127 results on '"Kyung-Hwan Jung"'
Search Results
2. Evaluating operator’s organ dose and effective dose according to the lead equivalent of radiation protection devices in performing angiography and interventional procedures
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Dong-Hee Han, Man-Seok Han, Seung-Jae Lee, Byung-Seok Shin, Jang-Oh Kim, Da-Eun Kwon, Kyung-Hwan Jung, Seung-Hwan Lee, and Cheol-Ha Baek
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General Physics and Astronomy - Published
- 2023
3. Correlation of cryogenic deformation mechanisms to excellent strength-ductility of CrCoNi medium entropy alloy processed by selective laser melting
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Kyung-Hwan Jung, Minh Tien Tran, Zhengtong Shan, Ho Won Lee, Sun-Kwang Hwang, Hyung Giun Kim, and Dong-Kyu Kim
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Biomaterials ,Metals and Alloys ,Ceramics and Composites ,Surfaces, Coatings and Films - Published
- 2023
4. Evaluation of the Effectiveness of Silicon for Radiation Shielding in Mammography
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Jang-Oh Kim, Dong-Hee Han, Kyung-Hwan Jung, Da-Eun Kwon, Byung-In Min, Seung-Jae Lee, and Cheol-Ha Baek
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Electrical and Electronic Engineering ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Published
- 2022
5. Enzymatic Syntheses of 1,2-Pentanediol Galactoside and 1,2-Decanediol Galactoside
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Kyung-Hwan Jung
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General Earth and Planetary Sciences ,General Environmental Science - Published
- 2022
6. Optimization of the design parameters for a thyroid care nuclide monitoring diverging collimator using Monte Carlo simulation
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Dong-Hee Han, Seung-Jae Lee, Jang-Oh Kim, Da-Eun Kwon, Kyung-Hwan Jung, and Cheol-Ha Baek
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General Physics and Astronomy - Published
- 2022
7. Effect of energy density on quasi-static and dynamic mechanical properties of Ti–6Al–4V alloy additive-manufactured by selective laser melting
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Ji-Hoon Jang, Youngsin Choi, Kyung-Hwan Jung, Hyung-Giun Kim, and Dong-Geun Lee
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Mechanics of Materials ,Mechanical Engineering ,General Materials Science - Published
- 2022
8. A Comparative Analysis of Metal Shielding for Mammography Using Monte Carlo Simulation
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JangOh Kim, Da-Eun Kwon, Dong-Hee Han, Kyung-Hwan Jung, Byung In Min, Cheol Ha Baek, and Chang-Lae Lee
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Electrical and Electronic Engineering ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Published
- 2021
9. Comparison and Evaluation of Monte Carlo Simulation Codes for Medical Radiation Shielding of Metal 3D-printed Materials
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Cheol-Ha Baek, Jang-Oh Kim, Jong-Seok Byeon, Seung-Jae Lee, Da-Eun Kwon, Dong-Hee Han, and Kyung-Hwan Jung
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General Physics and Astronomy - Published
- 2021
10. Antimicrobial Activity of Benzyl Alcohol Galactoside against Escherichia coli
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Kyung-Hwan Jung
- Published
- 2021
11. Antimicrobial Activity of
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Ji-Hae, Joo, Min-Hui, Han, Ja-I, Kim, Jong-Eun, Kim, Kyung-Hwan, Jung, Han Sun, Oh, Young Soo, Chung, Hyun Jin, An, Jae Duk, Lee, Gi-Seong, Moon, and Hyang-Yeol, Lee
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Anti-Infective Agents ,Plant Extracts ,Resveratrol ,Acne Vulgaris ,Smilax ,Humans ,Quercetin ,Propionibacterium acnes ,Microbial Sensitivity Tests ,Anti-Bacterial Agents - Abstract
The root of
- Published
- 2022
12. Microstructural study of the nano-scale martensitic lamellar α-Co and ε-Co phases of a Co–Cr alloy fabricated by selective laser melting
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Sung Hwan Lim, Hyun Woong Park, Yong Son, Gyung Bae Bang, Won Rae Kim, Hyung Giun Kim, and Kyung-Hwan Jung
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Materials science ,Alloy ,02 engineering and technology ,engineering.material ,01 natural sciences ,Biomaterials ,0103 physical sciences ,Lamellar structure ,Selective laser melting ,Composite material ,Microstructure ,010302 applied physics ,Mining engineering. Metallurgy ,TN1-997 ,Metals and Alloys ,021001 nanoscience & nanotechnology ,Co–Cr alloy ,Surfaces, Coatings and Films ,Transmission electron microscopy ,Martensite ,Vickers hardness test ,Ceramics and Composites ,Hardening (metallurgy) ,engineering ,0210 nano-technology ,Orientation relationship - Abstract
An interfacial microstructural study was carried out to clarify the hardening mechanism of an as-built Co–Cr alloy fabricated by selective laser melting (SLM). Using transmission electron microscopy, we found a unique martensitic lamellar microstructure with a specific orientation relationship between the α-Co and e-Co phases; specifically, a nanoscale microstructure consisting of (111)α-Co//(000 2 ¯ )e-Co and [0 1 ¯ 1]α-Co//[ 1 ¯ 2 1 ¯ 0]e-Co was formed on the Co–Cr alloy. The Co–Cr alloy fabricated by SLM with a martensitic microstructure achieved a Vickers hardness value of approximately 369.36 ± 11.86 HV without any secondary-phase particles such as carbides.
