Realization of acceleration control using multirate sampling method

This paper focuses on the realization of high‐performance motion control based on acceleration control. The characteristics of acceleration control are investigated and the relationship between the performance and sampling frequency of the system is discussed. This paper then describes that a higher sampling frequency is required for acquisition of output information than for updating the input value. Based on this idea, a new multirate sampling method for an acceleration control system is proposed. A disturbance observer for the multirate system is designed by adopting a new definition of disturbance torque. A bilateral system is introduced as a preeminent example of a system that requires robust acceleration control. Both simulations and experiments are performed on the system, and the validity of the proposition is verified by the results. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(4): 72–81, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20507     

Anode-supported micro tubular SOFCs for advanced ceramic reactor system

In this study, micro tubular SOFCs under 1 mm diameter have been fabricated and investigated at 450–550 °C operating temperature with H₂ fuel. The performance of the 0.8 mm diameter tubular SOFC was 110–350 mW cm⁻² at 450–550 °C operating temperatures. To maximize the performance of the cell as well as to optimize the geometry of tubular cells, a current collecting method used in the experiment was examined. A model was proposed to estimate the loss of performance for single cell due to the current collecting method as functions of anode tube length and thickness. The results showed that the losses of performance were calculated to be 0.8, 2.0, and 4.6% at 450, 500, and 550 °C operating temperatures, respectively, for the 0.8 mm diameter tubular SOFC with the length of 1.2 cm.     

Effects of mineral addition on the growth morphology of and arachidonic acid production by Mortierella alpina 1S-4

The culture conditions for arachidonic acid (AA) production by Mortierella alpina 1S-4 were investigated by means of a morphological study with the aims of obtaining a high AA yield and scale-up. In a 50-L jar fermentor study, a medium containing 3.1% soy flour and 1.8% glucose with 0.3% KH₂PO₄, 0.1% Na₂SO₄, 0.05% CaCl₂·2H₂O and 0.05% MgCl₂·6H₂O was found to be optimum. The AA yield reached 9.8 g/L/7 d, and the major morphology was small pellets (1–2 mm). However, in the case of the only addition of KH₂PO₄, the major morphology was filaments. The apparent viscosity increased to 2240 cp, thereby requiring a high agitation speed to maintain adequate oxygen tension, which caused mycelial damage due to shear stress and therefore a decrease in the AA yield. When a medium with Na₂SO₄, CaCl₂, and MgCl₂ was used, the major morphology was large pellets (2–3 mm), and mass transfer limitation through the pellet wall caused a decrease in the AA yield. Based on these results, a scale-up study was carried out under the optimal conditions described above. An AA yield of 10.9 g/L/8 d was obtained in a 10-kL industrial fermentor, and the major morphology was small pellets.     

How accurately people can discriminate the differences of floor materials with various elasticities.

Tactile ground surface indicators installed on sidewalks help visually impaired people walk safely. However, these indicators sometimes cause the nonvisually impaired to stumble. Thus, these indicators also have to be made safer and less of a problem for those who do not use them. There are several facilities in Japan that have installed floor materials of different elasticity to indicate paths for the visually impaired. However, the effectiveness of this method has not been tested. Therefore, this study examined how accurately people can discriminate differences in the elasticity of flooring samples. Flooring samples of different elasticity were presented by placing two walking boards made of plywood, each surfaced with one of three different flooring samples, in an end-to-end fashion. Ten young adults whose sight was temporarily cutoff by eye masks were asked to walk on the path for 144 trials and indicate whether the flooring samples were different or not. Interestingly, the percentages of correct answers were high for most pairs of samples. Moreover, there was a strong positive correlation between the percentage of correct answers and the magnitude of difference in floor elasticity. These results indicate that people can distinguish changes of flooring samples fairly accurately, even when there are no convexities, if there is sufficient difference in elasticity between the flooring samples.     

