Crack propagation prediction of CFRP retrofitted steel plates with different degrees of damage using BEM

Although carbon fibre reinforced polymer (CFRP) materials have proven effective in strengthening steel structures especially when used to improve fatigue behaviour, further study is required to investigate their effectiveness when applied at different stages of crack propagation in steel elements. This paper presents a numerical study on CFRP retrofitted steel plates with different degrees of damage using the boundary element method (BEM). The numerical results compared well with the experimental data, which demonstrated that the BEM is reliable for crack propagation analysis of CFRP laminate retrofitted steel plates. Finally, a parametric analysis was conducted to investigate the influence of bond length, bond width, CFRP stiffness and adhesive shear modulus on stress intensity factor (SIF) values.     

Are major economies on track to achieve their pledges for 2020? An assessment of domestic climate and energy policies

Many of the major greenhouse gas emitting countries have planned and/or implemented domestic mitigation policies, such as carbon taxes, feed-in tariffs, or standards. This study analyses whether the most effective national climate and energy policies are sufficient to stay on track for meeting the emission reduction proposals (pledges) that countries made for 2020. The analysis shows that domestic policies of India, China and Russia are projected to lead to lower emission levels than the pledged levels. Australia's and the EU's nationally legally binding policy framework is likely to deliver their unconditional pledges, but not the conditional ones. The situation is rather unclear for Japan, South Korea, Brazil and Indonesia. We project that policies of Canada and the USA will reduce 2020 emission levels, but additional policies are probably needed to deliver their pledges in full. The analysis also shows that countries are implementing policies or targets in various areas to a varying degree: all major countries have set renewable energy targets; many have recently implemented efficiency standards for cars, and new emission trading systems are emerging.     

Effect of the Type of Base and Number of Reaction Steps on the Degree of Quaternization and Molecular Weight of N-Trimethyl Chitosan Chloride

N-Trimethyl chitosan chloride (TMC), a chemically modified derivative of chitosan, is the first chitosan derivative shown to be an effective absorption enhancer for peptide and protein drugs across mucosal epithelia. TMC is synthesized by reductive methylation with methyl iodide in the presence of a strong base such as sodium hydroxide. In this reaction, the primary amino group on the C-2 position of chitosan is changed to a quaternary amino group. The charge density, as determined by the degree of quaternization, and probably also the molecular weight of TMC are important factors that influence the absorption enhancement effect and toxicity of this polymer. The molecular weight of the starting polymer decreases during the synthesis procedure due to factors such as the strong alkaline environment and elevated experimental temperatures. This study investigated the effects of two different bases, sodium hydroxide and dimethyl amino pyridine, together with a varying number and duration of reaction steps, on the degradation and the degree of quaternization of TMC polymers. ¹H-NMR (nuclear magnetic resonance) spectra showed a major increase in the degree of quaternization (21%–59%) of TMC with an increase in the number of reaction steps when sodium hydroxide was used as the base. Intrinsic viscosity values indicated that the use of dimethyl amino pyridine did not cause polymer degradation to the same extent as sodium hydroxide, but that the degree of quaternization of TMC stayed low (7.3%–9.6%) even when the number of reaction steps was increased. A combination of the two bases did not reduce polymer degradation, while the degree of quaternization was limited to relatively low values (12.5%–34.4%).     

Characterization of cellulose structure of Populus plants modified in candidate cellulose biosynthesis genes

The recalcitrant nature of lignocellulosic biomass is a combined effect of several factors such as high crystallinity and high degree of polymerization of cellulose, lignin content and structure, and the available surface area for enzymatic degradation (i.e., accessibility). Genetic improvement of feedstock cell wall properties is a path to reducing recalcitrance of lignocellulosic biomass and improving conversion to various biofuels. An advanced understanding of the cellulose biosynthesis pathway is essential to precisely modify cellulose properties of plant cell walls. Here we report on the impact of modified expression of candidate cellulose biosynthesis pathway genes on the ultra-structure of cellulose, a key carbohydrate polymer of Populus cell wall using advanced nuclear magnetic resonance approaches. Noteworthy changes were observed in the cell wall characteristics of downregulated KORRIGAN 1 (KOR) and KOR 2 transgenic plants in comparison to the wild-type control. It was observed that all of the transgenic lines showed variation in cellulose ultrastructure, increase in cellulose crystallinity and decrease in the cellulose degree of polymerization. Additionally, the properties of cellulose allomorph abundance and accessibility were found to be variable. Application of such cellulose characterization techniques beyond the traditional measurement of cellulose abundance to comprehensive studies of cellulose properties in larger transgenic and naturally variable populations is expected to provide deeper insights into the complex nature of lignocellulosic material, which can significantly contribute to the development of precisely tailored plants for enhanced biofuels production.     

