关键词： Fe-Ti alloys   Mechanical Alloying   Heat treatment   Amorphization   Crystallization kinetics  

摘要： The crystallization behaviors of mechanically alloyed amorphous Fe-Ti alloys were studied. The a-Fe phase formed during annealing as a result of the devitrification of the amorphous phase. According to the Kissinger plot, the crystallization activation energy (E) was obtained as 171 kJ/mol, which is close to the activation energy for the diffusion of Fe in a-Ti. According to the non-isothermal Johnson-Meh l-Avrami (JMA) analysis and obtaining the volume fraction of the crystalline phase from the differential scanning calorimetry (DSC) plots, the average Avrami exponent (n) was determined as 1.61 and 5.67 for low and high heating rates, respectively. Moreover, a method for obtaining the value of E based on the non-isothermal JMA analysis was proposed. The value of E was determined as similar to 185 and 191 kJ/mol respectively for low and high heating rates, which are consistent with the value determined from the Kissinger plot for all heating rates. (c) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

摘要： In a recent paper [J. Mater. Sci. Mater. Electron. 30(6), 15116-15129 (2019)] Akilan et al. have studied the physical properties of the thiosemicarbazide cadmium chloride monohydrate (TSCCCM) single crystals. The approach that has been used to study the optical properties of the specimens is likely to have errors. Consequently, the reported values of the reflectance, refractive index, as well as real and imaginary parts of the third-order susceptibility are most likely to be incorrect.

关键词： Hydrogel   Molecular dynamics   Xyloglucan   Self-assembly   Nanodroplets  

摘要： Indigenous polymers have functional implications in biomedicine due to the presence of an inherent favorable structural architecture that supports hydrogel formation. In this study, we present the molecular level characterization of xyloglucan hydrogels using experimental and molecular simulation methods. We studied supramolecular self-assembly of tamarind seed-derived xyloglucan induced by low molecular weight gelators to form dense networks and rationalized its capabilities as a multifunctional and multiresponsive matrix for holding hydrophobic nanometric oleic acid globules intact for extended periods, preventing coalescence triggered instability using computational methods and imaging. Computational studies using molecular dynamics simulations provided mechanistic evidences of molecular associations supported by strong hydrogen bonding interactions responsible for fundamental gel network formation. Real-time imaging studies revealed that the gel matrix immobilizes intact oleic acid globules within its framework preventing coalescence. Molecular dynamics studies further showed key interactions of xyloglucan with the surfactant polysorbate 60 involved in sustaining oleic acid globules within the gel matrix, which corroborate with FE-SEM results. This study is an interesting approach to understand how molecular level associations in xyloglucan-based hydrogels can control and preserve nanosized hydrophobic oils imparting tenability and long-term droplet stability. The study also brings new insights into the conformational flexibility of xyloglucan around molecules with favorable and unfavorable interactive chemistries. Graphical abstract .

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