Enhancement of electric conductivity of the rust layer by adsorption of water

The rust layers on the weathering steels exposed for 17 or 18 y at seven different sites in Japan were studied by electrochemical impedance under wet condition and measurement of amount of water vapor adsorbed. The transient of amount of adsorbed water vapor into the rust layer during humidity jump from 0% to 80% RH indicated that saturation of adsorbed water vapor took place within 1 h. From the semi-infinite model of diffusion, apparent diffusion coefficients of H₂O in the rust were calculated. It was found the apparent diffusion coefficient was higher when the amount of air-borne salt of exposure sites was higher. The impedance diagram of the rusted steels was analyzed with an equivalent circuit consisting of a series connection between an ohmic resistance and a parallel circuit of charge transfer resistance-redox capacitance. The double layer capacitance on the gold electrodes pressed onto the rust layer was further added on the circuit. The impedance showed that the rust layer behaved as a dielectric layer under dry condition, while the conductance was greatly enhanced with wet condition. The charge transfer resistance evaluated from the simulation under wet condition was largely dependent on the amount of air-borne salt in environment. It was concluded that the rust layer formed in the site with relatively large amount of air-borne salt revealed high conductivity under wet condition. For the rust formation followed by the Evans model during wet-dry cycles, the higher conductivity induced the more facilitative reduction of the rust layer under wet condition and the larger growth of the rust layer in a wet-dry cycle.     

Morphology of a hydrogen-bonded LC polymer prepared by photopolymerization-induced phase separation under an isotropic phase

A hydrogen-bonded LC polymer was prepared by photopolymerization of an LC blend composed of 4-(6-acryloyloxyhexyloxy)benzoic acid (A6OBA) and 4-hexyloxy-4′-cyanobiphenyl (6OCB), containing small amounts of an inhibitor and photoinitiator, at two different temperatures in an isotropic phase. To elucidate the factors determining the morphology of the obtained polymer (poly(A6OBA)), we chose two irradiation temperatures: one in the LC temperature range of the polymer, the other in the isotropic range. We investigated structures of the polymers by optical microscopy and scanning electron microscopy. SEM images showed that the film obtained at the lower temperature consisted of randomly extended fibers having a diameter of ca. 1.0 μm and some branches, whereas the film prepared at the higher temperature was composed of polymer particles with a diameter ca. 1.5 μm. By comparing these results with those of an earlier experiment in which we obtained macroscopically oriented LC fibers by photopolymerization under the LC phase of the blend, we infer the following; (i) the presence of an LC phase in the resulting polymer itself during photopolymerization is necessary for it to form fibrous morphology and (ii) the LC ordering field present prior to photopolymerization is not indispensable for the fibrous morphology but it is for the macroscopic orientation and reduction of the branches in the fibers.     

Passive Control of Steady Condensation Shock Wave

IntroductionA rapid expansion of moist air or steam in asupersonic nozzle gives rise to nonequilibriumcondensation phenomena. Thereby, the nozzle flow isaffected by the latent heat released by condensation ofwater vapouf, and if the heat released exceeds a certainquantity, a condensation shock wave will occur[1-4].Many works for the passive contfol of shockboundary layer interaction using the porous wall with aplenum underneath have been repofted on the applicationof the technique tO tfansonic…     

Improvement of thermal stability of alumina by addition of zirconia

To maintain a large surface area at elevated temperatures, zirconia was added to transition alumina. The addition of a small amount of zirconia resulted in a marked suppression of phase transformation from θ- to α-alumina. After heating at 1200°C, ZrO₂‐containing alumina exhibited a large surface area of 50 m₂/g. UV‐VIS and XRD measurements indicated that zirconia existed in a high dispersion state after calcining at 800°C. XPS measurement also showed that zirconia existed as monolayer. Zirconia monolayers are concluded to cover the alumina surface and the interaction between them may be the cause for the suppression of phase transformation and also for the maintenance of the large surface area at elevated temperatures. The interaction remains up to 1200°C, therefore, θ phase remained at 1200°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Study of the Gas Flow through a LNG Safety Valve

A safety valve functions to control an upper limit of pressure inside the LNG line of transportation.If the pressureinside the safety valve nozzle exceeds a pre-determined value on the valve sheet which plugs the nozzle,an ex-cess of LNG discharges through the gap between the nozzle exit and valve sheet.In this situation,the forces act-ing on the valve sheet are gasdynamic forces generated by the discharge of LNG and mechanical forces supportedby the spring behind the valve sheet. The flow through the gap is very complicated,involving vortices,flowseparation,and shock waves.These affect adversely on the system accompanying with noise and vibration.Thepresent study aims at understanding the flow physics of safety valve.A computational work using the two-dimensional,axisymmetric,compressible Navier-Stokes equations is carried out to simulate the gas flow betweenthe nozzle exit and valve sheet,and compared with the theoretical results. It has been found that there exists adistance between nozzle exit and valve sheet in which the thrust coefficient at the valve sheet increases abruptly.