Effect of sand mold models on the simulated mold restraint force and the contraction of the casting during cooling in green sand molds

In this work, the JIS AD12.1 (almost the same as A383.1) aluminum alloy was cast in a green sand mold. The restraint force from the sand mold and the contraction of the casting were measured dynamically from the solidifying temperature to the shake-out temperature using a dedicated device. Then, FEM (Finite Element Method) thermal stress analyses of the experiment were performed. The analyses adopted four types of representative constitutive equations and the mechanical properties of the green sand mold, which were quoted from previous research articles. As verification, this study dynamically compared the simulated restraint force and the contraction of casting with measured results and examined which mechanical properties are important for expressing the restraint force of the sand mold. This verification is the first attempt in the world. As a result, the simulated restraint force was estimated to be over ten times as large as the measured result in each type of equation because the yield stress of the sand mold used in our experiment was lower than those quoted from previous studies. The yield stress measured by a uniaxial compression test was 1/20 of the quoted values. When the measured yield stress was adopted in the simulation, the simulated restraint force and contraction approached the measured results. The yield stress of the sand mold was a dominant factor in the restraint force simulated by the thermal stress analyses. The yield stress of the green sand mold used in the casting process should be measured to predict the residual stress using FEM thermal stress analyses.     

A new identity dimensional D‐state observer for sensorless drive of permanent‐magnet synchronous motors

A new identity dimensionless D‐state observer whose state variables are the stator reaction flux and rotor flux is proposed for the sensorless drive of permanent‐magnet synchronous motors. Furthermore, sufficient conditions are newly and analytically derived for the observer gains that guarantee stable convergence of state variable estimates. Additionally, two new methods for designing observer gain are presented; these methods, the constant and speed‐dependent gain methods, satisfy the derived analytical conditions. The observer gain conditions used in the design methods are validated through extensive numerical experiments. In addition, typical design examples of the observer gains using the proposed design methods are presented. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 181(1): 45–61, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21200     

Effects of ethylene content of poly(ethylene‐co‐vinyl alcohol) on diameter of fibers produced by melt‐electrospinning

Rodlike samples were made from four kinds of poly(ethylene‐co‐vinyl alcohol) (EVAL) pellets with different ethylene contents. From these rodlike samples, fibers were produced using a melt‐electrospinning system equipped with a CO₂‐laser melting device. The effects on the fiber diameter of the ethylene content and the moisture regain of the rodlike samples were investigated. Furthermore, the physical properties of the fibers were investigated. The following conclusions were reached: (i) EVAL fibers having an average fiber diameter smaller than 1 μm can be obtained using the system developed; (ii) the diameter of EVAL fiber is influenced by the ethylene content and the moisture regain of the starting rods; (iii) the laser heating does not greatly decrease the melting point and the molecular weight of EVAL; and (iv) preferred crystal orientation can be seen in electrospun EVAL fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1368–1375, 2007     

Liqsedflow: Role of Two-Phase Physics in Subaqueous Sediment Gravity Flows

The paper describes an extension of the computational code LIQSEDFLOW proposed by the authors. The salient features of the code lie in its capability to describe the multi-phased physics of subaqueous sediment gravity flows. Specifically, it combines Navier-Stokes/continuity equations and equations for the advection and hindered settling of grains for a liquefied soil domain, with a consolidation equation for the underlying, progressively solidifying soil domain via a transition layer characterized by zero effective stress and a small yet discernible stiffness. Evolutions of the flow and solidification surfaces are traced as part of the solution using a volume-of-fluid (VOF) technique. The predicted features of the gravity flows of initially fluidized sediments with different concentrations conform to the observed performances in two-dimensional flume tests. The present results demonstrate the crucial role of two-phase physics, particularly solidification, in reproducing the concurrent processes of flow stratification, deceleration, and redeposition in subaqueous sediment gravity flows.     

生态与经济的共生——祝贺《中国园林》创刊25周年

<正>首先衷心祝贺《中国园林》创刊25周年!作为国际编委,能够拜读每期贵刊,我深感荣幸,值此机会想介绍日本社会和园林景观的最新动态,希望能给中国的读者一些参考。     

Metabolism of azo dyes by Lactobacillus casei TISTR 1500 and effects of various factors on decolorization

Lactobacillus casei TISTR 1500 was isolated from soil of a dairy wastewater treatment plant and selected as the most active azo dye degrader of 19 isolates. Growing cells and freely suspended cells of this strain completely degraded methyl orange, thereby decolorizing the medium. The strain stoichiometrically converted methyl orange to N,N-dimethyl-p-phenylenediamine and 4-aminobenzenesulfonic acid, which were identified by HPLC, GC, and GC-MS analyses. The enzyme activity responsible for the cleavage of the azo bond of methyl orange was localized to the cytoplasm of cells grown on modified MRS medium containing methyl orange. The effect of sugars, oligosaccharides, organic acids, metal ions, pHs, oxygen and temperatures on methyl orange decolorization by freely suspended cells was investigated. The optimal conditions for the decolorization of methyl orange by the Lactobacillus casei TISTR 1500 are incubation at 35 degrees C and pH 6 with sucrose provided as the energy source.     

