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Journal of Bionic Engineering 2017年第4期14卷 746-758页

作者： Loan Thi kim Au Hoang Vu Phan hoon Cheol Park Department of Advanced Technology Fusion and Artificial Muscle Research Center Konkuk University Seoul Korea

In previous work, we modified blade element theory by implementing three-dimensional wing kinematics and modeled the unsteady aerodynamic effects by adding the added mass and rotational forces. This method is referred to as Unsteady Blade Element Theory （UBET）. A comparison between UBET and Computational Fluid Dynamics （CFD） for flapping wings with high flapping frequencies （〉30 Hz） could not be found in literature survey. In this paper, UBET that considers the movement of pressure center in pitching-moment estimation was validated using the CFD method. We investigated three three-dimensional （3D） wing kinematics that produce negative, zero, and positive aerodynamic pitching moments. For all cases, the instantaneous aerodynamic forces and pitching moments estimated via UBET and CFD showed similar trends. The differences in average vertical forces and pitching moments about the center of gravity were about 10% and 12%, respectively. Therefore, UBET is proven to reasonably estimate the aerodynamic forces and pitching moment for flight dynamic study of FW-MAV. However, the differences in average wing drags and pitching moments about the feather axis were more than 20%. Since study of aerodynamic power requires reasonable estimation of wing drag and pitching moment about the feather axis, UBET needs further im- provement for hilzher accuracy.

关键词： blade element theory unsteady computational fluid dynamics flapping wings biomimetic

Structural,Sintering and Electrical Properties of Cr-doped La_(0.6)Sr_(0.4)Cr_xFe_(1-x)O_(3-δ)(x=0.10,0.20) Oxides

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Journal of Materials Science & Technology 2012年第7期28卷 654-660页

作者： LinlinZhu Jong Pyo kim Sou Hwan Son Jung hoon Park State Key SLaboratory of Catalysis.Dalian Institute of Chemical Physics Chinese~Academy of Sciences Dalian 116023 China Greenhouse Gas Research Center Climate Change Technology Research Division Korea Institute of Energy ResearchDaejeon 305-343 Korea College of Chemistry and Materials Science Liaoning University of Petroleum and Chemical Technology Fushun113001 China

The perovskite Cr-doped La0.6Sr0.4CrxFe1-xO3-δ （x=0.10, 0.20） oxides were synthesized via the citrate gel method. The perovskite forming of the Lao.6Sr0.4CrxFel-xO3-δ （x=0.10, 0.20） oxides were studied by ther- mogravimetric analysis （TG）, differential scanning calorimetry （DSC）, and X-ray diffraction （XRD）. Structural and chemical stability under H2-containing helium atmospheres of Lao.6Sro.4CrxFel-xO3-δ （x=0.10, 0.20） were investigated by TG and XRD. The sintering microstructures of the perovskite Lao.6Sr0.4Cr2Fel-xO3-δ （x--0.10, 0.20） ceramics were investigated by scanning electron microscopy （SEM）, and the electrical conduc- tivities of both oxide ceramics were also measured up to 900℃. The results demonstrated that the chemical stability of the Co-free ***.4CrxFe1-xO3-δ （x=0.10, 0.20） oxides was significantly improved compared to the Co-containing Lao.6Sr0.4C00.2Fe0.8O3-δ and Ba0.5Sr0.5Co0.8Fe0.2O3-δ oxides. The incorporation of Cr cations in the B-site of the pervoskite oxides resulted in the improved structural and chemical stability of the as-synthesized Lao.6Sr0.4CrxFe1-xO3-δ （x=0.10, 0.20） oxides.

关键词： Perovskite Crystal structure Sintering Electrical conductivity

Longitudinal Flight Dynamic Analysis on Vertical Takeoff of a Tailless Flapping-Wing Micro Air Vehicle

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Journal of Bionic Engineering 2018年第2期15卷 283-297页

作者： Loan Thi kim Au Vu Hoang Phan hoon Cheol Park Department of Advanced Technology Fusion and Artificial Muscle Research Center Konkuk University Seou105029 Korea

