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Synthesis and Solid-State NMR Structural Characterization of 13C-Labeled Graphite Oxide
Cai, W.,Piner, R. D.,Stadermann, F. J.,Park, S.,Shaibat, M. A.,Ishii, Y.,Yang, D.,Velamakanni, A.,An, S. J.,Stoller, M.,An, J.,Chen, D.,Ruoff, R. S. American Association for the Advancement of Scienc 2008 Science Vol.321 No.5897
<P>The detailed chemical structure of graphite oxide (GO), a layered material prepared from graphite almost 150 years ago and a precursor to chemically modified graphenes, has not been previously resolved because of the pseudo-random chemical functionalization of each layer, as well as variations in exact composition. Carbon-13 (13C) solid-state nuclear magnetic resonance (SSNMR) spectra of GO for natural abundance 13C have poor signal-to-noise ratios. Approximately 100% 13C-labeled graphite was made and converted to 13C-labeled GO, and 13C SSNMR was used to reveal details of the chemical bonding network, including the chemical groups and their connections. Carbon-13-labeled graphite can be used to prepare chemically modified graphenes for 13C SSNMR analysis with enhanced sensitivity and for fundamental studies of 13C-labeled graphite and graphene.</P>
Two competing soft modes and an unusual phase transition in the stuffed tridymite-type oxideBaAl2O4
Ishii, Y.,Mori, S.,Nakahira, Y.,Moriyoshi, C.,Park, J.,Kim, B. G.,Moriwake, H.,Taniguchi, H.,Kuroiwa, Y. American Physical Society 2016 Physical Review B Vol.93 No.13
<P>We investigated the structural phase transition of BaAl2O4, which has a network structure with corner-sharing AlO4 tetrahedra, via synchrotron x-ray thermal diffuse scattering measurements and first-principles calculations. BaAl2O4 shows the structural phase transition at T-C = 451.4 K from the P6(3)22 parent crystal structure to the low-temperature superstructure with a cell volume of 2a x 2b x c. This phase transition is unusual, in which two energetically competing phonon modes at M and K points soften simultaneously. When approaching T-C from above, the K-point mode appears first. However, this K-point mode is overcome by the later-developed M-point mode. The thermal diffuse scattering intensities from both modes increase sharply at T-C; therefore, both modes soften simultaneously. The first-principles calculations demonstrate that the M-point mode is electrostatically more preferable than the K-point mode and determines the eventual low-temperature structure, although these two modes are competing energetically. This competition is characteristic of BaAl2O4, which is ascribed to the structurally flexible network structure of this compound.</P>
Miller-Rushing, Abraham J.,Katsuki, Toshio,Primack, Richard B.,Ishii, Yukio,Lee, Sang Don,Higuchi, Hiroyoshi Botanical Society of America, Inc. (Columbus) * Bu 2007 American journal of botany Vol.94 No.9
<P>Climate change is affecting plant phenology worldwide. Phenological responses vary among species, but it is not clear how responses differ among closely related species. We examined a 25-yr record (1981-2005) of flowering times for 97 trees, representing 17 species and hybrids of cherry (Cerasus sp. or Prunus sp.) grown at Mt. Takao, in Tokyo, Japan. The cherry trees flowered earlier over time, by an average of 5.5 d over the 25-yr study. Earlier flowering was explained largely by a 1.8C increase in February-March mean monthly temperatures. Most species and hybrids flowered 3-5 d earlier for each 1C increase in temperature, but early-flowering taxa flowered as much as 9 d earlier for each 1C increase in temperature. Flowering durations and differences in flowering times among species were greater in warm years than in cold years. Species and individual trees also flowered longer in warm years. These results show that the flowering times of closely related species may change similarly in response to climate change, but that early-flowering species may diverge from the overall trend in a predictable way. Such changes in flowering may affect gene flow and pollination as the length of the flowering season increases.</P>
Ozar, B.,Brooks, C.S.,Euh, D.J.,Hibiki, T.,Ishii, M. North-Holland Pub. Co 2013 Nuclear engineering and design Vol.263 No.-
The interfacial area transport of vertical, upward, air-water two-phase flows in an annular channel has been investigated at different system pressures. The inner and outer diameters of the annular channel were 19.1mm and 38.1mm, respectively. Twenty three inlet flow conditions were selected, which covered bubbly, cap-bubbly, and churn-turbulent flows. These flow conditions also overlapped with twelve conditions of a previous study for comparison. The local flow parameters, such as void fractions, interfacial area concentrations (IAC), and bubble interface velocities, were measured at nine radial positions for the three axial locations and converted into area-averaged parameters. The axial evolutions of local flow structure were interpreted in terms of bubble coalescence, breakup, expansion of the gas-phase due to pressure drop and system pressure. An assessment of interfacial area transport equation (IATE) was made and compared with the experimental data. A discussion of the comparison between model prediction and the experimental results were made.