In recent years, several inverse solutions of magnetoencephalography (MEG) have been proposed. Among them, the multiple signal classification (MUSIC) method utilizes spatio-temporal information obtained from magnetic fields. The conventional MUSIC method is, however, sensitive to Gaussian noise and a sufficiently large signal-to-noise ratio (SNR) is required to estimate the number of sources and to specify the precise locations of electrical neural activities. In this paper, a new algorithm for solving the inverse problem using the fourth order MUSIC (FO-MUSIC) method is proposed. We apply it to the MEG source estimation problem. Numerical simulations demonstrate that the proposed FO-MUSIC algorithm is more robust against Gaussian noise than the conventional MUSIC algorithm.

In functional brain images obtained by analyzing higher human brain functions using functional magnetic resonance imaging (fMRI), one serious problem is that these images depict false activation areas (artifacts) resulting from image-to-image physiological movements of subject during fMRI data acquisition. In order to truly detect functional activation areas, it is necessary to eliminate the effects of physiological movements of subject (i.e., gross head motion, pulsatile blood and cerebrospinal fluid (CSF) flow) from fMRI time series data. In this paper, we propose a method for eliminating artifacts due to not only rigid-body motion such as gross head motion, but also non-rigid-body motion like the deformation caused by the pulsatile blood and CSF flow. The proposed method estimates subject movements by using gradient methods which can detect subpixel optical flow. Our method estimates the subject movements on a "pixel-by-pixel" basis, and achieves the accurate estimation of both rigid-body and non-rigid-body motion. The artifacts are reduced by correction based on the estimated movements. Therefore, brain activation areas are accurately detected in functional brain images. We demonstrate that our method is valid by applying it to real fMRI data and that it can improve the detection of brain activation areas.

We have developed optical encoding devices for processing femtosecond pulses. These devices are based on spectral separation devices and light modulators with fiber gratings. Experiments were made to encode a light pulse in the spectral domain. These experiments utilize the characteristics that a femtosecond light pulse has a very broad spectrum. An input femtosecond light pulse is decomposed into a series of wavelength components. Each wavelength component with narrow spectra <1 nm width is successfully extracted into a single mode fiber. Light modulators corresponding to wavelength components are assigned to the 1st bit, the 2nd bit, the 3rd bit, , the nth bit, respectively. All of the encoded wavelength components are again recombined into a single time-varying signal and transmitted through an optical fiber. Decoding at receiving site is made by the reverse operation. Encoding and decoding for 2-bit and 4-bit signals were demonstrated for 200 fs input light pulse with about 40 nm spectral width.

This paper studies effect of packet scheduling algorithms at routers on media synchronization quality in live audio and video transmission by experiment. In the experiment, we deal with four packet scheduling algorithms: First-In First-Out, Priority Queueing, Class-Based Queueing and Weighted Fair Queueing. We assess the synchronization quality of both intra-stream and inter-stream with and without media synchronization control. The paper clarifies the features of each algorithm from a media synchronization point of view. A comparison of the experimental results shows that Weighted Fair Queueing is the most efficient packet scheduling algorithm for continuous media among the four.

Spatial dynamic pattern formations or trails by organisms attract us, which remind us chaos and fractal. They seem to show the emergence of co-operation, job separation, or division of territories when genetic programming controls the reproduction, mutation, crossing over of the organisms. Recent research in social insect behavior suggests that swarm intelligence comes from pheromone or chemical trails, and models based on self-organization can help explain how colony-level behavior emerges out of interactions among individual insects. We try to explain the co-operative behaviors of social insect by means of density of organisms and their interaction with environment in simple simulations. We also study that MDL-based fitness evaluation is effective for improvement of generalization of genetic programming. At last, interspecific and intraspecific mathematical models are examined to expand our research into interspecific evolution.

For several years, more and more people are joining the Internet and various kind of packets (so called transaction-, block-, and stream-types) have been transmitted in the same network, so that poor network conditions cause loss of the stream-type data packets, such as voices, which request smaller transmission delay time than others. We consider a switching node (router) in a network as an N-series M/G/1-type queueing model and have mainly evaluated the fluctuation of packet delay time and end-to-end delay time, using the two moments matching method with initial value, then define the delay jitter D of a network which consists of jointed N switching nodes. It is clarified that this network is not suitable for voice packets transmission media without measures.

In order to navigate a mobile robot or an autonomous vehicle in indoor environment, which includes several kinds of obstacles such as walls, furniture, and humans, the distance between the mobile robot and the obstacles have to be determined. These obstacles can be considered as walls with complicated edges. This paper proposes a mobile-robot-navigation method by using the polar coordinate transformation from an omnidirectional image. The omnidirectional image is obtained from a hyperboloidal mirror, which has the prominent feature in sensing the surrounding image at the same time. When the wall image from the camera is transformed by the transformation, the straight lines between the wall and the floor appear in the curve line after transformation. The peak point represents the distance and the direction between the robot and the wall. In addition, the wall types can be classified by the pattern and number of peak points. They are one side wall, corridor and corner. To navigate the mobile robot, in this paper, it starts with comparing a peak point obtained from the real image with the reference point determined by designed distance and direction. If there is a difference between the two points, the system will compute appropriate wheel angle to adjust the distance and direction against the wall by keeping the peak point in the same position as the reference point. The experiments are performed on the prototype mobile robot. The results show that for the determining distance from the robot to the wall between 70-290 cm, the average error is 6.23 percent. For three types of the wall classification, this method can correctly classify 86.67 percent of 15 image samples. In the robot movement alongside the wall, the system approximately consumes the 3 frame/s processing time at 10 cm/s motion speed. The mobile robot can maintain its motion alongside the wall with the average error 12 cm from reference distance.

