Determination of triazine herbicides in juice samples by microwave‐assisted ionic liquid/ionic liquid dispersive liquid–liquid microextraction coupled with high‐performance liquid chromatography

A novel microextraction method, termed microwave‐assisted ionic liquid/ionic liquid dispersive liquid–liquid microextraction, has been developed for the rapid enrichment and analysis of triazine herbicides in fruit juice samples by high‐performance liquid chromatography. Instead of using hazardous organic solvents, two kinds of ionic liquids, a hydrophobic ionic liquid (1‐hexyl‐3‐methylimidazolium hexafluorophosphate) and a hydrophilic ionic liquid (1‐butyl‐3‐methylimidazolium tetrafluoroborate), were used as the extraction solvent and dispersion agent, respectively, in this method. The extraction procedure was induced by the formation of cloudy solution, which was composed of fine drops of 1‐hexyl‐3‐methylimidazolium hexafluorophosphate dispersed entirely into sample solution with the help of 1‐butyl‐3‐methylimidazolium tetrafluoroborate. In addition, an ion‐pairing agent (NH₄PF₆) was introduced to improve recoveries of the ionic liquid phase. Several experimental parameters that might affect the extraction efficiency were investigated. Under the optimum experimental conditions, the linearity for determining the analytes was in the range of 5.00–250.00 μg/L, with the correlation coefficients of 0.9982–0.9997. The practical application of this effective and green method is demonstrated by the successful analysis of triazine herbicides in four juice samples, with satisfactory recoveries (76.7–105.7%) and relative standard deviations (lower than 6.6%). In general, this method is fast, effective, and robust to determine triazine herbicides in juice samples.     

Effects of Shape of Crowders on Dynamics of a Polymer Chain Closure

Using 3D Langevin dynamics simulations,we investigate the effects of the shape of crowders on the dynamics of a polymer chain closure.The chain closure in spherical crowders is dominated by the increased medium viscosity so that it gets slower with the increasing volume fraction of crowders.By contrast,the dynamics of chain closure becomes very complicated with increasing volume fraction of crowders in spherocylindrical crowders.Notably,the mean closure time is found to have a dramatic decrease at a range of volume fraction of crowders 0.36-0.44.We then elucidate that an isotropic to nematic transition of spherocylindrical crowders at this range of volume fraction of crowders is responsible for the unexpected dramatic decrease in the mean closure time.     

8×4×2~n设计纯净两因子交互作用成分最大数的界

混水平部分因析设计在各类试验中有广泛应用.纯净效应准则是用于选取最优部分因析设计的重要准则之一.本文考虑含有一个八水平因子、一个四水平因子和若干二水平因子的8×4×2~n混水平设计,给出了分辨度为Ⅲ和Ⅳ的该类混水平设计包含纯净两因子交互作用成分最大数的上界和下界.下界通过构造特定设计而得到.     

Global well‐posedness of the 2D Euler‐Boussinesq system with stratification effects

This paper is concerned with the Cauchy problem of the two‐dimensional Euler–Boussinesq system with stratification effects. We obtain the global existence of a unique solution to this system without assumptions of small initial data in Sobolev spaces. Copyright © 2017 John Wiley & Sons, Ltd.     

二元翼型风洞的侧壁干扰与抽气研究

在二元翼型风洞实验段中的侧壁边界层将引起模型展向流动的不均匀性，使预想的二元流动受到三元扭曲，引起实验数据的误差，目前消除或减少侧壁干扰的有效方法之一是采用侧壁抽吸技术。本文就抽吸的有效性，抽吸区域和阻尼材料等问题进行了讨论和分析，并对抽吸技术中的问题提出了一些看法。     

Nonlinear Dynamics of Two-Degrees-of-Freedom Fluid Conveying Elasto-Visco-Plastic Model System

The local and global nonlinear dynamics of a two-degrees-of-freedom model system conveying fluid is studied. The undeflected model consistsof an inverted T formed by three rigid rods, with the tips of the twohorizontal rods resting on the viscous foundation. The foundationexhibits a visco-elasto-plastic response, including the Bauschingereffect. The vertical rigid rod of an annular cross-section is subjectedto a conservative (dead) force. Also, it conveys fluid having bothstatic and pulsation components. First, the method of multiple scales isused for the analysis of the local dynamics of the system withvisco-elastic response. Attention is focused on modal interactionphenomena in weak excitation at primary resonance and on hardsub-harmonic excitation. Two different asymptotic expansions areutilised to get a structural response for typical ranges of excitationparameters. Numerical integration of the governing equations is thenperformed to validate the results of asymptotic analysis in each case. Afull global nonlinear dynamics analysis of the visco-elasto-plasticsystem is performed. The role of plastic deformations in thedestabilisation of the system is discussed. Large-amplitude nonlinearoscillations of the visco-elasto-plastic system are studied, includingthe influence of material hardening and of static and periodiccomponents of pulsating fluid. Chaotic regimes of motion with andwithout plastic effects are considered. The results of the analysis maybe used in devices composed of a rather short tube connected to a notcompletely fixed foundation resting on the soil exhibitingelasto-plastic behaviour.     

