Numerical analysis of electrochemical characteristics and heat/species transport for planar porous-electrode-supported SOFC

In this work, a fully three-dimensional mathematical model for planar porous-electrode-supported (PES) solid oxide fuel cell (SOFC) has been constructed to simulate the steady state electrochemical characteristics and multi-species/heat transport. The variation of chemical species concentrations, temperature, potential, current and current density for two types of PES-SOFC developed by central research institute of electric power industry (CRIEPI) of Japan are studied in the co-flow pattern. In the numerical computation, the governing equations for continuity, momentum, mass, energy and electrical charge conservation are solved simultaneously using the finite volume method. Activation, ohmic, and concentration polarizations are considered as the main sources of irreversibility. The Butler–Volmer equation, Ohm's law, and Darcy's gas model with constant porosity and permeability are used to determine the polarization over-potential, respectively. The output voltages measured in experiments and calculated using the above models agree well. For the cell using the same material and manufacturing process, the results show the type-II PES-SOFC is with better performance. However, the electrolyte of type-II PES-SOFC should be with higher maximum ionic conductivity. Furthermore, these results will be used to evaluate the overall performance of a PES-SOFC stack, and to significantly help optimize their design and operation in practical applications.     

Two-dimensional analysis of substrate-trap effects on turn-oncharacteristics in GaAs MESFETs

Effects of substrate traps on turn-on characteristics of GaAs MESFETs are studied by two dimensional (2-D) simulation. When the off-state gate voltage is much more negative than the threshold (pinch off) voltage and the surface-state effects are small, abnormal current overshoot and subsequent slow transients are observed for the case with undoped semi-insulating substrate including an electron trap: EL2. Even if the surface-state effects are pronounced to show the large gate-lag, the drain current may show the overshoot-like behavior at relatively early periods. The case of Cr-doped substrate with a hole trap: Cr is also discussed     

A novel cartridge type powder feeder

In the present work, a novel cartridge type powder feeder is developed by applying ‘subliminal fluidization’, which is defined as partial aeration to the bed below minimum fluidization, but only for a limited region above the distributor, and by discharging solids together with the air through the tube located at the centre of the distributor. The distinct advantage of cartridge type feeder developed in this work lies in its simplicity of construction and operation giving quite an advantage for particulate material handling, transportation and metric feeding.Temporal solid efflux rates were measured for charcoal of mean sizes 220, 290 and 430 μm, glass beads of 265, 535 and 930 μm and spherical activated alumina (Neo beads) of 145 and 595 μm and density in the range of 1250 to 2500 kg/m³. Temporal flow rates of solids indicated that the solids efflux was independent of time and amount of material inside the bed and was only determined by the air supply from the distributor plate. Solids efflux rate was found to decrease with increased particle size and internal friction and reduced fluidization air flow rate. Solids efflux was found to vary slightly with the change in air humidity. A dimensionless correlation for solids efflux was developed as a function of fluidization number and the internal friction angle.     

Dielectric properties of mirin in the microwave frequency range

Dielectric properties of mirin (sweet rice wine for seasoning) at the microwave frequency range of 300–3000 MHz and temperature range of 5–70 °C were measured. The effects of temperature, frequency and liquid concentration on dielectric properties were investigated. Dielectric constant and loss factor were related to frequency by using the modified Cole–Cole equation. The important parameters such as relaxation wavelength, static dielectric constant and ionic conductivity were determined numerically under experimental conditions. It was concluded that the index of spread in the relaxation times depended on mirin concentration and it spread with increasing concentration. Penetration depth was calculated based on the collected dielectric properties data and it had a trough at mixture ratio (v/v) of 1:1 (original:water). The relationship between dielectric properties and temperature was determined at 915 MHz and 2450 MHz for commercial significance.     

