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22.
Development of PMN-PT single crystal/epoxy 1-3 composites for high-frequency ultrasonic transducers application is presented. The composite was fabricated by using a DRIE dry etching process with a 45% volume fraction of PMN-PT. A 35 MHz ultrasound flat transducer was fabricated with the composite, which was found to have an effective electromechanical coupling coefficient of 0.81, an insertion loss of 18 db, and a -6 dB bandwidth as high as 100%. Tungsten wire phantom image shows that the transducer had an axial resolution of 30 μm, which was in good agreement with the theoretical expectation. The initial results showed that the PMN-PT/epoxy 1-3 composite has many attractive properties over conventional piezoelectric materials for medical imaging applications. 相似文献
23.
The one-pot U-4CR and intramolecular O-alkylation sequence starting from 2-aminophenols in combination with α-bromoalkanoic acids, aldehydes, and isocyanides under controlled microwave heating has been established for a rapid access to highly functionalized 3,4-dihydro-3-oxo-2H-1,4-benzoxazines. With appropriate substitutions on the 1,4-benzoxazines, a microwave-assisted Cu-catalyzed intramolecular amidation was performed to furnish a novel class of heterocyclic conjugates of 1,4-benzoxazines with a 2-oxindole linked through a C-N single bond. 相似文献
24.
Xiubei Yang Dr. Yubin Fu Minghao Liu Shuang Zheng Xuewen Li Prof. Qing Xu Prof. Gaofeng Zeng 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(16):e202319247
Binding water molecules to polar sites in covalent organic frameworks (COFs) is inevitable, but the corresponding solvent effects in electrocatalytic process have been largely overlooked. Herein, we investigate the solvent effects on COFs for catalyzing the oxygen reduction reaction (ORR). Our designed COFs incorporated different kinds of nitrogen atoms (imine N, pyridine N, and phenazine N), enabling tunable interactions with water molecules. These interactions play a crucial role in modulating electronic states and altering the catalytic centers within the COFs. Among the synthesized COFs, the one with pyridine N atoms exhibits the highest activity, with characterized by a half-wave potential of 0.78 V and a mass activity of 0.32 A mg−1, which surpass those from other metal-free COFs. Theoretical calculations further reveal that the enhanced activity can be attributed to the stronger binding ability of *OOH intermediates to the carbon atoms adjacent to the pyridine N sites. This work sheds light on the significance of considering solvent effects on COFs in electrocatalytic systems, providing valuable insights into their design and optimization for improved performance. 相似文献
25.
Yuqiao Wang Wei Wang Gaofeng Li Qin Liu Tao Wei Baosong Li Caiyun Jiang Yueming Sun 《Mikrochimica acta》2016,183(12):3221-3228
We report on an electrochemical sensor for L-cysteine that consists of a glassy carbon electrode modified with a two-dimensional ternary nanocomposite prepared from platinum, magnetite, and reduced graphene oxide (referred to as Pt-Fe3O4/rGO). It was prepared by a solvothermal method and characterized by X-ray powder diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Electrochemical detection processes were investigated by cyclic voltammetry, amperometry, double potential step chronoamperometry and differential pulse voltammetry. The diffusion coefficient (7.41 × 10?7 cm2 s?1) and reaction rate constant (9.96 × 107 cm3 mol?1 s?1) were calculated via the Cottrell equation. The sensor, best operated in 0.1 M NaOH solution at a working voltage of 0.65 V vs. SCE, has a 10 μM detection limit and an analytical range that extends from 0.10 to 1.0 mM. The method is acceptably selective, stable, repeatable and reproducible due to the synergistic effect of the various components applied. The detection limit is 1.0 × 10?5 M. 相似文献
26.
The transient process of thermal stratification in liquid nitrogen (LN2) induced by lose of vacuum in a multi-layer insulated cryogenic tank is investigated both experimentally and numerically.
In the experiments, distribution and evolution of the liquid temperature is obtained using thermocouples. Then, two-dimensional
numerical computations are performed, using the two-fluid model together with nucleate boiling model as the closure correlations.
Comparison of the numerical results against the experimental data illustrates that the process of thermal stratification forming
and weakening, as well as the liquid temperature field are satisfactorily simulated. The computed results of liquid flow field
contribute to the understanding of this transient process. It is also demonstrated that the two-phase flow in the tank plays
an important role on thermal stratification. 相似文献
27.
Weiwei Zhang Xin Zhang Gaofeng Zeng Kang Wang Wenchao Zhang Rongjie Yang 《先进技术聚合物》2019,30(12):3061-3072
Flamability is one of the major issues for utilization of bisphenol A–type vinyl ester resin (VER) polymeric composites in practical applications. The thermal stability and mechanical property of VER composites containing octaphenyl polyhedral oligomeric silsesquioxane (OPS) were investigated and discussed in detail. With increasing the mass ratio of OPS, the residues yield at 800°C and bending strength at break of the VER/OPS composites were enhanced, accompanied with the gradually decreased values of the peak heat release rate, total heat release, and total smoke release due to the formation of dense carbon/silica protective layers that acted as a barrier to heat and mass transfer. In addition, the flame‐retardant mechanisms of condensed phase and gas phase were analyzed by XPS, TGA‐FTIR, and GC‐MS. The results showed that when OPS was incorporated to the resin matrix, the characteristic peaks intensity of the gaseous products was reduced obviously due to some of the characteristic groups still retained in condensed phase. Therefore, the significance of this work is providing an optional method to fabricate flame‐retarding VER composites with excellent mechanical properties. 相似文献
28.
In this paper, a class of anticipated backward stochastic differential equations driven by Teugels martingales associated with Lévy process is investigated. We obtain the existence and uniqueness of solutions to these equations by means of the fixed-point theorem. We show that a comparison theorem for this type of ABSDEs also holds under some slight stronger conditions. 相似文献
29.
2-Alkylaminobenzo[b]furans were isolated and characterized by X-ray crystal structural analysis, for the first time, from the Cu-catalyzed intramolecular amidation of hindered secondary amides under controlled microwave heating. A mechanism was proposed to account for competing Cu-catalyzed intramolecular N- and O-arylation pathways, which were controlled by the bulkiness of substituents on the nitrogen atom of secondary amides. 相似文献
30.
各级化学竞赛中有不少以结构高度对称的化合物为素材的试题,该类题目不仅可以考查学生空间想象能力,还可以考查如何将化学问题抽象为数学问题,利用数学方法解决化学问题的能力。本文讨论几种结构高度对称化合物的试题的解题思路。1由正八面体引出的对称问题【例1】已知[Co(NH3) 相似文献