Numerical Simulation of Edge Effect in Resin Transfer Molding for Plain-weave Fabric

Wenkai Yang,Shihong Lu,Wenhao Liu 한국섬유공학회 2020 Fibers and polymers Vol.21 No.9

Plain-weave fabric is a kind of fiber preform which has been commonly used in resin transfer molding (RTM) tomanufacture polymer composites. However, the edge area of plain-weave fabric is easy to shed yarns which will cause theuneven distribution of permeability between edge channel and center of mold in filling process of RTM. Meanwhile, theuneven distribution of permeability will cause the edge effect and seriously affect the final quality of composite materials. Inthis paper, a method to numerically calculate the permeability of edge channel which fully considers the edge area of plainweavefabric is proposed. The experiment and simulation of edge effect in filling process are performed. The results showthat the simulation of edge effect which applies the edge channel’s permeability calculated by this method are in goodagreement with the experimental results. The research in this paper is meaningful to improve the accuracy of edge effectsimulation so as to provide a reference for the design of mold structure.

Non-isothermal Simulation of Edge Effect in LCM Process for Plain-Weave Fabric

Wenkai Yang 한국섬유공학회 2023 Fibers and polymers Vol.24 No.11

Edge effect is a common phenomenon in liquid composite molding (LCM), which has a significant impact on the performance of composite components. Plain-weave fabric is widely used in LCM process. Nevertheless, the yarns of plain-weave fabric in edge area are easy to shed which will cause the edge effect. Meanwhile, the current LCM process is non-isothermal, which the infiltration effect and curing efficiency are improved by heating the resin and the mold. Few systemic researches can be found in the edge effect of LCM process caused by shedding yarns under non-isothermal conditions. This article applied a method to calculate the permeability which considered the yarn shedding of plain-weave fabric. A non-isothermal rheological model of resin is established through resin viscosity and differential scanning calorimetry (DSC) experiments. A simulation model of the edge effect due to yarns shedding under non-isothermal conditions is proposed. This model divides the flow region into the central area, edge area and gap area. Simulation of edge effect is realized by setting three different permeability areas and combining them with the non-isothermal rheological model. Simulation results of edge effect are verified by the non-isothermal flow experiments.

Catalytic pyrolysis of corn straw for deoxygenation of bio-oil with different types of catalysts

Wenkai Zhang,Ze Wang,Tengze Ge,Cuiguang Yang,Wenli Song,Songgeng Li,Rui Ma 한국화학공학회 2022 Korean Journal of Chemical Engineering Vol.39 No.5

Corn straw can be converted to bio-oil through pyrolysis. However, the application of bio-oil is severelyrestricted due to the high content of oxygen. Catalytic pyrolysis is an available way for deoxygenation of bio-oil, and thedeoxygenation reactions are strongly dependent on the type of catalyst. Whereas, the correlation between the deoxygenatedproducts and the catalyst types is still far from clear. In this work, the migration of O in the pyrolysis processwas investigated, and eight catalysts were screened for deoxygenation of bio-oil, with a lab-scale fixed-bed reactor. Theresults showed that with the increase of pyrolysis temperature, the content of O in bio-oil decreased below 400 oC andthen became stable and finally increased rapidly after 550 oC, indicating that the range of 400-550 oC was the propertemperature for deoxygenation. Eight catalysts (ZSM-5, SAPO-34, ZnO, MgO, -Al2O3, -Al2O3, acidified--Al2O3 andacidified--Al2O3) were tested, and it was found that a higher alkalinity of catalyst was favorable for decarboxylation ofbio-oil with more produced CO2, while a higher acidity was promoted the decrease of alcohols and carbonyls withmore generation of H2O and/or CO. MgO was judged as the optimal catalyst for deoxygenation of bio-oil. The qualityof bio-oil under the catalysis of MgO was best, with higher H/C and lower O/C.

