微流控芯片液滴生成与检测技术研究进展

微流控芯片液滴技术是一种操控微小体积液体的新技术,既可实现高通量微观样本的生成及控制,也可进行独立液滴的操作。分散的微液滴单元可作为理想的微反应器,在生物医药中的药物筛选、材料筛选和高附加值微颗粒材料合成领域展现出巨大的应用潜力。液滴微流控芯片是利用流体剪切力的改变,使互不相溶的两相流体在其界面处生成稳定、有序的液滴,目前微液滴的生成方法主要有水动力法、气动法、光控法和电动法等。基于液滴的微流控系统越来越多地被应用于执行复杂的多重反应、测量和分析,可以进行超小体积和超高吞吐量的化学和生物实验。对液滴微流控系统而言,液滴的速度、大小和内容物含量会影响最终的检验结果,因此对液滴形成速率和液滴的内容物含量的实时检测至关重要,目前最常用的液滴检测方法有光学检测技术与电学传感检测技术。对两相流液滴生成机理以及现有液滴生成技术开展了讨论分析,同时对液滴检测技术进行了评述。     

{111}晶面暴露对介孔金红石TiO2单晶光催化产氢的促进作用

光催化反应发生在半导体材料的表面,材料表面的原子/电子结构直接影响光催化剂的活性或选择性。因此,发展具有特定晶面的半导体光催化剂受到各国学者的普遍关注,被认为是调控光催化材料性能的有效途径之一。自2008年yang等首次合成高表面能{001}晶面占优的锐钛矿TiO2单晶以来,控制合成暴露不同晶面TiO2晶体的研究得到了迅猛的发展,已发展了多种方法合成了具有不同晶面的TiO2晶体。研究表明,选择性地暴露特定的活性晶面能够显著地提高光催化剂的活性或者改变光催化反应的选择性。但是,含有完整晶面构型的TiO2单晶样品的颗粒尺寸一般都较大,通常为几微米,因而显著增加了光生载流子传输与分离的难度,并且导致材料较小的比表面积,限制了对光催化活性的进一步提高。能否在合成含特定晶面单晶的同时增加多孔结构成为有效解决这一问题的关键。最近, Crossland等采用晶种模板法成功合成了介孔的锐钛矿TiO2单晶,并且通过光电器件研究证实了采用该思路可进一步提高材料的光电性能。金红石TiO2在光催化全分解水方面具有独特的优势,然而关于多孔单晶金红石TiO2的研究相对较少,尤其是合成热力学不稳定的高表面能{111}晶面完全暴露的多孔金红石单晶面临较大的技术挑战因而一直未见文献报道。本文利用晶种模板法,以TiCl4溶液为含Ti前驱体、NaF为形貌控制剂、采用水热处理制备出不同比例{111}晶面的介孔金红石单晶。我们前期工作表明, NaF可作为形貌控制剂合成低表面能{110)晶面占优的介孔金红石单晶。本文发现,通过改变NaF的添加量,可有效调变{111}/{110}晶面比例,最终合成完全暴露{111}高表面能的介孔金红石TiO2单晶。扫描电镜结果显示,当添加20 mg NaF时,合成{110}占优的具有高长径比的介孔晶体;当NaF用量增加到40 mg时{110}晶面进一步缩短;至80 mg时则制备出{111})高能面完全暴露的金红石TiO2晶体。值得注意的是,对比研究表明,不采用模板合成了与多孔晶体完全相对应的不同{111}/(110}晶面比例的实心金红石晶体。透射电镜及选区电子衍射以及结合X射线衍射进一步证实,多孔的金红石TiO2晶体与实心金红石单晶均都为单晶结构,孔结构贯穿于样品内部且具有较高的晶面结晶性。氮气吸附实验发现,虽然三个不同晶面比例介孔金红石单晶样品间的形貌具有显著的差异,但比表面积非常相近(分别为24,25,28 m2/g),孔径也都为50 nm左右,该值与所用SiO2模板球的直径以及TEM观察结果相一致。光催化产氢性能结果表明,选择性的暴露活性晶面显著提高了光催化活性,仅含高能面{111}的介孔金红石单晶样品具有最高的产氢速率(约800μmol h–1 g–1),比常规{110}晶面占优的介孔单晶样品速率提高了约一倍。尤其比实心单晶样品的产氢速率提高了至少一个数量级,这应归结于介孔结构特性所导致的表面反应活性位增加、电子传输距离缩短以及光吸收增强协同作用的结果。     

Modulating ion current rectification generating high energy output in a single glass conical nanopore channel by concentration gradient

Inspired by biological systems that have the inherent skill to generate considerable bioelectricity from the salt content in fluids with highly selective ion channels and pumps on cell membranes,herein,a fully abiotic,single glass conical nanopores energy-harvesting is demonstrated.Ion current rectification(ICR)in negatively charged glass conical nanopores is shown to be controlled by the electrolyte concentration gradient depending on the direction of ion diffusion.The degree of ICR is enhanced with the increasing forward concentration difference.An unusual rectification inversion is observed when the concentration gradient is reversely applied.The maximum power output with the individual nanopore approaches10~4pW.This facile and cost-efficient energy-harvesting system has the potential to power tiny biomedical devices or construct future clean-energy recovery plants.     

