Study on Reduction of MoO2 Powders with CO to Produce Mo2C

Molybdenum hemicarbide (Mo₂C), which is widely applied in steel and metal ceramics as well as catalysts, was successfully synthesized by using a simple method of reducing MoO₂ powders by CO. It was found that the final reduction product was all Mo₂C under both isothermal and nonisothermal conditions. However, the reduction mechanisms were significantly different at lower and higher temperatures: at lower temperatures (1070 to 1342 K), reduction of MoO₂ to Mo₂C followed a one‐step reaction (simultaneous reduction and carburization), while at higher temperatures (1423 to 1485 K), MoO₂ was first reduced to metallic Mo, and then Mo was carburized to Mo₂C. Mo₂C particles obtained at higher temperatures contained micrometer‐sized surface features which formed during the MoO₂ to Mo reduction step.     

富CoCr含量CoCrNiAlTi中熵合金的高温强韧化行为及微观机制

本工作研究了富CoCr含量的CoCrNi基中熵合金的高温力学性能及其变形机制。研究发现,经过热锻以及时效热处理,成分为Co_33.3Cr_30.6Ni_26.1Al₅Ti₅ (at%)中熵合金在600～800℃的温度范围内具有优异的瞬时拉伸性能。特别是,在700℃条件下出现反常屈服,屈服强度高达为944 MPa,拉伸塑性为16%,优于大多数镍基以及钴基高温合金。通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和三维原子探针(3D-APT)等手段,发现高体积分数的多主元γ′[(Ni,Co,Cr)₃(Al,Ti)]相的有序强化以及晶界处生成的多主元富(Co,Cr)面心立方相(fcc)结构相引起的晶界强化是该合金在高温条件下实现强韧化的主要因素。     

套筒致裂法检测混凝土强度应用于地面结构的探讨

介绍了一种矿山地下结构及围岩应力的测试方法－套筒致裂法，阐述了这种方法的原理和测试手段，探讨了把该方法应用于地面结构中检测混凝土强度的理论依据。     

Synthesis and electrochromic properties of aromatic polyimides bearing pendent triphenylamine units

A series of aromatic polyimides with pendent triphenylamine group were synthesized from equimolar mixtures of 4,4′-oxydianiline (ODA) and 4-(3,5-diaminobenzamido)triphenylamine (4), 4-(3,5-diaminobenzamido)-4′,4″-di-tert-butyltriphenylamine (t-Bu-4) or 4-(3,5-diaminobenzamido)-4′,4″-dimethoxytriphenylamine (MeO-4) with two aromatic tetracarboxylic dianhydrides (DSDA or 6FDA) via a conventional two-step procedure that included a ring-opening polyaddition to give poly(amic acid)s, followed by chemical imidization. These polyimides exhibited good solubility in polar organic solvents and could be solution-cast into flexible and strong films. They showed excellent thermal stability, with T_g values in the range of 284–309 °C. The polyimides derived from diamines t-Bu-4 and MeO-4 exhibited reversible electrochemical oxidation, accompanied by strong color changes with high contrast ratio and electrochromic stability. For the polyimides derived from diamine 4, the coupling reaction between the triphenylamine radical cations occurred during the oxidative process forming a tetraphenylbenzidine structure, which resulted in an additional oxidation state and color change together with enhanced near-IR absorption at fully oxidized state.     

An empirical study on user access to entertainment streaming media

I. Introduction Streaming media has been widely used over the Internet in recent years. However, the growing use in streaming media, which generally has large size, can have a significant impact on the user perceived latency and network congestion. A popular approach to reduce the response time and backbone bandwidth consumption is to deploy proxy caches at the edge of the Internet. Due to the large size and different popularity for different part of the streaming video, it is not practical …     

渐开线内插齿刀的优化设计

介绍了渐开线直齿内齿轮插齿刀的优化设计方法。论述了其数学模型的建立和优化方法的选择,并通过实例验证了优化设计的效果。     

An Innovative Customized Biomimetic Hydrogel for Drug Screening Application Potential: Biocompatibility and Cell Invasion Ability

The ability of Pluronic F127 (PF127) conjugated with tetrapeptide Gly-Arg-Gly-Asp (GRGD) as a sequence of Arg-Gly-Asp (RGD) peptide to form the investigated potential hydrogel (hereafter referred to as 3DG bioformer (3BE)) to produce spheroid, biocompatibility, and cell invasion ability, was assessed in this study. The fibroblast cell line (NIH 3T3), osteoblast cell line (MG-63), and human breast cancer cell line (MCF-7) were cultured in the 3BE hydrogel and commercial product (Matrigel) for comparison. The morphology of spheroid formation was evaluated via optical microscopy. The cell viability was observed through cell counting Kit-8 assay, and cell invasion was investigated via Boyden chamber assay. Analytical results indicated that 3BE exhibited lower spheroid formation than Matrigel. However, the 3BE appeared biocompatible to NIH 3T3, MG-63, and MCF-7 cells. Moreover, cell invasion ability and cell survival rate after invasion through the 3BE was displayed to be comparable to Matrigel. Thus, these findings demonstrate that the 3BE hydrogel has a great potential as an alternative to a three-dimensional cell culture for drug screening applications.     

Effect of coupling agent content on properties of composites made from polylactic acid and chrysanthemum waste

Chrysanthemum flower is among one of the highly sought after and widely planted flower crops, in particular for cultural and religious ceremonies. However, the chrysanthemum stem and stalk have little value and usually discard as by‐product waste from floristry. The objective of this research is to investigate the potential value of utilizing chrysanthemum stem and stalk as reinforcing fillers for thermoplastic composites. In this study, 2‐mm thick composite sheet containing predefined formulations of polylactic acid (PLA), chrysanthemum waste filler (CWF) ranging from 15 to 60 phr, and maleated polyethylene (MAPE) coupling agent up to 5 phr were prepared with the aid of Haake internal mixer and compression molding. The effect of MAPE loading on tensile, thermal, and morphological properties of PLA/CWF composites was investigated. The findings revealed that PLA/CWF composite attained improved tensile modulus compared to the neat PLA, and the tensile modulus increases with higher concentration of CWF. However, both tensile strength and elongation at break reduces with increase loading of CWF. Overall, PLA/CWF composites with MAPE shows better performance compared to those without MAPE, where an optimum strength of 21.8 MPa can be achieved with 60 phr CW and 3 phr MAPE. The measured tensile strength is comparable to alternatives natural fiber thermoplastic composites demonstrating its potential to be used in non‐structurally demanding application. J. VINYL ADDIT. TECHNOL., 26:10–16, 2020. © 2019 Society of Plastics Engineers     

Antibacterial activity of propolis against Staphylococcus aureus

In the present study, antimicrobial activity of the ethanolic extract of propolis (EEP), collected at different periods (June, August, and October-November) from various regions (Taipei, Mingchien, and Fanglia) in Taiwan, against Staphylococcus aureus was investigated. The effects of cell age, incubation temperature, and pH in response to EEP were also investigated. Depending on concentration, collecting area, and time, EEP exerted various degrees of antibacterial activity against S. aureus. The minimum inhibitory concentration of EEP tested ranged from <3.75 to 60 microg/ml, while the minimum bactericidal concentration ranged between 7.5 and 120 microg/ml against S. aureus. In general, a higher antibacterial activity was noted with EEP collected in August than other months. EEP of Mingchien-6 showed the most profound antibacterial activity among the EEP samples tested. The age of a bacterial culture affected its susceptibility to EEP. Cells in the late-exponential phase were most susceptible to EEP. Higher temperature (37 degrees C) and acidic pH enhanced the antibacterial activity of EEP.