- Published
- 2021
13. Melt Pool Characterization of Selective Laser Melting of AlSi10Mg based on Numerical Model of Single-Track Scanning Process
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Hyung Giun Kim, Kyung Hwan Jung, Gyung Bae Bang, Gun Jin Yun, and Kang-Hyun Lee
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Materials science ,Mechanical Engineering ,Numerical analysis ,Track (disk drive) ,Scientific method ,Selective laser melting ,Composite material ,Safety, Risk, Reliability and Quality ,Melt pool ,Industrial and Manufacturing Engineering ,Characterization (materials science) - Published
- 2021
14. Continuous Enzymatic Synthesis of Phenoxyethanol Galactoside
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Kyung-Hwan Jung
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chemistry.chemical_compound ,chemistry ,Biochemistry ,medicine ,Enzymatic synthesis ,medicine.disease_cause ,Galactoside ,Escherichia coli ,Phenoxyethanol - Published
- 2020
15. A facile and efficient method for the synthesis of crystalline tetrahydro-β-carbolines via the Pictet-Spengler reaction in water
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Gi-Seong Moon, Kyung-Hwan Jung, Sung-Kwon Moon, Hyang-Yeol Lee, and Hong-Ju Byeon
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Tryptamine ,Multidisciplinary ,Pictet–Spengler reaction ,Cancer therapy ,010405 organic chemistry ,Natural compound ,Biological techniques ,lcsh:R ,lcsh:Medicine ,One-Step ,010402 general chemistry ,01 natural sciences ,Environmentally friendly ,Article ,0104 chemical sciences ,Solvent ,chemistry.chemical_compound ,chemistry ,Organic chemistry ,Drug discovery and development ,lcsh:Q ,Tryptoline ,Cytotoxicity ,lcsh:Science - Abstract
A facile and efficient synthesis of tetrahydro-β-carbolines (tryptolines) in one step from tryptamine and aldehydes, in an environmentally friendly water solvent, has been investigated. This convenient and clean synthesis of various tryptolines was facilitated by l-tartaric acid, a natural compound, to obtain the desired products as clear crystals. Among the four crystalline products, the most substituted tryptoline 2 showed the best inhibitory activity against EJ cells and the least cytotoxicity, with an LC50 value of 1.49 mg/mL, against brine shrimp larvae.
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- 2020
16. Continuous Synthesis of Chlorphenesin Galactoside
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Kyung-Hwan Jung
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chemistry.chemical_compound ,chemistry ,Biochemistry ,medicine ,medicine.disease_cause ,Galactoside ,Escherichia coli - Published
- 2019
17. Antimicrobial Activity of Smilax china L. Root Extracts against the Acne-Causing Bacterium, Cutibacterium acnes, and Its Active Compounds
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Ji-Hae Joo, Min-Hui Han, Ja-I Kim, Jong-Eun Kim, Kyung-Hwan Jung, Han Sun Oh, Young Soo Chung, Hyun Jin An, Jae Duk Lee, Gi-Seong Moon, and Hyang-Yeol Lee
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Chemistry (miscellaneous) ,Organic Chemistry ,Drug Discovery ,Molecular Medicine ,Pharmaceutical Science ,skin acne ,antimicrobial activity ,Smilax china L ,Cutibacterium acnes ,cytotoxicity ,Physical and Theoretical Chemistry ,Analytical Chemistry - Abstract
The root of Smilax china L. is used in traditional Korean medicine. We found that the Smilax china L. root extract has strong antimicrobial activity against two Cutibacterium acnes strains (KCTC 3314 and KCTC 3320). The aim of this study was to identify the beneficial properties of Smilax china L. extracts for their potential use as active ingredients in cosmetics for the treatment of human skin acne. The high-performance liquid chromatography (HPLC) and liquid chromatography-hybrid quadrupole time-of-flight mass spectrometry (LC/QTOF/MS) methods were used to obtain the profile of secondary metabolites from the ethyl acetate-soluble fraction of the crude extract. Agar diffusion and resazurin-based broth microdilution assays were used to evaluate antimicrobial activity and minimum inhibitory concentrations (MIC), respectively. Among the 24 metabolites, quercetin, resveratrol, and oxyresveratrol were the most potent compounds against Cutibacterium acnes. Minimum inhibitory concentrations of quercetin, resveratrol, and oxyresveratrol were 31.25, 125, and 250 μg/mL, respectively.
- Published
- 2022
18. High-power energy harvesting and imperceptible pulse sensing through peapod-inspired hierarchically designed piezoelectric nanofibers
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Sukhyun Kang, Sang Hoon Kim, Han Bit Lee, Sungwook Mhin, Jeong Ho Ryu, Young Won Kim, Jacob L. Jones, Yong Son, Nak Kyu Lee, Kangpyo Lee, Yunseok Kim, Kyung Hwan Jung, Hyuksu Han, Suk Hee Park, and Kang Min Kim
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Renewable Energy, Sustainability and the Environment ,General Materials Science ,Electrical and Electronic Engineering - Published
- 2022
19. Laser beam melting process based on complete-melting energy density for commercially pure titanium
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Gyung Bae Bang, Min Ji Ham, Gun-Hee Kim, Hyung-Ki Park, Kang Min Kim, Hyung Giun Kim, Kyung-Hwan Jung, Won Rae Kim, Ohyung Kwon, and Chang-Woo Lee
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0209 industrial biotechnology ,Commercially pure titanium ,Fundamental study ,Range (particle radiation) ,Materials science ,Strategy and Management ,Thermodynamics ,02 engineering and technology ,Management Science and Operations Research ,021001 nanoscience & nanotechnology ,Industrial and Manufacturing Engineering ,Power (physics) ,020901 industrial engineering & automation ,Scientific method ,Energy density ,0210 nano-technology ,Porosity ,Laser beams - Abstract
Laser beam melting (LBM) based on the complete-melting energy density for commercially pure titanium (CP-Ti) was investigated. Process parameters were set corresponding to the thermodynamically calculated energy density for full melting of CP-Ti. From the calculated energy density, power of 50–250 W and scan speed of 371–1855 mm/s were derived with the fixed other conditions. Microstructural study on formation of pores was conducted to understand the change in part’s density. Fundamental study with wide range of LBM process parameters, particularly based on the complete-melting energy density, could confirm the effects like high density and porous structure.
