Superconducting Coupling Nature at Grain Boundaries in Bi2Sr2CaCu2Ox Glass-Ceramics

Superconducting coupling nature at grain boundaries in Bi₂Sr₂CaCu₂O _x glass-ceramics consisting mainly of the low- T _c phase was first examined by measuring superconducting properties and temperature or ac field dependence of ac complex susceptibility. It was found from the ac loss peaks that superconducting coupling at grain boundaries was basically characterized by three types of weak links. The weak-link behaviors at grain boundaries depended strongly on cooling conditions after annealing and annealing time and temperature. Particularly, it was found that the weak links at grain boundaries were improved by prolonged annealing at 840°C. The furnace-cooled glass-ceramics obtained by annealing at 820° or 840°C for about 200 h exhibited a critical transport current density (77 K, zero magnetic field) of about 200 A/cm².     

Hydrogen-bond-assisted isotactic-specific radical polymerization of N-isopropylacrylamide with pyridine N-oxide

Radical polymerization of N-isopropylacrylamide (NIPAAm) in CHCl₃ at low temperatures in the presence of pyridine N-oxide (PNO) was investigated. An isotactic poly(NIPAAm) with meso diad content of 61% was successfully prepared at −60 °C in the presence of a two-fold amount of PNO. Thermodynamic analysis suggested that the isotactic-specificity was entropically induced, probably due to conformational fixation near the propagating chain-end through coordination by PNO.     

An estimation of friction from the indentation of metals by acute-angled conical indenters

The paper describes a method for estimating the coefficient of friction (COF) between sliding surfaces by an indentation of an acute-angled indenter. The COF estimated by the method is compared with the COF measured by a friction tester. The conical indenter, which is made of WC and has an apex angle of 45°, is used for the experiments. A micro-Vickers hardness tester is used for the indentation tests. The friction tester used is one of Bowden–Leben type. A copper and a 0.45% carbon steel are used for the indentation and sliding specimens. The estimation of the COF is based on the equilibrium equation of indentation, which takes the friction between the contacting surfaces of the indenter and the specimen into consideration. The results show that the estimated COF is approximately equal to the measured one. Based on the results, the validity of this method is discussed.     

Effects of photo-induced graft polymerization of 2-methacryloyloxyethyl phosphorylcholine on physical properties of cross-linked polyethylene in artificial hip joints

Osteolysis caused by wear particles from polyethylene in the artificial hip joints is a serious issue. We have used photo-induced radical graft polymerization to graft 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer onto the surface of cross-linked polyethylene (CLPE-g-MPC) in order to reduce friction and wear at the bearing surface of the joint. The physical and mechanical properties of CLPE and CLPE-g-MPC were not significantly different, expect that the friction coefficient of untreated CLPE cups was 0.0075, compared with 0.0009 for CLPE-g-MPC cup, an 88% reduction. After 3.0 × 10⁶ cycles in the hip joint simulator test, we could not observe any wear of CLPE-g-MPC cups. We concluded that the advantage of photo-induced radical graft polymerization technique was that the grafted MPC polymer gave a high lubricity only on the surface and has no effect on the bulk properties of the CLPE substrate.     

Characterization of new types of mannosylerythritol lipids as biosurfactants produced from soybean oil by a basidiomycetous yeast, Pseudozyma shanxiensis

Mannosylerythritol lipids (MELs) are glycolipid biosurfactants produced by the yeast strains of the genus Pseudozyma. These show not only the excellent surface-active properties but also versatile biochemical actions. In course of MEL production from soybean oil by P. shanxiensis, new extracellular glycolipids (more hydrophilic than the previously reported MELs) were found in the culture medium. As a result of the structural characterization, the glycolipids were identified as a mixture of 4-O-[(2', 4'-di-O-acetyl-3'-O-alka(e)noyl)-beta-D-mannopyranosyl]-D-erythritol and 4-O-[(4'-O-acetyl-3'-O-alka(e)noyl-2'-O-butanoyl)-beta-D-mannopyranosyl]-D-erythritol. Interestingly, the new MELs possessed a much shorter chain (C(2) or C(4)) at the C-2' position of the mannose moiety compared to the MELs hitherto reported, which mainly possess a medium-chain acid (C(10)) at the position. They would thus show higher hydrophilicity and/or water-solubility, and expand the development of the environmentally advanced yeast biosurfactants.     

Microbial conversion of glycerol into glycolipid biosurfactants, mannosylerythritol lipids, by a basidiomycete yeast, Pseudozyma antarctica JCM 10317(T)

Microbial conversion of glycerol into functional bio-based materials was investigated, aiming to facilitate the utilization of waste glycerol. A basidiomycete yeast, Pseudozyma antarctica JCM 10317, efficiently produced mannosylerythritol lipids (MELs) as glycolipid biosurfactants from glycerol. The amount of MEL yield reached 16.3 g l(-1) by intermittent feeding of glycerol.     

The species fitness method for the evolution of cooperative behavior in a group task

This paper considers the evolution of cooperative behaviors as the interaction among agents using a genetic algorithm to improve the performance of the task in a group (group performance). Previous research often usedthe group fitness method, which evaluates group performance for the evolution of multiple groups in parallel. However, this entails large simulation costs and the evolution speed is slow.The individual fitness method that evaluates theindividual performance of the task entails a smaller simulation cost. However, it can not improve the group performance since each agent behaves selfishly. To optimize the group performance, it is important to include bothcompetition andsharing. Therefore, this paper presentsthe species fitness method, which shares the individual performances of agents belonging to the same species in a group that all have the same chromosomes. We show comparative experiments on these three methods on the evolutionary simulation of a foraging task in a group. To test the interaction among the agents, four kinds of species are evolved which show their communication ability by demonstrating whether the agent can send or receive the signal for food. Experimental results show that evaluating the species variance fitness leads the agents into reciprocative actions. This work was presented, in part, at the Third International Symposium on Artificial Life and Robotics, Oita, Japan, January 19–21, 1998     

Designing Double Pore Structure in Alkoxy-Derived Silica Incorporated with Nonionic Surfactant

The principle of designing double-pore structure in alkoxy-derived silica is described with the experimental system containing polyoxyethylene nonylphenylether. The formation of macropores is consistently explained in terms of the concurrence of a phase separation and a sol-gel transition in the polymerizing silica-surfactant-solvent system. The composition-morphology relationship exhibited a substantial variation depending on the length of oxyethylene units in the surfactant molecule. The mesopore volume obtained after basic solvent exchange and a heat-treatment suggested that the surfactant with shorter oxyethylene chain tends to be incorporated more in the gel phase to give higher mesopore volume. The small-angle X-ray scattering measurement of the gelling and aging system supported this hypothesis indicating micelle formation in the system containing a surfactant with shorter oxyethylene chain.