency is estimated as 205 GHz at the gate length of 0.05 µm and the drain breakdown voltage at this gate length is over 10 V. The values are satisfactory for millimeter wavelength power applications. The use of thin AlGaN layers has key importance to alleviate gate parasitic capacitance effects at this gate length.

In this paper, we describe the operation of circuits capable of more than 40-Gbit/s that we have developed using InP HEMT technology. For example, we succeeded in obtaining 43-Gbit/s operation for a full-rate 4:1Multiplier (MUX), 50-Gbit/s operation for a Demultiplexer (DEMUX), 50-Gbit/s operation for a D-type flip-flop (D-FF), and a preamplifier with a bandwidth of 40 GHz. In addition, the achievement of 90-Gbit/s operation for a 2:1MUX and a distributed amplifier with over 110-GHz bandwidth indicates that InP HEMT technology is promising for system operations of over 100 Gbit/s. To achieve these results, we also developed several design techniques to improve frequency response above 80 GHz including a symmetric and separated layout of differential elements in the basic SCFL gate and inverted microstrip.

In this paper, the time-frequency separation algorithm (TFS) proposed by Belouchrani and Amin is applied to ground penetrating radar (GPR) data to reduce ground clutter, that hides reflected waves from a near-surface planar interface. We formulated the problem with several assumptions so that narrow band signals, whose center frequency and baseband signal depend on propagation paths, are received at the receiver, when a wideband signal is radiated from a transmitter. These phenomena can be clearly seen in time-frequency distribution (TFD) of the received signal. In this paper, we adopted the TFS utilizing the TFD signature as a blind separation technique to separate the ground clutter from the target signals. We show numerical and experimental results in order to verify the validity of the problem formulation and the TFS. We carried out GPR measurements to measure permafrost in Yakutsk, Russia. We found the difference in TFD signatures between the ground clutter and the target signal in the experimental data. We could detect the upper boundary of the permafrost with the TFS in spite of the unstable ground clutter.

An approach is proposed for constructing a dependable server cluster composed only of server nodes with all nodes running the same algorithm. The cluster propagates an IP multicast address as the server address, and clients multicast requests to the cluster. A local proxy running on each client machine enables conventional client software designed for unicasting to communicate with the cluster without having to be modified. Evaluation of a prototype system providing domain name service showed that a cluster using this technique has high dependability with acceptable performance degradation.

Detecting the possibility of inference attacks is necessary in order to keep a database secure. Inference attacks mean that a user tries to infer the result of an unauthorized queries to the user. For method schemas, which are a formal model of object-oriented databases, it is known that the security problem against inference attacks is decidable in polynomial time in the size of a given database instance. However, when the database instance or authorization has slightly been updated, it is not desirable to check the entire database again for efficiency. In this paper, we propose several sufficient conditions for update operations to preserve the security. Furthermore, we show that some of the proposed sufficient conditions can be decided much more efficiently than the entire security check. Thus, the sufficient conditions are useful for incremental security checking.

This paper describes the architecture of ReVolver/C40 a scalable parallel machine for volume rendering and its prototype implementation. The most important feature of ReVolver/C40 is view-independent real time rendering of translucent 3D object by using perspective projection. In order to realize this feature, the authors propose a parallel volume memory architecture based on the principal axis oriented sampling method and parallel treble volume memory. This paper also discusses the implementation issues of ReVolver/C40 where various kinds of parallelism extracted to achieve high-perfromance rendering are explained. The prototype systems had been developed and their performance evaluation results are explained. As the results of the evaluation of the prototype systems, ReVolver/C40 with 32 parallel volume memory is estimated to achieve more than 10 frame per second for 2563 volume data on 2562 screen by using perspective projection. The authors also review the development of ReVolver/C40 from several view points.

Software certification is a notoriously difficult problem. From software reliability engineering perspective, certification process must provide evidence that the program meets or exceeds the required level of reliability. When certifying the reliability of a high assurance system very few, if any, failures are observed by testing. In statistical estimation theory the probability of an event is estimated by determining the proportion of the times it occurs in a fixed number of trials. In absence of failures, the number of required certification tests becomes impractically large. We suggest that subjective reliability estimation from the development lifecycle, based on observed behavior or the reflection of one's belief in the system quality, be included in certification. In statistical terms, we hypothesize that a system failure occurs with the hypothesized probability. Presumed reliability needs to be corroborated by statistical testing during the reliability certification phase. As evidence relevant to the hypothesis increases, we change the degree of belief in the hypothesis. Depending on the corroboration evidence, the system is either certified or rejected. The advantage of the proposed theory is an economically acceptable number of required system certification tests, even for high assurance systems so far considered impossible to certify.