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- 2019
20. Effects of sodium dodecyl sulfate surfactant on up-conversion luminescence of Er3+/Yb3+ -codoped NaLa (MoO4)2 nanocolloidal phosphor prepared by pulsed laser ablation in water
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Kang Min Kim, Sungwook Mhin, Jeong Ho Ryu, HyukSu Han, Won Rae Kim, Kyung-Hwan Jung Suk Hyun Kang, Yong Son, Jung-Il Lee, and Kwang Bo Shim
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chemistry.chemical_compound ,Materials science ,chemistry ,Pulmonary surfactant ,Ceramics and Composites ,Up conversion ,Phosphor ,Sodium dodecyl sulfate ,Luminescence ,Pulsed laser ablation ,Nuclear chemistry - Published
- 2019
21. Microstructure and mechanical anisotropy of CoCrW alloy processed by selective laser melting
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Dong-Kyu Kim, Seong-Hoon Kang, Ho Won Lee, Sun-Kwang Hwang, and Kyung-Hwan Jung
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010302 applied physics ,Materials science ,Mechanical Engineering ,02 engineering and technology ,Paris' law ,Plasticity ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Microstructure ,01 natural sciences ,Grain growth ,Mechanics of Materials ,0103 physical sciences ,General Materials Science ,Crystallite ,Texture (crystalline) ,Composite material ,0210 nano-technology ,Anisotropy ,Elastic modulus - Abstract
We have investigated the correlation between the microstructure and mechanical anisotropy of biomedical CoCrW alloy processed by selective laser melting (SLM). A phase analysis revealed that the as-SLM CoCrW alloy consisted of mostly the γ-fcc phase and little e-hcp phase. The as-SLM CoCrW microstructure featured the rotated cube texture, a strong texture along the building direction (BD) and a weaker texture along the front direction. To investigate the mechanical anisotropy, the external loading was applied either perpendicular or parallel to the BD (i.e., horizontal loading (⊥BD) or vertical loading (//BD), respectively). The rotated cube texture leads to a higher elastic modulus (~ 2.4 times), plastic flow stress, and microhardness in the horizontal loading. Macroscopic plastic anisotropy was elucidated by the Taylor factor analysis of polycrystalline aggregate. Strain-induced martensite transformation (SIMT) occurring in the horizontal loading ( e f = 6.9%) is responsible for significantly reduced elongation to fracture compared to the vertical loading ( e f = 32.8%). In the fatigue crack growth experiment, the threshold stress intensity range in the vertical loading is ~ 32% higher compared to the horizontal loading, leading to a retarded fatigue crack growth rate. A vertically elongated columnar granular structure due to the epitaxial grain growth along the BD results in anisotropic behavior of the fatigue crack growth.
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- 2019
22. Anisotropic Mechanical Behavior of Additive Manufactured AISI 316L Steel
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Kyung Hwan Jung, Kuk Hyun Song, Young Kook Lee, Y. D. Im, and Kyung Hoon Kim
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010302 applied physics ,Materials science ,Yield (engineering) ,Misorientation ,Metallurgy ,0211 other engineering and technologies ,Metals and Alloys ,food and beverages ,02 engineering and technology ,Strain hardening exponent ,Condensed Matter Physics ,01 natural sciences ,Grain size ,Mechanics of Materials ,0103 physical sciences ,Ultimate tensile strength ,Grain boundary ,Deformation (engineering) ,Dislocation ,021102 mining & metallurgy - Abstract
We investigated the relationship between the microstructure and mechanical properties of additive manufactured AISI 316L steel regarding the grain aspect ratio and orientation. For this purpose, two types of specimen (vertically and horizontally built) were prepared by a selective laser melting process, and the mechanical behavior was evaluated in different tensile directions. After this, to observe the characteristic grain boundary distributions such as grain size, shape, orientation, and intergranular misorientation, electron backscattering diffraction analysis was conducted on the initial and tensile-strained specimens. The specimen with a lower grain aspect ratio showed enhanced yield and tensile strengths arising from the higher strain hardening rate relative to the specimen with higher grain aspect ratio. In addition, the material composed of grains with a higher Taylor factor showed more accumulated dislocation density during tensile deformation when compared to the material composed of grains with a lower Taylor factor, which also contributed to the increase in tensile strengths because of the enhanced strain hardening rate.
- Published
- 2019
23. One-step synthesis of sulfur-incorporated graphene quantum dots using pulsed laser ablation for enhancing optical properties
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Suk Hyun Kang, Young Kyu Jeong, Yong Son, Kyung Hwan Jung, Kang Min Kim, Jeong Ho Ryu, and Won Rae Kim
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Laser ablation ,Photoluminescence ,Materials science ,business.industry ,Graphene ,Heteroatom ,Doping ,02 engineering and technology ,021001 nanoscience & nanotechnology ,medicine.disease_cause ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,law.invention ,010309 optics ,Optics ,law ,Quantum dot ,0103 physical sciences ,medicine ,Optoelectronics ,0210 nano-technology ,business ,Spectroscopy ,Ultraviolet - Abstract
To tune the electronic and optoelectronic properties of graphene quantum dots (GQDs), heteroatom doping (e.g., nitrogen (N), boron (B), and sulfur (S)) is an effective method. However, it is difficult to incorporate S into the carbon framework of GQDs because the atomic size of S is much larger than that of C atoms, compared to N and B. In this study, we report a simple and one-step method for the synthesis of sulfur-doped GQDs (S-GQDs) via the pulsed laser ablation in liquid (PLAL) process. The as-prepared S-GQDs exhibited enhanced fluorescence quantum yields (0.8% → 3.89%) with a huge improved absorption band in ultraviolet (UV) region (200 ∼ 400 nm) and excellent photo stability under the UV radiation at 360 nm. In addition, XPS results revealed that the PLAL process can effectively facilitate the incorporation of S into the carbon framework compared to those produced by the chemical exfoliation method (e.g., hydrothermal method). And also, the mechanisms related with the optical properties of S-GQDs was investigated by time-resolved photoluminescence (TRPL) spectroscopy. We believe that the PLAL process proposed in this study will serve as a simple and one-step route for designing S-GQDs and opens up to opportunities for their potential applications.
