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31.
OBJECTIVES: Single-component anaerobic adhesives are in common use in the electronics and engineering industries. They are generally diacrylate monomers which do not require conventional sources of heat, light or chemicals for activation. Their advantages include activation by the bonding substrate, as well as inhibition of polymerisation until the necessary anaerobic environment is created. The aim of this experiment was to determine whether metal attachments could be successfully bonded to enamel in vitro by such adhesives. METHODS: Metal attachments capable of providing an anaerobic environment were fabricated from one of three alloys: stainless steel, copper or cobalt-chromium. They were bonded to prepared human enamel with one of four adhesives: Orthodontic Concise, as a control, and three anaerobic adhesives, Perma Metal, Permabond A134 and Loctite 326. The specimens were then bond tested in shear to failure after bench curing for one of four time periods. RESULTS: The results were analysed in terms of mean force to debond (N) and 95% confidence intervals. Kaplan-Meier survival probabilities and log-rank tests were performed for the 10 min test times. CONCLUSIONS: Both Orthodontic Concise and the three anaerobic adhesives displayed a specificity towards different attachment alloys. Whereas Orthodontic Concise displayed the highest force to debond with stainless steel attachments, for the anaerobic adhesives this was true of the copper attachments. With stainless steel attachments, however, the force to debond with the anaerobic adhesives was similar to that observed with Orthodontic Concise and steel, at least after the relatively short 10 min bench curing time.  相似文献   
32.
The photovoltaic power system has a great future as a clean-energy alternative to fossil fuel which has many environmental problems such as gas exhaustion or air pollution. Sunlight, a source of energy for the system, is influenced greatly by weather conditions, seasons and times of day. Therefore it cannot supply constant electric power. The photovoltaic/fuel cell power hybrid system is assumed. It combines PV array, hydrogen generator, storage tank and fuel cells by using hydrogen. This system can supply constant electric power to the electric load in a solitary island separated from a commercial electric network. The possibility of this system is examined by computer simulation. Input data include the global irradiance on inclined plane and temperature of HASP data of Tokyo, ten kinds of electrical load forms with 400 MWh electric power a year, and conversion efficiencies of each subsystem. As a result of simulation, it was revealed that the area of PV array with 8170 m2 and the volume of hydrogen tank from 22 × 103 to 30 × 103 kl are necessary.  相似文献   
33.
We have recently succeeded in manufacturing low-caffeine tea (LCT) by employing a special picking method in the 3rd leaf period and shortening the leaf-rolling process. In the present study, the effect of this special method on the content of other physiologically active substances, such as catechins, theanine, and vitamin C, as well as the mechanism of reduction of caffeine content in the LCT were investigated using capillary electrophoresis. By comparing the various components of tea leaves at different picking periods with or without shortening of the rolling process, it was found that the delayed leaf picking period and shortening of the rolling process used in the manufacture of LCT selectively reduced the caffeine content while retaining catechins, theanine, and vitamin C at a sufficient level. Therefore, our study demonstrated that this modified method may be useful in the manufacture of decaffeinated green tea.  相似文献   
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To investigate the adaptability of a biped robot controlled by nonlinear oscillators with phase resetting based on central pattern generators, we examined the walking behavior of a biped robot on a splitbelt treadmill that has two parallel belts controlled independently. In an experiment, we demonstrated the dynamic interactions among the robot mechanical system, the oscillator control system, and the environment. The robot produced stable walking on the splitbelt treadmill at various belt speeds without changing the control strategy and parameters, despite a large discrepancy between the belt speeds. This is due to modulation of the locomotor rhythm and its phase through the phase resetting mechanism, which induces the relative phase between leg movements to shift from antiphase, and causes the duty factors to be autonomously modulated depending on the speed discrepancy between the belts. Such shifts of the relative phase and modulations of the duty factors are observed during human splitbelt treadmill walking. Clarifying the mechanisms producing such adaptive splitbelt treadmill walking will lead to a better understanding of the phase resetting mechanism in the generation of adaptive locomotion in biological systems and consequently to a guiding principle for designing control systems for legged robots.  相似文献   
37.
