Application of a novel polypropylene to the insulation of an electric power cable

Cross‐linked polyethylene (XLPE) has been widely adopted as insulating material for high‐voltage power cables up to 500 kV. Further improvement of electrical and thermal properties on insulating material is required in order to increase cable operation efficiency. Therefore, the development of novel insulating material possessing high thermal properties will be necessary. Recent progress of catalysis technology contributes to obtain new polymeric materials which may be applied to electrical insulation. The authors investigated the basic properties of newly developed stereoregular syndiotactic polypropylene (s‐PP) which is synthesized with homogeneous metallocene catalyst. Though recycling of cross‐linked polymers such as conventionally used XLPE may be difficult because of their poor heat deformation, the s‐PP which is not cross‐linked must be suitable for recycling. A series of experiments on its physical and electrical properties gave the following results.

• (1) s‐PP has sufficient flexibility compared with isotactic polypropylene (i‐PP ).
• (2) Both AC and lightning impulse breakdown strength of s‐PP in spite of no cross‐linking are superior to those of XLPE in the temperature range from 25 to 90 °C.
• (3) Degradation by copper of s‐PP is less than that of i‐PP.
• (4) s‐PP/VLDPE blend shows sufficient brittleness temperature for use.

These results suggested that s‐PP should serve as insulating material for power cables at higher‐temperature operation. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(1): 18–26, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002//eej.10210     

Metabolic disturbance of tryptophan-nicotinamide conversion pathway by putative endocrine disruptors, bisphenol A and styrene monomer

Bisphenol A, a monomer of polycarbonate plastics, disturbed the conversion pathway of the amino acid tryptophan to the vitamin nicotinamide. The conversion ratio of tryptophan to nicotinamide was reduced to 1/15 by feeding a diet containing 1% bisphenol A. A putative disturbing reaction is kynurenine-->3-hydroxykynurenine, which is catalyzed by kynurenine monohydroxylase. This is an FAD-enzyme and requires NADPH as a coenzyme. Styrene monomer (1% addition to a normal diet) did not affect the food intake or the body weight, but slightly reduced the conversion ratio of tryptophan-nicotinamide.     

Efficient frequency doubling of 1-W continuous-wave Ti:sapphire laser with a robust high-finesse external cavity

We demonstrated an intrinsic conversion efficiency of 56% from the input fundamental power to the generated second-harmonic power. The second-harmonic power of 581 mW was obtained from the external cavity with a LiB3O5 crystal through the frequency doubling of a 1.17-W Ti:sapphire laser at 746 nm, when the finesse of the robust external cavity was 260.     

Completing causal networks by meta-level abduction

Meta-level abduction is a method to abduce missing rules in explaining observations. By representing rule structures of a problem in a form of causal networks, meta-level abduction infers missing links and unknown nodes from incomplete networks to complete paths for observations. We examine applicability of meta-level abduction on networks containing both positive and negative causal effects. Such networks appear in many domains including biology, in which inhibitory effects are important in several biological pathways. Reasoning in networks with inhibition involves nonmonotonic inference, which can be realized by making default assumptions in abduction. We show that meta-level abduction can consistently produce both positive and negative causal relations as well as invented nodes. Case studies of meta-level abduction are presented in p53 signaling networks, in which causal relations are abduced to suppress a tumor with a new protein and to stop DNA synthesis when damage has occurred. Effects of our method are also analyzed through experiments of completing networks randomly generated with both positive and negative links.     

The role of voltage-gated Ca2+ channels in anoxic injury of spinal cord white matter

Dorsal column axons of the rat spinal cord are partially protected from anoxic injury following blockade of voltage-sensitive Na+ channels and the Na+/--Ca2+ exchanger. To examine the potential contribution of voltage-gated Ca2+ channels to anoxic injury of spinal cord axons, we studied axonal conduction in rat dorsal columns in vitro following a 60-min period of anoxia. Glass microelectrodes were used to record field potentials from the dorsal columns following distal local surface stimulation. Perfusion solutions containing blockers of voltage-gated Ca2+ channels were introduced 60 min prior to onset of anoxia and continued until 10 min after reoxygenation. Pharmacological blocking agents which are relatively selective for L- (verapamil, diltiazem, nifedipine) and N- (omega-conotoxin GVIA) type calcium channels were significantly protective against anoxia-induced loss of conduction, as was non-specific block using divalent cations. Other Ca2+ channel blockers (neomycin and omega-conotoxin MVIIC) that affect multiple Ca2+ channel types were also neuroprotective. Ni2+, which preferentially blocks R-type Ca2+ channels more than T-type channels, was also protective in a dose-dependent manner. These data suggest that the influx of Ca2+, through L-, N- and possibly R-type voltage-gated Ca2+ channels, participates in the pathophysiology of the Ca2+-mediated injury of spinal cord axons that is triggered by anoxia.