Brain-computer interfaces (BCIs) have been used by users to convey their intentions directly with brain signals. For example, a spelling system that uses EEGs allows letters on a display to be selected. In comparison, previous studies have investigated decoding speech information such as syllables, words from single-trial brain signals during speech comprehension, or articulatory imagination. Such decoding realizes speech recognition with a relatively short time-lag and without relying on a display. Previous magnetoencephalogram (MEG) research showed that a template matching method could be used to classify three English sentences by using phase patterns in theta oscillations. This method is based on the synchronization between speech rhythms and neural oscillations during speech processing, that is, theta oscillations synchronized with syllabic rhythms and low-gamma oscillations with phonemic rhythms. The present study aimed to approximate this classification method to a BCI application. To this end, (1) we investigated the performance of the EEG-based classification of three Japanese sentences and (2) evaluated the generalizability of our models to other different users. For the purpose of improving accuracy, (3) we investigated the performances of four classifiers: template matching (baseline), logistic regression, support vector machine, and random forest. In addition, (4) we propose using novel features including phase patterns in a higher frequency range. Our proposed features were constructed in order to capture synchronization in a low-gamma band, that is, (i) phases in EEG oscillations in the range of 2-50 Hz from all electrodes used for measuring EEG data (all) and (ii) phases selected on the basis of feature importance (selected). The classification results showed that, except for random forest, most classifiers perform similarly. Our proposed features improved the classification accuracy with statistical significance compared with a baseline feature, which is a phase pattern in neural oscillations in the range of 4-8 Hz from the right hemisphere. The best mean accuracy across folds was 55.9% using template matching trained by all features. We concluded that the use of phase information in a higher frequency band improves the performance of EEG-based sentence classification and that this model is applicable to other different users.

This report presents experimental measurements of mixed-mode oscillations (MMOs) generated by a weakly driven four-segment piecewise linear Bonhoeffer-van der Pol (BVP) oscillator. Such a roughly approximated simple piecewise linear circuit can generate MMOs and mixed-mode oscillation-incrementing bifurcations (MMOIBs). The laboratory experiments well agree with numerical results. We experimentally and numerically observe time series and Lorenz plots of MMOs generated by successive and nonsuccessive MMOIBs.

We study the coupled spatio-temporal variations of the electron density and the electric field (electron plasma oscillations) in high-electron mobility transistors using the developed device model. The excitation of electron plasma oscillations in the terahertz range of frequencies might lead to the emission of terahertz radiation. In the framework of the model developed, we calculate the resonant plasma frequencies and find the conditions for the plasma oscillations self-excitation (plasma instability) We show that the transit-time effect in the high-electric field region near the drain edge of the channel of high-electron mobility transistors can cause the self-excitation of the plasma oscillations. It is shown that the self-excitation of plasma oscillations is possible when the ratio of the electron velocity in the high field region, ud, and the gate length, Lg, i.e., the inverse transit time are sufficiently large in comparison with the electron collision frequency in the gated channel, ν. The transit-time mechanism of plasma instability under consideration can superimpose on the Dyakonov-Shur mechanism predicted previously strongly affecting the conditions of the instability and, hence, terahertz emission. The instability mechanism under consideration might shed light on the origin of terahertz emission from high electron mobility transistors observed in recent experiments.

Plasma oscillations in nanometer field effect transistors are used for detection and generation of electromagnetic radiation of THz frequency. Following first observations of resonant detection in 150 nm gate length GaAs HEMT, we describe recent observations of room temperature detection in nanometer Si MOSFETs, resonant detection in GaN/AlGaN HEMTs and improvement of room temperature detection in GaAs HEMTs due to the drain current. Experiments on spectrally resolved THz emission are described that involve room and liquid helium temperature emission from nanometer GaInAs and GaN HEMTs.

The minimization problem of an L2-sensitivity measure subject to L2-norm dynamic-range scaling constraints is formulated for a class of two-dimensional (2-D) state-space digital filters. First, the problem is converted into an unconstrained optimization problem by using linear-algebraic techniques. Next, the unconstrained optimization problem is solved by applying an efficient quasi-Newton algorithm with closed-form formula for gradient evaluation. The coordinate transformation matrix obtained is then used to synthesize the optimal 2-D state-space filter structure that minimizes the L2-sensitivity measure subject to L2-norm dynamic-range scaling constraints. Finally, a numerical example is presented to illustrate the utility of the proposed technique.

Experimental investigations on detection of terahertz radiation are presented. We used plasma wave instability phenomenon in nanometer Silicon field effect transistor. A 30 nm gate length transistor was illuminated by THz radiation at room temperature. We observe a maximum signal near to the threshold voltage. This result clearly demonstrates the possibility of plasma wave THz operation of these nanometer scale devices. The response was attributed to a non resonant detection. We also demonstrate the possibility to observe a resonant detection on the same devices.

