We describe a construction of a class of Optical Orthogonal Codes with maximum correlation 1. The construction can be used for constant weight code vectors. The cardinality of the constructed code is larger than known lower bounds.

OFDM modulation has attracted attention for fourth-generation mobile communication systems and high-speed wireless LANs. However, it has a very serious problem of large peak power. PTS (partial transmit sequences) has been proposed as one solution to this problem. In PTS, the OFDM subcarriers are divided into several clusters, and the phase of each cluster is rotated by a complex weight to minimize the PAPR (peak-to-average power ratio). However, the weight of the phase rotation must be sent to the mobile terminal by using a side information channel. In this paper, we propose two weight estimation methods at the receiver to avoid weight transmission in side information channels. The first method uses pilot signals, while the second is a blind estimation method that changes the weight pattern. We evaluate the performance of these methods by computer simulation.

The concept of a "standardized brain" is familiar in modern functional neuro-imaging techniques including PET and fMRI, but it has never been adopted for optical imaging studies that deal with a regional cortical area rather than the whole brain. In this paper, we propose a "standardized barrel cortex" for rodents, and present a method for mapping optically detected neural activity onto the standard cortex. The standard cortex is defined as a set of simple cortical columns, which are modeled on the cytoarchitectonic patterns of cell aggregates in cortical layer IV of the barrel cortex. Referring to its underlying anatomical structure, the method warps the surface image of individual cortices to fit the standard cortex. The cortex is warped using a two-dimensional free-form deformation technique with direct manipulation. Since optical imaging provides a map of neural activity on the cortical surface, the warping consequently remaps it on the standard cortex. Data presented in this paper show that somatosensory evoked neural activity is successfully represented on the standardized cortex, suggesting that the combination of optical imaging with our method is a promising approach for investigating the functional architecture of the cortex.

The requirement to realize large-capacity, high-speed and guaranteed Quality of Service (QoS) communications in IP networks is a recent development. A technique to satisfy these requirements, Multi-Protocol Label Switching (MPLS) is the focus of this paper. In the future, it is expected that congestion and faults on a Label Switched Path (LSP) will seriously affect service contents because various applications are densely served in a large area. In MPLS, however, methods to solve these problems are not clear. Therefore, this study proposes a concrete traffic engineering method to avoid heavy congestion, and at the same time, endeavors to realize a fault-tolerant network by autonomous restoration, or self-healing.

We propose new lossless medical image compression method based on hierarchical sorting technique. Hierarchical sorting is a technique to achieve high compression ratio by detecting the regions where image pattern varies abruptly and sorting pixel order by its value to increase predictability. In this method, we can control sorting accuracy along with size and complexity. As the result, we can reduce the sizes of the permutation-tables and reuse the tables to other image regions. Comparison using experimental implementation of this method shows better performance for medical image set measured by X-ray CT and MRI instruments where similar sub-block patterns appear frequently. This technique applies quad-tree division method to divide an image to blocks in order to support progressive decoding and fast preview of large images.

In this paper we discuss how one can delegate his power to authenticate or sign documents to others who, again, can delegate the power to someone else. A practical cryptographic solution would be to issue a certificate that consists of one's signature. The final verifier checks verifies the chain of these certificates. This paper provides an efficient and provably secure scheme that is suitable for such a delegation chain. We prove the security of our scheme against an adaptive chosen message attack in the random oracle model. Though our primary application would be agent systems where some agents work on behalf of a user, some other applications and variants will be discussed as well. One of the variants enjoys a threshold feature whereby one can delegate his power to a group so that they have less chance to abuse their power. Another application is an identity-based signature scheme that provides faster verification capability and less communication complexity compared to those provided by existing certificate-based public key infrastructure.

The backward direction Soft Output Viterbi Algorithm (a backward SOVA) is compared with the conventional SOVA (a forward SOVA) in turbo code decoding. We find noticeable performance improvement for the backward SOVA when it is not terminated, which turns out to be due to a smaller reliability value, indicating that the termination conditions of the turbo encoder strongly affect the performance of the backward SOVA decoder. We also propose a hardware efficient serially mixed SOVA decoder composed of a forward SOVA decoder and a backward SOVA decoder. Simulation results show that the proposed serially mixed SOVA decoder has a 0.2 dB coding gain at 2.0 dB Eb/No over the forward SOVA for a typical turbo code example.

