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Acceleration of aging behavior and improvement of mechanical properties of extruded AZ80 alloy through(10–12) twinning

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Journal of Magnesium and Alloys 2023年第2期11卷 671-683页

作者： hyun ji kim Ye jin kim Sung Hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea

The effects of pre-existing {10–12} extension twins on the precipitation behavior of an extruded AZ80 material during aging and on its mechanical properties after peak aging are investigated. The material containing {10–12} twins-which are formed by compression before aging(twinned material)-has a finer grain size and higher dislocation density than the extruded material. Although the peak hardnesses of the twinned and extruded materials are almost the same, the time to reach the peak hardness is considerably shorter in the former material than in the latter(4 h and 24 h, respectively). In the twinned material, the high dislocation density of the {10–12} twins promotes continuous precipitation, which results in the formation of numerous fine Mg17Al12precipitates within the twins in the early stage of *** formation of these continuous precipitates reduces the driving force for discontinuous precipitation, which consequently suppresses the formation and growth of coarse Mg17Al12precipitates at the grain boundaries. Despite its shorter peak-aging time, the 4 h-peak-aged twinned material shows higher tensile strength and elongation than the 24 h-peak-aged extruded material. These higher mechanical properties of the former material are attributed primarily to the presence of more abundant fine continuous precipitates, which are effective in strengthening the material, and less abundant coarse discontinuous precipitates, which can act as crack initiation sites. These results demonstrate that the introduction of {10–12} twins into wrought Mg–Al-based alloys can accelerate the Mg17Al12precipitation kinetics considerably and improve the strength and ductility of the peak-aged alloys simultaneously.

关键词： AZ80 alloy Twin Aging Precipitation Tensile properties

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Anti-obesity Effects of Ginsenosides in High-Fat Diet-Fed Rats

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Chinese Journal of Integrative Medicine 2019年第12期25卷 895-901页

作者： hyun-Jung Park ji hyun kim Insop Shim Department of Physiology College of MedicineKyung Hee UniversitySeoul(130-701)Republic of Korea Department of Food Science&Biotechnology College of Science and EngineeringSuwon-si(16227)Republic of Korea

Objective: To examine the anti-obesity effects of ginsenosides in Korea Red Ginseng(KRG, Panax ginseng) in rats fed with a high-fat diet(HFD). Methods: Twenty-five 4-week-old obesity rats after receiving an HFD for 5 weeks;subsequently, they were additionally treated with ginsenosides Rb1, Rd, Rg1, or Re(10 mg/kg, intraperitoneal injection) for a further 3 weeks(n=5 in each group). The control rats were fed a normal diet. The food consumption, body weight, locomotor activity, serum lipids, adipose tissues, nitric oxide(NO) expression, leptin, neuropeptide Y(NPY), cholecystokinin(CCK) in the brains were measured. Results: In the HFD-fed rats, body weight, body fat mass, serum levels of leptin and NO were significantly higher than in the control rats(P<0.05 or P<0.01). However, the treatment of Rd, Re, and Rb1 markedly decreased body fat mass and body weight(P<0.05). The serum level of leptin and NO in ginsenoside-treated rats were markedly lower than the control group(P<0.01). The expression of NPY and CCK in the hypothalamic nuclei showed insignificant difference among groups. However, the expression of NPY immunoreactive neurons in the hypothalamus was significantly reduced in the Rb1-treated group(P<0.05). Conclusion: PD-type ginsenoside Rb1 from the crude saponins of KRG may be a useful compound for the treatment of obesity and related disorders through the modulation of peripheral and central appetite-regulating signals.

关键词： Panax ginseng ginsenosides hypothalamus obesity

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Improved continuous precipitation kinetics and tensile properties of extruded AZ80 alloy through {10-12} twin formation

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Journal of Magnesium and Alloys 2023年第9期11卷 3323-3337页

作者： hyun ji kim Sumi Jo Sung Hyuk Park Department of Materials Science and Metallurgical Engineering Kyungpook National UniversityDaegu 41566the Republic of Korea

