Estimating long-term time-resolved indoor PM2.5 of outdoor and indoor origin using easily obtainable inputs

To evaluate the separate impacts on human health and establish effective control strategies, it is crucial to estimate the contribution of outdoor infiltration and indoor emission to indoor PM_2.5 in buildings. This study used an algorithm to automatically estimate the long-term time-resolved indoor PM_2.5 of outdoor and indoor origin in real apartments with natural ventilation. The inputs for the algorithm were only the time-resolved indoor/outdoor PM_2.5 concentrations and occupants’ window actions, which were easily obtained from the low-cost sensors. This study first applied the algorithm in an apartment in Tianjin, China. The indoor/outdoor contribution to the gross indoor exposure and time-resolved infiltration factor were automatically estimated using the algorithm. The influence of outdoor PM_2.5 data source and algorithm parameters on the estimated results was analyzed. The algorithm was then applied in four other apartments located in Chongqing, Shenyang, Xi'an, and Urumqi to further demonstrate its feasibility. The results provided indirect evidence, such as the plausible explanations for seasonal and spatial variation, to partially support the success of the algorithm used in real apartments. Through the analysis, this study also identified several further development directions to facilitate the practical applications of the algorithm, such as robust long-term outdoor PM_2.5 monitoring using low-cost light-scattering sensors.     

PREPARATION AND ELECTROCHEMICAL PROPERTIES OF NANOSCALE POROUS CARBON ELECTRODE MATERIALS BASED ON RICE PLANT SOOT

Supercapacitors are a kind of novel energy storage devices with long cycle stability and high power density. Electrode materials selection is one of the key factors that affect the properties of supercapacitors. Biomass-derived electrode materials – being low cost, renewable and environmentally friendly – are therefore attracting researchers’ attention. In this work, we adopted a simple process of carbonization and activation with rice plant soot, a common biomass material, as carbon source, and finally obtained the nanoscale porous carbon electrode (NPCE) materials. Then, the electrochemical properties of the as-prepared NPCE materials were tested in 6 M KOH, and the results indicated that the specific capacitance could reach 216?Fg^?1. Therefore, this low-cost, highly efficient technique is a significant milepost towards environmentally sustainable and commercially feasible fabrication of carbon electrode materials from biomass sources.     

Fermentation dynamics of Lactobacillus helveticus H9 revealed by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry

Lactobacillus (L.) helveticus H9 is a probiotic strain that can produce antihypertensive peptides during milk fermentation. This study analysed the dynamics of skim milk fermentation by L. helveticus H9 by ultra‐performance liquid chromatography coupled to quadrupole time‐of‐flight mass spectrometry (UPLC/Q‐TOF MS). A total of 1992 metabolites were detected from all of the fermented samples in the LC‐MS analysis by multivariate statistical analysis. Metabolites with variable importance in projection (VIP) values ≥2 were considered differentially abundant among samples and were responsible for the unique taste and nutritional and functional qualities of fermented milk. Valine, threonine, l ‐methionine, tyrosine, asparagine and leucine were the predominant amino acids produced during fermentation, and their quantities changed remarkably during the fermentation process. Citric acid and uric acid were the major, and only detectable, organic acids. Some intermediate metabolites, such as N‐acryloylglycine and nicotinamide‐N‐oxide, were also detected. Moreover, certain oligopeptides such as Val‐Leu, Lys‐Gly, Ala‐Glu, Asp‐Ser, Leu‐Pro and Val‐Phe‐Ala were not detected until the middle and late fermentation periods. This study demonstrated dynamic metabolic changes, providing a strong foundation for deciphering the physiological and biochemical mechanisms of the fermentation process.     

表面电荷的调控对钛表面纤维连接蛋白吸附能力影响的研究

通过对钛片表面电荷的调控来改变纯钛表面的蛋白吸附能力,改善其生物学性能。将大颗粒喷砂酸蚀的样本分别浸泡在不同的溶液中,分别观察检测不同样本表面形貌及表面元素构成,各组样本的表面粗糙度,以及各组样本表面的电荷状况。最后检测各组样本的纤维连接蛋白吸附能力。结果表明,各组样本表面具有相似的表面形貌,不同组表面因为浸泡的液体不同其表面元素各不相同;各组样本的表面粗糙度无显著差异;而浸泡在氯化钙溶液中的钛片具有最高蛋白吸附能力(P0.01),而对照组大颗粒喷砂酸蚀组吸附能力最弱。将钛片浸泡在含有二价钙离子的氯化钙溶液中可以改变钛片表面的电荷状态,提升蛋白吸附能力,从而改善其生物学性能。     

An orange-emitting phosphor BaSrGa4O8:Bi3+,K+ with unique one-dimensional chain structure for high index color WLEDs

