Speech can be modeled as short bursts of vocal energy separated by silence gaps. During typical conversation, talkspurts comprise only 40% of each party's speech and remaining 60% is silence. Communication systems can achieve spectral gain by disconnecting the users from the spectral resource during silence periods. This letter develops a simple and efficient Voice Activity Detection (VAD) algorithm to work in a mobile environment exhibiting dynamically varying background noise. The VAD uses a classification method involving the full-band energy, ratio of low-band energy to full-band energy, zero-crossing rate, and peakiness measure.

An analytical solution of the London equation for the weakly coupled grain model of high Tc superconducting thin films has been obtained in the case of finite thickness by taking full account of anisotropic conductivities. Using the solution, we provide general expressions for the transmission-line parameters of high Tc superconducting transmission lines. Dependences of the inductance and resistance on the grain size, coupling strength and film thickness have been numerically evaluated and discussed.

Recent progress of high-temperature superconductor Josephson junction technology is reviewed in the light of the future application to digital circuits. Among various types of Josephson junctions so far developed, ramp-edge-type junctions with a barrier layer composed of oxide materials in the vicinity of metal-insulator transition seem to offer a unique opportunity to fulfill all the requirements for digital circuit applications by virtue of their small junction dimensions, overdamped properties and relatively high IcRn product values at the temperature of around 30-40 K. Recently developed interface engineered junctions can be classified as junctions of this type. These junctions also raise an interesting problem in physics concerning the possibility of resonant tunneling of Cooper pairs via localized states in the barrier. From the viewpoint of practical applications, the improvement of the spread of the junction parameters is still a serious challenge to the present fabrication technology. Although interface engineered junctions seem to be most promising in this regard at present, 1σ spread of around 8% in the present fabrication technology is far from satisfactory for the fabrication of large-scale integrated circuits. The detailed understanding of the barrier formation mechanism in the interface engineered junction is indispensable not only for advancing this particular fabrication technology but also for improving other junction technology utilizing ramp-edge structures.

We report on progress in the development of high current density NbN/AlN/NbN tunnel junctions for application as submillimeter wave SIS mixers. A ultra-high current density up to 120 kA/cm2, roughly two orders of magnitude larger than any reported results for all-NbN tunnel junctions, was achieved in the junctions. The magnetic field dependence and temperature dependence of critical supercurrents were measured to investigate the Josephson tunneling behaviour of critical supercurrents in the high-Jc junctions. We have developed a low-noise quasi-optical SIS mixer with the high-current density NbN/AlN/NbN junctions and two-junction tuning circuits which employ Al/SiO/NbN microstriplines. The tuning characteristics of the mixer were investigated by measuring the response in the direct detection mode by using the Fourier Transform Spectrometer (FTS) and measuring the response in the heterodyne detection mode with the standard Y-factor method at frequencies from 670 to 1082 GHz. An uncorrected double sideband receiver noise temperature of 457 K (12hν/kB) was obtained at 783 GHz.

It is the purpose of this paper to review the generation of quantized voltage steps in Josephson-junctions, and also the recent practical application of these precise measurements. A 10-V Josephson-junction-array-voltage standard system has been established with a Josephson-junction-array, a phase-locked millimeter wave, and a precise null-detection system. Based on these technologies, the AC Josephson effect has been applied to other precise measurements such as DC error voltage of a multi-integrating analog-to-digital converter and for a pulse-width-modulation type precise voltage calibrator.

In this paper, we describe our superconducting digital technology that uses Nb/AlOx/Nb Josephson junctions. Superconducting devices have intrinsically superior characteristics than those of semiconductor devices, and Nb/AlOx/Nb junctions have ideal current-voltage characteristics for digital applications. Superconducting devices that use Nb/AlOx/Nb junctions have being actively developed because of their high speed and low power characteristics. Presently, we can fabricate more than twenty thousand junctions on one chip. Using niobium technology, a superconducting 4-kbit RAM has been already successfully developed. We have demonstrated the operation of a network system with a superconducting network chip. Some problems, such as difficulty in high-speed testing, disturbance from trapped magnetic flux and so on, have been overcome by techniques such as a clock-driven testing method, moat structures and so on. The developed technologies, such as the fabrication technology, the design technology for moat structures and so on, must become the basic keys for the development of digital applications based on a single flux quantum device, which will be a promising component for ultra-high speed systems in the twenty-first century.

