Surface modification mechanism of SiC particles using KH5X0 (X=5,6,7,8,9) silane coupling agents: First principle study

Silicon carbide surface modification is still a challenging task. Its modification mechanism is also still unclear. This paper provides a study of the surface modification mechanism of KH5X0 (X = 5, 6, 7, 8, 9) on the silicon carbide (111) using density functional theory. The electronic structures and densities of states of KH5X0 (X = 5, 6, 7, 8, 9) on SiC surfaces indicates that the surface modification mechanism is attributed to the electronic effects of the functional groups of KH5X0 (X = 5, 6, 7, 8, 9). From the results the easier it is for a functional group to obtain electrons, the better the modifying performance of silane coupling agent will be. Furthermore, the interface energy results showed that silicon carbide (111) modification performance by KH580 silane and KH590 silane is better than KH550, KH560, and KH570. The present work provides theoretical guidance for the fabrication of SiC heat sink products.     

Mixed convection flow of a Maxwell nanofluid with Hall and ion‐slip impacts employing the spectral relaxation method

This article investigates the Hall and ion‐slip impacts on the mixed convection flow of a Maxwell nanofluid over an expanding surface in a permeable medium. The impacts of Brownian movement and thermophoresis parameters, Soret, Dufour, viscous dissipation, chemical reaction, and suction parameters, are, moreover, considered. Using the similitude changes, the partial differential equations with regard to the momentum, energy, and concentration equations are transformed to an arrangement of nonlinear ordinary differential equations, which are handled numerically utilizing a spectral relaxation method (SRM). The impacts of noteworthy physical parameters on the velocities, thermal, and concentration distributions are investigated graphically. Moreover, the numerical values of skin‐friction coefficients, local Nusselt number, and Sherwood number for different values of the mixed convection parameter $\left(\gamma \right),$ Deborah number $\left(\lambda \right),$ Hall parameter $({\beta }_{\mathrm{H}}),$ ion‐slip parameter $({\beta }_{\mathrm{i}}),$ Dufour number (Du), and Soret number $\left(\mathit{Sr}\right)$ are computed and tabulated. It is discovered that ascent in Deborah number reduces both the stream and transverse velocity profiles, while the inverse pattern is seen with augmentation in the mixed convection parameter. In addition, inverse patterns of the stream and transverse velocity profiles are seen with expansion in magnetic, Hall, and ion‐slip parameters. Besides this, the temperature and concentration disseminations decline with augmentation in Dufour number and chemical reaction parameters, respectively. It is likewise seen that both the skin‐friction coefficients lessen with expansion in Deborah number, and they ascend with upgrade in blended convection and ion‐slip parameters, while the opposite condition is noticed with augmentation in Hall parameter. Furthermore, the reverse trends of local Nusselt and Sherwood numbers are discovered with expansion in the Dufour and Soret numbers.     

A Unified Analysis of Structured Sonar-Terrain Data Using Bayesian Functional Mixed Models

Sonar emits pulses of sound and uses the reflected echoes to gain information about target objects. It offers a low cost, complementary sensing modality for small robotic platforms. Although existing analytical approaches often assume independence across echoes, real sonar data can have more complicated structures due to device setup or experimental design. In this article, we consider sonar echo data collected from multiple terrain substrates with a dual-channel sonar head. Our goals are to identify the differential sonar responses to terrains and study the effectiveness of this dual-channel design in discriminating targets. We describe a unified analytical framework that achieves these goals rigorously, simultaneously, and automatically. The analysis was done by treating the echo envelope signals as functional responses and the terrain/channel information as covariates in a functional regression setting. We adopt functional mixed models that facilitate the estimation of terrain and channel effects while capturing the complex hierarchical structure in data. This unified analytical framework incorporates both Gaussian models and robust models. We fit the models using a full Bayesian approach, which enables us to perform multiple inferential tasks under the same modeling framework, including selecting models, estimating the effects of interest, identifying significant local regions, discriminating terrain types, and describing the discriminatory power of local regions. Our analysis of the sonar-terrain data identifies time regions that reflect differential sonar responses to terrains. The discriminant analysis suggests that a multi- or dual-channel design achieves target identification performance comparable with or better than a single-channel design. Supplementary materials for this article are available online.     

高质量浓度曲拉通X-100对煤泥浮选的抑制效应及机理

表面活性剂在煤泥浮选领域中应用广泛,且表面活性剂常被用于煤泥浮选促进剂,本文从另一个方面探究了表面活性剂在过量的情况下对煤泥浮选的抑制效应及其机理。以低灰煤粒和表面活性剂曲拉通X-100为研究对象,采用X射线光电子能谱(XPS)表征曲拉通X-100在煤表面的吸附状态,静态接触角测定仪测定曲拉通X-100对煤表面疏水性的影响,并探究了不同质量浓度曲拉通X-100液滴在煤粒表面的润湿与铺展情况,采用诱导时间测量仪分析不同质量浓度曲拉通X-100水溶液中的气泡与煤粒的黏附情况,最后通过紫外分光光度计定量表征浮选槽中残留曲拉通X-100质量浓度与不同浮选时间下浮选结果的对应关系。结果表明:高质量浓度曲拉通X-100会抑制煤粒上浮,随着浮选试验的进行,曲拉通X-100质量浓度逐渐降低,低质量浓度曲拉通X-100会促进煤粒被上浮气泡黏附而浮出;高质量浓度曲拉通X-100能够在煤粒表面发生有效吸附,该吸附属于物理吸附,且在一定程度上提高了煤表面的疏水性;高质量浓度曲拉通X-100水溶液更容易润湿煤表面,从而减缓了气泡-煤粒黏附过程中的液膜薄化与破裂速率;在高质量浓度曲拉通X-100水溶液中,气泡表面因罩盖有曲拉通X-100分子,导致气泡表面发生改性,难以与煤粒发生有效黏附。高质量浓度曲拉通X-100主要通过对气泡改性,以及减缓气泡与煤粒碰撞-黏附过程中的液膜薄化-破裂速率来抑制煤粒的浮选。     

