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81.
ZnO/SnO nanocomposites have been designed to enhance the band edge emission and suppress the defect emission of ZnO nanorods simultaneously. It is found that the intensity ratio between the band edge and defect emission can be improved by up to 4 orders of magnitude. The underlying mechanism is interpreted in terms of surface modification as well as carrier transfer from SnO nanoparticles to ZnO nanorods. Our approach is very useful for creating highly efficient optoelectronic devices. 相似文献
82.
Matthew L. Isherwood Peter R. Guzzo Alan J. Henderson Ming Min Hsia Jagjit Kaur Kassoum Nacro Venkateswara R. Narreddula Shailaja Panduga Rashmi Pathak Bharat Shimpukade Valentina Tan Kai Xiang Zhu Qiang Animesh Ghosh 《Tetrahedron: Asymmetry》2012,23(22-23):1522-1527
(7S,10R)-5-Methyl-2-((3-(trifluoromethyl)phenyl)sulfonyl)-5,6,7,8,9,10-hexahydro-7,10-epiminocyclohepta[b]indole 1a is a potent 5-HT6 antagonist (h5-HT6 Ki = 1.5 nM) which is derived from an epiminocyclohept[b]indole scaffold. In order to synthesize 1a on a multi-gram scale to support advanced biological testing, an efficient chiral resolution of the intermediate tert-butyl 2-bromo-5,6,7,8,9,10-hexahydro-7,10-epiminocyclohepta[b]indole-11-carboxylate 2 was developed. After derivatizing 2 with (1R)-(?)-menthyl chloroformate it was found that a single diastereomer 7a could be isolated by selective precipitation from n-hexane. The absolute stereochemistry of 7a was determined by X-ray crystallography and the structure was confirmed as (7S,10R)-tert-butyl 2-bromo-5,6,7,8,9,10-hexahydro-7,10-epiminocyclohepta[b]indole-11-carboxylate. Removal of the chiral auxiliary under basic conditions afforded intermediate 2a in >99% enantiomeric purity and with 80% yield based on recovery from the racemic compound 2. Intermediate 2a was used successfully to synthesize 5-HT6 antagonist 1a on a multi-gram scale. 相似文献
83.
Highly Facet‐Dependent Photocatalytic Properties of Cu2O Crystals Established through the Formation of Au‐Decorated Cu2O Heterostructures 下载免费PDF全文
Guo‐Zhi Yuan Chi‐Fu Hsia Zhen‐Wen Lin Chieh Chiang Prof. Yun‐Wei Chiang Prof. Michael H. Huang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(35):12548-12556
This work confirms the presence of a large facet‐dependent photocatalytic activity of Cu2O crystals through sparse deposition of gold particles on Cu2O cubes, octahedra, and rhombic dodecahedra. Au‐decorated Cu2O rhombic dodecahedra and octahedra showed greatly enhanced photodegradation rates of methyl orange resulting from a better separation of the photogenerated electrons and holes, with the rhombic dodecahedra giving the best efficiency. Au–Cu2O core–shell rhombic dodecahedra also displayed a better photocatalytic activity than pristine rhombic dodecahedra. However, Au‐deposited Cu2O cubes, pristine cubes, and Au‐deposited small nanocubes bound by entirely {100} facets are all photocatalytically inactive. X‐ray photoelectron spectra (XPS) showed identical copper peak positions for these Au‐decorated crystals. Remarkably, electron paramagnetic resonance (EPR) measurements indicated a higher production of hydroxyl radicals for the photoirradiated Cu2O rhombic dodecahedra than for the octahedra, but no radicals were produced from photoirradiated Cu2O cubes. The Cu2O {100} face may present a high energy barrier through its large band edge bending and/or electrostatic repulsion, preventing charge carriers from reaching to this surface. The conventional photocatalysis model fails in this case. The facet‐dependent photocatalytic differences should be observable in other semiconductor systems whenever a photoinduced charge‐transfer process occurs across an interface. 相似文献
84.