Estimation of the degree of hydration of concrete through automated machine learning based microstructure analysis – A study on effect of image magnification

The scanning electron microscopy (SEM) images are commonly used to understand the microstructure of the concrete. With the advancements in the field of computer vision, many researchers have adopted the image processing technique for the microstructure analysis. Most of the previous methods are not adaptable, non-reproducible, semi-automated, and most importantly all these methods are highly influenced by image magnification. Therefore, to overcome these challenges, this paper presents a machine learning based image segmentation method for microstructure analysis and degree of hydration measurement using SEM images. In addition, the authors looked into the impact of magnification of SEM images on the model accuracy and classifier training for the degree of hydration measurement considering two scenarios. First, the image segmentation was performed using a classifier of specific magnification, and then a common classifier is trained using the image of different magnification. The results show that the Random Forest classifier algorithm is suitable for microstructure analysis using SEM images. Through the statistical analysis, it has been proved that there is no significant effect of magnification on model training and accuracy for the degree of hydration measurement. So, a single classifier can be used to process the images of different magnification of a specimen which reduces the effort of training and computational time. The proposed method can generate highly accurate and reliable results in a shorter time and lower cost. Moreover, the findings in this research can be useful for researchers to determine the optimum magnification required for the microstructure analysis.     

稀土离子半径对稀土锆酸盐的组织结构和电学性能的影响

采用X射线衍射、高分辨透射电镜、选区电子衍射、拉曼光谱以及阻抗谱等手段研究了稀土锆酸盐(A_2Zr_2O_7)材料的晶体结构和电学性能,发现稀土锆酸盐A_2Zr_2O_7的有序度随稀土阳离子半径的减小逐渐降低。Sm_2Zr_2O_7和Eu_2Zr_2O_7陶瓷为有序的烧绿石相,而Gd_2Zr_2O_7和Dy_2Zr_2O_7为无序的缺陷型萤石相。与其它几种稀土锆酸盐的电导率相比,有序度相对较低的烧绿石相Eu_2Zr_2O_7具有最大的晶粒电导率(1.03×10~(-2)S·cm~(-1),1173 K)。     

茂名山阁高岭石晶体结构有序度研究

本文应用X射线衍射对茂名山阁高岭石晶体结构有序度进行了深入研究,作者提出应用嵌晶的厚度与宽度比值来判断高岭石结构有序度高低。研究结果表明,茂名山阁高岭石属典型的高有序度1T型高岭石,为国内少见。其衍射谱线分解非常清晰,(001)和(002)衍射线角宽度值0.20—0.32,结晶度指数1.29—1.47,(001)结晶方向有序序列晶胞数40—54个,嵌晶的厚度与宽度比值为0.70—0.98。随着高岭石埋深增大,其结构有序度呈下降趋势。     

Ionically Cross‐Linked Proton Conducting Membranes for Fuel Cells

For improving stability without sacrificing ionic conductivity, ionically cross‐linked proton conducting membranes are fabricated from Na⁺‐form sulfonated poly(phthalazinone ether sulfone kentone) (SPPESK) and H⁺‐formed sulfonated poly(2,6‐dimethyl‐1,4‐phenylene oxide) (SPPO). Ionically acid‐base cross‐linking between sulfonic acid groups in SPPO and phthalazone groups in SPPESK impart the composite membranes the good miscibility and electrochemical performance. In particular, the composite membranes possess proton conductivity of 60–110 mS cm⁻¹ at 30 °C. By controlling the protonation degree of SPPO within 40–100 %, the composite membranes with favorable cross‐linking degree are qualified for application in fuel cells. The maximum power density of the composite membrane reaches approximately 1100 mW cm⁻² at the current density of 2800 mA cm⁻² at 70 °C.     

PVA/UiO-66复合薄膜的制备及性能表征

采用溶剂热法合成出了金属有机骨架材料UiO-66,并通过流延法制备出了一系列PVA/UiO-66复合膜.通过红外光谱仪(FTIR)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、接触角、溶胀度、拉伸强度和透光性等表征方法,详细研究了UiO-66含量对复合膜各种物性的影响.结果表明,PVA在经富马酸交联后,耐水溶胀性...