Effects of supplied gas humidity change on PEFC transient power generation

Polymer electrolyte fuel cells (PEFCs, PEMFCs) are gaining increasingly more attention as clean and efficient energy‐conversion devices. Vapor and liquid transport has a strong impact on the power generation characteristics and efficiency of PEFCs, and so proper water management is needed for efficiency and durability. However, water transport factors are not well understood, particularly during unsteady operation—often the case in vehicles and distributed stationary power generators. In this study, to understand and generalize the effects of local water transport on PEFC performance, transient mass transport characteristics inside a PEFC were investigated experimentally and numerically. For this purpose, we developed an unsteady two‐dimensional numerical model based on mass‐ and charge‐conservation equations in the channel, gas diffusion layer (GDL), and membrane electrode assembly (MEA). As necessary parameters for model development, we measured the water content of the MEA, the membrane resistivity, the activation overvoltage, overall mass transfer coefficient, and so on. The membrane resistivity greatly increases as the relative humidity decreases. The activation overvoltage is also affected by the relative humidity, and not only by the current density and oxygen activity. Current load and voltage changes are frequently used as PEFC transient inputs, but lead to very complicated and intractable phenomena such as changes in the amount of generated water and electro‐osmosis, state of the electrical double layer, and so on. Hence, stepwise changes in the relative humidity of the supplied gas were adopted in this study. The experimental and numerical transient responses were in good agreement under most operating conditions, and the reliability of our measurement methods for the water transport properties and our numerical model were confirmed. Here we discuss the dominant factor in the transient responses, and conclude that the transport resistance at the PEM–GDL interface is the largest and most dominant factor in a relatively dry state under unsteady operating conditions. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20371     

Doping effect on sinterability of polycrystalline yttria: From the viewpoint of cation diffusivity

The sintering behavior of Y₂O₃ doped with 1 mol% of a trivalent or tetravalent cation was investigated by pressureless sintering in air. Ga³⁺ or Ge⁴⁺-doped Y₂O₃ bodies exhibited higher relative densities than the undoped Y₂O₃, while the La³⁺ or Zr⁴⁺-doping suppressed the densification of Y₂O₃. An interdiffusion experiment was performed on the diffusion couples of polycrystalline Er₂O₃ and Y₂O₃ doped with Ni²⁺ or Zr⁴⁺, which are some of the most effective and least effective dopants for the improvement of the sinterability, respectively. The lattice and grain boundary diffusion coefficients of the Er³⁺ cation in Y₂O₃ were increased by the Ni²⁺-doping, but were decreased by the Zr⁴⁺-doping. High-resolution transmission electron microscopy observations and nano-probe X-ray energy dispersive spectroscopy analyses confirmed that the dopant cations segregate along the grain boundaries without forming an amorphous phase. The doping effect on the sinterability of Y₂O₃ must result from the change in the diffusivity in Y₂O₃.     

Influence of quadrature‐axis reactance of large turbine generator on operation

Two‐pole large generators are extensively used in power utilities. Growing demand for electric power in recent years has led to substantial increases in the capacity of generators. In line with this trend, our company has manufactured two‐pole turbine generators in the 900,000‐kVA to 1,200,000‐kVA classes. As the capacity of generators becomes larger, equivalent circuits are increasingly expected to improve their precision in estimating operation characteristics. The Park model has been widely used as an equivalent circuit model. The Park model with quadrature axis transient reactance $x_{q}^{\prime}$ is claimed to be useful for accurately estimating the load rejection characteristics of turbine generators. However, it is difficult to measure $x_{q}^{\prime}$, few studies based on measured data have appeared. As one of the few examples, we have conducted a measured data on a 500,000‐kVA‐class generator. Recently, the authors obtained test data on $x_{q}^{\prime}$ of a 900,000‐kVA‐class generator. In this study, based on these data, we studied the effect of $x_{q}^{\prime}$ using the finite element method and a transient analysis program (EMTP‐ATP). © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 177(3): 17–27, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21099     

In vitro determination of basement membrane invasion predicts liver metastases in human gastrointestinal carcinoma

We described previously (H. Imamura, et al., Cancer Res., 54: 3620-3624, 1994) a quantitative and reproducible 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay for tumor cell invasiveness that uses a water-repellent, paraffin-treated Chemotaxicell chamber to produce a uniform Matrigel layer. In the present experiments, we studied 71 human gastrointestinal carcinomas, including 53 maintained as xenografts in nude mice and 18 fresh surgical specimens. We found a correlation between metastatic behavior and the percent invasion (PI) calculated from the MTT assay. Tumors producing liver metastases had a significantly higher PI than did tumors without liver metastases (P < 0.01), and seven of nine fresh tumors with a PI greater than 1.0 showed liver metastases within 2 years. No significant correlations were noted between the PI and clinicopathological factors. In the tumor xenografts, type IV collagenase activity was significantly higher in tumors with clinically evident liver metastases than in those without liver metastases (P < 0.05). Colorectal carcinomas with liver metastases and a high PI showed higher expression of matrix metalloproteinase 9 than matrix metalloproteinase 2 as assessed by gelatin zymography. Thus, the invasion-MTT assay is clinically useful for predicting liver metastases. Type IV collagenase plays an important role in the development of liver metastases from human gastrointestinal carcinoma.     

