Design of Lu2O3-reinforced Cf/SiC-ZrB2-ZrC ultra-high temperature ceramic matrix composites: Wetting and interfacial reactivity by ZrSi2 based alloys

The wettability and infiltration of molten ZrSi₂ and ZrSi₂-Lu₂O₃ alloys into C_f/SiC and B₄C-infiltrated C_f/SiC composites were investigated to understand the interfacial interactions that occur during the development of C_f/SiC-ZrC and C_f/SiC-ZrB₂-ZrC-Lu₂O₃ materials. A significant evaporation of Si from the liquid affected the wetting behaviour of the alloy when tested in a vacuum at 1670 °C. The better wetting and spreading of the alloy over the surface was observed for the composites with lower overall porosity (12 %). On the other hand, the formation of an outer dense layer, followed up by the uniform infiltrated region up to ～ 1 mm was observed for the C_f/SiC with higher porosity (21 %). The infiltrated alloy reacted with SiC matrix to form ZrC or with B₄C-infiltrated SiC matrix to form ZrB₂-ZrC-SiC. The Lu₂O₃ particles were not wetted by the melt, and were pushed away of the reaction zone by the solidification front.     

Composites of poly(vinyl acetate) filled with calcium carbonate: Microscopy,diffractometry and thermophysical properties

Calcium carbonate (CaCO₃) is used as filler in poly(vinyl acetate)(PVAc) composites to enhance the mechanical properties. The filler is often commercially surface treated with stearic acid to optimize the interfacial bonding and wetting. The effects of the interface on properties were studied using scanning electron microscopy (SEM) of films with initial and deformed morphologies. Plasticizing additives cause a significant change in the appearance of the films and a reduction in the glass transition temperature of the matrix from 40°C to ≈ 18°C, which was not altered by further addition of the filler. A PVAc composite fracture surface shows the particles adhering well to the matrix, suggesting good adhesion and reinforcement. The SEM study is complemented by WAXD, SEM/X-SEM, XPS, and thermal analysis.     

An investigation on renewable energy education at the university level in Turkey

In the present study, to discover how teaching of renewable energy sources in Turkey is carried out at the university level, a questionnaire was developed and applied at different universities in Turkey. The analyses conducted on the data obtained from the questionnaire revealed that education about geothermal, solar and wind energy is given at master’s level, other renewable energy sources are taught at the undergraduate level within the curriculum of some engineering courses. The teaching performed about renewable energy sources is in Turkish and at encyclopedic level. As preparing and obtaining the required materials are costly, some problems are encountered in the teaching of renewable sources. In Turkish universities, no degree about renewable energy sources is granted. Hence, the country must make use of the people having engineering degree to capitalize on its renewable energy sources. As there is no program specializing on providing training about the renewable energy sources, it seems to be difficult to find experts about this issue. The current state of renewable energy sources education seems to be inadequate and it should be expanded and strengthened.     

APPLICATION OF SPECTRAL METHODS TO THERMAL ANALYSIS OF NANOSCALE ELECTRONIC DEVICES

The transient thermal characteristics of nanoscale electronic devices operating at very high frequencies are studied by spectral methods. At such scales microscopic phenomena resulting from phonon collisions and phonon scattering become important. A device, consisting of an array of MOSFET transistors on silicon substrate, is considered as a test case. Thermal transport is represented by a reduced form of the Boltzmann transport equation: the thermal wave model or hyperbolic heat equation. The results indicate that spectral methods can be used effectively for the accurate prediction of the short-time transient effects in nanoscale devices. Such effects are amplified by a sharp increase in the operating voltage and the corresponding heat generation rate.     

Wall Resistance in Graphite-Block Heat Exchangers

Abstract

Accurate data have been obtained on the thermal conductivity of six grades of manufactured graphite. In particular, the effect of orientation, manufacturing process, and impregnant content on the thermal conductivity was investigated. Using the thermal conductivity data, a three-dimensional finite-element model has been set up to determine the wall resistance of a particular graphite block. The effect of the anisotropy of the extruded graphite on the wall resistance was investigated. It was found that the anisotropy can be neglected if the wall resistance is calculated by assuming that the blocks have an isotropic thermal conductivity equal to the thermal conductivity perpendicular to the direction of extrusion. Also, the phenol formaldehyde film on the surface of the heat exchanger channels was determined to have a significant thermal resistance. It was calculated that, for typical operating film coefficients with water on both sides, the overall heat transfer coefficient can be expected to increase by more than 50% if the resin layer is removed.     

