Cellular Neural Networks (CNNs) have been developed as a high-speed parallel signal-processing platform. In this paper, a generalized two-layer cellular neural network model is proposed for image processing, in which two templates are introduced between the two layers. We found from the simulations that the two-layer CNNs efficiently behave compared to the single-layer CNNs for the many applications of image processing. For examples, simulation problems such as linearly non-separable task--logic XOR, center point detection and object separation, etc. can be efficiently solved with the two-layer CNNs. The stability problems of the two-layer CNNs with symmetric and/or special coupling templates are also discussed based on the Lyapunov function technique. Its equilibrium points are found from the trajectories in a phase plane, whose results agree with those from simulations.

This paper gives a new sufficient condition for cellular neural networks with delay (DCNNs) to be completely stable. The result is a generalization of two existing stability conditions for DCNNs, and also contains a complete stability condition for standard CNNs as a special case. Our new sufficient condition does not require the uniqueness of equilibrium point of DCNNs and is independent of the length of delay.

In this paper we analyze an asymptotic stability of nonlinear singularly perturbed systems and propose a composite control with gain scheduling where the fast controller is the gain scheduled controller and the slow state plays a role of slowly varying parameters in gain scheduling. Specifically, the slow controller is designed by the slow manifold to stabilize the reduced slow system. As a result, the slow manifold of the system is the same as the designed manifold.

This paper presents data coding techniques for a stable single-bit noise-shaping quantizer, which has a cascade structure of a multi-bit ΣΔ modulator and a binary interpolator. The binary interpolator chooses a pre-optimized binary vector for each input sample and successively generates the chosen binary vector as an output bit stream. The binary vectors can have different lengths. The paper also proposes two methods to evaluate and bound output errors of a binary interpolator. A multi-bit ΣΔ modulator is designed to cause no overload for all possible input signals whose amplitudes are bounded to a specified level, and thus the ΣΔ modulator rigorously guarantees the stability condition. In design examples, we have evaluated Signal-to-Noise and Distortion Ratios (SNDRs) and noise spectra and then confirmed that our stable quantizers can sharply shape output noise spectra.

To elucidate the mechanism of topographic organization, we propose a simple topographic mapping formation model from generalized cell layer to generalized cell layer. Here generalized cell layer means that we consider arbitrary cell neighborhood relations. In our previous work we investigated a topographic mapping formation model between one dimensional cell layers. In this paper we extend the cell layer structure to any dimension. In our model, each cell takes a binary state value and we consider a class of learning principles which are extensions of Hebb's rule and Anti-Hebb's rule. We pay special attention to correlation type learning rules where a synaptic weight value is increased if pre and post synaptic cell states have the same value. We first show that a mapping is stable with respect to the correlational learning if and only if it is semi-embedding. Second, we introduce a special class of weight matrices called band type and show that the set of band type weight matrices is strongly closed and such a weight matrix can not yield a topographic mapping. Third, we show by computer simulations that a mapping, if it is defined by a non band type weight matrix, converges to a topographic mapping under the correlational learning rules.

This paper introduces the concept of hierarchical testability of data paths for delay faults. A definition of hierarchically two-pattern testable (HTPT) data path is developed. Also, a design for testability (DFT) method is presented to augment a data path to become an HTPT one. The DFT method incorporates a graph-based analysis of an HTPT data path and makes use of some graph algorithms. The proposed method can provide similar advantages to the enhanced scan approach at a much lower hardware overhead cost.

A highly stable oven-controlled crystal oscillator (OCXO) with low phase-noise characteristics has been developed using a dual-mode SC-cut quartz crystal oscillator. The OCXO uses a conventional oven-control system for coarse compensation and a digital-correction system, which uses B-mode signal in an SC-cut resonator as a temperature sensor, for fine compensation. Combining these two forms of compensation greatly improves the stability of the C-mode frequency without requiring a double-oven system. The experimental results indicated that the frequency stability of the proposed OCXO, including the frequency-temperature hysteresis, is ten times better than that of a conventional, free-running OCXO. The results also indicated that the proposed OCXO has good frequency retraceability and low phase-noise characteristics.

A cascode crystal oscillator is widely used for the stable frequency source of mobile communication equipments. Recently, IC production of the cascode crystal oscillator has become necessary. The cascode crystal oscillator is composed of a colpitts crystal oscillator and a cascode connected base-common buffer amplifier. The base bypass condenser prevents the area size reduction. In this paper, we have proposed the new structures of the cascode crystal oscillator suitable for integrated circuits. The proposed circuits have the advantages on reduction of the area size and start-up time without deteriorating the frequency stability against the load impedance variation and other performances. The simulation and experiment have shown the effectiveness of the proposed circuits.

