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Novel oxygen-enrichment method using annular air curtain for single-head roadway of plateau mine

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Building Simulation 2023年第7期16卷 1097-1113页

作者： zijun Li Rongrong Li Yu Xu Qiaoli wang School of Resources&Safety Engineering Central South UniversityChangsha 410083China

The low-oxygen environment restricts the exploitation of mineral resources on plateaus and affects miner’s safety.This paper proposes an oxygen-enrichment method using an annular air curtain.Through numerical simulation and experiments,it was confirmed that the proposed method improves the breathing environment in the single-head roadway of a plateau mine.Computational fluid dynamics(CFD)was used to investigate the oxygen-enriching effect and oxygen spatial distribution regularities after using the proposed oxygen-enrichment method in the single-head roadway of a plateau mine.The reliability of the CFD model was confirmed by experiment.Orthogonal testing was conducted to investigate the influence degree and optimal level combination of factors influencing oxygen enrichment.The results demonstrate that the annular air curtain effectively prevented oxygen loss,thus forming a local oxygen-rich space and improving the effective utilization rate of oxygen.Oxygen supply concentration and velocity are positively correlated with the oronasal oxygen mass fraction through a linear function,while the air curtain outlet wind velocity is negatively correlated with the oronasal oxygen mass fraction through a linear function.The annular air curtain diameter and oronasal oxygen mass fraction do not have an obvious functional relationship.When the annular air curtain diameter was greater than 0.9 m,the oronasal oxygen mass fraction was stable at approximately 25.30%.The influencing factors of the novel oxygen-enrichment method are,in descending order,as follows:oxygen supply concentration,annular air curtain diameter,air curtain outlet wind velocity,and oxygen supply velocity.The optimal level combination is oxygen supply concentration of 100%,oxygen supply velocity of 11 m/s,air curtain outlet wind velocity of 1.5 m/s,and annular air curtain diameter of 0.9 m.

关键词： plateau mine heading face oxygen enrichment air curtain CFD method

Ni-Al mixed metal oxide with rich oxygen vacancies: CO methanation performance and density functional theory study

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Chinese Journal of Chemical Engineering 2022年第6期35卷 73-83页

作者： Zhouxin Chang Feng Yu Zhisong Liu Zijun Wang Jiangbing Li Bin Dai Jinli Zhang Key Laboratory for Green Processing of Chemical Engineering of Xinjiang Bingtuan School of Chemistry and Chemical EngineeringShihezi UniversityShihezi 832003China Bingtuan Industrial Technology Research Institute Shihezi UniversityShihezi 832003China

Ni-Al mixed metal oxides have been successfully prepared by high shear mixer(HSM)and coprecipitation(CP)methods for low temperature CO methanation.In this work,Ni-Al(HSM-CP)catalyst presented small Ni crystallite size and high surface area,which all contribute to the methanation reaction at low temperature conditions.The obtained Ni-Al(HSM-CP)sample exhibited a mass of defective oxygen,thereby accelerating the dissociation of CO and ultimately increasing the activity of the catalyst.Ni-Al(HSM-CP)catalyst offered the best activity with CO conversion=100%and CH_(4) selectivity=93%at 300℃,and the CH_(4) selectivity can reach 81.8%at 200℃.In situ Fourier transform infrared spectroscopy and density functional theory show that CHO and COH intermediates with lower activation energy barriers are produced during the reaction,and hydrogen-assisted carbon–oxygen bond scission is more favorable.

关键词： Natural gas Carbon monoxide methanation High shear mixer Oxygen vacancy Homogeneous catalysis

NHC-catalyzed Redox-Neutral Aza-Benzoin Reaction of Aldehydes with Tetrahydroisoquinolines

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Chinese Journal of Chemistry 2020年第2期38卷 135-138页

作者： Di Jiang zijun Wu Jian wang School of Pharmaceutical Sciences Key Laboratory of Bioorganic Phosphorous Chemistry&Chemical Biology(Ministry of Education)Tsinghua UniversityBeijing 100084China

Summary of main observation and conclusion Tetrahydroisoquinoline derivatives are useful synthetic intermediates,which play an important role in the preparation of natural products,pharmaceuticals and other materials.Herein,we report an unprecedented redox-neutral aza-benzoin protocol to construct such scaffold.Upon exposure of tetrahydroisoquinolines to aromatic aldehydes in the prese nee of an NHC catalyst,the C-l acylated tetra hydroisoquinolines were obtained in moderate to good yields.

