This paper deals with the number of solutions of circuit equations of nonlinear resistive circuits composed of linear and nonlinear one-port resistors, dc sources and linear active elements. By referring to the v-i characteristics of real diodes we assume that the second derivative as well as the first derivative of the v-i characteristics of nonlinear resistors is positive. The necessary and sufficient conditions are given for the equation to have a finite number (2n) of solutions and further the extension of this result is discussed.

Josephson integrated circuit technology has progressed remarkably since niobium junctions were introduced in 1983. At present, it is feasible to make LSI level circuits, such as a few thousand gate microprocessor and a few kilobit memory. It has been demonstrated that these circuits are operated with much faster speed and lower power consumption than semiconductor circuits. This paper describes the performance of these circuits.

The R & D of EDTV (Extended Definition TV, or Enhance D TV) in Japan is reviewed. The EDTV is a television system with higher quality video and audio, and at the same time remains compatible with existing standards. First, IDTV (Improve D TV) is reviewed; it achieves better picture quality by sophisticated signal processing at TV receivers within existing standards. The main issue is the reduction of deficiencies caused by the current standards. Then, the EDTV is reviewed. This concept achieves much better picture quality by sending more information through the more efficient utilization of the transmission channel. Since originally proposed, it has been studied nation-wide in Japan under the direction of MPT (Ministry of Post and Telecommunications) with two stages: EDTV- and EDTV-. EDTV- broadcasting began in 1989, under the nickname "Clear-Vision", with IDTV techniques as the key technology for receivers. Proposed ideas and the historical process are reviewed. EDTV- is now under study for higher-resolution and wide-aspect TV with digital audio. The proposed techniques and related technical issues are summarized.

The 1950's was important period for Japanese electronic industry. It embarked in a new enterprise after the defeat of Japan in the World War. Dr. Masamitsu Kawakami of the Tokyo Institute of Technology made a great contribution to the leveling up of the people involved in electronics through his books "Denshikairo I-V". In this paper, activity of Dr. Kawakami in the field of active networks before and during the 1950's are introduced. It includes realization of negative and higher order impedances and the development of the theory of elementary active 2-ports. His works were inherited by the successors including the author. The development of a current inversion negative impedance converter, and its application to active network synthesis is reflected. The influence of these works on the research in the later age is also shown.

There are a number of problems in numerical computation which are of fundamental importance but for which no practicable method has been known. In this paper, problems concerning the norm, the rounding error and the partial differentiation are taken up, and what difficulties they have and why those difficulties have long been standing will be explained. Then, it will be shown that the method of "Fast Automatic Differentiation" which is attracting keen interest of those who are concerned will resolve all those difficulties through an effective method for partial differentiation. There, the concept of "computational graph" plays an important rôle. The relation to interval analysis will also be discussed from the point of view of assuring the quality of results of numerical computation.

The present status and the future prospect of superconducting electronics are briefly overviewed. The progress in Josephson technologies based on refractory superconductors such as Nb and NbN has made it possible to fabricate reliable and high performance in curcuits with LSI complexities. These innovations make superconducting devices in both digital and analog applications more realistic than they used to be. High temperature oxide superconducting devices are now intensively researched and it is needed to solve problems, i.e., single crystal thin films with multilayered structures and well defined interfaces between layers, before realizing useful device structures.

For communication relays, the contact reliability in the low electrical load circuit has been of great importance for the purpose of control of highly reliable electronic devices. With reference to the study of contact failure mechanism, the fact that the formation of black powder on the contact surface caused to increase contact resistance of relays in the organic gas atmosphere was well known. In this study, the electrical characteristics of black powder formed on the relay contacts was investigated in comparison with a sulfide. Cosequently, the interesting relationship between contact resistance and electrical breakdown was obtained. The inflection point was observed in voltage-current (V-I) characteristics for the black powder deposit which was more than 200 mΩ in contact resistance. And when the current increased, there occurred not only a decrease but also an increase in contact resistance. These results indicated that the accurate contact resistance should be evaluated using V-I characteristics. In addition to that, it was proposed that the allowable level of contact resistance for the contact failure was about 150 mΩ for the black powder deposit.

