The crosstalk characteristics of a long-wavelength monolithically integrated photoreceiver array are analyzed. The device consists of an array of transimpedance photoreceivers fabricated on a semi-insulating InP substrate. The distance between the photodetectors is large enough to suppress the photonic crosstalk. Therefore, the crosstalk of the device is mainly due to signal propagation from the channels through the power line shared by each channel on the chip. This crosstalk is inevitable to the photoreceiver arrays which employ common power lines. The magnitude of the crosstalk largely depends on the impedance of the power-supply circuit outside the chip. The crosstalk spectrum often has a peak and recess structure. The crosstalk peak at the edge of the operating band-width is due to the resonance characteristic of the transimpedance amplifier. The other peak and recess structures on the spectrum are due to the resonance phenomena of on-chip and off-chip capacitors and inductance on the power-supply line outside the chip. This crosstalk can be reduced by using on-chip bypass capacitance and dumping resistance. However, the resonance due to the capacitance and inductance on the power-supply circuit outside the chip can't be controlled by the on-chip components. Therefore, an optimized design for the power supply circuit outside the chip is also indispensable for suppressing crosstalk.

This paper presents an improved current-mode circuit for implementation of a chaotic neuron model. The proposed circuit uses a switched-current integrator and a nonlinear output function circuit, which is based on an operational transconductance amplifier, as building blocks. Is is shown by SPICE simulations and experiments using discrete elements that the proposed circuit well replicates the behavior of the chaotic neuron model.

We found degraded output power due to discoloration of an abnormal epitaxial layer caused by supercooling of residual melt in liquid phase epitaxy (LPE) process of AlGaAs/GaAs heteroface solar cells developed to improve conversion efficiency of solar cells for satellites. We studied the discoloration mechanism and found effective methods for obtaning a good epitaxial layer. Using these results, we manufactured about 80,000 pieces of solar cells and employed them in the Japanese domestic Communication Satellite-3 (CS-3) launched by National Space Development Agency of Japan (NASDA). Five years after launch, these solar cells are still supplying the output power than predicted. This paper describes reliability improvements for the surface of epitaxial layer and successful results aftes 5 years of space operation.

Non-homogeneous Poisson Processes (NHPP's) can be applied for analyzing reliability growth models for hardware and/or software. Evaluating the Mean Time Between Failures (MTBF's) for such processes, we can evaluate the present status (the degree of improvement). However, it is difficult to evaluate the MTBF's for such processes analytically except the simplest cases. The so-called instantaneous MTBF's which can be easily evaluated are applied in practice instead of the exact MTBF's. In this paper, we discuss both MTBF's analytically, and derive the conditions for the existence of both exact and instantaneous MTBF's. We further illustrate both MTBF's for the Weibull process and S-shaped reliability growth model numerically.

In this paper, we investigate the knowledge complexity of interactive proof systems and show that (1) under the blackbox simulation, if a language L has a bounded move public coin interactive proof system with polynomially bounded knowledge complexity in the hint sense, then the language L itself has a one move interactive proof system; and (2) under the blackbox simulation, if a language L has a three move private coin interactive proof system with polynomially bounded knowledge complexity in the hint sense, then the language L itself has a one move interactive proof system. These results imply that as long as the blackbox simulation is concerned, any language L AM＼MA is not allowed to have a bounded move public coin (or three move private coin) interactive proof system with polynomially bounded knowledge complexity in the hint sense unless AM = AM. In addition, we present a definite distinction between knowledge complexity in the hint sense and in the strict oracle sense, i.e., any language in AM (resp. IP) has a two (resp. unbounded) move public coin interactive proof system with polynomially bounded knowledge complexity in the strict oracle sense.

This paper describes an indexing framework for adaptive arrangement of mechanics problems in ITS (Intelligent Tutoring System). There have been some studies for adaptive arrangement of problems in ITS. However, they only choose a solution method in order to characterize a problem used in the practice. Because their target domains have been sufficiently formalized, this kind of characterization has sufficed to describe the relations between any two problems of such a class. In other words, here, it is enough to make students understand only the solution methods for the given class of problems. However, in other domains, it is also important to understand concepts used in the problems and not only to understand solution methods. In mechanics problems, concepts such as mechanical objects, their attributes, and phenomena composed of the objects and the attributes also need to be taught. Therefore, the difference between solution methods applied is not sufficient to describe the difference between two given problems. To use this type of problems properly in the practice, it is necessary to propose an advanced new characterization framework. In this paper, we describe a mechanics problem with three components: (1) surface structure, (2) phenomenon structure, (3) solution structure. Surface structure describes surface features of a problem with mechanical objects, their configuration, and each object's attributes given or required in the problem. Phenomenon structure is described by attributes and operational relations among them included in the phenomenon specific to the surface structure. Solution structure is described by a sequence of operational relations which compute required attributes from given attributes. We call this characterizing indexing because we use it as index of each problem. This paper also describes an application of the indexing to arrangement of problems. We propose two mechanisms of control: (a) reordering of a problem sequence, and (b) simplifying of a problem. By now, we have implemented basic functions to realize the mechanisms except for the part of interface.

