There has been growing interest in Broadband ISDN (B-ISDN) based on ATM (Asynchronous Transfer Mode) technologies, since ATM is expected to support a wide range of applications through high-speed and flexible multimedia communication capabilities. This paper reviews and discusses technical issues on multimedia communication protocols and services from the integration points of view of computer and communication technologies. An ISDN-based distributed multimedia and multi-party desktop conference system called MERMAID is introduced as an example which offers highly-sophisticated functions for remote collaborations among multiple users. This system, which was developed in early 1989 and has been used for daily research work since then, involves B-ISDN key technologies related to multimedia and multicast protocols, and computer architecture for groupware applications.

This paper discusses a way of identifying the network configuration of ATM-LANs, which are composed of a number of ATM hubs. In general, a Network Management System (NMS) sets and gets the necessary data to and from the network elements. In managing an ATM-LAN, the ATM connection between the NMS and each network element, namely the ATM hub, must be established in order to get and set the necessary data. This forms a remarkable contrast with conventional LANs such as the IEEE802.3 LAN, which is a shared media network and enables broadcast communication without setting up any connection. This paper proposes a new protocol and a procedure that establishes the ATM connection between the NMS and each ATM hub, while identifying the overall network configuration. First, this paper makes clear the peculiarity of the ATM-LAN in terms of automatically identifying the network configuration. Next, the identification protocol that achieves the required properties is precisely explained. Then, the proposed identification protocol is evaluated in terms of required bandwidth and identification time.

Asynchronous Transfer Mode (ATM) shared buffer switches have numerous advantages, but have the principal disadvantage that all switch traffic must pass through the bottleneck of a single memory. To achieve the most efficient usage of this bottleneck, the shared buffer is made blockable, resulting in a switch architecture that we call "throttled-buffer", which has several advantageous properties. Shared buffer efficiency is maximized while decreasing both capacity and power requirements. Asynchronous operation is possible, whereby peak link data rates are allowed to approach the aggregate switch rate. Multicasting is also efficiently supported. The architecture and operation of this low-cost switch are described in detail.

This paper discusses how to provide selective broadcast communication for a group of multiple entities in a distributed system by using high-speed communication networks. In the group communication, protocol data units (PDUs) sent by each entity have to be delivered atomically in some order to all the destinations in the group. In distributed applications, each entity sends a PDU only to a subset rather than all the entities, and each entity needs to receive all the PDUs destined to it from every entity in the same order as they are sent. We name such a broadcast service a selective order-preserving broadcast (SP) service. In this paper, we discuss how to design a distributed, asynchronous protocol which provides the SP service for entities.

The dielectric breakdown characteristics of a thin gate oxide during high-current ion implantation with an electron shower have been investigated by controlling the energy distribution of the electrons. Degradation of the oxide has also been discussed with regard to the total charge injected into the oxide during ion implantation in comparison with that of the TDDB (time dependent dielectric breakdown). Experimental results show that the high-energy and high-density electrons which concentrated in the circumference of the ion beam due to the space charge effect cause the degradation of the thin oxide. It was confirmed that eliminating the high-energy electrons by applying magnetic and electric fields lowers the electron energy at the wafer surface, thereby effectively suppressing the negative charge-up.

The stability conditions and stability factors of terminated active two port networks are investigated. They are expressed with the S parameters of active devices and the radii and centers of the circles defined by source and load terminations. The stability conditions are applied to specific cases. Some of the results correspond to the stability conditions expressed in Z, Y, H or G parameters and one of the other stability conditions of terminated two port network is similar to that for passive terminations which is expressed in S parameters. The various results derived in this paper are very useful for checking the stability of amplifiers, because both stability conditions and stability factors are simply calculated by using the S parameters without using the graphical method or transforming S parameters to Z, Y, H or G parameters. These stability conditions can be also used even if negative input or output resistance appears and even if the real part of source or load immittance is negative.

The modular and growable photonic ATM switch architecture described in this paper uses both time-division and wavelength-division multiplexing technologies, so the switch capacity can be expanded in both the time and frequency domains. It uses a new implementation of output buffering scheme that overcomes the bottleneck in receiving and storing concurrent ultra fast optical cells. The capacity in one stage of a switch with this architecture can be increased from 32 gigabits per second to several terabits per second in a modular fashion. The proposed switch structure with output channel grouping can greatly reduce the amount of hardware and still guarantee the cell sequence.

A case structure expression is one of the most important forms to represent the meaning of the sentence. Case structure analysis is usually performed by consulting case frame information in a verb dictionary. However, this analysis is very difficult because of several problems, such as word sense ambiguity and structural ambiguity. A conventional method for solving these problems is to use the method of selectional restriction, but this method has a drawback in the semantic marker (SM) method --the trade-off between descriptive power and construction cost. In this paper, we propose a method of case structure analysis based on examples in case frame dictionary This method uses the case frame dictionary which has some typical example sentences for each case frame, and it selects a proper case frame for an input sentence by matching the input sentence with the examples in the case frame dictionary. The best matching score, which is utilized for selecting a proper case frame for a predicate, can be considered as the score for the case structure of the predicate. Therefore, when there are two or more readings for a sentence because of structural ambiguity, the best reading of a sentence can be selected by evaluating the sum of the scores for the case structures of all predicates in a sentence. We report on experiments which shows that this method is superior to the conventional, coarse-grained SM method, and also describe the superiority of the example-based method over the SM method.

