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291.
292.
Toshiyuki Iwai 《Tetrahedron letters》2004,45(5):1083-1086
A variety of aromatic aldimines react with nonactivated alkyl iodides in the presence of zinc powder and a catalytic amount of chlorotrimethylsilane (TMSCl) in ethyl acetate-DMI to afford the corresponding α-alkylbenzylamine derivatives in good to excellent yields. 相似文献
293.
Calcium phosphate-vanadate apatite (CPVAP) works effectively as a catalyst for the aerobic oxidation of propargylic alcohols to the corresponding carbonyl compounds under an atmospheric pressure of molecular oxygen. Moreover, CPVAP can be readily separated by filtration and reused at least 10 times without appreciable loss of the catalytic activity. 相似文献
294.
Alexander G. Sobol Gerhard Wider Hideo Iwai Kurt Wüthrich 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):262-271
With the use of high magnetic fields and improved quality factor ratings of the probeheads in modern NMR spectrometers, radiation damping becomes more and more important. In addition, the demagnetizing field effect from protonated solvents gains significance with the increase of the magnetic field strength. During a typical NMR pulse sequence the magnetic fields caused by these effects become time-dependent, which makes the system nonlinear and may, for example, measurably influence the precession frequencies of all nuclei in the sample. Since radiation damping can affect signals that are several kilohertz away from the solvent resonance, the amplitude, phase, and frequency of the desired signals can be disturbed so as to give rise to spectral artifacts. In particular when difference methods are used to obtain the final spectrum, the data sets may be severely deteriorated by such artifacts. This paper investigates effects from the demagnetizing field and from radiation damping with a selection of pulse sequences in use for studies of macromolecular hydration, and strategies are described for the detection and elimination of the ensuing artifacts. 相似文献
295.
Velocity measurement of the diffuse object based on time-differentiated speckle intensity fluctuations 总被引:1,自引:0,他引:1
This paper proposes a new velocity measuring method for a moving diffuse object on the basis of the autocorrelation of time-differentiated speckle intensity fluctuations. The theoretical background and experimental verification of this method are given. The correlation length of time-differentiated speckle intensity fluctuations is defined by the point at which the correlation becomes zero. By means of the correlation length the object velocity is found to be accurately measured. 相似文献
296.
A low dislocation density of 107–8 cm−2 in GaN thin films on 6H-SiC(0001) substrates grown by metalorganic chemical vapor deposition was achieved. By considering possible origins of dislocations in the GaN/AlN/Sic structure, two major dislocation reduction routes are proposed; ultra-thin AlN buffer layers and smooth AlN surfaces in an atomic scale. Experimentally, the effects of the surface roughness and structural perfection of the AlN buffer layer on GaN film quality were extensively investigated as a function of AlN film thickness. The reduced dislocation density was realized by using ultra-thin AlN buffer layers having a thickness of 1.5 nm, which is below the critical value for misfit dislocation generation. The smoother surface morphology and enhanced structural quality of ultra-thin AlN buffer layers were found to be the main parameters in reducing the defect density in the GaN film. 相似文献
297.
Structures of amorphous anodic alumina films have been investigated by the X-ray radial distrubution function and the correlation method. The amorphous anodic alumina films are considered to contain AlO5 coordination polyhedra as well as AlO4 tetrahedra and AlO6 octahedra. Two types of conformation are taken into account by the correlation method; one (model A) is the conformation in which the above coordination polyhedra are arranged in a similar way to that found in the crystalline modifications of γ-Al2O3 within a short range of r < 4.5 Å and the other (model B) is the conformation in which coordination polyhedra are randomly arranged. The final model formed by mixing these two conformations (model A and B) in 1 : 1 ratio describes quantitatively the observed scattering intensity curves of the amorphous anodic alumina films. 相似文献
298.
Kohei Iwai Hiroshi Yamagishi Colin Herzberger Yuji Sato Hayato Tsuji Ken Albrecht Kimihisa Yamamoto Fumio Sasaki Hiroyasu Sato Aswin Asaithambi Axel Lorke Yohei Yamamoto 《Angewandte Chemie (International ed. in English)》2020,59(31):12674-12679
Microcrystallites are promising minute mirrorless laser sources. A variety of luminescent organic compounds have been exploited along this line, but dendrimers have been inapplicable owing to their fragility and extremely poor crystallinity. Now, a dendrimer family that overcomes these difficulties is presented. First‐, second‐, and third‐generation carbazole (Cz) dendrimers with a carbon‐bridged oligo(phenylenevinylene) (COPV2) core (GnCOPV2, n=1–3) assemble to form microcrystals. The COPV2 cores align uni/bidirectionally in the crystals while the Cz units in G2‐ and G3COPV2 align omnidirectionally. The dendrons work as light‐harvesting antennas that absorb non‐polarized light and transfer it to the COPV2 core, from which a polarized luminescence radiates. Furthermore, these crystals act as laser resonators, where the lasing thresholds are strongly coupled with the crystal morphology and the orientation of COPV2, which is in contrast with the conventional amorphous dendrimers. 相似文献
299.
Dr. Satoshi Suzuki Dr. Shunsuke Sasaki Amir Sharidan Sairi Riki Iwai Prof. Dr. Ben Zhong Tang Prof. Dr. Gen-ichi Konishi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(25):9940-9951
Twenty years ago, the concept of aggregation-induced emission (AIE) was proposed, and this unique luminescent property has attracted scientific interest ever since. However, AIE denominates only the phenomenon, while the details of its underlying guiding principles remain to be elucidated. This minireview discusses the basic principles of AIE based on our previous mechanistic study of the photophysical behavior of 9,10-bis(N,N-dialkylamino)anthracene ( BDAA ) and the corresponding mechanistic analysis by quantum chemical calculations. BDAA comprises an anthracene core and small electron donors, which allows the quantum chemical aspects of AIE to be discussed. The key factor for AIE is the control over the non-radiative decay (deactivation) pathway, which can be visualized by considering the conical intersection (CI) on a potential energy surface. Controlling the conical intersection (CI) on the potential energy surface enables the separate formation of fluorescent (CI:high) and non-fluorescent (CI:low) molecules [control of conical intersection accessibility ( CCIA )]. The novelty and originality of AIE in the field of photochemistry lies in the creation of functionality by design and in the active control over deactivation pathways. Moreover, we provide a new design strategy for AIE luminogens (AIEgens) and discuss selected examples. 相似文献
300.
Shibayama M Kawada H Kume T Matsunaga T Iwai H Sano T Osaka N Miyazaki S Okabe S Endo H 《The Journal of chemical physics》2007,127(14):144507
The microscopic structure of shear-induced gels for a mixed solution of 2-hydroxyethyl cellulose and nanometer-size spherical droplets has been investigated by in situ small-angle neutron scattering (SANS) with a Couette geometry as a function of shear rate gamma. With increasing gamma, the viscosity increased rapidly at gamma approximately 4.0 s(-1), followed by a shear thinning. After cessation of shear, the system exhibited an extraordinarily large steady viscosity. This phenomenon was observed as a shear-induced sol-gel transition. Real-time SANS measurements showed an increase in the scattering intensity exclusively at low scattering angle region. However, neither orientation of polymer chains nor droplet deformation was detected and the SANS patterns remained isotropic irrespective of gamma. It took about a few days for the gel to recover its original sol state. A possible mechanism of gelation is proposed from the viewpoint of shear-induced percolation transition. 相似文献