关键词： Density functional theory   Homogeneous catalysis   Ionic liquids   Esterification mechanism   Reaction kinetics  

摘要： The thermodynamic and kinetic aspects of the mechanism of butyl acetate synthesis catalyzed by the diprotic ionic liquid pyridinium hydrogen sulfate ([H-Pyr](+)[HSO4](-)) were investigated using density functional theory (DFT) at B3LYP/6-311 + G(d,p) level of calculation. Electronic structure and geometry for individual molecules (substrate, catalyst) were clarified using molecular electrostatic potential surface, natural bond orbital analysis and atoms in molecules theory. The DFT results elucidated the catalytic cycle, which involved the formation of a transition state via substrate-BAIL interaction. Hydrogen bond interactions were found to exist throughout the process of the catalytic cycle, which are of special importance for stabilizing the transition state. Thus, a mechanism involving cooperative hydrogen bonding for BAIL catalyzed butyl acetate synthesis was established. Based on the above mechanism, the calculated thermodynamic parameters were validated by the subsequent kinetic study. Such results may provide fundamental insights into the design of ionic liquid-based homogeneous catalysts for esters production. (C) 2019 Elsevier B.V. All rights reserved.

关键词： Chromatography   Deformation   Phase transitions   Order   Polymers  

摘要： Cross-linked liquid crystalline polymers (CLCPs) incorporated with photochromic azobenzene moieties can exhibit large and reversible deformations under the exposure of actinic lights. To practically utilize CLCPs in applications such as flexible photoresponsive actuators and soft robots, the user-defined diverse deformation modes have been demonstrated by controlling the liquid crystalline phases and polymer architectures. However, conventional all-atom molecular dynamics (AA MD) simulation is unsuitable for modeling complicated phases and conducting a parametric study of the photomechanical effect in terms of the polymer morphology due to its excessive computational cost. Therefore, a multiscale analysis framework based on coarse-grained molecular dynamics (CG MD) simulations is developed in this study. The mesoscale CLCP network model is constructed to satisfy the structural and thermodynamic properties of the full-atomistic reference. Also, the photoisomerization process is operated by integrating multiscale phenomena as follows. The AA MD reference describes the quantum events by implementing reactive rotational potential for trans-to-cis conversion, and corresponding CG potential sets are derived based on the associated structural changes. Because the mesoscale photoswitching potential is transferable to a wide range of cis-concentrations, the light-induced sequential-smectic-nematic-isotropic phase transition is realized. The results show that corruptions of the smectic layer and nematic orientational order reversely influence the overall shape of the network, which causes different photodeformation modes under each transition. Furthermore, the light-induced disordering behaviors are combined with the mechanical deformations of the polymer according to various light and temperature conditions. We expect the presented work contributes to the precise prediction and design of the optomechanical behaviors of photoresponsive devices.

关键词： PATIENT-ventilator dyssynchrony   CARDIAC pacing  

关键词： Polymer gels   Ionic liquids   Network formation  

摘要： We report an ion gel with ultralow polymer content based on two key materials: 1 wt% tetra-arm poly(ethylene glycol) (TetraPEG) and 99 wt% ionic liquid (herein, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide, [C(2)mIm] [FSA]). We performed kinetics analysis on the TetraPEG network formation in [C(2)mIm] [FSA], i.e., AB-type cross-end coupling reaction of two different TetraPEGs with thiol (SH) and maleimide (MA) terminals (TetraPEG-SH and TetraPEG-MA). In neat [C(2)mIm] [FSA], no gelation occurred at room temperature, whereas the reaction successfully proceeded when 1-ethylimidazole (C(2)Im) was added in this reaction as a catalyst. The apparent reaction rate constant (k(gel)') was determined by varying C(2)Im concentration, and the network connectivity (p) was estimated to be p similar to 98% toward the end of the reaction. The results indicated that the TetraPEG prepolymers could be successfully gelled in [C(2)mIm] [FSA] despite extremely low polymer content (1 wt%), which allows us to prepare an ideally homogeneous polymer network gel with a large amount of ionic liquid. The ionic conductivity measurements demonstrated that the 1 wt% TetraPEG ion gel showed ideal liquid-like ion-conducing properties that were comparable to those of neat ionic liquid.

关键词： snake   locomotion   neuromechanics   biomechanics   collisions  

摘要： Limbless animals like snakes inhabit most terrestrial environments, generating thrust to overcome drag on the elongate body via contacts with heterogeneities. The complex body postures of some snakes and the unknown physics of most terrestrial materials frustrates understanding of strategies for effective locomotion. As a result, little is known about how limbless animals contend with unplanned obstacle contacts. We studied a desert snake, Chionactis occipitalis, which uses a stereotyped head-to-tail traveling wave to move quickly on homogeneous sand. In laboratory experiments, we challenged snakes to move across a uniform substrate and through a regular array of force-sensitive posts. The snakes were reoriented by the array in a manner reminiscent of the matter-wave diffraction of subatomic particles. Force patterns indicated the animals did not change their self-deformation pattern to avoid or grab the posts. A model using open-loop control incorporating previously described snake muscle activation patterns and body-buckling dynamics reproduced the observed patterns, suggesting a similar control strategy may be used by the animals. Our results reveal how passive dynamics can benefit limbless locomotors by allowing robust transit in heterogeneous environments with minimal sensing.

