A series of 4-alkyl-4′-alkoxylbiphenyls, which are one of the representative calamitic liquid crystals having a small aromatic core moiety, has been synthesized and their charge carrier transport properties are characterized in order to examine how small the core size can be for a high mobility. The biphenyls exhibit both smectic B and E phases and the hole transport characterized by a high mobility of 10−3 cm2 V−1 s−1 in the smectic mesophases. The mobility depends on temperature in both smectic phases, and furthermore it depends on the electric field in the smectic E phase. The fact that such a small molecule of biphenyl exhibits the mobility comparable to those of triphenylenes and TPD (N,N′-diphenyl-N,N′-bis(3-methylphenyl)[1,1′-biphenyl]-4,4′-diamine) gives an insight into the molecular design of high mobility liquid crystalline materials.
This paper discusses the technical feasibility of the multimedia metropolitan area network based on the tree‐shaped broadband network, employing two‐way CATV technology. In the proposed network, all information can flow on any transmission line through the headend. This leads to the following features, which cannot be realized in the star network as in the telephone network: Flexible services are provided. An efficient information communication service can easily be realized. It is easy to provide the highspeed broadband service at a low cost. The security of the network can be improved. The following systems were developed by the authors as examples of the information communication services utilizing those features: TDMA circuit switching service using “time‐slotted bus with control window,” CSMA/CD packet switching service using “beat signal level detection,” and TDMA video switching service, where several video signals are multiplexed as analog signals. Those services can be provided to more than 10,000 subscribers in a service area of diameter 20 km or more. The system is expected to provide the basis for the information communication in local communities, together with the widespread use of urban‐type CATV.
This paper attempts to realize the TDMA circuit switching service on the broadband tree-shaped network applying the two-way coaxial CATV techniques. The improvement of the time-slotted bus system with controller window proposed previously by the authors is dis-CUSSed.To make this system practical, such problems as simplification of terminal device and expansion of service scale must be solved. For this purpose, the "center measurement method" and the "variable width control window method" are developed anew. The former is a system which measures such parameters as the round-trip transmission delay at the central control device and notifies the terminal of the result.By improving the down-link transmission quality of the control window, which is important from the viewpoint of the stable operation of the whole system and by reducing the high-speed operation functions, the terminal 1 device is simplified. The latter is to adjust the control window width according to the traffic. By this scheme, the number of contained time-slots, i.e., the number of serviceable subscribers, can be increased without reducing the wide service area of the broadband tree-shaped network. A prototype system was constructed based on those two system improvements, and an experimental evaluation was attempted on the experimental two-way CATV system with a total length of 7.9 km. As a result, it was verified that the foregoing improvements are useful and matched to each other.
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