An improvement of the fiber-optic transceiver having both transmitter and receiver functions of optical time-domain reflectometers is examined. The improvement is achieved by introducing an external optical amplifier without changing the previously reported configuration. The characteristics of the transmitted Q-switched pulse and the receiver gain is studied theoretically and experimentally to estimate the performance improvement. It is found that the introduction of the external optical amplifier is a simple and effective way to the performance improvement.

We sketch two algorithms that solve the undirected st-connectivity problem in a small amount of space. One is due to Nisan, Szemeredy and Wigderson, and takes space O(log3/2n), where n denotes the number of nodes in a give undirected graph. This is the first algorithm that overcame the Savitch barrier on the space complexity of the problem. The other is due to Tarui and this author, and takes space O(sw(G)2 log2 n), where sw(G) denotes the separation-width of a given graph G. Their result implies that the st-connectivity problem can be solved in logarithmic space for any class of graphs with separation-width bounded above by a predetermined constant. This class is one of few nontrivial classes for which the st-connectivity problem can be solved in logarithmic space.

Recently, digital contents are copied easily because of the development of digital technology. So digital watermark technique which aims at copyright protection of digital contents becomes more and more important, and various watermarking methods have been proposed. In this paper, we proposed a method of digital watermark for still image by using wavelet packets, and examine the robustness of the watermarking method against several image processings. This method can be easily applied to the watermark for video because in this method, embedded data are detected without original image. Therefore, we extend the wavelet-based watermarking method to the case of watermark for video.

Maximum Satisfiability Problem (MAX SAT) is one of the most natural optimization problems. Since it is known to be NP-hard, approximation algorithms have been considered. The aim of this survey is to show recent developments of approximation algorithms for MAX SAT.

For measuring high frequency ultrasonic fields which are often spatially distributed and transient, an array probe with small element sensors is highly required. In this paper, we propose a fiber-optic micro-probe array which is based on wavelength-division-multiplexing technique. The element sensor consists of a micro optical cavity of 100 µm long made at the end of optical fiber. Optical path length of the cavity is changed by the applied acoustic field, and the modulation of output light intensity is monitored at another end of the fiber for the information of the acoustic field. Array of sensor elements and a light source as well as a photo detector are connected together by an optical star coupler. The Fabry-Perot resonance wavelength of each sensor element is designed different one another, and the outputs from the sensors are discriminated by sweeping the wavelength of light source with the use of a tunable semiconductor laser. In this paper, the performance of the micro-probe array is discussed experimentally.

Magnetic tape incorporating a soft magnetic alloy film has been developed to reduce the electromagnetic interference (EMI) noise current in an electrical cable. The advantage of the magnetic film compared to a ferrite core is shown using an eddy current loss model. The magnetic film exhibited the expected high-loss characteristics above 30 MHz. Laminated resin gives the tape sufficient strength to be wound inside a cable sheath. The fabricated 60- and 90-µm-thick tape wound along the whole cable length exhibited noise reduction ratios of 4 to 5 dB for both radiated emission in the range from 30 to 300 MHz, and surge immunity with a magnetic substance whose volume was one-sixth that of a conventional ferrite core. The tape also exhibited no significant degradation in the mechanical and environmental tests and showed the practical durability.

Although in recent years, considerable efforts have been exerted on treating the congestion control problems of ABR services in the ATM networks, the focus has been so far mostly on unicast applications. The inclusion of the emerging multicast services in the design of congestion control schemes is still at its infancy. The generic rate-based closed-loop congestion control scheme proposed by the ATM Forum for ABR services suffers from large delay-bandwidth product. VS/VD behavior is therefore proposed by the Forum as an supplement. In this paper, two VS/VD behavior congestion control schemes for multicast ABR services in the ATM networks are examined : forward explicit congestion notification (FECN) and backward explicit congestion notification (BECN). Their performances are analyzed and compared. We further observe that both VS/VD schemes alleviate the problem of consolidation noise and consolidation delay of the RM cells returning from the downstream nodes. The alleviation of consolidation noise and consolidation delay is a major concern of most present researches. Simulation results are also given to support the validity of our analysis and claims.

