Environmental Control of Triplet Emission in Donor–Bridge–Acceptor Organometallics

Carbene‐metal‐amides (CMAs) are a promising family of donor–bridge–acceptor molecular charge‐transfer (CT) emitters for organic light‐emitting diodes. A universal approach is demonstrated to tune the energy of their CT emission. A blueshift of up to 210 meV is achievable in solid state via dilution in a polar host matrix. The origin of this shift has two components: constraint of thermally‐activated triplet diffusion, and electrostatic interactions between guest and polar host. This allows the emission of mid‐green CMA archetypes to be tuned to sky blue without chemical modifications. Monte‐Carlo simulations based on a Marcus‐type transfer integral successfully reproduce the concentration‐ and temperature‐dependent triplet diffusion process, revealing a substantial shift in the ensemble density of states in polar hosts. In gold‐bridged CMAs, this shift does not lead to a significant change in luminescence lifetime, thermal activation energy, reorganization energy, or intersystem crossing rate. These discoveries offer new insight into coupling between the singlet and triplet manifolds in CMA materials, revealing a dominant interaction between states of CT character. The same approach is employed using materials which have been chemically modified to alter the energy of their CT state directly, shifting the emission of sky‐blue chromophores into the practical blue range.     

一种压电半导体纳米线的热电耦合性能研究

采用有限元分析方法,研究了一种n型压电半导体纳米线(氧化锌)的电热耦合性能,分析了外部温度对氧化锌纳米线内部机械场、电场及电流场分布的影响,并讨论了本构方程线性化对电学参数的影响。研究结果表明,温度对氧化锌纳米线的电场、载流子浓度和电流密度影响很大,采用线性本构和非线性本构求得的电场、电子浓度和电流密度最大相差分别为24%,32%和68%,基于非线性本构分析压电半导体的电学性能会引起很大误差。该研究结果可为压电半导体器件利用温度调控电场、电流提供理论依据。     

煤炭地下气化过程中温度场及其传热特征研究进展

煤炭地下气化(UCG)技术作为一种环境友好的采煤方法,可被用来开发深部煤层与矿井遗留的煤炭资源。当地下气化时,随着气化时间的推移,煤炭在煤层内部"燃烧"逐渐形成气化炉,炉内温度最高可达1 200℃。从UCG过程中的放热反应出发,综述了热量来源、温度场的变化及其传热特征等,总结了研究温度场的重要手段。分析认为,UCG是一个复杂的温热动态变化过程,在此过程中氧化还原反应、吸热和放热的可逆反应同时进行,导致了气化炉的温度场及其传热机制的复杂性。研究气化过程传热机制的方法主要有物理模拟、试验监测、理论计算和数值模拟4种,各自具有不同的适应性。其中,物理模拟的可操控性强,但是难以解决地层接触关系导致的接触热阻误差;试验监测能真实反映温度场等的变化情况,但是实际操作的经济性差;理论计算通过对气化过程的拆分,从理论角度定性定量了UCG的温度场特征,但理论计算难以考虑到温度渗流等对温度的影响;数值模拟借助计算机进行温度场的多场耦合,综合考虑了渗流、变形、温度等对传热的影响,但多场的物理耦合计算难度较大,且煤层及岩石的热物理性质随温度变化会产生较大的差异,导致数值建模的计算难度增加,制约了数值模拟方法的...     

A review of methods,applications and limitations for incorporating fluid flow in the discrete element method

The past decade has witnessed the substantial growth in research interests and progress on the subject of coupled hydro-mechanical processes in rocks and soils, driven mainly by the surge of research in unconventional hydrocarbon reservoirs and associated hazards. Many coupling techniques have been developed to include the effects of fluid flow in the discrete element method (DEM), and the techniques have been applied to a variety of geomechanical problems. Although these coupling methods have been successfully applied in various engineering fields, no single fluid/DEM coupling method is universal due to the complexity of engineering problems and the limitations of the numerical methods. For researchers and engineers, the key to solve a specific problem is to select the most appropriate fluid/DEM coupling method among these modeling technologies. The purpose of this paper is to give a comprehensive review of fluid flow/DEM coupling methods and relevant research. Given their importance, the availability or unavailability of best practice guidelines is outlined. The theoretical background and current status of DEM are introduced first, and the principles, applications, and advantages and disadvantages of different fluid flow/DEM coupling methods are discussed. Finally, a summary with speculation on future development trends is given.     

高职模具类人才培养新模式的研究与实践

为了解决传统教学无法全面培养人才的问题,采用"课程融合+时空耦合+过程结合"的方式开展人才培养研究。以注射模设计与制造生产过程为导向,构建大项目牵引下的跨越课程、跨越学期的课程融合新模式,利用信息通信技术及互联网平台,将互联网与传统教学进行深度融合,创造新的教学生态,构建多元多维互动的时空耦合教学新关系,以全方位评价为引导,构建课程多元多维的评价新机制。以3个班级为对象开展不同模式下的教学,对试验班级成绩进行分析,研究结果表明:课程融合+时空耦合+过程结合新模式培养的学生更好地完成了综合项目,获得了较好的教学效果。     

Thermal-fluid and electromagnetic coupling analysis and test of a traction motor for electric vehicles

This paper proposes a multi-phasic coupling analysis and test of a 50 kW traction motor for electric vehicles. The temperature-dependent properties of the electrical and magnetic materials of the interior permanent magnet traction motor are not negligible over a wide operation range of the vehicle. The heat produced by the electromagnetic power loss changes the motor’s properties, and in turn the motor performance changes to produce a different power loss. This two-way coupled electromagnetic and thermal-fluid analysis of the torque and speed curve and the transient thermal response at a rated operation point are simulated and compared with the traditional one-way coupling analysis. The simulation results are also compared with and proved by experiments on a prototype motor. The experimental results show that it is critical and necessary to predict the motor performance by means of the proposed two-way coupling analysis that provides more accurate information than the traditional one-way coupling analysis.     

