任意取向多个介质旋转椭球的散射场

本文提出了一种用于计算任意取向多个介质椭球电磁散射的混合方法.利用扩展边界条件(EBC)导出具有旋转轴对称单个椭球以球面波矢量函数为基底的T矩阵,结合球矢量波函数旋转定理和递推T矩阵方法,给出多个任意取向介质椭球的散射场.数值例子验证了该混合方法的计算精度和有效性.     

啤酒中测定双乙酰含量的EBC法的改进

EBC法是测定啤酒双乙酰的常规方法,但大量报道此法再生性和重复性较差,本文对影响此方法的一些因素进行了考查,发现酸碱度是影响EBC法的一个重要因素,并对EBC法进行改进。     

Tailorable thermal expansion in leucite-pollucite materials derived from geopolymers for environmental barrier coatings

The K[AlSi₂O₆]-Cs[AlSi₂O₆] pseudo-binary system was synthesized by geopolymer crystallization. The thermal expansion properties of these materials were studied by in situ high-temperature X-ray diffraction to characterize thermal expansion behavior for potential application as environmental barrier coatings. Tailorable thermal expansion through changing cation stoichiometry allowed reduced thermal expansion mismatch with SiC_f/SiC composites compared to rare-earth-based coatings.     

High-temperature Na2SO4 interaction with air plasma sprayed Yb2Si2O7 + Si EBC system: Topcoat behavior

The high-temperature interaction between ~2.5 mg/cm² of Na₂SO₄ and an atmospheric plasma sprayed (APS) Yb₂Si₂O₇ topcoat–Si bond coat system on SiC CMC substrates was studied for times up to 240 h at 1000°C–1316°C in a 0.1% SO₂–O₂ gaseous environment. Yb₂Si₂O₇ reacted with Na₂SO₄ to form Yb₂SiO₅ and an intergranular amorphous Na-silicate phase. Below 1200°C, the reaction was sluggish, needing days to cause morphological changes to the “splat microstructure” associated with APS coatings. The reaction was rapid at 1200°C and above, needing only a few hours for the entire topcoat to transform into a granulated microstructure consisting of Yb₂SiO₅ and Yb₂Si₂O₇ phases. Na₂SO₄ deposits infiltrated the Yb₂Si₂O₇ topcoat and transformed into an amorphous Na-silicate in less than 1 h at all exposure temperatures. Quantitative assessment of the Yb₂SiO₅ area fraction in the topcoat showed a linear decrease over time at 1316°C, attributed to reaction with the SiO₂ thermally grown oxide (TGO) formed on the Si bond coat and rapid transport through the interpenetrating amorphous Na-silicate grain boundary phase. It was predicted that nearly 2 weeks is needed for complete removal of Yb₂SiO₅ from the topcoat at 1316°C for a single applied loading of Na₂SO₄.     

基于FPGA的可重用的VXI系统的设计

提出了一种可重用的VXI系统的实现方法;该系统的硬件结构是使用PPC405GP和FPGA来实现,并采用了一种简单且通用的总线和功能模块进行通信;这种系统结构使得该系统的功能升级和扩展变得非常容易,接口电路的设计也很简单;基于该平台,开发人员只需将接口定义了解清楚,就可以进行VXI产品的开发设计,而不需要花费大量的时间和精力来学习CPU系统以及VXI总线;该设计方法已成功应用于产品开发,应用结果表明,该设计方法的引入极大地提高了VXI产品的开发效率。     

Sol–gel alumina environmental barrier coatings for SiC grit

SiO₂ surface film is insufficient to protect SiC from the oxidation at widely varying partial pressures of oxygen, in particular in the presence of water vapor (e.g. in gas turbines) and also in other environments, e.g. during brazing for hard “tipping” of turbine blades. This work demonstrates that sol–gel alumina, coated on 0.5 mm coarse SiC grit, may form an acceptable, up to 10 μm thick “environmental barrier coating” EBC for some of these applications. The sol–gel has advantages over other methods (such as CVD) is the simplicity and low cost. We have used NH₄OH pre-treatment to hydroxylate surface of SiC prior to applying alumina coating. Such modified SiC/SiO₂ surface helped to deposit the positively charged alumina sol, and thus allowed to build thick coatings on the SiC grit. There is some indication that these coatings partially convert to mullite through reaction at the interface with the native silica on SiC. Oxidation resistance tests at 1200 °C were performed to show effectiveness of such coated SiC grit.     