关键词： Kinetic parameters   Oxidation   Vinyl   Cations   Extrusion  

摘要： This work presents ferrate(VI) ((FeO42-)-O-VI, Fe-VI) oxidation of a wide range of sulfonamide antibiotics (SAs) containing five- and six-membered heterocyclic moieties (R) in their molecular structures. Kinetics measurements of the reactions between Fe-VI and SAs at different pH (6.5-10.0) give species specific second-order rate constants, k(5) and k(6) of the reactions of protonated Fe-VI (HFeO4-) and unprotonated Fe-VI ((FeO42-)-O-VI) with protonated SAs (FIX), respectively. The values of k5 varied from (1.2 +/- 0.1) x 10(3) to (2.2 +/- 0.2) x 10(4) M-1 s(-1) while the range of k(6) was from (1.1 +/- 0.1) x 10(2) to (1.0 +/- 0.1) x 10(3) M-1 s(-1) for different SAs. The transformation products of reaction between Fe-VI and sulfadiazine (SDZ, contains a six-membered R) include SO2 extrusion oxidized products (OPs) and aniline hydroxylated products. Comparatively, oxidation of sulfisoxazole (SIZ, a five-membered R) by Fe-VI has OPs that have no SO2 extrusion in their structures. Density functional theory calculations are performed to demonstrate SO2 extrusion in oxidation of SDZ by Fe-VI. The detailed mechanisms of oxidation are proposed to describe the differences in the oxidation of six- and five-membered heterocyclic moieties (R) containing SAs (i.e., SDZ versus SIZ) by Fe-VI.

关键词： Inverse problem   Force reconstruction   Augmented Kalman Filter   Structural dynamics  

摘要： Kalman-type filtering tends to become one of the favorite approaches for solving joint input-state estimation problems in the structural dynamics community. This article focuses on the applicability of the Augmented Kalman Filter (AKF) for reconstructing mechanical sources, addressing a set of practical issues that are frequently encountered in the engineering practice. In particular, this paper aims to help the reader to better apprehend some of the advantages and limitations of the application of the AKF in the context of purely input estimation problems. The present paper is not a simple collection of test cases, since it introduces a novel state-space representation of dynamical systems, based on the generalized-a method, as well as further insights in the tuning of Kalman filters from the Bayesian perspective. In this work, the various practical situations considered lead us to recommend to employ collocated acceleration measurements, when reconstructing excitation sources from the AKF. It is also demonstrated that the violation of some of the feasibility conditions proposed in the literature doesn't necessarily imply the failure of the estimation process. (C) 2018 Elsevier Ltd. All rights reserved.

关键词： 机械工程   多提系统动力学   参数分析  

摘要： 机械工程由于通常具有多个自由度以及各类活动构架,所以对其的受力分析难度较高,当前已经开发出了多体系统的动力学分析理念,通过对相关思想的使用,提高受力分析工作的效率。基于对多体系统动力学相关思想和应用流程的研究,本文提出了在具体的机械工程中,这一力学分支的应用方法,让其能够在机械工程领域中更好地发挥其应有作用。

关键词： 计量   气动肌肉   动力学建模   膝关节   四连杆   力矩控制  

摘要： 目的:为实现气动肌肉机械腿关节角度跟踪,设计两自由度气动肌肉机械腿。方法:对拮抗气动肌肉到关节传动问题,建立关节驱动机构模型;主要分析四连杆膝关节力矩静态特性,设计膝关节力矩到气动肌肉拉力的映射关系。机械腿摆动采用双闭环控制策略,外环为位置PD控制,在控制输出中加上机械腿动力学计算力矩项;内环为气动肌肉拉力控制,设计拉力前馈控制器和误差补偿控制器。结果:进行机械腿摆动控制仿真和实验,关节角度跟踪误差在±3°以内。结论:结果表明关节建模有效,动力学控制可实现机械腿关节角度跟踪。

关键词： Polymer-matrix composites (PMCs)   Wear   Mechanical properties   Interface/interphase  

摘要： This paper reviews the application of molecular dynamics simulations on mechanical and tribological properties of polymer composites reinforced by carbon nanotubes and graphene sheet as reinforcements. A variety of simulation studies on modelling, calculation and analysis on enhanced elastic, tensile, fracture properties of carbon nanotubes and graphene sheet/polymer composites are introduced and reviewed. The capabilities of molecular dynamics simulations on exploring inherent mechanisms on improved tribological properties of carbon nanotubes and graphene sheet/polymer composites from atomic views are particularly discussed. Different methods of surface modifications of the two nano reinforcements on further enhancing the strength of polymer composites are summarized. Summary and recommendations for potential researches are also provided. This review is intended to provide a state-of-the-art and better understanding on applications of carbon nano tubes and graphene sheet for enhancing mechanical and tribological properties of polymer composites by molecular dynamics simulations, and inspire future efforts in this area.