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排序方式: 共有261条查询结果,搜索用时 15 毫秒
21.
John F Kennedy Harish Kumar Parmjit S Panesar Satwinder S Marwaha Rita Goyal Anupama Parmar Sukhwinder Kaur 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2006,81(6):866-876
In this review, a comprehensive and illustrative survey is made of the regioselective synthesis of esters of sugars and related compounds using lipases. The main emphasis has been given to the screening and use of commercially available lipases for the enzymatic esterification of neutral monosaccharides, disaccharides, sugar alcohols and their selected ether and ester derivatives. The effect of solvents and solubilizing agents in improving the yields of the resultant sugar fatty acid esters has been incorporated. Further, solvent‐free esterification with molten fatty acids, use of ionic liquids and microwave radiations for improvement in the methodology have also been discussed. Copyright © 2006 Society of Chemical Industry 相似文献
22.
The microwave drill is a novel process for creating shaped holes in nonconductive materials. Its inherent material selectivity makes the microwave drill ideally suited for the controlled removal of ceramic coatings from underlying metallic substrates. In this paper, it is shown that the microwave drill process can drill through ceramic thermal barrier coatings (TBCs) to uncover an array of simulated cooling holes. The concept, apparatus, and procedure for successful drilling are described, and the potential for use in the production of advanced gas turbine components is discussed. 相似文献
23.
Diagnosis of Unmagnetized Plasma Electron Number Density and Electron-neutral Collision Frequency by Using Microwave 总被引:1,自引:0,他引:1
The plasma diagnostic method using the transmission attenuation of microwaves at double frequencies (PDMUTAMDF) indicates that the frequency and the electron-neutral collision frequency of the plasma can be deduced by utilizing the transmission attenuation of microwaves at two neighboring frequencies in a non-magnetized plasma. Then the electron density can be obtained from the plasma frequency. The PDMUTAMDF is a simple method to diagnose the plasma indirectly. In this paper, the interaction of electromagnetic waves and the plasma is analyzed. Then, based on the attenuation and the phase shift of a microwave in the plasma, the principle of the PDMUTAMDF is presented. With the diagnostic method, the spatially mean electron density and electron collision frequency of the plasma can be obtained. This method is suitable for the elementary diagnosis of the atmospheric-pressure plasma. 相似文献
24.
采用正交表L9(34)进行了烟草中总氮测定消化条件的筛选实验。实验考察了四个因子:称样量、硫酸钾用量、硫酸用量、氧化汞用量,每个因子各三水平的实验条件,经过直观分析、方差分析,确定在显著性水平0.10上,称样量和氧化汞用量都是显著的,硫酸钾用量和硫酸用量不显著;在显著性水平0.05上,氧化汞用量是显著的,称样量、硫酸钾用量和硫酸用量不显著。选用称样量和氧化汞用量的最优条件,即称样量0.3g、氧化汞用量0.1g,对硫酸钾用量和硫酸用量。主要考虑节约实验成本,选择硫酸钾用量1g和硫酸用量5mL为最终实验条件。 相似文献
25.
Daisuke Shimamoto Kimiyasu Sato Yoshiki Sugimoto Yuji Hotta 《International Journal of Applied Ceramic Technology》2019,16(6):2380-2384
Carbon fiber reinforced plastic (CFRP) composites have been considered quite eminent structural materials. For more extensive applications, however, more rapid forming methods of the CFRP composites are required. As for CFRP composites with thermoplastic matrices, microwave heating and pressing with ceramic molds should be promising. In the present work, zirconia molds with varied thermal conductivity were employed to give a desired shape to the CFRP composites heated with microwave irradiation. Experimental results showed that use of the zirconia molds with smaller thermal conductivity results in shorter necessary time for the forming process. Mechanism of the notable change in the heating efficiency is discussed as well. 相似文献
26.
Yuan Zeng Jianghao Liu Feng Liang Haiyue Xu Haijun Zhang Shaowei Zhang 《Journal of the American Ceramic Society》2019,102(5):2426-2439
Highly-dense ZrB2–SiC ceramics with excellent mechanical properties including Vickers hardness of 24.5 GPa and fracture toughness of 4.8 MPa/m1/2 were successfully prepared, by spark plasma sintering of the raw powders synthesized by a novel molten-salt and microwave co-assisted boro/carbothermal reduction (MSM-BCTR) method. Compared with the processing conditions required for synthesizing ZrB2–SiC by conventional reduction method, the present MSM-BCTR method possessed a variety of significant merits including the smaller material cost, lower processing temperature (1200°C), and remarkably higher efficiency (soaking time as short as 20 minutes). More importantly, the ZrB2–SiC powders, resultant from MSM-BCTR treatment, were verified to have single-crystalline nature and uniform well-grown anisotropic morphologies (rod-like ZrB2 and sheet-like SiC) as well as great potential in promoting the mechanical properties of their bulk counterparts. This great achievement was mainly ascribed to the specific MSM-BCTR conditions characterized by microwave heating and molten-salt medium. 相似文献
27.
Jie Zhang Yu Luo Zhenxing Yue Longtu Li 《Journal of the American Ceramic Society》2019,102(1):342-350
A multilayer cofired architecture was proposed and demonstrated to achieve high-Q and temperature-stable microwave dielectrics in a derived system, Zn1.01Nb2O6-TiO2. This approach could effectively allow the chemical reactions between Zn1.01Nb2O6 and TiO2 occur at a rather narrow area (~12 μm), the interfaces of heterogeneous layers, where the diffusion of Zn, Nb, and Ti could be observed. Such interfaces could act as the in situ “glues” to connect each layer well. The effects of stacking scheme and TiO2 content on the microwave dielectric properties of layered architectures were investigated systematically. The resonant frequency, Q-factor, and electric field distribution were reported using the eigenmode solver of high-frequency structure simulator. Among the available layer architectures, the optimized microwave dielectric characteristic was observed in Zn1.01Nb2O6/TiO2/Zn1.01Nb2O6 stacked with 0.058 mol TiO2 (~1.84 vol%). The τf can be effectively tuned to approximately +0.53 ppm/°C, and importantly, a high Q × f value ~99 500 GHz together with εr ~26.8 was achieved. This design could be beneficial for opening up new ways to develop high-performance microwave dielectrics based on current material systems and therefore to meet with the high requirements for 5G wireless communication components and multilayer packing technology. 相似文献
28.
29.
Camouflage is an emerging application of metamaterials owing to their exotic electromagnetic radiative properties. Based on the use of a selective emitter and an absorber as the metamaterials, most reported articles have suggested the use of single‐band camouflage, however, multispectral camouflage is a challenging issue owing to a difference of several orders of magnitude in the unit cell structure. Herein, hierarchical metamaterials (HMMs) for multispectral signal control when dissipating the absorbed energy of microwaves through the selective emission of infrared (IR) waves from the unit cell structure of the HMM are demonstrated. Integrating an IR selective emitter (IRE) with a microwave selective absorber, multispectral signal control with the large‐sized unit cell structures of up to 10 cm are realized. With an IRE, the emissive power from the HMM toward 5–8 µm is 1570% higher than the Au surface, which is preventing the occurrence of thermal instability. Furthermore, we determine that the signature levels of targeted IR waves (8–12 µm) and microwaves (2.5–3.8 cm) are reduced by up to 95% and 99%, respectively, when applying the HMM. 相似文献
30.