Lateral growth of GaAs on patterned {-1-1-1}B substrates for the fabrication of nano wires using metalorganic molecular beam epitaxy

We have grown GaAs nano wire structures (45 × 20 nm²) buried in AIAs layers by lateral metalorganic molecular beam epitaxy on the terraced sidewalls of mesa-grooved (-1-1-1)B substrates. The growth of GaAs occurred primarily on the sidewall of the mesa-grooves and not on the (-1-1-1)B surface for arsenic pressures greater than 2.0 × 10⁻³ Pa at a substrate temperature of 480°C. An (0-1-1) facet formation during the lateral epitaxy at the intersection region between the bottom (-1-1-1)B surface and the (1-2-2)A sidewall has been directly observed by real-time scanning microprobe reflection high-energy electron diffraction. The growth rate on the (0111) facet was estimated from the variation of its width with growth time.     

Activities of FexO in CaO + CaF2 + SiO2 + FexO quaternary slags by disposable electrochemical oxygen probes

The activities of Fe_xO in CaO + CaF₂ + SiO₂ + Fe_xO quaternary slags were measured by means of solid-oxide galvanic cell. The Fe_xO activities in the slags are influenced by CaF₂ as well as SiO₂. At constant Fe_xO mole fractions, e.g., , at low SiO₂ mole fractions i.e., , the substitution of CaF₂ for CaO has an effect of raising the Fe_xO activity. At higher SiO₂ mole fractions, e.g., , however, such an effect becomes insignificant.     

New design for the high-performance drive system for DC brushless motor

The dc brushless motor, permanent magnet-type synchronous motor (PM motor), has been used widely in industrial robots, the machine tools for factory, and factory automations. Therefore, it is more desirable to improve the performance of the PM motor variable speed control system. Although only the torque component current is adjusted as the control method for the PM motor, so-called Vector Control, it is expected that the developed characteristics will be added to the PM motor. In this paper, new driving methods for the PM motor and a new design method for the variable speed control system are presented. The new motor driving methods which bring to the PM motor a new driving performance, e.g., a quick transient response or high-efficiency motor driving, can be implemented by controlling not only the torque component current, but also the magnetizing component current. A developed optimal control theory, i.e., the error system technique, is employed for designing the control system. The control law is endowed with a steady robustness against the variation of the system parameters and the ability of compensating the delay time due to the control processing. The effectiveness of the proposed method is confirmed by simulations and experiments.     

Using model uncertainty for robust optimization in approximate inference control

Recently, the optimization-by-inference approach has been proposed as a new means for solving high-dimensional optimization problems quickly. Approximate Inference COntrol (AICO) is one of the most successful and promising methods that implement the optimization-by-inference approach. AICO is able to solve stochastic optimal control problems and has already been successfully used in many applications. However, it is known that the iterative inference of AICO sometimes fails to converge to the optimal solution. To make the optimization more robust, in this paper, we propose to take model uncertainty into account. In AICO, the cost function to be minimized is accurate around a particular state of a given stochastic system, but the accuracy is uncertain in regions far from that state. Because using such an uncertain function is harmful to the convergence, we modify AICO, so that it does not use the function in uncertain regions. Our method is easy to implement and does not add much computational time to the original AICO. Experiments using two different scenarios show that our method substantially improves AICO in terms of the rate at which the algorithm produces convergent results.     

Decomposition of peroxide on carboxymethyl cellulose and its ability to initiate graft copolymerization

The decomposition of the peroxide group on fibrous carboxymethyl cellulose (CMC) and its ability to initiate graft copolymerization were investigated. The peroxide on CMC liberated hydrogen peroxide when the sample was heated in an aqueous medium. The decomposition of the peroxide was markedly increased by the use of ferrous salt and the irradiation with light of λ > 300 nm. The grafting of methyl methacrylate on CMC peroxide was initiated by heating or irradiating with light, where the rate of grafting and the reciprocal of the average molecular weight of grafts in general were proportional to the square root of the peroxide content of the sample. The peroxide content of the sample was related closely to the number of grafts in initiation. The number was estimated as 17 times for thermal initiation and 6 times for photoinitiation at the maximum values. The CMC peroxide showed a marked activity toward photografting of acrylamide, acrylic acid, acrylonitrile, and vinyl acetate on the substrate.     

Studies of the initiation mechanism of ferric ion–hydrogen peroxide systems in graft copolymerization on cellulose

The decomposition of hydrogen peroxide by ferric ion adsorbed on cellulose, the lowering of the degree of polymerization of cellulose, and the graft copolymerization in the systems containing methyl methacrylate were studied. As the amount of ferric ion adsorbed on cellulose and the concentration of hydrogen peroxide became higher, the amount of decomposition of hydrogen peroxide and the number of scissions of cellulose chains with higher rates at the initial stage of reaction were both observed to increase. It was recognized that the graft copolymerization was hardly initiated, while such initial reactions were proceeding. Assuming that the hydrogen peroxide decomposed with a higher rate was indifferent to the initiation reaction, a certain relationship was found between the amount of ferric ion adsorbed on cellulose ànd the initiation efficiency of hydrogen peroxide in graft copolymerization.     

