Assessment of chemical and microbiological parameters of indoor swimming pool atmosphere using multiple comparisons

The aim of this study was to evaluate the air quality of an indoor swimming pool, analyzing diurnal and seasonal variations in microbiological counts and chemical parameters. The results indicated that yeast and bacteria counts, as well as carbon dioxide (CO₂), nitrogen oxides (NO_x) and O₃ concentrations, showed significant diurnal difference. On the other hand, temperature, relative humidity (R.H.), yeast counts and concentrations of CO₂, particles, O₃, toluene, and benzene showed seasonal differences. In addition, the relationship between indoor and outdoor air and the degree of correlation between the different parameters have been calculated, suggesting that CO₂, fine particles and NO_x would have indoor origin due to the human activity and secondary reactions favored by the chemical and environmental conditions of the swimming pool; while O₃, benzene and toluene, would come from outside, mainly. The overall results indicated that indoor air quality (IAQ) in the swimming pool building was deficient by the high levels of CO₂ and microorganisms, low temperatures, and high R.H., because frequently the limits established by the legislation were exceeded. This fact could be due to the poor ventilation and the inadequate operation of heating, ventilation, and air‐conditioning systems.     

Low dielectric constant polyimide mixtures fabricated by polyimide matrix and polyimide microsphere fillers

Polyimide microspheres were prepared via non‐aqueous emulsion polymerization by using pyromellitic dianhydride (PMDA) as anhydride monomer and 2,2‐bis(4‐(4‐aminophenoxy)phenyl)propane as amine monomer. The polyimide microspheres were well characterized by Fourier transform infrared spectroscopy, SEM and laser particle size analyzer. They were spherical in shape and monodisperse and their size was 31–33 μm. Polyimide mixtures formed by polyimide microspheres as fillers and polyimide composed of pyromellitic and dianhydride 4,4′‐oxydianiline (ODA) as matrix were investigated with regard to thermal properties, dielectric properties and mechanical properties. With 10%–50% polyimide microspheres in the polyimide mixtures, the dielectric constants were 2.26–2.48 (1 MHz) and the loss tangents were 0.00663–0.00857 (1 MHz), which were both significantly lower than the values for ODA‐PMDA polyimide. The decomposition temperature and glass transition temperature were above 440 and 290 °C. The polyimide mixtures possessed excellent thermal resistance. When the percentage of polyimide microsphere addition was 30%, the polyimide mixtures had the largest tensile strength (128.50 MPa) and elongation at break (9.01%). These results indicate that the polyimide microspheres were used as both low dielectric fillers and reinforcing fillers. © 2020 Society of Chemical Industry     

一种相位测试用曲口面天线的设计与应用

相位测试技术可满足不同外形天线罩的在线测试需求。通过数值仿真,设计最佳变换曲线完成矩形 传输波导与圆形辐射天线的拟合连接,能够有效降低天线驻波比,实现测试探头的高增益收发,提升测试有效性。 在维持驻波比参数前提下,对天线口面弧线给予二次曲率调整,可以适应不同外形天线罩的测试稳定性要求。根据 仿真结果加工的低驻波比反射相位测试天线,已应用于多个型号天线罩成型中的相位在线测试,提高了监控的有效 性,验证了设计仿真结果的正确性。     

Structure and electrical properties of Zn-doped BiFeO3 films

BiFe_1−xZn_xO₃ (x = 0, 0.5, 1, 1.5, 2 mol%) (BFZO) films were prepared on ITO/glass substrates by a sol-gel method. The effects of different Zn contents on the structures and electrical properties of the BFZO films were investigated. From X-ray diffraction (XRD), microstructure and X-ray spectroscopy (XPS) results, the BFZO films with a Zn content of 1 mol% showed a better crystal structure and grain development, and the Fe²⁺ and oxygen vacancy concentrations in this sample were the lowest among all the evaluated BFZO films. The P-E hysteresis loop indicated that the BFZO films with 1 mol% Zn had the highest remanent polarization (2Pr), which was 82.4 μC/cm², along with a coercive field (2E_c) of 887 kV/cm at the tested electric field of 857 kV/cm. The BFZO film with 1 mol% Zn had the lowest leakage current density, which was 3.54 × 10⁻⁷ A/cm² at the tested electric field of 200 kV/cm. Both at high and low electric fields, the space charge-limited current (SCLC) conduction mechanism was the main leakage mechanism. When the test frequency was 10⁵ Hz, the dielectric constant was 133, and the dissipation factor was 0.015.     

