Design and evaluation of a high-performance switch architecture for free-space photonic switching systems is described. The switch is constructed of 22 switching elements and employs special multistage interconnection patterns. The connection setup algorithm and the control procedure at the switching elements are based on a "rerouting algorithm."" Performance analysis shows that the blocking probability of the switch is easily controlled by increasing the number of switching stages. Example implementations of this switch are shown in which birefringent plates, polarization controllers, etc. are used.

State of the arts on guided-wave optical switch arrays are reviewed. In this paper, electro-optic Ti:LiNbO3 devices are mainly described in comparison with crosspoint switch element structures and switch array architectures. Packaging technologies and stability problems are discussed for practical system applications. Recent development on other materials such as semiconductor waveguides, thermo-optic glass/polymer waveguides are also reviewed briefly.

To enhance the extinction ratio (ER) of NRZ-to-inverted-RZ converter based on cross-gain compression of a semiconductor optical amplifier (SOA), a modified terahertz optical asymmetric demultiplexer (TOAD) is cascaded. ER is improved from 1.6-6.7 dB to 5.4-14.5 dB, depending on the intensity of input optical NRZ signal. The proposed NRZ-to-inverted-RZ converter enhances and regulates ER to a high value (14.5 dB) for very wide optical NRZ signal intensity range.

We apply two acceleration techniques for the backpropagation algorithm to an iterative gradient descent algorithm called the network inversion algorithm. Experimental results show that these techniques are also quite effective to decrease the number of iterations required for the detection of input vectors on the classification boundary of a multilayer perceptron.

One of the most important problems in machine learning is to predict a binary value by observing a sequence of outcomes, up to the present time step, generated from some unknown source. Vovk and Cesa-Bianchi et al. independently proposed an on-line prediction model where prediction algorithms are assumed to be given a collection of prediction strategies called experts and hence be allowed to use the predictions they make. In this model, no assumption is made about the way the sequence of bits to be predicted is generated, and the performance of the algorithm is measured by the difference between the number of mistakes it makes on the bit sequence and the number of mistakes made by the best expert on the same sequence. In this paper we extend the model by introducing a notion of investment. That is, both the prediction algorithm and the experts are required to make bets on their predictions at each time step, and the performance of the algorithm is now measured with respect to the total money lost, rather than the number of mistakes. We analyze our algorithms in the particular situation where all the experts share the same amount of bets at each time step. In this shared bet model, we give a prediction algorithm that is in some sense optimal but impractical, and we also give an efficient prediction algorithm that turns out to be nearly optimal.

Spot-size-converter integrated semiconductor optical amplifiers have been developed as gate elements for optical switch matrices. An S-shape waveguide has been introduced to prevent re-coupling of unguided light to the output fiber. An angled-facet structure effectively suppressed light reflection at the end facets. Consequently, a high extinction ratio of 70 dB and a high fiber-to-fiber gain of 20 dB were achieved. Sufficient optical coupling characteristics to a flat-ended single-mode fiber with a coupling loss of 3.5 dB were also demonstrated.

We propose novel all-optical functional devices using waveguide X-junctions with localized third order optical nonlinearity, where one branch is made from a Kerr-like nonlinear material and the rest are made from linear ones. All-optical switching operations can be obtained because of bistable like nonlinear dispersion characteristics in linear and nonlinear coupled guided-wave systems. The performances of the devices are analyzed by the Beam Propagation Method (BPM) modified for nonlinear waveguides combined with the nonlinear normal mode analysis. The methods to construct the waveguides with localized nonlinearity are also discussed by utilizing the technologies for the selective control of a band-gap energy of semiconductor Multi Quantum Well (MQW) structures and the performances of the designed devices are presented.