We report on the fabrication and operation of all-NbN single flux quantum (SFQ) circuits with resistively shunted NbN/AlN/NbN tunnel junctions fabricated on silicon substrates. The critical current varied by about 5% in 400 NbN/AlN/NbN junction arrays, where the junction area was 88 µm2. Critical current densities of the NbN/AlN/NbN tunnel junctions showed exponential dependence on the deposition time of the AlN barrier. By using the 12-nm-thick Cu film as shunted resistors, non-hysteretic current-voltage characteristics were achieved. From dc-SQUID measurements, the sheet inductance of our NbN stripline was estimated to be around 1.2 pH at 4.2 K. We designed and fabricated circuits consisting of dc/SFQ converters, Josephson transmission lines, and T flip-flop-based SFQ/dc converters. The circuits demonstrated correct operation with a bias margin of more than 15% at 4.2 K.

Inductive Logic Programming (ILP) is a study of machine learning systems that use clausal theories in first-order logic as a representation language. In this paper, we survey theoretical foundations of ILP from the viewpoints of Logic of Discovery and Machine Learning, and try to unify these two views with the support of the modern theory of Logic Programming. Firstly, we define several hypothesis construction methods in ILP and give their proof-theoretic foundations by treating them as a procedure which complets incomplete proofs. Next, we discuss the design of individual learning algorithms using these hypothesis construction methods. We review known results on learning logic programs in computational learning theory, and show that these algorithms are instances of a generic learning strategy with proof completion methods.

Carbon-doped base InP/InGaAs heterojunction bipolar transistor (HBT) technology for millimeter-wave application is presented. Ultra-high carbon doping of InGaAs layers lattice-matched to InP with hole concentrations in excess of 1 1020 /cm3 has been achieved using a chemical beam epitaxy (CBE). Heavily carbon-doped base InP/InGaAs HBT epi structures were grown and small area, self-aligned HBTs with 1.5 µm emitter finger width were fabricated using triple mesa etching and polyimide planarization techniques. The fabricated small area transistors showed a common-emitter current gain cut-off frequency (fT) as high as 200 GHz. Preliminary device reliability test results showed the potential of the heavily carbon-doped base InP/InGaAs HBT for high performance microwave and millimeter-wave applications. Applications of the InP/InGaAs single heterojunction bipolar transistor (SHBT) and double heterojunction bipolar transistor (DHBT) to a direct-coupled feedback amplifier and a power transistor, respectively, are presented.

We propose a new probabilistic ID-based non-interactive key sharing scheme that has non-separable secret-key functions and a non-separable common-key function. The proposed scheme uses the calculation over modulo-P, modulo-Q and over integer ring for realizing non-separability. This proposed scheme has a large threshold against linear attack by the collusive entities.

Diffraction pattern functions of an E-polarized scattering by a wedge composed of perfectly conducting metal and lossless dielectric with arbitrary permittivity are analyzed by applying an improved physical optics approximation and its correction. The correction terms are expressed into a complete expansion of the Neumann's series, of which coefficients are calculated numerically to satisfy the null-field condition in the complementary region.

High-temperature superconducting (HTS) films have low surface resistance in the microwave region. This indicates that HTS passive microwave devices, for example, filters and antennas, are promising for commercial use. For superconducting filters, low insertion loss, sharp skirt property and high attenuation value out of band are important, and for superconducting antennas, electrically small antennas and super-directive high-gain antennas are useful. It is known that the elliptic filter has a sharp skirt property compared with that of a Chebyshev filter. We examined a cross-coupled filter which is one type of elliptic filter. The insertion loss of the filter was approximately 0.3 dB. The skirt property of the four-resonator cross-coupled filter was almost equal to that of an eight-resonator hairpin filter. We also examined a cryocooler cooling system for superconducting antenna and measured the relative gain, directivity and power capability of an HTS antenna. The gain of the HTS patch antenna was approximately 10 dB larger than that of a normal conducting antenna. The large gain of the HTS antenna was caused by the low surface impedance and enhancement effect of the dielectric window of the cooling system.

The arrangement graph An,k is not only a generalization of star graph (n-k=1), but also more flexible. Designing efficient broadcasting algorithm on a regular interconnection network is a fundamental issue for the parallel processing techniques. Two contributions are proposed in this paper. Initially, we elucidate a first result to construct n-k edge-disjoint spanning trees in an An,k. Second, we present efficient (one/all)-to-all broadcasting algorithms by using constructed n-k spanning trees, where height of each spanning tree is 2k-1. The arrangement graph is assumed to use one-port and all-port communication models and packet-switching (or store-and-forward) technique. Using n-k spanning trees allows us to present efficient broadcasting algorithm in the arrangement graphs and outperforms previous results. This is justified by our performance analysis.

