A DNS assessment of linear relations between filtered reaction rate,flame surface density,and scalar dissipation rate in a weakly turbulent premixed flame

Linear relations between (i) filtered reaction rate and filtered flame surface density (FSD) and (ii) filtered reaction rate and filtered scalar dissipation rate (SDR), which are widely used in Large Eddy Simulation (LES) research into premixed turbulent combustion, are examined by processing DNS data obtained from a statistically 1D planar flame under weakly turbulent conditions that are most favourable for the two approaches (flamelet combustion regime, single-step chemistry, equidiffusive mixture, adiabatic burner, and low Mach number). The analysis well supports the former approach provided that the filtered reaction rate is combined with filtered molecular transport term. In such a case, both the RANS and LES FSD approaches are based on local relations valid within weakly perturbed flamelets. Accordingly, simply recasting RANS expressions to a filtered form works well. On the contrary, while the FSD and SDR approaches appear to be basically similar at first glance, the analysis does not support the latter one, but shows that a ratio of the filtered reaction rate to the filtered SDR is strongly scattered within the studied flame brush, with its conditionally mean value varying significantly with Favre-filtered combustion progress variable. As argued in the paper, these limitations of the LES SDR approach stem from the fact that it is based on a relation valid after integration over weakly perturbed flamelets, but this relation does not hold locally within such flamelets. Consequently, when a sufficiently small filter is applied to instantaneous fields, the filter may contain only a part of the local flamelet, whereas the linear relation holds solely for the entire flamelet and may not hold within the filtered flamelet volume. Thus, the present study implies that straightforwardly recasting well-established RANS equations to a filtered form is a flawed approach if the equations are based on integral features of local burning.     

Sr与CH3I 反应的的准经轨线计算—能量分布和转动取向

首次构造了放热反应Sr+CH3I的LEPS势能面,并进行了准经典轨线计算。重点计算了该反应产物平动能、振动能、转动能分布和转动取向与碰撞能的关系。其他方面如在更广碰撞能范围内的反应截面以及产物振动分布也做了研究,以便与相应的实验结果相比较—反应截面、产物振动分布与实验吻合。计算结果表明,随着碰撞能的增加,产物转动取向逐渐增强;平动能、转动能、振动能均增加,但平动能占总可用资能的比例下降。     

The AME2016 atomic mass evaluation (Ⅱ).Tables,graphs and references

This paper is the second part of the new evaluation of atomic masses,AME2016.Using least-squares adjustments to all evaluated and accepted experimental data,described in Part Ⅰ,we derive tables with numerical values and graphs to replace those given in AME2012.The first table lists the recommended atomic mass values and their uncertainties.It is followed by a table of the influences of data on primary nuclides,a table of various reaction and decay energies,and finally,a series of graphs of separation and decay energies.The last section of this paper lists all references of the input data used in the AME2016 and the NUBASE2016 evaluations(first paper in this issue).     

Self-cleaning of SiO2-TiO2 coating: Effect of sonochemical synthetic parameters on the morphological,mechanical, and photocatalytic properties of the films

Among the different properties of the hydrophobic semiconductor surfaces, self-cleaning promoted by solar illumination is probably one of the most attractive from the technological point of view. The use of sonochemistry for nanomaterials' synthesis has been recently employed for the associated shorter reaction times and efficient route for control over crystal growth and the management of the resulting material's photocatalytic properties. Moreover, the sol–gel method coupled to sonochemistry modifies the chemical environment, with reactive species such as •OH and H₂O₂, which yield a homogeneous synthesis. Therefore, in the following investigation, the sol–gel method was coupled to sonochemistry to synthesize a SiO₂@TiO₂ composite, for which the sonochemical amplitude of irradiation was varied to determine its effect on the morphology and mechanical and self-cleaning properties. SEM and AFM characterized the samples of SiO₂@TiO₂ composite, and while the micrographs indicate that a high ultrasonic energy results in an amorphous SiO₂@TiO₂ composite with a low rugosity, which was affected in the determination of the contact angle on the surface. On the other hand, FTIR analysis suggests a significant change in both SiO₂-SiO and SiO₂-TiO₂ chemical bonds with changes in vibrations and frequency, corroborating an important influence of the sonochemical energy contribution to the hydrolysis process. Raman spectroscopy confirms the presence of an amorphous phase of silicon dioxide; however, the vibrations of TiO₂ were not visible. The evaluation of hydrophobic and self-cleaning properties shows a maximum of ultrasonic energy needed to improve the contact angle and rhodamine B (RhB) removal.     

