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排序方式: 共有236条查询结果,搜索用时 46 毫秒
101.
102.
将偏最小二乘法用于可见分光光度分析,建立一种同时测定阳离子黄X–8GL、阳离子红X–FG、阳离子艳蓝RL三组分混合染料含量的新方法。在380~780 nm范围内,将测定的26组混合溶液的吸光度值作为校正集,另8组混合溶液的吸光度值作为预测集,结合二阶差分法确定最佳主成分数。测得三组分混合体系中校正集的相关系数分别为0.9988,0.9994,0.9964;交互验证均方根误差(RMSECV)分别为0.0754,0.1852,0.2168;预测集的相关系数分别为0.9984,0.9996,0.9981;预测均方根误差(RMSEP)分别为0.1086,0.1877,0.2515。该方法无需样品分离,可为染色过程中多组分染料浓度的在线监测提供技术支撑。 相似文献
103.
Hongyun Wang 《Applied Mathematics Letters》2009,22(1):79-83
A molecular motor utilizes chemical free energy to generate a unidirectional motion in a viscous media. The stochastic motion of a motor is governed by a Langevin equation coupled to the chemical occupancy state. The change of chemical occupancy state is governed by a discrete Markov process. The Stokes efficiency was introduced to measure how “efficiently” the motor uses chemical free energy to drive through the surrounding fluid. For the overdamping case where the effect of inertia is ignored, it was proved that the Stokes efficiency is bounded by 100% [H. Wang, G. Oster, The Stokes efficiency for molecular motors and its applications, Europhysics Letters 57 (2002) 134–140]. Here we present a proof for the general case. 相似文献
104.
Hong Zhou Wei Kang Arthur Krener Hongyun Wang 《ournal of non Newtonian Fluid Mechanics》2010,165(7-8):425-434
We apply the observability rank condition to study the observability of various viscoelastic fluids under imposed shear or extensional flows. In this paper the observability means the ability of determining the viscoelastic stress from the time history of the observations of the first normal stress difference. We consider four viscoelastic models: the upper convected Maxwell (UCM) model, the Phan–Thien–Tanner (PTT) model, the Johnson–Segalman (JS) model and the Giesekus model. Our study reveals that all of the four models have observability for all stress components almost everywhere under shear flow whereas under extensional flow most of the models have no observability for the shear stress component. More specifically, for UCM and JS models under imposed shear flow, the observations of the first normal stress difference allow the reconstruction of all components of viscoelastic stress. For UCM and JS models under extensional flow, the two normal stress components can be determined from the measurements of the first normal stress difference; the shear stress component does not affect the evolution of the normal stress components and consequently it cannot be extracted from the observations. Under shear flow, the PTT and Giesekus models have observability almost everywhere. That is, all components of the viscoelastic stress can be determined from the observations when the vector formed by the components of viscoelastic stress does not lie on a certain surface. Under extensional flow, the PTT model has observability almost everywhere for normal stress components whereas the Giesekus model has observability almost everywhere for all stress components. We also run simulations using the unscented Kalman filter (UKF) to reconstruct the viscoelastic stress from observations without and with noises. The UKF yields accurate and robust estimates for the viscoelastic stress both in the absence and in the presence of observation noises. 相似文献
105.
考察了各种不同介质中,芳醛、丙二腈和苯硫酚为原料的一锅反应,发现在离子液体1-正丁基-3-甲基咪唑四氟硼酸盐([bmim]BF4)介质中,反应能够在较短时间内高产率地生成2-氨基-4-苯基-6-(苯基硫基)-3,5-二氰基吡啶衍生物,且没有1,4-二氢吡啶副产物的生成.该方法具有反应条件温和、产率高、选择性好和环境友好等优点,且离子液体容易回收,可循环使用. 相似文献
106.
107.
Flavonoids belong to a class of plant secondary metabolites that have a polyphenol structure. Flavonoids show extensive biological activity, such as antioxidative, anti-inflammatory, anti-mutagenic, anti-cancer, and antibacterial properties, so they are widely used in the food, pharmaceutical, and nutraceutical industries. However, traditional sources of flavonoids are no longer sufficient to meet current demands. In recent years, with the clarification of the biosynthetic pathway of flavonoids and the development of synthetic biology, it has become possible to use synthetic metabolic engineering methods with microorganisms as hosts to produce flavonoids. This article mainly reviews the biosynthetic pathways of flavonoids and the development of microbial expression systems for the production of flavonoids in order to provide a useful reference for further research on synthetic metabolic engineering of flavonoids. Meanwhile, the application of co-culture systems in the biosynthesis of flavonoids is emphasized in this review. 相似文献
108.
双杂原子 Fe-V-β 沸石的合成、表征及催化性能 总被引:2,自引:0,他引:2
采用水热合成法在 SiO2-Fe2O3-V2O5-(TEA)2O-H2O-NH4F 体系中合成了 Fe-V-β 沸石, 并用 X 射线衍射、红外光谱、固体漫反射光谱、热重-差热分析、扫描电镜-能量色散谱仪和等离子体发射光谱等技术对沸石样品进行了表征, 探讨了影响 Fe-V-β 沸石合成的因素. 结果表明, 按摩尔比组成SiO2:Fe2O3:V2O5:(TEA)2O:H2O:NH4F = 60:(0.1~0.75):(0.1~0.75):(17~18):(550~ 650):(30~50) 配制初始反应混合物, 可以制备出结晶良好的 Fe-V-β 沸石, 且 Fe 和 V 原子进入到沸石骨架. 所得 Fe-V-β (Si/(Fe+V) = 30) 沸石在 H2O2 氧化苯乙烯反应中表现出最高的催化活性, 苯乙烯转化率为 25.4%, 苯甲醛、苯乙醛和苯乙酮的选择性分别为 69.1%, 22.5% 和 4.1%. 相似文献
109.
Zheng Y Newland B Tai H Pandit A Wang W 《Chemical communications (Cambridge, England)》2012,48(25):3085-3087
We explore a kinetically controlled strategy to suppress the gelation in the homopolymerization of multi-vinyl monomers (MVMs) via RAFT polymerization. We report the generation of 3D single cyclized polymer structures from the RAFT process, which significantly contradicts the classic F-S theory. This approach enables synthesis of a new generation of nanosize macromolecular architectures. 相似文献
110.