For multimedia communications, the computational scalability of a multimedia codec is required to match with different working platforms and integrated services of media sources. In this paper, two condensed stochastic codebook search approaches are proposed to progressively reduce the computation required for the algebraic code excited linear predictive (ACELP) and multi-pulse maximum likelihood quantization (MP-MLQ) coders. By reducing the candidates of the codebook before search procedure, the proposed methods can effectively diminish the computation required for the ITU-T G.723.1 dual rate speech coder. Simulation results show that the proposed methods can save over 50 percent for the stochastic codebook search with perceptually intangible degradation in speech quality.

Low-crosstalk 1.3-µm Fabry-Perot laser diode (FP-LD) and photodiode (PD) arrays are developed. The arrays are fabricated on semi-insulating substrates and their anodes and cathodes are separated channel by channel to suppress inter-channel electrical crosstalk at high frequency. Crosstalk of less than -30 dB is achieved between neighboring LDs at 3.125 GHz. This is low enough for BER characteristics observed under asynchronous operation of a 4-channel LD array to be no worse than those under single-channel operation. Excellent uniformity of both LD and PD characteristics, high-temperature operation of the LD array, and low-voltage operation of the PD array are also attained. These arrays are suitable for low-cost high-bit-rate parallel optical communications.

LiNbO3 optical modulators for band-operation with a resonant modulating electrode are investigated in this paper. We propose an asymmetric resonant structure consisting of two arms of modulating electrodes, where one arm is open-ended and the other arm is short-ended. The voltage standingwave was enhanced by the resonance of the electrodes, so that effective optical modulation was achieved, while the length of the modulating electrode was much shorter than the conventional travelingwave-type electrodes. The optical response at 6.2 GHz of a resonant modulator designed by maximizing the normalized induced phase was 4.94 of the response at dc with a non-resonant modulator.

A highly sensitive optical sampling system has been produced by using sum-frequency generation in a periodically poled lithium niobate crystal. When the relations between crystal length and wavelength bandwidth and SFG conversion efficiency were investigated theoretically and experimentally, a system with a 1.4-mm-long periodically poled lithium niobate crystal was found to have a 22.5-nm wavelength bandwidth and a SFG conversion efficiency ten times that of a similar system with a 3-mm-long KTP crystal. The SNR of the system with the 1.4-mm-long PPLN crystal was about 7 dB higher than that of the system with a 3-mm-long KTP crystal, and a temporal resolution better than 1 ps was obtained by using compressed optical sampling pulses. The eye diagram of a 10-Gbit/s RZ optical signal with a 1-mW peak power could be observed, and the eye diagram of a 160-Gbit/s RZ optical signal could be observed clearly.

Generalized Pulse Spectrum Technique (GPST) is a method to solve the inverse problems of wave-propagation and diffusion-dominated phenomena, and therefore has been popularly applied in image reconstruction of time-resolved diffuse optical tomography. With a standard GPST for simultaneous reconstruction of absorption and scattering coefficients, the products of the gradients of the Green's function and the photon-density flux, based on the photon-diffusion equation, are required to calculate the diffusion-related Jacobian matrix. The adversities are of two-folds: time-consuming and singular in the field near the source. The latter causes a severe insensitivity of the algorithm to the scattering changes deep inside tissue. To cope with the above difficulties, we propose in this paper a modified GPST algorithm that only involves the Green's function and the photon-density flux themselves in the scattering-related matrix. Our simulated and experimental reconstructions show that the modified algorithm can significantly improve the quality of scattering image and accelerate the reconstruction process, without an evident degradation in absorption image.

We present a scalar multiplication algorithm with recovery of the y-coordinate on a Montgomery-form elliptic curve over any non-binary field. The previous algorithms for scalar multiplication on a Montgomery form do not consider how to recover the y-coordinate. So although they can be applicable to certain restricted schemes (e.g. ECDH and ECDSA-S), some schemes (e.g. ECDSA-V and MQV) require scalar multiplication with recovery of the y-coordinate. We compare our proposed scalar multiplication algorithm with the traditional scalar multiplication algorithms (including Window-methods on the Weierstrass form), and discuss the Montgomery form versus the Weierstrass form in the performance of implementation with several techniques of elliptic curve cryptosystems (including ECES, ECDSA, and ECMQV). Our results clarify the advantage of the cryptographic usage of Montgomery-form elliptic curve in constrained environments such as mobile devices and smart cards.

