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排序方式: 共有285条查询结果,搜索用时 31 毫秒
31.
Songyi Ham Hee‐Jeong Jang Yookyung Song Prof. Kevin L. Shuford Prof. Sungho Park 《Angewandte Chemie (International ed. in English)》2015,54(31):9025-9028
Herein, we report a general synthetic pathway to various shapes of three‐dimensional (3D) gold nanoframes (NFs) embedded with a Pt skeleton for structural rigidity. The synthetic route comprises three steps: site‐specific (edge and vertex) deposition of Pt, etching of inner Au, and regrowth of Au on the Pt framework. Site‐specific reduction of Pt on Au nanoparticles (NPs) led to the high‐quality of 3D Au NFs with good structural rigidity, which allowed the detailed characterization of the corresponding 3D metal NFs. The synthetic method described here will open new avenues toward many new kinds of 3D metal NFs. 相似文献
32.
Alcohol-containing potassium organotrifluoroborates as starting reagents were prepared from their corresponding dibromobenzenes through a sequential one-pot reaction. The oxidation reactions of these substrates, which were carried out using 3.0 equiv of 8 N Jones reagent in acetone at 0 °C, provided a high yield of the desired carbonyl-functionalized compounds. In addition, the cross-coupling reactions of these organocarbonyltrifluoroborates were successfully performed in the presence of 3 mol % of Pd(PPh3)4 catalyst at 100 °C. 相似文献
33.
Robinson James W. Ham Mooyoung 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1975,3(4):222-226
Zinc ion pulses with varying amplitudes up to 1 mA have been extracted from a vacuum discharge. Repetitive operation of the pulsed discharge at 5300 Hz was maintained for 24 min. Breakdown of the 0.4 mm vacuum gap was accomplished by ramp-charging a 270 pF capacitor connected across the gap until breakdown occurred, the capacitor then being discharged through the gap. Stable operation was maintained by feedback control of the electrode spacing. The anode was eroded at 10 mg/C by the discharge, with 65 percent of the anode material being deposited on the cathode in the form of a fiber. 相似文献
34.
Ham Levanon 《Chemical physics letters》1982,90(6):465-471
A laser photolysis study of ZnTPP (P) oriented in nematic and isotropic cyanohexylbiphenyl (6CB) as a function of added 1.4-benzoquinone (Q) is reported. In the absence of Q, enhancement of triplet absorption below the clearing point (nematic phase) is observed. It is attributed to the improved alignment of the optical transition in the ordered matrix and also to the increase in the intersystem crossing efficiency. T−S1. In the presence of Q in the nematic phase. An additional increase in triplet absorption is noticed. This result is interpreted in terms of a triplet radical pair [P+√…Q−√]T,RP formation which is facilitated by the ordering in the liquid crystal, thus providing an additional channel for triplet formation. The triplet PT in 6CB (nematic or isotropic) is quenched with a second-order rate of ≈108 M−1 s−1 as compared to 2 × 109 M−1 s−1 in toluene. 相似文献
35.
P.H. Cannington Norman S. Ham 《Journal of Electron Spectroscopy and Related Phenomena》1979,15(1):79-82
Photoelectron spectra, excited by He I radiation, of the following amino acids were measured:- alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophane, tyrosine, 4-hydroxyproline, β-alanine, γ-aminobutyric acid and δ-aminovaleric acid. The spectra showed a number of bands of low ionization energy (<13 eV) and these have been assigned to photoionizations from the NH2 and COOH groups. For the α-amino acids with complex side-chains extra bands arising from easily-ionizable electrons in aromatic rings or atomic lonepairs, such as sulphur or oxygen atoms, were also identified. Perturbation arguments together with the spectra of closely related molecules have been used to confirm the assignments. During measurement, decomposition occurred for aspartic acid, asparagine and histidine, while glutamic acid and glutamine cyclized. 相似文献
36.
Reaction of cyclohexadienylium-Fe(CO)3 complexes (7) and (8) with sodiomalono-nitrile gives the carbo-spirocyclic derivatives (9) and (10), whilst reaction with benzylamine and removal of iron leads to the azaspirocyclic enones (15) and (16), respectively. 相似文献
37.
We consider hypergraphs as symmetric relational structures. In this setting, we characterise finite axiomatisability for finitely generated universal Horn classes of loop-free hypergraphs. An Ehrenfeucht–Fraïssé game argument is employed to show that the results continue to hold when restricted to first order definability amongst finite structures. We are also able to show that every interval in the homomorphism order on hypergraphs contains a continuum of universal Horn classes and conclude the article by characterising the intractability of deciding membership in universal Horn classes generated by finite loop-free hypergraphs. 相似文献
38.
Subluminal and superluminal propagation in Er<Superscript>3+</Superscript> doped fiber Bragg grating
Z. C. Zhuo B. S. Ham 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(1):117-121
The method to pump the FBG written into an Er3+-doped optical fiber is proposed to decrease or increase the group velocity of a probing pulse based on the fact that a pump-induced
process changes the refractive index and dispersion associated with the 4I15/2-4I13/2 transition in Er3+-doped optical fiber. The system equations are derived. The group velocity modification is numerically demonstrated and discussed
with the effects of an optical pump power, fiber Bragg grating length, doping concentration of Er3+ ions, and modulation amplitude of the grating. 相似文献
39.
Won Seok Ham Julius Hillenbrand Jrme Jacq Christophe Genicot Tobias Ritter 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(2):542-546
(Hetero)arylamines constitute some of the most prevalent functional molecules, especially as pharmaceuticals. However, structurally complex aromatics currently cannot be converted into arylamines, so instead, each product isomer must be assembled through a multistep synthesis from simpler building blocks. Herein, we describe a late‐stage aryl C?H amination reaction for the synthesis of complex primary arylamines that other reactions cannot access directly. We show and rationalize through a mechanistic analysis the reasons for the wide substrate scope and the constitutional diversity of the reaction, which gives access to molecules that would not have been readily available otherwise. 相似文献
40.
Alex van der Ham Thomas Hansen Dr. Gerrit Lodder Dr. Jeroen D. C. Codée Dr. Trevor A. Hamlin Dr. Dmitri V. Filippov 《Chemphyschem》2019,20(16):2103-2109
Lithium ion selective crown ethers have been the subject of much research for a multitude of applications. Current research is aimed at structurally rigidifying crown ethers, as restructuring of the crown ether ring upon ion binding is energetically unfavorable. In this work, the lithium ion binding ability of the relatively rigid 8-crown-4 was investigated both computationally by density functional theory calculations and experimentally by 1H and 7Li NMR spectroscopy. Although both computational and experimental results showed 8-crown-4 to bind lithium ion, this binding was found to be weak compared to larger crown ethers. The computational analysis revealed that the complexation is driven by enthalpy rather than entropy, illustrating that rigidity is only of nominal importance. To elucidate the origin of the favorable interaction of lithium ion with crown ethers, activation strain analyses and energy decomposition analyses were performed pointing to the favorable interaction being mainly electrostatic in nature. 8-crown-4 presents the smallest crown ether reported to date capable of binding lithium ion, possessing two distinct conformations from which it is able to do so. 相似文献