Tan δ of ethylene-propylene rubber in cryogenic temperature region–effects of additives and sample thickness

The authors have been developing extruded polymer insulated superconducting power cables. Dielectric loss in electrical insulation cannot be ignored in superconducting cables since conductor loss in the cables is minimal. Studies so far show that ethylene-propylene rubber (EPR) is suitable as an electrical insulating material in the extruded polymer insulated superconducting cable design because it demonstrates excellent mechanical and relatively good electrical qualities at a cryogenic temperature. Widely used EPR includes some kinds of additives; however, their effect on tan δ of EPR at cryogenic temperature remains unknown. The effect of additives such as crosslinking agent and fillers on tan δ of EPR was examined at temperatures of between 4.2 K and 300 K. Thickness dependence of tan δ was also measured using EPR films of different thickness and an extruded EPR insulated cable sample. The results show that additives increase tan δ of relatively thin films of EPR even in the cryogenic temperature region; however, they do not have an intolerable dielectric loss in comparison with conductor loss and heat inflow of the superconducting cable. The remedy to tan δ increase due to the polymer contraction relative to shielding wires has been established.     

ac treeing of ethylene-propylene rubber in cryogenic temperature region

The authors have proved that ethylene-propylene rubber (EPR) is suitable for the solid electrical insulating material of superconducting and cryoresistive cables due to its excellent mechanical and good electrical properties. It is imperative to study the treeing resistivity of EPR in view of long-term reliability as a cable insulator. The objectives of this paper are to establish an ac treeing test method of opaque EPR samples with fillers and to examine the treeing resistivity of EPR at both liquid-nitrogen and room temperatures and the effect of fillers on treeing resistivity. It was found that EPR has enough resistance to ac treeing at liquid-nitrogen temperature and that fillers improve ac treeing resistivity slightly. High reliability of EPR insulation is expected during long-term operation at cryogenic temperature.     

On the max-entropy rule for a binary search tree

Summary A modified max-entropy rule is proposed for constructing nearly optimum binary search tree in the case of ordered keys with given probabilities. The average cost of the trees obtained by this rule is shown to be bounded by the entropy of the probability distribution plus a constant not larger than one. An algorithm for implementing this rule is then suggested and its complexity is investigated in a probabilistic setting.     

A further note on the dual structure in information theory

This note is a continuation of the former one [2]. First, Duality Theorems in information theory will be explicitly presented. Secondly a communication scheme with side information will be considered. We shall construct another scheme without side information so that these two schemes will become equivalent in a cost-distortion duality sense, allowing the Duality Theorems to hold in the former scheme. An example will then be given with additional purpose to illustrate how the cost-distortion performance of communication will change according as side information is available or not.     

Texture and electromigration lifetime improvements in layered Al-alloy metallization with underlying Ti by controlling water adsorption on SiO2 substrates

The effect of residual gas constituents and substrate temperature during Ti sputtering on the texture of TiN/Ti films deposited on SiO₂/Si substrates has been investigated. The Ti(002) and TiN(111) preferred texture of the films deposited at 350°C was found to be improved drastically by increasing the H₂O partial pressure from 1×10⁻⁹ to 3×10⁻⁸ Torr. Both of the Ti(002) and TiN(111) textures showed a similar H₂O partial pressure and substrate temperature dependence because of the epitaxial transfer between these planes. The improved Ti(002) texture was attributed to the self-assembly of Ti atoms on the SiO₂ surface, which had a low surface free energy due to the formation of surface OH groups. Two kinds of layered Al-alloy interconnects, AlSiCu/Ti/TiN/Ti and AlCu/TiN/Ti, were fabricated with the highly textured TiN/Ti film, and their Al(111) texture and electromigration lifetime were then evaluated. It was confirmed that both of the interconnects have strong Al(111) texture and longer EM lifetimes.     

Lesser Bear—a light‐weight process library for SMP computers

We have designed and implemented a light‐weight process (thread) library called ‘Lesser Bear’ for SMP computers. Lesser Bear has high portability and thread‐level parallelism. Creating UNIX processes as virtual processors and a memory‐mapped file as a huge shared‐memory space enables Lesser Bear to execute threads in parallel. Lesser Bear requires exclusive operation between peer virtual processors, and treats a shared‐memory space as a critical section for synchronization of threads. Therefore, thread functions of the previous Lesser Bear are serialized. In this paper, we present a scheduling mechanism to execute thread functions in parallel. In the design of the proposed mechanism, we divide the entire shared‐memory space into partial spaces for virtual processors, and prepare two queues (Protect Queue and Waiver Queue) for each partial space. We adopt an algorithm in which lock operations are not necessary for enqueueing. This algorithm allows us to propose a scheduling mechanism that can reduce the scheduling overhead. The mechanism is applied to Lesser Bear and evaluated by experimental results. Copyright © 2001 John Wiley & Sons, Ltd.     

A new memory allocation method for shared memory multiprocessors with large virtual address space

This paper proposes a new memory allocation method for shared memory multiprocessors with large virtual address spaces. An evaluation of its performance is also presented. For effective use of shared memory multiprocessors, it is important that no processor's execution is blocked. If several processors simultaneously access a shared variable, their processes are blocked and access to the variable is serialized. Thus, frequent access to shared variables reduces the parallelism. In particular, the parallelism is significantly reduced when a special shared variable – the ‘allocation pointer’ – is frequently accessed in the dynamic object allocation by an application program. In this paper, we propose a new method for allocating physical memory pages where the allocation pointer is monotonically increased in the virtual address space in contrast to the conventional method. This allows the critical sections for access to the allocation pointer to be executed effectively and atomically by using the fetch-and-add primitive. Our method improves the application program's parallelism by access to the allocation pointer with considerably short blocking time to the process. © 1997 John Wiley & Sons, Ltd.     

Lesser Bear: A lightweight process library for SMP computers—scheduling mechanism without a lock operation

We have designed and implemented a lightweight process (thread) library called ‘Lesser Bear’ for SMP computers. Lesser Bear has thread‐level parallelism and high portability. Lesser Bear executes threads in parallel by creating UNIX processes as virtual processors and a memory‐mapped file as a huge shared‐memory space. To schedule thread in parallel, the shared‐memory space has been divided into working spaces for each virtual processor, and a ready queue has been distributed. However the previous version of Lesser Bear sometimes requires a lock operation for dequeueing. We therefore proposed a scheduling mechanism that does not require a lock operation. To achieve this, each divided space forms a link topology through the queues, and we use a lock‐free algorithm for the queue operation. This mechanism is applied to Lesser Bear and evaluated by experimental results. Copyright © 2002 John Wiley & Sons, Ltd.