This paper proposesd a non-blocking multi-stage ATM switch based on a hierarchical-cell-resequencing (HCR) mechanism and high-speed WDM interconnection and reports on its feasibility study. In a multi-stage ATM switch, cell-based routing is effective to make the switch non-blocking, because all traffic is randomly distributed over intermediate switching stages. But due to the multi-path conditions, cells may arrive out of sequence at the output of the switching fabric. Therefore, resequencing must be performed either at each output of the final switching stage or at the output of each switching stage. The basic HCR switch performs cell resequencing in a hierarchical manner when switching cells from an input-lines to a output-line. As a result, the cell sequence in each output of the basic HCR switch is recovered. A multi-stage HCR switch is constructed by interconnecting the input-lines and output-lines of these basic HCR switches in a hierarchical manner. Therefore, the cell sequence in each final output of the switching fabric is conserved in a hierarchical manner. In this way, cell-based routing becomes possible and a multi-stage ATM switch with the HCR mechanism can achieve 100% throughput without any internal speed-up techniques. Because a large-capacity multi-stage HCR switch needs a huge number of high-speed signal interconnections, a breakthrough in compact optical interconnection technology is required. Therefore, this paper proposes a WDM interconnection system with an optical router arrayed waveguide filter (AWGF) that interconnects high-speed switch elements effectively and reports its feasibility study. In this architecture, each switch element is addressed by a unique wavelength. As a result, a switch in a previous stage can transmit a cell to any switch in the next stage by only selecting its cell transmission wavelength. To make this system feasible, we developed a wide-channel-spacing optical router AWGF and compact 10-Gbit/s optical transmitter and receiver modules with a compact high-power electroabsorption distributed feedback (EA-DFB) laser and a new bit decision circuit. Using these modules, we confirmed stable operation of the WDM interconnection. This switch architecture and WDM interconnection system should enable the development of high-speed ATM switching systems that can achieve throughput of over 1 Tbit/s.

To enhance the extinction ratio (ER) of NRZ-to-inverted-RZ converter based on cross-gain compression of a semiconductor optical amplifier (SOA), a modified terahertz optical asymmetric demultiplexer (TOAD) is cascaded. ER is improved from 1.6-6.7 dB to 5.4-14.5 dB, depending on the intensity of input optical NRZ signal. The proposed NRZ-to-inverted-RZ converter enhances and regulates ER to a high value (14.5 dB) for very wide optical NRZ signal intensity range.

This paper proposes a fast synchronization scheme with a short preamble signal for high data rate wireless LAN systems using orthogonal frequency division multiplexing (OFDM). The proposed OFDM burst format for fast synchronization and the demodulator for the proposed OFDM burst format are described. The demodulator, which offers automatic frequency control and symbol timing detection, enables us to shorten the preamble length to one quarter that of a conventional one. Computer simulation results show that the degradation in required Eb/N0 due to the synchronization scheme is less than 1 dB in a selective Rayleigh fading channel.

Predicate Circumscription is a fundamental formalization of common sense reasoning. In this paper, we study a new approximation formula of it. In our previous works, we investigated Lifschitz's pointwise circumscription and its generalization, which functions as a finite approximation to predicate circumscription in the first-order framework. In this paper, at first, we study the ability of the generalized pointwise circumscription more closely, and give a simple example which shows that it cannot be complete even when a minimized predicate has only finite extension on the minimal models. Next, we introduce a new approximation formula, called finite constructive circumscription, in order to overcome that limitation. Finally, we compare expressive power of the two approximation methods with of predicate circumscription schema, and propose a open problem that should be solved to clarify that the completeness of predicate circumscription schema with respect to minimal model semantics.

Design and evaluation of a high-performance switch architecture for free-space photonic switching systems is described. The switch is constructed of 22 switching elements and employs special multistage interconnection patterns. The connection setup algorithm and the control procedure at the switching elements are based on a "rerouting algorithm." Performance analysis shows that the blocking probability of the switch is easily controlled by increasing the number of switching stages. Example implementations of this switch are shown in which birefringent plates, polarization controllers, etc. are used.

In this paper, we discuss the problem of active training data selection for improving the generalization capability of a neural network. We look at the learning problem from a function approximation perspective and formalize it as an inverse problem. Based on this framework, we analytically derive a method of choosing a training data set optimized with respect to the Wiener optimization criterion. The final result uses the apriori correlation information on the original function ensemble to devise an efficient sampling scheme which, when used in conjunction with the learning scheme described here, is shown to result in optimal generalization. This result is substantiated through a simulated example and a learning problem in high dimensional function space.

In this paper, a scheme to remove clouds and their shadows from remotely sensed images of Landsat TM over land has been proposed. The scheme uses the image fusion technique to automatically recognize and remove contamination of clouds and their shadows, and integrate complementary information into the composite image from multitemporal images. The cloud regions can be detected on the basis of the reflectance differences with the other regions. Based on the fact that shadows smooth the brightness changes of the ground, the shadow regions can be detected successfully by means of wavelet transform. Further, an area-based detection rule is developed in this paper and the multispectral characteristics of Landsat TM images are used to alleviate the computational load. Because the wavelet transform is adopted for the image fusion, artifacts are invisible in the fused images. Finally, the performance of the proposed scheme is demonstrated experimentally.