- Published
- 2020
24. Publisher Correction: Graphene Oxide Quantum Dots Derived from Coal for Bioimaging: Facile and Green Approach
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Sungwook Mhin, Byoung-Soo Lee, Yong Son, Kang Min Kim, Jeong Ho Ryu, Kwang Bo Shim, Kyung-Hwan Jung, Suk Hyun Kang, Taeseup Song, and HyukSu Han
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Multidisciplinary ,Materials science ,Graphene ,business.industry ,lcsh:R ,Oxide ,lcsh:Medicine ,Nanotechnology ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,Quantum dot ,lcsh:Q ,Coal ,lcsh:Science ,business - Abstract
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
- Published
- 2020
25. Effect of laser power on oxygen and nitrogen concentration of commercially pure titanium manufactured by selective laser melting
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Hyung Giun Kim, Seung-Min Yang, Won Rae Kim, Gun-Hee Kim, Kyung-Hwan Jung, Tae-Wook Na, Chang-Woo Lee, Hyung-Ki Park, Jong Min Park, and Ohyung Kwon
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010302 applied physics ,Materials science ,Fabrication ,Mechanical Engineering ,Analytical chemistry ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Nitrogen ,Oxygen ,chemistry ,Mechanics of Materials ,0103 physical sciences ,General Materials Science ,Limiting oxygen concentration ,Laser power scaling ,Selective laser melting ,0210 nano-technology ,Nitriding ,Titanium - Abstract
This study analyzed the variation of mechanical properties and its causes with increasing the laser power in the fabrication of pure titanium by selective laser melting (SLM). SLM samples were fabricated using commercially pure titanium grade 1 powder when the scan speed was 1000 mm/s and the laser power as 120, 200, 280, 360, and 440 W, respectively. As the laser power increased, the hardness and strength of the samples increased gradually. During the SLM processing, the concentrations of oxygen and nitrogen in the SLM samples were increased, which resulted in the increase of hardness and strength. The SLM equipment used in this study removed oxygen in the chamber by flowing high purity argon gas and fabricates the sample while preserving the oxygen concentration in the atmosphere to 0.2%. Evaluating the possibility of oxidation and nitriding during the SLM process by thermodynamic analysis, it was found that the process occurred under conditions in which temperature and residual oxygen and nitrogen partial pressure led to oxidation and nitriding.
- Published
- 2018
26. Optimal Design of Patient-Specific Total Knee Arthroplasty for Improvement in Wear Performance
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Kang Min Kim, Hyoung-Taek Hong, Kyoung-Tak Kang, Kyung-Hwan Jung, and Yong-Gon Koh
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Optimal design ,0206 medical engineering ,Total knee arthroplasty ,lcsh:Medicine ,02 engineering and technology ,Article ,patient-specific total knee arthroplasty ,03 medical and health sciences ,0302 clinical medicine ,Gait (human) ,wear performance ,Medicine ,Femoral component ,optimal design ,Parametric statistics ,030222 orthopedics ,business.industry ,lcsh:R ,General Medicine ,Patient specific ,Gait cycle ,020601 biomedical engineering ,Reliability engineering ,External rotation ,business ,gait cycle - Abstract
Life expectancy is on the rise and, concurrently, the demand for total knee arthroplasty (TKA), which lasts a lifetime, is increasing. To meet this demand, improved TKA designs have been introduced. Recent advances in radiography and manufacturing techniques have enabled the production of patient-specific TKA. Nevertheless, concerns regarding the wear performance, which limit the lifespan of TKA, remain to be addressed. This study aims at reducing the wear in patient-specific TKA using design optimization and parametric three-dimensional (3D) finite-element (FE) modelling. The femoral component design was implemented in a patient-specific manner, whereas the tibial insert conformity remained to be determined by design variables. The gait cycle loading condition was applied, and the optimized model was validated by the results obtained from the experimental wear tests. The wear predictions were iterated for five million gait cycles using the computational model with force-controlled input. Similar patterns for internal/external rotation and anterior/posterior translation were observed in both initial and optimal models. The wear rates for initial and optimal models were recorded as 23.2 mm3/million cycles and 16.7 mm3/million cycles, respectively. Moreover, the experimental wear rate in the optimal design was 17.8 mm3/million cycles, which validated our optimization procedure. This study suggests that tibial insert conformity is an important factor in influencing the wear performance of patient-specific TKA, and it is capable of providing improved clinical results through enhanced design selections. This finding can boost the future development of patient-specific TKA, and it can be extended to other joint-replacement designs. However, further research is required to explore the potential clinical benefits of the improved wear performance demonstrated in this study.
