This letter deals with the reliability function in the case of periodic preventive replacement of items in order to increase MTBF, that is, two replacement policies; strictly periodic replacement (SPR) and randomly periodic replacement (RPR). We stress on simple introduction of the reliability theory under preventive replacement policies using the Laplace transform and obtain the theoretical results of SPR and RPR. Then these results are applied to the Weibull distribution and finally in order to show useful information of preventive replacement, the numerical results of SPR are provided.

New focused ion beam (FIB) methods for microscopic cross-sectioning and observation, microscopic crosssectioning and elemental analysis, and aluminum film microstructure observation are presented. The new methods are compared to the conventional methods and the conventional FIB methods, from the four viewpoints such as easiness of analysis, analysis time, spatial resolution, and pinpointing precision. The new FIB methods, as a result, are shown to be the best ones totally judging from the viewpoints shown above.

An analog approach alternative to the Hopfield method is presented for solving constrained combinatorial optimization problems. In this new method, a saddle point of a Lagrangian function is searched using a constrained dynamical system with the aid of an appropriate transformation of variables. This method always gives feasible solutions in contrast to the Hopfield scheme which often outputs infeasible solutions. The convergence of the method is proved theoretically and some effective schemes are recommended for eliminating some variables for the case we resort to numerical simulation. An analog electronic circuit is devised which implements this method. This circuit requires fewer wirings than the Hopfield networks. Furthermore this circuit dissipates little electrical power owing to subthreshold operation of MOS transistors. An annealing process, if desired, can be performed easily by gradual increase in resistance of linear resistors in contrast to the Hopfield circuit which requires the variation in the gain of amplifiers. The objective function called an energy is ensured theoretically to decrease throughout the annealing process.

Reflection type optical switches with intersecting waveguides and curved electrodes are newly proposed. The guided incident mode is expanded into an infinite spectrum of plane wavelets. The effects of light tunneling into the transmission port is taken care of by treating the 3-layer structure and using its reflection and transmission coefficients in estimation of the extinction ratios. It is found that the electrode curved in the form of an exponential spiral provides remarkably improved power reflectivity. This is because it poses a constant angle of incidence (smaller than the critical angle) to all variously oriented impinging wavelets. In this way, all plane wavelets are made to undertake total reflections. These total reflections result in considerably high extinction ratios to be achivable at the transmission port. It is also shown that the electrode length is shorter and the intersection angle is wider than those corresponding to a straight electrode. Therefore, it is concluded that the curvature of the electrode improves the switching characteristics of the device.

The paper proposes and reports on pototyping a work bench system for novice Prolog programmers which consists of a visually-structured interactive tracer and a prototype-based programming support. The tracer actually is a simulated interpreter in Prolog. It is interpreted by a Prolog interpreter being embedded with facilities interfacing programs in Prolog and the objects programmed in C. It displays, by way of these objects, the past, current and future goals, highlights variable sharing and value substitution, and marks the current goals and backtrack choice points. It is at user's will to let the tracer show and hide subgoals as well as to let it backtrack when it failed, step back for redoing or terminate tracing. The programming support module first provides the programmer with structural prototype patterns and the roles of the constituent functions. We developed a support system for the 2 types of recursive definitions. After having selected the prototype, the user is requested to specify the data types and the names of variables to be put in the arguments, which propagate through the structure. The support module then offers a menu of primitive or user-registered constituent functions as may be useful in processing and/or obtaining user-specified types of data. Thirdly the system lets the user express his/her intention by sample input-output data instances in his/her task goals. It makes the values propagate through the structures thus motivating the user to design the constituent functions. At the goal recursion point, the user is allowed to creep into examining the definitions of the reduced versions of the instances, helping the user find the condition with which the recursion terminates. Finally the module assists the user to convert the structural descriptions into Prolog programs.

Via electromigration (EM) performance of aluminum based metallization (AL) systems has been investigated for vias chains of 1500-4000 vias of 1.0 micron diameter. The results show that via EM lifetime can not be enhanced by a simple increase of M2 step coverage in AL/AL vias because the EM induced voids are formed at AL/AL via interface where electrons flow from Ml to M2 even in the case of very poor M2 step coverage. The voids are induced by the boundary layer in AL/AL vias, where a temperature gradient causes discontinuity of aluminum atoms flux. The failure location is not moved though via EM lifetime can be improved by controlling stress in passivation, sputter etch removal thickness and grain size of the first metal. Next, the effect of the boundary layer are eliminated by depositing titanium under the second aluminum or depositing WSi on the first aluminum. In the both cases, via EM lifetime are improved and the failure locations are changed. Especially WSi layer suppresses the voids formation rather than titanium. Models for the failure mechanism in each metallization system are further discussed.

