Optimizing the computing process of relational databeses is important in order to increase their applicability. The process consists of operations involving many relational tables. Among basic operations, joins are the most important because they require most of the computational time. In this paper, we consider to execute such joins on many relational tables by the merge-scan method, and try to find the optimum join order that minimizes the total size of intermediate tables (including the final answer table). The cost is important in its own right as it represents the memory space requirement of the entire computation. It can be also viewed as an approximate measure of computational time. However, it turns out that the problem is solvable in polynomial time only for very restricted special cases, and in NP-hard in general.

We analyze current gain of the semiconductor-high Tc superconductor (HiTcSu)-semiconductor hot clectron transistor (HET) by taking into account quantum mechanical reflection (QMR) at the base-collector interface. Due to the small Fermi energy of HiTcSu, the QMR takes a minimum value when injected electrons pass just above the maximum of the collector barrier. With appropriate biasing voltage between base and collector, the QMR is found to be less than 0.05. The current gain is analyzed using the result of the QMR as function of base thickness, temperature, and the Fermi level of the emitter. With InAs and Si chosen as prototypes of semiconductors, the possibility to achieve current gain as large as 0.9 is indicated.

Electric contact is one of the most important noise sources of electromagnetic noise. Hence, the noise of contact switching has been researched from various points of view with respect to the generation mechanism and properties. However, many phenomena have been remained not being investigated yet. In this paper, we describe our recent investigations about characteristics of the induced noise that is produced by the break of silver contact. The number of TTL IC's malfunction in the relay switching are counted under conditions of inductive load (10mH), circuit current (0.1-2A), and low source voltage (24V). From this experimental results, it became clear that the rate of malfunction decreased with increasing circuit current. To clarify its phenomenon, the circuit current dependence of the induced noise voltage was measured. It was observed that the level of induced noise voltage became the maximum in the current range of 0.2-1A. This property is discussed by the occurrence mechanism of each discharge mode on the break of contacts and the observation of induced noise corresponding to its mode.

This paper describes recent speech database efforts in Japan in which the author has been involved. The JEIDA Japanese Common Speech Data Corpus was first reported in 1986. It has been converted to DAT recently. The JEIDA Noise Database has been released to the public recently. It contains various kinds of environmental noise and standard noise for sound level calibration. The 'Spoken Language' project collected speech data including continuous speech spoken by 10 males and 10 females. The 'Spoken Japanese' project, started in 1989, attempts to collect various dialectal speech from all over Japan and create speech databases. A compact disc containing a fairy tale and weather forecast spoken by 20 dialect speakers has been produced. It also describes the Continuous Speech Database Committee which was established recently by the Acoustical Society of Japan.

We produced a double-layer thin-film heater to detrap magnetic flux in a SQUID sensor. The heater is integrated on a sensor chip, and consists of a lower resistor layer and an upper superconducting layer to cancel the magnetic field produced by the heater current. The SQUID sensor is cooled below its critical temperature with a temperature gradient to detrap the flux completely. To make the gradient, we had to decrease heater power to zero over an interval exceeding 10-4 second in our experiment, which is almost equal to the sensor chip's thermal time constant. The integrated heater effectively controls the temperature profile and detraps flux in the sensor.

The superconducting bridges with constrictions as small as 0.5 µm were fabricated by high-quality Ba2YCu3Ox thin films on silicon with buffer layers. The observed I-V characteristics of this bridge could be successfully analyzed by the modified form of Aslamazov and Larkin theory which shows that our microbridge junction is a homogeneous wide superconducting bridge and the characteristics of this bridge are not dependent on the defects such as grain boundaries of the film.

We have found a low frequency current oscillation in the n+-AlxGa1-xAs/GaAs (x0.4) modulation-doped electron systems under high electric field applied at low temperatures (77 K or lower). This paper gives a possible explanation for this on the basis of an enhanced Real-Space-Transfer (RST) of two-dimensional carriers caused by the field crowding at the local region along the heterointerface. This model explained the observed low frequency current oscillation semi-quantitatively.