This paper proposes an efficient algorithm for finding preimages of the reduced MD4 compression function consisting of only the first round and the third round. We thus show that the reduced MD4 is not a one-way function.

With the advent of digital video and digital broadcasting, copyright protection of video data has been one of the most important issues. We present in this paper a novel method of digital watermark for video data based on the discrete wavelet transform. In this method, we embed the watermark in the lowest frequency components of each frame in the uncoded video by using a controlled quantization process. The watermark can be extracted directly from the decoded video without access to the original video. Experimental results show that the proposed method gives the watermarked image of better quality and is robust against MPEG coding and re-encoding. Furthermore, we discuss multiple watermarking with regard to the generational copy control for video contents.

Watermarking methods that employ orthogonal transformations are very robust against non-geometrical modifications such as lossy compression, but attaining robustness against image translation or cropping is difficult. This report describes a watermarking method that increases robustness against geometrical modifications such as image translation and cropping by embedding watermark data in the frequency component of an image and detecting that data by considering the phase difference of the coefficients that results from translation of the image. Experimental results demonstrate the robustness of this method against both non-geometrical image changes and image translation and cropping.

A multilayer perceptron is usually considered a passive learner that only receives given training data. However, if a multilayer perceptron actively gathers training data that resolve its uncertainty about a problem being learnt, sufficiently accurate classification is attained with fewer training data. Recently, such active learning has been receiving an increasing interest. In this paper, we propose a novel active learning strategy. The strategy attempts to produce only useful training data for multilayer perceptrons to achieve accurate classification, and avoids generating redundant training data. Furthermore, the strategy attempts to avoid generating temporarily useful training data that will become redundant in the future. As a result, the strategy can allow multilayer perceptrons to achieve accurate classification with fewer training data. To demonstrate the performance of the strategy in comparison with other active learning strategies, we also propose an empirical active learning algorithm as an implementation of the strategy, which does not require expensive computations. Experimental results show that the proposed algorithm improves the classification accuracy of a multilayer perceptron with fewer training data than that for a conventional random selection algorithm that constructs a training data set without explicit strategies. Moreover, the algorithm outperforms typical active learning algorithms in the experiments. Those results show that the algorithm can construct an appropriate training data set at lower computational cost, because training data generation is usually costly. Accordingly, the algorithm proves the effectiveness of the strategy through the experiments. We also discuss some drawbacks of the algorithm.

Recent progresses in high Tc superconducting quantum interference device (SQUID) magnetometers are discussed. First, intrinsic sensitivity of the SQUID at T=77 K is discussed. For this purpose, transport and noise properties of the bicrystal junction are clarified, and optimization of junction parameters is shown. We also discuss the quality of the SQUID from a comprehensive comparison between experiment and simulation of the SQUID characteristics. Next, we discuss issues to guarantee correct operation of the SQUID magnetometer in noisy environment, such as a method to avoid flux trapping due to earth magnetic field, high-bandwidth electronics and gradiometer. Finally, we briefly describe application fields of the high Tc magnetometer.

We have developed a parameter optimization tool, Monte Carlo Josephson simulator (MJSIM), for rapid single flux quantum (RSFQ) digital circuits based on a Monte Carlo yield analysis. MJSIM can generate a number of net lists for the JSIM, where all parameter values are varied randomly according to the Gaussian distribution function, and calculate the circuit yields automatically. MJSIM can also produce an improved parameter set using the algorithm of the center-of-gravity method. In this algorithm, an improved parameter vector is derived by calculating the average of parameter vectors inside and outside the operating region. As a case study, we have optimized the circuit parameters of an RS flip-flop, and investigated the validity and efficiency of this optimization method by considering the convergency and initial condition dependence of the final results. We also proposed a method for accelerating the optimization speed by increasing 3σ spreads of the parameter distribution during the optimization.

The abilities of fuzzy inference methods in modeling of complicated systems are implemented to electromagnetics for the first time. The very popular and well known monopole antenna is chosen as a general example and a fast, simple and accurate fuzzy model for its input impedance is made by introducing a new point of view to impedance basic parameters. It is established that a surprisingly little number of input data points is sufficient to make a full model and also the system behavior (dominant rules) are saved as simple membership functions. The validity of the derived rules is confirmed through applying them to the case of thin-angled monopole antenna and comparing the results with the measured. Finally using the spatial membership function context, input impedance of thick-angled monopole antenna is predicted and a novel view point to conventional electromagnetic parameters is discussed to generalize the modeling method.