We propose an optical computing architecture called pure optical parall array logic system (P-OPALS) as an instance of sophisticated optical computing system. On the P-OPALS, high density images can be processed in parallel using the optical system with high resolving power. We point out problems on the way to develop the P-OPALS and propose logical foundation of the P-OPALS called single-input optical array logic (S-OAL) as a solution of those problems. Based on the proposed architecture, an experimental system of the P-OPALS is constructed by using three optical techniques: birefringent encoding, selectable discrete correlator, and birefringent decoding. To show processing capability of the P-OPALS, some basic parallel operations are demonstrated. The results obtained indicate that image consisting of 300 100 pixels can be processed in parallel on the experimental P-OPALS. Finally, we estimate potential capability of the P-OPALS.

This paper describes the use of optical interconnections in switching systems and discusses our recent achievements in this area. Switching system interconnections are classified based on their application layers. The evolution of optical interconnections in switching systems in discussed in terms of such system requirements as cost, size, and throughput. Recent achievements are discussed: an optical inter-module connector, a free-space digital switch, and a large-capacity optically intra-connected ATM switch.

Student contradictions are the essentials of concepts and knowledge acquisition processes of a student, in the course of tutoring. This paper presents a new perspective to represent student contradictions and a student modeling architecture to capture them. The formulation of a student modeling mechanism enables flexible decision making by using information obtained from students. A nonmonotonic and inductive student model inference system HSMIS has been developed and formulated to cope with modeling contradictions, which basically embodies advanced representation power, sufficiently high adaptability and generality. The HSMIS is evaluated and compared with other representative systems in order to demonstrate its effectiveness.

Beam-steering devices are attractive for spatial optical interconnections. Those devices are essential not only for fixed connecting routed optical interconnections, but for flexible connecting routed optical interconnections. The flexible connecting routed optical interconections are more powerful than the conventional fixed connecting routed ones. Structures and characteristics of beam-steering devices, a beam-scanning laser diode and a fringe-shifting laser diode, are reported for those interconnections. Using these lasers, the configurations of several optical interconnections, such as optical buses and optical data switching links as examples of fixed and flexible connecting routed optical interconnections are discussed.

The connection admission control is one of preventive traffic control in ATM networks. The one objective of connection admission control is to keep the network load moderate so as to achieve a performance objective associated with quality of services (QOS). Because the cell loss rate is more sensitive to offered load than the average queuing delay in ATM networks, QOS requirement associated with cell loss rate is considered. The connection admission control acts as one of the major roles in traffic control. The job of connection admission control is to make an acceptance decision for connection set-up request to control the network load. This paper proposed and evaluated a connection admission control method. The proposed method is suitable for real time operation even in large diversity of connection types, because the amount of calculation for connection admission control is reduced remarkably compared to conventional algorithms. Moreover, the amount of calculation for the algorithm does not increase even when the number of connection types increases. The proposed method uses probability function for the number of cells transferred from multiplexed connections and uses recursive equations in estimating cell loss rate.

This paper points out that there are two types of claw free families with respect to a level of claw freeness. We formulate them as weak claw free families and strong claw free families. Then, we present sufficient conditions for each type of claw free families. (A similar result is known for weak claw free families.) They are represented as some algebraic forms of one way functions. A new example of strong claw free families is also given.

A transmission data format for high-speed optical parallel interconnections is proposed and a 4-channel transmitter and receiver link module operating at up to 1.2 Gb/s per channel is demonstrated. The data format features "Group Multiplexing and Coding." In this scheme, input several tens channels are multiplexed and coded in group into reduced channels, resulting in burst-mode compatible, skew-free transmission, and low power-consumption of a link module. Experiments with fabricated modules comfirm that our data coding in multichannel optical transmission is promising for use in high-speed interconnections in information and switching systems.

