Time decay of magnetic properties in perpendicular magnetic recording media was studied. It was suggested that magnetization in media with a low energy ratio, KV/kT, of 50 is thermally stable in the absence of a demagnetizing field while coercivity exhibits a large time dependence. Magnetization in perpendicular recording media exhibited an appreciable time decay even for films with a large energy ratio of 300. The decay is attributed to the small perpendicular squareness due to a large perpendicular demagnetizing field acting in the media. The recording density dependence of the time decay in the output was explained in terms of the change in the demagnetizing field with the density. It is concluded that the use of media with large squareness as well as large energy ratio effectively reduces time decay in the output.

Methods of automatically adjusting delay time and feedback gain in controlling chaos by delayed feedback control are proposed. These methods are based on a gradient-descent procedure minimizing the squared error between the current state and the delayed state. The method of adjusting delay time and that of adjusting feedback gain are applied to controlling chaos in numerical calculations of Rossler Equation and Duffing equation, respectively. Both methods are confirmed to be successful.

This paper proposes a new multiuser detector, quasi-decorrelating detector (QDD), for a synchronous CDMA system. The QDD has the same complexity as that of decorrelator detector (DD) although it uses feedback loops, the number of which is adjustable to balance the near-far resistance and noise enhancement. The results show that the QDD outperforms the DD under various operational conditions. The impact of different spreading codes on the performance of the QDD is studied. It is shown that the Gold code is the best spreading code suitable for the QDD.

In this paper, we present an error concealment method to recover damaged blocks for block-based image coding schemes. Imperfect transmission of image data results in damaged blocks in the reconstructed images. Hence recovering damaged image blocks is needed for reliable image communications. To recover damaged blocks is to estimate damaged blocks from the correctly received or undamaged neighborhood information with a priori knowledge about natural images. The recovery problem considered in our method is to estimate a larger block, which consists of a damaged block and the undamaged neighborhood, from the undamaged neighborhood. To find an accurate estimate, a set of the feature vectors is introduced and an estimate is expressed as a linear combination of the feature vectors. The proposed method recoveres damaged blocks by projecting the undamaged neighborhood information onto the feature vectors. The sequential projections onto the feature vectors algorithm is proposed to find the projection coefficients of the feature vectors to minimize the squared difference of an estimate and the undamaged neighborhood information. We tested our algorithm through computer simulations. The experimental results showed the proposed method ourperforms the frequency domain prediction method in the PSNR values by 4.0-5.0dB. Tthe reconstructed images by the proposed method provide a good subjective quality as well as an objective one.

Nonlinear phenomena in perpendicular magnetic recording employing a single-pole head and a double-layered medium were investigated. First, measurement of linear superposition in the time domain indicated than the amount of nonlinear transition shift (NLTS) was less than 10 nm. It was concluded that the nonlinearity was caused by transition shift, not by waveform distortion. By interpreting the results, we proved that the NLTS was strongly related with head field gradient and interference field from recorded magnetization. Dependence on head parameter was examined by experiments. Based on the results, a single-pole head with which transition shift can be reduced was proposed. Pseudo-random sequence analysis revealed that NLTS was several percent even at 318 kFRPI, or at a bit interval of 80 nm, which agreed with the result of measurement of linear superposition in the time domain analysis. Experiments showed that NLTS increases the shortest bit length, in contrast with the case of longitudinal recording.

Optical transmission systems with large capacity employing wavelength-division multiplexing (WDM) techniques are now widely under development. Optical amplifiers, especially Erbium-Doped Fiber Amplifiers (EDFA's), are vital components for such transmission systems. Optical amplifiers in WDM systems are employed as common amplifiers for all WDM'ed optical carriers, therefore, change in power of a specific carrier gives rise to gain fluctuation of the remaining carriers. In this paper, we discuss about automatic gain control (AGC) of EDFA for WDM'ed optical carriers under transient gain saturation. Two methods have been reported to perform AGC, i.e., pump feedback control method and compensation light feedback control method. Theory and experimental results have been already reported on pump feedback control method. Here, theory has been generalized to be applicable for compensation light feedback method including schematics with amplified spontaneous emission (ASE) as a probe light to measure the gain of EDFA. Experimental results have confirmed the analysis. Good performance has been obtained for both methods with simple electronic circuits and ASE has been found to work as an excellent probe light source.