- Published
- 2019
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27. Microstructure of As-cast Co-Cr-Mo Alloy Prepared by Investment Casting
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Jung-Il Lee, Jong Bum Park, Yong Son, Kyung-Hwan Jung, Kang Min Kim, and Jeong Ho Ryu
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010302 applied physics ,Investment casting ,Alloy ,Metallurgy ,technology, industry, and agriculture ,General Physics and Astronomy ,02 engineering and technology ,engineering.material ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,Corrosion ,Carbide ,law.invention ,Optical microscope ,law ,Phase (matter) ,0103 physical sciences ,engineering ,Grain boundary ,0210 nano-technology - Abstract
The microstructure of a cobalt-base alloy (Co-Cr-Mo) obtained by an investment casting process was studied. This alloy complies with the ASTM F75 standard and is widely used in the manufacturing of orthopedic implants owing to its high strength, good corrosion resistance, and excellent biocompatibility. This work focuses on the resulting microstructures arising from normal industrial environmental conditions. The characterization of the samples was carried out using optical microscopy, field emission scanning electron microscopy and energy-dispersive spectroscopy. In this study, the as-cast microstructure is an γ-Co (face-centered cubic) dendritic matrix with the presence of a secondary phase, such as M23C6 carbides precipitated at grain boundaries and interdendritic zones. These precipitates are the main strengthening mechanism in this type of alloy. Other minority phases, such as the σ phase, were also detected, and their presence could be linked to the manufacturing process and environment.
- Published
- 2018
28. Atmosphere Gas Carburizing for Improved Wear Resistance of Pure Titanium Fabricated by Additive Manufacturing
- Author
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Seok-Hong Min, Hyung Guin Kim, Chang-Woo Lee, Kyung-Hwan Jung, Hyo Kyu Kim, Hyung-Ki Park, Byung-Soo Lee, and Tae Kwon Ha
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0209 industrial biotechnology ,Materials science ,Mechanical Engineering ,Metallurgy ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Carburizing ,Atmosphere ,Wear resistance ,020901 industrial engineering & automation ,chemistry ,Mechanics of Materials ,General Materials Science ,0210 nano-technology ,Titanium - Published
- 2017
29. Simple preparation of graphene quantum dots with controllable surface states from graphite
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Kyung Hwan Jung, Kang Min Kim, Suk Hyun Kang, Yong Son, Young Kyu Jeong, Gae Seok An, HyukSu Han, and Sung Churl Choi
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Laser ablation ,Photoluminescence ,Materials science ,Graphene ,General Chemical Engineering ,Sonication ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,Chemical engineering ,chemistry ,Quantum dot ,law ,Graphite ,0210 nano-technology ,Luminescence ,Carbon - Abstract
Graphite is economic and earth-abundant carbon precursor for preparing graphene quantum dots (GQDs). Here, we report a facile and green approach to produce GQDs from graphite flakes via a pulsed laser ablation (PLA) method assisted by high-power sonication. A homogeneous dispersion of graphite flakes, caused by high-power sonication during PLA, leads to the formation of GQDs following a laser fragmentation in liquid (LFL) rather than laser ablation in liquid (LAL) mechanism. The final product of GQDs exhibits the distinct structural, chemical, and optical properties of pristine graphene itself. However, graphene oxide quantum dots (GOQDs) with abundant surface oxygen-rich functional groups are readily formed from graphite flakes when high-power sonication is not employed during the PLA process. GQDs and GOQDs show a significantly different luminescence nature. Hence, selective production of either functional GQDs or GOQDs can be achieved by simply turning the high-power sonication during the PLA process on and off. We believe that our modified PLA process proposed in this work will further open up facile and simple routes for designing functional carbon materials.
- Published
- 2019
30. Laser wavelength modulated pulsed laser ablation for selective and efficient production of graphene quantum dots
- Author
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HyukSu Han, Jeong Ho Ryu, Kyung Hwan Jung, Kwang Bo Shim, Kang Min Kim, Suk Hyun Kang, and Byoung-Soo Lee
- Subjects
Photoluminescence ,Materials science ,business.industry ,Graphene ,General Chemical Engineering ,Oxide ,Coulomb explosion ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,0104 chemical sciences ,Nanomaterials ,law.invention ,chemistry.chemical_compound ,Wavelength ,chemistry ,Quantum dot ,law ,Optoelectronics ,0210 nano-technology ,business - Abstract
Graphene quantum dots (GQDs) and graphene oxide quantum dots (GOQDs) can be used in different applications such as optoelectronic and biomedical applications, respectively. Hence, the selective synthesis of GQDs and GOQDs is highly desirable but challenging. Here, we present GQDs and GOQDs selectively prepared by an easy and simple pulsed laser ablation in liquid (PLAL) method by controlling the laser wavelength. The obtained GQDs and GOQDs showed a significantly different optoelectronic nature mainly due to the existence of surface oxygen-rich functional groups (e.g. carboxyl or hydroxy groups). Also, we described a possible mechanism for the formation of oxygen functional groups during the PLAL process based on the Coulomb explosion model, which can give further insight for designing functional carbon materials.
- Published
- 2019
31. Graphene Oxide Quantum Dots Derived from Coal for Bioimaging: Facile and Green Approach
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Yong Son, Sungwook Mhin, Kang Min Kim, Taeseup Song, Jeong Ho Ryu, HyukSu Han, Kyung-Hwan Jung, Kwang Bo Shim, Byoung-Soo Lee, and Suk Hyun Kang
- Subjects
0301 basic medicine ,Materials science ,Oxide ,lcsh:Medicine ,chemistry.chemical_element ,Nanotechnology ,Carbon nanotube ,Article ,law.invention ,Pulsed laser ablation ,03 medical and health sciences ,chemistry.chemical_compound ,0302 clinical medicine ,law ,Coal ,lcsh:Science ,Multidisciplinary ,business.industry ,Graphene ,lcsh:R ,Publisher Correction ,030104 developmental biology ,chemistry ,Quantum dot ,lcsh:Q ,business ,Carbon ,030217 neurology & neurosurgery - Abstract
Graphene oxide quantum dots (GOQDs) are usually prepared using expensive carbon precursors such as carbon nanotubes (CNT) or graphene under the strong acidic condition, which requires an additional purifying process. Here, we first develop a facile pulsed laser ablation in liquid (PLAL) technique for preparing GOQDs using earth-abundant and low-cost coal as a precursor. Only ethanol and coal are used to produce GOQDs with excellent optical properties. The prepared GOQDs exhibit excellent optoelectronic properties which can be successfully utilized in bioimaging applications.
