电极距离对4,4’-联苯二硫酚分子器件非弹性电子隧穿谱的影响

基于杂化密度泛函理论和格林函数方法, 计算了4,4’-联苯二硫酚分子器件的非弹性电子隧穿谱, 并研究了电极距离对该非弹性电子隧穿谱的影响. 计算结果表明, 非弹性电子隧穿谱随电极距离的改变呈明显不同的特征, 从而表明了分子的非弹性电子隧穿谱技术能够灵敏地反映出分子器件的微观结构. 研究结果显示, 垂直于电极表面的振动模式对非弹性电子隧穿谱具有较大的贡献.     

二茂铁自组装分子结中电荷隧穿与跳跃传输的机理研究

采用硫醇自组装单层膜结合悬浮纳米线技术制备了分子结器件, 对比研究了非电活性的1-十一烷基硫醇(C11)和电活性的二茂铁己硫醇(FHT)分子结的电荷传输特性. 结合两种传输机理, 提出一种新的模型拟合了分子结的电流-电压特性, 发现了氧化还原活性中心二茂铁(Ferrocene, Fc)可以使电荷传输机理由隧穿变成隧穿与跳跃共存. 结合变温实验验证了这一机理, 并对这种混合机理出现的原因进行了分析.     

水在金属表面解离吸附的全维量子动力学

正分子在金属表面解离吸附的动力学研究在多相催化等工业过程中占有重要的地位。在过去的20多年里,科学家们为发展可靠的理论来精确描述分子在固体表面的解离吸附动力学付出了巨大的努力1-6。由于反应中可能存在的量子效应,如量子隧穿、零点能、反应共振等,量子动力学研究是最为可靠的。但是由于高维量子动力学研究的困难,以往精确的量子动力学理论只局限于研究双原子分子在固体表面解离吸附这类包含六个     

双笼氟化富勒烯分子C_(20)F_(18)(CO)_2C_(20)F_(18)电子输运性能的第一性原理研究

以双笼氟化富勒烯C_(20)F_(18)(CO)_2C_(20)F_(18)为中心分子,与Ag(100)纳米线电极连接构筑分子电子器件,通过第一性原理和非平衡格林函数相结合的方法,对器件的电子输运特性进行了研究.结果显示,在外加偏压的作用下,中心分子的前线轨道逐渐定域在分子的左侧,电子透射通道被阻塞,所对应的共振隧穿峰被压制,器件的电流-电压特性曲线在0.3~0.8V区间内表现出明显的负微分电阻(NDR)现象.     

分子印迹表面等离子共振传感器在食品安全检测中的最新研究进展

分子印迹聚合物具有空间结构选择性高、稳定性好和制备过程简单等特点,结合表面等离子共振传感器,可用于分子间相互作用和结合特性的研究。随着石墨烯、量子点等纳米材料的出现和广泛应用,基于分子印迹技术的表面等离子共振传感器的灵敏度获得了改善,促进了该技术在食品安全检测领域的快速发展。该文基于分子印迹技术简要介绍了表面等离子共振传感器芯片的制备技术、分析体系及其优点,重点分析了国内外将分子印迹-表面等离子共振传感器用于食品安全检测的最新研究成果,阐释了分子印迹-表面等离子共振技术的优势,并展望了该技术在食品安全分析领域的发展趋势。     

低聚对亚苯基亚乙烯基分子导线电子传输机理研究

合成了12个OPV分子导线(分成乙酰巯基与氨基端基两个系列),采用导电原子力显微镜和扫描隧道显微镜-裂分结的方法对该类分子导线的电学性能进行了表征.通过分析单分子电阻与分子长度、温度以及电场的依赖关系,发现OPV分子导线的电子传输机理在临界长度为2.0 nm处发生了由隧穿传导向跳跃传导的转变.通过对比分子末端分别为巯基和氨基的单分子电导值,考察了不同的连接基团对OPV分子导线电子传输性能的影响,发现末端基团只影响分子的接触电阻,但不改变分子导线本身的电子传输机理.利用密度泛函理论和非平衡格林函数方法对OPV分子导线的电学特性进行了理论研究,结果表明分子的前线轨道能级与金电极的相对位置决定了OPV分子导线的电子传输机理.     