Connector contact resistance may become unstable if fretting occurs. Such motions result in the formation of insulating oxides on the surface of base metal contacts or organic polymers on contacts made of platinum group metals. These degradations are termed fretting corrosion and frictional polymerization, respectively. Motion may be caused by external vibration or fluctuating temperature. The lower the frequency of movement, the fewer the number of cycles to contact failure. Increasing the contact normal load or reducing the amplitude of movement may stabilize the connection. Tin and palladium and many of their alloys are especially prone to fretting failure. Tin mated to gold is worse than all-tin contacts. Gold and high gold-silver alloys that are softer when mated to palladium stabilize contact resistance since these metals transfer to the palladium during fretting; but flash gold coatings on palladium and palladium nickel offer marginal improvement for the gold often quickly wears out. Dissimilar metal contact pairs show behaviors like that of the metal which predominates on the surface by transfer. Contact lubricants can often prevent fretting failures and may even restore unlubricated failed contacts to satisfactory service.

This paper introduces a material management system for newspapers that was developed for The Yomiuri Shimbun. Material transferred to the system is stored in a material database and sent to terminals located in the related sections. The material can be processed effectively just by checking information on the terminals. Special requirements for this system will be discussed first in the paper, then problem-solving will be explored.

The security of the ElGamal-type signature scheme is based on the difficulty of solving a discrete logarithm problem. If a random value that is introduced in the signing procedure is small, then the time for generating signature can be reduced. This strategy is particularly advantageous when a signer uses a smart card. In this paper, we show that the secret key can be computed efficiently if the random value is less than O(q) where q is the order of the generator.

The applicability of composite materials containing laminar solid lubricants to sliding contacts was studied. Performances of several composite materials prepared by incorporating solid lubricants with the basic alloys of the Cu-Nb system and Cu-Sn system were investigated to test the suitability of the composite materials as sliding contacts. As a result, it was clarified that the composite materials based on Cu-Sn alloy were superior to those based on Cu-Nb alloy and those containing only WS2 and not MoS2 were more effective in reducing both the contact resistance and the coefficient of friction. Based on the relationship between the contact resistance and the coefficient of friction obtained in this experimental study, the author proposed a new model for electric contact of composite materials.

Simple expressions for constriction resistance of multitude conducting spots were analytically formulated by Greenwood. These expressions, however, include some approximations. Nakamura presented that the constriction resistance of one circular spot computed using the BEM is closed to Maxwell's exact value. This relative error is only e=0. 00162 [%]. In this study, the constriction resistances of two, five and ten conducting spots are computed using the boundary element method (BEM), and compared with those obtained using Greenwood's expressions. As the conducting spots move close to each other, the numerical deviations between constriction resistances computed using Greenwood's expressions and the BEM increase. As a result, mutual resistance computed by the BEM is larger than that obtained from Greenwood's expressions. The numerical deviations between the total resistances computed by Greenwood's expressions and that by the BEM are small. Hence, Greenwood's expressions are valid for the total constriction resistance calculation and can be applied to problems where only the total resistance of two contact surfaces, such as a relay and a switch, is required. However, the numerical deviations between the partial resistances computed by Greenwood's expression and that by the BEM are very large. The partial resistance calculations of multitude conducting spots are beyond the applicable range of Greenwood's expression, since Greenwood's expression for constriction resistance of two conducting spots is obtained by assuming that the conducting spots are equal size. In particular, the deviation between resistances of conducting spots, which are close to each other, is very large. In the case of partial resistances which are significant in semiconductor devices, Greenwood's expressions cannot be used with high precision.

This paper proposes a novel one-way hash function that can serve as a tool in achieving authenticity and data integrity. The one-way hash function can be viewed as a representative of a family of fast dedicated one-way hash functions whose construction is based on linear cellular automata over GF(a). The design and analysis of security of the function is accomplished by the use of very recently published results on cellular automata and their applications in cryptography. The analysis indicates that the one-way hash function is secure against all known attacks. A promising property of the proposed one-way hash function is that it is especially suitable for compact and fast implementation.