Wide-band, low-ripple underwater transducers with high-power acoustic radiation capability have been designed on the basis of multiple-mode filter synthesis theory. They are composed of triple acoustic matching plates and double backing plates with optimized specific acoustic impedances,besides piezoelectric ceramic elements. One of the backing plates employs a Fe damping-alloy to suppress unwanted response peaks in the frequency range above the passband region. Two 33 array transducers were fabricated, each with a center frequency of 200 kHz, one as a transmitter and the other as a receiver. The two transducers show high-sensitivity, low-ripple and wide-band transmitting and receiving responses. Then, the transducers were applied in a color video picture digital transmission system.Clear color video pictures, composed of 256240 pixels, were successfully received within one second.

An improvement of Q evaluation is discussed. The Resonance Curve Area method was confirmed to give a deviation in the order of 6104. The result was three times more accurate than the widely known Q evaluating method which utilizes the cursor function installed in a network analyzer. A discussion is also made on the physical validity of the RCA method. It is shown that the application of the RCA method improves the accuracy of the cavity perturbation method. Actual measurements have shown that the deviation of dielectric constant is less than 1% and that of the loss tangent is less than 3%, in the order of 104. The accuracy of the RCA method was estimated to be three times that of the conventional cavity perturbation technique. The consistency of the perturbation with other methods has also confirmed. The accuracy comparison to more accurate formulae derived from a rigorous solution have shown that the difference is sufficiently small.

A high-efficiency air cooling system is one of the keys to achieving high throughput in an ATM switching system for Broadband ISDN. Our approach is to cool the multichip modules plugged into a planar packaging system by using a two-phase thermosyphon cold-plate with an air-cooled condenser. Physically separating the cold-plate and the air-cooled condenser and connecting item by small diameter pipes is the key to applying this cooling technology to large planar packaging systems to increase volumetric packaging densities. Furthermore, thermosyphon technology allows the heat transfer process to operate without any external pumping power. Therefore this cooling system is regarded an extended high-performance air cooling system. The optimum structure was investigated while focusing on ways to reduce the external thermal resistance. The external thermal resistance between the system's cold-plate and air inlet was measured to be 0.21 K/W at an air velocity of 2 m/s and a cooling duty of 150 watts. Using this external thermal resistance value, we simulated the cooling characteristics of an MCM containing a 44 array of 10-mm-square LSI chips on an alumina substrate measuring 100100 mm. For an allowable temperature rise of 60, simulated thermal resistance was 6 K/W at an air flow of 2 m/s. This allows a power dissipation of more than 160 watts per MCM and a heat flux of 1.6 W/cm2. This system will extend the applicability of air cooling to power levels generally considered to lie in the domain of liquid cooling, and thus to the ATM switching nodes for B-ISDN.

It is an important problem whether or not we can reject the disturbances from distributed parameter circuit. In order to analyze this problem structurally, it is necessary to investigate the basic equation of distributed parameter circuit in the framework of state space. Since the basic equation has two parameters for time and space, the state value belongs to an infinite-dimensional space. In this paper, the disturbance-rejection problems with incomplete state feedback and/or incomplete state feedback and feedforward for infinite-dimensional systems are studied in the framework of geometric approach. And under certain assumptions, necessary and/or sufficient conditions for these problems to be solvable are proved.

The timing jitter reductions with differently shaped optical bandpass filters are discussed and the transmission distance achievable against the timing jitter is evaluated using optical bandpass filters in several tens of Gb/s soliton transmission. Experimental confirmation of timing jitter reduction with optical bandpass filters is demonstrated in 10Gb/s optical soliton recirculating loop experiments by measuring the timing jitter and the bit error rates.

In this paper, we study a dynamic bandwidth control which is expected an effective use of network resources in transmitting highly bursty traffic generated by, e.g., interconnected LAN systems. First, a new LAN traffic model is proposed in which correlation of not only packet interarrival times but also packet lengths are considered. An analytic model for a LAN-ATM gateway is next introduced. It employs the dynamic bandwidth control using the proposed LAN traffic model and some performance measures are derived by it. The analytic model takes into account the probability that a bandwidth increase request may be rejected. Finally, some numerical examples are provided using the analysis method and performance comparisons between the dynamic and fixed bandwidth controls are made. As a result, it is quantitatively indicated that () if the equivalent bandwidth is used in average, the dynamic bandwidth control keeps packet and cell loss rates one to two orders lower than the fixed bandwidth control, () when the more strict QOS in terms of loss rate is requested, the dynamic bandwidth control can become more effective.