有机分子笼的合成及应用

近年来,作为一类具有永久空腔结构的三维有机分子,有机分子笼引起了科研工作者的广泛关注,在超分子化学中（主要是主客体相互作用）扮演着重要角色。早期研究中通常采用不可逆法制备有机分子笼,往往存在反应步骤多、分离提纯复杂、合成难度大等问题。为了有效解决上述问题,研究人员将动态共价化学引入到有机分子笼的合成中,从而简单、高效地制备出一系列不同的有机分子笼。关于有机分子笼的应用研究也在不断拓展中。研究发现,有机分子笼不仅在分子识别、分子反应器等方面存在广阔的应用前景,而且其可以通过自组装形成多孔材料,在气体吸附、分离等领域展现了巨大的应用潜能。本文中,我们综述了有机分子笼在合成方法（主要基于动态共价化学反应）及应用研究方面的最新进展。     

偶氮苯自组装单分子膜中长程电子转移机理

利用自组装技术在金电极表面构造了具有不同前端健长度偶氮苯功能化的单分子膜体系：Au／S（CH2）nNHCO-N＝N-OCH2CH3（n＝2，3，4，6）．研究结果表明，仍氮苯到金电极的表现电子转移速率随它们之间的距离长度的增加而呈指数性的下降趋势．基于Marcus电子隧穿理论，得到了此自组装膜体系的长程电子隧穿系数ρ＝（1．35±0．2）／CH2在和可逆电活性分子自组装膜体系及理论计算相比较的基础上，从偶氮苯分子自组装膜结构与电子转移过程的关系角度对这一结果进行了分析和说明．     

不同亲水性探针分子在金电极上硫醇自组装跨膜动力学研究

采用扫描电化学显微镜测定了不同亲水性氧化还原电对在硫醇修饰的金电极表面上的异相电子转移速率常数. 分别选择铁氰化钾[K3Fe(CN)6]和N,N,N',N'-四甲基-1,4苯二胺(TMPD)作为氧化还原探针,根据得到的反馈曲线拟合出异相电子转移速率常数. 比较这些速率常数可以看出, 修饰层对疏水性的TMPD分子显示出更好的穿透性. 通过一个简单的模型可以解释TMPD的穿透过程, 在TMPD电子隧穿的前后存在着单层膜和水溶液间的快速平衡, 而隧穿作为决速步骤, 其表观速率常数也比K3Fe(CN)6的大. 通过计算得到TMPD的隧穿因子β为1.2/CH2.     

有机分子与聚电解质静电吸附成膜特性研究

选取多种有机分子及聚电解质，采用静电吸附自组装法制备了聚电解质，聚电解质、聚电解质，有机分子、有机分子，有机分子的复合薄膜，讨论了这些体系的静电吸附成膜特性及其成膜机理．     

On-line monitoring of the residence time distribution along a kneading block of a twin-screw extruder

An on-line Residence Time Distribution (RTD) measuring set-up that enables the characterisation of twin screw extruders at short axial increments is presented. It uses the light emission of a fluorescent tracer (perylene) to generate concentration versus time curves, which are then used to determine the usual RTD parameters, delay time, mean residence time and variance. The system is initially mounted on a rectangular die coupled to a single screw extruder, on-line and off-line measurements being directly contrasted. Then, the optical probe is positioned at several points along the axis of a modular co-rotating twin screw extruder, on-line and off-line data being again compared. Having gained confidence in the measuring technique, an experimental unit utilizing a transparent barrel is used to characterize the evolution of RTD along a kneading block of a twin screw extruder.     

Residence time distribution from a continuous Couette flow device

This paper describes an experimental study of residence time distribution (RTD) by pulse response analysis in a continuous Couette flow device with rotating inner cylinder and stationary outer cylinder. The experiments were performed under conditions of (a) negligible and (b) significant influence of molecular diffusion and (c) Taylor vortex flow. Diethylene glycol and water were used as the test fluids with congo red dye and potassium permanganate solution as tracers respectively. A unique RTD described by an analytical expression was observed for experiments with low axial Reynolds number under the condition of negligible influence of molecular diffusion. For most experiments performed under conditions of significant influence of molecular diffusion and Taylor vortex flow regime over the ranges 0 < Ta < 118 and 0.4 < Re < 5.5, the RTD can be described by a dispersion model. The system behaves as a near-plug flow vessel at Ta ≈ 60. The critical Taylor number for this geometry as defined by the minimum dispersion number for a given flowrate is slightly higher than that without axial flow.     

Spectrum analysis of radiotracer residence time distribution for industrial and environmental applications

Radiotracer signal analysis and recognition still represents challenges in industrial and environmental applications specially in residence time distribution (RTD) measurement. This paper presents a development for the RTD signal recognition method that is based on power density spectrum (PDS). In this development, the features are extracted from the signals and/or from their higher-orders statistics (HOS) (Bispectrum and Trispectrum) instead of PDS. The HOS are estimated using direct, indirect and parametric estimations. The recognition results are analyzed and compared for different HOS estimation in order to select the best HOS estimation method for the purpose of RTD signal recognition. The artificial neural networks are used for training and testing of the proposed method. The proposed method is tested using RTD signals obtained from the measurements carried out using radiotracer technique. The simulation results show that the parametric estimation of the Trispectrum gives the higher recognition rate and is the most reliable for the RTD signal recognition.     