This study investigates the effect of{10-12}deformation twins on the continuous precipitation behavior of an extruded Mg-8.0Al-0.5Zn-0.2Mn(AZ80)alloy during *** extruded AZ80 alloy is compressed along the transverse direction to introduce{10-12}twins,followed by an aging treatment at 300℃.The extruded material exhibits a twin-free microstructure with low internal strain energy,whereas the pre-twinned material possesses abundant{10-12}twins and has high internal strain *** aging results reveal that the peak-aging time of the pre-twinned material(1 h)is one-eighth of that of the extruded material(8 h).Although Mg_(17)Al_(12)continuous precipitates(CPs)are observed in both the peak-aged materials,these CPs are much smaller and more densely distributed in the pre-twinned material despite the significantly shorter aging *** CPs size in the peak-aged materials increases in the following order:twinned region in the pre-twinned material(0.47μm)

关键词： AZ80 alloy {10-12}twin Aging Continuous precipitation Tensile properties

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Influence of undissolved second-phase particles on dynamic recrystallization behavior of Mg–7Sn–1Al–1Zn alloy during low-and high-temperature extrusions

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Journal of Materials Science & Technology 2021年第12期71卷 87-97页

作者： hyun ji kim Sang-Cheol jin Jae-Gil Jung Sung Hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu41566Republic of Korea Implementation Research Division Korea Institute of Materials ScienceChangwon51508Republic of Korea

This study investigates the effects of fine and coarse undissolved particles in a billet of the Mg–7 Sn–1 Al–1 Zn(TAZ711)alloy on the dynamic recrystallization(DRX)behavior during hot extrusion at low and high temperatures and the resultant microstructure and mechanical properties of the *** this end,partially homogenized(PH)and fully homogenized(FH)billets are extruded at temperatures of250 and 450°*** PH billet contains fine and coarse undissolved Mg_(2) Sn particles in the interdendritic region and along the grain boundaries,*** fine particles(<1μm in size)retard DRX during extrusion at 250°C via the Zener pinning effect,and this retardation causes a decrease in the area fraction of dynamically recrystallized(DRXed)grains of the extruded *** addition,the inhomogeneous distribution of fine particles in the PH billet leads to the formation of a bimodal DRXed grain structure with excessively grown grains in particle-scarce *** contrast,in the FH billet,numerous nanosized Mg_(2) Sn precipitates are formed throughout the material during extrusion at 250°C,which,in turn,leads to the formation of small,uniform DRXed grains by the grain-boundary pinning effect of the *** the PH billet is extruded at the high temperature of 450°C,the retardation effect of the fine particles on DRX is weakened by their dissolution in theα-Mg matrix and the increased extent of thermally activated grain-boundary *** contrast,the coarse Mg_(2) Sn particles in the billet promote DRX during extrusion through the particle-stimulated nucleation phenomenon,which results in an increase in the area fraction of DRXed *** both low and high extrusion temperatures,the extruded material fabricated using the PH billet,which contains both fine and coarse undissolved particles,has a lower tensile strength than that fabricated using the FH billet,which is virtually devoid of second-phase *** lower strength of the former is attributed mai

关键词： Mg–Sn alloy Second-phase particle Extrusion Homogenization Dynamic recrystallization

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Prediction models for recurrence in patients with small bowel bleeding

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World Journal of Clinical Cases 2023年第17期11卷 3949-3957页

作者： ji hyun kim Seung-Joo Nam Division of Gastroenterology and Hepatology Department of Internal MedicineKangwon National University School of MedicineChuncheon 24341South Korea

Obscure gastrointestinal bleeding(OGIB)has traditionally been defined as gastrointestinal bleeding whose source remains unidentified after bidirectional *** can present as overt bleeding or occult bleeding,and small bowel lesions are the most common *** small bowel can be evaluated using capsule endoscopy,device-assisted enteroscopy,computed tomography enterography,or magnetic resonance *** the cause of smallbowel bleeding is identified and targeted therapeutic intervention is completed,the patient can be managed with routine ***,diagnostic tests may produce negative results,and some patients with small bowel bleeding,regardless of diagnostic findings,may experience *** those at risk of rebleeding can help clinicians form individualized surveillance *** studies have identified different factors associated with rebleeding,and a limited number of studies have attempted to create prediction models for *** article describes prediction models developed so far for identifying patients with OGIB who are at greater risk of *** models may aid clinicians in forming tailored patient management and surveillance.