Enhanced calcium–magnesium–aluminosilicate (CMAS) resistance of GdAlO3 (GAP) for composite thermal barrier coatings

The impact of calcium–magnesium–alumino-silicate (CMAS) degradation is a critical factor for development of new thermal and environmental barrier coatings. Several methods of preventing damage have been explored in the literature, with formation of an infiltration inhibiting reaction layer generally given the most attention. Gd₂Zr₂O₇ (GZO) exemplifies this reaction with the rapid precipitation of apatite when in contact with CMAS. The present study compares the CMAS behavior of GZO to an alternative thermal barrier coating (TBC) material, GdAlO₃ (GAP), which possesses high temperature phase stability through its melting point as well as a significantly higher toughness compared with GZO. The UCSB laboratory CMAS (35CaO–10MgO–7Al₂O₃–48SiO₂) was utilized to explore equilibrium behavior with 50:50 mol% TBC:CMAS ratios at 1200, 1300, and 1400°C for various times. In addition, 8 and 35 mg/cm² CMAS surface exposures were performed at 1425°C on dense pellets of each material to evaluate the infiltration and reaction in a more dynamic test. In the equilibrium tests, it was found that GAP appears to dissolve slower than GZO while producing an equivalent or higher amount of pore blocking apatite. In addition, GAP induces the intrinsic crystallization of the CMAS into a gehlenite phase, due in part to the participation of the Al₂O₃ from GAP. In surface exposures, GAP experienced a substantially thinner reaction zone compared with GZO after 10 h (87 ± 10 vs. 138 ± 4 μm) and a lack of strong sensitivity to CMAS loading when tested at 35 mg/cm² after 10 h (85 ± 13 versus 246 ± 10 μm). The smaller reaction zone, loading agnostic behavior, and intrinsic crystallization of the glass suggest this material warrants further evaluation as a potential CMAS barrier and inclusion into composite TBCs.     

基于SAPI技术的双语混读在CAI开发中的应用

介绍了如何利用VB,通过调用语音引擎SAPI,结合数据库技术,如何实现英语学习软件开发,从设计思路、实现原理和实现方式做了详细介绍,并提出了一种新的思路：双语学英语,从而摆脱了传统的必须依赖电脑屏幕学习英语的弊端。     

Density functional theory and machine learning guided search for RE2Si2O7 with targeted coefficient of thermal expansion

Density functional theory (DFT) calculations and machine learning (ML) methods are used to establish a relationship between the crystal structures of rare-earth (RE) disilicates (RE₂Si₂O₇) and their coefficient of thermal expansion (CTE). The DFT total energy data predict the presence of several energetically competing crystal structures, which is rationalized as one of the reasons for observing polymorphism. An ensemble of support vector regression models is trained to rapidly predict the CTE as a function of RE₂Si₂O₇ crystal chemistry. Experiments subsequently validated the structure and CTE predictions for Sm₂Si₂O₇.     

Feasibility research of Yb3Al5O12 garnet as environmental barrier coating materials

In this work, Yb₃Al₅O₁₂ (YbAG) garnet, as a new material for environment barrier coating (EBC) application, was synthesized and prepared by atmospheric plasma spraying (APS). The phases and microstructures of the coatings were characterized by XRD, EDS and SEM, respectively. The thermal stability was measured by TG-DSC. The mechanical and thermal-physical properties, including Vickers hardness (H_v), fracture toughness (K_IC), Young's modulus (E), thermal conductivity (κ) and coefficient of thermal expansion (CTE) were also measured. The results showed that the as-sprayed coating was mainly composed of crystalline Yb₃Al₅O₁₂ and amorphous phase which crystallized at around 917 °C. Moreover, it has a hardness of 6.81 ± 0.23 GPa, fracture toughness of 1.61 ± 0.18 MPa m^1/2, as well as low thermal conductivity (0.82–1.37 W/m·K from RT-1000 °C) and an average coefficient of thermal expansion (CTE) (∼6.3 × 10⁻⁶ K⁻¹ from RT to 660 °C). In addition, the thermal shock and water-vapor corrosion behaviors of the Yb₃Al₅O₁₂-EBC systems on the SiC_f/SiC substrates were investigated and their failure mechanisms were analyzed in details. The Yb₃Al₅O₁₂ coating has an average thermal shock lifetime of 72 ± 10 cycles as well as an excellent resistance to steam. These combined properties indicated that the Yb₃Al₅O₁₂ coating might be a potential EBC material. Both the thermal shock failure and the steam recession of the Yb₃Al₅O₁₂-EBC systems are primarily associated with the CTE mismatch stress.