Role of refractive index in sum frequency generation intensity of salt solution interfaces

Sum frequency generation spectroscopy (SFG) has been widely used to study the interfacial chemistry of aqueous salt solutions of biological or environmental importance. Most of the SFG data analysis used the same bulk refractive index for different salt concentrations despite of the variations of the refractive indices. Here we systematically investigate the influence of the refractive index on the SFG intensities at various experimental conditions. It is discovered that the SFG intensities are the most sensitive to the refractive index at solid/liquid interfaces nearby the total internal reflection geometries. At air/liquid interfaces, the effect of the refractive indices is also nonegligible. Consequently some important SFG results, such as the response of water structures to the ionic strength at the SiO₂/aqueous interfaces, are necessary to be reevaluated. These conclusions on the effect of the small variations of the refractive index are generally useful for the common practice of SFG data analysis.     

氢化物发生–原子吸收光谱法测定铅粉中痕量砷、锑

建立氢化物发生–原子吸收光谱法联用测定铅粉中痕量砷、锑的方法。试样用稀硝酸溶解,用5%抗坏血酸溶液作为砷(Ⅴ)、锑(Ⅴ)的预还原剂,5%的硫脲溶液作为其它元素的掩蔽剂,选用1%硼氢化钠溶液作为还原剂,氢化物反应在10%盐酸介质中进行。在优化的试验条件下,砷、锑的质量浓度在0~20 ng/m L范围内与吸光度线性相关,相关系数r2分别为砷0.999 6,锑0.993 8,方法的检出限分别为砷0.40 ng/m L,锑0.75 ng/m L。砷、锑测定结果的相对标准偏差分别为4.96%,6.27%(n=6),铅粉样品加标回收率分别为砷87.6%,锑79.3%。该方法准确可靠,可用于测定铅粉中痕量砷、锑。     

Symbolic generation of large multibody system dynamic equations using a new semi-explicit Newton/Euler recursive scheme

Summary The aim of this paper is to show that multibody systems with a large number of degrees of freedom can be efficiently modelled, taking conjointly advantage of a recursive formulation of the equations of motion and of the symbolic generation capabilities.Recursive schemes are widely used in the field of multibody dynamics since they avoid the explosion of the number of arithmetical operations in case of large multibody models. Within the context of our field of applications (railway dynamics simulation), explicit integration schemes are still prefered and thus oblige us to compute the generalized accelerations at each time step. To achieve this, we propose a new formulation of the well-known Newton/Euler recursive method, whose efficiency will be compared with a so-called O(N) formulation.A regards the symbolic generation, often decried due to the size of the equations in case of large systems, we have recently implemented recursive multibody formalisms in the symbolic programme ROBOTRAN [1]. As we shall explain, the recursive nature of these formalisms is particularly well-suited to symbolic manipulation.All these developments have been successfully applied in the field of railway dynamics, and in particular allowed us to analyse the dynamic behaviour of several railway vehicles. Some typical results related to a completely non-conventional bogie will be presented before concluding.     

电动力学中衰减机械系统的非线性振荡方法

衰减机械系统的非线性振荡可用来研究长约瑟夫逊结的电动力学方程式，而这方程式等同于弱衰减机械系统的非线性振荡。本文应用的方法是将控制方程线性化及结合谐波平衡法（线性谐波平衡法）而产生色散关系，再把平均法应用在弱非线性的耗散系统中得到非常准确的瞬变反应。在此提出的方法不仅考虑能量耗散，而且利用简单的线性代数等式关系来代替冗长及复杂的分析近似解。     

Accurate Higher-Order Analytical Approximate Solutions to Large-Amplitude Oscillating Systems with a General Non-Rational Restoring Force

A new approximate analytical approach for accurate higher-order nonlinear solutions of oscillations with large amplitude is presented in this paper. The oscillatory system is subjected to a non-rational restoring force. This approach is built upon linearization of the governing dynamic equation associated with the method of harmonic balance. Unlike the classical harmonic balance method, simple linear algebraic equations instead of nonlinear algebraic equations are obtained upon linearization prior to harmonic balancing. This approach also explores large parameter regions beyond the classical perturbation methods which in principle are confined to problems with small parameters. It has significant contribution as there exist many nonlinear problems without small parameters. Through some examples in this paper, we establish the general approximate analytical formulas for the exact period and periodic solution which are valid for small as well as large amplitudes of oscillation.     

有界噪声激励下单摆-谐振子系统的混沌运动

研究了具有同宿轨道和周期轨道的可积单摆-谐振子系统在弱Hamilton摄动(即弱耦合摄动)和弱非Hamilton摄动(即阻尼和有界噪声微扰)下的混沌运动．用Melnikov方程预测Hamilton系统中可能存在混沌运动的参数域，并用Poincare截面验证解析结果．用数值方法计算了有阻尼与有界噪声激励下系统的最大Lyapun0V指数和Poincare截面，结果表明有界噪声在频率上的扩散减小了引发系统产生混沌运动的效应。     

First-Passage Time of Duffing Oscillator under Combined Harmonic and White-Noise Excitations

The first-passage time of Duffing oscillator under combined harmonic andwhite-noise excitations is studied. The equation of motion of the system is firstreduced to a set of averaged Itô stochastic differential equations by using thestochastic averaging method. Then, a backward Kolmogorov equation governing theconditional reliability function and a set of generalized Pontryagin equationsgoverning the conditional moments of first-passage time are established. Finally, theconditional reliability function, and the conditional probability density and momentsof first-passage time are obtained by solving the backward Kolmogorov equation andgeneralized Pontryagin equations with suitable initial and boundary conditions.Numerical results for two resonant cases with several sets of parameter values areobtained and the analytical results are verified by using those from digital simulation.