Measurement results of two cascaded EDFAs (initial amplifier and boost amplifier) are reported for AM-FDM video distribution systems. A CNR of 55.5 dB and an output of 13.35 dBm (21.6mW) are measured. Distortion is measured by the two-tone method. On the basis of the measured distortion values, composite second-order distortion (CSO), composite triple beat distortion (CTB) and cross-modulation (XM) in a 40-channel transmission are estimated to be less than 56.9 dB, 66.3 dB and 74.6 dB, respectively. CNR values are strongly dependent on the erbium fiber length. They are degraded by light reflected from the input and output ports of the erbium fiber.

This paper describes an overview of our speech understanding system and reports on the recent results of the sentence recognition experiments. The system, we call SUSKIT-, recognizes database queries in natural Japanese sentences. The user is expected to speak sentence by sentence. Among the difficult problems to overcome, this study paid the prime attentions to how to cope with the contextual variations of pronunciations and how to verify partial sentence hypotheses in a hierarchical system. The SUSKIT- predicts words strings in a top-down manner, however, the verification of hypotheses against the input speech is done using a unit independent of word boundaries. Words are not suitable units of verification because the smoothing effect owing to phonetic contexts makes it difficult to recognize short words. In order to avoid the misrecognition caused by the smoothing effect across word boundaries, the SUSKIT- dynamically extracts those phoneme strings bounded by the easily detectable phonemes from the predicted word string as verification templates. The left-to-right timesynchronous beam-search strategy was adopted for searching likely sentences. We carried out sentence recognition experiments using the speech corpus consists of 159 sentences read by three Japanese male speakers. The task perplexity was 8.3. Using the speaker-dependent HMM parameters, we obtained the sentence recognition rates of 83.0-92.5%.

Given a plane graph G, a trail of G is said to be dual if it is also a trail in the geometric dual of G. We show that the problem of partitioning the edges of G into the minimum number of dual trails is NP-hard.

A new high speed switch module was constructed using a high temperature superconducting bulk core (YBa2Cu3O7-x or Bi2Sr2CaCu2O8) in the liquid nitrogen and two switching transistors having maximum rate of 1 A. The main part of the module is the Royer oscillator type magnetic multivibrator. The multivibrator starts to oscillate by applying a ON signal pulse current (ION) to a coil set around the core, and stops oscillation by applying a OFF signal pulse current (IOFF) to a small transistor which shorts another coil of the core. This module switched with the turn-on time tON of about 0.2µs and the turn-off time tOFF of about 0.2µs when two switching transistors having a maximum rate of 1 A used. The values of tON and tOFF is about 1/10 and 1/100 (due to the Meissner effect or zero inductance effect) that of the multivibrator transistor module using an amorphous ferromagnetic core. These transistor switch modules are applicable to construct high-speed inverters for the control of the small motors having high rotation speed.

We have fabricated and measured step-edge microbridges of on-axis sputter-deposited YBCO films using the steps which exist on the cleaved surface of MgO substrate. The microbridges fabricated over the step behaved as Josephson devices, exhibiting clear Shapiro steps with microwave irradiation at 4.2 K. The critical current of the step-edge microbridge is one to two orders reduced from the critical current of the microbridge that has no steps within the same bridge region. The ICRN product is 0.5-1 mV with normal resistance of 1-4 Ω. The present technique utilizing the cleaved steps of MgO is useful for studying basic characteristics of the weak links with the step-edge structure.

Rf properties of the coupling circuit between the dc SQUID and the multiturn input coil have been studied in order to investigate the origin of the degradation of the SQUID characteristics due to the input coil. It is pointed out that rf properties of the coupling circuit become important due to the existence of the rf currents generated from Jasephson junctions. The rf properties of the coupling circuit have been measured by using the expanded model of the circuit with Cu electrodes. We observe that resonant structures appear in rf properties of the coupling circuit. This means that the SQUID coil coupled to the input coil can not be expressed by a simple inductance, as is not the case of the isolated SQUID. It is shown that the resonant structures result from the standing wave occurring in the coupling circuit. It is also shown that the resonant structures can be suppressed with the damping resistors. Based on the experimental results, a circuit model of the coupling circuit is obtained, which explains well the experimental results. The obtained results are useful to study the effect of the input coil on SQUID characteristics.

