Let T1, , Tn be n spanning trees rooted at node r of graph G. If for any node v, n paths from r to v, each path in each spanning tree of T1, , Tn, are internally disjoint, then T1, , Tn are said to be independent spanning trees rooted at r. A graph G is called an n-channel graph if G has n independent spanning trees rooted at each node of G. We generalize the definition of n-channel graphs. If for any node v of G, among the n paths from r to v, each path in each spanning tree of T1, , Tn, there are k internally disjoint paths, then T1, , Tn are said to be (k,n)-independent spanning trees rooted at r of G. A graph G is called a (k,n)-channel graph if G has (k,n)-independent spanning trees rooted at each node of G. We study two fault-tolerant communication tasks in (k,n)-channel graphs. The first task is reliable broadcasting. We analyze the relation between the reliability and the efficiency of broadcasting in (k,n)-channel graphs. The second task is secure message distribution such that one node called the distributor attempts to send different messages safely to different nodes. We should keep each message secret from the nodes called adversaries. We give two message distribution schemes in (k,n)-channel graphs. The first scheme uses secret sharing, and it can tolerate up to t+k-n listening adversaries for any t < n if G is a (k,n)-channel graph. The second scheme uses unverifiable secret sharing, and it can tolerate up to t+k-n disrupting adversaries for any t < n/3 if G is a (k,n)-channel graph.

A new type of fiber Fabry-Perot interferometer buried in a fiber connector housing was proposed. The transmission spectra revealed double peaks due to birefringence in the fiber and the peak separation showed a temperature dependence as large as -7. 7 MHz/deg, which was 2 orders of magnitude larger than that estimated from the thermal characteristics of its component materials.

Pb(ZrxTi1-x)O3 (PZT) thin films were prepared on various electrodes. When Ir system materials were used as electrodes, fatigue properties of PZT thin films were improved. Moreover, in the case of the PZT thin film on an Ir/IrO2 electrode, not only fatigue but imprint properties were clearly improved. We could find these improvements were caused by good barrier effect of IrO2 from secondary ion mass spectroscopy (SIMS) analysis. By applying these Ir system electrodes, we fabricated stacked capacitors on polycrystalline silicon (poly-Si) plugs. In spite of high temperature thermal processing, we found poly-Si plugs were ohmically connected with the bottom electrodes of the capacitors from hysteresis measurements and I-V characteristics, and could greatly expect them for practical use.

Recently, reliable Pb (Ti, Zr) O3 (PZT) thin-film capacitors with robust switching endurance were fabricated successfully by incorporating oxidizable metal and oxide electrodes. However, the reasons for the drastic improvement in the switching endurance property was not clear. Degradation of polarizations by switching is called "polarization fatigue. " This paper describes the mechanisms of polarization fatigue, and discusses ways for improving of that property from the standpoints of microstructure, and of interactions between the PZT and the electrode materials of the capacitors. It is clearly identified that the causes of the fatigue are the unexpected formation of a surface transition layer of PZT, which is strongly dependent on the crystallization process, and a decrease in the interfacial capacitances due to the accumulation of oxygen vacancies between the PZT and non-oxidizable metal electrodes with high work functions such as Pt. Oxidizable metal and oxide electrodes suppress by oxidation-reduction reactions the accumulation of oxygen vacancies. Fatigue-free PZT thin-film capacitors can be formed if oxidizable metal or conductive oxide electrodes are incorporated in columnar-grain-structured PZT thin-film. In sharp contrast, fatigue and retention properties of PZT thin-film capacitors with Ir electrodes were degraded by modification of the PZT with 1 atm%-Nb and 1 atm%-La even though its grain structures were columnar.

It is important to test the various kinds of interconnect faults between chips on a card/module. When boundary scan design techniques are adopted, the chip to chip interconnection test generation and application of test patterns is greatly simplified. Various test generation algorithms have been developed for interconnect faults. A new interconnect test generation algorithm is introduced. It reduces the number of test patterns by half over present techniques. It also guarantees the complete diagnosis of multiple interconnect faults.

In this paper, we consider a simple development process consisting of design and debug phases, which is derived from actual concurrent development process for embedded software at a certain company. Then we propose two-phase project control that examines the initial development plan at the end of design phase, updates it to the current status of the development process and executes the debug phase under the new plan. In order to show the usefulness, we define three imaginary projects based on actually executed projects in a certain company: the project that executes debug phase under initial plan, the project that applies the proposed approach, and the project that follows a uniform plan. Moreover, to execute these projects, we use the project simulator, which has already been developed based on GSPN model. Judging from the number of residual faults in all products, we found that project B is the best among them.

In B-ISDN, network reliability is a very significant theme. This paper proposes the Failure-Resistant Virtual Path (FRVP) scheme that prevents any information loss even with network failure, to realize a high-end reliability service in B-ISDN. The FRVP scheme is based on simple parallel transmission established using the superior characteristics of ATM. In the FRVP scheme, the transmitter duplicates user cells and transmits them across several VPs simultaneously. The receiver chooses the perfect cells and sends them to the user. As a result, the cell stream output by the receiver is not affected by VP failure if at least one VP remains active. I develop a prototype FRVP system and conduct field trials using NTT's nationwide ATM testbed network. The FRVP scheme is shown to achieve extremely-reliable ATM networks and services.

