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排序方式: 共有198条查询结果,搜索用时 31 毫秒
111.
当带有光学成像探测制导系统的高速飞行器在大气层内飞行时,光学窗口与来流之间会形成复杂的凹腔绕流流场,产生气动光学效应。建立了求解超声速流场的高精度LES/RANS混合算法模型,研究了超声速流动条件下的Settles三维凹腔流动;在计算得到精确流场数据的基础上,研究了凹腔剪切层区域的光学传输效应。结果表明,凹腔流动的剪切层结构将引起光线抖动,导致严重的波面畸变,明显降低光强斯特雷尔(Strehl)比,严重影响光学传输性能,进而大大降低光学制导精度。 相似文献
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采用外差探测方式, 建立了全光纤结构的激光多普勒测振仪,用来测量经空气传播耦合引起的散射体振动,以期感知振源振动信息。实验探索了散射体材料、固定方式和相对振源位置等对空气耦合振动的影响,得到了200~2700 Hz频率范围内6种散射体振动响应特性曲线。结果表明:通过空气耦合引起的散射体振动,在相同振源振幅下,散射体振动的振幅一般随频率升高而升高; 在材料、固定方式和相对振源位置等因素中,散射体材料对振动响应特性的影响是主要的,后两者只影响局部细节。 相似文献
114.
Mohanad Bashari Ahmed Eibaid Jinpeng Wang Yaoqi Tian Xueming Xu Zhengyu Jin 《Ultrasonics sonochemistry》2013,20(1):155-161
In our current research work, the effect of ultrasound irradiation on the enzymatic activity and enzymatic hydrolysis kinetic parameters of dextran catalysis by dextranase were investigated. Furthermore, the effects of ultrasound irradiation on the structure of dextranase were investigated with the aid of fluorescence spectroscopy and circular dichroism (CD) spectroscopy. The maximum activity of dextranase was observed when the sample was treated with ultrasound at 25 kHz, 40 W for 15 min, under which the enzyme activity increased by 13.43% compared the routine thermal incubation at 50 °C. Experimental Kinetics results, demonstrated that, both the Vmax and KM values of dextranase increased with ultrasound-treated compared with the incubation at 50 °C. Likewise, both the catalytic and specificity constants were higher under the effects of an ultrasonic field, indicating that, the substrate is converted into the product at an increased rate when compared with the incubation at 50 °C.On the other hand, fluorescence and CD spectra reflected that the ultrasound irradiation had increased the number of tryptophan on dextranase surface with increased α-helix by 15.74% and reduced random coil by 5.41% upon ultrasound-treated dextranase protein compared to the control, which were helpful for the improvement of its activity. 相似文献
115.
Mohanad Bashari Pei Wang Ahmed Eibaid Yaoqi Tian Xueming Xu Zhengyu Jin 《Ultrasonics sonochemistry》2013,20(4):1008-1016
In this research work, dextranase has immobilized onto calcium alginate beads using a novel ultrasound method. The process of immobilization of the enzyme was carried out in a one-step ultrasound process. Effects of ultrasound conditions on loading efficiency and immobilization yield of the enzyme onto calcium alginate beads were investigated. Furthermore, the activity of the free and immobilized enzymes prepared with and without ultrasound treatment, as a function of pH, temperature, recyclability and enzyme kinetic parameters, was compared. The maximum loading efficiency and the immobilization yield were observed when the immobilized dextranase was prepared with an ultrasonic irradiation at 25 kHz, 40 W for 15 min, under which the loading efficiency and the immobilization yield increased by 27.21% and 18.77%, respectively, compared with the immobilized enzymes prepared without ultrasonic irradiation. On the other hand, immobilized enzyme prepared with ultrasonic irradiation showed Vmax and KM value higher than that for the immobilized enzyme prepared without ultrasonic irradiation, likewise, both the catalytic and specificity constants of immobilized enzyme prepared with ultrasonic irradiation were higher than that for immobilized enzyme prepared without ultrasound, indicating that, this new ultrasonic method improved the catalytic kinetics activity of immobilized dextranase at all the reaction conditions studied. Compared with immobilized enzyme prepared without ultrasound treatment, the immobilized enzymes prepared with ultrasound irradiation exhibited: a higher pH optimum, optimal reaction temperature, activation energy, and thermal stability, as well as, a higher recyclability, which, illustrating the effectiveness of the sonochemical method. To the best of our knowledge, this is the first report on the effect of ultrasound treatments on the immobilization of dextranase. 相似文献
116.