Dysfunction of nitric oxide induces protein kinase C activation resulting in vasospasm after subarachnoid hemorrhage

We hypothesize that the interaction between protein kinase C (PKC) and nitric oxide (NO) plays a role in the modulation of cerebral vascular tone, and the disturbance of this interaction following subarachnoid hemorrhage (SAH) results in vasospasm. To prove this hypothesis with direct evidence, PKC activities of smooth muscle cells of canine basilar arteries in the control and in the SAH groups were measured by an enzyme immunoassay method. N omega-nitro-L arginine (L-NA), an inhibitor of NO production, enhanced PKC activity. This enhancement was inhibited neither by 8-bromo-guanosine 3',5'-cyclic monophosphate (8-bromo-cGMP) nor SIN-1, a NO releasing agent. PKC activity in the SAH was significantly higher than in the control; however, no further enhancement was produced with L-NA. In the SAH, PKC activity was not inhibited either by 8-bromo-cGMP or SIN-1. We conclude that NO maintains an appropriate vascular tone through inactivation of PKC, and that this effect is disturbed following SAH, resulting in PKC-dependent vascular contraction, such as vasospasm. On the other hand, once PKC has been activated, NO precursors do not inhibit PKC. These facts indicate NO inactivates PKC through the inhibition of phosphatidylinositol breakdown.     

Hand-mirror cells acute lymphoblastic leukemia (L3)

To our knowledge, this report represents the first confirmed case in Japan of a 15-year-old boy with acute lymphoblastic leukemia (ALL).L3 with hand-mirror cells (HMC) in the bone marrow. HMC lymphoid leukemia is an unusual variant of ALL in which the bone marrow lymphoblasts manifest distinctive hand-mirror morphologic features. HMC lymphoblast is characterized by an asymmetric foot-like cytoplasmic process that extends from the portion of the cell, thus giving it the light-microscopic appearance responsible for its name. Besides ALL, HMC has been reported in acute myeloblastic leukemia (AML), blastic crisis of chronic myelogenous leukemia, non-Hodgkin's lymphoma, and infectious mononucleosis. HMC has been reported to be prevalent in ALL.L1 and L2 as compared with L3.     

Velocity and turbulence measurements in a cylindrical bath subject to centric bottom gas injection

Laser Doppler velocimeter (LDV) measurements were made to clarify the fluid flow behavior in a bath subject to centric bottom gas injection. Correlations of the axial mean velocity and turbulence components in the gas-liquid two-phase flow region,i.e., in the bubbling jet region, were proposed as functions of the inner diameter of nozzle, gas flow rate, and densities of gas and liquid. Measured values of the flow rate, momentum, and kinetic energy of water rising upward were approximated satisfactorily by these empirical correlations. In addition, the Reynolds shear stress was calculated and compared with measured values. Formerly Graduate Student, Osaka University,     

Hydrogen production by combining two types of photosynthetic bacteria with different characteristics

The double-layer photobioreactor using two types of photosynthetic bacteria, Rhodobacter sphaeroides RV and its reduced-pigment mutant, MTP4, was developed for efficient hydrogen production. The two types of bacteria had different characteristics on light energy, hydrogen production rate and conversion efficiency. MTP4 produced hydrogen more efficiently under high light conditions and RV did so under low light conditions. Illuminated light toward the surface of a photobioreactor quasi-exponentially declines as it penetrates into the reactor. When two types of bacteria were placed using the developed reactor according to this light distribution, the hydrogen production rate reached 3.64 l/m²/h at a light intensity of 500 W/m² in 24 h and the conversion efficiency of light energy to hydrogen was 2.18%. These values were 33% higher than those of only using RV. The low light in the deep part of the reactor was utilized efficiently, resulting in a higher hydrogen production rate.     

Potential of renewable energy sources and its applications in Yakushima Island

A study was carried out to see if the potential of renewable energy sources other than hy droelectric power, such as wind, photovoltaic, solar thermal, biomass and waste energy sources, can meet the current energy consumption in Yakushima. The current electricity consumption can be covered by wind and photovoltaic energy sources. The total potential of wind and photovoltaic energy sources is 5.4 times as much as the current electricity consumption. LP gas and kerosene can be replaced by solar thermal and biogas energy. The potential of plant biomass and municipal waste is not sufficient (approximately one third) to cover the rest of the fossil fuels (gasoline, diesel oil and heavy oil). Also, plant biomass and municipal waste must be converted into fluid form. This shortage can be covered by the po tential of wind and photovoltaic energy sources. We also investigated the possibility of tourism expansion using the potential of wind and photovoltaic energy sources. Taking into account three types of capacity (energy, accommodation and transportation), Yakushima can accept approximately four times as many tourists as the current number of tourists.