表面织构形状对牙轮钻头轴承摩擦学性能影响的实验研究

牙轮钻头滑动轴承作为钻头破岩过程中传递载荷的关键部件,在低速重载的钻井过程中易发生黏着磨损失效。为改善牙轮钻头滑动轴承的耐磨性能,利用纳秒激光雕刻技术,在牙轮钻头滑动轴承轴颈表面加工了面积比为10%、深度为20μm的圆形、矩形、三角形及复合织构;基于赫兹相似理论,设计近似模拟钻头轴承工况的环-块配对副单元实验方案,并在UMT摩擦试验机上开展织构形状对钻头滑动轴承摩擦副摩擦因数、磨损量、温升变化和微观形貌影响规律的实验研究。结果表明:仿生织构的形状及布置方式对减摩和耐磨效果影响极大,其中圆形、矩形织构的减摩和耐磨性能最优,其次为三角形织构,而复合织构反而增大了摩擦因数及磨损量;单一织构对试件磨损量及温升的影响不大,而复合织构在增加摩擦的同时温度有明显升高,不利于井下高温环境下延长牙轮钻头寿命。     

沿空切顶成巷段巷道围岩变形规律研究

以宏景塔一矿回采工作面为研究对象,基于切顶卸压无煤柱自动成巷技术原理,采用数值模拟计算和现场实测的方法,对该矿成巷段巷道围岩支承压力分布及围岩变形规律进行分析。研究结果表明:随着工作面向前推进,巷道围岩支承压力呈先增大后减小最后趋于稳定的变化趋势,支承压力稳定值为13.5 MPa;受工作面回采动压的影响,距离工作面70 m以内,锚索受力急剧增大到恒阻值、巷道围岩变形明显;距离工作面70~150 m,锚索受力迅速减小、巷道围岩变形逐渐变缓;在距离工作面150 m之后,锚索受力仅有微量变化、巷道围岩变形趋于稳定。因此确定支护体回撤保守安全位置为工作面后方150 m。工程实践表明:所设支护体回撤距离能够应对巷道围岩变形,成巷效果良好。     

提高Mn系低温脱硝催化剂抗硫抗水性能的国内外研究概述

介绍了氮氧化物的来源、SCR脱硝的反应机理和工艺流程、催化剂的硫和水中毒机理,重点介绍了国内外学术和工业界为提高催化剂抗硫和抗水性能所做的研究和尝试,旨在推动低温SCR技术的进展,促进该技术早日实现在工业上的大规模应用。     

肾脏内科住院患者感染病原菌分布及耐药性分析

目的:调查肾脏内科住院患者感染病原菌分布和耐药性，为临床治疗细菌感染的抗菌药物选择提供依据。方法:收集2016年1月至2019年6月期间入住皖南医学院弋矶山医院肾脏内科患者送检标本培养阳性病原菌数据。结果:共培养出286株细菌，以呼吸道感染和泌尿道感染为主。革兰阴性菌占比89.51%，革兰阳性菌占比10.49%。革兰阴性菌中，肠杆菌科细菌检出前三位细菌分别是大肠埃希菌、肺炎克雷伯菌和阴沟肠杆菌，非发酵阴性菌检出前二位细菌分别是铜绿假单胞菌、鲍曼不动杆菌；其中产超广谱β内酰胺酶细菌（ESBLs）检出率为32.87%，以大肠埃希菌和肺炎克雷伯菌为主，对氨曲南和头孢曲松耐药率分别为83.8%和100%；碳青霉烯类耐药菌检出率为6.29%。在革兰阳性菌中金黄色葡萄球菌最常见，其中耐甲氧西林金黄色葡萄球菌（MRSA）检出率为4.89%。结论:在本院肾脏内科住院患者细菌感染中，产ESBLs大肠埃希菌和肺炎克雷伯菌检出率高。     

耐腐蚀水性铝颜料的制备及表征

为了提高铝颜料在水性涂料中的耐腐蚀性能，以正硅酸乙酯（ TEOS）为前驱物，通过溶胶-凝胶反应在铝颜料表面形成了一层致密的二氧化硅包覆薄膜，通过优化固含量、溶剂种类及 TEOS的用量，提高铝颜料的耐碱性。利用扫描电镜、刮板试验、接触角测试、析氢实验进行表征，结果表明：以无水乙醇为溶剂，铝金属颜料固含量为 10%，升温至 50 ℃后，逐滴加入 6 g TEOS，再升温至 80 ℃，该条件下制备的 SiO₂膜包覆后的铝颜料具有优异的耐碱性，同时表面性能由疏水性转变成亲水性，对铝颜料起到了很好的保护作用。     