It has been an urgent need for developing a new bright long-wave emitting phosphor to improve the color rendering index (CRI) of white light-emitting diodes (WLEDs). Here, based on the concept of oxygen vacancy-induced long-wave emission by Bi³⁺ doping, we selected BaSrGa₄O₈ as the matrix, which has a low-dimensional chain structure that can produce enough oxygen vacancies. After the introduction of Bi³⁺, orange emission was successfully achieved. To further improve the luminescence efficiency, the system of BaSrGa₄O₈:Bi³⁺,K⁺ was designed. Interestingly, although significant emission enhancement was obtained, the material showed reduced absorption with increased oxygen vacancies. More detailed experimental evidences confirm that oxygen vacancies can activate Bi³⁺ to achieve long-wave emission. Our results provide a new way to design Bi³⁺-based long-wave emitting phosphors with low-dimensional crystal structure. Finally, a WLED device containing BaSrGa₄O₈:Bi³⁺,K⁺ was fabricated and exhibited an enhanced CRI, which shows a promising application in WLEDs.     

A study of external surface pressure effects on the properties for lithium-ion pouch cells

Lithium-ion pouch cells are widely used in electric vehicles because of their high energy density than other structures. There is an unavoidable external surface pressure between the cells in the process of packing and driving of electric vehicles. The influence of external surface pressure on the main properties of the lithium-ion pouch cell has been studied, which is of great significance to packing batteries and reusing retired cells. In this study, a testing device applied for the measurement of constant external surface pressures of lithium-ion pouch cells was first proposed and the different pressure stress-strain distribution on the external surface of cells under semirigid material pads were analyzed by simulation. The effects of pressure on the capacity, internal resistance, and open circuit voltage of fresh and aged LiNi_xCo_yMn_zO₂ (NCM) lithium-ion pouch cells are analyzed through experiments under 1 Mpa external surface pressure. The results show that the internal resistance of fresh cells tends to decrease. The average percentage of the maximum reduction of internal resistance is 13.28%. The experiments also demonstrate that the capacity of aging cells increased by 2.3%. Irreversibility of capacity improvement indicates applying appropriate external surface pressure can improve the secondary utilization efficiency of aging cells.     

Mechanical degradation of proton exchange membrane during assembly and running processes in proton exchange membrane fuel cells with metallic bipolar plates

The mechanical degradation of the proton exchange membrane (PEM) is one of the main aspects affecting the lifetime of proton exchange membrane fuel cells (PEMFCs). It was observed in our previous study that the stress/strain distribution in the PEM of fuel cells with metallic bipolar plates (BPPs) is more complex, owing to manufacturing and assembly errors of the BPPs. The present study further concentrates on the stress/strain evolution in the membrane of fuel cells throughout the assembly and running processes by a finite element model. In membranes at the joint area between the gasket and gas diffusion layers, a serious stress concentration aggravated as the misalignment displacement increases. As for the membrane in reaction area, the plastic strain reaches highest level at the center of the groove after hygrothermal loading. The maximum stress is mainly relevant to the temperature and humidity and has little concern with the misalignment. The model and results of this study offer guidance regarding the design of PEMFC. Owing to the stress concentration, an additional protection should be set in the joint area, and the assembly error should be limited within 0.05 mm.     

三维圆弧型井眼轨道设计模型的拟解析解

为了研究三维圆弧型井眼轨道设计方程组是否存在解析解以及如何有效求解，使用消去法从多元非线性方程组中推导出其中的某个未知数满足一个特征多项式方程，并且证明了该方程组的拟解析解可以由特征多项式方程的实数根和已知设计参数构成的解析公式计算得到；如果极点多项式非恒等于0，则当特征多项式次数不超过5时，如果有解则为解析解，否则为数值解。通过使用C++类实现多项式加减法、乘法的计算方法，提出了多项式实数根的分隔算法、并用二分法快速求解出多项式全部实数根的计算方案。该方法在数学上经严格推导，计算方案简洁、稳健，在三维井眼轨道设计、智能钻井定向控制中具有应用价值。     

Van der Waals Epitaxy of III-Nitride Semiconductors Based on 2D Materials for Flexible Applications

III-nitride semiconductors have attracted considerable attention in recent years owing to their excellent physical properties and wide applications in solid-state lighting, flat-panel displays, and solar energy and power electronics. Generally, GaN-based devices are heteroepitaxially grown on c-plane sapphire, Si (111), or 6H-SiC substrates. However, it is very difficult to release the GaN-based films from such single-crystalline substrates and transfer them onto other foreign substrates. Consequently, it is difficult to meet the ever-increasing demand for wearable and foldable applications. On the other hand, sp²-bonded two-dimensional (2D) materials, which exhibit hexagonal in-plane lattice arrangements and weakly bonded layers, can be transferred onto flexible substrates with ease. Hence, flexible III-nitride devices can be implemented through such 2D release layers. In this progress report, the recent advances in the different strategies for the growth of III-nitrides based on 2D materials are reviewed, with a focus on van der Waals epitaxy and transfer printing. Various attempts are presented and discussed herein, including the different kinds of 2D materials (graphene, hexagonal boron nitride, and transition metal dichalcogenides) used as release layers. Finally, current challenges and future perspectives regarding the development of flexible III-nitride devices are discussed.