- Published
- 2019
32. Enzymatic Synthesis of 1, 2-Hexanediol Galactoside by Whole Cells of β-Galactosidase-containing Recombinant Escherichia coli
- Author
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Kyung-Hwan Jung and Yi-Ok Kim
- Subjects
0106 biological sciences ,Electrospray ,Chromatography ,Silica gel ,Sodium ,chemistry.chemical_element ,medicine.disease_cause ,01 natural sciences ,Galactoside ,0104 chemical sciences ,Adduct ,010404 medicinal & biomolecular chemistry ,Hydrolysis ,chemistry.chemical_compound ,chemistry ,Biochemistry ,010608 biotechnology ,Galactose ,medicine ,Escherichia coli - Abstract
side (HD-G) by a transgalactosylation reaction using β-galactosidase (β-gal)-containing recombinant Escherichia coli cells. The transgalactosylation reaction was carried out under high-lactose conditions for 24 hr. After 12 hr had elapsed, a new spot was identified by thin-layer chromatography (TLC) analysis, and we presumptively designated this new spot as HD-G. The n, we carried out the purification of the presumptive HD-G spot from the reaction mixture by using silica gel chromatography, and its mass was measured by electrospray ionization-mass spectrometry. The purified new spot on the chromatograph was identified a sodium adduct ion ([M+Na] + , m/z = 303.1423) of HD-G. In addition, when purified HD-G was hydrolyzed using commercially available E. coli β-gal, it was observed that a galactose molecule was released from HD-G. That is, it was demonstrated that HD-G is a galactoside derivative of HD. Finally, we confirmed that HD-G was enzymatically synthesized by E. coli β -gal as a new molecular entity. In the future, we plan to determine the minimum inhibitory concentrations of HD-G against different bacterial species. The cytotoxicity of HD-G against human skin cells will also be examined. It is expected hopefully that the galactosylation of HD would improve the functionality of HD-G.
- Published
- 2016
33. Refining effect of electron beam melting on additive manufacturing of pure titanium products
- Author
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Hyung Giun Kim, Kyung Hwan Jung, Chang-Woo Lee, Byoung Soo Lee, Yong Keun Ahn, and Hyung-Ki Park
- Subjects
Imagination ,Materials science ,Chemical substance ,media_common.quotation_subject ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,law.invention ,Magazine ,law ,General Materials Science ,media_common ,Refining (metallurgy) ,Mechanical Engineering ,Metallurgy ,Final product ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,0104 chemical sciences ,chemistry ,Mechanics of Materials ,Cathode ray ,0210 nano-technology ,Science, technology and society ,Titanium - Abstract
The refining effect of electron beam melting (EBM) during the additive manufacturing of Ti products was studied by comparing unused Grade-2 commercially pure (CP) Ti powder to an equivalent powder that had been recycled 50 times. The pre-heating and blasting processes that occur during recycling were found to degrade the perfectly spherical morphology of the powder, and the concentration of O and N were also increased by about 15%. This resulted in it changing to a Grade-3 CP Ti powder; however, the purity of the final product was improved to Grade-1 CP Ti by the slight refining effect of the EBM process.
- Published
- 2017
34. Fabrication of porous pure titanium via selective laser melting under low-energy-density process conditions
- Author
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Hyung-Ki Park, Hyung Giun Kim, Won Rae Kim, Gyung Bae Bang, Hyo-Tae Jeong, Ohyung Kwon, Kyung-Hwan Jung, and Gun-Hee Kim
- Subjects
Metal forming and shaping ,Materials science ,Fabrication ,Laser processing ,chemistry.chemical_element ,02 engineering and technology ,Crystal structure ,010402 general chemistry ,01 natural sciences ,Sintering ,Specific surface area ,lcsh:TA401-492 ,Porous materials ,General Materials Science ,Selective laser melting ,Composite material ,Porosity ,Mechanical Engineering ,Partial melting ,021001 nanoscience & nanotechnology ,Microstructure ,0104 chemical sciences ,chemistry ,Mechanics of Materials ,lcsh:Materials of engineering and construction. Mechanics of materials ,Powder technology ,0210 nano-technology ,Titanium - Abstract
By controlling specific process conditions in the selective laser melting (SLM) of commercially pure Ti powder (Grade 1), a porous structure was fabricated to achieve a high specific surface area. Additive manufacturing was employed through SLM to control the energy density to be lower than that required for the complete melting of Ti powders by operating at a power of 80 to 480 W and a scan speed of 1750 to 10,500 mm/s. The range of the process conditions, i.e., complete melting, partial melting, and unmelted, was determined based on the observations of the microstructure parallel to the building direction. When the powders were pre-sintered and not melted under specific process conditions with an energy density lower than that required for complete melting, porous microstructures were formed with open pores. In addition, interfacial microstructural studies were conducted to confirm the presence of residual powder, which settled onto the strut, resulting in a higher specific surface area. These indicate that the SLM process can enhance the porosity, even with a specific design of lattice structures, as fluidic materials are expected to flow through the open porous structure.
