Selective adsorption behaviors of guest molecules COR in the hexamer host networks at liquid/solid interface

Here,the selective adsorption behaviors of guest molecule COR in two hexamer host grids were investigated by means of scanning tunnelling microscope(STM).The assembled structures of small functional organic molecules TTBTA and TATBA were thermodynamically stable.Interestingly,the introduction of the guest molecule COR destroyed the original hexamer structure of TTBTA and combined with it to form a new triangular host-guest system.Different from TTBTA,the introduction of the guest molecule COR did not affect the six-membered ring structure of TATBA.Furthermore,the co-assembly structure of TTBTA/TATBA/COR was established and the guest molecule COR showed preferential adsorption to the TATBA host grid.Density functional theory(DFT) calculations had been performed to disclose the mechanism of the involved assemblies.     

Impact of pressure on transport properties of AlGaN/GaN high electron mobility transistor

The properties of Al_xGa_1−xN/GaN high electron mobility transistor (HEMT) impacted by pressure are characterized quantitatively. The results indicate that the dislocation density increases as the critical thickness decreases with increasing pressure. The two-dimensional electron gas density was found to be linearly changeable with the pressure. A simulation has been completed to verify the influence of electron mobility. The results show that the misfit dislocation scattering induced by the pressure is a major limiting factor for the properties of HEMT.     

Robust output feedback cruise control for high-speed train movement with uncertain parameters

In this paper,the robust output feedback cruise control for high-speed train movement with uncertain parameters is investigated.The dynamic of a high-speed train is modeled by a cascade of cars connected by flexible couplers,which is subject to rolling mechanical resistance,aerodynamic drag and wind gust.Based on Lyapunov’s stability theory,the sufficient condition for the existence of the robust output feedback cruise control law is given in terms of linear matrix inequalities(LMIs),under which the high-speed train tracks the desired speed,the relative spring displacement between the two neighboring cars is stable at the equilibrium state,and meanwhile a small prescribed H∞ disturbance attenuation level is guaranteed.One numerical example is given to illustrate the effectiveness of the proposed methods.     

Regulating Charge Transfer of Lattice Oxygen in Single-Atom-Doped Titania for Hydrogen Evolution

Single-atom catalysts have attracted much attention. Reported herein is that regulating charge transfer of lattice oxygen atoms in serial single-atom-doped titania enables tunable hydrogen evolution reaction (HER) activity. First-principles calculations disclose that the activity of lattice oxygen for the HER can be regularly promoted by substituting its nearest metal atom, and doping-induced charge transfer plays an essential role. Besides, the realm of the charge transfer of the active site can be enlarged to the second nearest atom by creating oxygen vacancies, resulting in further optimization for the HER. Various single-atom-doped titania nanosheets were fabricated to validate the proposed model. Taking advantage of the localized charge transfer to the lattice atom is demonstrated to be feasible for realizing precise regulation of the electronic structures and thus catalytic activity of the nanosheets.     

Evaluation of radiation damage behavior in polyimide aerogel by infrared camera and photoacoustic spectroscopy

In this work, the optical absorption and thermal properties of polyimide aerogel have been investigated by Infrared Camera, ultraviolet–visible and photoacoustic spectroscopy under low energy proton irradiation. The characterization method of the infrared camera can obtain the optical absorption ratio, and meanwhile get the information of specific heat capacity. Moreover, it can acquire the nature information of damaged area rather than the overall performance. The results show an increase in optical absorption after proton irradiation, which is in good coincidence with Ultraviolet–visible spectroscopy analysis. And the specific heat capacity decreased linearly with proton fluences, which can be attributed to the irradiation damage and carbonization in polyimide aerogel. The Raman spectra suggested the cleavage of chemical bonds and carbonization in polyimide aerogel. This work provides the novel, non-destructive and sensitive methods to characterize irradiation damage of aerogel.     

机械化学法制备金属-有机骨架及其复合物研究进展

金属-有机骨架(MOFs)是由金属离子/簇和多齿状有机配体通过配位键桥联而形成的多孔晶态材料。MOFs材料具有孔隙率高、比表面积大、尺寸可调、结构易修饰、功能多样化等特点,使其在气体吸附、分离和催化等方面都具有潜在应用价值。到目前为止,在MOFs合成的几种常见方法中,机械化学法(即在无溶剂或极少量溶剂的情况下研磨固体反应物进行的反应)作为一种清洁、绿色、高效的合成手段逐渐引起人们的关注。本综述总结了近年来机械化学合成MOFs及其复合物的典型进展,目的是为机械化学法合成MOFs及其复合材料提供一个通用而易于理解的概述。目前的研究进展表明,机械化学法是一种实用且环境友好的合成方法,为低成本、宏量生产MOFs及其复合物提供了可能。     