Comparative Effects and Safety of Full-Endoscopic Versus Microscopic Spinal Decompression for Lumbar Spinal Stenosis: A Meta-Analysis and Statistical Power Analysis of 6 Randomized Controlled Trials

Zechuan Yang,Huan Wang,Wenkai Li,Weihua Hu 대한척추신경외과학회 2022 Neurospine Vol.19 No.4

Objective: This meta-analysis with statistical power analysis aimed to evaluate the difference between full-endoscopic and microscopic spinal decompression in treating spinal stenosis. Methods: We searched PubMed, Embase, CENTRAL (Cochrane Central Register of Controlled Trials), and CNKI (China National Knowledge Infrastructure) for relevant randomized controlled trials (RCTs) regarding the comparison of full-endoscopic versus microscopic spinal decompression in treating lumbar spinal stenosis through February 28, 2022. Two independent investigators selected studies, extracted information, and appraised methodological quality. Meta-analysis was conducted using RevMan 5.4 and STATA 14.0, and statistical power analysis was performed using G*Power 3.1. Results: Six RCTs involving 646 patients met selection criteria. Meta-analysis suggested that, compared with microscopic decompression, full-endoscopic spinal decompression achieved more leg pain improvement (mean difference [MD], -0.20; 95% confidence interval [CI], -0.30 to -0.10; p = 0.001), shortened operative time (MD, -12.71; 95% CI, -18.27 to -7.15; p < 0.001), and decreased the incidence of complications (risk ratio, 0.43; 95% CI, 0.22–0.82; p = 0.01), which was supported by a statistical power of 98.57%, 99.97%, and 81.88%, respectively. Conclusion: Full-endoscopic spinal decompression is a better treatment for lumbar spinal stenosis, showing more effective leg pain improvement, shorter operative time, and fewer complications than microscopic decompression.

H2 Metabolism revealed by metagenomic analysis of subglacial sediment from East Antarctica

Zhifeng Yang,Yu Zhang,Yongxin Lv,Wenkai Yan,Xiang Xiao,Bo Sun,Hongmei Ma 한국미생물학회 2019 The journal of microbiology Vol.57 No.12

Subglacial ecosystems harbor diverse chemoautotrophic microbial communities in areas with limited organic carbon, and lithological H2 produced during glacial erosion has been considered an important energy source in these ecosystems. To verify the H2-utilizing potential there and to identify the related energy-converting metabolic mechanisms of these communities, we performed metagenomic analysis on subglacial sediment samples from East Antarctica with and without H2 supplementation. Genes coding for several [NiFe]- hydrogenases were identified in raw sediment and were enriched after H2 incubation. All genes in the dissimilatory nitrate reduction and denitrification pathways were detected in the subglacial community, and the genes coding for these pathways became enriched after H2 was supplied. Similarly, genes transcribing key enzymes in the Calvin cycle were detected in raw sediment and were also enriched. Moreover, key genes involved in H2 oxidization, nitrate reduction, oxidative phosphorylation, and the Calvin cycle were identified within one metagenome-assembled genome belonging to a Polaromonas sp. As suggested by our results, the microbial community in the subglacial environment we investigated consisted of chemoautotrophic populations supported by H2 oxidation. These results further confirm the importance of H2 in the cryosphere.

Research on Fuzzy Fractional Order PID Control of Liquid Temperature in Displacement Digester

Minghui Li,Wenkai Wu,Xingkui Yang 한국펄프·종이공학회 2020 펄프.종이기술 Vol.52 No.5

Erratum: Optimal Structure Design and Performance Analysis of Multiphase Twin screw Pump for Wet Gas Compression

Xuejing Zhang,Junhu Yang,Wenkai Bei,Wei Han,Canyang Chen,Le Yang 한국유체기계학회 2021 International journal of fluid machinery and syste Vol.14 No.3

Optimal Structure Design and Performance Analysis of Multiphase Twin-screw Pump for Wet Gas Compression

Xuejing Zhang,Junhu Yang,Wenkai Bei,Wei Han,Canyang Chen,Le Yang 한국유체기계학회 2021 International journal of fluid machinery and syste Vol.14 No.2

