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31.
Efficient methods have been developed to synthesize azetidine, pyrrolidine, and indoline compounds via palladium-catalyzed intramolecular amination of C-H bonds at the γ and δ positions of picolinamide (PA) protected amine substrates. These methods feature relatively a low catalyst loading, use of inexpensive reagents, and convenient operating conditions. Their selectivities are predictable. These methods highlight the use of unactivated C-H bond, especially the C(sp(3))-H bond of methyl groups, as functional groups in organic synthesis. 相似文献
32.
Time-harmonic solution of Lamb wave scattering in a plane-strain waveguide with irregular thickness is investigated based on stair-step discretization and stepwise mode matching. The transfer relations of the transmission matrices and reflection matrices are derived in both directions of the waveguide. With these, an explicit expression of the scattering matrix is derived. When the scattering region of an inner irregular defect is geometrically divided into several parts composed of sub-waveguides with variable thicknesses and void regions with vertical free edges corresponding to the plate surfaces, the scattering matrix of the whole region could then be derived by modal matching along the artificial boundaries, as explicit functions of all the scattering matrices of the sub-waveguides and reflection matrices of the free edges. The effectiveness of the formulation is examined by numerical examples; the calculated scattering coefficients are in good accordance with those obtained from numerical simulation models. 相似文献
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Lin Shuyu 《Ultrasonics》1995,33(6):445-448
Langevin ultrasonic transducers are widely used in high-power ultrasonics and underwater sound. In ultrasonic cleaning, a matching metal horn rather than a metal cylinder is used as the radiator in order to enhance the radiating surface and improve the acoustic matching between the transducer and the processed medium. To raise the effect of ultrasonic cleaning, the standing wave in the cleaning tank should be eliminated. One method to eliminate the standing wave in the tank is to use the multifrequency ultrasonic transducer. In this paper, the Langevin ultrasonic horn transducer, with two resonance frequencies, is studied. The transducer consists of two groups of piezoelectric ceramic elements: the back metal cylinder, the middle metal cylinder and the front matching metal horn. The vibrational modes of the transducer are analysed, and resonance frequency equations of the transducer in the half-wave and the all-wave vibrational modes are derived. According to the resonance frequency equations, transducers with two resonance frequencies are designed and made. The resonance frequencies, the effective electromechanical coupling coefficients and the equivalent electric impedances of the transducers are measured. It is shown that the measured resonance frequencies are in good agreement with the computed results, and the transducer can be excited to vibrate at two resonance frequencies, which correspond to the half-wave and the all-wave vibrational modes of the transducer. 相似文献
35.
STOCHASTICMODELOFPERIODICOPERATIONPERFORMANCEFORTHECONTINUOUSCOUNTER-CURRENTADSORPTIONPROCESSSunShuyu(ChemicalEngineeringRese... 相似文献
36.
A method for quantitative determination of fish sperm deoxyribonucleic acid(fsDNA) was developed by using titanium dioxide(TiO2) as an adsorbent and near-infrared diffuse reflectance spectroscopy(NIRDRS). The selective enrichment of fsDNA was proved by comparing the adsorption efficiency of bovine serum albumin, tyrosine and tryptophan, and the low adsorption background of TiO2 was illustrated by comparing the spectra of four commonly-used inorganic adsorbents(alkaline aluminium oxide, neutral aluminium oxide, nano-hydroxyapatite and silica). The spectral feature of fsDNA can be clearly observed in the spectrum of the sample. Partial least squares(PLS) model was built for quantitative determination of fsDNA using 28 solutions, and 13 solutions with interferences were used for validation of the model. The results showed that the correlation coefficient(R) between the predicted and the reference concentration is 0.9727 and the recoveries of the validation samples are in the range of98.2%–100.7% 相似文献
37.
Quantitative determination of serum triglycerides was achieved in diffuse reflectance mode using silver mirror as the substrate to enhance the spectral features. 相似文献
38.
Yulan Zhu Shuyu Zhou Yuhe Kan Zhongmin Su 《International journal of quantum chemistry》2007,107(7):1614-1623
Density functional theory (DFT) and time‐dependent DFT (TDDFT) are applied to study seven asymmetric π‐conjugated porphyrins with extended benzoheterocycles: quinoline, indole, benzoimidazole, benzothiazole, benzooxazole, 2,1,3‐benzothiadiazole, and 2,1,3‐benzoxadiazole. The solvation effects on the excitation energies for these porphyrin derivatives in chloroform are taken into account by using the continuum model (C‐PCM) combined with TDDFT, and this method makes a closer agreement with the experimental values, especially for the B‐bands of these objects. Great efforts have been made on investigating the influences of the fused aromatic units of the porphyrins on the absorption properties as these can be particularly important for many applications. Benzoheterocycle introduction and solvent effects have been systemically investigated, and close agreement is obtained between calculated and measured UV–vis spectra. These theoretical data could shed light on future synthetic chemistry. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
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Guohua Xie Mingzhou Chen Michael Mazilu Shuyu Zhang A.K. Bansal Kishan Dholakia Ifor D. W. Samuel 《Laser \u0026amp; Photonics Reviews》2016,10(1):82-90
The spatial coherence of organic light‐emitting diodes (OLEDs) is an important parameter that has gained little attention to date. Here, we present a method for making quantitative measurements of the spatial coherence of OLEDs using a Young's double‐slit experiment. The usefulness of the method is demonstrated by making measurements on a range of OLEDs with different emitters (iridium and europium complexes) and architectures (bottom and top emitting) and the fringe visibility is further manipulated by gratings embedded in external diffractive optical elements. Based on the experiments and simulation of the results, we quantitatively determine the spatial coherence lengths of several OLEDs and find them to be a few micrometers. A 60% increase in the spatial coherence length was observed when using a narrow bandwidth emitter and a metal‐coated grating.