Graft copolymerization to cellulose in the presence of hydrogen peroxide with ultraviolet irradiation

The decomposition of hydrogen peroxide in the presence of cellulose with ultraviolet irradiation and graft copolymerization occurring upon addition of methyl methacrylate to this system was investigated. Graft copolymerization barely began in the hydrogen peroxide system without ultraviolet irradiation, but was markedly accelerated by ultraviolet irradiation. Ultraviolet light is capable of initiating the graft copolymerization even without addition of hydrogen peroxide, and this capability is enhanced further with the use of hydrogen peroxide. However, an increase in the hydrogen peroxide concentration was observed to exercise a zero or negative effect on the number of grafts. Such a phenomenon is absent in the ceric ion initiator system and, in the present study, is believed to be brought about by a characteristic enhancement of the stabilization of grafting sites effected by hydroxyl radicals. The number of grafts of copolymers obtained in the present initiator system is only approximately 0.085 mmole/100 g of cellulose at its maximum and is within the range of results obtained for the hydrogen peroxide initiator system in general.     

Structural and mechanical characterization of platelet graphite nanofibers

Platelet graphite nanofibers have been characterized by scanning electron microscopy, transmission electron microscopy, electron diffraction, X-ray photoemission spectroscopy, and atomic force microscopy. The results show that the graphene sheets are stacked parallel to each other and are perpendicular to the fiber axis; the interlayer spacing is 0.34 nm. A small fraction of carbon atoms are bonded to oxygen. Solid-state nuclear magnetic resonance shows that hydrogenated carbons are under the detection limit (<5%) and that the nanofibers are dominated by sp²-bonded carbons. Mechanical measurements were made on individual nanofibers by nanoindentation.     

Polymer optical fiber for near infrared use

Using the empirical simulation that we developed to estimate loss spectra of amorphous polymers, we predicted the intrinsic loss spectrum of fluorine-containing polyarylate (FPAr) that should have a small attenuation loss in the near infrared region. Loss of FPAr is smaller than that of poly (methyl methacrylate), which is a typical optical polymer used as a core material in polymer optical fiber (POF), above 720 nm. FPAr was synthesized by phase transfer catalyzed polycondensation of 2,2-bis (4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane with isophthaloyl dichloride. Its glass-transition temperature (T_g) by DSC is 163°C. This indicates that FPAr has higher heat resistance than polycarbonate (PC) by about 10°C. A film of 100μm thick has over 85% transmittance from 330 to 900 nm. Values from a tension test are similar to those of PC. As a result, FPAr is expected to be a good core polymer for POF, because of its high T_g, good transparency, and good flexibility. Next, the POF made of FPAr was fabricated by a melt-flow spinning method. It had larger attenuation loss than predicted. The difference from the simulation was extrinsic loss caused by the fabricating process. Therefore, when a more suitable fabricating process is developed, loss of FPAr-POF can be decreased, so that it will be applicable to optical communications in the near infrared region. © 1993 John Wiley & Sons, Inc.     

Updating of adventitious fuel pin failure frequency in sodium-cooled fast reactors and probabilistic risk assessment on consequent severe accident in Monju

Experimental studies, deterministic approaches and probabilistic risk assessments (PRAs) on local fault (LF) propagation in sodium-cooled fast reactors (SFRs) have been performed in many countries because LFs have been historically considered as one of the possible causes of severe accidents. Adventitious-fuel-pin-failures (AFPFs) have been considered to be the most dominant initiators of LFs in these PRAs because of their high frequency of occurrence during reactor operation and possibility of fuel-element-failure-propagation (FEFP). A PRA on FEFP from AFPF (FEFPA) in the Japanese prototype SFR (Monju) was performed in this study based on the state-of-the-art knowledge, reflecting the most recent operation procedures under off-normal conditions. Frequency of occurrence of AFPF in SFRs which was the initiating event of the event tree in this PRA was updated using a variety of methods based on the above-mentioned latest review on experiences of this phenomenon. As a result, the frequency of occurrence of, and the core damage frequency (CDF) from, AFPF in Monju was significantly reduced to a negligible magnitude compared with those in the existing PRAs. It was, therefore concluded that the CDF of FEFPA in Monju could be comprised in that of anticipated transient without scram or protected loss of heat sink events from both the viewpoint of occurrence probability and consequences.