Elimination of fictitious penetrating rays from PO and hybridization with AFIM

Physical optics (PO) is an approximation method for high‐frequency scattering and diffraction problems. But PO fields are inaccurate in the shadow region where the source is screened by the scatter. Two key factors of the error for PO are (i) edge diffraction coefficients and (ii) existence of fictitious penetrating rays. The correction with respect to the former has been extensively investigated by many authors using various ray techniques such as GTD, UTD, and UAT. On the other hand, the latter was identified recently by the authors. This paper proposes novel PO‐based calculation procedures termed PO‐AF and PTD‐AF, where PO and Aperture Field Integration Method (AFIM) are merged with the help of special elementary diffraction coefficients. These can uniformly cover the whole angular region and only the error factor (ii) is removed in PO‐AF while both (i) and (ii) are removed in PTD‐AF. The theoretical backgrounds of PO currents are discussed in terms of field equivalence theorem and visualization of EM waves. Next, new methods are proposed and their validity is numerically demonstrated for 2D scattering problems of a strip, a corner reflector, and a cylinder of circular arc. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(2): 1–10, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20037     

Preparation of γ-alumina thin membrane by sol-gel processing and its characterization by gas permeation

-alumina porous membranes without pinholes or cracks were prepared by the sol-gel process. The boehmite sol obtained from hydrolysation of aluminium isopropoxide was applied to the inner surface of a porous supporting tube by a dipping procedure. The effects of sol concentration and the repetition number of dipping-drying-firing procedure on the membrane performance were investigated by scanning electron microscopy, X-ray diffraction and the Brunauer-Emmett-Teller method in connection with the micro-structure of the membrane. Gas permeation measurements were also conducted. The gas permeation through the thin membranes is well explained by Knudsen's flow, indicating the pores are controlled finely and homogeneously.     

FORMATION AND FLOW OF GAS BUBBLES IN A PRESSURIZED BUBBLE COLUMN WITH A SINGLE ORIFICE OR NOZZLE GAS DISTRIBUTOR

The characteristics of gas bubbles in a 5 cm diameter bubble column equipped with a single orifice of 1,3 or 5 mm diameter were investigated under system pressure of 0.1-15 MPa. The formation of gas bubbles was strongly affected by the system pressure. Under high pressures a dispersed gas jet was formed at gas velocities where spherical gas bubbles would have been formed at atmospheric pressure. The critical gas velocity between the bubbling regime and the jetting regime was correlated with the liquid phase Weber number and the gas phase Reynolds number based on the gas velocity at the orifice. Bubble size and gas holdup in the main part of the bubble column were also affected by the bubble formation pattern at the distributor     

Performance of solvothermally prepared Ga2O3-Al2O3 catalysts for SCR of NO with methane

The solvothermal reaction of mixtures of aluminum isopropoxide (AIP) and gallium acetylacetonate (Ga(acac)₃) directly yielded the mixed oxides of γ-Ga₂O₃-Al₂O₃. In the solvothermal synthesis, the crystal structure of mixed oxides was controlled by the initial formation of γ-Ga₂O₃ nuclei. The mixed oxides prepared in diethylenetriamine have extremely high activities for selective catalytic reduction (SCR) of NO with methane as a reducing agent. With increasing crystallite size of the spinel structure, the catalytic activity increased. The ratio of the amount of methane consumed by combustion to total methane conversion was proportional to the density of acid sites on the surface of the mixed oxides. The mixed oxide catalysts prepared in diethylenetriamine had lower densities of acid sites and showed a higher methane-efficiency for CH₄-SCR than those prepared in other solvents. These catalysts maintained their high activity even when the reaction was carried out under the severe conditions (i.e., high space velocity and low NO concentration).     

Hydrocarbons with a homoconjugated polyene system and their monoepoxy derivatives: Sex attractants of geometrid and noctuid moths distributed in Japan

Although several sex pheromones of the family Geometridae have been characterized, investigations on Japanese species are limited. In order to obtain more information, screening using known sex pheromones and their analogs was carried out. The (Z,Z,Z)-3,6,9-triunsaturated and (Z,Z)-6,9-diunsaturated hydrocarbons with straight C¹⁹-C²¹ chains were synthesized by the Grignard coupling reaction as a key step starting from linolenic and linoleic acids, respectively. Oxidation of the homoconjugated trienes withm-chloroperoxybenzoic acid yielded a 111 mixture of three monoepoxy derivatives that could be separated by silica gel chromatography. The chemical structure of each positional isomer was confirmed using two-dimensional NMR techniques and MS measurements, which enabled characteristic fragment ions from the isomers to be identified. Field tests using lures incorporating only one of the above six hydrocarbons or nine epoxides were carried out in a forest in Tokyo. Consequently, attraction of male moths of 14 geometrid species in addition to four species in another family, the Noctuidae, was observed. It was concluded that hydrocarbons with a homoconjugated polyene system and the monoepoxy derivatives are important components of sex pheromones produced by Japanese lepidopterous insects, particularly the geometrid moths.     