In this paper, we propose a spectral interpolation method using a distortion geodesic line, which is defined as the curve with minimal accumulated distortion. We apply the distortion geodesic line to interpolation of two given spectra (vectors). The first part of this paper describes the definition of the distortion geodesic line. It is shown that a geodesic line is characterized by the Riemannian metric which is introduced as a bilinear form of the second partial derivatives of a given distortion measure. The second part describes an inequality for the WLR measure on several interpolating curves. This inequality guarantees that the accumulated WLR distortion value for any two given spectra, ƒ(0) and ƒ(1), on the correlation interpolation curve, is always smaller than the direct WLR value dWLR(ƒ(0), ƒ(1)). This property is easily extended to a category of several distortion measures. The third part describes an application of the distortion geodesic line to spectral interpolation, and numerically shows that the interpolation line on the correlation parameter is the best of several kinds of LPC based parameters.

A multi-chip superconducting computer named ETL-JC1 has been constructed based on Josephson computer technology developed in the Electrotechnical Laboratory through 1980s. The technology covers various fields such as material and fabrication technology, logic and memory circuit design, and computer archtecture. Some key technologies for making the ETL-JC1 have been developed; niobium (Nb) tunnel junction integration process, LSI logic circuits, memory chips of a 1-kbit ROM and a 1-kbit RAM, the CAD system for Josephson LSI design, and a multi-phase power supply system. The computer system was totally designed by the RISC (reduced instruction set computer) architecture. It consists of four Josephson LSI chips of an arithmetic/logic unit, a sequence control unit, a program memory unit, and a data memory unit, which are essential to execute computer functions. The four chips were fabricated with a 3-µm Nb/Al-oxide/Nb junction integration technology. The ETL-JC1 was constructed by connecting four Josephson LSI chips on a non-magnetic printed circuit board. Test programs were executed on the ETL-JC1 and the correct execution of all the 27 kinds of instruction including memory access, subroutine call/return, and so on, which are sufficient to make and computer program, was confirmed. A total power dissipation was 6.2 mW in whole circuits of the ETL-JC1 consisting of more than 22,000 Josephson junctions. Operation speed of 1 GIPS (Giga-instruction per second) can be expected with a single CPU in this system according to computer logic simulations.

We propose a new type of the digital neuron model by using multi-input multilevel-quanitized digital phase-locked loop (MM-DPLL), where the input is represented by the phase modulated signal. It is shown that this model has the characteristics of the neuron; spatial summation, temporal summation and thresholding. We applied our model to the pattern recognition and to the Hopfield type associative memory, in order to verify that the network by this model can operate properly. In the pattern recognition, we used the perceptron convergence procedure (delta rule), and confirm the possibility of learning by modifying the connection weights. In the associative memory, we confirm that the network can learn five digit patterns of the fundamental memories, and also can recall the correct pattern for the noisy input pattern.

As an application of superconducting devices to electronic engineering, a novel Josephson fuzzy processor is proposed. Since the integrated circuit technologies of superconducting device were successfully developed by using a hard material such as niobium, several kinds of prototype Josephson processor for a general purpose computer have been constructed. Although a Josephson fuzzy processor is a special purpose computer, it is one of the most promising processors suitable for digital application of Josephson elements. The key function of the fuzzy processor is achieved by Mini-Max circuits. In this paper the principle of construction of the Mini-Max circuit using SQUIDs is mainly described in detail and simulation results are illustrated to show how high performance processor can be realized with a reliable operation. Main advantages of the processor are the very simple construction by use of SQUIDs, very high speed operation and ultra low power dissipation.

Spread spectrum systems have been recently studied and developed for commercial applications, because they have some advantages such as robustness against interference and a noise, low probability of intercept, realization of code-division multiple access, high accuracy ranging and so on. In this paper we analyze the information security of spread spectrum systems into confidentiality, untraceability, authenticity, and antijamming property and present some measures to achieve these properties using cryptographic techniques. We show that the spreading sequences play central role in the information security issues of spread spectrum systems. A generation method of the spreading sequence having high-security property is proposed.