The mechanism of formation of surface roughness and extrusion swelling of the extrudate and the steady-shear viscous flow behavior in the region of high shear rate for branched polymers were investigated using two low-density polyethylenes and their sheared samples. These two polyethylenes varied in their degree of branching, molecular weight, and molecular weight distribution but were similar in their melt flow index. The effect of molecular parameters, especially long-chain branching, on viscoelastic properties in the molten state was also considered. Samples of various degree of shearing level were prepared by passing them repeatedly through an extruder. Results of intrinsic viscometry, gel permeation chromatography, and infrared spectroscopy of the original and the sheared samples indicate that no appreciable variation between them takes place in the molecular parameters during the process of extrusion shearing. Both surface roughness and extrusion swelling of the extrudate diminish with increase in the extent of shear. The extrusion shearing affects the surface roughness and extrusion swelling of the extrudate as well as the capillary entrance effect more markedly for the highly branched polymers with considerably higher molecular weight than for the less branched species with bell-type molecular weight distribution. These results demonstrate that heterogeneity becomes more conspicuous with the degree of long-chain branching level, and therefore the role of long-chain branching in the development of the heterogeneity is particularly important. It is suggested that the secondary heterogeneous structure arises through phase separation or from the heterogeneous formation of strongly entangled network at the branching point of the long-chain branching in the manufacturing process of the low-density polyethylene and that its presence causes the distinctive viscoelastic properties of long-chain branched polymer melts.  相似文献   
38.
In an investigation of the behavior and formation mechanism of melt fracture the flow properties of molten ethylene–vinyl acetate (EVA) copolymer in the region of high shear rate were measured with a capillary-type rheometer. EVA copolymer differs slightly in flow curve from low-density polyethylene (LDPE); it seems, however, that the difference is due to the difference in molecular weight distribution (MWD) rather than to the materials themselves. The fluidity of molten EVA copolymer having a narrow MWD is equivalent to that of LDPE having a broad MWD and, generally, EVA copolymer has a higher fluidity than LDPE. It is expected that the fluidity increases with incorporation of vinyl acetate at the same MWD and the same M?w. The critical shear rate increases with melt index and temperature. It cannot be found that the materials themselves and the MWD directly influence the critical point of melt fracture formation when the melt index is taken as a parameter. The critical viscosity (ηc) at which melt fracture forms decreases in an almost straight line with an increase of melt index. It was found from the studies of end correction and behavior of melt fracture formation that melt fracture occurs at the inlet of the die, and it is supposed that the melt fracture formation is caused by the elastic turbulence in the flow pattern due to a failure of recoverable shear strain at the die inlet.  相似文献   
39.
To improve the dispersibility of vapor grown carbon fiber (VGCF) in solvents, the grafting of copolymer containing vinyl ferrocene (VFE) onto the surface by ligand-exchange reaction between ferrocene moieties of the copolymer and polycondensed aromatic rings of VGCF was investigated. The copolymer containing VFE was prepared by the radical copolymerization of VFE with methyl methacrylate (MMA) using 2, 2′-azobisisobutyronitrole as an initiator. It was found that by heating of VGCF with poly(VFE-co-MMA) in the presence of AlCl3 and Al powder, the copolymer was grafted onto the wall-surface: the percentage of grafting reached to 57.5%. It is considered that the copolymer was grafted onto VGCF surface by ligand-exchange reaction between ferrocene moieties of the copolymer and polycondensed aromatic rings of VGCF. In addition, carboxyl groups were successfully introduced onto VGCF wall-surface by the ligand-exchange reaction of 1,1′-dicarboxyferrocene with VGCF in the presence of AlCl3 and Al powder. The carboxyl groups on VGCF were reacted with hydroxyl-terminated polymers to give the corresponding polymer-grafted VGCF. The polymer-grafted VGCF gave a stable colloidal dispersion in solvents for grafted polymer. The electric properties of composite prepared from polymer-grafted VGCF in solvent vapor were investigated.  相似文献   
40.
Phthalocyanine ultrathin films were prepared by a successive dip/dry process of hydroxy-group-bearing substrates into a dilute solution of phthalocyanine with silanol group at its coordination center (Pc). Amounts of adsorbed Pc on the substrate were monitored using a quartz crystal microbalance. At each dip/dry cycle, the adsorbed Pc corresponded to the mass of a single Pc layer flat on the surface. On the other hand, similar results could not be achieved with a pre-polymerized Pc, which showed Langmuir-type adsorption onto the substrate, probably due to the forming of a horizontally aligned monolayer. The Pc ultrathin film was specifically formed on an n-hexanol-presented substrate, although the Pc ultrathin films could not be formed with shorter ethanol- or longer undecanol-presented substrates. Furthermore, a hetero-structured Pc ultrathin film was prepared using an alternative second component Pc.  相似文献   
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