Graph products have important role in constructing many useful networks. It is known that there are four basic graph products. Properties of each product have been studied individually. We propose a unified approach to these products based on the distance in graphs, and new two products on graphs. The viewpoint of products based on the distance introduced here provides a family of products that includes almost known graph products as extremal ones and suggests new products. Also,we study relations among these six products. Finally, we investigate several classes of graph products in those context.

A new sensing method for measuring directly flow velocity by using low coherence interference techniques is proposed and demonstrated. In this method, a temporally fluctuating signal, not the Doppler frequency shift, is detected. Theoretical analysis shows that a spectrum of light backscattered from a particle takes a Gaussian form whose width is simply proportional to the flow velocity. The measured velocity is in good agreement with the actual flow velocity derived from the flow rate. The dynamic range of this sensing method is governed by the frequency range of the FFT processor used and is estimated to be 1.4 10-4 14 m/s. The depth position can be adjusted with an accuracy of approximately 30 µm which is determined by the coherence length of the light source. The velocity distribution along the depth is easily measured by changing mechanically the length of the reference arm in the low coherence interferometer.

We review public-key cryptosystems from lattice problems, which are inspired by Ajtai's remarkable result, and consider their security from the point of view of both theory and practice. We also survey recent results on the power of the lattice reduction algorithm in cryptanalysis.

The wavelength demultiplexer, using cascaded optical fiber gratings and circulators, was proposed and developed for application to optically amplified wavelength-division multiplexing (WDM) submarine cable systems with 100 GHz channel spacing. Our proposed demultiplexer cannot only achieve high wavelength selectivity, small excess loss and effective allocation of dispersion compensation fibers for each channel, but also be upgraded without affecting other existing channels. By using this demultiplexer, it has been successfully confirmed that 8 WDM channels were demultiplexed even after 6,000 km transmission including separate compensation of accumulated chromatic dispersion in each channel.

In the phase locked loop (PLL) frequency synthesizer which is used in a higher frequency region, the prescaler method is employed in order to increase the operating frequency of the programmable divider. However, since the fixed divider whose division ratio is same as the prescaler is installed at the following stage of the reference divider, the reference frequency is decreased and the performance of the PLL frequency synthesizer is degraded. The prescaler PLL frequency synthesizer using multi-programmable divider is one of the counter measures answering the request. In this paper we propose the reduction of the number of programmable dividers by using the (N+1/2) programmable divider. The effectiveness of the proposed method is confirmed by experimental results.

This paper deals with two-processor scheduling for general acyclic SWITCH-less program nets with random node firing times. First, we introduce a hybrid priority list L* that has been shown to generate optimal schedules for the acyclic SWITCH-less program nets with unity node firing times, of which AND-nodes possess at most single input edge. Then considering the factors of existence of the AND-nodes with two input edges as well as random node firing times, we extend L* to design a new dynamic priority list Ld and four static priority lists {Lsii=1,2,3,4}; and then combining Ld and Lsi (i=1,2,3,4) we propose four hybrid priority lists {L*ii=1,2,3,4}. Finally, we apply genetic algorithm to evaluate the schedules generated by the four lists through simulations on 400 program nets. Our simulation results show two of the four lists can generate reasonably good schedules.

Metallic pair lines transmitting high-frequency information signals above several tens MHz are often used without being twisted, as flat floor cable installed in buildings, ribbon-type cables installed in computer equipment, and traces in printed circuit boards. However, the conversion characteristics of untwisted unbalanced metallic pair lines connecting unbalanced circuits have not been investigated over a wide range of frequencies in the MHz region. First, we developed a method to estimate effective power conversion factors using a cascade connection of F matrices, where the unbalance in impedance and admittance of each pair line is distributed uniformly along the line. As a result some useful information was obtained about the balance-unbalance conversion characteristics of the effective power which can be used to suppress EMI phenomena in wiring, especially over several decades of high frequencies. Next, we attempted to apply the conversion characteristics of untwisted unbalanced pair lines obtained at frequencies below several MHz to techniques for searching for the return circuits of conductors installed in buildings. It was clarified experimentaly that the depth of the equivalent ground plane can be estimated by comparing the measured conversion values of TV feeder lines installed at the place being tested with reference values measured in advance on a copper plate .