Fourier synthesis of ultrafast optical-pulse trains was demonstrated using a simplified experimental configuration consisting of three independent continuous-wave lasers and a semiconductor optical amplifier (SOA) used as a four-wave mixer. When the three lasers were phase-locked, ultrafast optical-pulse trains were successfully generated at repetition frequencies ranging from 504 GHz to 1.8 THz with high waveform stability.

This paper addresses the problem of designing an unconditionally secure conference system that fulfills the requirements of both traceability and dynamic sender. In a so-called conference system, a common key is shared among all authorized users, and messages are encrypted using the shared key. It is known that a straightforward implementation of such a system may present a number of security weaknesses. Our particular concern lies in the possibility that unauthorized users may be able to acquire the shared key by illegal means, say from one or more authorized but dishonest users (called traitors). An unauthorized user who has successfully obtained the shared key can now decrypt scrambled messages without leaving any evidence on who the traitors were. To solve this problem, in this paper we propose a conference system that admits dynamic sender traceability. The new solution can detect traitors, even if the sender of a message is dynamically determined after a shared key is distributed to authorized users. We also prove that this scheme is unconditionally secure.

In this paper, we discuss the impossible differential cryptanalysis for the block cipher Zodiac. The main design principles of Zodiac include simplicity and efficiency. However, the diffusion layer in its round function is too simple to offer enough security. The impossible differential cryptanalysis exploits such weakness in Zodiac. Our attack using a 14-round impossible characteristic derives the 128-bit master key of the full 16-round Zodiac faster than the exhaustive search. The efficiency of the attack compared with exhaustive search increases as the key size increases.

We present the new 128-bit block cipher called Camellia. Camellia supports 128-bit block size and 128-, 192-, and 256-bit key lengths, i.e. the same interface specifications as the Advanced Encryption Standard (AES). Camellia was carefully designed to withstand all known cryptanalytic attacks and even to have a sufficiently large security leeway. It was also designed to suit both software and hardware implementations and to cover all possible encryption applications that range from low-cost smart cards to high-speed network systems. Compared to the AES finalists, Camellia offers at least comparable encryption speed in software and hardware. An optimized implementation of Camellia in assembly language can encrypt on a Pentium III (1.13 GHz) at the rate of 471 Mbits per second. In addition, a distinguishing feature is its small hardware design. A hardware implementation, which includes encryption, decryption, and the key schedule for 128-bit keys, occupies only 9.66 K gates using a 0.35 µm CMOS ASIC library. This is in the smallest class among all existing 128-bit block ciphers. It perfectly meets the current market requirements in wireless cards, for instance, where low power consumption is essential.

A novel sensor system of denture base type was developed for simultaneous monitoring of salivary pH and tissue temperature in the oral cavity. Fundamental components of the monitoring system, sensor devices and sensor configuration are showed in this paper. The sensor units consist of IrO2 electrode and thermistor circuit implanted in the denture base that is tightly fixed in the oral cavity. The signals are transmitted by PFM-FM telemeter system that can be used for health care of the aged people without restraint of their daily behavior while at work, sleeping and even at exercise. Some of results concerning the basic characteristics of the sensor system and continuously monitored physiological data were obtained from the preliminary experiments. Availability of the whole system and monitoring method was discussed.

In a shared buffer packet switch, a good buffer management scheme is needed to reduce the overall packet loss probability and improve the fairness between different users. In this paper, a novel buffer control scheme called partial sharing and partial partitioning (PSPP) is proposed. The PSPP is an adaptive scheme that can be dynamically adjusted to the changing traffic conditions while simple to implement. The key idea of the PSPP is that part of the buffer space, proportional to the number of inactive output ports, is reserved for sharing between inactive output ports. This portion of buffer is called PS buffer. The residual buffer space, called PP buffer, is partitioned and distributed to active output ports equally. From the analysis results, we only need to reserve a small amount of PS buffer space to get good performance for the entire system. Computer simulation shows the PSPP control is very robust and very close to the performance of pushout (PO) buffer management scheme which is a scheme considered as optimal in terms of fairness and total loss ratio while too complicated for implementation.

LSR (Label Switching Router)s in MPLS (Multiprotocol Label Switching) networks map arriving IP flows into some labels on Layer 2 switching fabric and establish LSP (Label Switching Path)s. By using LSPs, LSRs not only transmit IP datagrams fast by cut-through mechanism, but also solve traffic engineering issue to optimize the delay of some IP datagram flows. So far, we have analyzed the performance of LSR focusing only on the maximum number of LSPs which can be set on Layer 2. In this paper, we will also consider the bandwidth allocated to each LSP and analyze the IP datagram transmission delay and the cut-through rate of LSR. We suppose the label mapping method as the data-driven scheme in the analytical model, so that the physical bandwidth of LSR is shared by both the default LSP for hop-by-hop transmission and the cut-through LSPs. Thus, we will investigate the impact of the bandwidth allocation among these LSPs on the performance.