This paper proposes a new methodology for diagnosing transistor leakage faults with information on IDDQ and logic values at primary output lines. A hierarchical approach is proposed to identify the faults that do not exist in the circuit through comparing their IDDQ and logic behaviors predicted by simulation with observed responses. Several techniques for handling intermediate faulty voltages in fault simulation are also proposed. Further, an approach is proposed to generate diagnostic vectors based on IDDQ information. In addition, a method for identifying IDDQ equivalent faults is proposed to reduce the time needed for diagnostic vector generation and to improve diagnostic resolution. Experimental results show that the proposed methodology often confines diagnosed faults to only a few gates.

We have developed a half-duplex spread spectrum-direct sequence (SS-DS) 2. 4 GHz band transceiver (T/R) unit having a smaller size and lower power consumption. A highly efficient elastic SAW convolver with chirp interdigital transducers (IDTs) has been used in the correlation circuit of receiver unit. The code shift keying (CSK) modulation is used in the T/R unit. The size of T/R unit is 90 50 11 mm and the weight is 75 grams. The power consumption of T/R unit is 1. 4 watts. We found that the bit error rate (BER) was less than 10-6 over the range of 0-150 m outdoors and 0-80 m indoors without a digital error detection and correction method. In this case, the data rate was 102 kbps and the transmit RF power was 2. 5 mW/MHz. The electrical characteristics, anti-interference and anti-multipath fading were also evaluated.

This paper presents almost rigorous Wiener-Hopf solutions to the plane wave scattering by a conducting finite thin plate. The final field expressions are given in an analytically compact form and the results are accurate as long as the plate width is greater than the wavelength. Numerical examples are given for the near and far field distributions. A criterion is also proposed to estimate under what condition the ray tracing method holds.

We discussed on relationship between the width of slit ray and the accuracy of the measurement system for surface profile of electric contact. To obtain resolution of 10 [µm], we designed the mechanism which keeps constant the focal length between the object and the lens. As a result, the width of slit ray was clear in the whole surface. A section image could measured exactly and enhanced the resolution.

Coulombs law of friction, in which the coefficient of friction is constant independently of apparent area of contact and applied load, is deduced from the modern adhesion theory. That is, the friction resistance is caused by shearing of solid/solid junctions which are formed through plastic deformation of surface asperities of mating solids. In so-called point contact, on the other hand, different experimental results from Coulombs law have been sometimes reported. In these cases, coefficient of friction is not constant, but reduces with increasing normal load. A weighty interpretation for these facts developed formerly is that Hertzian contact area acts as an effective zone to generate the friction resistance. This interpretation has, however, an important doubt, as the Hertzian contact area is not formed through plastic but through elastic deformation of solids. If the friction resistance is generated in an elastic contact area, the adhesion theory of friction would be shaken at its standing basis. To give an explanation of this inconsistency between the experimental facts reported previously and the adhesion theory of friction, the authors propose a new idea in this paper. The plastic deformation occurs at surface asperities even in Hertzian contact. If the rubbing condition is kept dry, the friction resistance would be generated only at those plastically deformed zone dotted in the elastic contact area, so that Coulombs law is realized. If the rubbing condition is kept wet, the clearance between mating surfaces in the elastic contact zone is filled with any lubricant or contaminant molecules, the friction resistance would be generated through shearing of them within the Hertzian area. In this case, the coefficient of friction would be proportional to(load)-1/3, which is close to observational facts reported previously. An experimental verification made in this study can describe the authors proposal.

It is well known that the existence of electrically resistive film layers formed on contact surfaces increases contact resistance and it causes a nonlinear relationship between voltage and current observed in a contact layer. Nonlinear distortion voltages can be detected by our sensitive detection system based on the dual frequency method when a thin film exists on the surface. In this study, multilayer films of polyimide (PI) was used as an ideal material of ultra thin film, because of electrically good insulator with simple molecular structure, to study non-linearity through metal-insulator-metal contact. The number of deposited layers between one and twenty one were formed on three types of substrates; (a) evaporated gold on a glass plate, (b) gold plate and (c) evaporated gold on gold plate, to obtain good insulating film. Where each layer of PI film has 0. 4 nanometer thickness. A pin contact was made by pressing a bent gold wire on the PI film. It is concluded that [1]; the second-order distortion voltage increases exponentially as the film thickness increases, [2]; polarity of the surface potential of PI depends on the film thickness, and that I-V characteristic depends on the polarity of the surface potential.