关键词： Obscure gastrointestinal bleeding Prediction model Rebleeding Small bowel bleeding Video capsule endoscopy

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Promoting dynamic recrystallization and improving strength and ductility of Mg-7Bi alloy through Al addition

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Journal of Magnesium and Alloys 2024年第8期12卷 3339-3356页

作者： Gun Woong An Sang-Cheol jin hyun ji kim Sumi Jo Sung Hyuk Park Department of Materials Science and Metallurgical Engineering Kyungpook National UniversityDaegu 41566Republic of Korea Graduate School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea

This study investigated the influence of the addition of Al to a Mg-7Bi(B7,wt%)alloy,particularly its recrystallization behavior during extrusion and its resulting mechanical *** addition of 2 wt%Al to the B7 alloy resulted in a lower grain size,a reduction in the number density of fine Mg3Bi2 particles,and a higher area fraction of relatively coarse Mg3Bi2 particles in the extrusion *** microstructural changes increased the nucleation sites for recrystallization,reduced the Zener pinning effect,and enhanced particle-stimulated nucleation,all of which promoted dynamic recrystallization behavior during *** a result,the area fraction of recrystallized grains in the extruded alloy increased from 77%to 94%.The extruded B7 alloy exhibited a strongfiber texture,whereas the extruded Mg-7Bi-2Al(BA72)alloy had a weak-texture,which was attributed to the minimal presence of unrecrystallized grains and the dispersed orientation of the recrystallized *** tensile yield strength(TYS)of the extruded BA72 alloy was higher than that of the extruded B7 alloy(170 and 124 MPa,respectively),which resulted from the enhanced grain-boundary and solid-solution strengthening *** tensile elongation(EL)of the BA72 alloy also exceeded that of the B7 alloy(20.3%and 6.1%,respectively),the result of the uniform formation of fine twins under tension in the former and the formation of a few coarse twins among the unrecrystallized grains in the ***,the addition of a small amount of Al to the B7 alloy significantly improved both the strength and ductility of the extruded alloy,resulting in a remarkable increase in the product of the TYS and EL from 756 to 3451 MPa%and expanding its potential range of applications as a lightweight extruded structural component.

关键词： Mg-7Bi alloy Al addition Extrusion Recrystallization Microstructure

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Variations in microstructure and bending formability of extruded Mg–Al–Zn–Ca–Y–MM alloy with precompression and subsequent annealing treatment conditions

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Journal of Magnesium and Alloys 2022年第9期10卷 2475-2490页

作者： Jong Un Lee Sang-Hoon kim Dong Hee Lee hyun ji kim Young Min kim Sung Hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea Agency for Defense Development Daejeon 34186Republic of Korea Implementation Research Division Korea Institute of Materials ScienceChangwon 51508Republic of Korea

In this study, the bending formability of an extruded Mg–9Al–1Zn–0.3Mn–0.9Ca–0.6Y–0.5 MM(AZXWMM91100, wt%) alloy at room temperature is significantly improved through application of a combined precompression and subsequent annealing(PCA) treatment. As the amount of precompression applied along the extrusion direction(ED)(i.e., the total strain) increases from 4% to 6%, the area fraction of ED-oriented grains of the PCA-treated alloy increases, which consequently causes an improvement in its bending formability because these grains accommodate larger tensile strain along the ED during bending. As the temperature of the subsequent annealing treatment increases from 350 ℃ to 450 ℃, both the area fraction of the ED-oriented grains and the average grain size increase, and the residual dislocation density decreases owing to the promotion of boundary migration and occurrence of the recovery process at higher ***, the bending formability of both the 4%-precompressed and the 6%-precompressed samples increases with an increase in the annealing temperature. However, when the precompressed samples are annealed at 300 ℃, their bending formability is lower than that of the extruded alloy because the dislocations formed by precompression remain even after the subsequent annealing at this temperature.