It is important for LSI system designers to estimate computational errors when designing LSI's for numeric computations. Both for the prediction of the errors at an early stage of designing and for the choice of a proper hardware configuration to achieve a target performance, it is desirable that the errors can be estimated in terms of a minimum of parameters. This paper presents a theoretical error analysis of multiply-accumulation implemented by distributed arithmetic(DA) and proposes a new method for estimating the mean-squared error. DA is a method of implementing the multiply-accumulation that is defined as an inner product of an input vector and a fixed coefficient vector. Using a ROM which stores partial products. DA calculates the output by accumulating the partial products bitserially. As DA uses no parallel multipliers, it needs a smaller chip area than methods using parallel multipliers. Thus DA is effectively utilitzed for the LSI implementation of a digital signal processing system which requires the multiply-accumulation. It has been known that, if the input data are uniformly distributed, the mean-squared error of the multiply-accumulation implemented by DA is a function of only the word lengths of the input, the output, and the ROM. The proposed method for the error estimation can calculate the mean-squared error by using the same parameters even when the input data are not uniformly distributed. The basic idea of the method is to regard the input data as a combination of uniformly distributed partial data with a different word length. Then the mean-squared error can be predicted as a weighted sum of the contribution of each partial data, where the weight is the ratio of the partial data to the total input data. Finally, the method is applied to a two-dimensional inverse discrete cosine transform (IDCT) and the practicability of the method is confirmed by computer simulations of the IDCT implemented by DA.

This paper is concerned with the continuous relation between models of the plant and the predicted performances of the system designed based on the models. To state the problem more precisely, let P be the transfer matrix of a plant model, and let A be the transfer matrix of interest of the designed system, which is regarded as a performance measure for evaluating the designed responses. A depends upon P and is written as A=A(P). From the practical point of view, it is necessary that the function A(P) should be continuous with respect to P. In this paper we consider the linear quadratic optimal servosystem with integrators (LQI) scheme as the design methodology, and prove that A(P) depends continuously on the plant transfer matrix P if the topology of the family of plants models is the graph topology. A numerical example is given for illustrating the result.

An efficient algorithm is presented for finding all solutions of piecewise-linear resistive circuits. In this algorithm, a simple sign test is performed to eliminate many linear regions that do not contain a solution. This makes the number of simultaneous linear equations to be solved much smaller. This test, in its original form, is applied to each linear region; but this is time-consuming because the number of linear regions is generally very large. In this paper, it is shown that the sign test can be applied to super-regions consisting of adjacent linear regions. Therefore, many linear regions are discarded at the same time, and the computational efficiency of the algorithm is substantially improved. The branch-and-bound method is used in applying the sign test to super-regions. Some numerical examples are given, and it is shown that all solutions are computed very rapidly. The proposed algorithm is simple, efficient, and can be easily programmed.

The structural necessary and sufficient condition for "the transition-liveness means the place-liveness and vice-versa" of a subclass NII of general Petri nets is given as "the place and transition live Petri net, or PTL net, ÑII". Furthermore, "the one-token-condition Petri net, or OTC net, II" which means that every MSDL (minimal structural deadlock) is "transition and place live" under at least one initial token, i.e., II is "transition and place live" under the above initial marking. These subclasses NII, ÑII( NII), and II(ÑII) are almost the general Petri nets except at least one MSTR(minimal structural trap) and at least one pair of "a virtual MSTR or a virtual STR" and "a virtual MSDL" of an MBTR (minimal behavioral trap) in connection with making an MSDL transition-live.