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.

We propose a new and fast full search (FS) motion estimation algorithm for video coding. The computational reduction comes from sequential rejection of impossible candidates with derived formula and subblock norms. Our algorithm reduces more the computations than the recent fast full search (FS) motion estimation algorithms.

A 2D photonic crystal surface-emitting laser using a triangular lattice is developed, and current-injected lasing oscillation is demonstrated. From consideration of the Bragg diffraction condition in the 2D triangular-lattice structure, it is shown that the 2D coupling phenomenon occurs in the structure. As a result of the 2D periodicity of the structure, the longitudinal mode and lateral mode can be controlled, and stable single-mode oscillation is possible over a large 2D area. The lasing mode of the structure is analyzed by calculating the photonic band diagram by the 2D plane-wave expansion method, and we show that four band edges at which the lasing oscillation can occur exist at the Γ point. Current-injected lasing oscillation is successfully demonstrated at room temperature under pulsed conditions. The threshold current density is 3.2 kA/cm2 and the lasing wavelength is 1.285 µm. From the near-field and far-field patterns, it is shown that large-area 2D (diameter 480 µm) lasing oscillation occurs in the device and the divergence angle is very narrow (less than 1.8). We also demonstrate the correspondence between the measured lasing wavelengths and calculated band diagram by comparing the polarization characteristics with the calculated distribution of the electromagnetic field. The results indicate that 2D coherent lasing oscillation occurs due to the multi-directional coupling effect in the 2D photonic crystal. Finally, we show that the polarization patterns of the lasers can be controlled by introducing artificial lattice defects from the theoretical calculation.

The vertical-cavity surface-emitting laser (VCSEL) is becoming a key device in high-speed optical local-area networks (LANs) and even wide-area networks (WANs). This device is also enabling ultra parallel data transfer in equipment and computer systems. In this paper, we will review its physics and the progress of technology covering the spectral band from infrared to ultraviolet by featuring materials, fabrication technology, and performances such as threshold, output power, polarization, modulation and reliability. Lastly, we will touch on its future prospects.

An algorithm based on the wavelet transform (WT) was developed to analyze the QRS complex in a three-dimensional magnetocardiogram (3-D MCG) recorded from 3 normal subjects and 1 patient with anterior myocardial infarction (MI). By using a wavelet equivalent filter constructed with the WT algorithm, the high frequency components of the QRS complex related to the late fields (LF) were detected for the patient with anterior MI at different scale. We quantified the high frequency components of the QRS complex by calculating root-mean-square (RMS) value at different scale. The LF mainly existed in the frequency band of about 35.5 to 110.5 Hz with the amplitude of about 0.1 to 0.4 pT for Bx, By, and Bz components. In order to discuss the activities of the heart between the normal subject and the patient with anterior MI, we have also evaluated the spatial energy distribution (SED) of the QRS complex by displaying isoenergy contour maps at different scale. Being different from the normal subject, the patient with anterior MI represented different the pattern of the SED in various frequency band for the ST segment of the QRS complex of Bx, By, and Bz components. It is efficient to use the WT algorithm for analyzing the QRS complex in the 3-D MCG.

In this paper, we propose a method to reconstruct current distributions in the human brain from neuromagnetic measurements. The proposed method is based on the weighted lead-field synthetic (WLFS) filtering technique with the weighting factors calculated from the results of previous source space scanning. In this method, in addition to the depth normalization technique, weighting factors of the WLFS are determined by the cost values previously calculated based on the multiple signal classification (MUSIC) scan. We performed computer simulations of this method under noisy measurement conditions and compared the results to those obtained with the conventional WLFS method. The results of the simulations indicate that the proposed method is effective for the reconstruction of the current distributions in the human brain using magnetoencephalographic (MEG) measurements, even if the signal-to-noise ratio of the measured data is relatively low. We applied the proposed method to the magnetoencephalographic data obtained during a mental image processing task that included object recognition and mental rotation operations. The results suggest that the proposed method can extract the neural activity in the extrastriate visual region and the parietal region. These results are in agreement with the results of previous positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) studies.

