Characteristic of an AC chopper circuit with LC filters in the input and output side

LC filters are connected to both the input and output side of the AC chopper circuit in order to remove the switching ripple and harmonics. Characteristics of THD and input power factor are examined by simulation and experiments. When the load is resistive, characteristics are minimally influenced by the filters. In the case of an inductive load, since two poles exist owing to the input and output filters, waveform distortion becomes large. This paper shows that THD can be improved by reducing input filter capacitance. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(2): 45–52, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20304     

Elution of sodium caseinate from agar-based gel matrixes in simulated gastric fluids

Elution of sodium caseinate from agar/psyllium composite gels was investigated in simulated gastric fluids to determine predominant mechanical parameters of gels for the elution kinetics and to predict the kinetics using the parameters. When the concentration of agar was fixed at 0.5% in the composite gels, elastic moduli determined by creep tests decreased with increasing concentration of psyllium, while viscosities increased. Compression load upon syringing through an enteral tube increased with increasing concentration of psyllium, whereas the surface-volume diameter d_3,2 of gel particles after syringing decreased. The elution kinetics of sodium caseinate from cylindrical gels was described using two different diffusion coefficients; D₁ and D₂ (D₁ > D₂) and the diameter of gels. Both diffusion coefficients decreased with increasing concentration of psyllium, resulting in 1.9 × 10⁻⁶ (for D₁) and 6.7 × 10⁻⁸ (for D₂) cm²/min by 1.5% addition, which corresponded to approx. 30% and 45% of the control (i.e., 0% psyllium), respectively. The fraction ratio of sodium caseinate having D₁ was not sensitive to psyllium concentration; approx. 80%–85% in the concentration range tested. D₁ was inversely proportional to viscosities determined by creep tests, particularly one from the Voigt body η₁ in the 4-element mechanical model. When cube gels were divided into smaller ones without changing the total volume, elution rates were inversely proportional to the cube length, where the diffusion coefficients did not change. The elution kinetics of sodium caseinate from the gel matrixes was anticipated using η₁ of gels before syringing and d_3,2 of gel particles after syringing when the usage of gels for percutaneous endoscopic gastrostomy is assumed.     

High-temperature properties of extruded titanium composites fabricated from carbon nanotubes coated titanium powder by spark plasma sintering and hot extrusion

Pure titanium matrix composite reinforced with carbon nanotubes (CNTs) was prepared by spark plasma sintering and hot extrusion via powder metallurgy process. Titanium (Ti) powders were coated with CNTs via a wet process using a zwitterionic surfactant solution containing 1.0, 2.0 and 3.0 wt.% of CNTs. In situ TiC formation via reaction of CNTs with titanium occurred during sintering, and TiC particles were uniformly dispersed in the matrix. As-extruded Ti/TiCs composite rods were annealed at 473 K for 3.6 ks to reduce the residual stress during processing. After annealing process, the tensile properties of the composites were evaluated at room temperature, 473, 573 and 673 K, respectively. Hardness test was also performed at room temperature up to 573 K with a step of 50 K. The mechanical properties of extruded Ti/CNTs composites at elevated temperature were remarkably improved by adding a small amount of CNTs, compared to extruded Ti matrix. These were due to the TiC dispersoids originated from CNTs effectively stabilized the microstructure of extruded Ti composites by their pinning effect. Moreover, the coarsening and growth of Ti grain never occurred even though they were annealed at 573, 673 K for 36 ks and 673 K for 360 ks, respectively.     

Retardation of Crystallization of Diacylglycerol Oils Using Polyglycerol Fatty Acid Esters

Liquid oil containing high concentrations of diacylglycerols (DAG > 80 %, hereafter referred to as DAG-rich oil) is generally more likely to cause precipitation at chilled temperatures (clouding phenomena) than triacylglycerol-based oil. The clouding phenomena that occur during long-term storage of DAG-rich oil are unwanted in consumer products and therefore, must be prevented. In the present study, we attempted to retard precipitation by adding food emulsifiers, polyglycerol fatty acid esters (PGFE) containing different fatty acid moieties. DSC, polarized optical microscopy, and X-ray diffraction studies revealed that the addition of 0.2 % PGFE containing palmitic and oleic acid moieties very effectively retarded precipitation in the DAG-rich oil. To confirm these observations, we prepared a model DAG oil to mimic DAG-rich oil and examined the retardation behavior of high-melting DAG fractions using PGFE. The results are discussed in terms of the effects of PGFE additives on the pre-nucleation processes of high-melting fractions in DAG-rich oil.     