运移路径模拟和应用尝试

油气二次运移的方式和方向对具体指出盆地油气资源量所赋存的位置有决定性的意义.在运载层中推动油气运动的作用力主要是浮力和毛细管力,而盖层则起着毛细管阻力作用.因此盖层的形状及空间分布就成了影响运移路径重要的封盖因素.该文试图根据盖层的几何形状特性,建立运移路径模拟模型,开发微机软件运行实施.在一个具体盆地进行运移路径模拟应用的结果反映,与已知勘探情况基本符合,能够检验油气期次性运移的地质概念,可以揭示运移过程,预测可能的运移聚集位置.     

基于信道状态特征的手势动作识别技术研究

手势识别作为人和机器之间重要的交互手段,在日常生活中具有广泛的应用场景。基于无线信号特别是WiFi的手势识别由于其无接触、成本低等优点成为当前热门的方式。为解决传统基于无线信号手势识别算法没有充分利用信号相位特征的缺点,本文提出利用WiFi信道状态信息幅值和相位结合的方式进行手势识别。通过子载波降维和动作曲线提取对接收的WiFi信号进行处理,并将信号的幅值和相位结合,利用机器学习算法对数据进行训练和分类,实现了单手向前、单手向后、单手向左、单手向右、单手向上和单手向下六种手势的识别。实验结果显示,本文算法在近距离和远距离下的精确度分别为96%和92%。     

Investigation of the Gas‐Liquid Flow in a Stopper‐Rod Controlled SEN

The behaviour of two‐phase gas‐liquid flows in a stopper‐rod controlled submerged entry nozzle (SEN) is investigated in water model experiments. The observed two‐phase flow patterns can be classified into either bubble coring or bubbly slug. The scaling of the two‐phase flows by means of similarity parameters is discussed. In the experiments, it is found that the liquid flow rates depend strongly on the two‐phase flow patterns. Additionally, the influence of swirl on the flow patterns is investigated in detail. It is shown that swirl has a marked impact on the transition from bubble coring to bubbly slug. Finally, an estimation of the two‐phase argon‐steel flow patterns in industrialscale SEN flows is given.     

Failure Analysis of a Location Axle in Tracked Tractor

In this study, a failure analysis was performed on the location axle (brace axle) of a blade on a tracked tractor used in agricultural areas. The analysis included evaluation of the macrostructure of the damage and the microstructure of the material, as well as a chemical analysis of the material. A commercial finite element method software package was used to determine the behavior of the location axle under the defined boundary conditions. After all the examination steps were completed, the main reason for the damage was determined to be manufacture and material error despite the presence of fatigue tracks in the damaged area. In addition, a heat treatment was carried out with the specimens taken from the damaged area and microstructure was re-examined. The experimental and simulation evaluation results provide a technical basis for suggestions to prevent future damage to the location axle.     

Preparation of PbS thin films: A new electrochemical route for underpotential deposition

Nanostructured thin films of lead sulfide have been synthesized by a new electrochemical approach based on the underpotential deposition (UPD) of Pb and S from the saturated solution of PbS containing excess of PbS particles as a source of Pb²⁺ and S²⁻ at various temperatures.We have demonstrated that this new electrochemical route is a simple method with several advantages, including better control of the growth conditions and a one-step process to obtain the nanostructures of PbS. Scanning probe microscopy studies indicate that the growth of PbS nanofilms follows a two-dimensional layer-by-layer growth kinetics at the beginning of electrodeposition but a three-dimensional growth dominates after the formation of the first few layers. The results of morphological and structural investigations reveal that PbS nanostructures grown by this method are single-crystalline in cubic structure and have a preferential orientation along the [2 0 0] direction. The optical absorption spectra of PbS nanostructures show the blue-shift with respect to those of the bulk counterpart, which are attributed as quantum-size effect.