关键词： Iron   Allenes   Catalysts   Nuclear magnetic resonance spectroscopy   Catalysis  

摘要： The iron-catalyzed hydroarylation of allenes was accomplished by weak phenone assistance. The C-H activation proceeded with excellent efficacy and high ortho-regioselectivity in proximity to the weakly coordinating carbonyl group for a range of substituted phenones and allenes. Detailed mechanistic studies, including the isolation of key intermediates, the structural characterization of an iron-metallacycle, and kinetic analysis, allowed the sound elucidation of a plausible catalytic working mode. This mechanistic rationale is supported by detailed computational density functional theory studies, which fully address multi-spin-state reactivity. Furthermore, in operando nuclear magnetic resonance monitoring of the catalytic reaction provided detailed insights into the mode of action of the iron-catalyzed C-H alkylation with allenes.

关键词： Molecular dynamics  

摘要： The formation of the Cu-Pt nanocontacts has been investigated by means of classical molecular dynamics simulations. The simulations of the mechanically controlled break junction experiment have been performed in wide ranges of temperatures (0-300 K) and at relative Pt concentrations (0-20%). The structure of the breaking area has been studied 2 ns before the final breaking of the nanocontacts. The length of the breaking area increases with the increase of the temperature and decreases with the increase of the relative Pt concentration. The structure of the breaking area has been investigated by means of the radial distribution function method. The breaking area usually has one of the following structures: (i) a bulk-like structure, (ii) a structure consisting of centered icosahedrons rotated 90 degrees, or (iii) an icosahedral structure composed of pentagonal rings. The structure of the breaking area is almost independent of the temperature and the stretching direction due to the strong Cu-Pt interaction.

关键词： T-cells  

摘要： In this period of intense interest in human immunity, we attempt here to quantify the immune response against pathogen invasion through T-cell population dynamics. Borrowing concepts from equilibrium statistical mechanics, we introduce a new description of the immune response function (IMRF) in terms of fluctuations in the population number of relevant biological cells (effector and regulatory T-cells). We use a coarse-grained chemical reaction network model (CG-CRNM) to calculate the number fluctuations and show that the response function derived as such can, indeed, capture the crossover observed in a T-cell driven immune response. We employ the network model to learn the effect of vitamin-D as an immunomodulator. We solve our CG-CRNM using a stochastic Gillespie algorithm. Depending on the effector T-cell concentration, we can classify immune regulation regimes into three categories: weak, strong, and moderate. The IMRF is found to behave differently in these three regimes. A damped cross-regulatory behavior found in the dynamics of effector and regulatory T-cell concentration in the diseased states correlates well with the same found in a cohort of patients with specific malignancies and autoimmune diseases. Importantly, the crossover from the weakly regulated steady state to the other (the strongly regulated) is accompanied by a divergence-like growth in the fluctuation of both the effector and the regulatory T-cell concentration, characteristic of a dynamic phase transition. We believe such steady-state IMRF analyses could help not only to phase-separate different immune stages but also aid in the valuable connection between autoimmunity, optimal vitamin-D, and consequences of immunosuppressive stress and malignancy.

关键词： Hydrocarbons   Thiols   Monomers   Polymerization   Ethers  

摘要： The effect of thiol substitution in radical thiol-ene reactions has been studied by using model, monofunctional thiols as well as multifunctional thiol monomers along with the assessment of their subsequent polymerization reactions and polymer mechanical behavior. FT-IR was used to monitor the polymerization rate and quantify the overall conversion. While the total conversion was observed to range from 70% to 100%, the polymerization rate was found to decrease by as much as 10-fold as the thiol substitution was changed from primary to tertiary. Analogous multi-thiol monomers of similar structure but varying substitution were synthesized to observe the effect of substitution type on polymerization kinetics and polymer behavior. Methylation at the alpha-carbon was varied from primary to tertiary to observe these differences. Mechanical properties were assessed by using dynamic mechanical analysis and water sorption experiments, where the glass transition temperatures were found to be within 1-2 degrees C as thiol substitution varied. Furthermore, primary thiol films absorbed 1 3% more water than secondary thiol films. Resin shelf stability experiments were performed by using rheometry to measure storage time-dependent viscosity changes, and it was found that secondary thiol films remained relatively stable for up to 100 times longer than their primary counterparts. It was concluded that while there are differences under relatively slow initiation conditions, at typical initiation rates all three thiol substitutions may be made to react at similar rates for both monofunctional and polymeric systems.