It is often desired to change the cutoff frequencies of digital filters in some applications like digital electronic instruments. This paper proposes a design of variable lowpass digital filters with wider ranges of cutoff frequencies than conventional designs. Wave digital filters are used for the prototypes of variable filters. The proposed design is based on the frequency scaling in the s-domain, while the conventional ones are based on the z-domain lowpass-to-lowpass transformations. The first-order approximation by the Taylor series expansion is used to make multiplier coefficients in a wave digital filters obtained from a frequency-scaled LC filter become linear functions of the scaling parameter, which is similar to the conventional design. Furthermore this paper discusses the reduction of the approximation error. The curvature is introduced as the figure of the quality of the first-order approximation. The use of the second-order approximation to large-curvature multiplier coefficients instead of the first-order one is proposed.

Experimental evidence of a two-step enhancement in electromigration lifetime is presented through pulsed testing that extends over a wide frequency range from 7 mHz to 50 MHz. It is also found, through an accompanying failure analysis, that the failure mechanism is not affected by current pulsing. Test samples were the lowew metal lines and the through-holes in double-level interconnects. The same results were obtained for both samples. The testing temperature of the test conductor was determined considering the Joule heating to eliminate errors in lifetime estimation due to temperature errors. A two-step enhancement in lifetime is extracted by normalizing the pulsed electromigration lifetime by the continuous one. The first step occurs in the frequency range from 0.1 to 10 kHz where the lifetime increases with (duty ratio)-2 and the second step occurs above 100 kHz with (duty ratio)-3. The transition frequency in the first-step enhancement shifts to the higher frequency region with a decrease in stress temperature or an increase in current density, whereas the transition frequency in the second step is not affected by these stress conditions. The lifetime enhancement is analyzed in relation to the relaxation process during the current pulsing. According to the two-step behavior, two distinct relaxation times are assumed as opposed to the single relaxation time in other proposed models. The results of the analysis agree with the experimental results for the dependence on the frequency and duty ratio of pulses. The two experimentally derived relaxation times are about 5 s and 1 µs.

This paper presents two approaches for computing the reliability of complex networks subject to two kinds of failure, open failure and shorted failure. The reliabilities of some series-parallel networks are considered by many analysts. However a practical system is more complex. The methods given in this paper can be applied not only to a series-parallel network but also to a non-series-parallel network which is composed of non-identical and independent components subject to two kinds of failure. This paper also deals with a network subject to flow quantity constraint such as the one which is required to control j or more separate paths. For such a system it is difficult to obtain system reliability because the number of states to be considered in this system is extremely large compared to a conventional 2-state device system. In this paper we obtain the reliabilities for such systems by a combinatorial approach and by a simulation approach.

In 1963, the authors began to develop a tuning circuit (hereafter referred to as the 'circuit') consisting of an inductor, fixed capacitors and a variable capacitor. The circuit required very high accuracy and stability, and the aging influence on resonant frequency needed to be Δf/f0 0.12% for 20 years. When we started, there was no methodology available for designing such a long-term stable circuit, so we reinvestigated our previous studies concerning aging characteristics and formed a design concept. We designed the circuit by bearing in mind that an inductor was subject to natural and stress demagnetization (as indicated by disaccommodation), and assumed that a capacitor changed its characteristics linearly over a logarithmic scale of time. (This assumption was based on short-term test results derived from previous studies.) We measured the aging characteristics of the circuits at room temperature for 20 years, from 1966. The measurement results from the 20-year study revealed that the aging characteristics predicted by the design concept were reasonably accurate.

In this paper we investigate the AM languages that seem to be located outside NP co-NP. We give two natural examples of such AM languages, GIP and GH, which stand for Graph Isomorphism Pattern and Graph Heterogeneity, respectively. We show that the GIP is in ΔP2 AM co-AM but is unlikely to be in NP co-NP, and that GH is in ΔP2 AM but is unlikely to be in NP co-AM. We also show that GIP is in SZK. We then discuss some structural properties related to those languages: Any language that is polynomial time truth-table reducible to GIP is in AM co-AM; GIP is in co-SZK if SZK co-SZK is closed under conjunctive polynomial time bounded-truth-table reducibility; Both GIP and GH are in DP. Here DP is the class of languages that can be expressed in the form X Y, where X NP and Y co-NP.

This paper presents a zero-knowledge interactive protocol that demonstrates two factors a and b of a composite number n (=ab) are really known by the prover, without revealing the factors themselves. Here the factors a and b need not be primes. The security of the protocol is based on the difficulty of computing discrete logarithms modulo a large prime.