Optimization of crystal microstructure in piezoelectric ceramics by multiscale finite element analysis

A multiscale finite element method based on homogenization theory is employed to optimize the microstructure of polycrystalline piezoelectric ceramics so as to maximize the homogenized macrostructural piezoelectric response. This analysis reveals that two specific microstructures, layered or alternating [1 1 1]-oriented structures, result in a piezoelectric response that exceeds that of the single-crystal. The layered structure consists of ordered 120°-rotated layers maximizing d₃₃₃, while the alternating structure consists of adjacent grains rotated by 180° in three dimensions optimizing d₃₁₁. These heterogeneous structures maximize the internal strain in polycrystalline aggregates by optimizing electrical and mechanical effects.     

Differential expression of MHC class II antigens and cathepsin L by subtypes of cortical epithelial cells in the rat thymus: an immunoelectron microscopic study

To better comprehend the thymic microenvironment, it is necessary to identify the antigenic profile of cortical thymic epithelial cells (cTECs) that are involved in the development of major histocompatibility complex (MHC)-restricted T cells. Ultrastructurally, cTECs can be classified into four morphologically distinct subtypes: subcapsular/perivascular (EC1), pale (EC2), intermediate (EC3) and dark (EC4) cells. Several immunohistochemical studies were done on cTECs at the light and electron microscopic levels, but not with reference to the above subtypes. In the present paper, we analysed the expression of MHC class II antigen and cathepsin L by individual cTEC subtypes at the electron microscopic level. We show that (1) MHC class II antigens are expressed on the cell surfaces except on the basal surface of EC1, both on the cell surface and in intracytoplasmic vacuoles of EC2, and only in the intracytoplasmic vacuoles of EC3 and EC4, and (2) that cathepsin L is expressed strongly and uniformly throughout the cytoplasm of EC2, but weakly and non-uniformly in the cytoplasm of EC1, EC3 and EC4. These results show that MHC class II antigen expression and cathepsin L expression is heterogeneous in cTEC subtypes and suggest that EC2 might play a significant role in the development of CD4+ T cells.     

A sulphur matrix complex,elastic fibril composed of a fine core of amorphous elastin and microfibrils was largely accumulated in the aortic intima of aged rats

We examined elastic fibrils in the aortic intima of aged rats with elastin staining, elastase digestion and X-ray microanalysis. The innermost elastic lamina, heavily stained by a brief treatment with azure II-toluidine blue without heating, was thin and fragmented, and an amorphous substance that stained weakly to moderately was accumulated in the thick subendothelial space of 26-28-month-old rat aortas. The substance was always present in the intimas; to a large extent in the aged rats but rarely in 5-month-old rats, and disappeared after digestion with elastase. The amorphous substance was identified as elastic fibrils approximately 0.1-0.2 microm in diameter under an electron microscope with tannic acid-uranyl acetate/lead citrate staining. Elastase digestion revealed that elastic fibrils were composed of a number of microfibrils, which were 10-12 nm in diameter, in and around a fine core of amorphous elastin. X-ray microanalysis revealed a clear peak of sulphur in the elastic fibrils.     

Analysis of kink-related backgating effect in GaAs MESFET

Two-dimensional simulation of backgating effect in a GaAs MESFET is made in which impact ionization of carriers and deep donors “EL2” in the substrate are considered. The kink-related backgating is reproduced, which is qualitatively consistent with recent experiments. Based on the simulated results, physical mechanism of kink-related backgating effect is discussed     

Bacterial cellulose membrane as separation medium

A thin membrane of bacterial cellulose (BC) obtained from Acetobacter culture was tested for its performance as a dialysis membrane in aqueous systems. The BC membrane showed superior mechanical strength to that of a dialysis-grade regenerated cellulose membrane, allowing the use of a thinner membrane than the latter. As a result, the BC membrane gave higher permeation rates for poly(ethylene glycols) as probe solutes. The cutoff molecular weight of the original BC membrane, significantly greater than that of regenerated cellulose, could be modified by concentrated alkali treatments of the membrane. The nature of the change at the ultrastructural level caused by the alkali treatments was studied by X-ray diffraction and scanning electron microscopy. © 1993 John Wiley & Sons, Inc.