Non-proportional loading in sequentially linear analysis for 3D stress states

Sequentially linear analysis (SLA), a non-incremental-iterative approach towards finite element simulation of quasi-brittle materials, is based on sequentially identifying a critical integration point in the model, to reduce its strength and stiffness, and the associated critical load multiplier (λ_crit), to scale the linear analysis results. In this article, two novel methods are presented to enable SLA simulations for non-proportional loading situations in a three-dimensional fixed smeared crack framework. In the first approach, the cubic function in the load multiplier is analytically solved for real roots using trigonometric solutions or the Cardano method. In the second approach, the load multiplier is expressed as a function of the inclination of a potential damage plane and is deduced using a constrained optimization approach. The first method is preferred over the second for the validation studies due to computational efficiency and accuracy reasons. A three-point bending beam test, with and without prestress, and an RC slab tested in shear, with and without axial loads, are used as benchmarks. The proposed solution method shows good agreement with the experiments in terms of force-displacement curves and damage evolution.     

Passivation of Surface and Interface States in AlGaN/GaN HEMT Structures by Annealing

The Ni/AlGaN interfaces in AlGaN/GaN Schottky diodes were investigated to explore the physical origin of post-annealing effects using electron beam induced current (EBIC), current–voltage (I–V) characteristics, and X-ray photoelectron spectroscopy (XPS). The EBIC images of the annealed diodes showed that the post-annealing process reduces electrically active states at the Schottky metal/AlGaN interfaces, leading to improvement of diode performance, for example a decrease in reverse leakage current and an increase in Schottky barrier heights. Pulsed I–V characteristics indicate the Fermi level is up-shifted after annealing, resulting in a larger sheet carrier density at the AlGaN/GaN interface. Unintentional oxidation of the free AlGaN surface during the post-annealing process, revealed by XPS analysis, may prevent electron trapping near the drain-side of the gate edges. We suggest that the post-annealing process under an optimized conditions can be an effective way of passivating AlGaN/GaN heterojunction field-effect transistors.     

第六代光纤通信系统--量子光纤通信

光具有波粒二重性.现有的光通信系统只基于光信号的波动性.在量子光通信的分析基础上,提出了基于粒子性的第六代光通信系统--量子光纤通信系统,并提出了一种新的量子高速调制方式--利用光孤子调制量子态.     

硫化物钝化对InAs纳米线光学特性的影响

针对InAs纳米线表面氧化造成的发光效率低的问题,采用十八硫醇和硫化铵钝化了由化学气相沉积设备生长的闪锌矿结构的InAs纳米线。对硫化物钝化前后的InAs纳米线进行温度依赖的光致发光光谱测试。实验结果表明,十八硫醇和硫化铵钝化的InAs纳米线在25 K温度下的发光效率与未钝化的InAs纳米线相比分别提高了～6倍和～7倍,此外,可以在室温下探测到硫化铵钝化的InAs纳米线的光致发光,这为未来基于InAs纳米线的中红外纳米光子器件提供了可能性。     

Effect of various adsorbates on electronic states of the thin diamond-like carbon films

The influence of the adsorbed impurity molecules onto energy spectrum of electronic states of the DLC films deposited on SiO₂/Si substrates by direct ion beam from hydrocarbon IC plasma was studied by charge-based deep level transient spectroscopy (Q-DLTS). The strong sensitivity of Q-DLTS spectra to the presence of the vapor water and alcohol at room temperature was found. The principle is that adsorption of any molecules on the surface of the DLC film results in a change of energy spectrum of the electronic states (or trapping centers) at the DLC film surface. For example, a new peak appeared in Q-DLTS spectra in presence of the vapor water and electron state density increased in several orders. Moreover, the effect of different adsorbed molecules (species) on the surface electron states was different and independent, so that different molecules can be detected separately. It was shown to differentiate a few thousand molecules of virtually any impurity adsorbed by DLC film's surface. Such strong surface phenomena of the thin DLC films may be exploited in novel sensitive and selective chemical sensor devices.     

Analysis of the fluorescence of mechanically processed defect-laden hexagonal boron nitride and the role of oxygen in catalyst deactivation

ABSTRACT

The use of hexagonal boron nitride (h-BN) as a non-metal heterogeneous catalyst has been a popular subject in research since the discovery of its catalytic properties in 2016. Previous work found that an activation step was necessary for producing an effective catalyst. Density functional theory (DFT) calculations indicate defect sites, such as nitrogen (V_N) and boron (V_B) vacancies, bind favourably to olefins, hydrogen, and oxygen. In particular, the visible fluorescence intensity of processed h-BN increased with the length of exposure to air. The fluorescence behaviour of dh-BN powders when exposed to air after exposure to species such as argon, propene, and carbon dioxide is presented. Density of state calculations for molecular and atomic oxygen bound to V_N and V_B show that this increase in fluorescence may be due to atomic oxygen binding to V_N. The fluorescence emission behaviour observed in dh-BN powders and its relationship to DOS of oxygen species bound to catalytically active defect sites provides a better understanding of potential deactivation modes for catalysts based on dh-BN.     

Geldart-B类颗粒在气固流化床中的床层膨胀与流型转变

采用理论推导和经验公式相结合方法,建立了Geldart-B类颗粒在流化床中流化过程的床层膨胀比(R)的通式,并在全取值范围内构建了床层膨胀比的收敛迭代公式。采用不同颗粒的流化实验数据对上述通式(模型)进行了验证,结果表明该模型很好地预测了床层膨胀比。进一步讨论了床层膨胀比与鼓泡流化流型变化之间的关系,给出了临界膨胀比的取值规律。有关床层膨胀比的研究结果一定程度上可有效改善流化床的监控,优化操作条件选取。     

Mechanisms of glycosyltransferases: the in and the out

Getting into a transition state: Glycosyltransferases retain a critical role in glycobiology. The design of potent glycosyltransferase inhibitors may be facilitated by considering the mechanistic evidence presented by Davies and Davis and co-workers that strengthens the case that retaining glycosyltransferases function through a single front-side, S(N)i-type mechanism.     

Dynamics of liquid-liquid systems based on linear thermodynamics of irreversible processes

The use of non-equilibrium models for integrated processes involving liquid-liquid systems has increased in recent years. These processes often exhibit complex dynamic behavior. These dynamical systems still pose many open questions, e.g. with regard to the sources of multiple steady states (MSS). This article analyzes the effect of mass transfer on the MSS of these systems. A generalized non-equilibrium modeling approach based on linear thermodynamics of irreversible processes (LTIP) is presented, and the dynamics of the system is studied systematically. It is shown that the non-linearity present in even the simplest non-ideal activity model acts as a source for MSS. The parameters that affect the solubility, e.g. temperature, can play a critical role on the existence of MSS in the system. A geometrical visualization of the MSS is also illustrated.     

绝热功的两点释疑

功是个过程量,2个定态之间所经历的过程不同,则功就不同。但2个定态之间的绝热功却与过程无关,只与始末状态有关。本文解释了绝热功所表现的特殊性,及如何理解绝热功与过程无关,并举例加以说明。