We consider oscillators consisting of a reactance circuit and a negative resistor. They may happen to have multi-mode oscillations around the anti-resonant frequencies of the reactance circuit. This kind of oscillators can be easily synthesized by setting the resonant and anti-resonant frequencies of the reactance circuits. However, it is not easy to analyze the oscillation phenomena, because they have multiple oscillations whose oscillations depend on the initial guesses. In this paper, we propose a Spice-oriented solution algorithm combining the harmonic balance method with Newton homotopy method that can find out the multiple solutions on the homotopy paths. In our analysis, the determining equations from the harmonic balance method are given by modified equivalent circuit models of "DC," "Cosine" and "Sine" circuits. The modified circuits can be solved by a simulator STC (solution curve tracing circuit), where the multiple oscillations are found by the transient analysis of Spice. Thus, we need not to derive the troublesome circuit equations, nor the mathematical transformations to get the determining equations. It makes the solution algorithms much simpler.

We propose an analysis method for Franz-Keldysh (FK) oscillations appearing in photoreflectance (PR) spectra of heterojunction device structures, which enables precise and simultaneous evaluation of the built-in electric field strength and band-gap energy. Samples for PR measurements were n+-GaAs/n-Al0.3 Ga0.7 As/i-GaAs heterostructures with different Al0.3Ga0.7As-layer thickness. We have found that the phase of the FK oscillations originating from the i-GaAs buffer layer depends on the Al0.3 Ga0.7 As-layer thickness. We have derived a calculation model for FK oscillations that includes the interference of probe light. From the comparison of the calculated spectra with the measured spectra, we conclude that mixing of the real and imaginary parts of a modulated dielectric function, which is caused by the probe-light interference, gives rise to the phase shift of the FK oscillations. Our FK-oscillation analysis method reduces ambiguity in the estimation of band-gap energy that is considerable in a conventional analysis.

This paper presents circuit models for the description of the frequency-dependent behavior of coils for horizontal deflection in CRTs. This enables CRT circuit designers to use circuit simulation programs to predict the high-frequency behavior of the interaction between the deflection coils and the drive circuit. An overview is given of the major phenomena that occur in CRT deflection coils at various frequencies. Models are presented for the dissipative, the capacitive, and the resonant behavior in successive frequency intervals. With these models, phenomena such as power dissipation and ringing can not only be related to design parameters, but can also be calculated from impedance characteristics which are relatively easy to measure.

We present calculations of the linear-response conductance of a SiGe based single-electron transistor (SET). The conductance and the discrete charging of the quantum dot are calculated by free-energy minimization. The free-energy calculation takes the discrete level-spectrum as well as complex many-body interactions into account. The tunneling rates for tunneling through the source and lead barrier are calculated using Bardeen's transfer Hamiltonian formalism. The tunneling matrix elements are calculated for transitions between the zero-dimensional states in the quantum dot and the lowest subband in the one-dimensional constriction. We compare the results for the conductance peaks with those from calculations with a constant tunneling rate where the shape of the peaks is only due to energetic arguments.

In this paper we study the evolution of the resonance zones that appear in connection with a Hopf-pitchfork bifurcation exhibited by a Z2-symmetric electronic circuit. These regions, bounded by curves of folds (saddle-node bifurcations) may be closed or open depending on the values of the parameters. An angular degeneracy on the torus bifurcation curve originates the banana shape of Arnold's tongues. The presence of homoclinic bifurcations is also pointed out.

The analysis of the Takens-Bogdanov bifurcation of the equilibrium at the origin in the Chua's equation with a cubic nonlinearity is carried out. The local analysis provides, in first approximation, different bifurcation sets, where the presence of several dynamical behaviours (including periodic, homoclinic and heteroclinic orbits) is predicted. The local results are used as a guide to apply the adequate numerical methods to obtain a global understanding of the bifurcation sets. The study of the normal form of the Takens-Bogdanov bifurcation shows the presence of a degenerate (codimension-three) situation, which is analyzed in both homoclinic and heteroclinic cases.

In this paper, oscillation modes produced in a Josephson circuit and its application to digital systems are described. The analysis is performed using an analog simulator to model the Josephson junction, in addition to computer simulation. The experimental results concerning oscillation modes agree well with the simulation results. The main advantage of the mapping for the oscillation modes is that it allows understanding of the relationships among oscillation modes and circuit parameters at first sight. In addition, a novel application of nonlinear oscillation to digital systems is described.