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Mesoscopic-Scale Numerical Investigation Including the Influence of Process Parameters on LPBF Multi-Layer Multi-Path Formation

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Computer Modeling in Engineering & Sciences 2021年第1期126卷 5-23页

作者： Liu Cao Institute for Systems Rheology School of Mechanical and Electrical EngineeringGuangzhou UniversityGuangzhou Higher Education Mega CenterGuangzhou510006China

As a typical laser additive manufacturing technology,laser powder bed fusion(LPBF)has achieved demonstration applications in aerospace,biomedical and other ***,how to select process parameters quickly and reasonably is still themain concern of LPBF *** order to quantitatively analyze the influence of different process parameters(laser power,scanning speed,hatch space and layer thickness)on the LPBF process,the multilayer and multi-path forming process of LPBF was predicted based on the open-source discrete element method framework Yade and the open-source finite volume method framework *** on the design of experiments method,a four-factor three-level orthogonal test scheme was designed,and the porosity and surface roughness data of each calculation scheme were *** analyzing the orthogonal test data,it was found that as the laser power increased,the porosity decreased,and as the scanning speed,hatch space,and layer thickness increased,the porosity *** addition,the influence of laser power and scanning speed on surface roughness showed a trend of decreasing first and then increasing,while the influence of scanning distance and layer thickness on surface roughness showed amonotonous increasing *** order of the influence of each process parameter on porosity was:scanning speed>laying thickness>laser power>hatch space,and the order of the influence of each process parameter on surface roughness was:hatch space>layer thickness>laser power>scanning *** the porosity of the part is most sensitive to scanning speed,and the surface roughness is the most sensitive to hatch *** above conclusions are expected to provide process control basis for actual LPBF production of the 316L stainless steel alloy.

关键词： Laser powder bed fusion process parameter porosity surface roughness orthogonal test method numerical simulation

Relationship between depression,smartphone addiction,and sleep among Chinese engineering students during the COVID-19 pandemic

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World Journal of Psychiatry 2023年第6期13卷 361-375页

作者： Wen-Juan Gao Yan Hu Jun-Lin Ji Xin-Qiao Liu Institute of higher education Beihang UniversityBeijing 100191China school of Public Administration Beihang UniversityBeijing 100191China Research Center for Beijing higher education Development Beihang UniversityBeijing 100191China school of education Tianjin UniversityTianjin 300350China

BACKGROUND Existing research has demonstrated that depression is positively related to smartphone addiction, but the role of sleep has not been discussed thoroughly, especially among engineering undergraduates affected by the coronavirus disease 2019 *** To evaluate sleep as a mediator of the association between smartphone addiction and depression among engineering *** Using a multistage stratified random sampling method, a cross-sectional survey was conducted among 692 engineering undergraduates from a top engineering university in China, and data were collected by self-reported electronic questionnaires. The data included demographic characteristics, such as age, gender, the Smartphone Addiction Scale-Short Version(SAS-SV), the 9-item Patient Health Questionnaire, and the Pittsburgh Sleep Quality Index. Pearson correlation and multiple linear regression analyses were used to examine the association between smartphone addiction and depression, while structural equation models were established to evaluate the possible mediating role of *** Based on the cutoffs of the SAS-SV, the rate of smartphone addiction was 63.58 percent, with 56.21 percent for women and 65.68 percent for men, among 692 engineering students. The prevalence of depression among students was 14.16 percent, with 17.65 percent for women, and 13.18 percent for men. Smartphone addiction was positively correlated with depression, and sleep played a significant mediating effect between the two, accounting for 42.22 percent of the total effect. In addition, sleep latency, sleep disturbances, and daytime dysfunction significantly mediated the relationship between depression and smartphone addiction. The mediating effect of sleep latency was 0.014 [P < 0.01;95% confidence interval(CI): 0.006-0.027], the mediating effect of sleep disturbances was 0.022(P < 0.01;95%CI: 0.011-0.040), and the mediating effect of daytime dysfunction was 0.040(P < 0.01;95%CI: 0.024-0.059). Th

关键词： Smartphone addiction Depression Pittsburgh Sleep Quality Index Engineering students COVID-19 Mediating effect