- Published
- 2020
35. Graphene Quantum Dots: Fundamental Understanding of the Formation Mechanism for Graphene Quantum Dots Fabricated by Pulsed Laser Fragmentation in Liquid: Experimental and Theoretical Insight (Small 38/2020)
- Author
-
Sungwook Mhin, Kyung Hwan Jung, HyukSu Han, Won Rae Kim, Jeong Ho Ryu, Kangpyo Lee, Kang Min Kim, Heechae Choi, Yong Son, and Suk Hyun Kang
- Subjects
Biomaterials ,Pulsed laser ,Materials science ,Fragmentation (mass spectrometry) ,Graphene ,law ,Quantum dot ,General Materials Science ,Nanotechnology ,General Chemistry ,Multiwalled carbon ,Biotechnology ,law.invention - Abstract
The pulsed laser fragmentation in liquid (PLFL) process is a promising technique for the synthesis of carbon‐based functional materials. However, a fundamental deep understanding of the formation of graphene quantum dots (GQDs) from multiwalled carbon nanotubes (MWCNTs) by PLFL has still not been achieved despite the high demand. In article number 2003538, Jeong Ho Ryu, Hyuksu Han, Kang Min Kim, and co‐workers report a mechanism for the formation of GQDs from MWCNTs by the PLFL process, through the combination of experimental and theoretical studies.
- Published
- 2020
36. Fundamental Understanding of the Formation Mechanism for Graphene Quantum Dots Fabricated by Pulsed Laser Fragmentation in Liquid: Experimental and Theoretical Insight
- Author
-
Suk Hyun Kang, Kangpyo Lee, Kang Min Kim, HyukSu Han, Won Rae Kim, Kyung Hwan Jung, Sungwook Mhin, Heechae Choi, Jeong Ho Ryu, and Yong Son
- Subjects
Pulsed laser ,Materials science ,Graphene ,Nanotechnology ,02 engineering and technology ,General Chemistry ,Plasma ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Pulsed laser deposition ,law.invention ,Biomaterials ,Amorphous carbon ,Fragmentation (mass spectrometry) ,Quantum dot ,law ,Critical energy ,General Materials Science ,0210 nano-technology ,Biotechnology - Abstract
The pulsed laser fragmentation in liquid (PLFL) process is a promising technique for the synthesis of carbon-based functional materials. In particular, there has been considerable attention on graphene quantum dots (GQDs) derived from multiwalled carbon nanotubes (MWCNTs) by the PLFL process, owing to the low cost and rapid processing time involved. However, a fundamental deep understanding of the formation of GQDs from MWCNTs by PLFL has still not been achieved despite the high demand. In this work, a mechanism for the formation of GQDs from MWCNTs by the PLFL process is reported, through the combination of experimental and theoretical studies. Both the experimental and computational results demonstrate that the formation of GQDs strongly depends on the pulse laser energy. Both methods demonstrate that the critical energy point, where a plasma plume is generated on the surface of the MWCNTs, should be precisely maintained to produce GQDs; otherwise, an amorphous carbon structure is favorably formed from the scattered carbons.
- Published
- 2020
37. Pulsed laser ablation based synthetic route for nitrogen-doped graphene quantum dots using graphite flakes
- Author
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Suk Hyun Kang, Yong Son, Byoung-Soo Lee, Young Kyu Jeong, Kyung Hwan Jung, Jeong Ho Ryu, Kang Min Kim, and Won Rae Kim
- Subjects
Photoluminescence ,Materials science ,General Physics and Astronomy ,chemistry.chemical_element ,Quantum yield ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,law.invention ,law ,Graphite ,Spectroscopy ,business.industry ,Graphene ,Surfaces and Interfaces ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Graphene quantum dot ,0104 chemical sciences ,Surfaces, Coatings and Films ,chemistry ,Quantum dot ,Optoelectronics ,0210 nano-technology ,business ,Carbon - Abstract
Graphene quantum dots (GQDs) prepared by pulsed laser ablation in liquid (PLAL) process face barriers to commercialization due to their poor optical properties and the use of expensive carbon precursors. In this work, we report a one-step route for the preparation of N-doped graphene quantum dots (NGQDs) with excellent optical properties using a low-cost carbon precursor. The as-prepared NGQDs exhibited excellent optical properties and high quantum yield compared to pristine graphene quantum dots (0.8% → 9.1%) due to the presence of the N atoms. A possible recombination mechanism of NGQDs was investigated by time-resolved photoluminescence spectroscopy. The increase of N atoms incorporated in the GQDs resulted in an increased fraction of the short recombination lifetime from the intrinsic state. We also report a possible mechanism for the formation of the N atoms in the GQDs structure during the PLAL process, which is explained based on the plasma plume, cavitation collapse, and nitrogen precursor decomposition model.