Investigation of characterization method for nanoparticles in roadside atmosphere by thermal desorption-gas chromatography/mass spectrometry using a pyrolyzer

Atmospheric nanoparticles (<0.050 microm) have caused great concern recently due to their potential to affect human health. However, little is known about the chemical composition, sources, and atmospheric behavior of atmospheric nanoparticles. Although gas chromatography/mass spectrometry (GC/MS) after solvent extraction is a commonly used and powerful method for the identification of nonpolar organic compounds in particles, solvent-extraction methods are difficult to apply to nanoparticles because nanoparticles are present in small masses in spite of their high number concentrations. Therefore, we made an attempt to apply thermal desorption-GC/MS (TD-GC/MS), which was expected to be more sensitive than solvent-extraction methods, to atmospheric nanoparticles. A commercial pyrolyzer was used for TD. Prior to the application, the optimum TD-GC/MS conditions for atmospheric particles and diesel exhaust particles (DEP) collected on filters were investigated. Various TD parameters, including desorption time and temperature, were investigated using these test samples and a n-alkanes standard solution. The optimum TD conditions were as follows: ramped desorption from 50 degrees C to 450 degrees C at 50 degrees C min(-1) and then hold for 2 min. Desorption was incomplete at temperatures of 250 degrees C or lower, and considerable pyrolysis occurred at temperatures of 550 degrees C or higher. The TD-GC/MS performance, including the linearity of the calibration curves, repeatability, detection and quantification limits, and sample recovery, under the optimized conditions was evaluated for n-alkanes. It was found that the TD-GC/MS could be applied to extremely small amount of particles (e.g., 5 microg for DEP). The TD-GC/MS was applied to the size-resolved particles, including the nanoparticle fraction (0.0290-0.0580 microm), from roadside atmosphere, and the concentrations of C18-C33 n-alkanes in the particles were determined. The chromatogram pattern of the roadside 0.102-0.163 microm (major size range for DEP) particles was similar to that of the DEP sample. The chromatogram pattern of the roadside nanoparticles was similar to that of diesel lubricating oil, although the proportion of less volatile compounds was slightly larger in the nanoparticles. It is suggested that lubricating oil strongly contributed to the nonpolar organic composition of the roadside nanoparticles, and that more volatile organic compounds in the nanoparticles evaporated in the atmosphere. It was shown that the TD-GC/MS is effective for characterization of atmospheric nanoparticles.     

Antireflective porous layer formation on multicrystalline silicon by metal particle enhanced HF etching

Antireflection of silicon (Si) surface is one key technology for the manufacture of efficient solar cells. Metal particle enhanced HF etching is applied to produce uniform antireflecting porous layer on multicrystalline Si wafers that cannot be uniformly texturized by anisotropic etching with an alkaline solution. Fine platinum (Pt) particles are deposited on multicrystalline n-Si wafers by electroless displacement reaction in a hexachloroplatinic acid solution containing HF. Both macroporous and luminescent microporous layers are uniformly formed by immersing the Pt-particle-deposited multicrystalline Si wafers in a HF solution. The reflectance of the wafers is reduced from 30% to 6% by the formation of porous layer. The photocurrent density of photoelectrochemical solar cells using porous multicrystalline n-Si has a 25% higher value than non-porous Si cells.     

Buckling assessment procedure for large diameter vessel with multiple local thin areas subjected to external moment

The procedures described in Ibaraki FFS rule (2006) based on the p-M (internal pressure ratio and external bending moment ratio) method (Konosu and Mukaimachi, 2006) were used to predict the plastic initiation condition and the collapse condition for cylinders with a local thin area (LTA) subjected to combined internal pressure and bending moment. The effective wall thickness, t*, for the buckling assessment on a vessel with an LTA was proposed for use instead of wall thickness based on approximation which simply took into account only the effect of section modulus reduction (Konosu and Mukaimachi, 2006). The buckling evaluation on a vessel with an LTA was presented by Mukaimachi and Konosu (2009) and that was shown to be easily and adequately conducted by applying t* to the well-known Donnell's or Miller's equation. In this paper, the attention was focused on the procedure for assessing the buckling of large D/t vessels with multiple aligned or non-aligned local thin areas. From the comparison with the results of non-linear FEA, a combination rule and a buckling assessment procedure for multiple LTAs (flaws) subjected to external moment are proposed. The interaction-affected area for multiple cracks can be applied as the combination rule to evaluate the buckling of a large diameter vessel with multiple flaws subjected to external moment. From the comparison between the buckling loads of FEA results and the conventional buckling equations using the measured yield stress, an additional safety factor ‘ks’ is proposed so as to maintain the margin of 1.5. When the specified minimum yield stress is applied to Donnell's or Miller's equations, the margin for the buckling load of a cylinder with multiple flaws is more than 2.08 and 2.29, respectively.