As promising copy networks of very large multicast switching networks for Broadband ISDN, multi-stage Recursive Copy Networks (RCN) have been proposed recently. In the multicast switch structure, the RCN precedes a point-to-point switch. At an RCN, all the copies of a master cell are generated recursively, i.e., a few copies of the master cell are made initially, and by considering each of these copies to be master cells, more copies are made which, in turn, are again considered to be master cells to make still more copies, the process thus progressing recursively till all the required copies are made. By this principle of recursive generation of copies, the number of copies that can be generated is independent of the hardware size of the RCN. A limitation of RCNs is that buffer sizes at all stages except the first stage have to be large so as to keep the cell loss due to buffer overflow within desired limits. This paper inspects a flow control scheme by which the probability of buffer overflow can be kept low, even though the buffer sizes at later stages are not large. Under this flow control procedure, a cell is not transmitted from a stage to the succeeding stage, if the occupancy level of the buffer of the succeeding stage exceeds a threshold. We study by simulation the performance aspects of such a flow control scheme in RCNs under cut-through switching scheme and under store-and-forward switching scheme. At high load intensities, the overflow probability can be reduced by an order of magnitude in 2-stage RCNs and by two orders of magnitude in 3-stage RCNs. To restrict the overflow probability within a given limit, the required buffer size is less under flow control than under no flow control. The implementation of the flow control is simple and the control overhead is small, thereby making the scheme attractive for implementation in high speed switching environments. Further, the proposed flow control scheme does not disturb the cell sequence.

In this paper, we present some novel concepts and photonic devices for use in optical interconnects. First, we review the progress of surface emitting lasers while featuring materials and performances including thresholds, power output, RIN, linewidth, and so on. Advanced technology for aiming at spontaneous emission control, photon recycling, polarization control, wavelength tuning, integration etc. will be considered. Then we touch on some other possible devices for optical interconnects. Lastly, we discuss on lightwave subsystems applying these devices and concepts.

This paper describes the current situations and future directions of intelligent CAI researches/development in Japan. Then necessity of intelligence in CAIs/Educational systems are thought over corresponding to the model of teaching and the cognitive model of human learning like the situated learning, knowledge construction and so on. Originally, the main aims of ITSs/ICAIs are to tealize the high level environment of individual teaching/learning. So it is the most important to incorporate the intellectual function of teaching into the system. Whatever kinds of teaching purposes ITSs have, they have the quite complex structure which consists of the domain knowledge base (Expert system), student model, the tutoring knowledge base, the powerful human interface, and sophisticated inference engine with plural functions by artificial intelligence technology. In this paper, the technological and educational points of view are discussed, surveyed and summarized based on intelligent teaching functions of ITSs/ICAIs. Moreover, the meaning of new paradigm from ITSs to ILE are mentioned under the new technology of networking and multi-media.

This paper describes the effective countermeasures for exfoliation of large-sized ceramic capacitors, deterioration of dummy resistors and developement of a spark sensor with UVtrons at 300-500 kW transmitting stations. Cracks and exfoliation were found at the electrode of large-sized ceramic capacitors in the output circuit of the 500 kW transmitter. The exfoliation was caused by the temperature rise and the thermal fatigues at the electrode with the Nickel plating including Irons. A pure Nickel-plated electrode including no Irons and a new soldering method using disk-typed solder with a large adhesive area are employed in order to reduce the temperature rise. The temperature rise of the improved capacitor was 18 lower than the conventional one. Deterioration of ELEMA resistors of the 300 kW dummy antenna was discovered. The damage of the resistor was caused by the concentration of the electric current followed by the thermal stress cycle which made mechanical exhaustion at the electrode. Therefore, oval-shaped type resistors with much longer electric current path (20% up) to suppress the concentration of current flow and much slower temperature rise are newly developed. In case that sparks occurred at DC or RF high voltage impressed sections of the high power transmitting equipment, the discharged points could be seriously damaged by the transmitter energy itself. In orded to prevent this, a spark detector using UV (Ultra violet) trons is developed and installed at the matchign circuit of the 500 kW transmitter. Conventional UV sensors with only one UVtron could not detect feeble discharges and sparks with a duration time of less than 150 ms because of false outputs by the back ground noise. Since choosing three out of four UV trons system is employed, possibility producing a false output will be just one to 445 years theoretically. This means extremely reliable and sensitive spark detection system are constructed. These countermeasures have improved reliability of the transmitting equipment greatly. No damages have been found in the transmitters ever since.