This paper focuses on flow control in high-speed networks. Each node in a network handles its local traffic flow on the basis of only the information it is aware of, but it is preferable that the decision-making of each node leads to high performance of the whole network. To this end, we investigate the relationship between the flow control mechanism of each node and network performance. We consider the situation in which the capacity of a link in the network is changed but individual nodes are not aware of this. Then we investigate the stability and adaptability of the network performance, and discuss an appropriate flow control model on the basis of simulation results.

In a fixed-channel-allocation (FCA) cellular network, a fixed number of channels are assigned to each cell. However, under this scheme, the channel usage may not be efficient because of the variability in the offered traffic. Different approaches such as channel borrowing (CB) and dynamic channel allocation (DCA) have been proposed to accommodate variable traffic. Our work expands on the CB scheme and proposes a new channel-allocation scheme--called mobile-assisted connection-admission (MACA) algorithm--to achieve load balancing in a cellular network, so as to assure network communication. In this scheme, some special channels are used to directly connect mobile units from different cells; thus, a mobile unit, which is unable to connect to its own base station because it is in a heavily-loaded "hot" cell, may be able to get connected to its neighboring lightly-loaded cold cell's base station through a two-hop link. Research results show that MACA can greatly improve the performance of a cellular network by reducing blocking probabilities.

In video conference systems over the Internet, audio and video data are often lost due to UDP packet losses, resulting in degradation of assurance. In this paper we describe a high-assurance video conference system applying the following two techniques: (1) packet loss recovery using convolutional codes, which improves the assurance of communication; and (2) Xcast, a multicast scheme that is designed for relatively small groups, reducing the bandwidth required for a multi-point conference. We added these functions to a GateKeeper (GK), a device used in conventional conference systems. Encoding/decoding and Xcast routing were then implemented as the upper layer for the UDP. We examined the functions of the system over the Internet in a multi-point conference between three sites around Tokyo, as well as a conference between Tokyo and Korea. We also investigated the effectiveness of the proposed system in experiments using an Internet simulator. Experimental results showed that the quality of received picture was improved in comparison with the case where no encoding schemes were applied.

Digital rights management in client-server environments requires the establishment of client integrity, in order to protect sensitive (secret) information from loss or misuse. Clients are vulnerable to powerful man-in-the-middle attacks through malicious software (viruses, etc.), which is undetectable by conventional anti-virus technology. We present such powerful viruses and demonstrate their ability to compromise clients. Furthermore, we introduce a defense against all viruses, which is based on simple hardware devices that execute specialized protocols to establish client integrity and protect against sensitive data loss.

Direct conversion techniques commonly used for the transmitter in basestation rely on analog performance of the quadrature modulator. In this paper, simulated results show that imperfections in analog quadrature modulation--gain and phase error and dc offset--have a devastating effect on digital predistortion for power amplifier linearization circuits. We construct compensation circuit to remove these errors, and conduct an experiment. The imbalance errors are compensated by using the output spectrum of modulator. The image spurious (-56.74 dBm) with gain, phase and the dc offset spurious (-43.83 dBm) are reduced to -93.21 dBm and -93.56 dBm, respectively. These experimental results illustrate that modulation errors can be eliminated.

REX is a reconfigurable experimental system for evaluating and developing parallel computer systems. It consists of large-scale FPGAs, and enables the systems to be reconfigured from their processors to the network topology in order to support their evaluation and development. We evaluated REX using several implementations of parallel computer systems, and showed that it had enough scalability of gates, memory throughput and network throughput. We also showed that REX was an effective tool because of its emulation speed and reconfigurability to develop systems.

Schottky gas sensors of CO were fabricated using high quality AlGaN/GaN/Si heterostructures. The CO sensors show good sensitivity in the temperature range of 250 to 300 (530%, at 160 ppm CO in N2) and fast response comparable with SnO2 sensors. A two-region linear regime was observed for the dependence of sensitivity on CO concentration. GaN sensors on Si substrate offer the possibility of integration with Si based electronics. The gas sensors show slow response with time, the change of material properties possibly in the presence of large thermal stress.

This paper proposes the conditional LZ complexity and analyzes its property. Especially, we show an inequality corresponding to Ziv's inequality concerning a distinct parsing of a pair of sequences. Further, as a byproduct of the result, we show a simple proof of the asymptotical optimality of Ziv's universal source coding algorithm with side information.