The alloy of Ag (40wt%)-Pd(60wt%) has been used in the electrical contacts of electromechanical devices due to its superior contact properties. There is currently, an increasing trend to decrease the size of electromechanical devices. However, it has been difficult to obtain a high contact force and the high restoring force of contacts, and these problems cause contact failures such as high contact resistance. In response to this problem, the alloy is overlaid with an Au layer which is not affected by oxide films. However, when the contacts are subjected to an unacceptable amount of mechanical shock, adhesion of the Au overlay occurs easily. In order to solve these difficulties, it can be proposed to cover the contact surface with high electric conductive oxide films. With this concept, the Au overlay should be unnecessary. In the present study, to reduce the high contact resistance of the Ag-Pd alloy contaminated with an oxide film, very small amounts of Mg and Cr were used in separate doping trials to the alloy. The improvement of contact resistance characteristics is the focus of the present study. Specimens of Ag (40wt%)-Pd(60wt%), Ag-Pd-Mg(0.1, 0.5 and 1.0wt%), and Ag-Pd-Cr(0.1 and 0.5wt%) were oxidized at elevated temperatures to accelerate the process of oxidation, and the growth kinetic law of oxide films grown on the surfaces were evaluated by ellipsometry. The effect of the oxide film on the contact resistance characteristics were then clarified. A marked improvement of the contact resistance caused by the oxide film was found for the Ag-Pd alloy with a Mg doping agent. However, for the Cr doping agent, a low contact resistance was not obtained as same as the Ag-Pd alloy itself.

The showering arc waveforms generated when contact is being separate have poor reproducibility whose causes are not sufficiently clear. This paper describes that the contact surface conditions which change with the number of contact operations are deeply related to the showering arc waveforms. First, it is experimentally shown that the contacts' surface roughness increases with the number of contact operations, and the growth model of contact surface roughness is proposed based on the change of contact resistance for the number of contact operations. Second, the growth model of molten metal bridge is proposed based on the fact that the showering arc waveforms change with the number of contact operations and the evaluation indexes of showering arc are proposed.

Surface damage of the electrical contact is a primary cause of failure in many electronic devices which use sliding contacts. Therefore, the quantitative observation of the contact surface is one of the most important subjects for improvement of contact reliability. In this study, in order to clarify the relationship between the contact resistance and the damage on the contact surface, a digital image measuring system (DIMS) was developed. A shadow image processing technique (SIPT) was applied to the damage analysis on the sliding contact surface. The damage width on the contact surface and the damaged image could be obtained with a 3-D graphic image by applying both DIMS and SIPT. Part of the relationship between the damage on the contact surface and the contact resistance could be obtained in the case when Cu is used for the moving contact and Cu and Ni are used for the static contact.

This paper proposes a frequency diversity transmission scheme that obtains a frequency diversity gain and does not degrade spectrum efficiency; it utilizes multiple carrier frequencies alternately, not simultaneously. This scheme improves the bit error rate (BER) of significant information bits by sacrificing that of insignificant bits in fading channels. Simulation results show that the error floor of significant information bits is reduced to less than 1/5 while that of insignificant bits is doubled. They also show that the proposed scheme improves the received 4-bit ADPCM voice signal-to-noise ratio (SNR) by approximately 4 dB even when the frequency correlation is 0. 5.

A simulation model for natural convection was developed for determining the surface temperature distribution in base plates with rectangular vertical fins in communication equipment. An estimated velocity derived from the buoyancy and pressure drop equations in a duct was used for laminar forced convection cooling simulations in parallel plates. Temperature distributions in finned plates were calculated by numerical integration of the heat conduction equation. An experimental study was also performed, to check these simulation results, by changing the height of fins, the pitch of fins, and the heat generation conditions. Experimental results and analytical results were found to agree well. Also, this simulation method was extended to analyze natural convection cooling in vertical base plates with inclined parallel fins. We placed alternately on the plates the sections without fins and the sections with fins on the plates. Using the inclined fins, air flow rate between fins was large and fresh air flew into the fins from the side of the plates. The natural convective heat-transfer rate for inclined fins was found to be 14% higher than that for vertical fins.

We show that under some conditions an attacker can break the public-key cryptosystem proposed by J. Schwenk and J. Eisfeld at Eurocrypt '96 which is based on the difficulty of factoring over the ring Z/nZ [x], even though its security is as intractable as the difficulty of factoring a rational integer. We apply attacks previously reported against RSA-type cryptosystems with a low exponent to the Schwenk-Eisfeld cryptosystem and show a method of breaking the Schwenk-Eisfeld signature with a low exponent.

Vehicular speed response phase locked loop (VSR-PLL) is a novel circuit to remove a steady-state frequency offset which arises in the receiver with directive antenna. In this paper, the circuit is applied to Ricean fading environment. For the application of VSR-PLL to Ricean statistics channel, the Doppler shift information of direct wave must be obtained because the self-oscillation frequency of VCO is controlled by using the information. This paper describes an estimation method for the Doppler shift of the direct wave, and shows the several results of the performance analysis for the estimation method and proposed VSR-PLL with the method. As a result, we found that the proposed VSR-PLL could reduce the irreducible bit-error rate for QPSK system from about 10-2 to 10-3 on several conditions.