The efficiency of multiphase twin-screw pump decreases sharply under wet gas conditions (GVF>95%) with severe vibration and thermal problems. Based on the design characteristics of twin-screw pump and screw compressor, a design method of multigradient variable pitch decompression screw pump is to address these problems in this paper. This method keeps the cross section profiles of screw pump unchanged,only changes the pitch of screw. According to the design concept of decompression of screw compressor, the screw rotor is divided into three regions from the inlet to the outlet. The pitch of screw and thread width in these regions are designed separately to increase the volumetric efficiency of the screw pump and reduce the vibration. The effective clearance leakage model of twin-screw pump is simplified and modified. Considering two-phase back flow and combining mechanical model with thermodynamic model, the flow capacity, volumetric efficiency, pressure, and temperature distribution of new and conventional screw pumps are predicted by non-isothermal compression model. The calculations show that the design scheme of multi-gradient variable-pitch decompression screw pump can solve the volumetric efficiency and vibration problems under wet gas conditions fundamentally and can significantly reduce the power consumption of screw pump. However, the problem of temperature rise of screw pump still exists. Cooling system for the screw pump should be designed to continuously cool the screw pump.

The effects of a summer reading program for migrant children in migrant schools: First-year results from a randomized experiment

Qian Guo,Young-Suk Grace Kim,Yan Liu,Yan Peng,WENKAI SUN,Yijie Wang,Li Yang 서울대학교 교육연구소 2021 Asia Pacific Education Review Vol.22 No.1

Thanks to urbanization, some developing countries have a large migrant population. Academic performance of migrant children is usually far from satisfactory, much to the concern of educators and legislators. Meanwhile, research has attested to the importance of reading skill development by the end of third grade for later academic achievement. Against this background, we evaluated the effects of providing self-selected, developmentally appropriate books on the reading performance and summer reading amount of students in migrant schools in China, employing a randomized controlled trial. The intervention program improved rising second-graders’ word reading scores and summer reading amount. It proved particularly beneficial to low-performing children and children from disadvantaged families. The findings have implications for improving the academic achievement of migrant children in migrant schools in China and similar developing countries, especially where parental support may not be expected for the academic development of children.

Response of Photosynthetic Characteristics to Different Salicylic Acid Concentrations in Relation to Waterlogging Resistance in Zanthoxylum armatum

Peiyun Wang,Chengyi Su,Jiaojiao Wu,Yuxin Xie,Jiangtao Fan,Jingyan Wang,Wenkai Hui,Hua Yang,Wei Gong 한국원예학회 2023 원예과학기술지 Vol.41 No.4

Zanthoxylum armatum (Rutaceae) is an important spice and a traditional medicinal plant in southwest China. Owing to its shallow root system, it is highly susceptible to waterlogging stress. To evaluate how an exogenous salicylic acid (SA) application reduces photosynthetic damage in Z. armatum under waterlogging stress conditions, the content of photosynthetic pigments and gas exchange and chlorophyll fluorescence parameters were studied under different SA concentrations (0, 1 and 2 mM) and different numbers of waterlogging days (1, 2 and 3 d) to identify the mechanisms underlying the seedlings’ waterlogging response. The results showed that waterlogging significantly affects the photosynthetic characteristics in leaves. An exogenous SA application increased the contents of photosynthetic pigments as well as the transpiration rate (Tr), net leaf photosynthetic rate (Pn), stomatal conductance (Gs), water use efficiency (WUE), actual quantum efficiency (ΦPSII), photosystem II (PSII) maximum quantum efficiency (Fv/Fm), PSII photochemical efficiency in light (Fv'/Fm'), and electron transport rate (ETR), whereas the treatment decreased the intercellular carbon dioxide concentration (Ci), non-photochemical quenching coefficient (NPQ) and minimum fluorescence (Fo). Therefore, the SA application helps improve the photosynthetic efficiency and reduce photodamage to Z. armatum in the event of waterlogging stress.