A feedback-based congestion control mechanism is essential to realize an efficient data transfer service in packed-switched networks. TCP (Transmission Control Protocol) is a feedback-based congestion control mechanism, and has been widely used in the current Internet. An improved version of TCP called TCP Vegas has been proposed and studied in the literature. It can achieve better performance than TCP Reno. In previous studies, performance analysis of a window-based flow control mechanism based on TCP Vegas only for a simple network topology has been performed. In this paper, we extend the analysis to a generic network topology where each connection is allowed to have a different propagation delay and to traverse multiple bottleneck links. We first derive equilibrium values of window sizes of TCP connections and the number of packets waiting in a router's buffer. We also derive throughput of each TCP connection in steady state, and investigate the effect of control parameters of TCP Vegas on fairness among TCP connections. We then present several numerical examples, showing how control parameters of TCP Vegas should be configured for achieving both stability and better transient performance.

Several gateway-based congestion control mechanisms have been proposed to support an end-to-end congestion control mechanism of TCP (Transmission Control Protocol). One of promising gateway-based congestion control mechanisms is a RED (Random Early Detection) gateway. Although effectiveness of the RED gateway is fully dependent on a choice of control parameters, it has not been fully investigated how to configure its control parameters. In this paper, we analyze the steady state behavior of the RED gateway by explicitly modeling the congestion control mechanism of TCP. We first derive the equilibrium values of the TCP window size and the buffer occupancy of the RED gateway. Also derived are the stability condition and the transient performance index of the network using a control theoretic approach. Numerical examples as well as simulation results are presented to clearly show relations between control parameters and the steady state behavior.

Stability of slotted ALOHA systems with retransmission cutoff, in which a packet is discarded after the certain number of unsuccessful transmissions, is investigated on slow-frequency-hopped channels with the aid of the catastrophe theory. The result of this paper can be viewed as extension of the result derived by Kim. The balance function is first formulated. Then, the cusp point and the bifurcation sets are numerically evaluated. We visualize how retransmission cutoff effects on bistable region. Using the result, we can design parameters of slotted ALOHA systems with retransmission cutoff such that the system operates with the unique stable equilibrium point.

This short paper is a written version of one part of the plenary address given at the November 1999 NOLTA symposium held at the Hilton Waikoloa Village in Hawaii. I was invited by Professor Shin'ichi Oishi, a general vice-chairman of the symposium, to give a survey of some of my own research. I was happy to do that--in the context of a description of what Bell Labs.' research environment was like in its math center in the 1960's, and why I feel that today's young researchers are often too constrained in that they are typically not encouraged to try to do really interesting work. Here the emphasis is on only the origins of input-output stability theory.

In order to enhance the performance, many database management systems (DBMSs) execute transactions at isolation level 2 rather than at isolation level 3, the strict two phase locking, even if it sacrifices consistency to a certain degree. Cursor stability, a variant of isolation level 2 in relational DBMSs (RDBMSs), has been widely used as a useful technique for obtaining concurrency achievable at level 2 without much sacrificing consistency. However, cursor stability is much less usable in object-relational DBMSs (ORDBMSs) because navigational applications in ORDBMSs can suffer from critical inconsistency problems such as dangling pointers, lost updates, and reading inconsistent complex objects. In this paper, we propose a new isolation level, navigation stability, that prevents the inconsistency problems of cursor stability for navigational applications, while avoiding significant degradation of the concurrency of level 3. First, we analyze the inconsistency problems of cursor stability for navigational applications. Second, we define navigation stability as an extension of cursor stability and show that it solves those inconsistency problems of cursor stability in ORDBMSs. Third, through extensive simulation, we show that navigation stability significantly enhances the performance compared with level 3. For workloads consisting of transactions of long duration, compared with level 3, the throughput of navigation stability is enhanced by up to 200%; the average response time reduced by as much as 55%; and the abort ratio reduced by as much as 77%. From these results, we conclude that navigation stability is a useful isolation level in ORDBMSs that can be used in place of isolation level 3 to improve the performance and concurrency without significant sacrifice of consistency.

This paper is concerned with the controller synthesis for feedback systems with saturation based on the LPV system representation. The LPV system representation, combined with use of the detailed structure of saturation nonlinearity, enables us to reduce the conservativeness. In this paper, we develop a new iterative algorithm for designing a linear time-invariant controller which locally stabilizes the nonlinear closed-loop system and achieves the prescribed quadratic control performance. The present design method provides an explicit expression for a guaranteed domain of attraction, and maximizes the estimated region of the plant states for which the stability and the prescribed quadratic performance are satisfied. A numerical example shows the effectiveness of the present design method.

