膨胀剂对约束条件下UHPC早期抗裂性能影响的试验研究

超高性能混凝土(UHPC)在钢桥面铺装结构中由于铺装材料受到钢板、栓钉等的约束,加上材料本身水胶比小,更易收缩,早期容易承受拉应力导致开裂。通过在拌和过程中添加膨胀剂可以起到减小收缩的作用,但该方法对于约束条件下的UHPC铺装的早期抗裂性能提升是否有促进作用,仍需通过更多试验进行合理评估和深入研究。通过圆环法对3组不同配方的UHPC在均匀约束条件下的早期抗裂性能进行定量测试,并将试验数据进行回归分析和计算,得到了各组的平均应力发展速率,进而评估了各组的开裂风险等级。试验结果表明,通过在UHPC中加入适量膨胀剂,可使其最终收缩应力减小,并可降低其收缩应力发展速率,进一步降低其在约束条件下的开裂风险。     

Comparative study of Ti-C-Ni-Al,Ti-C-Ni-Fe,and Ti-C-Ni-Al/Ti-C-Ni-Fe coatings produced by magnetron sputtering,electro-spark deposition,and a combined two-step process

Comparative study of Ti-C-Ni-Fe, Ti-C-Ni-Al, and Ti-C-Ni-Al/Ti-C-Ni-Fe coatings obtained by electro-spark deposition (ESD) using TiCNi electrode, magnetron sputtering (MS) of TiCNiAl target, and a combination of these methods (MS-ESD) was carried out. The coating microstructures and elemental compositions were studied by means of X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, and glow discharge optical emission spectroscopy. The materials were tested in terms of their hardness, elastic modulus, elastic recovery, crack resistance, friction coefficient, and wear resistance under sliding, impact and abrasive conditions, as well as corrosion- and oxidation resistance. The work demonstrated that the utilization of a combined two-step MS-ESD technology permits to obtain bilayers made of Ti-C-Ni-Al/Ti-C-Ni-Fe coatings with improved crack-, wear- and oxidation resistance compared with their single-layered Ti-C-Ni-Al counterparts deposited by MS, and with reduced friction coefficient and enhanced corrosion resistance compared with ESD Ti-C-Ni-Fe coatings.     

A model of splats deposition state and wear resistance of WC-10Co4Cr coating

In this research both low temperature high velocity oxygen-fuel flame (LT-HVOF) and high velocity oxygen-fuel flame (HVOF) techniques were employed to prepare WC-10Co4Cr splats and coatings. In situ cutting of WC-10Co-4Cr splats was carried out with focused ion beam (FIB), and a model was proposed to describe how the wear resistance of WC-10Co4Cr coatings was correlated with its residual stress state and the splats deposition state. It was observed that in LT-HVOF spraying process, WC-10Co4Cr splats were slightly melted showing "hill" shape, while in HVOF spraying process, the splats were half melted having the appearance of "concavity". The residual stress of WC-10Co4Cr coatings is determined by the size, melting state, flight speed and temperature gradient of splats. In this paper, the quantitative function formula involving heating temperature and the flight speed of the powder is put forward for the first time to predict the wear resistance of the WC-10Co4Cr coatings. This will provide a theoretical basis for engineering practice and an effective way to save costs.     

Effect of the calcium alumino-titanate particle size on the microstructure and properties of bauxite-SiC composite refractories

Alkali resistance and thermo-mechanical properties of the transition zone of cement rotary kilns refractories are the key factors affecting their service life. Calcium alumino-titanate (CAT) containing bauxite-SiC composites were prepared using bauxite, SiC, CAT, Guang Xi white clay, α-alumina, and metallic silicon powder as starting materials and Al(H₂PO₄)₃ as the binder. The effects of the CAT particle size on the phase composition, microstructure, thermo-mechanical properties, and alkali resistance of the CAT-containing bauxite-SiC composites during firing were investigated. The results reveal that the CAT particle size strongly affects the composites’ microstructure and sintering densification. With decreasing particle size, the particle-particle and particle-matrix interfacial bonding deteriorates gradually. When CAT particles are added, the specimens show higher strength, refractoriness under load, and residual rupture strength than the specimens with fine CAT powders. Specimens with fine CAT powders show lower coefficient of thermal expansion compared to the specimens with CAT aggregates. The alkali attack test confirms that the bauxite-SiC composite refractories with CAT aggregates show better alkali resistance than those with CAT fine powder. According to the alkali mechanism, 1) K vapors penetrate the specimen through the open and connected pores and cracks, 2) K vapors react with anorthite and corundum to form kalsilite accompanied by the formation of a liquid phase and new cracks.     

Layered double hydroxide coatings on magnesium alloys: A review

Layered double hydroxides (LDHs) as a class of anionic clays have extensive applications due to their unique structures. Nowadays, the emphasis is laid on the development of LDH coatings for corrosion resistance and medical applications. Thus, this review highlights synthetic methods of LDH coatings and LDH-based composite coatings on magnesium alloys. Special attention is focused on self-healing, biocompatible and self-cleaning LDH-based composite coatings on magnesium alloys.     