A digest is provided of work carried out at the Institute of Cancer Research to develop freehand elastography and apply it to breast investigations. Topics covered include the development of freehand elastography and its relationship to other methods, a description of the system for off-line clinical evaluation of the freehand method, comparison of the physical performances of freehand and mechanical elastography, early clinical results on 70 breast tumours, real-time imaging, quantitative elastography and psychophysical aspects of the detection and assessment of elastic lesions. Progress in developing this new medical imaging modality is occurring rapidly throughout the world and its future looks promising.

This paper presents a method for detection of calcification, which is an important early sign of breast cancer in mammograms. Since information of calcifications is located in inhomogeneous background and noises, it is hard to be detected. This method uses wavelet packet transform (WPT) for elimination of the background image related to low frequency components. However, very high frequency signals of noises exist with the calcifications and make it hard to suppress them. Since calcification location can be represented as vertical, horizontal, and diagonal edges in time-frequency domain, the edges in spatial domain can be utilized as a filter for noise suppression. Then the image from inverse transform will contain only required information. A free-response operating characteristic (FROC) curve is used to evaluate a performance of proposed method by applying it to thirty images of calcifications. The results show 82.19 percent true positive detection rate at the cost of 6.73 false positive per image.

Fast packet switches for variable-size packets have become an everyday necessity with the rapid growth in the volume of Internet traffic. Such switches can be designed in two different ways, either by segmenting packets into smaller fixed-size cells and designing packet switches for such cells, or by designing generic packet switches for variable-size packets, where packet segmentation and reassembly can be omitted. The second option is investigated in this paper. The synchronous operation mode with time-limited bulk service is selected. The switching fabric is assumed to be internally non-blocking and provided with input queues. A previous maximum switch throughput analysis has been done under the assumption that the length of the time slot is fixed set to its minimum allowed value (Tmin). In this work, a so-called time-slot stretch factor (SF) is introduced. The actual time-slot length is determined by multiplying Tmin with the SF, where SF. Next, a so-called Internet traffic-source model is proposed based on findings from real IP traffic measurements. The performance implications of the proposed time-slot length modification are analyzed by discrete-event computer simulation. The maximum switch throughput is increased by increasing the SF value, e.g. for uniform packet size distribution and SF=10, the maximum switch throughput is increased from 75% to 97%. The influence of the traffic-source characteristics on the maximum switch throughput is decreased when SF value is increased. In order to prevent any possible throughput degradations, it is advisable to use integer SF values. Packet delay analysis has revealed that by increasing the SF value, the mean packet delay is also increased. Nevertheless, it is shown that the number of switch input and output ports is the most important factor to be considered when packet delay is at stake. Service class differentiation inside investigated packet switch is possible and is not affected by the increasing SF value. Such a packet switch is suitable for implementation in wide area networks, due to high transmission speeds and the small number of switch ports.

Besides single byte errors which are caused by single chip failures, semiconductor memories used in some applications, such as satellite memory systems, are highly vulnerable to random double bit errors. It is therefore necessary to design Double bit Error Correcting--Single b-bit byte Error Correcting (DEC-SbEC) codes which correct both random double bit errors and single b-bit byte errors. This correspondence proposes a class of generic DEC-SbEC codes that are applicable to computer memory systems using recent high density DRAM chips with wide I/O data, such as, 8, 16 or 32 bits per chip. The proposed DEC-S8EC codes are suitable for memory systems using DRAM chips with 8-bit I/O data, and require 24 check bits for practical information lengths such as 64 and 128 bits.

In this paper, a design method of neural-net based PID controllers is proposed for multivariable nonlinear systems with mutual interactions. The proposed method adopt both a static pre-compensator and some multi-layered neural networks. The former is used for roughly decoupling the controlled object, and the latter is used in order to improve decoupling and to linearize the approximately decoupled controlled object. Also the design scheme based on the relationship between PID law and the generalized minimum variance control (GMVC) law is adopted. The effectivenes of the proposed control scheme is evaluated on a simulation example.

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.

Improvement of the absorbing boundary conditions for triangle-hexagonal dual cell grids in the time domain method is described in this paper. The magnetic field components, which are evaluated by the electric fields at the circumcenters of the triangle cells, are conformed to Berenger's perfectly matched layer absorbing boundary conditions. The electric field is linearly interpolated by the fields at the vertices. The lower reflection coefficients in the frequency range for the equilateral and non-equilateral triangle cells are demonstrated.