Preparation and characterization of monodisperse silica nanoparticles via miniemulsion sol–gel reaction of tetraethyl orthosilicate

Monodisperse silica nanoparticles were prepared via miniemulsion sol–gel reaction of tetraethyl orthosilicate (TEOS). Hexadecane (HD) or hexadecyltrimethoxysilane was used as costabilizer to effectively retard the Ostwald ripening process involved in TEOS miniemulsion. The Ostwald ripening behavior was characterized by dynamic light scattering (DLS), and it was adequately described by the modified Kabal’nov equation. The miniemulsion sol–gel reaction of TEOS/HD with a volume fraction (φ _c) of 0.024 at 80 °C is stable in the pH range 6–10. By contrast, gelation of reacting miniemulsions occurs at 70 and 100 min at pH 4 and 5, respectively. The weight-average silica particle size (d _w) of colloidal products prepared at 80 °C and pH 7 decreases from 59 to 36 nm with low polydispersity index (PDI, in the range 1.02–1.03), determined by transmission electron microscopy, when the φ _c of HD increases from 0.024 to 0.23. At constant φ _c (0.024), the resultant silica nanoparticles show larger d _w (83 nm) and PDI (1.35) for the TEOS/HD system at pH 10 as compared to the counterpart of pH 7. Furthermore, for the TEOS/HD system at pH 7 and low φ _c (0.024), d _w increases significantly with temperature being increased from 25 to 80 °C. By contrast, the effect of temperature on silica nanoparticle size becomes insignificant when a high level of HD (φ _c = 0.23) is used. Zeta potential measurements and field emission scanning electron microscopy were used to characterize the surface charge density and morphology of resultant silica nanoparticles.     

Large-eddy simulation of atmospheric boundary layer flow through wind turbines and wind farms

Accurate prediction of atmospheric boundary layer (ABL) flow and its interactions with wind turbines and wind farms is critical for optimizing the design (turbine siting) of wind energy projects. Large-eddy simulation (LES) can potentially provide the kind of high-resolution spatial and temporal information needed to maximize wind energy production and minimize fatigue loads in wind farms. However, the accuracy of LESs of ABL flow with wind turbines hinges on our ability to parameterize subgrid-scale (SGS) turbulent fluxes as well as turbine-induced forces. This paper focuses on recent research efforts to develop and validate an LES framework for wind energy applications. SGS fluxes are parameterized using tuning-free Lagrangian scale-dependent dynamic models. These models optimize the local value of the model coefficients based on the dynamics of the resolved scales. The turbine-induced forces (e.g., thrust, lift and drag) are parameterized using two types of models: actuator-disk models that distribute the force loading over the rotor disk, and actuator-line models that distribute the forces along lines that follow the position of the blades. Simulation results are compared to wind-tunnel measurements collected with hot-wire anemometry in the wake of a miniature three-blade wind turbine placed in a boundary layer flow. In general, the characteristics of the turbine wakes simulated with the proposed LES framework are in good agreement with the measurements in the far-wake region. Near the turbine, up to about five rotor diameters downwind, the best performance is obtained with turbine models that induce wake-flow rotation and account for the non-uniformity of the turbine-induced forces. Finally, the LES framework is used to simulate atmospheric boundary-layer flow through an operational wind farm.     

Recognizing hand gestures using the weighted elastic graph matching (WEGM) method

This paper proposes a weighted scheme for elastic graph matching hand posture recognition. Visual features scattered on the elastic graph are assigned corresponding weights according to their relative ability to discriminate between gestures. The weights' values are determined using adaptive boosting. A dictionary representing the variability of each gesture class is expressed in the form of a bunch graph. The positions of the nodes in the bunch graph are determined using three techniques: manually, semi-automatically, and automatically. Experimental results also show that the semi-automatic annotation method is efficient and accurate in terms of three performance measures; assignment cost, accuracy, and transformation error. In terms of the recognition accuracy, our results show that the hierarchical weighting on features has more significant discriminative power than the classic method (uniform weighting). The hierarchical elastic graph matching (WEGM) approach was used to classify a lexicon of ten hand postures, and it was found that the poses were recognized with a recognition accuracy of 97.08% on average. Using the weighted scheme, computing cycles can be decreased by only computing the features for those nodes whose weight is relatively high and ignoring the remaining nodes. It was found that only 30% of the nodes need to be computed to obtain a recognition accuracy of over 90%.     

高效液相色谱-串联质谱法测定火腿肠制品中11种杂环胺类化合物

目的 建立高效液相色谱-串联质谱法同时测定火腿肠制品中11种杂环胺类化合物含量的分析方法.方法 样品经5 mL水、10 mL 1％氨水乙腈(体积分数)振荡提取后,4 g Na2SO4,1g NaCl盐析,上清液经EMR-Lipid除脂小柱净化,以HSS T3色谱柱(2.1 mm×100 mm,1.8μm)分离待测物,采...     

食盐的质量安全管理及多品种盐发展的行业现状

盐业体制改革极大地释放了市场活力,食盐行业由国家宏观调控转变为市场调节生产和流通,全国各地监管部门加大了对食盐产品的质量安全管控。当前我国多品种盐市场蓬勃发展,品种繁多,但多品种盐行业标准体系不健全,由此导致行业发展出现诸多问题。本研究介绍了盐改后食盐的质量安全管理情况,幵对多品种盐目前的行业现状迚行深入剖析,有助于维护盐业市场秩序,促迚盐业市场规范健康有序发展。     

鱼类保活及运输方法的研究进展

结合鱼类保活运输中的主要因素(温度、水质、监控措施和鱼的自身体质等),详细阐述了活鱼运输的几种方法(尤其是模拟冬眠运输法),列举了几种常用麻醉剂的使用及优缺点。同时提出鱼类保活运输中亟待解决的问题,并对保活技术的发展趋势进行了预测。     

冀东典型蔬菜种植区设施土壤重金属特征

目的 探究冀东典型蔬菜种植区(唐山市和承德市)设施土壤重金属特征.方法 对设施大棚进行调查并采集表层土壤样品,检测其重金属,即镉(Cd)、汞(Hg)、砷(As)、铅(Pb)、铬(Cr)、铜(Cu)、锌(Zn)含量,并依据HJ/T 333—2006《温室蔬菜产地环境质量评价标准》进行了土壤质量评价.结果 除As外,其他重...     

A new blood flow volume sensor with embedded estimation of SpO2 to maximize its accuracy

Microsystem Technologies - A new portable blood flow volume (BFV) sensor is developed from the function of estimating oxygen saturation (SpO2) implemented inherently to maximize the accuracy of...