人为扰动的模型势函数及其动力学特征

目前,结合高精度从头算方法和全维量子动力学计算,对四原子气相反应,理论计算可以获得与实验结果完全一致的结果。一般情况下,一个精确的量子动力学模拟需要一个精确的势能面,但是在实际的计算当中,势能面的拟合误差是不可避免的。在本文中,我们考察了在模型势能面外加各种扰动时的动力学反应行为,在2维的势能面上进行了量子动力学计算。反应速率常数对近反应能垒区域或最小能量反应路径上的干预是较为敏感的,但是在势能面上的其它地方加入的外加干扰对反应速率影响不大。本文给出一个比较重要的和比较简单的结论,在量子动力学模拟中,在精确的势能面上增加相关的扰动,会帮助我们更深入地理解给定类型的反应,对于一个特定体系,其精确势能面上可以作为一个模型体系研究。     

The Ame2020 atomic mass evaluation(II).Tables,graphs and references

This is the second part of the new evaluation of atomic masses,Ame2020.Using least-squares adjustments to all evaluated and accepted experimental data,described in Part I,we derived tables with numerical values and graphs which supersede those given in Ame2016.The first table presents the recommended atomic mass values and their uncertainties.It is followed by a table of the influences of data on primary nuclides,a table of various reaction and decay energies,and finally,a series of graphs of separation and decay energies.The last section of this paper provides all input data references that were used in the Ame2020 and the Nubase2020 evaluations.     

分级构建势能面中低级别势能面精度

通过构建一系列H3体系的UHF(UCCSD(T)、DFT-B3LYP、UMP2)/vtz和UCCSD(T)/avqz级别的势能面,研究了分级构建方案中低级别势能面对最终势能面精度的影响. 基于这些势能面计算得到的H+H₂反应的总反应几率表明,UCCSD(T)/avqz势能面的精度与著名的BKMP2势能面非常接近,得到的势垒略微偏高. 作为对比,尽管低级别理论(UHF、UMP2、DFT-B3LYP)加上vtz基组在复杂体系中得到了广泛地应用,但是它们对这个最简单的反应只能提供一个定性的描述. 另一方面,尽管这些理论不能准确描述这个反应,但是可以应用它们来得到分级构建中的低级别势能面,从而建立精度级别为UCCSD(T)/avqz的势能面,使得所需要的UCCSD(T)/avqz能量的数目大大减少.     

Adsorption and dissociation of ammonia on Au(1 1 1) surface: A density functional theory study

Periodic density functional theory (DFT) calculations using plane waves had been performed to systematically investigate the stable adsorption amine and its dehydrogenated reaction on Au(1 1 1) surface. The equilibrium configuration including on top, bridge, and hollow (fcc and hcp) sites had been determined by relaxation of the system. The adsorption both NH₃ on top site and NH₂ on bridge site is favorable on Au(1 1 1) surface, while the adsorption of NH on hollow (fcc) site is preferred. The adsorbates are adsorbed on the gold surface with the interaction between p orbital of adsorbate and the d orbital of gold atoms. The interaction between adsorbate and gold slab is more evident on the first layer than on any others. Furthermore, the dissociation reaction of NH₃ on clean gold surface, as well as on the pre-covered oxygen atom and pre-covered hydroxyl group surface had been investigated. The results show that the dehydrogenated reaction energy barrier on the pre-covered oxygen gold surface is lower. The adsorbed O can promote the dehydrogenation of amine. Additionally, OH as the product of the NH₃ dissociation reaction participates in continuous dehydrogenation reaction, and the reaction energy barrier is the lowest (22.77 kJ/mol). The results indicated that OH_ads play a key role in the dehydrogenated reaction on Au(1 1 1) surface.     

