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排序方式: 共有418条查询结果,搜索用时 250 毫秒
41.
The magnetic and electrical properties of high-quality single crystals of A-site disordered (solid solution) Ln0.5Ba0.5MnO3 are investigated near the phase boundary between the spin-glass insulator and colossal-magnetoresistive ferromagnetic metal, locating near Ln=Sm. The temperature dependence of the ac susceptibility and the x-ray diffuse scattering of Eu0.5Ba0.5MnO3 are analyzed in detail. The uniformity of the random potential perturbation in Ln0.5Ba0.5MnO3 crystals with a small bandwidth yields, rather than the phase separation, an homogeneous short ranged charge or orbital order which gives rise to a nearly atomic spin-glass state. Remarkably, this microscopically disordered "charge-exchange-glass" state alone is able to bring forth the colossal magnetoresistance. 相似文献
42.
Kuriyama M Soeta T Hao X Chen Q Tomioka K 《Journal of the American Chemical Society》2004,126(26):8128-8129
A catalytic asymmetric arylation of sterically tuned imines with arylboroxines was developed by using N-Boc-l-valine-connected amidomonophosphane rhodium(I) catalyst in n-PrOH. The TMS group used for the steric tuning of imines is convertible to other functionalities that are applicable as a key foothold for the carbon-carbon bond-forming coupling reactions. 相似文献
43.
Tomohisa Yasuhara Katsumi Nishimura Ken-ichi Yamada Kiyoshi Tomioka 《Tetrahedron letters》2004,45(15):3043-3045
(±)-γ-Lycorane 3 was synthesized in 52% overall yield via seven steps from 5 by employing the highly stereoselective nitro-Michael cyclization of 5 to 9 and diastereoselective conjugate addition of aryllithium to a nitroolefin 10 as two key steps. 相似文献
44.
The straightforward methodology for the construction of chiral arene-fused-piperidine motifs using a highly enantioselective addition of 2-trityloxymethylaryllithiums to cyclic and acyclic nitroalkenes has been developed. The versatility of the process was highlighted by the first asymmetric synthesis of a dopamine D1 full agonist, A-86929. 相似文献
45.
A novel addition reaction of an aromatic hydrazine to the diketone derivative of C60 occurs highly regioselectively with an unusual migration of two hydrogen atoms from the hydrazine to the fullerene and affords a fluorescent product having a methylene carbon along the orifice. 相似文献
46.
A series of diazides of 1,2-diphenylacetylenes was photolyzed in matrices at low temperature and transient photoproducts were characterized by using IR, UV/vis methods combined with ESR studies. Theoretical calculations were also used to understand the experimental findings. The introduction of phenylethynyl groups on phenyl azides has little effect on the photochemical pathway. Thus, upon photoexcitation, (phenylethynyl)phenyl azides afforded the corresponding triplet nitrene, which is in photoequilibrium with the corresponding azacycloheptatetraene. In marked contrast, azidophenylethynyl groups exhibited a dramatic effect not only on the photochemical pathway of phenyl azides but also on the electronic and molecular structure of the photoproducts. The patterns of the effect depended upon the relative position of azide groups in the diphenylacetylene unit. Whenever two azide groups were situated in a conjugating position with respect to each other, as in p,p'-, o,o'-, and p,o'-bis(azides), the azides always resulted in the formation of a quinoidal diimine diradical in which unpaired electrons were extensively delocalizedin the pi-conjugation. The situation changed rather dramatically when azide groups were introduced in the meta position. Thus, the formation of azacycloheptatetraene was noted in the photolysis of the m.m'-isomer. ESR studies indicated the generation of a quintet state that was shown to be a thermally populated state with a very small energy gap of ca. 100 cal mol(-1). The m,p'-isomer was shown to be an excellent precursor for the high-spin quintet dinitrene. The IR spectra of the photoproduct showed no bands ascribable to azacycloheptatetraene. The observed spectra were in good agreement with that calculated for the quintet state. Strong EPR signals assignable to the quintet state were observed, along with rather weak signals due to mononitrenes. Moreover, the quintet bis(nitrene) was rather photostable under these conditions. 相似文献
47.
Yasuhara T Nishimura K Yamashita M Fukuyama N Yamada K Muraoka O Tomioka K 《Organic letters》2003,5(7):1123-1126
[reaction: see text] An omega-nitro-alpha,beta,psi,omega-unsaturated ester underwent a chemoselective conjugate addition of a nitroolefin moiety with aryllithium to produce a psi-aryl-omega-nitro-alpha,beta-unsaturated ester, which was then stereoselectively cyclized by intramolecular nitro-Michael reaction giving a functionalized cyclohexane applicable to the total synthesis of (+/-)-alpha- and beta-lycoranes. 相似文献
48.
Kise T Ogasawara T Ashida M Tomioka Y Tokura Y Kuwata-Gonokami M 《Physical review letters》2000,84(9):1986-1989
We propose a measurement setup for detecting quantum noise over a wide frequency range using inelastic transitions in a tunable two-level system as a detector. The frequency-resolving detector consists of a double quantum dot which is capacitively coupled to the leads of a nearby mesoscopic conductor. The inelastic current through the double quantum dot is calculated in response to equilibrium and nonequilibrium current fluctuations in the nearby conductor, including zero-point fluctuations at very low temperatures. As a specific example, the fluctuations across a quantum point contact are discussed. 相似文献
49.
50.
Susumu Kuwamura Yuuki Yoshinoya Noriaki Miura Fumiaki Tsumuraya Makoto Sakamoto Naoshi Baba 《Optical Review》2011,18(1):19-26
A bispectral method for astronomical speckle imaging utilizes an average speckle bispectrum of an object to derive its Fourier
phase. There has been, however, a problem in conventional bispectral algorithm owing to difficulty in processing bispectral
data in a four-dimensional (4D) space. In this paper, we propose an implementation to overcome this problem, where a one-dimensional
(1D) object projection is reconstructed from a two-dimensional (2D) average bispectrum of speckle projections, and object
projections so obtained at various angles are then tomographically combined into a 2D object image. In this tomographic approach,
processes are separable into those for individual projection angles, implying that bispectral data required to be stored at
a time are from 4D to 2D and computation time can be substantially reduced by parallelizing angle-by-angle processes. We have
performed experiments using simulated and observed data, and have demonstrated the feasibility of the present approach with
an achievable accuracy comparable to that of a conventional approach. 相似文献