A local area network (LAN) can now provide high-speed data communications in a local area environment to establish distributed processing among personal computers and workstations, and the need for interconnecting LANs, which are geographically distributed, is naturally arising. Asynchronous Transfer Mode (ATM) technology has been widely recognized as a promising way to provide the high-speed wide area networks (WAN) for Broadband Integrated Services Digital Network (B-ISDN), and the commercial service offerings are expected in the near future. The ATM network seems to have a capability as a backbone network for interconnecting LANs, and the LAN interconnection is expected to be the first service in ATM networks. However, there remain some technical challenges for this purpose; one of the main difficulties in LAN interconnection is the support of connectionless traffic by the ATM network, which is basically a connection-oriented network. Another one is the way of achieving the very high-speed data transmission over the ATM network. In this paper, we first discuss a LAN internetworking methodology based on the current technology. Then, the recent deployments of LAN interconnection methods through B-ISDN are reviewed.

Connectionless service for LANs interconnection will be provided in ATM networks at an early stage of B-ISDN era. This service will be provided on connection oriented mode at ATM technology. To perform this service, ATM connections using the dedicated bandwidth for this service are established semi-permanently between the nodes accommodating LANs. On these ATM connections, connectionless service among LANs is provided. It is important for private networks to utilize this bandwidth efficiently for reducing communication cost. In this paper, the architecture to provide connectionless service in private networks is described. Next, the allocation schemes of the bandwidth for this service and their performance are considered. We discuss the following schemes and compare them. One scheme is to establish semi-permanent ATM connections between the nodes with LAN interfaces. The bandwidth for each connection is individually assigned between these nodes. In another scheme, CLSFs (Connection-Less Service Functions) are introduced for connectionless service and connections are established via CLSFs. We show the latter scheme is superior because it brings out the effectiveness of statistical multiplexing of ATM technology and it leads to the reduction of the allocated bandwidth.

This paper deals with methods for interconnection between two local private networks that are geographically separated. A scheme is first presented to chain low bit-rate physical circuits into one logical circuit, over which ATM cells are transmitted as if there is one circuit with a high bit-rate capacity. In particular, use of existing low bit-rate circuits, e.g., 384/1536 kbit/s PDH leased line services and N-ISDN switched channels, is considered. The paper discusses two methods to permit chaining of physical circuits, and identifies their advantages and applications. By using the ATM-based circuit-chaining method, dynamic capacity control of the interconnection is then introduced with the use of an ATM-based rate adaptation. This is intended to provide a flexible and cost-effective capacity control compared to the existing TDM-based control. It is also possible to realize non-stop operation of changing capacity by establishment and release of chained circuits, which will lead to high reliability and robustness of private networks. Finally, delay characteristics introduced by the method are evaluated based on a computer simulation which gives a short and acceptable delay.

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.

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.

The demand for large-capacity photonic switching systems will increase as regular broadband ISDN (B-ISDN) spreads and full-motion video terminals replace telephones. Large-scale and economical optical fiber transmission lines have been built based on time-division (TD) multiplexing. To reduce costs, it is important to increase the channel multiplexity of both transmission and switching systems by using TD and wavelength-division (WD) or frequency-division (FD) technologies. We surveyed photonic switching systems' architecture and switching network structures. Switching can be divided into circuit or synchronous transfer mode (STM) switching, and asynchronous transfer mode (ATM) switching. A variety of photonic STM and ATM switching systems based on the two switching technologies have recently been proposed and demonstrated.

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.

The theoretical modelling bandgap narrowing and percentage of ionized impurity atoms for uncompensated uniformly doped silicon containing conventional impurities (B, P, As, Sb) under thermodynamic-equilibrium conditions is presented. As distinct from existing approaches, this modelling is valid for impurity concentrations up to electrically-active-impurity-concentration limits and for the temperature range from 40 K up to 400 K. A relevant and efficient calculation software is proposed. The results of the calculations are compared with the results extracted by many authors from measurement data. A good agreement between these results is noted and possible reasons of some discrepancies are pointed out. The present modelling and software can be used for investigation of BJT charge-neutral regions as well as diffused or implanted resistors.

Leakage enhancement after an ESD event has been analyzed for output buffer LDD MOSFETs. The HBM ESD failure threshold for the LDD MOSFETs is only 200-300 V and the failure is the leakage enhancement of the off-state MOSFETs called as "soft breakdown" leakage. This leakage enhancement is supposed to be caused by trapped electrons in the gate oxide and/or creation of interface states at the gate overlapped drain region due to snap-back stress during the ESD event. The mechanism of the lekage can be explained by band-to-band and/or interface state-to-band tunneling of electrons. The improvement of the HBM ESD threshold has been also evaluated by using two types of drain engineering which are additional arsenic implantation for the output LDD MOSFETs and "offset" gate MOSFET as a protection circuit for the output pins. By using these drain engineering, the threshold can be improved to more than 2000 V.