关键词： materials. quinoline aldehydes

Asymptomatic and pre-symptomatic infection in Coronavirus Disease 2019 pandemic

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Medical Review 2022年第1期2卷 66-88页

作者： Yutong wang Ke Zheng Wenjing Gao Jun Lv Canqing Yu Lan wang Zijun Wang Bo wang Chunxiao Liao Liming Li Department of Epidemiology and Biostatistics School of Public HealthPeking University38 Xueyuan RoadHaidian DistrictBeijing 100191China Peking University Centre for Public Health and Epidemic Preparedness and Response Beijing 100191China National Institute for Communicable Disease Control and Prevention Chinese Center for Disease Control and PreventionBeijingChina Meinian Public Health Institute Peking University Health Science CenterBeijingChina

With the presence of Coronavirus Disease 2019(COVID-19)asymptomatic infections detected,their proportion,transmission potential,and other aspects such as immunity and related emerging challenges have attracted people’s attention.We have found that based on highquality research,asymptomatic infections account for at least one-third of the total cases,whereas based on systematic review and meta-analysis,the proportion is about one-fifth.Evaluating the true transmission potential of asymptomatic cases is difficult but critical,since it may affect national policies in response to COVID-19.We have summarized the current evidence and found,compared with symptomatic cases,the transmission capacity of asymptomatic individuals is weaker,even though they have similar viral load and relatively short virus shedding duration.As the outbreak progresses,asymptomatic infections have also been found to develop long COVID-19.In addition,the role of asymptomatic infection in COVID-19 remains to be further revealed as the severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)variants continue to emerge.Nevertheless,as asymptomatic infections transmit the SARS-CoV-2 virus silently,they still pose a substantial threat to public health.Therefore,it is essential to conduct screening to obtain more knowledge about the asymptomatic infections and to detect them as soon as possible;meanwhile,management of them is also a key point in the fight against COVID-19 community transmission.The different management of asymptomatic infections in various countries are compared and the experience in China is displayed in detail.

关键词： asymptomatic coronavirus disease 2019 presymptomatic severe acute respiratory syndrome coronavirus 2.

Novel quantitative structure activity relationship models for predicting hexadecane/air partition coefficients of organic compounds

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Journal of Environmental Sciences 2023年第2期124卷 98-104页

作者： Ya wang Weihao Tang zijun Xiao Wenhao Yang Yue Peng Jingwen Chen Junhua Li State Key Joint Laboratory of Environment Simulation and Pollution Control School of EnvironmentTsinghua UniversityBeijing 100084China Key Laboratory of Industrial Ecology and Environmental Engineering(MOE) School of Environmental Science and TechnologyDalian University of TechnologyLinggong Road 2Dalian 116024China

Predicting the logarithm of hexadecane/air partition coefficient(L)for organic compounds is crucial for understanding the environmental behavior and fate of organic compounds and developing prediction models with polyparameter linear free energy relationships.Herein,two quantitative structure activity relationship(QSAR)models were developed with 1272 L values for the organic compounds by using multiple linear regression(MLR)and support vector machine(SVM)algorithms.On the basis of the OECD principles,the goodness of fit,robustness and predictive ability for the developed models were evaluated.The SVM model was first developed,and the predictive capability for the SVM model is slightly better than that for the MLR model.The applicability domain(AD)of these two models has been extended to include more kinds of emerging pollutants,i.e.,oraganosilicon compounds.The developed QSAR models can be used for predicting L values of various organic compounds.The van derWaals interactions between the organic compound and the hexadecane have a significant effect on the L value of the compound.These in silico models developed in current study can provide an alternative to experimental method for high-throughput obtaining L values of organic compounds.

关键词： L value Quantitative structure-activity relationship Multiple linear regression Support vector machine Oraganosilicon compounds

Experimental and numerical study on improvement performance by wave parallel flow field in a proton exchange membrane fuel cell

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Chinese Journal of Chemical Engineering 2022年第5期35卷 90-102页

作者： zijun Li Shubo wang Sai Yao Xueke wang Weiwei Li Tong Zhu Xiaofeng Xie School of Mechanical Engineering and Automation Northeastern UniversityShenyang 110819China Institute of Nuclear and New Energy Technology Tsinghua UniversityBeijing 100084China Beijing Institute of Space Launch Technology Beijing 100076China

The performance and operation stability of proton exchange membrane fuel cells(PEMFCs)are closely related to the transportation of reactants and water management in the membrane electrode assembly(MEA)and flow field.In this paper,a new three-dimensional wave parallel flow field(WPFF)in cathode was designed and analyzed throughout simulation studies and an experimental method.The experimental results show that the performance of PEMFC with WPFF outperforms that of PEMFC with straight parallel flow field(SPFF).Specifically,the peak power density increased by 13.45%for the PEMFC with WPFF as opposed to PEMFC with SPFF.In addition,the flow field with area of 11.56 cm^(2) was formed by the assembly of transparent end plate used for cathode and the traditional graphite plate used for anode.To understand the mechanism of the novel flow field improving the performance of PEMFC,a model of PEMFC was proposed based on the geometry,operating conditions and MEA parameters.The thickness of gas diffusion layers(GDL),catalytic layers(CL)and proton exchange membrane were measured by scanning electron microscope.The simulation result shows that compared with SPFF,the WPFF based PEMFC promote the oxygen transfer from flow channel to the surface of CL through GDL,and it was beneficial to remove the liquid water in the flow channel and the MEA.