This paper describes a new free-space optical switch structure based on cascaded beam shifters (each consists of a liquid-crystal polarization controller array and a birefringent plate). This structure comprises 2-input, 2-output switching elements that are locally connected by links. It is applicable to a variety of switching networks, such as a Clos network. The switching network based on this structure is an analog switch that is transparent to signal format, bit rate, and modulation type, so it can handle various types of optical signals. Theoretical feasibility studies indicate that compact large-scale switches (i.e., 100-1000 ports) with relay lens systems can be implemented using beam shifters with a 0.4-dB insertion loss and a 30-dB extinction ratio. Experimental feasibility studies indicate that a 1024-cell beam shifter module with a 0.5-dB insertion loss and a 23-dB extinction ratio is possible at present. An alignment-free assembly technique using precise alignment guides is also confirmed. An experimental 8-stage, 1024-input 256-output concentrator shows low insertion loss characteristics (6.8dB on average) owing to the low-loss beam shifters and the alignment-free assembly technique. Practical switching networks mainly require the improvement of the extinction ratio of the beam shifter module and the development of a fiber pig-tailing technique. This switch structure is applicable to transparent switching networks such as subscriber line concentrators and inter-module connectors.

The photonic Space-Division (SD) switching network is attractive for constructing flexible broadband networks. This paper first describes possible applications of the network. A broadband STM switching system, Digital Cross-connect System (DCS) and Video signal distribution switch, especially for HDTV signals, are attractive near term applications. Recent activities on photonic SD switching network developments aiming at these application are also reviewed. A 128 line prototype switching system has been developed. This system utilizes LiNbO3 photonic switch matrices, semiconductor traveling wave amplifiers (TWAs) and three dimensional optical interconnections for multi stage switching networks. It is confirmed that the system has been operating in providing 150Mb/s TV phone services and 600Mb/s HDTV distribution services with high stability. An experimental optical Digital Crossconnect System (optical DCS) has also been demonstrated. Line failure restoration operation at 2.4Gb/s has been successfully demonstrated. These experimental demonstrations prove that practical photonic switching systems are feasible with current technologies.

Among various photonic switching technologies, photonic frequency division multiplexing technology is most promising. In this paper a novel photonic FDM (Frequency Division Multiplexing) system is proposed. The proposed system consists of n (multiplicity of frequencies) independent subnetworks, each of which is identified by a specific frequency, and of which each network topology is identical. When a connection is required by a terminal, the network selects a subnetwork that can afford it, and assigns a frequency representing the selected subnetwork to the terminal. This system eliminates frequency converting devices and traffic concentration equipment, which will reduce the size and cost of the system. A very small sized switching system of very large capacity will be easily realized. In this paper, first we will address the basic concept of the proposed system, and then discuss some technical problems and their solutions concerning network configuration, switch matrix structure, subscriber network configuration, control scheme and frequency multiplicity. Some experimental results are also mentioned.

This paper describes Japanese spoken sentence recognition using hybrid language modeling, which combines the advantages of both syntactic and stochastic language models. As the baseline system, we adopted the HMM-LR speech recognition system, with which we have already achieved good performance for Japanese phrase recognition tasks. Several improvements have been made to this system aimed at handling continuously spoken sentences. The first improvement is HMM training with continuous utterances as well as word utterances. In previous implementations, HMMs were trained with only word utterances. Continuous utterances are included in the HMM training data because coarticulation effects are much stronger in continuous utterances. The second improvement is the development of a sentential grammar for Japanese. The sentential grammar was created by combining inter- and intra-phrase CFG grammars, which were developed separately. The third improvement is the incorporation of stochastic linguistic knowledge, which includes stochastic CFG and a bigram model of production rules. The system was evaluated using continuously spoken sentences from a conference registration task that included approximately 750 words. We attained a sentence accuracy of 83.9% in the speaker-dependent condition.

A family of new generalized LR parsing algorithms are proposed which make use of a set of ancestors tables introduced by Kipps. As Kipps's algorithm does not give us a method to extract any parsing results, his algorithm is not considered as a practical parser but as a recognizer. In this paper, we will propose two methods to extract all parse trees from a set of ancestors tables in the top vertices of a graph-structured stack. For an input sentence of length n, while the time complexity of the Tomita parser can exceed O(n3) for some context-free grammars (CFGs), the time complexity of our parser is O(n3) for any CFGs, since our algorithm is based on the Kipps's recognizer. In order to extract a parse tree from a set of ancestors tables, it takes time in order n2. Some preliminary experimental results are given to show the efficiency of our parsers over Tomita parser.