This paper proposes a high-speed VP bandwidth control scheme for ATM networks that utilizes a distributed control mechanism. First, the characteristics of VPs are compared with those of digital paths in STM networks. A distributed control scheme is adopted for rapid control. The basic elements and the necessary distributed function, the control algorithm, and the message transmission mechanism, are elucidated. The bandwidth alteration time with the proposed algorithm is estimated by considering network element processing and queuing delay. The proposed VP bandwidth control scheme can be applied to both public networks and leased line services. Finally, this paper focuses on its application to leased line services, and discusses the resource reduction effects of the proposed scheme.

Observations of rain depolarization characteristics were conducted using the CS-2 and CS-3 beacon signals (19.45GHz, circular polarization, elevation angle=49.5) during seven years of 1986-1992 at Neyagawa, Osaka. The mean cross-polar phase relative to the co-polar phase of each rainfall event is distributed in a comparatively wide range from -100 to -150. This large variation is suggested to be caused by the difference of raindrop size distribution (DSD) in addition to that of rain intensity. The effects of DSD are examined by rain attenuation statistics for specific months, together with direct measurements of raindrop diameters on the ground for several rainfall events. Compared with representative DSD models, the effects of the Joss-drizzle type with relatively small raindrops primarily appear in "Baiu (Tsuyu)" period, while the effects of the Marshall-Palmer type which represents a standard type are enhanced in "Shurin (Akisame)" period. On the other hand, the effects of the Joss-thunderstorm type with comparatively large raindrops do not indicate a very clear seasonal variation. Possible improvements of XPD performed by differential phase shifters are generally found to be lower than 10dB for the rain depolarization due to the effect of residual differential attenuation after the cancellation of differential phase shift. Such XPD improvements are, however, very sensitive to the type of DSD, and it is suggested that the improvements are at least greater than 6dB for the Joss-drizzle type, whereas they are less than 6dB for the Marshall-Palmer and Joss-thunderstorm types. The effects of the XPD improvements are thus related to rainfall types, i.e., the type of DSD, and the improvements are considerably dependent upon the seasons in which each rainfall type frequently appears.

We extend the concept "optical instanton" to arbitrary dielectric media. For these general cases the exact analytical approach is no longer available. We derive an approximate analytical solution that would be valid in the vicinity of the light cone. A comparison is made between the analytical and the numerical solutions.

High Definition Television (HDTV) is likely to be one of the major services in the Broadband Integrated Services Digital Network (B-ISDN). The transmission of HDTV signals on digital networks requires the adoption of sophisticated compression techniques to limit the bit-rate requirements and to provide high-quality and cost-effective network services. A flexible coding scheme that supports various bit-rates is needed to support the various services expected which will have different requirements. This paper describes the design of an HDTV codec based on a subband DCT coding algorithm that can encode original 1.2 Gb/s HDTV signals to less than 50Mb/s. A configuration that efficiently bridges HDTV and standard TV signals is also proposed. Computer simulation results show that the degradation caused by the bridging function is insignificant. In the coder, first stage quadrature mirror filters (QMFs) decompose the input signal into two bands in the horizontal direction, while the second stage filters decompose the two bands into four bands in the vertical direction. Adaptive DCT (Discrete Cosine Transform) is adopted for horizontal-low and vertical-low (LL) signal coding. High-band signals are coded by adaptive DPCM and PCM. To maximize bit-rate reduction efficiency, DCT coding is adaptively applied to either the intra-field signals, the inter-field signals, or the motion compensated inter-frame signals. Bi-directional inter-frame prediction is applied to the adaptive DCT coding to improve coding performance at low bit rates. The same prediction mode as for LL signal is applied to adaptive DPCM coding of LH and HL signals. Compatibility is realized by a configuration in which both the TV signal components and the residual signal, derived by subtracting the TV signal from the LL signal, are encoded.

A wavelength-insensitive reflector is demonstrated with a fibre loop which has an asymmetry in the constituent coupler. The reflector is made by thinning one of two identical fibres. The reflected power is more than 0.6 dB (87%) over the wavelength region of 1.2-1.35 µm and 1.42-1.65 µm. The transmitted power is less than 30 dB in the 1.23-1.63 µm region and less than 40 dB at 1.3 and 1.55 µm.