Current dependence of performance of TES microcalorimeters and characteristics of excess noise

We are developing transition edge sensor (TES) microcalorimeter arrays for future Japanese astronomy missions. Although 6.6 eV energy resolution for 5.9 keV and 74 μs decay time are achieved, our energy resolution was limited by the excess noise of unknown origin. The dominant noise showed 1/R dependence and it only appeared when the current through the TES, I, is larger than 10 μA. This is explained if we assume a constant voltage noise source with a level of 2(4kT_CR_n)^1/2. We also investigated the influence of I on the TES performance and found the TES sensitivity is reduced when the ratio of current to the critical current I/I_C is large. It can explain the reduction of observed when operated without a magnetic shield. We also found a strong correlation between I_C and or the baseline width. Thus, we conclude that I_C is an essential parameter for the TES performance.     

Numerical computation of cross‐coupled algebraic Riccati equations related to H2/H∞ control problem for singularly perturbed systems

In this paper, we present a numerical algorithm to the cross‐coupled algebraic Riccati equations(CARE) related to H₂/H_∞ control problems for singularly perturbed systems (SPS) by means of Newton's method. The resulting algorithm can be widely used to solve Nash game problems and robust control problems because the CARE is solvable even if the quadratic term has an indefinite sign. We prove that the resulting iterative algorithm has the property of the quadratic convergence. Using the solution of the CARE, we construct the high‐order approximate H₂/H_∞ controller. Copyright © 2004 John Wiley & Sons, Ltd.     

Determination of atomistic deformation of tricalcium silicate paste with high-volume fly ash

We examined the effect of incorporating high-volume fly ash on the atomic arrangement and interatomic deformation behavior of calcium silicate hydrates in tricalcium silicate paste upon exposure to external forces. The interatomic structural changes and strains under compressive load were assessed using synchrotron in situ high-energy X-ray scattering-based atomic pair distribution function analysis. Three different types of strains, which were (a) macroscopic strains from gauges on the surfaces of specimen, (b) strains in a reciprocal space (Bragg peak shift), and (c) strains in real space (PDF peak shift), were compared to each other. All monitored and calculated strains for tricalcium silicate-fly ash (50 wt% fly ash) paste were compared with the counterparts of the pure tricalcium silicate paste. Pair distribution function analysis in the range of r < 10 Å indicated that the atomic arrangement of tricalcium silicate-fly ash was similar to that of synthetic calcium silicate hydrates followed by that of pure tricalcium silicate paste. Moreover, the pair distribution function refinement results revealed that the calcium silicate hydrate structure in tricalcium silicate-fly ash paste was similar to tobermorite 11 Å, unlike that in pure tricalcium silicate paste. The interatomic strain of tricalcium silicate-fly ash in the real space (r < 20 Å) was smaller than that of tricalcium silicate under compression, which suggested that the incompressibility of calcium silicate hydrates at atomistic scale was enhanced by the incorporation of fly ash into it. This was likely to be caused by the increased silicate polymerization of calcium silicate hydrates, which was attributed to the increase in the amount of silicate in their structure via the addition of fly ash.     

Condensation of organic binary mixtures flowing horizontally in a horizontal tube bundle

Both heat and mass transfer in the gas phase and heat transfer in the liquid phase are examined experimentally for film condensation of organic binary mixtures such as ethanol-water and methanol-water. Experimental results on the average heat flux, vapor-liquid interface temperature and liquid-phase Nusselt number are compared with analytical solutions based on stagnant film theory and heat-transfer relationships for film condensation from a pure vapor. Experimental heat transfer results agree well with the analytical solutions, except that the experimental liquid-phase Nusselt numbers under conditions of low mass fraction of water are considerably higher than predicted by the analytical solutions. This high value of the liquid-phase Nusselt number is considered to be caused by dropwise condensation in the liquid phase. However, its effect on the tube bundle is not so remarkable compared with that in gravity-controlled condensation on a vertical surface. This is considered to be caused by the condensate inundation effect. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res, 25(6): 342–361, 1996