This paper first analyzed the longitudinal dynamic behavior during vertical takeoff without control of a Flapping-Wing Micro Air Vehicle （FW-MAV）. The standard linear flight dynamics based on small disturbances from trim condition was not applicable for our analysis because the initial flight condition, which was at rest on the ground, could be such a large disturbance from the trim condition that the linearization is invalid. Therefore, we derived linearized Equations of Motion （EoM） which can treat an untrimmed flight condition as a reference for disturbances. The Computational Fluid Dynamic （CFD） software ANSYS Fluent was used to compute the aerodynamic forces and pitching moments. Three flight modes were found： a fast subsidence mode, a slow subsidence mode and a divergence oscil- latory mode. Due to divergence oscillatory mode, the deviation from the reference flight grew with time; the FW-MAV tumbled without control. The simulation showed for the first 0.5 second after leaving the ground （the time that is long enough for delay of feedback control）, the FW-MAV flew up to a height of 6 cm with small horizontal and pitching motion, which is close to a vertical flight.

关键词： bioinspired FW-MAV flight dynamics vertical takeoff CFD linear theory

Variation in dynamic deformation behavior and resultant yield asymmetry of AZ80 alloy with extrusion temperature

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Journal of Materials Science & Technology 2020年第11期42卷 225-236页

作者： Sang-hoon kim Sang Won Lee Byoung Gi Moon Ha Sik kim Sung Hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu702701South Korea Implementation Research Division Korea Institute of Materials ScienceChangwon51508South Korea

In this work,variation in the dynamic recrystallization(DRX)and dynamic precipitation behavior of AZ80 alloy during extrusion due to changes in extrusion temperature was investigated,and the resultant microstructure and yield asymmetry were *** the extrusion temperature increases from 250℃to 350℃,the primary DRX mechanism changes from twin-induced DRX to discontinuous DRX,resulting in an increase in the DRX area fraction and un DRXed grain *** addition,as the extrusion temperature rises,Mg17Al12 precipitation during extrusion decreases sharply throughout the extruded *** reduction in the compressive yield strength(CYS)with increasing extrusion temperature is more pronounced than it is for the tensile yield strength(TYS),which ultimately increases the yield asymmetry of the extruded *** higher extrusion temperature has less of an influence on the TYS due to the promotion of certain hardening *** the other hand,the greater reduction in the CYS is attributed to the increased fraction and size of regions in which{1012}twins predominantly form and the lower amount of precipitates,which effectively facilitates{1012}twinning.

关键词： Magnesium alloys Extrusion Recrystallization Precipitation Yield asymmetry

Extrusion limit diagram of AZ91–0.9Ca–0.6Y–0.5MM alloy and effects of extrusion parameters on its microstructure and mechanical properties

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Journal of Magnesium and Alloys 2022年第12期10卷 3447-3458页

作者： Dong HeeLee Ye Jin kim Sang-hoon kim Byoung Gi Moon Sung Hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea Agency for Defense Development Daejeon 34186Republic of Korea Advanced Metals Division Korea Institute of Materials ScienceChangwon 51508Republic of Korea

An AZ91–0.9Ca–0.6Y–0.5MM(AZXWMM91100) alloy, which has higher corrosion resistance, ignition resistance, and extrudability than a commercial AZ91 alloy, has been developed recently. In this study, the AZXWMM91100 alloy is extruded at various temperatures(300–400 ℃) and ram speeds(1–14.5 mm/s), and the cracking behaviors, microstructure, and tensile properties of the extruded materials are systematically analyzed. On the basis of the pressure limit and surface and internal cracking limit, the extrusion limit diagram providing a safe extrusion processing zone is established. All of the materials extruded at temperatures and speeds within the safe extrusion processing zone have high surface quality and moderate tensile ductility with an elongation higher than 10%. Moreover, they have a fully recrystallized grain structure and contain undissolved particle stringers arranged parallel to the extrusion direction. The grain size of the extruded material does not show any relationship with the Zener–Hollomon parameter(Z). However, the yield strength(YS) of the extruded material is inversely proportional to the logarithm of the Z value, and their relationship is expressed as YS =-31.2·log(Z) + 536. These findings may broaden the understanding of the AZXWMM91100 alloy with excellent chemical and physical properties and provide valuable information for the development of high-performance extruded Mg products using this alloy.