Natural spontaneous speech is so ambiguous that a system for understanding it requires the cooperation of many knowledge sources. Thus, in order to integrate speech processing and language processing, it is necessary to provide a system with a mechanism for supporting such cooperation. We propose here a general framework for cooperative problemsolving, based on the blackboard model and a TMS (truth maintenance system), with an enhanced proving function. In this framework, a reasonably consistent interpretation is automatically kept on the blackboard, while each knowledge source performs its own inference and puts the results on the blackboard. Based on this framework, a model has been established for a system which can understand spontaneous speech through the cooperation of independent knowledge sources. Most notably, prosodic information is used as suprasegmental cues to infer the structure of spontaneous speech. This allows robust parsing of spoken sentences. The feasibility and validity of our basic framework have been confirmed by computer simulation experiments on spontaneous speech.

The BAMBOO algorithm is an expert system rule generating algorithm developed from the well-known C4 decision tree algorthm. Because BAMBOO's search is less restricted than C4's it usually finds simpler rules than C4. Both algorithms have problems with incomplete search and brittleness. These problems can be avoided by layering both algorithms together with other algorithms, generating independent rule sets and selecting a subset of rules to use in the final expert system. This learning strategy is referred to as parallel generalisation. Problems of search and brittleness are because the algorithms have a single fixed bias. By layering several algorithms together the effect is of a single algoritm selectively applying many heuristics. Because selecting rules is much easier than generating rules, the select procedure has its own parameterised bias. The layered algorithm is much more flexible than the single algorithms, in addition to generating more accurate and concise rule sets. Brittleness is avoided as when one algorithm produces a worst case rule set other algorithms generate better rules. Parallel generalisation can be improved by altering the algorithms to cooperate moer.

The transport properties of low energy quasi-particles across the base layer in superconducting base transistors has been described using the Boltzmann equation which is based on the BCS theory. In order to investigate these transport properties, the Boltzmann equation was solved by means of the Monte-Carlo method which includes the acoustic phonon scattering mechanism. For the isotropic Nb system at 3 (K), a large mean-free path of L6.710-2 (cm) and a diffusion coefficient of D2.5105 (cm/s) were obtained. The base layer transit time was estimated to be about 0.3 (ps) for a 1000 () thin Nb base at 3 (K). We also applied this method in the case of the oxide high-Tc superconductor YBa2Cu3O7, by modifying the corresponding parameter value.

This paper describes syntax/semantics oriented spoken Japanese understanding systems named "SPOJUSSYNO/SEMO" and compares them. At first these systems make Hidden-Markov-Models (HMM) based on word units automatically by concatenating syllables. Then a word lattice is hypothsized by using a word spotting algorithm and word-based HMMs for an input utterance. In SPOJUS-SYNO, the time-synchronous left-to-right parsing algorithm is executed to find the best word sequence from the word lattice according to syntactic & semantic knowledge represented by a context free semantic grammar. In SPOJUS-SEMO, the knowledges of syntax and semantics are represented by a dependency and case grammar. These systems were implemented in the "UNIX-QA" task with the vocabulary size of 521 words. Experimental result shows that the sentence recognition/understanding rate was about 80/87% for six male speakers for the SPOJUS-SYNO, but was very low performance for the SPOJUS-SEMO.

This paper describes an overview of Japanese text dictation system composed of an acoustic processor and a linguistic processor. The system deals with 843 conceptual words and 431 functional words. The phoneme recognition is carried out using a modified LVQ2 method which we propose. The phoneme recognition score was 86.1% for 226 sentences uttered by two male speakers. The linguistic processor is composed of a processor for spotting Bunsetsu-units and a syntactic processor. The structure of the Bunsetsu-unit is effectively described by a finite-state automaton. The test-set perplexity of the finite-state automaton is 230. In the processor for spotting Bunsetsu-units, using a syntax-driven continuous-DP matching algorithm, the Bunsetsu-units are spotted from a recognized phoneme sequence and then a Bunsetsu-unit lattice is generated. In the syntactic processor, the Bunsetsu-unit lattice is parsed based on the dependency grammar. The dependency grammar is expressed as the correspondence between a FEATURE marker in a modifier-Bunsetsu and a SLOT-FILLER marker in a head-Bunsetsu. The recognition scores of the Bunsetsu-unit and conceptual words were 73.2% and 85.7% for 226 sentences uttered by the two male speakers.