End Effects for Anti-Plane Shear Deformations of Periodically Laminated STrips with Imperfect Bonding

The axial decay of Saint-Venant end effects is investigated for anti-plane shear deformations of semi-infinite generally laminated anisotropic strips. Imperfect bonding conditions are imposed at the interfaces. The analytical approach, using a displacement field which decays exponentially in the axial direction, gives rise to a transcendental equation for the real eigenvalues. The decay rate for the stresses is given in terms of the smallest positive eigenvalue. Laminated strips with periodic layout are then considered. In the presence of imperfect bonding, the effective shear elastic moduli, computed through a homogenization method, depend on the total number of slipping interfaces in the laminate. Numerical examples confirm that the decay lengths computed with effective shear moduli represent the asymptotic values (for an increasing number of layers) for those of periodically laminated strips. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the transient non-Fickian dispersion theory

The Fickian dispersion equation is the basic relationship used to describe the nonconvective mass flux of a solute in a porous medium. This equation prescribes a linear relationship between the dispersive mass flux and the concentration gradient. An important characteristic of the Fickian relationship is that it is independent of the history of dispersion (e.g. the time rate of change of the dispersion flux). Also, the dispersivities are supposed to be medium constants and invariant with temporal and spatial scales of observation. It is believed that in general these restrictions do not hold. A number of authors have proposed various alternative relationships. For example, differential equations have been employed that prescribe a relationship between the dispersion flux and its time and space derivatives. Also, stochastic theories result in integro-differential equations in which dispersion tensor grow asymptotically with time or distance. In this work, three different approaches, which lead to three different non-Fickian equations with a transient character, are discussed and their primary features and differences are highlighted. It is shown that an effective dispersion tensor defined in the framework of the transient non-Fickian theory, grows asymptotically with time and distance; a result which also follows from stochastic theories. Next, principles of continuum mechanics are employed to provide a solid theoretical basis for the non-Fickian transient dispersion theory. The equation of motion of a solute in a porous medium is used to provide a rigorous derivation of various dispersion relationships valid under different conditions. Under various simplifying assumptions, the generalized theory is found to agree with the conventional Fickian theory as well as several other non-Fickian relationships found in the literature. Moreover, it is shown that for nonconservative solutes, the traditional dispersion tensor is affected by the rate of mass exchange of the solute.Also with National Institute of Public Health and Environmental Protection (RIVM), PO Box 1; 3720BA Bilthoven, The Netherlands     

不同体型建筑物尾流作用下的高层建筑的风荷载特性

采用高频底座力天平方法,研究了不同断面形状的施扰建筑对一典型断面受扰建筑的静力和动力干扰影响,分析了正方形断面施扰建筑和非正方形断面施扰建筑的干扰效应的差异和产生差异的干扰机理。结果表明:施扰建筑断面形状的改变对静力干扰的影响不显著,但对于动力响应方面则有非常明显的影响。由于位于上游的切角断面施扰建筑脱落的在其尾流中的漩涡频率要明显大于正方形断面施扰建筑的涡脱频率,使得其产生的最大包络动力干扰因子值(EIF)要显著高于断面为正方形施扰建筑的EIF值,最大可达4.41(顺风向)和3.69(横风向),相比断面为正方形的高出142%和82.7%。     

A non-linear model for the dynamics of open cross-section thin-walled beams—Part I: formulation

A non-linear one-dimensional model of inextensional, shear undeformable, thin-walled beam with an open cross-section is developed. Non-linear in-plane and out-of-plane warping and torsional elongation effects are included in the model. By using the Vlasov kinematical hypotheses, together with the assumption that the cross-section is undeformable in its own plane, the non-linear warping is described in terms of the flexural and torsional curvatures. Due to the internal constraints, the displacement field depends on three components only, two transversal translations of the shear center and the torsional rotation. Three non-linear differential equations of motion up to the third order are derived using the Hamilton principle. Taking into account the order of magnitude of the various terms, the equations are simplified and the importance of each contribution is discussed. The effect of symmetry properties is also outlined. Finally, a discrete form of the equations is given, which is used in Part II to study dynamic coupling phenomena in conditions of internal resonance.