The connectivity augmentation problem asks to add to a given graph the smallest number of new edges so that the edge- (or vertex-) connectivity of the graph increases up to a specified value k. The problem has been extensively studied, and several efficient algorithm have been discovered. We survey the recent development of the algorithms for this problem. In particular, we show how the minimum cut algorithm due to Nagamochi and Ibaraki is effectively applied to solve the edge-connectivity augmentation problem.

Characteristics of an FBG hydrophone are described under various conditions. The developed FBG hydrophone detects an acoustic field in water with good performances: linear response,high sensitivity,high stability,wide dynamic range as large as 90 dB and wide operation frequency range from a few kHz to a few MHz. A WDM FBG hydrophone consisting of two FBGs in serial connection can detect simultaneously amplitudes and phases of acoustic fields at different points,which in turn allows a directive measurement of an acoustic field in water.

This paper proposes a new self-healing scheme that differentiates the bandwidth requirement for each network service on ATM networks. First, we show the necessity of our proposed scheme. In the future network, we must satisfy two demands, rapid restoration from failure and differentiated bandwidth requirements. The conventional restoration scheme, called the self-healing scheme, realizes rapid restoration, but does not support bandwidth differentiation; the new self-healing scheme proposed herein does. We also show that the proposed scheme reduces the spare resources required for backup. The scheme can be realized as a simple extension of the conventional self-healing scheme. Finally, simulations show that the proposed scheme requires fewer spare resources while offering comparable restoration time to the conventional approach against any demand pattern.

This paper describes how voltage fluctuation in the DC power supply of a digital IC can be reduced, by means of molding the package-pin in a ferrite-resin composite. The voltage fluctuation of the DC power supply, when the input terminal was driven by a 40 MHz, 5 Vp-p pulse wave, was measured using an oscilloscope. Simultaneously, the voltage spectrum of the fluctuation was measured using a spectrum analyzer. As a result, the voltage fluctuation was decreased by about 50 % when the IC package-pins were molded in a ferrite-resin composite, in which the µiac of the ferrite powder equalled 100, and the powder content was 80 weight-%. In the same IC, there was the reduction effect of the voltage spectrum of the fluctuation was recognized in the frequency range 40 MHz to 1 GHz.

Satellite-terrestrial (ST) networks, in which many nodes are interconnected by both satellite and terrestrial networks, can efficiently support multicast services. This is because satellite broadcasting is suitable for a large multicast group and a terrestrial network is suitable for a small multicast group. An ST network requires a multicast routing algorithm that can select the appropriate satellite and terrestrial routes. Conventional dynamic routing algorithms for terrestrial networks cannot construct an efficient multicast routing tree because they basically select a less-expensive route when a node is added. We have developed a dynamic routing algorithm, a virtual-cost-based algorithm, for ST networks that selects the route to use according to the multicast group size when a node is added to the group. Simulation showed that the proposed algorithm is advantageous when nodes are added to or removed from the multicast group during steady-state simulation.

A radiated immunity test method using fields in a three-dimensional Helmholtz-coil set is described. The incident field to equipment under test (EUT) is generated by an orthogonally structured three sets of Helmholtz coil. Using this structure, the resultant field can be generated with arbitrary amplitude and direction. Therefore, the three dimensional immunity characteristics of an EUT can be cleared. The resultant field is calculated numerically and it is established that the field distribution is uniform inside the three dimensional Helmholtz-coil set. This is also confirmed through comparison with measured results. As an example, the immunity test of a cathode ray tube (CRT) display is made and the immunity map of CRT is obtained without reseting placement of EUT. Such map makes us understand the physical meaning and weak points.