Effects of SDBS and ZrO2 additives on the microstructure and properties of silicon-bonded SiC porous ceramics

Porous silicon-bonded silicon carbide (SBSC) ceramics were prepared under argon atmosphere, with silicon as pore former and bonding material, simultaneously, sodium dodecyl benzene sulfonate (SDBS) and ZrO₂ as sintering additives, the effects of SDBS and ZrO₂ on the porosity, pore size, mechanical, physical and thermal properties and microstructures were investigated. The results suggested that suitable content of SDBS and ZrO₂ could not only effectively lower the sintering temperature to 1450 °C due to the sticky flow of molten silicon, but also increase the pore structure and improve the bending strength. The reason for this is that SDBS decomposed into Na₂O which reacted with ZrO₂ and impurity SiO₂, which was the native oxide film on the surface of SiC particles, to form a bonding phase between SiC particles to improve the bending strength; meanwhile, the disappearances of impurity SiO₂ would benefit the bond of molten silicon and silicon carbide particles, and silicon melt leaving pores in its original position to increase the pore structure. The optimal apparent porosity, bending strength, average pore size, gas permeance and residual bending strength after thermal shock cycles of SBSC porous ceramic sintered at 1450 °C with 5 wt% SDBS and 6 wt% ZrO₂ were 38.33%, 55.4 MPa, 11.3 μm, 106.4 m³/m²·h·kPa and 28.2 MPa, respectively.     

CFD modeling of thermal contact resistance between solid contacting surfaces

Heat transfer has considerable applications in different industries such as designing of heat exchanger, nuclear reactor cooling, control system for spacecraft, and designing of microelectronics cooling. As the surfaces of two metals contact each other, this issue becomes so crucial. Thermal contact resistance (TCR) is one of the key physical parameters in heat transfer of mentioned surfaces. Measuring the experimental value of TCR in laboratory is highly expensive and difficult. As an alternative, numerical modeling methods could be engaged. In this study, inverse problem method solution is utilized as a proper method for estimation of TCR value. In this order, three different configurations (flat-flat, flat-cylinder, and cylinder-cylinder) were utilized in two steady and unsteady state conditions to predict the value of TCR. A comparison between the measured values and obtained values from the simulation show the errors for flat-flat, flat-cylinder, and cylinder-cylinder configuration after 10 min from starting the experiment are 4.6074%, 0.1662%, and 0.5622%, respectively. And in steady-state condition, the corresponding errors are 6.06e-3%, 1.506%, and 0.846%, respectively. In conclusion, the final results establish the fact that the inverse problem method solution can predict TCR values between contacting surfaces.     

Electrical oscillation generation with current-induced resistivity switching in VO2 micro-channel devices

We report large amplitude modulation waveforms as large as ~ 10 V using vanadium dioxide micro-channel devices operating under current-controlled conditions. The self-sustained electrical oscillations were generated by controlling the applied current in the negative differential resistance region of the investigated devices. An appropriate value of internal capacitance was achieved as parasitic capacitance in the device structure to stabilize the electrical oscillations. This eliminates the need of an external pulsed source or any external passive component connected to the micro-channel devices. Amplitude and frequency of the oscillation were tuned by illuminating the device micro-channel with an external laser. An equivalent circuit model was developed to simulate the waveforms. A good agreement between experiment and simulation was verified.     

Pharmacokinetic Parameters of HIV-1 Protease Inhibitors

Since the beginning of the HIV epidemic, research has been carried out to control the virus. Understanding the mechanisms of replication has given access to the various classes of drugs that over time have transformed AIDS into a manageable chronic disease. The class of protease inhibitors (PIs) gained notice in anti-retroviral therapy, once it was found that peptidomimetic molecules act by blocking the active catalytic center of the aspartic protease, which is directly related to HIV maturation. However, mutations in enzymatic internal residues are the biggest issue for these drugs, because a small change in biochemical interaction can generate resistance. Low plasma concentrations of PIs favor viral natural selection; high concentrations can inhibit even partially resistant enzymes. Food-drug/drug-drug interactions can decrease the bioavailability of PIs and are related to many side effects. Therefore, this review summarizes the pharmacokinetic properties of current PIs, the changes when pharmacological boosters are used and also lists the major mutations to help understanding of how long the continuous treatment can ensure a low viral load in patients.