碳黑颗粒生长模型的初步研究

本文利用反应类(Reaction Class)概念和矩(Moment)方法,研究了层流预混甲烷火焰中碳黑颗粒的成核与长大过程。模型综合考虑了颗粒的成核、颗粒间由于碰撞的聚合、以及气态组分在颗粒表面的生长。通过数值计算预报了碳黑颗粒平均粒径、总表面积、体积分数和数密度,以及萘(A4)和乙炔(C2H2)在颗粒表面的增长速率。     

表面催化反应模型中关联噪声诱导非平衡相变

建立含有关联噪声的双分子-单分子(DM)表面催化反应延迟反馈模型,该模型能同时显示一级和二级非平衡动力学相变,即在一级和二级非平衡动力学相变之间的反应窗口展现.讨论双分子在DM延迟反馈模型中两种吸附机制,即局域和随机吸附模型.研究结果表明:1)外部噪声及两噪声关联性致使反应窗口的宽度收缩;2)内部噪声对非平衡动力学相变行为的影响依赖两噪声关联性,即当两噪声负关联,内部噪声致使反应窗口的宽度变宽;而当两噪声正关联时,内部噪声致使反应窗口的宽度收缩;3)关联噪声致使反应窗口变化对DM模型中一级和二级非平衡动力学相变研究具有重要的科学意义.     

ClONO2异构化反应和分解反应的理论研究

用B3LYP/6 31+G(d)和MP2 (Full) /6 31+G(d)优化ClONO2 及其分解反应和异构化反应的过渡态和产物的分子结构 .在B3LYP/6 31+G(d)水平上计算了相关分子的振动频率 .ClONO2 的几何结构、振动频率和红外强度与实验测量值符合得很好 .找到了未曾报道的立体异构体 .对这一立体异构体进行了高级别理论方法CCSD(T) /6 311G(d)和QCISD(T) /6 311G(d)的几何结构优化和振动频率计算 ,表明它是一个稳定的立体异构体 .在所研究的几种反应中 ,ClONO2 分解为NO2 +ClO是最容易进行的反应 .而ClONO2 异构为立体异构体的反应是最难进行的反应 .其所需克服的过渡态的能垒为 4 81.5 2kJ/mol,而反应吸收能量为 2 99.85kJ/mol.次难进行的是ClONO2 经TS1到反应中间体M1,再经TS12而分解为ClNO +O2 的反应 .这个反应通道所需克服过渡态的能垒为 4 2 1.5 5kJ/mol,反应吸收能量为 15 7.98kJ/mol.从以上分析可知 ,和ClO +NO2 反应生成ClONO2 比较 ,ClONO2 具有较好的稳定性 .     

Electrochemical in situ surface enhanced Raman spectroscopic characterization of a trinuclear ruthenium complex,Ru‐red

