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.

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.

Recently, as multimedia and high-speed traffic become more popular on the Internet, the various traffic requiring different qualities of service (QoS) will co-exist. In addition, classified service based on Diff-Serv (Differentiated Service), MPLS (Multi-Protocol Label Switching),etc., have come into wide use. Today's Internet environment requires routers to perform control mechanisms in order to guarantee various QoSs. In this paper, we propose a buffer management scheme for the Internet router that uses class-based priority control. This paper focuses on per-flow queueing, and evaluates the performance of the proposed buffer management scheme. Realization of differentiated services and dissolution of buffer occupation by specific flow is expected by the proposed control.

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.

We have demonstrated active mode hopping suppression in external-cavity semiconductor lasers including a diffraction grating as a wavelength-selecting device. The feedback control nullifies the difference between the oscillation wavelength and selected wavelength based on observed changes in diffraction angle. The control has suppressed mode hopping over a 7.5 times wider span than without control. And when combined with conventional mode hopping suppression techniques, mode-hop-free oscillation is achieved over 130 nm. Our approach can be used for most Littman-type external-cavity semiconductor lasers with simple attachments; it will be useful for continuous wavelength sweeping and for long-term wavelength stabilization.

A tunable external-cavity InGaAs/AlGaAs quantum-well laser using a grating coupler monolithically integrated in a selectively disordered waveguide is demonstrated. The laser consists of an amplifier with a narrow channel for lateral single-mode guiding and a tapered section, a grating coupler for output beam collimation and wavelength dispersion, and an external half mirror. Selective quantum-well disordering technique using SiO2 caps of different thicknesses and rapid thermal annealing was employed to reduce the passive waveguide loss in the grating coupler region. Loss reduction from 40 cm-1 to 3 cm-1 was accomplished. Resultant increase of the grating coupler efficiency and expansion of the effective aperture length led to significant improvement of the laser performances. The maximum output power of 105 mW and wide tuning range of 21.1 nm centered at 997 nm were obtained. The well collimated output beam of full diffraction angles at half maximum of 0.16 0.18 was obtained.

We propose a call admission control (CAC) scheme for the reverse link of direct sequence-code division multiple access (DS-CDMA) systems with multi-class traffic, in which the admissibility of the set of requested channels is decided by checking the outage probability of the total composite power at a cell-site receiver. The reverse link capacities under various traffic conditions are evaluated. From numerical results, we see that the proposed scheme can utilize a given radio resource more effectively as compared with the existing scheme using constraints on the individual power levels.

The differentiated services (Diffserv) architecture is a potential solution for providing quality of service (QoS) on the Internet. Most existing studies focus on providing service differentiation among few service classes. In this paper, we propose an approach which can achieve per-flow weighted fair rate allocation in a differentiated services network. Following the design philosophy of the Diffserv model, in the proposed approach core routers do not need to keep per-flow information. An edge router adjusts the transmission rate of a flow based on the feedback carried on control packets, which are inserted by the ingress edge router and returned by the egress edge router. Core routers periodically estimate the fair share rate of each virtual flow and mark the results in control packets. We use both simulations and analysis to evaluate the performance of the proposed approach. The analytical results show that our approach allows a system to converge to weighted fair rate allocations in limited time. Through the simulation results, we can further validate the analytical results, and demonstrate that better throughput can be achieved.

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.

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.

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.

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 the estimation of effort needed to update program codes according to given design specification changes. In the Object-Oriented incremental development (OOID), the requirement changes occur frequently and regularly. When a requirement change occurs, a design specification is changed accordingly. Then a program code is updated for given design specification change. In order to construct the development plan dynamically, a simple and fast estimation method of efforts for code updating is strongly required by both developers and managers. However, existing estimation methods cannot be applied to the OOID. We therefore try to propose a straightforward approach to estimate effort for code updating, which reflects the specific properties of the OOID. We list up following factors of the effort estimation for OOID: (1) updating activities consist of creation, deletion, and modification, (2) the target to be updated has four kinds of types (void type, basic type, library type, and custom type), (3) the degree of information hiding is classified into private, protected and public, and (4) the degree of inheritance affects updating efforts. We then propose a new formula E(P,σ) to calculate the efforts needed to update a program P according to a set of design specification changes σ. The formula E(P,σ) includes weighting parameters: Wupd, Wtype, Winf-h and Winht according to the characteristics (1), (2), (3) and (4), respectively. Finally, we conduct experimental evaluations by applying the formula E(P,σ) to actual project data in a certain company. The evaluation results statistically showed the validity of the proposed approach to some extent.

In this paper, we propose a new digital signature scheme based on a third order linear feedback shift register for signing documents. This signature scheme is different from most of the signature schemes that are based on discrete logarithm problem, elliptic curves discrete logarithm problem, RSA or quadratic residues. An efficient algorithm for computing kth term of a sequence is also presented. The advantage of this scheme is that the computation is efficient than Schnorr scheme. We also show that the security of the proposed signature scheme is equivalent to that of Schnorr signature scheme.

Technique of Measuring 3-D velocity vector components is important for the correct diagnosis of the blood flow pattern and quantitative assessment of intratumor perfusion. However, present equipment based on ultrasonic Doppler can not provide us true 3-D velocity. To overcome the problem, we previously proposed a new method of 3-D velocity vector measurement. The method uses 2-D array probe and enable us to obtain three components of velocity vector with real time by integrating the Doppler phase shift on the each element with the relative small single aperture compared with conventional method. Basic performance of the method has been evaluated by computer simulation. In this paper, to evaluate the feasibility of the proposed method, experimental investigation using a simple ring array probe and a phantom were carried out. Three components of velocity vector for different velocity magnitude and flow direction were measured. Experimental results validated its ability of measuring 3-D velocity and its feasibility.

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.

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.

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.

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.

In the magnetic stimulation of the peripheral nerve fiber with the figure-of-eight coil, the nerve fiber beneath the figure-of-eight coil is considered to be stimulated with the lowest intensity when it is parallel to the junction of the figure-of-eight coil. However, some experimental studies with the magnetic peripheral stimulation showed that the large compound muscle action potential is elicited with the figure-of-eight coil oriented in the other directions. In the present study, we try to explain the cause of such a discrepancy with the analysis of the model of the magnetic nerve stimulation, and confirm the validity of the result obtained from the model analysis by the experimental study of the magnetic peripheral nerve stimulation. We show that the threshold for the nerve excitation become lowest not only when the junction of the figure-of-eight coil is parallel to the nerve fiber but also when that is perpendicular to the nerve fiber.