关键词： Fuel cells Transport process Computational fluid dynamics Flow regimes Water management

Coupled relationships among anammox,denitrification, and dissimilatory nitrate reduction to ammonium along salinity gradients in a Chinese estuarine wetland

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Journal of Environmental Sciences 2021年第8期33卷 39-46页

作者： zijun Zhou Lei Ge Yufang Huang Yuqian Liu Siyang wang Institute of Yellow River Water Resources Protection Zhengzhou 450003China Yellow River Institute of Hydraulic Research Zhengzhou 450003China

Salinization in estuarine wetlands significantly alters the balance between their nitrogen(N)removal and retention abilities but these processes have not yet been characterized effectively.In the present study,the potential rates of sediment denitrification,anaerobic ammonium oxidation(anammox),and dissimilatory nitrate reduction to ammonium(DNRA)were mapped using N isotope tracing methods along salinity gradients across the Yellow River Delta wetland(YRDW)in China.The contribution of anammox to total dissimilatory N transformations in YRDW was merely 6.8%,whereas denitrification and DNRA contributed 52.3%and 40.9%,respectively.The potential rate of denitrification(5.82μmol/kg/h)decreased significantly along salinity gradients and markedly exceeded DNRA potential rate(2.7μmol/kg/h)in fresh wetlands,but was lower than that of DNRA in oligohaline wetlands(3.06 and 3.18μmol/kg/h,respectively).Moreover,a significantly positive relationship between salinity and DNRA/denitrification was obeserved,indicating that increased salinity may favor DNRA over denitrification.Furthermore,total sulfur(TS)content and ratio of total organic carbon to total nitrogen(C/N)increased with the salinity gradient and showed evident positive relationships with the DNRA/denitrification ratio.In this study,we proved that increased salinization resulted in the dominance of DNRA over denitrification,possible through the addition of S and alteration of the C/N in estuarine wetlands,leading to increased N retention in estuarine wetlands during salinization,which would enhance the eutrophication potential within wetlands and in downstream ecosystems.

关键词： Denitrification Anammox DNRA Salinity C/N ratio

Does More Trading Lead to Better Market Linkage?Evidence from the Commodity Futures Markets

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China Finance and Economic Review 2018年第1期7卷 50-72页

作者： Hung-Gay Fung Zijun Wang Lin Zhao College of Business Administration&Office of International Services and Program University of Missouri-St.LouisUSA Department of Finance College of BusinessUniversity of Texas at San AntonioUSA Department of Finance Martha and Spencer Love School of BusinessElon UniversityUSA

In this study,we use eight pairs of commodity futures data to investigate the impact of the recently launched nighttime trading session by Chinese futures exchanges.We conduct a thorough empirical analysis on the cross-market information transmission mechanisms between China and the U.S.We apply various econometric analyses including the co-integration analysis,the forecast error variance decomposition analysis,and the volatility spillover analysis with a bivariate GARCH model.Findings in this study indicate that,after the launching of nighttime-trading hours in China,the price discovery function of the Chinese futures market is noticeably improved,and that the Chinese market began to dominate the U.S.market in the bidirectional volatility spillover process.Thus,the introduction of the nighttime-trading hours appears to be an effective step toward China’s long-term goal of establishing pricing power in key commodities on the global financial market.

关键词： Chinese futures market market linkage nighttime trading

New Benchmark for Household Garbage Image Recognition

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Tsinghua Science and Technology 2022年第5期27卷 793-803页

作者： Zhize Wu Huanyi Li Xiaofeng wang zijun Wu Le Zou Lixiang Xu Ming Tan School of Artificial Intelligence and Big Data Hefei UniversityHefei 230601China School of Energy Materials and Chemical Engineering Hefei UniversityHefei 230601China

Household garbage images are usually faced with complex backgrounds,variable illuminations,diverse angles,and changeable shapes,which bring a great difficulty in garbage image classification.Due to the ability to discover problem-specific features,deep learning and especially convolutional neural networks(CNNs) have been successfully and widely used for image representation learning.However,available and stable household garbage datasets are insufficient,which seriously limits the development of research and application.Besides,the state-of-the-art in the field of garbage image classification is not entirely clear.To solve this problem,in this study,we built a new open benchmark dataset for household garbage image classification by simulating different lightings,backgrounds,angles,and shapes.This dataset is named 30 classes of household garbage images(HGI-30),which contains 18 000 images of 30 household garbage classes.The publicly available HGI-30 dataset allows researchers to develop accurate and robust methods for household garbage recognition.We also conducted experiments and performance analyses of the state-of-the-art deep CNN methods on HGI-30,which serves as baseline results on this benchmark.

关键词： benchmark household garbage image classification deep convolutional neural networks