To study the fate of a molecular di‐μ‐oxo‐bridged trinuclear ruthenium complex, [(NH₃)₅Ru–O–Ru(NH₃)₄–O–Ru(NH₃)₅]⁶⁺, also known as Ru‐red, during the electro‐driven water oxidation reaction, electrochemical in situ surface enhanced Raman spectroscopy (SERS) investigations have been conducted on an electrochemically roughened gold surface in acidic condition. It was previously described that on a basal plane pyrolitic graphite electrode in 0.1 M H₂SO₄ aqueous solution, Ru‐red undergoes one electron oxidative conversion into a stable higher oxidation state ruthenium complex, Ru‐brown, at <1.0 V (vs normal hydrogen electrode (NHE)), and this leads to water oxidation and dioxygen release, but the fate of Ru‐red during electrochemistry was not studied in much detail. In this investigation, Ru‐red dispersed in acid electrolyte and immobilized on a roughened gold electrode without Ru‐red in solution has been subjected to anodic controlled potential experiments, and in situ SERS was carried out at various potentials in succession. The electrochemical SERS data obtained for Ru‐red are also compared with in situ SERS results of an electrodeposited ruthenium oxide thin film on the Au disk. Our study suggests that on a gold electrode in sulfuric acid solution containing Ru‐red, one electron oxidative conversion of Ru‐red to a higher oxidation state ruthenium compound, Ru‐brown, occurs at ca. 0.74 V (vs NHE), as supported by the electrochemical in situ SERS experiments. Moreover, at higher potentials and on Au disk, the Ru‐red / Ru‐brown are not stable and slowly decompose or electro‐oxidize leading to deactivation of the tri‐ruthenium catalytic system in acidic medium. Copyright © 2013 John Wiley & Sons, Ltd.     

Theoretical Study on Mechanism of Cycloadditional Reaction Between Dichloro-Germylidene and Formaldehyde

用MP2/6-31G^*方法研究了单线态二氯亚甲基锗烯与甲醛环加成反应的反应机理,该反应有两条相互竞争的主反应通道,同时伴随着两中间体(INT3和INT4)副产物的生成. 第一条主反应通道所生成的物种为三员环中间体(INT1)和Ge-O顺位的四员环产物(P1);第二条主反应通道所生成的物种为Ge-O对位的扭曲四员环中间体(INT2)和氯迁移产物(P2);P1和INT2分别与甲醛(R2)的进一步作用而导致了两副产物的生成.     

Theoretical study of the mechanism of cycloaddition reaction between dichloromethylene silylene and formaldehyde

The mechanism of cycloaddition reaction between singlet dichloromethylene silylene and formaldehyde has been investigated using a MP2/6-31G* method, including geometry optimization and vibrational analysis for the stationary points on the potential energy surface. The energies of different conformations are calculated by CCSD(T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the cycloaddition reaction between singlet dichloromethylene silylene and formaldehyde has three competitive dominant reaction channels: (1) the two reactants first form a highly strained three-membered ring intermediate INT1c, which then isomerizes to an active four-membered ring product P1 via a transition state TS1c by ring-increasing reaction; Subsequently, P1 further reacts with formaldehyde to form the more stable silapolycyclic product P2; (2) the two reactants first form a four-membered ring intermediate INT1b by the [2?+?2] cycloaddition reaction, which then isomerizes to the four-membered ring product P3.1 via a transition state TS3.1, resulting from the chlorine transfer reaction; (3) INT1b further reacts with formaldehyde to form a silapolycyclic intermediate INT4, which then isomerizes to a silapolycyclic product P₄ via a transition state TS4.     

基于双核模型的粒子交换势能面与熔合几率的研究(英文)

研究了基于双核模型的粒子交换势能面.原子核的形变效应对于势能面的形状有较大的影响.在反应过程中,作为反应时间函数的动态形变的变化是显著的.通过求解主方程,对一些基于冷熔合机制的反应道的全熔合几率也进行了讨论. The Potential Energy Surface (PES) for particle exchange in Di nuclear system is studied in detail. It is found that the nuclear deformation effect can change the shape of PES significantly. The dynamical deformation as a function of the reaction time in the reaction process is investigated in a simple model and we found that its variation with time is dramatic. The fusion probabilities P-CN of some reaction channels based on the mechanism of cold fusion are also calculated.     