The crosstalk characteristics of a long-wavelength monolithically integrated photoreceiver array are analyzed. The device consists of an array of transimpedance photoreceivers fabricated on a semi-insulating InP substrate. The distance between the photodetectors is large enough to suppress the photonic crosstalk. Therefore, the crosstalk of the device is mainly due to signal propagation from the channels through the power line shared by each channel on the chip. This crosstalk is inevitable to the photoreceiver arrays which employ common power lines. The magnitude of the crosstalk largely depends on the impedance of the power-supply circuit outside the chip. The crosstalk spectrum often has a peak and recess structure. The crosstalk peak at the edge of the operating band-width is due to the resonance characteristic of the transimpedance amplifier. The other peak and recess structures on the spectrum are due to the resonance phenomena of on-chip and off-chip capacitors and inductance on the power-supply line outside the chip. This crosstalk can be reduced by using on-chip bypass capacitance and dumping resistance. However, the resonance due to the capacitance and inductance on the power-supply circuit outside the chip can't be controlled by the on-chip components. Therefore, an optimized design for the power supply circuit outside the chip is also indispensable for suppressing crosstalk.

A two-cascaded image processing approach to enhance the subtle differences in X-ray CT image is proposed. In the method, an asymmetrical non-linear subfilter is introduced to reduce the noise inherent in the image while preserving local edges and directional structural information. Then, a subfilter is used to compress the global dynamic range of the image and emphasize the details in the homogeneous regions by performing a modular transformation on local image den-sities. The modular transformation is based on a dynamically defined contrast fator and the histogram distributions of the image. The local contrast factor is described in accordance with Weber's fraction by a two-layer neighborhood system where the relative variances of the medians for eight directions are computed. This method is suitable for low contrast images with wide dynamic ranges. Experiments on X-ray CT images of the head show the validity of the method.

This paper discusses the fully three-dimensional finite difference time domain (FDTD) method to analyze a monopole antenna mounted on a rectangular conducting box covered with a layer of dielectric. The effects of the conductivity and the permittivity of the dielectric layer are investigated. It is shown that all calculation results agree very well with the measured data.

MultiWave data compression algorithm is based on the multiresolution wavelet techniqu for decomposing Electrocardiogram (ECG) signals into their coarse and successively more detailed components. At each successive resolution, or scale, the data are convolved with appropriate filters and then the alternate samples are discarded. This procedure results in a data compression rate that increased on a dyadic scale with successive wavelet resolutions. ECG signals recorded from patients with normal sinus rhythm, supraventricular tachycardia, and ventriular tachycardia are analyzed. The data compression rates and the percentage distortion levels at each resolution are obtained. The performance of the MultiWave data compression algorithm is shown to be superior to another algorithm (the Turning Point algorithm) that also carries out data reduction on a dyadic scale.

This paper presents an adaptive rate error control scheme for digital communication over time-varying channels. The cyclic code with majority-logic decoding is used in a cascaded way as an inner code to create a simple and powerful hybrid-ARQ error control scheme. Inner code is used only for error correction and the outer code is used for both error correction and error detection. When an error is detected, retransmission is required. The unsuccessful packets are not discarded as with conventional schemes, but are combined with their retransmitted copies. Approximations for the throughput efficiency and the undetectable error probability are given. A high reliability coupled with a simple high-speed implementation makes it suitable for high data rate error control over both stationary and nonstationary channels. Adaptive error control scheme becomes the best solution for time-varying channels when the optimum code is selected according to the actual channel conditions to enhance the system performance. The main feature of this system is that the basic structure of the encoder and decoder need not be modified while the error-correction capability of the code increases. Results of a comparative analysis show that the proposed scheme outperforms other similar ARQ protocols.

In order to develop silicon ICs operating up to above 450, Integrated Injection Logic (IIL) was chosen. A new structure for IIL was designed through experimental and theoretical studies of pn junctions, transistors, and IIL at high temperatures. A 5-µm design rule was used. The new IIL was fabricated by a specially developed combined process of ion implantation and low temperature epitaxy. The IIL was fully operational from room temperature to 454, and the output amplitude of a nine-stage ring oscillator was about 30 mV at 454. The minimum delay time of the IIL was 22 nsec at 454. The minimum power-delay product was 11 pJ and was one-third of that for IILs fabricated by 10-µm rule at 50.

This paper describes and analyzed several indices in assessing algorithms of data compression of electrocardiograms, such as the cross correlation (CC), the percent root mean square difference (PRD), and a new measure of standardized root mean square difference (SRD). Although these indices are helpful to objectively evaluate the algorithms, the visual examination of the reconstructed waveform is indispensable to decide the optimal compression ratio. This paper presents the clinical significance of selected waveforms which are prone to be distorted or neglected in the restored waveforms but are crucial for cardiologists to diagnose the patient. A database of electrocardiograms is also proposed for the comparative evaluation of compression algorithms.