Observation of topological charge transformations in acoustic vortex using passive periodic systems

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Science China(Physics,Mechanics & Astronomy) 2025年第1期Mechanics & Astronomy) .卷 140-147页

作者： Di-Chao Chen Xie Liu Changqing Xu Da-Jian Wu Ying Cheng Xiao-Jun Liu school of Physics and Technology Nanjing Normal University Key Laboratory of Modern Acoustics School of Physics Nanjing University

Vortex transmutation utilizes a periodic system, which not only enables the alteration of the topological charge(TC) of unstable input vortices but also facilitates their transformation into stable structures. This approach is crucial for investigating the characteristics of vortices in various wave systems. Here, we achieve acoustic vortex TC transmutation by employing a welldesigned dual-structured plate external system(DPES). The interactions between the acoustic vortex and the finite-order discrete rotational symmetry lead to the transformation of its topological charge when complete rotational symmetry is broken to Nthorder discrete symmetry. Our results experimentally demonstrate the acoustic vortex TC transmutation based on passive artificial structures, enabling numerous applications in particle manipulation and information multiplexing as well as advancing our understanding and control over free-space acoustic vortices.

关键词： acoustic vortex topological charge transformation artificial structure

Structural, elemental, optical and magnetic study of Fe doped ZnO and impurity phase formation

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Progress in Natural Science:Materials International 2014年第2期24卷 142-149页

作者： S.Karamat R.S.Rawat P.Lee T.L.Tan R.V.Ramanujan Natural Science and Science education National Institute of Education Nanyang Technological University COMSATS Institute of Information Technology Department of Physics Middle East Technical University school of Material Science and Engineering Nanyang Technological University Nanyang Avenue

We have prepared a series of(ZnO)1-x(Fe2O3)x≤0.10bulk samples with various concentrations of Fe dopant by ball milling and investigated their structural, compositional, optical and magnetic properties by means of X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS),Raman spectrometer and vibrating sample magnetometer(VSM), respectively. Information about different impurity phases was obtained through Rietveld refinements of XRD data analysis. XPS results showed different valence states(Fe2+ tand Fe3+) supported by shaking satellite peaks in samples. With increasing Fe doping percentage, the crystal quality deteriorated and a shift of E2 low band(characteristic of ZnO) has been observed in Raman spectra. Energy band gap estimated from reflectance UV–vis spectroscopy showed shift for all bulk samples. The magnetic behavior was examined using a vibrating sample magnetometer(VSM), indicating ferromagnetic behavior at room temperature(300 K). The effective magnetic moment per Fe atom decreases with increase in doping percentage which indicates that ferromagnetic behavior arises from the substitution of Fe ions in the ZnO lattice.

关键词： Fe doped ZnO Dilute magnetic semiconductor Rietveld refinements X-ray spectroscopy Band gap Magnetic moment

Can a polycentric structure affect travel behaviour?A comparison of Melbourne, Australia and Riyadh, Saudi Arabia

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Journal of Modern Transportation 2014年第3期22卷 156-166页

作者： M.Alqhatani S.Setunge S.Mirodpour school of Civil Environmental and Chemical EngineeringRMIT University Ministry of higher education

This study models the impact of the shift from a monocentric private-car-oriented city to polycentric public-transport-oriented city. Metropolitan areas have suffered traffic problems in particular increase in travel time and travel distance. Urban expansion, population growth and road network development have led to urban sprawl in monocentric cities. In many monocentric cities, travel time and distance has steadily increased and is only expected to increase in the future. Excessive travel leads to several problems such as air pollution, noise, congestion, reduction in productive time, greenhouse emissions, and increased stress and accident rates. This study examines the interaction of land use and travel. A model was developed and calibrated to Melbourne and Riyadh conditions and used for scenario analysis. This model included two parts： a spatial model and a transport model. The scenario analysis included variations of residential and activity distribution, as well as conditions of public transport service.