Recent Advances in Atomic-scale Storage Mechanism Studies of Two-dimensional Nanomaterials for Rechargeable Batteries Beyond Li-ion

Developing new types of rechargeable batteries with high energy densities and low cost have received increasing attentions, aiming to reduce the dependence on high-priced lithium. Beyond Li-ion batteries, the potential alternatives including Na-ion batteries, Li-S batteries and Li-air batteries have been investigated recently, which are required to be viable for commercial applications. From this point of view, to understand the electrochemical reaction mechanisms and kinetics of these batteries has become the key challenge to make breakthroughs in the field of new energy storage. In this review, we present a critical overview of the two dimensional nanomaterials-based batteries (except Li-ion-based batteries) that could meet such demonds. To develop new energy storage devices with more promising performances, the microstructure evolution and atomic scale storage mechanism of these batteries are comprehensively summarized. In addition, the major challenges and opportunities of advanced characterization techniques are finally discussed. We do hope that this review will give the readers a clear and profound understanding of the electrochemical reaction mechanisms and kinetics of the as-discussed batteries, thus effectively contributing to the smart design of future-generation energy storage devices.     

基于非齐次复合Poisson过程的正交异性钢桥面板细节疲劳裂纹随机扩展研究

传统的正交异性钢桥面板疲劳损伤评估常采用确定性和可靠性分析方法,忽略了疲劳裂纹扩展的随机性影响,针对这一问题,提出钢桥面板细节疲劳随机扩展分析方法。本文以南溪长江大桥为工程背景,基于长期车辆荷载监测数据,建立了车辆荷载非齐次复合Poisson过程模型。建立钢桥面板有限元模型,采用瞬态分析方法将随机车辆荷载转化成细节疲劳应力,基于线弹性断裂力学理论推导U肋-顶板焊接细节疲劳裂纹扩展时变微分方程,实现宏观关系式疲劳应力幅次数-疲劳损伤至微观表达式应力时间序列-疲劳损伤转换,讨论了车载次序及超载对疲劳裂纹扩展的影响。研究结果表明,非齐次复合泊松过程模型能够较好描述随机车流运营状态,车辆荷载的次序对疲劳裂纹扩展速率的影响不可忽略,重车排序靠前时能够促使疲劳裂纹扩展增速,南溪长江大桥细节点的车辆超载迟滞效应修正系数取值0.804。     

Microstructural model for cyclic hardening in F-actin networks crosslinked by α-actinin

The rheology of F-actin networks has attracted a great attention during the last years. In order to gain a complete understanding of the rheological properties of these novel materials, it is necessary the study in a large deformations regime to alter their internal structure. In this sense, Schmoller et al. (2010) showed that the reconstituted networks of F-actin crosslinked with α-actinin unexpectedly harden when they are subjected to a cyclical shear. This observation contradicts the expected Mullins effect observed in most soft materials, such as rubber and living tissues, where a pronounced softening is observed when they are cyclically deformed.We think that the key to understand this stunning effect is the gelation process. To define it, the most relevant constituents are the chemical crosslinks – α-actinin –, the physical crosslinks – introduced by the entanglement of the semiflexible network – and the interaction between them. As a consequence of this interaction, a pre-stressed network emerges and introduces a feedback effect, where the pre-stress also regulates the adhesion energy of the α-actinin, setting the structure in a metastable reference configuration. Therefore, the external loads and the evolvement of the trapped stress drive the microstructural changes during the cyclic loading protocol. In this work, we propose a micromechanical model into the framework of nonlinear continuum mechanics. The mechanics of the F-actin filaments is modelled using the wormlike chain model for semiflexible filaments and the gelation process is modelled as mesoscale dynamics for the α-actinin and physical crosslink. The model has been validated with reported experimental results.     

Two-dimensional function photonic crystals

In this paper, we have studied two-dimensional function photonic crystals, in which the dielectric constants of medium columns are the functions of space coordinates , that can become true easily by electro-optical effect and optical kerr effect. We calculated the band gap structures of TE and TM waves, and found the TE (TM) wave band gaps of function photonic crystals are wider (narrower) than the conventional photonic crystals. For the two-dimensional function photonic crystals, when the dielectric constant functions change, the band gaps numbers, width and position should be changed, and the band gap structures of two-dimensional function photonic crystals can be adjusted flexibly, the needed band gap structures can be designed by the two-dimensional function photonic crystals, and it can be of help to design optical devices.