关键词： Magnesium Extrusion Bending Formability Texture

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Prospects for nucleic acid-based therapeutics against hepatitis C virus

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World Journal of Gastroenterology 2013年第47期19卷 8949-8962页

作者： Chang Ho Lee ji hyun kim Seong-Wook Lee Department of Molecular Biology Institute of Nanosensor and BiotechnologyDankook UniversityYongin 448-701South Korea

In this review,we discuss recent advances in nucleic acid-based therapeutic technologies that target hepatitis C virus(HCV)*** the HCV genome is present exclusively in RNA form during replication,various nucleic acid-based therapeutic approaches targeting the HCV genome,such as ribozymes,aptamers,siRNAs,and antisense oligonucleotides,have been suggested as potential tools against *** acids are potentially immunogenic and typically require a delivery tool to be utilized as *** limitations have hampered the clinical development of nucleic acid-based ***,despite these limitations,nucleic acid-based therapeutics has clinical value due to their great specificity,easy and large-scale synthesis with chemical methods,and pharmaceutical ***,nucleic acid therapeutics are expected to broaden the range of targetable molecules essential for the HCV replication cycle,and therefore they may prove to be more effective than existing therapeutics,such as interferon-αand ribavirin combination *** review focuses on the current status and future prospects of ribozymes,aptamers,siRNAs,and antisense oligonucleotides as therapeutic reagents against HCV.

关键词： Hepatitis C virus Nucleic acid-based therapeutics Ribozyme Aptamer siRNA Antisense oligonucleotide

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Usefulness of artificial intelligence in gastric neoplasms

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World Journal of Gastroenterology 2021年第24期27卷 3543-3555页

作者： ji hyun kim Seung-Joo Nam Sung Chul Park Division of Gastroenterology and Hepatology Department of Internal MedicineKangwon National University School of MedicineChuncheon 24289Kangwon DoSouth Korea

Recently,studies in many medical fields have reported that image analysis based on artificial intelligence(AI)can be used to analyze structures or features that are difficult to identify with human *** diagnose early gastric cancer,related efforts such as narrow-band imaging technology are ***,diagnosis is often ***,a diagnostic method based on AI for endoscopic imaging was developed and its effectiveness was confirmed in many *** gastric cancer diagnostic program based on AI showed relatively high diagnostic accuracy and could differentially diagnose non-neoplastic lesions including benign gastric ulcers and *** AI system has also been developed that helps to predict the invasion depth of gastric cancer through endoscopic images and observe the stomach during endoscopy without blind ***,if AI is used in the field of endoscopy,it is expected to aid in the diagnosis of gastric neoplasms and determine the application of endoscopic therapy by predicting the invasion depth.

关键词： Artificial intelligence Convolutional neural network Gastric neoplasm Esophagogastroduodenoscopy Diagnosis Invasion depth

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Effect of pre-deformation on precipitation behavior of AZ80 alloy:Comparison of slip-and twinning-dominant deformation

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Journal of Magnesium and Alloys 2024年第9期12卷 3616-3630页

作者： hyun ji kim Sang Cheol jin Sumi Jo Sung Hyuk Park Department of Materials Science and Metallurgical Engineering Kyungpook National UniversityDaegu 41566Republic of Korea Graduate School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea

This study investigates the effect of the deformation mode on the precipitation behavior of an extruded Mg-8.0Al-0.5Zn-0.2Mn(AZ80)*** alloy samples are compared after the application of 3.5%tension and 3.5%compression along the extrusion direction to induce slip-dominant and twinning-dominant deformation modes,*** pre-compressed(PC)sample,which contained numerous{10-12}tension twins,has a reduced grain size and a higher internal strain than the pre-tensioned(PT)sample,which is attributed to the inherent internal strain that occurs during the formation and growth of the *** a result,the precipitation behavior of the PC sample is accelerated,leading to its short peak aging time of 32 h,which is lower than those of the PT and as-extruded samples(48 and 100 h,respectively).Furthermore,fine continuous precipitates(CPs)rapidly form within the{10-12}twins,contributing to the enhanced *** precipitates(DPs),which have a hardness comparable to the CP-containing twinned regions,in the PC sample experience less coarsening during aging than those in the PT sample due to growth inhibition by the{10-12}***,the{10-12}twins generated under the twinning-dominant deformation condition lead to enhanced precipitation behaviors,including the preferential formation and refinement of CPs and the suppressed coarsening of ***,pre-deformation that occurs{10-12}twinning exhibits more pronounced effects on precipitation acceleration and microstructural modification than slip-inducing pre-deformation.

关键词： AZ80 alloy Slip Twinning Precipitation Hardness

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