Surface Modification of Poly(vinylidene fluoride) Ultrafiltration Membranes with Chitosan for Anti-Fouling and Antibacterial Performance

Weiwei Xia,Manman Xie,Xia Feng,Li Chen,Yiping Zhao 한국고분자학회 2018 Macromolecular Research Vol.26 No.13

A graft copolymer (PVDF-g-PAA) having poly(vinylidene fluoride) (PVDF) backbones and poly(acrylic acid) (PAA) side chains was synthesized using the radical polymerization method and the PVDF-g-PAA copolymer membrane was prepared via immersion phase inversion. Then the chitosan was immobilized on the surface of the copolymer membrane by covalent bond. The morphology, surface chemical structure and performance of the modified membranes were characterized by scanning electron microscopy, attenuated total reflection-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, water contact angle, permeation measurement, antifouling and antibacterial tests. The results showed that the contact angle of the modified membrane decreased, and the water flux increased from 37.74Lm-2h-1 for pure PVDF membrane to 119.43 Lm-2h-1, which indicated that the modified membrane had higher hydrophilicity than unmodified membrane. The modified membrane has better antifouling properties than pure PVDF membrane due to the increase of surface hydrophilicity, and the highest water flux recovery ratio can achieve 93.2%. Furthermore, the modified membrane showed good antibacterial activity (E. coli), and the maximum antibacterial ratio of the modified membrane was 89.6%.

Aerodynamic effect of wind barriers and running safety of trains on high-speed railway bridges under cross winds

Weiwei Guo,He Xia,Raid Karoumi,Tian Zhang,Xiaozhen Li 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.20 No.2

For high-speed railways (HSR) in wind prone regions, wind barriers are often installed onbridges to ensure the running safety of trains. This paper analyzes the effect of wind barriers on the runningsafety of a high-speed train to cross winds when it passes on a bridge. Two simply-supported (S-S) PCbridges in China, one with 32 m box beams and the other with 16 m trough beams, are selected to performthe dynamic analyses. The bridges are modeled by 3-D finite elements and each vehicle in a train by amulti-rigid-body system connected with suspension springs and dashpots. The wind excitations on the trainvehicles and the bridges are numerically simulated, using the static tri-component coefficients obtained froma wind tunnel test, taking into account the effects of wind barriers, train speed and the spatial correlationwith wind forces on the deck. The whole histories of a train passing over the two bridges under strong crosswinds are simulated and compared, considering variations of wind velocities, train speeds and without orwith wind barriers. The threshold curves of wind velocity for train running safety on the two bridges arecompared, from which the windbreak effect of the wind barrier are evaluated, based on which a beamstructure with better performance is recommended.

Patterns of Cancer-Related Risk Behaviors Among Construction Workers in Hong Kong: A Latent Class Analysis Approach

Xia, Nan,Lam, Wendy,Tin, Pamela,Yoon, Sungwon,Zhang, Na,Zhang, Weiwei,Ma, Ke,Fielding, Richard Occupational Safety and Health Research Institute 2020 Safety and health at work Vol.11 No.1

Background: Hong Kong's construction industry currently faces a manpower crisis. Blue-collar workers are a disadvantaged group and suffer higher levels of chronic diseases, for example, cancer, than the wider population. Cancer risk factors are likely to cluster together. We documented prevalence of cancer-associated lifestyle risk behaviors and their correlates among Hong Kong construction workers. Methods: Data were collected from workers at 37 railway-related construction worksites throughout Hong Kong during May 2014. Tobacco use, alcohol consumption, unbalanced nutrition intake, and physical inactivity were included in the analysis. Latent class analysis and multivariable logistic regression were performed to identify the patterns of risk behaviors related to cancer, as well as their impact factors among construction workers in Hong Kong. Results: Overall, 1,443 workers participated. Latent class analysis identified four different behavioral classes in the sample. Fully adjusted multiple logistic regression identified age, gender, years of Hong Kong residency, ethnicity, educational level, and living status differentiated behavioral classes. Conclusion: High levels of lifestyle-related cancer-risk behaviors were found in most of the Hong Kong construction workers studied. The present study contributes to understanding how cancer-related lifestyle risk behaviors cluster among construction workers and relative impact factors of risk behaviors. It is essential to tailor health behavior interventions focused on multiple risk behaviors among different groups for further enlarging the effects on cancer prevention.

Crystallization characteristics prediction of coal slags based on SiO2–Al2O3–CaO–Fe2O3–MgO components

Xuan Weiwei,Zhang Jiansheng,Xia Dehong 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.59 No.-

Crystallization inside the liquid slag can increase the viscosity, affecting flow down the wall which is associated with the temperature of critical viscosity (Tcv). Four groups of synthetic slags with different Si/Al, Si + Al, CaO, Fe2O3 ratios were sorted to study the crystallization characteristics including the crystallization tendency as well as crystallization temperature (Tcrys). Samples with base–acid ratio (R > 0.7) and Si/Al in the range of 1–4 are liable to crystallize with obvious crystallization peak on DSC curve, and the influence of R is more than that of Si/Al. The crystallization temperature (Tcrys) is found to display a linear relationship with the liquidus temperature (Tliq). The deviation of real coal slag with synthetic slag is associated with the crystalline phases as well as the raw minerals present in the ash.