关键词： Monocentric Polycentric Private mode Public transport Four-step transport modelling

Enhancing Overseas Chinese Graduate Employability:The Case of Chinese Graduates with Finnish Academic Qualifications

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Frontiers of education in China 2014年第3期9卷 377-402页

作者： Yuzhuo CAI higher education Group School of ManagementUniversity of TampereTampere 33014Finland

This paper explores ways to enhance overseas Chinese graduate employability by taking Finnish-educated Chinese students/graduates as an *** so doing,it understands that graduate employability development is a joint effort of multiple stakeholders including students,graduates,academics,program coordinators,employers,and ***,it provides arguments and suggestions for how to enhance the employability of these graduates in terms of the labor market context,employers’beliefs and actions,the responsibilities of higher education institutions,and student/graduate *** also points out two major challenges faced by overseas Chinese graduates as well as their educational providers,which are linked respectively to gaps between what graduates acquire in higher education and what is required in the labor market,as well as gaps from the employers’perspective:areas where employers need to understand more about universities and catch up with new ideas generated by them.

关键词： graduate employability employers Finnish higher education intern-ational students Chinese graduates

A machine learning approach to map crystal orientation by optical microscopy

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npj Computational Materials 2022年第1期8卷 70-78页

作者： Mallory Wittwer Matteo Seita school of Mechanical and Aerospace Engineering Nanyang Technological UniversitySingaporeSingapore school of Materials Science and Engineering Nanyang Technological UniversitySingaporeSingapore

Mapping grain orientation in crystalline solids is essential to investigate the relationships between local microstructure and crystallography and interpret materials *** of the main techniques used to perform these studies is electron backscatter diffraction(EBSD).Due to the limited measurement throughput,however,EBSD is not suitable for characterizing samples with long-range microstructure heterogeneity,nor for building large material libraries that include numerous *** present a machine learning approach for high-throughput crystal orientation mapping,which relies on the optical technique called directional reflectance *** successfully apply our method on Inconel 718 specimens produced by additive manufacturing,which exhibit complex,spatially-varying *** results demonstrate that optical orientation mapping on a metal alloy is *** our method is data-driven,it can be easily extended to different alloy systems produced using different manufacturing processes.

关键词： alloy microstructure crystal

Toeplitz operators on Fock-Sobolev spaces with positive measure symbols

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Science China Mathematics 2014年第7期57卷 1443-1462页

作者： WANG XiaoFeng CAO GuangFu XIA Jin school of Mathematics and Information Science and Key Laboratory of Mathematics and Interdisciplinary Sciences of the Guangdong higher education Institute Guangzhou University

We discuss Toeplitz operators on Fock-Sobolev space with positive measure *** FockCarleson measure,we obtain the characterizations for boundedness and compactness of Toeplitz *** also give some equivalent conditions o... 详细信息

关键词： Fock-Sobolev space Toeplitz operator boundedness compactness Schatten p-class

Glass-forming ability and corrosion performance of Mn-doped Mg-Zn-Ca amorphous alloys for biomedical applications

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Rare Metals 2018年第7期37卷 579-586页

作者： Jian-Li Wang Yin Wan Zhi-Jun Ma Yong-Chun Guo Zhong Yang Ping Wang Jian-Ping Li school of Materials and Chemical Engineering Xi'an Technological University

In the present work, ribbon and 2-mm rod samples of Mg-Zn-Ca-Mn alloys were prepared by meltspinning and copper mold injection methods, respectively. Effects of Mn doping on glass-forming ability and corrosion performance in simulated body fluid of Mg65Zn30Ca5 alloy were studied through X-ray diffraction, scanning electron microscopy, differential scanning calorimeter, and electrochemical and immersion tests. Results show that with the Mn addition increasing, all the ribbon samples are completely in amorphous state. However, the microstructure of 2-mm rod samples transfers from fully amorphous for the Mn-free alloy to almost polycrystalline state with precipitated Mg, Mn, and MgZn phases. Glass-forming ability of Mg65Zn30Ca5 alloy is decreased by Mn addition. Results of electrochemical and immersion tests demon- strate that the Mn-doped samples exhibit more negative corrosion potential and larger corrosion current density, suggesting that the corrosion resistance decreases with doping amount of Mn element increasing.

关键词： Mg-Zn-Ca amorphous alloys Mn doping Glass-forming ability Corrosion performance