Optically transparent Li–Al–CO3 layered double hydroxide thin films on an AZ31 Mg alloy formed by electrochemical deposition and their corrosion resistance in a dilute chloride environment

An optically transparent Li–Al–CO₃ layered double hydroxide (LDH) film was formed on an AZ31 substrate by applying DC voltage between the cathode (AZ31) and the anode (stainless steel) in a Li⁺/Al³⁺ aqueous solution. The film thickness increased with electrolysis time. The LDH-coated sample exhibited low corrosion rate in NaCl solution, which was consistent with the results from long-term corrosion testing in a high-humidity environment. The LDH film exhibited good corrosion performance, which mainly resulted from its high hydrophobicity and its increased surface pH value during corrosion testing.     

All-ceramic lead-free percolative composite with a colossal dielectric response

All-ceramic lead-free percolative composite, comprising RuO₂ with high electrical conductivity denoted as the conductive phase and ferroelectric (K, Na)NbO₃ ceramics, was developed. Structural analysis revealed a uniform distribution of conductive ceramic grains within the ceramic matrix. Consequently, the dielectric response in the (K, Na)NbO₃–RuO₂ composite follows the predictions of the percolation theory. Thus, close to the percolation point exceptionally high values of the dielectric constant were obtained—values as high as 20,000 were detected at room temperature at 1 kHz. Fit of the data, obtained for samples of different compositions, revealed critical exponent and percolation point, which reasonably agree with the theoretically predicted values.     

Improved properties of PTFE composites filled with glass fiber modified by sol–gel method

PTFE/GF(glass fiber) composites are widely applied in high-frequency printed circuit board (PCB) substrate materials due to the excellent dielectric properties of PTFE and the low thermal expansion coefficient of GF. However, the poor interface compatibility between PTFE and GF affects the performance of the composite substrates. In this study, tetraethyl orthosilicate (TEOS) was used as the silicon source, and polydimethylsiloxane (PDMS) was the organic precursor to modify the surface of GF through the sol–gel method to promote the interface compatibility of GF and PTFE. The modified GF noted T-GF was filled in PTFE to prepare PTFE/T-GF composites. SEM, FTIR, XPS, and contact angle confirmed that organic–inorganic hybrids were successfully loaded on GF's surface. Moreover, compared with PTFE/GF and the conventional coupling agent modified GF filled PTFE composites, the PTFE/T-GF exhibited improved dielectric constant (2.305), decreased dielectric loss (9.08E^?4), higher bending strength (21.45 MPa) and bending modulus (522 MPa), better thermal conductivity (0.268 W/m*K) and lower CTE (70 ppm/°C), making it has promising application as the substrate materials for high frequency PCB.

     

二维 Volterra-Fredholm 积分方程数值算法研究及收敛性分析

针对一类二维非线性Volterra-Fredholm积分方程,提出利用二维Block-Pulse函数为基函数进行数值求解。首先,引入Block-Pulse函数的定义及基函数的向量表示形式;其次,根据二维Block-Pulse函数的不相交性和正交性推导了基向量的积分算子矩阵和乘积算子矩阵;然后,基于该算子矩阵将待求问题转化为一系列向量的乘积形式,利用配点法离散未知变量获得原问题的数值解;最后,通过两个具体的数值算例对所提算法的可行性和收敛性进行了验证。     

Navier-Stokes/Darcy 模型的 BDF2 模块化梯度散度稳定格式的数值分析

Navier-Stokes/Darcy 方程可用来模拟河流中的污染物对地下水的污染问题,以及血液在血管及器官间的渗透问题等,由于其在实际中的广泛应用,对其数值方法的研究受到广泛关注。提出了求解Navier-Stokes/Darcy方程的BDF2模块化梯度散度稳定数值格式,这种格式通过增加稳定化项,提高了解的有效性和精确性,在保留梯度散度稳定格式优点的同时,可以有效的避免大的稳定化参数对解的非正常影响,给出了格式的稳定性和误差分析。最后,通过数值算例验证了理论分析的正确性。     