Aerodynamic effect of wind barriers and running safety of trains on high-speed railway bridges under cross winds

Guo, Weiwei,Xia, He,Karoumi, Raid,Zhang, Tian,Li, Xiaozhen Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.20 No.2

For high-speed railways (HSR) in wind prone regions, wind barriers are often installed on bridges to ensure the running safety of trains. This paper analyzes the effect of wind barriers on the running safety of a high-speed train to cross winds when it passes on a bridge. Two simply-supported (S-S) PC bridges in China, one with 32 m box beams and the other with 16 m trough beams, are selected to perform the dynamic analyses. The bridges are modeled by 3-D finite elements and each vehicle in a train by a multi-rigid-body system connected with suspension springs and dashpots. The wind excitations on the train vehicles and the bridges are numerically simulated, using the static tri-component coefficients obtained from a wind tunnel test, taking into account the effects of wind barriers, train speed and the spatial correlation with wind forces on the deck. The whole histories of a train passing over the two bridges under strong cross winds are simulated and compared, considering variations of wind velocities, train speeds and without or with wind barriers. The threshold curves of wind velocity for train running safety on the two bridges are compared, from which the windbreak effect of the wind barrier are evaluated, based on which a beam structure with better performance is recommended.

Changes of Carbohydrates Metabolism and Enzymes Activities in Low Temperature Storage for Bulbs of Lilium Oriental hybrids

Yiping Xia,Chunhui Huang,Guifang He,Weiwei Xu 한국원예학회 2006 한국원예학회 기타간행물 Vol.- No.-

Nonlinear aerostatic stability analysis of Hutong cable-stayed rail-cum-road bridge

Man Xu,Weiwei Guo,He Xia,Kebing Li 한국풍공학회 2016 Wind and Structures, An International Journal (WAS Vol.23 No.6

To investigate the nonlinear aerostatic stability of the Hutong cable-stayed rail-cum-road bridge with ultra-kilometer main span, a FEM bridge model is established. The tri-component wind loads and geometric nonlinearity are taken into consideration and discussed for the influence of nonlinear parameters and factors on bridge resistant capacity of aerostatic instability. The results show that the effect of initial wind attack-angle is significant for the aerostatic stability analysis of the bridge. The geometric nonlinearities of the bridge are of considerable importance in the analysis, especially the effect of cable sag. The instable mechanism of the Hutong Bridge with a steel truss girder is the spatial combination of vertical bending and torsion with large lateral bending displacement. The design wind velocity is much lower than the static instability wind velocity, and the structural aerostatic resistance capacity can meet the requirement.

Numerical analysis of wind field induced by moving train on HSR bridge subjected to crosswind

Wang, Yujing,Xia, He,Guo, Weiwei,Zhang, Nan,Wang, Shaoqin Techno-Press 2018 Wind and Structures, An International Journal (WAS Vol.27 No.1

To investigate the characteristics of the combined wind field produced by the natural wind field and the train-induced wind field on the bridge, the aerodynamic models of train and bridge are established and the overset mesh technology is applied to simulate the movement of high-speed train. Based on ten study cases with various crosswind velocities of 0~20 m/s and train speeds of 200~350 km/h, the distributions of combined wind velocities at monitoring points around the train and the pressure on the car-body surface are analyzed. Meanwhile, the difference between the train-induced wind fields calculated by static train model and moving train model is compared. The results show that under non-crosswind condition, the train-induced wind velocity increases with the train speed while decreases with the distance to the train. Under the crosswind, the combined wind velocity is mainly controlled by the crosswind, and slightly increases with the train speed. In the combined wind field, the peak pressure zone on the headstock surface moves from the nose area to the windward side with the increase of wind velocity. The moving train model ismore applicable in analyzing the train induced wind field.

Dynamic analysis of train-bridge interaction system with flexible car-body

Wang Kunpeng,Xia He,Xu Man,Guo Weiwei 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.9

Lighter vehicles are used in high-speed trains and urban rail transit trains, which leads to lesser stiffness of car-bodies, so car-bodyflexibility should be considered in dynamic analysis of the train-bridge system. In this paper, the vehicle model is established based onflexible multi-body dynamics, in which the car-body is simulated with an Euler beam, and the movement of the car-body is the superpositionof its rigid displacement and the generalized displacement of vibration mode of the Euler beam with free boundaries. The dynamicanalysis model of train-bridge model is established using the flexible car-body model. A case study is performed of an ICE3 train runningon a (48+80+48) m three-span continuous girder bridge. The calculated results show that the car-body flexibility has little influence onbridge responses and vehicle running safety indices, but great influence on car-body accelerations. It is necessary to consider the car-bodyflexibility, especially in studying the influence of additional bridge deformations on vehicle responses.

Rectifying resistance switching behaviors of SnO2 microsphere films modulated by top electrodes

Rongchun Yuan,Weiwei Xia,Mengxue Xu,Zhilei Miao,Shudong Wu,Xiuyun Zhang,Junhui He,Qiang Wang 한국물리학회 2020 Current Applied Physics Vol.20 No.3

Based on the bipolar resistive switching (RS) characteristics of SnO2 films, we have fabricated a new prototypical device with sandwiched structure of Metal/SnO2/fluorine-doped tin oxide (FTO). The SnO2 microspheres film was grown on FTO glass by template-free hydrothermal synthesis, which was evaporated with various commonly used electrodes such as aluminium (Al), silver (Ag), and gold (Au), respectively. Typical self-rectifying resistance switching behaviors were observed for the RS devices with Al and Au electrodes. However, no obvious rectifying resistance switching behavior was observed for the RS device with Ag electrode. Above results were interpreted by considering the different interface barriers between SnO2 and top metal electrodes. Our current studies pave the ways for modulating the self-rectifying resistance switching properties of resistive memory devices by choosing suitable metal electrodes.