Effect of the temperature dependence of fluid properties on the migration of an interface in double-diffusive natural convection

Experimental observation has shown that a slightly tilted sharp interface between two convection layers in double-diffusive natural convection migrates perpetually upward gradually with time. This movement of an interface cannot be explained by a simple mathematical model of constant physical properties. The present paper studies the numerical analyses of two-layer convection with the temperature dependence of the properties of the fluid. The perpetual upward migration of an interface was found to be promoted mainly by the temperature dependence of the volumetric coefficient of thermal expansion and also by that of the kinematic viscosity. However, the diffusion coefficient was independent of the migration. The upward migration of an interface appears to be caused by the difference between the intensity of etching due to the flow along the hot wall in the lower layer and that along the cold wall in the upper layer.     

Crystal face dependent chemical effects in surface-enhanced Raman scattering at atomically defined gold facets

Among electromagnetic and chemical (CM) contributions to surface-enhanced Raman scattering (SERS), the former is becoming controllable according to the recent progress in nanofabrication of plasmonic metal structures. However, it is still difficult to control the latter effect. Here, the degree of each contribution to SERS signals is examined on well-defined single crystalline facets of gold by using optical field localization within sphere-plane type plasmonic cavities. Crystal face dependent SERS studies of aminobenzenthiol adsorbates clearly show the distinction between CM enhancements on different surfaces, suggesting that the CM-activity of "SERS-hotspots" is closely related to interfacial dipoles formed at metal-molecular junctions.     

Contribution of Ti addition to characteristics of extruded Cu40Zn brass alloy prepared by powder metallurgy

The aim of this paper was to investigate the properties of Cu40ZnTi for the purpose of developing a new high-strength, lead-free brass by powder metallurgy. The effect of Ti addition on precipitation hardening behavior of Cu40Zn (denoted as BS40) brass was studied with respect to mechanical properties and microstructures. BS40 and Cu40Zn − 1.0 wt.%Ti (denoted as BS40-A) brass powders were prepared by water atomization process, and β phase was retained in the raw powders predominately. The BS40 powder and Ti powder were elementally mixed to prepare Cu40Zn + 0.5 wt.%Ti (denoted as BS40-B) and Cu40Zn + 1.0 wt.%Ti (denoted as BS40-C) premixed powders. The alloy powders and premixed powders were solidified at 1053 K for 600 s by spark plasma sintering (SPS) and extruded subsequently. It was observed that Cu₂ZnTi intermetallic compound (IMC) and CuZnTi metastable phase resulted from the reaction between Ti and CuZn showed distinct grain refinement effect on extruded Cu40Zn brass. Thus, the excellent strengthening effect processes by precipitation hardening and deform working was obtained, which responding to an yield strength of 345 MPa, and a ultimate tensile strength of 597 MPa, showed 65.9% and 30.4% higher than that of extruded Cu40Zn brass, respectively.     

Synthesis and electrochemical characterization of Pt catalyst supported on Sn0.96Sb0.04O2−δ with a network structure

We synthesized a Pt catalyst supported on Sn_0.96Sb_0.04O_2−δ with a random network structure for the cathode of the polymer electrolyte fuel cell (PEFC). The Sn_0.96Sb_0.04O_2−δ support, synthesized by the flame combustion method, was in the form of nanometer-sized particles with a partially agglomerated structure similar to that of carbon black (CB) and with a high surface area, 125 m² g⁻¹. The structure was considered to be beneficial in reducing the contact resistance between the Sn_0.96Sb_0.04O_2−δ support particles and in dispersing the nanometer-size Pt particles. We applied the nanocapsule method to synthesize the Sn_0.96Sb_0.04O_2−δ-supported Pt catalyst (Pt/Sn_0.96Sb_0.04O_2−δ). The electrochemically active surface area (ECA) of Pt reached a maximum of 60.2 m² g_(Pt)⁻¹, and the high values were maintained during the potential step cycling test (0.9–1.3 V) simulating the start/stop cycling of PEFCs. The oxygen reduction reaction activity of the Pt/Sn_0.96Sb_0.04O_2−δ catalyst exceeded that of Pt supported on carbon black (Pt/CB). We conclude that the random network structured Sn_0.96Sb_0.04O_2−δ might be a good candidate support material for the cathode of PEFCs.