面向流屑角突变建模的切削状态参数经验公式的获得及应用

从提高流屑角突变模型的预测精度出发,建立了切削状态参数与3个切削控制参数之间关系的新经验公式。提出了一种通过迭代法准确设定有限元仿真软件刀-屑摩擦因数的方法,并通过直角切削Al6061-T6工件的有限元仿真试验,获得了一组不同切削控制参数组合条件下的切削状态参数数据。根据该数据拟合出剪切角φ、刀-屑摩擦角β、剪切应力τs关于刀具前角γ0、进给量f和切削速度v的经验公式,并通过一组直角切削试验,验证了所得经验公式的有效性。将新建经验公式应用于流屑角突变建模过程后,所得模型关于突变临界切削宽度的平均预测误差减小了27.2%。     

Effect of Sr doped the YFeO3 rare earth ortho-ferrite on structure,magnetic properties,and microwave absorption performance

Given the remarkable performances of rare earth multiferroic ortho-ferrites with magnetic optical and dielectric properties, the Y_1-xSr_xFeO₃ (x = 0, 0.05, 0.1, 0.15) perovskite structure microwave absorbing ferrite materials was successfully synthesized by Sr²⁺ ions A-site doping based on sol-gel technology in this paper. The XRD of all samples was refined with FullProf software, which confirmed the formation of the orthogonal perovskite structure (SG: Pnma). The SEM and TEM results display the average particles size of the samples is distributed between 110 and 160 nm. The increase of Sr doping concentration leads to the increase of particles size, which may be related to the growth of preferred orientation and incomplete substitution. The XPS analysis shows that Fe³⁺ was accompanied by the presence of Fe²⁺ with the doping of Sr²⁺ ions and oxygen vacancies increased significantly. The samples change from weak ferromagnetic state to paramagnetic state with the increase of Sr content. The minimum reflection loss (RL) of the Y_0.95Sr_0.05FeO₃ samples at 12.2 GHz reached −30.87 dB with thickness of 2.2 mm, where its effective absorption bandwidth (EAB, RL ≤ −10 dB) reached 2.4 GHz (11.3–13.7 GHz). Moreover, the EAB of the Y_0.85Sr_0.15FeO₃ samples reached 2.64 GHz, and the corresponding range is 9.0–11.6 GHz (X-band).     

A recurrent neural network using historical data to predict time series indoor PM2.5 concentrations for residential buildings

Due to the severe outdoor PM2.5 pollution in China, many people have installed air-cleaning systems in homes. To make the systems run automatically and intelligently, we developed a recurrent neural network (RNN) that uses historical data to predict the future indoor PM2.5 concentration. The RNN architecture includes an autoencoder and a recurrent part. We used data measured in an apartment over the course of an entire year to train and test the RNN. The data include indoor/outdoor PM2.5 concentration, environmental parameters and time of day. By comparing three different input strategies, we found that a strategy employing historical PM2.5 and time of day as inputs performed best. With this strategy, the model can be applied to predict the relatively stable trend of indoor PM2.5 concentration in advance. When the input length is 2 h and the prediction horizon is 30 min, the median prediction error is 8.3 µg/m³ for the whole test set. For times with indoor PM2.5 concentrations between (20,50] µg/m³ and (50,100] µg/m³, the median prediction error is 8.3 and 9.2 µg/m³, respectively. The low prediction error between the ground-truth and predicted values shows that the RNN can predict indoor PM2.5 concentrations with satisfactory performance.     

Quantitative study of the kinetics of hydrogen evolution reaction on aluminum surface and the influence of chloride ion

The behaviors and kinetics of hydrogen evolution reaction (HER) on pure aluminum with passive film in the presence and absence of chloride ion are quantitatively investigated by using the tip generation/substrate collection mode of scanning electrochemical microscopy (SECM) with dual Al/Pt ultramicroelectrode (UME) as tip electrode and Pt UME as substrate electrode. The standard rate constants k⁰ and transfer coefficients α_H of HER in ClO₄⁻- and Cl⁻-containing solution are 6.9 × 10⁻⁷ cm/s and 0.22, 7.1 × 10⁻⁶ cm/s and 0.19, respectively. Results show that the kinetic of HER is slow and the destruction of Cl⁻ on passive film can significantly promote the HER on Al surface. Moreover, these α_H far less than commonly used 0.5 in corrosion research, can explain the great difference between theoretical Tafel slopes and experimental results. Besides, the existence of current plateau in Al electrode explains the large difference in corrosion potential during parallel testing.     

基于项目的电类课程过程性考核模式的探索与应用

目前高等学校的考核方式存在一定的弊端:考试内容中记忆成分占比较大、考试形式单一、一次考试定成绩、考试反馈不够等等,因此应该加大过程性考核的比例,增加平时成绩的占比,注重学习过程中对知识的积累,针对电类课程特点,课程具有实践性、工程性、创新性,因此探索基于项目的过程性考核方式,促进以学为中心的教学方式,克服教师的满堂灌的现象,提高学生的创新实践能力。     

ZL109铝合金车削表面完整性实验研究

设计了三因素四水平正交车削实验,综合运用极差分析、方差分析等方法,研究了切削参数对硅铝合金ZL109车削表面完整性的影响规律,得到了切削参数对于表面粗糙度、残余应力和显微硬度的影响程度和趋势,分析了ZL109车削表面完整性的形成机理,以期为切削参数优选提供实验和理论基础。研究结果表明,进给量f对表面粗糙度具有显著影响,切削速度v和进给量f增加会导致表面残余拉应力增大,显微硬度受切削参数的影响较小。