In order to construct fuzzy systems automatically, there are many studies on combining fuzzy inference with neural networks. In these studies, fuzzy models using self-organization and vector quantization have been proposed. It is well known that these models construct fuzzy inference rules effectively representing distribution of input data, and not affected by increment of input dimensions. In this paper, we propose a destructive fuzzy modeling using neural gas network and demonstrate the validity of a proposed method by performing some numerical examples.

A new current-mode sampled-data chaos circuit is proposed. The proposed circuit is composed of an operation block, a parameter block, and a delay block. The nonlinear mapping functions of this circuit are generated in the neuro-fuzzy based operation block. And these functions are determined by supervised learning. For the proposed circut, the dynamics of the learning and the state of the chaos are analyzed by computer simulations. The design conditions concerning the bifurcation diagram and the nonlinear mapping function are presented to clarify the chaos generating conditions and the effect of nonidealities of the proposed circuit. The simulation results showed that the nonlinear mapping functions can be realized with the precision of the order of several percent and that different kinds of bifurcation modes can be generated easily.

In this paper, we discuss an emergent behavior of a multi-elevator system. The system includes multiple elevators in an office building and the Poisson arrival of passengers as its input. Elevators move up and down to serve calls and carry passengers according to given working rules. The system is a representative discrete event dynamic system, and is a nonlinear complex system. When people leave a building at the closing time, the down-peak traffic of passengers occurs. We show numerically that (1) this causes a jamming effect, which reduces the transportation efficiency, (2) there exists a threshold in the arrival rate of passengers, at which the traffic rate starts decreasing, and (3) this jamming effect is due to the synchronization of elevators. Then we propose a dispatching control that prevents elevators from synchronizing. This control is applied to each elevator as an anxiliary working rule. We can remove the jamming effect and recover the transportation efficiency by the control.

This paper presents an event-driven approach to the timing verification of latch-synchronized systems. The proposed method performs critical path extraction and timing error detection at the same time, and extracts the critical path only if necessary. By doing so, the complexity of analysis is reduced and efficiency is greatly improved over the conventional approaches which detect timing errors after extracting the complete critical paths of the system. Experimental results show that, compared to the existing methods, it provides a more than 12-fold improvement in speed on the average for ISCAS benchmark circuits, and the relative efficiency of analysis improves as the circuit size grows.

This paper proposes a piecewise linear non-autonomous chaos generator that includes a switched inductor with time delay. The dynamics can be grasped by using piecewise exact solutions and one-dimensional return map can be derived rigorously. Using the return map, we formulate bifurcation equations and clarify tangent bifurcation route to chaos. Rough global bifurcation sets are given. Some of chaotic attractors are verified in the laboratory.

This paper proposes a high-speed crosspoint-buffer-type ATM switch, named Scalable-Distributed -Arbitration (SDA) switch. The SDA switch employs a new arbitration scheme that allows the switch to be scalable. The SDA switch has a crosspoint buffer and a transit buffer at every crosspoint. Arbitration is executed between the crosspoint buffer and the transit buffer. The arbitration selects a cell based on delay time using a synchronous counter. The selected cell is transferred from a crosspoint buffer to the output port by way of several transit buffers. Since arbitration is executed in a distributed manner at each crosspoint and the arbitration time does not depend on the switch size, the SDA switch can be expanded to realize large throughput. Numerical results show that the SDA switch ensures fairness in terms of delay time. In addition, the maximum delay time and the required crosspoint buffer size of the SDA switch are reduced, compared with those in the conventional switch based on ring arbitration. Thus, the proposed SDA switch based on the new arbitration scheme has a simple and expandable architecture,and will be suitable for future high-speed multimedia ATM networks.

This paper proposes an FFT (Fast Fourier Transform) interference detection for interference suppression which combines notch filtering and FEC (forward error correction) to improve the Pe (probability of error) performance degradation due to co-channel interference in digital satellite communication systems. The proposed FFT interference detection scheme can determine the co-channel interference carrier frequency, power, and bandwidth precisely by using the power detection threshold suitable for the desired signal power spectrum, and the notch filter characteristic can be set according to the results. The interference suppression with the proposed scheme achieves the degradation in required Eb/No to only 1.0 dB at a Pe of 10-4 compared to that with the optimum notch filter (ideal detection) in unknown CW (continuous wave) and FM (frequency modulation) co-channel interference environments. Moreover, the proposed scheme improves the required Eb/No by 6.5 dB compared to that without a notch filter in an FM interference environment with interference carrier frequency offset normalized by the desired signal clock rate of 0.52, desired to undesired (interference) signal power ratio of 3 dB and interference bandwidth at 10 dB down power point from the peak normalized by the desired signal clock rate of 0.25.