Fiber loss fluctuations due to manual handling are sometimes inevitable when it comes to touching cable connection points during maintenance and operational activities. These fluctuations cause momentary input optical power changes and give raise to bit errors in receivers. This phenomenon is a serious problem for fiber optic subscriber systems in which cable construction and maintenance frequently take place. Measures to counter this degradation have to be considered to realize stable transmission characteristics. As a result of this consideration, the loss fluctuation tolerance of digital optical receivers has been investigated for fiber optic subscriber transmission systems. From the viewpoint of design and adjustment, the most effective method to solve the fluctuation problem is to adopt d.c. balanced transmission line coding. A receiver having an optimum low cutoff frequency for this type of coding performs well against fiber loss fluctuations without adjustment for special operational conditions.

In this paper, the existential lower bounds on asymptotic distance ratios of error-correcting codes with J(J2) levels of unequal error protection given by encoding and decoding methods based on the concept of the generalized concatenated codes are obtained. The constructive concatenated codes with unequal error protection are proposed for high and low code rates. The formaer is constructed by the generalized version of Justesen codes. The latter is constructed by the secondorder concatenation with the generalized concatenated codes. Comparing the existential lower bounds on asymptotic distance ratios with those of the constructive concatenated codes, the lower bounds of the constructive codes are lower than the existential lower bounds.

Recently, transducers with high resolution are required in the fields of ultrasonic imaging and non-destructive testing. The plano-convex and plano-concave transducers treated in this paper are suitable for these purposes. These transducers show the focusing effect and broad frequency bandwidth for the radiation of ultrasonic pulses. These two features show the high lateral-distance and time resolutions respectively. However, the principle of the focusing effect on these transducers has been vague until now. This focusing effect will be discussed in this paper. The mechanisms of the focusing effect for ultrasonic pulses radiated from the plano-convex and plano-concave transducers are cleared through two experiments using a wedged transducer and a semi-cylindrical transducer. Also, the formulas for the geometrical focal points of pulses radiated from each transducer are derived, and its calculations are compared with the measurements.

A set of international standards is becoming effective in late 1990 to early 1992 for coding of bi-level pictures, natural still pictures and moving pictures. This paper presents an overview of collaborative standardization activities carried out in CCITT, ISO/IEC and their sub-committees, and summarizes technical features of respective standards.

Logarithmic arithmetic (LA) is a very fast computational method for real numbers. And its precision is better than a floating point arithmetic of equivalent word length and range. This paper shows a method to use LA in computer graphics--picture generation of almost any kind. Various experiments are done--from curve drawing to 3D image generation. The results are all excellent for quality and speed.

This paper considers processor utilization in faulty hypercube multiprocessor. The utilization is proportional to the continuity of processor allocation model based on Gray code. Busy and faulty processors make this model fragmented. That prevents assigning of larger tasks onto hypercube and decreases processor utilization. A set of procedures is derived which reassigns active tasks so that a new task configuration along with faulty processors makes as little damage as possible to the continuity of allocation model. First, a hypercube fragmentation measure is defined and a task reassigning technique presented. Then, procedures are given which determine: (1) active tasks to be reassigned, (2) their new optimal locations and (3) the shortest reassigning paths. At last, it is proved that while increasing processor utilization, presented scheme minimizes task reconfiguration overhead.

A numerical analysis was made of anomalous modal interference patterns of the sunrise VLF signals as observed on transequatorial east-west paths. The Earth-ionosphere waveguide modal propagation parameters were obtained below an anisotropic inhomogeneous ionosphere with the realistic earth's magnetic field and an exponential electron density profile at a frequency of 18.6 kHz. Numerical estimation of the mode conversion coefficients of day modes to night modes was also made for some sunrise terminator model. Dominantly propagating modes which produced modal interference effects in a nighttime waveguide were identified from the efficiency of the generation of nighttime modes by the first day mode in passing through the terminator. Large reduction in the mode conversion ratio of the two dominantly propagating modes at night within the equatorial region was caused by the reduction in the efficiency of the conversion of day mode 1 into dominantly propagating lower night mode on account of a change in mode character along the path. Anomalous increase in the interference spacing near the magnetic equator was obtained numerically using some exponential profiles although its maximum value was two times as large as that obtained experimentally.

This paper describes the advanced underground radar techniques developed by authors using signal processing to noise and clutter rejection, to pulse compression, to antenna beam compression and to target's identification. Underground radars which were developed and are developing in Japan are also introduced.