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31.
A simple and efficient transmission line model is proposed here to study how the transmission characteristics of photonic crystal waveguides are tailored by introduction of stubs patterned in the photonic crystal lattice. It is shown that band-pass and band-stop optical filters can be easily designed and optimized when stubs of appropriate length are brought in. Since the lengths of the designed stubs are not necessarily integer multiples of the photonic crystal lattice constant, a geometric shift in a portion of the photonic crystal structure is shown to be essential. The proposed model is verified by using a rigorous numerical method. An excellent agreement is observed between the numerical results and the transmission characteristics as extracted by the proposed model. 相似文献
32.
Khashayar Rajabimoghadam Yousef Darwish Umyeena Bashir Dylan Pitman Sidney Eichelberger Maxime A. Siegler 《Journal of Coordination Chemistry》2019,72(8):1346-1357
AbstractIn this research article, we report the synthesis and structural characterization of a family of first-row metal complexes bearing redox-active ligands with tunable H-bonding donors. We observed that these coordination complexes can adopt three different geometries and that they are stabilized by intramolecular multicenter H-bonding interactions, which are systematically modified by changing the metal ion (Co, Ni, Cu, Zn), the ligand scaffold (variations in the diamine and ureanyl substituents used) and the solvent of crystallization. 相似文献
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Moghimi A Rastegar MF Ghandi M Taghizadeh M Yari A Shamsipur M Yap GP Rahbarnoohi H 《The Journal of organic chemistry》2002,67(7):2065-2074
The synthesis and structural characterization of a novel generation of crown ethers, 3, 5 and 6 containing pyrilium, thiopyrilium, and pyridinium subunits, respectively, are reported. The crown ether unit is potentially capable of forming host-guest complexes with inorganic and organic cations, while the heteroaromatic cationic unit is suitable to bind with anions. A variety of physicochemical methods including electrospray mass spectrometry, UV-vis spectroscopy, solution and solid-phase NMR, and X-ray crystallography were applied for structural characterization of the new crown ether derivatives. The (1)H and (13)C NMR studies indicate rapid rotation of the B9C3 unit about the C-C bond that connects the two units to each other. Single crystals for 3, 4, and 5 were successfully obtained, and their X-ray crystal structures were resolved. The perchlorate anion in 3 (orthorhombic, space group P2(1)2(1)2(1)) and 5 (orthorhombic, space group P2(1)) is far from O(+) and close to S(+). The solid-phase structure of 3 and 5 show small deviation from planarity for the four aromatic rings, whereas two of the aromatic rings in 4 are out of heteroaromatic ring. Spectrophotometric studies in methanol solution revealed that the ligand 3 can be successfully applied to selective amino acid recognition. 相似文献
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Khashayar Karimian Farajolah Mohanazadeh Shaheen Rezai 《Journal of heterocyclic chemistry》1983,20(4):1119-1121
Covalent immobilization of the thiazole nucleus on a chloromethylated polystyrene copolymer results in the formation of a catalytically active thiazolium salt, capable of repeated acyloin and benzoin condensations. The nature of the solvent and the substituents on the thiazolium nucleus has been found to have marked effects of the rate of catalysis. 相似文献
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Interplay of quantum mechanical calculations and experimental data on hyperfine coupling constants of ethyl radical in zeolites at several temperatures was engaged to study the geometries and binding energies and to predict the temperature dependence of hyperfine splitting of a series of alkyl radicals in zeolites for the first time. The main focus is on the hyperfine interaction of alkyl radicals in the NaY and HY zeolites. The hyperfine splitting for neutral free radicals and free radical cations is predicted for different zeolite environments. This information can be used to establish the nature of the muoniated alkyl radicals in the NaY and HY zeolites via muSR experiments. The muon hyperfine coupling constants of the ethane radical cation in these zeolites are very large with relatively little dependence on temperature. It was found that the intramolecular dynamics of alkyl free radicals are only weakly affected by their strong binding to zeolites. In contrast, the substrate binding has a significant effect on their intermolecular dynamics. 相似文献
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Percival PW Brodovitch JC Ghandi K McCollum BM McKenzie I 《Journal of the American Chemical Society》2005,127(39):13714-13719
There is a pressing need to identify and monitor reaction intermediates in water at high temperatures and pressures, but conventional techniques have limited capability for studying transient free radicals under such challenging conditions. Apparatus has now been developed to permit muon avoided-level crossing spectroscopy (muLCR) of organic free radicals in superheated water. The combination of muLCR with transverse-field muon spin rotation (TF-muSR) provides the means to identify and characterize free radicals via their nuclear hyperfine coupling constants. Because the radicals are derived from the addition of muonium (Mu = mu+ e-) to unsaturated compounds, the ensuing muoniated free radicals correspond to conventional organic free radicals but with a muon spin label substituted for one of the protons. Muon spin spectroscopy is the only technique presently being used to characterize transient free radicals under hydrothermal conditions in an unambiguous manner, free from interference from other reaction intermediates. This paper demonstrates how muoniated radicals can be used to monitor the species present in hydrothermal systems, and examples are presented from two classes of reaction: dehydration of alcohols and enolization of ketones. Spectra are displayed and hyperfine constants reported for muoniated forms of the following free radicals in superheated water (typically 350 degrees C at 250 bar): 2-propyl, 2-methyl-2-propyl (tert-butyl), and 2-hydroxy-2-propyl. The latter radical is the product of muonium addition to both the keto and the enol forms of acetone, but different isotopomers are produced according to which reaction channel is dominant. This should prove invaluable in future studies of the role of enols in combustion. 相似文献
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Tetra-alkyl Phosphonium ionic liquids are phosphonium salts with melting points near room temperature. We report the NMR studies
of water-trihexyl (tetradecyl) phosphonium chloride ionic liquid mixtures. The proton chemical shifts were used to investigate
the intermolecular interactions in mixtures of ionic liquids and water. The OH chemical shifts were found to decrease as the
water concentration in the ionic liquid increased, and their rate of change with temperature decreased with water concentration.
The CH2 and CH3 chemical shifts were found to move downfield with the increase in temperature, and moved further downfield as water concentration
was decreased. The interface of experimental data and the results of quantum calculations suggest a significant binding of
phosphonium cations to chloride anion and water molecules. As well, the analysis of the data suggests a possible transformation
from cationchloride-water configuration at low water concentrations to cation-water-water at higher water concentrations.
Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users. 相似文献
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An efficient frequency-domain method, the phase variation monitoring (PVM) method, is proposed to determine the electromagnetic eigenmodes in two-dimensional photonic crystal waveguides. The proposed method is based on monitoring the reflection and transmission coefficients of incident plane waves. It is successfully applied to an illustrative line-defect photonic crystal waveguide and proved to be capable of calculating the in-plane leakage through the finite-size photonic crystal surrounding the line-defect. Calculation of the leakage loss is not only important for proper understanding of wave propagation within the defect but also for its significant role in applications of photonic structures. 相似文献
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