524,288 NbN-based Josephson junctions were integrated to produce a programmable Josephson voltage standard (PJVS) on a die of 15 mm 15 mm, and the PJVS circuit was cooled to 10 K using a cryocooler and operated with a current margin of about 1.0 mA. Although an output voltage of 10 V was required for a voltage standard, the circuit was designed to generate the maximum output voltage of 17 V because it was difficult to avoid a reduction of the output voltage due to defects. Although a perfect chip without any defect was rarely fabricated, the high voltage chip that generated at least 10 V was fabricated with the fabrication yield of larger than 30%. The fabrication yield was also improved by optimizing the film growth conditions to reduce the film stress and the number of particles. Applications for a secondary voltage standard and an ac Josephson voltage standard are also described.

For two decades, our colleagues and we have been developing our multiple learning environments in mathematical education for upper secondary school learners, and have been reporting our learner-centered system in the latest four WCCE Conferences (WCCE/1981/1985/1990/1995). In our latest learning multimedia system, individual learners have to meet a complex network structure in which objectives are arranged in the form of non-linear linking and to proceed actively to their own goals. In order to support their exploring learning, we developed several instructional navigation tools from an instructional view point. This paper presents our instructional navigation technology and its tools. The feature of our present system is to provide a supportive environment where individual learners can set up their own goals, create their own paths for their goals through instructional materials, and construct their own instructional structure based on instructional strategies. This feature is remarkably different from a traditional CAI system in which learners are only directed through the courseware via a linear selection of menus. Also this feature fundamentally differs from general navigation technologies by which a user is able to traverse a series of nodes among non-linear network structure, because our navigation must present individual learners with some easily learnable sequences of objectives based on their object and interest. For this purpose, this system has three chracteristic technologies, i.e. focusing, sequencing and clustering ones. These are very useful for them to make their decisions in order to reach their own goals. This paper consists of (1) ideas of instructional navigation, (2) map technology and (3) navigation technology.