Preparation of Ca(OH)2 nanoparticles by impinging stream reaction precipitation method

In this paper, Ca(OH)₂ nanoparticles are prepared by impinging stream co-precipitation method. The process of preparing nanoparticles by impinging stream is optimized. The influence of process variable, such as dispersant type, dispersant dosage, circulating flow rate, reactant concentration ratio of OH⁻ and Ca²⁺, reaction temperature and circulation time, on the particle size of Ca(OH)₂ nanoparticle are investigated. The results show that the concentration ratio of reactants has a significant effect on the size of Ca(OH)₂ nanoparticles. The optimal process conditions are obtained by single factor experiment, PEG6000, 3.3% dispersant dosage, Q = 1000 L · h⁻¹, C = 1.88, T = 46.68°C and t = 60 min. The average particle size of Ca(OH)₂ nanoparticles prepared under these conditions is 107.67 nm. According to the microstructure analysis, the prepared Ca(OH)₂ nanoparticles samples have high purity and a good crystal structure. The powder dispersed with a marked hexagonal crystal shape and good thermal decomposition.     

Large wood loads in an urban stream: The role of recruitment limitation versus transport dominance

Large wood (LW) has important physical and ecological functions in streams. Riparian vegetation is extensively removed during urban expansion, and urban streams may experience enhanced fluvial transport of LW due to flashy hydrology. In this study, LW loads were assessed for three reaches on North Buffalo Creek, an urban stream located in Greensboro, North Carolina, United States. These three reaches have similar hydrology but different riparian vegetation densities. We measured the frequencies and sizes of both in-channel LW and riparian vegetation across the three reaches. Our results showed that the recently reforested reach had greater LW volume (22.5 m³/km) compared to the unmanaged forested site (16 m³/km) and the site with low riparian vegetation density (4.78 m³/km). The difference in LW frequency among reaches was statistically significant ($p=.05$). However, the difference in the volume of individual pieces was not significantly different across reaches ($p=.84)$, indicating that a similar size of wood is recruited across the three sites. Our findings also showed that there is a positive relationship between riparian vegetation frequency and in-channel LW frequency, which are significantly related as a power function. Spatial lag models (integrating upstream riparian trees) did not show better results compared to a non-lagged model, suggesting that storage and recruitment were predominantly local and that the LW distribution at our reaches is limited by recruitment rather than dominated by fluvial transport. Our findings suggested that a fully forested watershed is not needed to provide some of the benefits of wood to urban streams.     

Combining taxonomic and functional approaches to assess land-use impacts on macroinvertebrate assemblages and improve bioindication

Most studies exploring land use impacts have focused on taxonomic metrics, but interest in the functional approach has increased because it helps to understand the relationships between community structure and functioning of aquatic ecosystems. We evaluated how functional and taxonomic approaches, and the association between them, contribute to assessing the effects of land use on macroinvertebrate assemblages of lowland streams. We sampled benthic macroinvertebrates in 17 sites with different land uses (agricultural, peri-urban, and extensive livestock) in Buenos Aires, Argentina. We computed the taxonomic metrics and biotic indexes as well as functional richness (FRic), divergence (FDiv), dispersion (FDis), and Rao diversity indexes for each site. We performed general linear mixed models to compare land-uses, a redundancy analysis, and also performed correlation analysis between taxonomic and functional indexes. Taxonomic richness was significantly higher in extensive livestock than in the other two land uses, while Shannon diversity was significantly different between land uses (extensive livestock > peri-urban > agriculture). FRic and FDiv were significantly lower in peri-urban land use than in agricultural and extensive livestock sites. Only taxonomic richness showed a significant and positive relationship with FRic, FDis, and Rao, but they fit better to a logarithmic function. Therefore, an increase in taxonomic richness and Shannon diversity did not necessarily imply an increase in the functional aspects of the macroinvertebrate assemblage. Using only one of these approaches could lead to partial evaluations and loss of information. Combining them could improve bioindication and predictive potential and help assess the effects of multiple stressors on freshwater ecosystems to improve biomonitoring.     

State of the art on quality control for data streams: A systematic literature review

These days, endless streams of data are generated by various sources such as sensors, applications, users, etc. Due to possible issues in sources, such as malfunctions in sensors, platforms, or communication, the generated data might be of low quality, and this can lead to wrong outcomes for the tasks that rely on these data streams. Therefore, controlling the quality of data streams has become increasingly significant. Many approaches have been proposed for controlling the quality of data streams, and hence, various research areas have emerged in this field. To the best of our knowledge, there is no systematic literature review of research papers within this field that comprehensively reviews approaches, classifies them, and highlights the challenges.In this paper, we present the state of the art in the area of quality control of data streams, and characterize it along four dimensions. The first dimension represents the goal of the quality analysis, which can be either quality assessment, or quality improvement. The second dimension focuses on the quality control method, which can be online, offline, or hybrid. The third dimension focuses on the quality control technique, and finally, the fourth dimension represents whether the quality control approach uses any contextual information (inherent, system, organizational, or spatiotemporal context) or not. We compare and critically review the related approaches proposed in the last two decades along these dimensions. We also discuss the open challenges and future research directions.     

撞击流—水力空化制备壳聚糖/蒙脱土复合材料及其应用

目的:解决传统机械搅拌制备壳聚糖/蒙脱土复合材料耗时长且不利于放大生产的问题。方法:利用撞击流—水力空化的方法制备壳聚糖/蒙脱土复合材料，考察了壳聚糖用量、壳聚糖相对分子质量、反应时间和反应温度4个因素对复合材料有机烧失率的影响，进而采用L₉(3⁴)正交试验优化制备材料的最佳方法。通过红外光谱、X射线衍射、扫描电镜、比表面分析仪对复合材料进行结构表征。结果:制备壳聚糖/蒙脱土复合材料的最优方案为：壳聚糖用量25 g、壳聚糖相对分子质量150万、空化时间20 min、空化反应温度80℃。在此条件下制备的复合材料的有机烧失率为37.42%,表征结果证明壳聚糖已成功负载到蒙脱土上，且复合材料依然具有蒙脱土的多孔结构。结论:撞击流—水力空化法与传统机械搅拌方法制备的复合材料相比，结构更疏松，比表面更大，有机烧失率、蔗汁脱色率更高，且撞击流—水力空化制备法更节省时间。     

An innovative application of multiple impinging jet flow field in fuel cells

The flow field in a fuel cell is expected to distribute the reactants as uniformly as possible over the active plate, support the reasonable pressure drop across the channel and maximize the mass transfer through the catalyst layers. To simultaneously accomplish these requirements, an innovative multiple impingement jet flow field (MIJFF) is proposed in this study. A three-dimensional thermo-fluid simulation is used to evaluate the proposed idea and compare its performance against the commonly used parallel field flow (PFF). The domain of calculations includes a channel with multiple impingement jets linked to a porous gas diffusion layer under low Reynolds flow conditions. The results reveal that the suggested MIJFF design significantly increases the transport of the reactant gases through the catalyst layer. The penetration depth into the catalyst layer in the MIJFF arrangement is higher than that of the PFF setup and the use of the catalyst layer is optimized, which in turn can lead to a reduction of the activation drop. Compared to a PFF design under similar operating conditions, the mean Nusselt number is shown to increase by a factor of about 3.5 in the MIJFF setup. Furthermore, the temperature is more uniformly distributed in the MIJFF pattern which results in more effective distribution of the reactant gases over the active surface. The current study shows that under equal pressure drop conditions, the MIJFF exhibits a much higher performance than a PFF channel design. That is while the corresponding flow rate for the MIJFF is much lower than that of PFF.