A comparison of BF3 ·Bu2O and Cl-N2PF6 as catalysts for cationic homopolymerization and copolymerization of trioxane has been made by employing high resolution nuclear magnetic resonance techniques. While no substantial difference was detected for the homopolymerization, two important differences were observed for the copolymerization with ethylene oxide; viz., 1) with Cl-NPF6 there is a lower build-up of formaldehyde concentration; 2) with Cl[sbnd]N2PF6, a lesser amount of cyclic compounds containing ethylene oxide units is formed (e.g., 1,3-dioxolane). Both observations suggest that depolymerization occurs to a lesser extent with the cl-N2PF6 catalyst. 相似文献
85.
86.
The Mössbauer effect has been applied to a wide variety of objects related to Chinese archaeology. Besides ceramic artifacts, materials like porcelain, glazes, bronzes, ancient coins, ancient mineral drugs, and even fossils were studied. This article reviews these applications with particular emphasis on the study of the famous terracotta warriors and horses of the Qin Dynasty. 相似文献
87.
Relaxation dynamics of an optically excited ligand field state and strong modulation of oscillator strengths of ligand field transitions by coherent acoustic phonon in gamma-Fe(2)O(3) nanocrystals were investigated through transient absorption measurements. A near-infrared pump beam prepared the lowest excited ligand field state of Fe(3+) ions preferentially on the tetrahedral coordination site. A time-delayed visible probe beam monitored the dynamics of various ligand field transitions and modification of their oscillator strengths by a coherent lattice motion. Transient absorption data exhibited dynamic features of a few distinct time scales, 100 fs, 1 ps, and 17-100 ps, as well as intense oscillatory features resulting from a coherent acoustic phonon. The initial decay of the induced absorption in 100 fs has been attributed to the exchange interaction-mediated energy transfer from the tetrahedral to octahedral Fe(3+) sites. The dynamics of slower time scales were assigned to the vibrational and electronic relaxations. Excitation of the ligand field state created a coherent acoustic phonon resulting in unusually intense modulation of the transient absorption signal despite its predominantly local nature and relatively small vibronic coupling. Excitation of each Fe(3+) ion in the nanocrystal was estimated to modulate up to 60% of its contribution to the total absorption intensity of the nanocrystal. The intense modulation of the absorption has been attributed to the strongly modulated oscillator strength of the ligand field transitions rather than oscillating Frank-Condon overlap. Dynamic modification of the metal-ligand orbital overlap and exchange interaction between the neighboring metal ions are the main factors responsible for the modulation of the oscillator strength. 相似文献
88.
Sulin ZhangK.Jimmy Hsia Arne J. Pearlstein 《Journal of the mechanics and physics of solids》2002,50(3):549-569
Fracture of a thin ductile layer sandwiched between stiff substrates often results from growth and coalescence of microscopic cavities ahead of an extending crack. Cavitation induced by plastic flow in a confined, ductile layer is analyzed here to evaluate the interfacial fracture toughness of such sandwich structures. For rigid-plastic materials, a new method is proposed in which the potential flow field of a fluid is used to approximate the plastic deformation. The principle of virtual work rate is applied to determine the equivalent traction-separation law. The method is demonstrated and validated for spherically symmetric cavity growth, for which an exact solution exists. We then study in detail the growth of an initially spherical cavity in a cylindrical bar of finite length subject to uniform traction at its ends. The results show that the stress-separation curves depend strongly on initial cavity size and the strain-hardening exponent, and weakly on the nominal strain. The method has clear advantages over numerical methods, such as finite-element analysis, for parametric study of cavity growth with large plastic deformation. 相似文献
89.
Y.F. Hsia N. Fang H.M. Widatallah D.M. Wu X.M. Lee J.R. Zhang 《Hyperfine Interactions》2000,126(1-4):401-406
Some experimental results in the case of anisotropic media are at variance with the Einstein-Stokes formula of Brownian motion and the Singwi-Sjölander model. The disagreement comes from the anchor effect. The concept of “pseudoparticle” is introduced in order to retain the Singwi-Sjölander formalism. Mössbauer spectroscopy can be used to estimate the thickness of the anchored liquid-crystalline molecular textures forming on the surface of Brownian particles. 相似文献
90.
A special class of solutions for multiobjective programming problems with set functions is considered. A subset of nondominated solutions, called properD-solution set, with respect to a given domination structure is characterized under two situations, with and without inequality constraints.The authors greatly appreciate valuable comments received from the referees. 相似文献