Soret and Dufour effects between two rectangular plane walls with heat source/sink

This study addresses the thermo‐diffusion and the diffusion‐thermo phenomena in a semi‐infinite absorbent channel whose walls are contracting/expanding, with heat source/sink effects. The governing partial differential equations with suitable boundary conditions are transformed to a system of dimensionless ordinary differential equations. An analytic solution of the problem has been found using a technique called homotopy analysis method (HAM). HAM gives consistently valid answers to the problem over an extensive variety of parameters and also provides better accuracy. To validate the analytical results, a comparison has been presented with a numerical solution calculated by using the parallel shooting method. The effects of dimensionless parameters, that is, deformation parameter, Reynolds number, Soret and Dufour numbers, and heat source/sink parameter on the expressions of velocity, temperature, and concentration profiles are analyzed graphically to understand the physics of the deformable channel. It has been noted that the velocity across the channel is higher for the expanding channel, as compared to that for the contracting channel. Also the Soret and Dufour number increases the temperature of the fluid, and decreases the concentration. The temperature profile has an increasing behavior in the case of heat source, and a decreasing behavior in the case of heat sink.     

半导体激光器辐照损伤效应实验研究进展

半导体激光器(LD)工作在空间辐射或核辐射环境中时,会受到辐照损伤的影响而导致器件性能退化。文章回顾了不同时期研制的LD(从早期的GaAs LD到量子阱LD和量子点LD)在辐照效应实验方面的研究进展,梳理了国际上开展不同辐射粒子或射线(质子、中子、电子、伽马射线)诱发LD辐射敏感参数退化的实验规律,分析总结了当前LD辐照效应实验方法研究中亟待解决的关键技术问题,为今后深入开展LD的辐照效应实验方法、退化规律、损伤机理及抗辐射加固技术研究提供理论指导和实验技术支持。     

Optimal filtering and control for wireless networked closed-loop control systems

This article studies the optimal filtering and control for wireless networked control systems (WNCSs). In WNCSs, packets may be lost in both control and feedback channels and user datagram protocol is usually used to improve the performance of the real-time control. Relevant literature indicates that the conventional optimal filtering for such a system cannot be applied in practice due to the complex calculation with Gaussian mixtures. This paper proposes a novel scheme to realize the optimal filtering and the linear quadratic Gaussian control for WNCSs, in which the controlled node performs a local estimation and the remote-control node performs the final estimation and control, and a synchronization of two estimators is guaranteed by a communication mechanism. An optimal filtering algorithm is developed, the stability condition of the filtering error covariance is obtained, optimal finite-horizon and infinite-horizon control are derived, and the stability of the closed-loop control system is proved. Numerical simulations show the validity and feasibility of the theoretical results.     

Impact of ZrO2 alloying on thermo-mechanical properties of Gd3NbO7

The ZrO₂ alloying effect is widely used to optimize the thermo-mechanical properties of potential thermal barrier coatings. In this study, dense x mol% ZrO₂-Gd₃NbO₇ with C222₁ space group were manufactured via a solid-state reaction. The crystalline structure was determined through X-ray diffraction and Raman spectroscopy, when the surface morphology was observed by scanning electron microscopy. ZrO₂-Gd₃NbO₇ had identical orthorhombic crystal structures, and there was no second phase. The crystalline structure of ZrO₂-Gd₃NbO₇ shrunk with the increasing ZrO₂ content as indicated by XRD and Raman results. The heat capacity and thermal diffusivity of ZrO₂-Gd₃NbO₇ were 0.31–0.43 J g⁻¹ K⁻¹ (25–900 °C) and 0.25–0.70 mm²/s (25–900 °C), respectively. It was found that ZrO₂-Gd₃NbO₇ had much lower thermal conductivity (1.21–1.82 W m⁻¹ K⁻¹, 25–900 °C) than YSZ (2.50–3.00 W m⁻¹ K⁻¹) and La₂Zr₂O₇ (1.50–2.00 W m⁻¹ K⁻¹). The thermal expansion coefficients (TECs) were higher than 10.60 × 10⁻⁶ K⁻¹ (1200 °C), which were better than that of YSZ (10.00 × 10⁻⁶ K⁻¹) and La₂Zr₂O₇ (9.00 × 10⁻⁶ K⁻¹). The mechanical properties of Gd₃NbO₇ change little with the increasing ZrO₂ content, Vickers hardness was about 10 GPa, and Young's modulus was about 190 GPa, which was lower than YSZ (240 GPa). Compared with previous work about alloying effects, much lower thermal conductivity was obtained. Due to the high melting point, high hardness, low Young's modulus, ultralow thermal conductivity and high TECs, it is believed that ZrO₂-Gd₃NbO₇ is promising TBCs candidate.     

Predicting the damage development in epoxy resins using an anisotropic damage model

For fiber-reinforced plastics, the strain-rate dependent response is governed by the matrix behavior. In this work, the Goldberg model is considered for the epoxy matrix constitutive material model. Moreover, the strain-rate dependency is achieved by direct influence on the elastic modulus, the inelastic strain, and the material strain to failure. In addition, an anisotropic damage response is implemented and extended through a strain-rate dependent definition. Since the constitutive model relies on nonphysical parameters, a parameter study is further performed. Additional numerical investigations using a micro-mechanical model are performed. Tension and shear loading conditions are evaluated and the influence of different strain rates is explored. Furthermore, the implemented anisotropic damage model is compared and discussed against an isotropic damage model.