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排序方式: 共有689条查询结果,搜索用时 31 毫秒
681.
A Ni/PMe2Ph catalyst is found to effect regioselective addition of cyanoformate esters across 1,2-dienes, giving rise to 3-alkoxycarbonyl-3-butenenitriles. Functional groups such as cyano, protected hydroxyl, and amino groups in the 1,2-diene substrates are tolerated. Isomerization of the initial products to thermodynamically more stable isomers takes place possibly through further oxidative addition of the C-CN bond of 3-alkoxycarbonyl-3-butenenitriles to Ni(0) followed by reductive elimination. The cyanoesterification products undergo further addition across alkynes in the presence of a Ni/P(4-CF3-C6H4)3 catalyst. 相似文献
682.
Hideki Taguchi Kazuhiro Hirata Hiroyasu Kido Yasuo Takeda Masaki Kato Ken Hirota 《Solid State Sciences》2009,11(7):1222-1225
Orthorhombic distorted K2NiF4-type (Ca1+xNd1?x)CrO4 (0.00 ≤ x ≤ 0.15) was synthesized using a standard ceramic technique. The cell parameters (a and c) decreased, whereas the cell parameter (b) increased with the increase in x. The variation in the global instability index (GII) indicated that the crystal stability of (Ca1+xNd1?x)CrO4 was not influenced by the Cr4+ ion content. At all temperatures, the electrical conductivity (σ) of (Ca1+xNd1?x)CrO4 increased with the increase in x. (Ca1+xNd1?x)CrO4 was a p-type semiconductor and exhibited hopping conductivity in a small-polaron model in the temperature range of 290 K ≤ T ≤ 713 K. The Cr4+ ion acts as an acceptor, and the electron transfer through the Cr3+–O–Cr4+ path becomes active as a result of the Cr4+ ion content and the Cr–O(1) distance. 相似文献
683.
684.
Kentaro Hirata 《Potential Analysis》2009,30(2):165-177
In an unbounded domain Ω in ℝ
n
(n ≥ 2) with a compact boundary or Ω = ℝ
n
, we investigate the existence of limits at infinity of positive superharmonic functions u on Ω satisfying a nonlinear inequality like as
where Δ is the Laplacian and c > 0 and p > 0 are constants. The result is applicable to positive solutions of semilinear elliptic equations of Matukuma type.
This work was partially supported by Grant-in-Aid for Young Scientists (B) (No. 19740062), Japan Society for the Promotion
of Science. 相似文献
685.
We report a hybrid atomic packing scheme comprised of a covalent-bond-mediated "stereochemical" structure and a densely packed icosahedron in a bulk metallic glass Pd40Ni40P20. The coexistence of two atomic packing models can simultaneously satisfy the criteria for both the charge saturation of the metalloid element and the densest atomic packing of the metallic elements. The hybrid packing scheme uncovers the structural origins of the excellent glass forming ability of Pd40Ni40P20 and has important implications in understanding the bulk metallic glass formation of metal-metalloid alloys. 相似文献
686.
Koki Yoshizawa Dr. Keisuke Hirata Prof. Shun-ichi Ishiuchi Prof. Masaaki Fujii Dr. Anne Zehnacker 《Chemphyschem》2023,24(18):e202300172
Alkali metal complexes of cyclic dipeptide cyclo Tyr-Tyr have been studied under cryogenic ion trap conditions. Their structure was obtained by combining Infra-Red Photo-Dissociation (IRPD) and quantum chemical calculations. The structural motif strongly depends on the relative chirality of the tyrosine residues. For residues of identical chirality, the cation interacts with one amide oxygen and one of the aromatic rings only; the distance between the aromatic rings does not change with the nature of the metal. In contrast, for residues of opposite chirality, the metal cation is located in between the two aromatic rings and interacts with both of them. The distance between the two aromatic rings strongly depends on the metal. Electronic spectra obtained by Ultra Violet Photodissociation (UVPD) spectroscopy and analysis of the UV photo-fragments shed light on the excited state deactivation processes, which depend on both the chirality of the residue and that of the metal ion core. Na+ stands out by the presence of low-lying charge transfer states resulting in the broadening of the electronic spectrum. 相似文献
687.
Kazuhiko Okitsu Yasuhiro Hayakawa Tomuo Yamaguchi Masashi Kumagawa Akira Hirata Syogo Fujiwara Yasunori Okano Nobuyuki Imaishi Shinichi Yoda Toshihiko Oida 《Crystal Research and Technology》1996,31(8):969-978
A mixing experiment of multicomponents melts was performed using a uniform temperature furnace in the Second International Microgravity Laboratories (IML-2) mission. Growth morphologies and Ga concentration profiles were analyzed for the samples with the compositional ratio of 0.5 In–0.5 Ga–1.0 Sb grown under microgravity and on earth. The sample with free surface grown under microgravity was nearly spherical in shape, except some parts with projections. Ga was dispersed homogeneously in the bulk because the mixing was enhanced by Marangoni convection due to the concentration gradient. On the other hand, the sample grown on earth was a double cylindrical shape with different diameters, and Ga concentration decreased from top to bottom, showing clearly the effect of gravity. Many needle crystals were formed in both space and earth samples due to rapid cooling. The average size of the needle crystals grown in space was larger than that of the earth sample. 相似文献
688.
689.