Hamilton–Jacobi equation,reaction action surface and the emergence of the force concept in chemical reaction dynamics

A combination of Hamilton–Jacobi equation and fast marching algorithm can be used to study reaction dynamics by converting the potential energy surface to a reaction action surface. The reaction action surface has been found to be an important tool in theoretical chemistry, allowing us to provide a different force-based perspective of chemical reactions. Several properties such as reaction force, reaction force surface, reaction path force and reaction path force constant have been defined and calculated by using the reaction action surface. This paper investigates these newly defined properties in order to understand the role they play in chemical reaction with reference to a model 4-well potential energy surface.     

Aerosol Catalysis on Nickel Nanoparticles

Nickel nanoparticles produced by spark discharges were used as aerosol catalyst for the formation of methane. The available surface area of the particles was determined using different methods. It was found that the surface area available for nitrogen adsorption and, therefore, for the methanation reaction remained virtually constant during restructuring of the agglomerates while the surface area based on the mobility was significantly reduced. In general, the reaction parameters such as activation energy and reaction rates agree well with the values for single nickel crystals and foils. At temperatures above 350°C the activation energy and the photoelectric activity of the particles decrease indicating the formation of graphite on the particle surface. Also the change of the work function points to the build up of multiple layers of graphite on the particle surface. The surprisingly low temperature for the surface deactivation may indicate an enhanced formation of carbon atoms at the surface.     

Diffusion-influenced reactions

We summarize three of our recent results on diffusion-influenced reactions in solutions. All deal with the concentration dependence of the reaction rate when the reactants must first diffuse together before reaction can occur. When one species (the sink species) is not dilute, the rate cannot be obtained by solution of a pair diffusion equation; the correlations among the sinks for the diffusing species must be accounted for. First, we consider fluorescence quenching when the quenchers are not dilute. For charged quenchers and fluorophores we discuss how the solution dielectric constant and ionic strength can strongly influence the deviations from the linear Stern-Volmer behavior (the dilute sink result) which arise due to the sink correlations. Second, we consider heterogeneous catalysis where a reactive species is adsorbed onto a surface and must surface diffuse to reactive sites (the sinks). We find that surface diffusion can be an important factor contributing to the rate of reaction; especially when surface diffusion is rapid relative to the adsorption/desorption rate. Third, we discuss diffusion influenced reactions with sinks which are long ellipsoids. Dilute long ellipsoids provide a large rate enhancement relative to a spherical sink; we show that this rate enhancement survives when nondilute ellipsoids are considered.     

Impact of surface science on the understanding of kinetics of heterogeneous catalytic reactions

The kinetics of chemical reactions in gas and liquid phases are usually described by employing the conventional mass-action law equations. The laws governing the kinetics of heterogeneous catalytic reactions are as a rule much more complex due to adsorbate–adsorbate lateral interactions, surface heterogeneity, spontaneous and adsorbate-induced changes in a surface, and/or limited mobility of reactants. The importance of these factors was recognized by the heterogeneous catalysis community far before the surface-science era. Only with the development of surface science, however, has it become possible to study in detail the non-ideality of rate processes on solid surfaces. In the present paper, we survey the main conceptual results currently available in this field and illustrate the impact of surface science on its development. Specifically, we outline the approaches used to describe elementary reaction steps and the whole reaction kinetics near and far from equilibrium, including such topics as kinetic phase transitions, pattern formation, kinetic oscillations and chaos, and pressure- and structure-gap problems. All these phenomena and problems are demonstrated to provide promising opportunities for further experimental and theoretical studies.     

Localized surface plasmon resonance scattering imaging and spectroscopy for real-time reaction monitoring

Abstract

In the last decade, plasmonic nanoparticles-based scattering imaging and spectroscopy has introduced the analysis and sensing to the single nanoparticle and molecule level, such as the biomolecules adsorption process and the quantitative detection of small molecules and ions. Recently, this technology has also been focus on the real-time and in-situ reaction monitoring, which is a new emerging branch of the single-nanoparticle imaging, revealing the reaction dynamic information and the related controlling factors. In this mini-review, recent applications of plasmon resonance scattering imaging and spectroscopy in the real-time reaction monitoring in the past 5?years are highlighted and discussed.