关键词： 电厂   设备检修   措施  

摘要： 随着国家经济实力的发展与社会的进步,对于电力的需求日益增长。电力作为当今世界上最为重要的能源之一,已经是人类离不开的东西。火力发电设备的优质性能不但能为广大群众提供良好的保证,对推进电力运营企业的发展也有着重要作用。目前我国仍旧是以火力发电厂为核心的电能供给方式,火电厂的效率直接关系到产能。火力发电作为重要的电力来源,在我国现阶段技术趋于成熟,但应用于其中的机械动力设备经常会发生故障,做好火力发电设备的维修工作,是我们现在首要考虑的问题。本文就现阶段电厂关于机械动力设备检修和管理力方面做了简单的讨论。

标准号: GB/T 38943.2-2020

摘要： GB/T 38943的本部分规定了使用外部动力的电力驱动土方机械(EMM)电气系统及其部件的特定安全要求。本部分适用于车载电压在50 V～36 kV范围内任何频率的交流电和75 V～36 kV范围内的直流电，包括任何重复率脉动直流电的户外使用的机器。设备内部的电压不是车载电压，因此不在本部分范围内。

关键词： Copolymerization   Styrenes   Monomers   Copolymers   Reactivity  

摘要： The statistical anionic copolymerization of isoprene (I) and styrene (S) is commonly used to synthesize tapered block copolymers, enabling control of the phase behavior by adjusting the order-disorder transition temperature, T-ODT. Alkyllithium initiation in hydrocarbons is known to afford tapered block copolymers of I and S in one step. The effect of tetrahydrofuran (THF) on the copolymerization kinetics and the resulting copolymers was systematically investigated by increasing the [THF]/[Li] ratio from 0 to 2500 (0 to 29%(vol) THF). For this purpose, in situ near-infrared (NIR) spectroscopy was employed as a versatile and fast method to track the highly accelerated consumption of the individual monomers. Changes in the I/S comonomer sequence and in the polyisoprene (PI) regioisomers, caused by variation of the THF concentration, were independently determined via NMR and in situ NIR spectroscopy. Reactivity ratios were determined as a function of the [THF]/[Li] ratio. They revealed a gradual reversal from r(I) >> r(S) over r(I) approximate to r(S) to r(I) << r(S). Corresponding changes in the copolymer composition profile up to a complete inversion are evident in thermal properties and morphologies. Although all copolymers possess the same comonomer composition (50%(mol) = 57%(vol) polystyrene (PS) units), small-angle X-ray scattering and transmission electron microscopy give evidence of a wide variation in bulk morphologies depending on the gradient profile. Overall, the phase diagram is symmetric, and the succession of phases bears certain similarities to the PI-b-PS case. This is discussed in terms of the increasing incompatibility of PS with 3,4-PI and the more symmetric polymer conformational parameter. The degree of segregation, as well as the nanodomain structure, was found to control the mechanical properties, showing a remarkably different viscoelastic response leading to either hard/brittle or ductile/soft materials. The accessibility of tailored gradient

关键词： crosslinking   degradation   grafting   kinetics   mechanical properties  

摘要： Rubber blends are widely used for combining the advantages of each rubber component. However, to date, how to determine and distinguish the vulcanization kinetics for each single rubber phase in rubber blends during the co-vulcanization process is still a challenge. Herein, high-resolution pyrolysis gas chromatography-mass spectrometry (HR PyGC-MS) was employed for the first time to investigate the vulcanization kinetics of natural rubber (NR) and styrene-butadiene rubber (SBR) in NR/SBR blends filled with modified silica (SiO2). The reaction rates of crosslinking of each rubber phase in NR/SBR were calculated, which showed that the crosslinking rates of NR were much lower than those of SBR phase in the unfilled blends and blends filled with unmodified and silane modified silica. Interestingly, the vulcanization rates of NR and SBR phase were approximately same in the vulcanization accelerator modified silica filled blends, showing better co-vulcanization. In addition, the vulcanization accelerator modified silica was uniformly dispersed and endowed rubber blends with higher mechanical strength compared to the untreated silica. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48838.

关键词： 动力机械及工程   人工智能   交叉融合   教学  

摘要： 该文探讨了在动力机械及工程传统专业中引入新兴人工智能学科知识及方法的教学思考,综述了国内外人工智能学科的蓬勃发展现状,提出了把传统专业与新兴人工智能专业相结合的“动力机械及工程+人工智能”专业教学的必要性、可行性及具体实施方法。在教学内容、教学方式上培养学生扎实的专业素养,与时俱进地掌握人工智能相关知识和方法,进行专业素养的拓展与延伸,以在社会就业、科研研究、工程管理等方面永葆生机与活力,真正落地化、专业化投身建设社会主义现代化强国的潮流。学生学会获取国内外的“动力机械及工程+人工智能”专业知识的方法及途径,汲取新的学科知识,这对拓宽动力机械及工程专业学生的学术眼界、培养适应国际化潮流的新型复合型人才具有重要作用。

关键词： 机械臂   并联机构   动力学建模   Lagrange方程  

摘要： 提出一种双闭环5-DOF机械臂,该机械臂在((2-UPS)+U)PU构型的基础上增加闭环结构,得到新的拓扑构型2-UPS+((2-UPS)+U)PU,闭环结构的引入使得机构获得更高的承载能力且为拓扑新的构型提供了新思路。应用矢量链法,建立了机构的位置模型;推导了支链驱动速度、支链摆动角速度与运动平台广义速度Vo的映射,建立了机构的独立变量q与运动平台广义速度Vo之间的解耦矩阵;建立了机构支链中的摆动杆、伸缩杆质心速度与运动平台广义速度Vo之间映射,并基于虚功原理建立了机构的动力学模型,将推导的动力学模型变换成具有Lagrange动力学形式的动力学模型;在Adams仿真软件中建立该机构的虚拟样机模型,通过仿真验证了推导的动力学模型的正确性。