Particulate media composed of very small particles were studied to determine high-density recording performance and thermal stability. Studied media included metal particulate media with mean particle length of 71, 102 and 148 nm, and Ba ferrite particulate media with mean diameter of 22, 28 and 50 nm. Using a loss-term simulation program, taking into account gap-loss, spacing-loss and particle length loss, the recording capability (D20 of 265 kFRPI for MP and 290 kFRPI for Ba ferrite media) was estimated. Thermal stability was evaluated from magnetization time decay measurements. It was found that MP media with large Ku values and 71 nm particles were satisfactorily stable, and the particle volume is still large enough in respect of thermal stability. However, 22-nm Ba ferrite media were less stable, primarily because of small Ku values and particle volume. It was also clarified that positive inter-particle interaction accelerates magnetization time decay, in the presence of a large reverse field.

A model of interactive videoconference is proposed for investigating the interactivity of the videoconference. Through running a prototype videoconferencing system over ATM networks, we observed that the system stability would degrade abruptly if the interaction demand from conferees exceeds what the system control can support. By using the proposed model, we formulate the problem of achieving high interactivity and stability as maximizing interactivity by tuning system parameters subject to some stability constraints. Solving the problem is non-trivial since it involves unpredictable network delays. We thus develop practical approaches that can choose and dynamically adjust, according to the network condition, the values of system parameters to meet the stability constraints and improve the interactivity. Finally, we validate our approaches and provide guidelines on choosing the parameter values by conducting experiments and simulations.

The chemical stability of the constituent elements in polycrystalline Sr-Bi-Ta-O thin film with various Bi content prepared by metalorganic chemical vapor deposition (MOCVD) was investigated by X-ray photoelectron spectroscopy (XPS). Moreover, that of the epitaxial films was also investigated to estimate the effect of the grain boundary in polycrystalline films. Therefore, only the Bi element drastically changed from Bi3+ state to Bi0 one by the Ar sputtering. This change increased with increasing the Ta/Bi mole ratio in the film from 0.64 to 1.67. This result was observed not only for the polycrystalline films but also for the epitaxial films, suggesting that this is the grain character not grain boundary one. The stability and the leakage character of the film strongly depend on the constituent of the film.

Optimization procedure on higher order Delta-sigma (ΔΣ) modulator coefficients is proposed. The procedure is based on the higher order ΔΣ modulator stability judgement method. The application specification can be satisfied with the proposed method. The 4th order modulator examples are illustrated. Optimized coefficients and its behavior model simulation results demonstrated that this methodology is suitable for the design of higher order ΔΣ AD converter. The coefficients tolerance up to 2% is allowed for switched-capacitor implementation, with not more than 3.5 dB SNR (Signal to Noise Ratio) degradation. The optimized coefficients improves 2 to 3 bit of the modulator's resolution than the previous proposed algorithm, and remains the stable input limit satisfies the original design requirement.

We consider a dynamically reconfigureable network where dynamically changing traffic is offered. Rearrangement and adjustment of network capacity can be performed to maintain Quality of Service (QoS) requirements for different traffic classes in the dynamic traffic environment. In this work, we consider the case of a single, dynamic traffic class scenario in a loss mode environment. We have developed a numerical, analytical tool which models the dynamically changing network traffic environment using a time-varying, fluid-flow, differential equation; of which we can use to study the impact of adaptive capacity adjustment control schemes. We present several capacity adjustment control schemes including schemes which use blocking and system utilization as means to calculate when and how much adjustment should be made. Through numerical studies, we show that a purely blocking-based capacity adjustment control scheme with a preset adjustment value can be very sensitive to capacity changes and can lead to network instability. We also show that schemes, that uses system utilization as a means to calculate the amount of capacity adjustment needed, is consistently stable for the load scenarios considered. Finally, we introduce a minimum time interval threshold between adjustments, which can avoid network instability, in the cases where the results showed that capacity adjustment had been performed too often.

The use of the column-rank of the system sensitivity matrix as a testability measure for parametric faults in linear analog circuits was pioneered by Sen and Saeks in 1970s, and later re-introduced by several others. Its practical use has been limited by how it can be calculated. Numerical algorithms suffer from inevitable round-off errors, while traditional symbolic techniques can only handle very small circuits. In this paper, an efficient method is introduced for the analysis of Sen and Saeks' analog testability. The method employs determinant decision diagram based symbolic circuit analysis. Experimental results have demonstrated the new method is capable of handling much larger analog circuits.