Dongmei Du Mei Qin Zhengyu Zhou Aiping Fu 《International journal of quantum chemistry》2012,112(2):351-358
The accurate pKa determinations for three carboxylic acids have been investigated using the combination of the extended clusters‐continuum model at B3LYP/6‐31+g(d,p) and B3LYP/6‐311++g(d,p) levels. To take into account of the effect of the water combined with carboxylic acids in different positions, eleven molecular clusters were considered. Among these clusters, the one involving the carboxylic acid wrapped up with water molecules and saturated with hydrogen bonds (four hydrogen bonds around ? COOH) leads to the best B3LYP pKa results compared to the experimental data. For those clusters saturated with hydrogen bonds, when n = 3 (the number of water molecules), the average absolute errors between the calculated pKa results and experimental data of these three carboxylic acids were 0.19 (0.23) and 0.12 (0.22) pKa at B3LYP/6‐31+g(d,p)//PCM (IEFPCM) and B3LYP/6‐311++g(d,p)//PCM (IEFPCM) levels, respectively; when n = 4, they are 0.53 (1.23) and 1.09 (1.03) pKa, respectively. On the basis of the above results, the molecular cluster saturated with four hydrogen bonds formed by three waters and one carboxylic acid molecule was the chief existence in the carboxylic acid solution. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012 相似文献
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118.
Huiying Yan Zhengyu Bai Shujun Chao Qian Cui Lu Niu Lin Yang Jinli Qiao Kai Jiang 《Ionics》2014,20(2):259-268
Carbon nanotubes are believed to be powerful materials for constructing novel hybrid composites with desirable functionalities and applications in many fields. Therefore, a better understanding of the functionalization of multiwalled carbon nanotubes (MWCNTs) holds the key to a better performance of the hybrid properties. In this paper, with a series of aromatic bifunctional molecule additives, modified MWCNTs were used as composite supports for synthesizing nanostructured palladium catalysts for formic acid oxidation. The additives contain anthranilic acid, o-phenylenediamine, salicylic acid, catechol, and phthalic acid. The influence of the different bifunctional groups (such as –NH2, –OH, –COOH, and their mixed groups) on the morphologies, particle sizes, and electrical properties of Pd nanocrystals was intensively studied. Transmission electron microscopy measurement demonstrates that the palladium nanoparticles were well dispersed on the surface of MWCNTs with a relatively narrow particle size distribution in the presence of the additives. Cyclic voltammetry and chronoamperometry tests demonstrate that the functional groups of the additives play an important role in electrocatalytic activity and stability for formic acid oxidation, and the influence law of various functional groups on electrocatalytic activity and stability is also investigated in this paper. We hope it can provide certain theoretical guidance meaning and practical reference value in future studies. 相似文献
119.
Ailin Yuan Chunling Zheng Zhengyu Zhang Lu Yang Chao Liu Haibo Wang 《Journal of fluorescence》2014,24(2):557-561
A novel quinazolinone compound containing quinazoline-fused moiety has been synthesized as fluorescence Off-On sensor QQ. The probe exhibited highly selective and sensitive recognition toward trivalent ferric ion (Fe3+) over other metal ions in HEPES buffer solution (10 mM, pH?=?7.0, DMF-H2O, 9:1, v/v). The significant quenching in the fluorescence spectral could be served as a selective fluorescence Off-On sensor. The titration study indicated the formation of 1:1 complex between QQ and Fe3+. 相似文献
120.
Zhengyu Zhou Benni Du Fu Aiping Weichao Zhang 《International journal of quantum chemistry》2003,94(1):44-50
For the reactant ClONO2 the equilibrium geometry and energy have been calculated by using various density functional (DFT) theory methods. The harmonic vibrational frequencies were computed using the B3LYP method for the ground state of the reactant; the results were in good agreement with those of the experiment. It was shown that the DFT methods were superior to other ab initio methods in optimizing geometry and predicting vibrational frequencies. In the process of forming the products from the dissociation reactions of ClONO2, the results indicated it undergoes the TS2, but not the TS1 transition state. According to the relative energies of various species, the potential energy surface reflected intuitively the mechanisms of these dissociation reactions. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 44–50, 2003 相似文献