As a means of improving the rate of convergence of the conventional echo canceller using the learning identification method, the authors have previously proposed a linear predictive algorithm. This algorithm shows better convergence than the learning identification method. However, in this algorithm, as well as in the learning identification method, a compromise is necessary between a relatively large step gain required for fast convergence and the relatively small step gain needed for noise insensitivity in the presence of noise. In this paper a new algorithm based on the linear predicitive algorithm is proposed, in which the step gain is determined as a function of the estimated values of noise and the parameters-error of the echo path model in order to improve both the rate of convergence and the noise insensitivity simultaneously. The efficiency of the proposed algorithm is examined by computer simulations. It has been shown that the proposed algorithm gives about twice the rate of convergence and about 10 dB lower parameters-error in the stationary state in comparison with the learning identification method. Besides, it has been proved that this algorithm guarantees non-divergence of the echo path model even during the period of double-talking" without any control device such as a double-talking detector.

A new class of circuits for the realization of second-order filters with finite transmission zeros is proposed. The proposed circuits have their pole frequency to be independent of the amplifier gain. Design formulae with all the capacitors to be arbitrarily chosen are presented. Additionally, a new single amplifier third-order low-pass notch filter circuit is also proposed. The design formulae with all the capacitors arbitrarily chosen are explicit and extremely simple.

A depolarization phenomenon at 34.5 GHz due to wet snow was observed in a horizantal terrestrial path of 1.3 km. Data during snowfall show fairly large degradations of XPD in comparison with data during rain and theoretical values based upon the model of deformed raindrop, under the condition of the same copolar attenuation. Much larger deformation of snowflake than that of raindrop must be assumed to explain such inclination by the model of depolarization due to an oblate spheroidal snowflake. Effective differential propagation constants of snow, which are derived from measurements of XPD and phase difference between cross- and co-polar components, show that depolarization due to wet snow at 34.5 GHz comes from not only differential phase shift but also differential attenuation. A certain kind of anomalous depolarization on Earth-space paths may be explained by the model of depolarization due to wet snow.

A double-layer resist-film technique to fabricate the undercut profiles in optical and electron beam lithography is described. The process consists of successive spin-coating of two different resist films, developing the top resist layer, and etching the bottom layer in oxygen plasma. Oxygen plasma etching experiments have been accomplished to fabricate the desired undercut profiles. Diazo resists have been chosen as the top resist layer and PBS as the bottom resist layer. With the optimization of resists and plasma etching conditions, undercut profiles suitable for lift-off metallization are obtained with better pattern width control and better undercut control.

Using an electrically controllable (EC) Echelette grating which consists of numerous thin glass-plates on a unimorph transducer, the wavelength selection and intracavity modulation are demonstrated at CO₂ 10.6 µm laser, together with the basic characteristics of the grating and theoretical treatments. Under intracavity setting of the grating in three-mirror configuration of a resonator, the initially oscillated CO₂ line, P22, is typically moved into P18 line with 100V applied to the grating. On the intensity modulation, about 30% of modulation is also obtained with only 10 V.

An extraction method of density contour lines of gray level pictures is described. Two kinds of quads composed of four image pixels and non-image pixels are defined for making the density contour lines simple closed paths. From the resultant density contour lines of simple closed paths, a tree graph is made for executing the recognition of a house included in a monochromatic aerial photo of an urban area.

Fourier reconstruction has orginally been one of the methods for three-dimensional structure reconstruction in medical applications such as the computed tomography (CT). The technique is found to be applicable to designing circularly symmetric FIR digital filters. The algorithm is simple, straightforward and practical. The approach basically consists of designing a one-dimensional (1-D) FIR prototype, rotating its frequency response in the two-dimensional (2-D) frequency plane, inverse Fourier transforming and then windowing the result. An unlimited number of profections at different orientations of the obtained impulse response are essentially identical with the 1-D FIR prototype. The even size 2-D FIR filters can also be designed. The impulse response has eightfold (octagonal) symmetry. The frequency response is shown to have nearly circular symmetry that is evaluated with rms and maximum absolute errors.

A nonlinear electric circuit model of the whole length basilar membrane (BM) of the human is constructed. It is of transmission analogue type. Nonlinearity is introduced into its loss factors, using resistors and Ge diodes. By observing the membrane velocity of the model, we examine: (i) response to combination tones (CT) with two primary tones of frequency f_L, f_H and level L_L, L_H (f_Lf_H), (ii) 2f_Lf_H CT cancellation characteristics, (iii) two-tone wuppression and (iv) other responses. Suppressed tone has frequency f₁(characteristic frequency (CF) of given section) and level L₁, and suppressor tone has frequency f₂ and level L₂. Distribution of 2f_Lf_H CT component shows that at some sections it cominates the primaries in amplitude, while 2f_Hf_L component is very much smaller all along the model. The 2f_Lf_H CT distribution patterns in the model, when it is cancelled, seem to indicate good correspondence with the psychophysical cancellation. Three CT cansellation characteristics (L_LL_H varied, L_L varied, f_H varied) show good agreement with psychophysical experiments, including the nonmonotonic behavior of the CT. It seems to be possible to have more agreement by using sharper tuning property and stronger nonlinearity. For frequency f₁f₂, average value of BM velocity shows two-tone suppression, but for f₂f₁, it shows a little suppression. It will be worthwhile to consider other variables, such as BM displacement or acceleration, as model output.

The authors report about the basic theory and the experimental results of a new highly stable dc voltage regulator with high efficiency by the method of switching and continuous control. A key point of this circuit is to do switching control of the input voltage in order to regulate the voltage across the series control element so as to become a required minimum value.

Using an integrated optical circuit, a new device for Two-Dimensional (2-D) Walsh transforming is proposed. The feature is that both the wiring line and adder circuit in conventional devices are replaced with one crossing point of two optical fibers. A light signal is injected into the input terminals, the addition on the way is performed by light, and the subtraction is carried out in the last stage.

In the case of rigid disk files, improvements in the recording medium and the head are required to increase bit density. This letter reports a high recording density of 2600 bit/mm (65000 bit/i), achieved by using high coercive force (100 Oe) sputtered γ-Fe₂O₃ thin film media and a narrow gap (2g0.15µm)head.

The frequency of an AlGaAs DH laser has been stabilized with respect to a Fabry-Perot interferometer by controlling the injection current. The frequency stability of 2.110¹² was obtained at τ90 ms, which was better than the free-funning stability by three orders of magnitude.