Influence of hydrogen on electrochemical behavior of Ni-based superalloy 718

Numerous studies have shown that Ni-based superalloy 718 may be sensitive to hydrogen embrittlement and have highlighted the dominant roles played by the hydrogen solubility and the hydrogen trapping. Samples were hydrogenated by cathodic polarization in molten salts under different conditions to vary the diffusible hydrogen content and to saturate the different hydrogen traps present in the microstructure strengthened by precipitation. Open circuit potential and galvanic coupling measurements were conducted in order to characterize the effect of diffusible and trapped hydrogen on electrochemical behavior and to discuss the possibility of galvanic coupling between zones with different hydrogen contents.     

Control Model for Large‐Sized Gantry Type Linear Motor Slider

At present, many industrial carrier devices utilize linear motor sliders. However, a heavier load requires a linear motor (which is an example of a direct drive device) to get higher power, compared with a rotary motor with a ball screw slider (which is an example of an indirect drive device). In order to obtain higher power at a lower cost, a linear slider with multiple motors can be utilized, for example, a gantry type linear motor slider. Moving the gantry type slider requires two linear motors that are set up in parallel to enable synchronization control. Some conventional synchronization control methods have been proposed for the parallel twin linear slider; however, a large‐scaled gantry type linear motor slider has two unique problems: mechanical distortion caused by the limitations of installation environment and coupling caused by joints with low stiffness. This paper proposes a control model to solve these problems, and an identification method of each parameter. Furthermore, the effectiveness of the control model is verified by comparison with simulation results and experimental results.     

Preparation and properties of fluorinated silicon two‐component polyurethane hydrophobic coatings

A polyurethane (PU) hydrophobic coating was prepared by the two‐component method, polycarbonate diol and isophorone diisocyanate becoming a two‐phase composition. The PU films with hydrophobic surface were prepared by establishing a rough structure on the surface of silica (SiO₂) modified with silane coupling agents (γ‐(2,3‐epoxypropoxy)propytrimethoxysilane (KH560) and (heptadecafluoro‐1,1,2,2‐tetradecyl)trimethoxysilane (FAS)). First, the surface of SiO₂ was covered by a layer of hydrophobic methyl and fluorocarbon (C–F) groups. Then, the SiO₂ and modified SiO₂ were obtained by the introduction of KH560 and FAS with the silanol reaction by ultrasonic stirring. The effect of SiO₂ and modified SiO₂ on the structure and hydrophobic properties of PU was investigated by a series of test instruments. The results showed that the introduction of SiO₂ and modified SiO₂ was beneficial for increasing the roughness of the PU coating surface; the roughness of FAS/SiO₂‐PU could reach up to 14.790 nm, four times better than pure PU. A hydrophobic modified PU coating with water contact angle 123° was fabricated by using the hydrophobic C–F group FAS as a low surface energy material and establishing a micro rough structure on the surface of PU. Moreover, PU modified with KH560 and FAS can reduce the glass transition temperature (T_g) of soft segments, resulting in improvement of micro‐phase separation. © 2020 Society of Chemical Industry     

超精密气体静压系统节流器法向随机微振动研究

以无气腔平面节流器为研究对象,对节流器流固耦合法向随机微振动进行了理论仿真和实验研究。受限于节流器厚度与气膜厚度尺寸的差异和输入初始边界条件,建立了节流器的COMSOL仿真简化模型,对节流器-气膜微流场进行双向流固耦合数值模拟。仿真结果表明,节流器的法向随机微振动幅值关于节流器中心对称,且由中心向边缘逐渐增大;微振动幅值随气体入口流速的增大而增大。实验采用纳米级激光测振仪,依次测量供气压力为0.1,0.2,…,0.5 MPa时尺寸为75 mm×50 mm×14 mm的HEXAGON双环联结型节流器多个不同位置的法向振动,实验结果表明,法向随机微振动幅值分布特性与仿真结果一致,关于节流器中心对称,且由中心向边缘逐渐增大,验证了节流器法向微振动的"跷跷板"振动形式;在0.5 MPa供气压力下,边缘振动幅值超过1 nm。对实验数据进行功率谱密度分析,结果表明不同供气压力下法向随机微振动均在9.4 kHz和10.6 kHz处产生较大功率,可认为与节流器-气膜流固耦合系统的固有频率有关。研究结果有效地揭示了节流器法向随机微振动的特性,为气体静压系统避开随机共振区、优化气体静压系统的设计提供了理论指导。