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Hiroshi Takahashi

Bio: Hiroshi Takahashi is an academic researcher from Fukushima Medical University. The author has contributed to research in topics: Optical fiber & Catalysis. The author has an hindex of 32, co-authored 279 publications receiving 3655 citations. Previous affiliations of Hiroshi Takahashi include Kogakuin University & National Institute of Radiological Sciences.
Topics: Optical fiber, Catalysis, Zeolite, Neutron, Adsorption


Papers
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Journal ArticleDOI
TL;DR: In this paper, the conductivity of polycrystalline CsH2PO4/silica composite was measured in the temperature range from 150 to 250 °C under a humid condition.

191 citations

Journal ArticleDOI
TL;DR: In this article, the potential and ac impedance spectra were measured to construct a model to describe porous Sm 1-x Sr x CoO 3 (SSC) cathodes for solid oxide fuel cells (SOFCs).
Abstract: Overpotential and ac impedance spectra were measured to construct a model to describe porous Sm 1-x Sr x CoO 3 (SSC) cathodes for solid oxide fuel cells (SOFCs). Analysis of the impedance spectra revealed that there are three processes involved in the overall electrochemical reaction; (i) the adsorption/desorption process on the surface of the electrode. (ii) the ionic conduction in the bulk SSC, and (iii) the diffusion of oxygen in the gas phase. It was found that in air atmosphere, the reaction processes (i) and (ii) were dominant, while the diffusion process of gaseous oxygen was fast enough not to limit the overall reaction rate. A reaction model for the porous SSC cathodes used in SOFCs was proposed to determine the electrode resistance hy taking processes (i) and (ii) into account. It was found that our model explained the experimental results well. These results suggested the possibility of using our model to describe the cathodes with high ionic conductivity and to design the high-performance cathode systematically. The validity of the analysis hy conventional equivalent circuit was also discussed.

130 citations

Journal ArticleDOI
TL;DR: In this article, the changes in Si/Al ratios and Q units during the aging and the crystallizing processes were investigated by means of 29Si magic-angle spinning NMR spectroscopy.
Abstract: Faujasite zeolite is synthesized hydrothermally after an aging process under various conditions. Hydrogel is formed during the aging, and the amount increases with increasing the duration. Aluminosilicate species included in the hydrogel phase during the aging is investigated for the changes in Si/Al ratios and Q units during the aging and the crystallizing processes by means of 29Si magic-angle spinning NMR spectroscopy. Aging for more than 1 day is necessary to obtain faujasite with high crystallinity. The distribution in Q4 units in the hydrogel is gradually changed, and the aluminosilicate species having mainly a Q4(4Al) unit is obtained after 7 days of aging, while 2 days of aging results in remanent silicate species derived from the starting silica source. The former gives faujasite crystallites with higher crystallinity, sharper particle size distribution, and a lower Si/Al ratio. On the basis of these findings, the crystallization mechanism is discussed.

119 citations

Journal ArticleDOI
TL;DR: In this article, temperature-programmed reduction (TPR) was performed to investigate the reducibility of the NiO/YSZ composite that is related to the anode of solid oxide fuel cells (SOFCs).
Abstract: Temperature-programmed reduction (TPR) was performed to investigate the reducibility of the NiO/YSZ composite that is related to the anode of solid oxide fuel cells (SOFCs). The TPR profiles were found to be affected by preparation method, composition and pretreatment conditions. The calcination temperature strongly affected the reduction behavior; the TPR profile of the sample calcined at 1723 K shows a high temperature reduction peak that was not found in the TPR profile of the sample calcined at 1473 K. Such a difference in the TPR profiles can be attributed to the presence of distinct states of NiO species, which are due to the difference of interactions between NiO and YSZ. Five distinct states of NiO species are shown to be present in the NiO/YSZ composite.

110 citations

Journal ArticleDOI
TL;DR: In this paper, a simulation model for a tubular solid oxide fuel cell (SOFC) was developed by the object-based approach to calculate the current distribution, gas concentration distribution, and temperature distribution at the steady states and transient operation states.

109 citations


Cited by
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Journal ArticleDOI
01 Jan 1994-Carbon
TL;DR: In this paper, a review of the surface chemistry of carbon blacks and other activated carbons is given, focusing on surface oxides with emphasis on the chemical methods used in the assessment and identification of surface functional groups.

2,705 citations

Journal ArticleDOI
TL;DR: These advances have led to dozens of active SOFC development programs in both stationary and mobile power and contributed to commercialization or development in a number of related technologies, including gas sensors, solid-state electrolysis devices, and iontransport membranes for gas separation and partial oxidation.
Abstract: Recent worldwide interest in building a decentralized, hydrogen-based energy economy has refocused attention on the solid oxide fuel cell (SOFC) as a potential source of efficient, environmentally friendly, fuel-versatile electric power. Due to its high operating temperature, the SOFC offers several potential advantages over polymer-based fuel cells, including reversible electrode reactions, low internal resistance, high tolerance to typical catalyst poisons, production of high-quality waste heat for (among other uses) reformation of hydrocarbon fuels, as well as the possibility of burning hydrocarbon fuels directly. Today, SOFCs are much closer to commercial reality than they were 20 years ago, due largely to technological advances in electrode material composition, microstructure control, thin-film ceramic fabrication, and stack and system design. These advances have led to dozens of active SOFC development programs in both stationary and mobile power and contributed to commercialization or development in a number of related technologies, including gas sensors,1 solid-state electrolysis devices,2 and iontransport membranes for gas separation and partial oxidation.3 Many reviews are available which summarize the technological advances made in SOFCs over the last 15-35 yearssreaders who are primarily interested in knowing the state-of-the art in materials, design, and fabrication (including the electrodes) are encouraged to consult these reviews.4-12 This review focuses on the factors governing SOFC cathode performancesadvances we have made over † Dedicated to Brian Steele, 1929-2003. Researcher, Entrepreneur, Consensus Seeker. 4791 Chem. Rev. 2004, 104, 4791−4843

2,033 citations

BookDOI
01 Jan 2011
TL;DR: Firm evidence is provided for Foxp3+CD25+CD4+ Treg cells as an indispensable cellular constituent of the normal immune system for establishing and maintaining immunologic self-tolerance and immune homeostasis.
Abstract: Despite the skepticism that once prevailed among immunologists, it is now widely accepted that the normal immune system harbors a T-cell population, called regulatory T cells (Treg cells), specialized for immune suppression. It was first shown that depletion of a T-cell subpopulation from normal rodents produced autoimmune disease. Search for a molecular marker specific for such autoimmune-preventive Treg cells has revealed that the majority, if not all, of them constitutively express the CD25 molecule as depletion of CD25+CD4+ T cells spontaneously evokes autoimmune disease in otherwise normal rodents. The expression of CD25 by Treg cells has made it possible to delineate their developmental pathways, in particular their thymic development, and establish simple in vitro assay for assessing their suppressive activity. The marker and the in vitro assay have helped to identify human Treg cells with similar functional and phenotypic characteristics. Recent efforts have shown that natural Treg cells specifically express the transcription factor Foxp3 and that mutations of the Foxp3 gene produce a variety of immunological diseases in humans and rodents. Specific expression of Foxp3 in natural Treg cells has enabled their functional and developmental characterization by genetic approach. These studies altogether have provided firm evidence for Foxp3+CD25+CD4+ Treg cells as an indispensable cellular constituent of the normal immune system for establishing and maintaining immunologic self-tolerance and immune homeostasis. Treg cells are now within the scope of clinical use to treat immunological diseases and control physiological and pathological immune responses.

1,745 citations