This peper proposes a simplified model of the well-known two-neuron neural oscillator. By eliminating one of the two positive feedback synapses in the neural oscillator, learning for the in-phase control of the oscillator is shown to be achievable via a very simple learning rule. The learning rule is devised in such a way that only the plasticity of two synaptic weights are required. We demonstrate some examples of the synchronization learning to validate the efficiency of the learning rule, and finally by illustrating the dynamics of the synchronization learning and by using computer simulation, we show the convergence behavior and the stability of the learning rule for the two-neuron simple neural oscillator.

This letter describes a new computational method to obtain the bifurcation parameter value of a limit cycle in nonlinear autonomous systems. The method can calculate a parameter value at which local bifurcations; tangent, period-doubling and Neimark-Sacker bifurcations are occurred by using properties of the characteristic equation for a fixed point of the Poincare mapping. Conventionally a period of the limit cycle is not used explicitly since the Poincare mapping needs only whether the orbit reaches a cross-section or not. In our method, the period is treated as an independent variable for Newton's method, so an accurate location of the fixed point, its period and the bifurcation parameter value can be calculated simultaneously. Although the number of variables increases, the Jacobian matrix becomes simple and the recurrence procedure converges rapidly compared with conventional methods.

This paper presents a new multi-clustering network for the purpose of intelligent data classification. In this network, the first layer is a self-organized clustering layer and the second layer is a restricted clustering layer with a neighborhood mechanism. A new clustering algorithm is developed in this system for the efficiently use of parallel processors. This parallel algorithm enables the nodes of this network to be independently processed in order to minimize data communication load among processors. Using the parallel processors, the quite low calculation cost can be realized among the conventional networks. For example, a 4-processor parallel computing system has shown its ability to reduce the time taken for data classification to 26.75% of a single processor system without declining its performance.

The pattern spectrum has been proposed to represent morphological size distribution of an image. However, the conventional pattern spectrum cannot extract approximate shape information from image objects spotted by noisy pixels since this is based only on opening. In this paper, a novel definition of the pattern spectrum, morphological multiresolution pattern spectrum (MPS), involving both opening and closing is proposed. MPS is capable of distinguishing details from approximate information of the image.

A fully differential folded cascode CMOS OP amp is combined with an adaptive bias OTA to increase the slew rate, and a continuous-time CMFB circuit with a push-pull type combination of a NMOS input and a PMOS input differential amplifiers is used to maximize the output voltage swing. The fabricated OP amp using a 0.8 µm digital CMOS process gives more than three times improvement in slew rate with a 15% increase in DC power consumption and a 7.5% increase in chip area compared to the conventional OP amp fabricated on the same die. The output voltage swing was measured to be -0.75 V -0.7 V at the supply voltage of +/-1.2 V.

Based on a new search strategy using circuit simulation and simulated annealing with local search, a design tool is proposed to automate design or tuning process for CMOS operational amplifiers. A special-purpose circuit simulator and some heuristics are used to accomplish the design within reasonable time. For arbitrary circuit topology and specifications, the discrete optimization of cost function is performed by global and local search. Through the comparision of design results and the design of a low-power high-speed CMOS operational amplifier usable in 10-b 25-MHz pipelined A/D converters, it has been demonstrated that this tool can be used for designing high-performance operational amplifiers with less design knowledge and effort.

This paper reports the thermal stability of particulate media, which include Co-Fe oxide, CrO2, and thick and thin MP tapes. By measuring the time decay of magnetization at room temperature, fluctuation fields were obtained as a function of reverse applied field. It was clarified that the fluctuation field has a constant and minimum value when the reverse applied field is equal to coercivity. Minimum fluctuation fields for the four particulate tapes were measured at several environmental temperatures ranging from -75 to +100. It was also clarified that the fluctuation field normalized by remanence coercivity increases as the environmental temperature increases for all tapes, indicating that it is a good measure of thermal stability. Activation volumes were also deduced as a function of temperature.