Significant population genetic structuring in Rhyzopertha dominica across Turkey: Biogeographic and practical implications

Rhyzopertha dominica is a key pest of stored grain. Understanding the movement of this beetle on broad geographic scales is crucial, particularly when developing strategies to prevent the spread of phosphine resistance. We assessed population genetic structuring in this pest across Turkey, using a combination of mitochondrial (cytochrome oxidase I) and microsatellite markers. In addition, we screened samples for Wolbachia, as this endosymbiont has previously been suggested to be associated with low mitochondrial genetic diversity in this beetle. Mitochondrial genetic diversity was low, with only six haplotypes identified. The genetic diversity was, however, substantially higher than that previously found in Australia or India, suggesting that R. dominica may have originated in the Middle East. Wolbachia were detected only at a single site, indicating they are not impacting the mitochondrial genetic diversity of R. dominica across Turkey. Microsatellite markers indicated there is significant geographic genetic structuring across Turkey, even among sites less than 100 km apart, suggesting there is little movement of beetles across regions within the country. This contrasts with the significantly higher levels of gene-flow found in Australia and the United States. We suggest that the limited movement of beetles across Turkey may be due to a combination of the historically localised agricultural practices (which limits anthropogenic movement among regions), and the mountainous landscape (which limits active flight among regions). Our results demonstrate that the movement of stored product pests may differ significantly across studies conducted in different countries. As a consequence, phosphine resistance management strategies must incorporate region specific information on the extent of beetle movement.     

A dense and compact laser cladding layer with solid metallurgical bonding significantly improved corrosion resistance of Mg alloy for engineering applications

Although Mg alloy attracts great attention for engineering applications because of high specific strength and low density, low corrosion resistance limits its extensive use. In this study, Mg–Al–Zn–Mn alloy was treated via a laser cladding process to generate a dense and compact laser cladding layer with solid metallurgical bonding on the substrate for improving corrosion resistance, effectively hindering the corrosion pervasion into Mg alloy. The corrosion current density declined from 103 μA/cm² for Mg alloy to 13 μA/cm² for the laser cladding layer in NaCl aqueous solution. Moreover, the laser cladding layer was slightly corroded in comparison with Mg alloy in NaCl aqueous solution. Besides, the microhardness of the cladding layer reached a mean value of 170.5 HV, 3.1 times of Mg alloy (56.8 HV) due to the in situ formation of hardening intermetallic phases. Wear resistance of laser cladding layer was also obviously improved. These results demonstrated that the laser cladding layer obviously enhanced anticorrosion property of Mg alloy for engineering applications.     

电驱液压式大截面导线压接设备自动化研究

现有的压接设备可控性差、操作复杂,导致压接质量因人而异。针对此问题,提出了基于DDVC技术的导线压接设备自动化控制方案,建立了速度控制系统数学模型,应用Simulink进行仿真,分析系统性能。建立了基于DEFORM的耐张线夹压接实验模型,获得了耐张线夹压接的最佳加载速度曲线,并以此作为压接设备速度控制系统的Simulink仿真模型输入,对压接过程进行了仿真分析。结果表明:开环控制时系统存在一定的超调,加入PID控制后可有效抑制超调;所设计的压接设备可很好地跟随最佳压接曲线,跟随误差仅为0. 904 mm·s-1。研究成果对改进压接设备、提高压接质量提供了新的解决方案。     

Synthesis and Characterization of Telmisartan-Derived Cell Death Modulators to Circumvent Imatinib Resistance in Chronic Myeloid Leukemia

New strategies to eradicate cancer stem cells in chronic myeloid leukemia (CML) include a combination of imatinib with peroxisome proliferator-activated receptor gamma (PPARγ) ligands. Recently, we identified the partial PPARγ agonist telmisartan as effective sensitizer of resistant K562 CML cells to imatinib treatment. Here, the importance of the heterocyclic core on the cell death-modulating effects of the telmisartan-derived lead 4′-((2-propyl-1H-benzo[d]imidazol-1-yl)methyl)-[1,1′-biphenyl]-2-carboxylic acid ( 3 b ) was investigated. Inspired by the pharmacodynamics of HYL-6d and the selective PPARγ ligand VSP-51, the benzimidazole was replaced by a carbazole or an indole core. The results indicate no correlation between PPARγ activation and sensitization of resistant CML cells to imatinib. The 2-COOH derivatives of the carbazoles or indoles achieved low activity at PPARγ, while the benzimidazoles showed 60-100 % activation. Among the 2-CO₂CH₃ derivatives, only the ester of the lead ( 2 b ) slightly activated PPARγ. Sensitizing effects were further observed for this non-cytotoxic 2 b (80 % cell death), and to a lesser extent for the lead 3 b or the 5-Br-substituted ester of the benzimidazoles ( 5 b ).     

Coupling heat storage to nuclear reactors for variable electricity output with baseload reactor operation

Nuclear reactors produce heat and thus can couple to heat storage systems to provide dispacthable electricity while the reactor operates at full power. Six classes of heat storage technologies couple to light-water reactors with steam cycles. Firebrick Resistance-Heated Energy Storage (FIRES) converts low-price electricity into high-temperature stored heat for industry or power. FIRES and brick recuperators coupled to nuclear brayton power cycles may enable high-temperature reactors to buy electricity when prices are low and sell electricity at higher price.