Problems of residence time distribution analysis with applications of radiotracers

The applications of radiotracers for determination of impulse response as Residence Time Distribution (RTD) as well as technical conditions for realization of experiment in industry create special requests for data processing. The table of required corrections and methods for RTD analysis with the basic information is presented. The methods for the raise background subtraction, correction for variable flow and new algorithms for RTD analysis from response to arbitrary input function and from the response distorted by the recirculation flow in so called black or gray box system are presented.     

Residence time distribution study for the catalytic packing MULTIPAK®

Residence time distribution (RTD) experiments were carried out using the catalytic packing MULTIPAK® in a 250 mm inner diameter column. The axial dispersion coefficients and dynamic liquid hold-up were derived from the RTD curves. Both hold-up and axial Péclet number were correlated in terms of gas and liquid Reynolds numbers. Free-draining experiments were performed to determine the dynamic and static liquid hold-ups. The measured axial dispersion coefficients were higher than those presented in other studies. The dynamic hold-up derived from RTD agreed with total hold-up from free-draining experiments. The static hold-up was found very high, even higher than the dynamic one, due to the liquid accumulated inside the catalyst bed. Possibly, the liquid considered “static” from the viewpoint of the free-draining experiments becomes “dynamic” during the normal column operation.     

Residence time distribution study in a pilot-scale gas–solid fluidized bed reactor using radiotracer technique

This paper describes a radiotracer study carried out to measure residence time distribution (RTD) of coal particles in a pilot-scale gas–solid fluidized bed reactor (FBR). Gold-198 labelled on coal particles was used as radiotracer. RTD measurements were conducted for selected operating conditions and mean residence times (MRTs) of the coal particles were determined. Gamma function model was used to simulate the measured RTD data and mixing of coal particles in the reactor was investigated. Based on the results, the performance of the air distributor used in the reactor was evaluated.     

Determination of residence time distribution in polymer processing apparatus using tracer techniques

Tracer techniques, based on neutron activation analysis and ashing procedures, are discussed with reference to measurement of material residence time distribution (RTD) through polymer processing apparatus. Particular emphasis is given to details of experimental techniques employed, their reproducibility, and ultimately to their application for characterisation of polymer RTD in twin-screw extrusion and injection moulding machinery.     

Radiotracer investigation of phosphoric acid and phosphatic fertilizers production process

In the phosphoric acid production process, the time a particle spends inside the chemical reactor (residence time) is of paramount importance to process engineers. Residence time distribution (RTD) gives information on the efficiency of the chemical reactor, on the efficiency of the process, and also the availabilities of the reactive volume for the reaction (active volume vs. dead volume). Traditionally, chemical engineers used chemical tracer to determine the RTD. However, first disadvantage is that the chemical tracer could not allow an online diagnosis: the samples containing chemical tracer have to go to a lab for analysis, second disadvantage is that the chemical tracer is less sensitive than radioactive ones because of its adsorption onto strata or its retention in rocks. Consequently, chemical tracer results are not always precise and cannot convincingly explain the multiple flow-path model. Radioactive tracers are the only tracers capable of measuring the active RTD with high degree of precision and give information on the internal recirculation rate. In this work, we will describe the application of radiotracer method for RTD measurement in the phosphoric acid production process and give results and discussion of each case encountered.     

Identification of Non-Volatile Compounds Generated during Storage That Impact Flavor Stability of Ready-to-Drink Coffee

Coffee brew flavor is known to degrade during storage. Untargeted and targeted LC/MS flavoromics analysis was applied to identify chemical compounds generated during storage that impacted the flavor stability of ready-to-drink (RTD) coffee. MS chemical profiles for sixteen RTD coffee samples stored for 0, 1, 2, and 4 months at 30 °C were modeled against the sensory degree of difference (DOD) scores by orthogonal partial least squares (OPLS) with good fit and predictive ability. Five highly predictive untargeted chemical features positively correlated to DOD were subsequently identified as 3-caffeoylquinic acid, 4-caffeoylquinic acid, 5-caffeoylquinic acid, 3-O-feruloylquinic acid, and 5-O-feruloylquinic acid. The increase in the six acidic compounds during storage was confirmed by sensory recombination tests to significantly impact the flavor stability of RTD coffee during storage. A decrease in pH, rather than an increase in total acidity, was supported to impact the coffee flavor profile.