The bio-activation of pozzolanic activity of circulating fluidized-bed fly ash by Paenibacilllus mucilaginosus

The present investigation reports an eco-friendly biotechnology applying Paenibacilllus mucilaginosus (P.m), a silicate solubilizing bacteria, to activate pozzolanic activity of CFA. The results show SiO₂ and Al₂O₃ dissolution rate of CFA treated by P.m and its Ca²⁺ absorption capacity in saturated Ca(OH)₂ solutions are increased compared to raw CFA indicating that pozzolanic reactivity of CFA is improved by P.m. One reason is destruction of the anhydrite coating layer of CFA particles surface through P.m erosion. Another reason is promotion of SiO₂ dissolution caused by deformation and destruction of Si-O-Si (Al) bonds by P.m. Carbonic anhydrase activity of P.m is one of the main factors involved in dissolution of SiO₂, which also induces CaCO₃ mineralization. The hardening characteristics and hydration products of CFA-15% lime system with different content of P.m further confirm the effects of P.m on pozzolanic activity of CFA. 40% P.m incorporation is conducive to promote CFA hydration, ettringite earlier formation and bio-mineralization, thereby improving the mechanical properties of hardened mortar. Incorporation of 40% P.m in cement blended with CFA results in that CFA content is increased by 5–20% and the 28d strength improved by 11.5–23.9 MPa. This is the first report of microbial activation of CFA pozzolanic activity.     

基于Agent的井下透水事故逃生模型研究

为探讨井下发生透水事故时矿工逃生的可能性和成功逃生的比率,帮助矿工在复杂的井下环境和突发事故中准确选择逃生路线,建立了基于Agent的井下透水事故逃生模型。通过对井下人员在灾害中的生理和心理的需求进行分析,提取出了模型的运行规则。利用RePast软件建模仿真矿工的逃生行为,随机地生成逃生路线。模型运行结果表明：在井下发生透水事故时,利用模型生成的逃生路线能够有效降低井下人员的死亡率,帮助Agent安全逃生。     

模糊免疫PID控制在矿用设备座椅减振系统中的应用

针对现有矿用设备座椅减振系统因弹簧无法控制而导致减振效果不佳的问题,介绍了一种矿用设备座椅减振系统的组成及工作原理,重点阐述了模糊免疫PID控制在该系统中的应用方案。该系统以PLC为主控制器,通过气缸组件工作状态的变化调整气体弹簧的刚度,从而实现座椅减振;针对系统非线性、时变性、滞后性等特点,采用模糊免疫PID控制策略进行减振控制。仿真和应用结果表明,采用模糊免疫PID控制的矿用设备座椅减振系统鲁棒性高,驾驶员乘坐舒适性好,满足实际使用要求。     

Optimal βk-stable interval in VPRS-based group decision-making: A further application

This study extends the extant research on use of variable precision rough set (VPRS) for group decision-making (GDM), where the optimal β_k-stable interval is derived for the best group consensus. Firstly, we introduce the basic concepts a VPRS model encompasses, and the approach of VPRS-based GDM. Next, using a mathematical programming approach, we derive the optimal β_k-stable interval for DM_k. Then, an application in petroleum project investment risk management, including risk-based project selection and risk ranking, is investigated. The results suggest that β_k-stable intervals have significant impacts on risk management.     

中间相炭微球的活化与成孔过程的研究

以沥青中间相炭微球为原料，采用KOH作活化剂制备高比表面积活性炭。考察了碱炭比、活化温度和保温时间等工艺因素对活性炭结构与碘吸附性能的影响。研究表明：活性炭的比表面积、总孔容与碘吸附性能随碱炭比、活化温度和保温时间的变化均呈先增大后减小的趋势，孔径分布随碱炭比的增大、活化温度的提高和保温时间的延长向孔径增大的方向位移。由于具有独特的层状结构，中间相炭微球在KOH活化成孔过程中表现出明显的各向异性，与垂直层面方向上相比，孔隙更容易在平行层面方向上形成和生长。