Junction leakage current of trench isolation devices is strongly influenced by trench configuration. The origin of the leakage current is the mechanical stress that is generated by the differential thermal expansion between the Si substrate and the SiO2 filled isolation trench during the isolation forming process. A two-dimensional mechanical stress simulation was used to analyze trench-isolated devices. The simulated distribution and magnitude of stress were found to agree with Raman spectroscopic measurements of actual devices. The stress in the deeper regions between deep trenches is likely to increase greatly as the size of devices diminishes, so it is important to reduce this stress and thus suppress junction leakage current.

A new kind of optical local area network (LAN), using a demand assign wavelength division multiple access (DA-WDMA) scheme, has been proposed. The proposed LAN consists of two parts; an ordinary standardized LAN and an overlaid network using wavelength division (WD) channels. The proposed network can provide bit-rate independent communication channels on the ordinary LAN without limiting the capacities for the other channels. It also exhibits upgrade possibilities from present standardized networks. An access controller, which consists of software in addition to the ordinary LAN controller, a digital signal processor (DSP) etc., was developed for DA-WDMA control. The network node operation has been demonstrated using guided-wave acousto-optic (AO) mode converters as a tunable wavelength add-drop multiplexer (ADM).

A photonic network with a space- and frequency switching capability is proposed. It provides point-to-point and point-to-multipoint connections without internal blocking. The switching network exclusively uses frequency switching stages and a shared-medium architecture. Our proposal is compared with similar published networks which are either also constructed solely from frequency switching stages or from frequency and space switching stages. It is shown that the proposed switching network features fewer optical and opto-electronic components, fewer different types of component/module, lower losses, a higher capacity and an easier expansibility.

Numerical simulation of the hydrodynamic semiconductor device equations requires powerful numerical schemes. A Space-time Galerkin/Least-Squares finite element formulation, that has been successfully applied to problems of fluid dynamic, is proposed for the solution of the hydrodynamic device equations. Similarity between the equations of fluid dynamic and semiconductor devices is discussed. The robustness and accuracy of the numerical scheme are demonstrated with the example of a single electron carrier submicron silicon MESFET device.

The aim of this study is to evaluate mental workload (MWL) quantitatively by HRV (Heart Rate Variability) measures. The electrocardiography and the respiration curve were recorded in five different epochs (1) during a rest condition and (2) during mental arithmetic tasks (addition). In the experiment, subjects added two numbers. The work levels (figures of the number in the addition) were set to one figure, two figures, three figures and four figures. The work level had effects on the mean percent correct, the number of answers and the mean processing time. The psychological evaluation on mental workload obtained by the method of paired comparison increased with the work level. Among the statistical HRV measures, the number of peak and trough waves could distinguish between the rest and the mental loading. However, mental workload for each work level was not evaluated quantitatively by the measure. The HRV measures were also calculated from the power spectrum estimated by the autoregressive (AR) model identification. The ratio of the low frequency power to the high frequency power increased linearly with the work level. In conclusion, the HRV measures obtained by the AR power spectrum analysis were found to be sensitive to changes of mental workload.

Ice depolarization characteristics are discussed using cross-polarization discrimination (XPD) observations of the CS-2 beacon signal (19.45GHz, right-hand circular polarization, elevation angle of 49.5) in the stratus type rainfall events, which show a clear bright band in the simultaneous X-band radar observations. Both amplitude and phase of the mean ice depolarizations are deduced in each rainfall event by subtracting theoretical rain depolarizations from the observed values. In spite of the difference in rainfall rates on the ground, the inferred depolarizations indicate much the same amplitude and phase as those directly obtained in pure ice depolarization events without appreciable rain depolarizations. The origin of the ice depolarizations in the stratus type events, as well as in the pure ice events, seems to be ice crystals near the cloud top which are not very much concerned with the ground rainfall rates. Compared with the radar measurements above the bright band, the ice depolarizations are approximately proportional to the vertical length of the ice region at least up to 3km above the bright band. This result yields the equivalent "specific depolarization" per unit path length: |Ci|610-3km-1 (44dB in XPD) for the mean ice depolarizations in each event. Using this coefficient, the ice effects (XPD), which refer to the deviations of the observed depolarizations from the theoretical rain depolarization, are well described as a function of the height ratio of the ice region to the rain region in the stratus type events. Finally, the ice effects (XPD) are calculated against vertical lengths of the ice region in the case of specific rain heights of 2-4 km. These calculations are performed for various rainfall rates of 2-15mm/h in view of ground-based rain observations.

Central switches are expected to operate at the rate of Terabit per second in high speed networks, like the B-ISDN. Photonic switches using lightwave technology based on wavelength division multiplexing (WDM) and frequency division multiplexing (FDM) are promising ones for high speed switching. Such lightwave networks are mainly divided into two groups, according to the number of hops required for packets to arrive at their destinations: single-hop networks such as networks using star coupler and multihop networks such as Manhattan Street Network and ShuffleNet. In this paper we focus our attention on multihop networks and propose a mesh network, referred to as RookNet, for high speed communication. The average transmission delay time and maximum throughput of RookNet is approximately analyzed. It is shown that, as the number of nodes goes to infinity, the maximum throughput aproaches 0.433 and 0.485 when each node is equipped with no internal buffer and internal buffers of infinite capacity for relayed packets, respectively.