关键词： Magnesium Extrudability Extrusion limit diagram Microstructure Tensile properties

Factors associated with significant liver fibrosis assessed using transient elastography in general population

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World Journal of Gastroenterology 2015年第4期21卷 1158-1166页

作者： Seng Chan You Kwang Joon kim Seung Up kim Beom Kyung kim Jun yong Park Do Young kim Sang hoon Ahn Won Jae Lee Kwang-Hyub Han Department of Internal Medicine Yonsei University College of MedicineSeoul 120-752South Korea Division of Endocrinology and Metabolism Yonsei University College of MedicineSeoul 120-752South Korea Institute of Gastroenterology Yonsei University College of MedicineSeoul 120-752South Korea Liver Cirrhosis Clinical Research Center Seoul 120-752South Korea Seoul Gookgwain School Seoul 110-521South Korea

AIM: To investigate the prevalence of significant liver fibrosis assessed using transient elastography(TE) and its predictors in asymptomatic general ***: A total of 159 subjects without chronic viral hepatitis who underwent comprehensive medical health check-up between January 2012 and July 2012 were prospectively recruited. Significant liver fibrosis was defined as liver stiffness value > 7.0 k ***: The mean age and body mass index(BMI) of the study population(men 54.7%) was 56.0 years and 24.3 kg/m2. Among the study subjects, 11(6.9%) showed significant liver fibrosis. On univariate analysis, BMI, alanine aminotransferase(ALT), homeostasis model assessment of insulin resistance, carotid intimal media thickness(IMT), number of calcified plaques on carotid ultrasound, and visceral fat area on computed tomography were significantly higher in subjects with significant liver fibrosis than in those without(all P < 0.05). However, on multivariate analysis, BMI [odds ratio(OR) =1.487; P = 0.045], ALT(OR = 1.078; P = 0.014), carotid IMT(OR = 3.244; P = 0.027), and the number of calcified carotid plaques(OR = 1.787; P = 0.031) were independent predictors of significant liver fibrosis. CONCLUSION: The prevalence of significant liver fibrosis assessed using TE was 6.9% in apparently healthy subjects. High BMI, high ALT, thicker carotid IMT, and higher numbers of calcified carotid plaqueswere independently associated with the presence of significant liver fibrosis.

关键词： Transient elastography Healthy subjects Fibroscan

An improved brain MR image binarization method as a preprocessing for abnormality detection and features extraction

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Frontiers of Computer Science 2017年第4期11卷 717-727页

作者： Sudipta ROY Debnath BHATTACHARYYA Samir Kumar BANDYOPADHYAY Tai-hoon kim Department of Computer Science and Engineering Institute of Computer Technology (UVPCE) Ganpat University Ahmadabad 380060 India Information Technology Department College of Engineering Bharati Vidyapeeth deemed University Pune 411043 India Department of Computer Science and Engineering University of Calcutta Technology Campus Kolkata 700098 India Department of Convergence Security Sungshin Women's University Seoul 136-742 Korea

This paper propose a computerized method of magnetic resonance imaging （MR/） of brain binarization for the uses of preprocessing of features extraction and brain ab- normality identification. One of the main problems of MR/ binarization is that many pixels of brain part cannot be cor- rectly binarized due to extensive black background or large variation in contrast between background and foreground of MR/. We have proposed a binarization that uses mean, vari- ance, standard deviation and entropy to determine a thresh- old value followed by a non-gamut enhancement which can overcome the binarization problem of brain component. The proposed binarization technique is extensively tested with a variety of MR/and generates good binarization with im- proved accuracy and reduced error. A comparison is carried out among the obtained outcome with this innovative method with respect to other well-known methods.

关键词： image binarization thresholding image pre-processing segmentation performance analysis accuracy es-timation MRI of brain entropy

Microstructural characteristics of AZ31 alloys rolled at room and cryogenic temperatures and their variation during annealing

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Journal of Magnesium and Alloys 2020年第2期8卷 537-545页

作者： Sang Won Lee Sang-hoon kim Sung Hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea

This study investigates the microstructural characteristics of AZ31 Mg alloys rolled at room temperature(RT)and cryogenic temperature(CT)and the variation in their microstructure and hardness during subsequent *** induces the formation of more side cracks than does RT rolling,because of the reduction in the ability of the material to accommodate deformation at ***{10-11}contraction and{10-11}-{10-12}double twins are formed in both the material rolled at RT and that rolled at CT,because the grains of the initial material are favorably oriented for{10-11}twinning under *** RT-rolled material has a higher dislocation density than the cryorolled material,and more twins are uniformly distributed throughout the former *** a result,static recrystallization during subsequent annealing is more pronounced in the RT-rolled material,which results in the formation of a highly recrystallized homogeneous microstructure after *** contrast,the formed twins are predominantly present along the shear bands in the cryorolled material,as a result of which this material has an inhomogeneous bi modal structure containing a large amount of coarse unrecrystallized grains after *** hardness of the annealed RT-rolled material is higher than that of the annealed cryorolled material owing to the finer grain structure of the former.

关键词： Magnesium Rolling Cryogenic temperature Annealing Microstructure

Dietary vitamin D intake and vitamin D related genetic polymorphisms are not associated with gastric cancer in a hospital-based case-control study in Korea

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The Journal of Biomedical Research 2018年第4期32卷 257-263页

作者： Sang-yong Eom Dong-Hyuk Yim Dae-hoon kim Hyo-Yung Yun Young-Jin Song Sei-Jin Youn Taisun Hyun Joo-Seung Park Byung Sik kim yong-Dae kim Heon kim Departments of Preventive Medicine and Medical Research Institute College of Medicine Departments of Preventive Medicine and Surgery College of Medicine Departments of Preventive Medicine and Internal Medicine College of Medicine Dartment of Food and Nutrition Chungbuk National UniversityCheongju 28644Korea Department of Surgery College of MedicineEulji UniversityDaejon 301746Korea Department of Surgery Asan Medical CenterCollege of MedicineUlsan UniversitySeoul 138736Korea

There have been few studies on the association between vitamin D levels and gastric cancer in Asian populations,but no studies have been performed on the interactions between vitamin D intake and polymorphisms in the vitamin D *** effects of vitamin D intake,vitamin D related genetic polymorphisms,and their association with the incidence of gastric cancer were investigated in a hospital case-control study,including 715 pairs of newly diagnosed gastric cancer patients and controls matched for age and *** between vitamin D intake and plasma vitamin D concentrations were also assessed in a subset of *** statistically significant difference was observed in the dietary intake of vitamin D between the patients and controls,nor were there any evident associations between vitamin D intake and risk of gastric cancer in multivariate *** D intake significantly correlated with the circulating 25-hydroxyvitamin D levels,but not with the active form of the vitamin,1,25-dihydroxyvitamin *** were no statistically significant interactions between vitamin D intake,and VDR or TXNIP *** study suggests that dietary vitamin D intake is not associated with gastric cancer risk,and the genetic polymorphisms of vitamin D-related genes do not modulate the effect of vitamin D with respect to gastric carcinogenesis.

关键词： gastric cancer vitamin D vitamin D receptor gene-environment interaction

Texture tailoring and bendability improvement of rolled AZ31 alloy using {10-12} twinning: The effect of precompression levels

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Journal of Magnesium and Alloys 2019年第4期7卷 648-660页

作者： Jong Un Lee Ye Jin kim Sang-hoon kim Jeong Hun Lee Min-Seong kim Shi-hoon Choi Byoung Gi Moon Young Min kim Sung Hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea Ulsan Regional Division Korea Institute of Industrial TechnologyUlsan 44413Republic of Korea Department of Printed Electronics Engineering Sunchon National UniversitySuncheonJeonnam 57922Republic of Korea Implementation Research Division Korea Institute of Materials ScienceChangwon 51508Republic of Korea

In this study,the texture of a rolled Mg alloy is effectively modified through the application of precompression and subsequent annealing treatment,leading to a remarkable improvement in the bending formability of the alloy at room *** induces lattice reorientation through{10-12}twinning,and annealing treatment reduces the stored strain energy of the precompressed material,which results in the formation of a stable grain structure with two dominant texture *** an increase in precompression,the tensile strain in the outer region of the bending samples is accommodated to a greater extent due to more pronounced{10-12}twinning and basal *** a result,the bending formability of the material at room temperature improves with greater *** variation in microstructure,texture,and bending behavior in relation to the degree of precompression is discussed in detail.

关键词： Magnesium Bending Formability Twinning Texture