- Published
- 2020
38. Chlorphenesin Galactoside Production using Immobilized β-galactosidase-producing Escherichia coli
- Author
-
Kyung-Hwan Jung
- Subjects
chemistry.chemical_compound ,Chemistry ,medicine ,Alginate bead ,medicine.disease_cause ,Escherichia coli ,Galactoside ,Microbiology - Published
- 2015
39. Study of Alloying Behavior of Metal Cation Precursors via Polymer Solution Route
- Author
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Sang-Jin Lee, Kyung-Hwan Jung, Choong-Hwan Jung, and Jin-Sung Lee
- Subjects
Modeling and Simulation ,Metals and Alloys ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Published
- 2015
40. Ethanol Production from Glycerol Using Immobilized Pachysolen tannophilus During Microaerated Repeated-Batch Fermentor Culture
- Author
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Kyung-Hwan Jung, Woon Yong Choi, Hye-Geun Cha, Do-Hyung Kang, Hyeon-Yong Lee, and Yi-Ok Kim
- Subjects
Glycerol ,Chromatography ,Ethanol ,biology ,General Medicine ,Cells, Immobilized ,biology.organism_classification ,Diatomaceous Earth ,Applied Microbiology and Biotechnology ,Pachysolen tannophilus ,chemistry.chemical_compound ,chemistry ,Batch Cell Culture Techniques ,Biofuel ,Biofuels ,Fermentation ,Saccharomycetales ,Ethanol fuel ,Ethanol metabolism ,Biotechnology - Abstract
Herein, we established a repeated-batch process for ethanol production from glycerol by immobilized Pachysolen tannophilus. The aim of this study was to develop a more practical and applicable ethanol production process for biofuel. In particular, using industrial-grade medium ingredients, the microaeration rate was optimized for maximization of the ethanol production, and the relevant metabolic parameters were then analyzed. The microaeration rate of 0.11 vvm, which is far lower than those occurring in a shaking flask culture, was found to be the optimal value for ethanol production from glycerol. In addition, it was found that, among those tested, Celite was a more appropriate carrier for the immobilization of P. tannophilus to induce production of ethanol from glycerol. Finally, through a repeated-batch culture, the ethanol yield (Ye/g) of 0.126 ± 0.017 g-ethanol/g-glycerol (n = 4) was obtained, and this value was remarkably comparable with a previous report. In the future, it is expected that the results of this study will be applied for the development of a more practical and profitable long-term ethanol production process, thanks to the industrial-grade medium preparation, simple immobilization method, and easy repeated-batch operation.
- Published
- 2015
41. Enzymatic Synthesis of 2-Phenoxyethanol Galactoside by Whole Cells of ��-Galactosidase-Containing Escherichia coli
- Author
-
Hyang Yeol Lee and Kyung Hwan Jung
- Subjects
Chromatography ,Galactose ,Galactosides ,General Medicine ,beta-Galactosidase ,medicine.disease_cause ,Mass spectrometry ,Applied Microbiology and Biotechnology ,Galactoside ,Hydrolysate ,chemistry.chemical_compound ,chemistry ,Covalent bond ,Yield (chemistry) ,Escherichia coli ,medicine ,Molecule ,Ethylene Glycols ,Biotechnology - Abstract
We investigated whether β-galactosidase (β-gal)-containing Escherichia coli cells could transfer a galactose to 2-phenoxyethanol, resulting in 2-phenoxyethanol galactoside (PE-Gal). PE-Gal was confirmed by liquid chromatography-mass spectrometry. In addition, we also confirmed that a galactose molecule was covalently bonded with PE during thin-layer chromatography analysis of the β-gal hydrolysate of PE-Gal. The yield for PE-Gal synthesis was about 37.5% (weight basis), which was about 7-8 times greater than that of a previous report. In addition, the concentration of β-gal (0.96 U/ml) used in this PE-Gal synthesis was about 20 times less than that in a previous report.
- Published
- 2014
42. Evaluating Carriers for Immobilizing Saccharomyces cerevisiae for Ethanol Production in a Continuous Column Reactor
- Author
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Hyeon-Yong Lee, Do-Hyung Kang, Yi-Ok Kim, Kyung-Hwan Jung, Woon Yong Choi, and Hye-Geun Cha
- Subjects
Immobilization carrier ,Saccharomyces cerevisiae ,Biology ,Microbiology ,Husk ,chemistry.chemical_compound ,Ethanol fuel ,Chromatography ,Ethanol ,business.industry ,Biosorption ,food and beverages ,Straw ,Sawdust ,Yeast ,Biotechnology ,Infectious Diseases ,chemistry ,Ethanol production ,visual_art ,visual_art.visual_art_medium ,Fermentation ,business ,Continuous column reactor ,Research Article - Abstract
We evaluated a more practical and cost-effective immobilization carriers for ethanol production using the yeast Saccharomyces cerevisiae. Three candidate materials-rice hull, rice straw, and sawdust-were tested for their cell-adsorption capacity and operational durability. Derivatizations of rice hull, rice straw, and sawdust with the optimal concentration of 0.5 M of 2-(diethylamino)ethyl chloride hydrochloride (DEAE · HCl) resulted in > 95% adsorption of the initial yeast cells at 2 hr for DEAE-rice hull and DEAE-sawdust and in only approximately 80% adsorption for DEAE-rice straw. In addition, DEAE-sawdust was found to be a more practical carrier for immobilizing yeast cells in terms of operational durability in shaking flask cultures with two different speeds of 60 and 150 rpm. Furthermore, the biosorption isotherms of DEAE-rice hull, -rice straw, and -sawdust for yeast cells revealed that the Qmax of DEAE-sawdust (82.6 mg/g) was greater than that of DEAE-rice hull and DEAE-rice straw. During the 404-hr of continuous column reactor operation using yeast cells immobilized on DEAE-sawdust, no serious detachment of the yeast cells from the DEAE-sawdust was recorded. Ethanol yield of approximately 3.04 g/L was produced steadily, and glucose was completely converted to ethanol at a yield of 0.375 g-ethanol/g-glucose (73.4% of the theoretical value). Thus, sawdust is a promising practical immobilization carrier for ethanol production, with significance in the production of bioethanol as a biofuel.
- Published
- 2014
43. Numerical study of the effect of prior deformation history on texture evolution during equal channel angular pressing
- Author
-
Won-Woong Park, Kyung-Hwan Jung, Yong-Taek Im, Yong-Shin Lee, and Dong-Kyu Kim
- Subjects
Pressing ,Materials science ,General Computer Science ,Metallurgy ,General Physics and Astronomy ,General Chemistry ,Plasticity ,Deformation (meteorology) ,Rotation ,Simple shear ,Computational Mathematics ,Mechanics of Materials ,General Materials Science ,Extrusion ,Texture (crystalline) ,Severe plastic deformation ,Composite material - Abstract
It is experimentally well known that mechanical properties of the material depend on crystallographic texture distribution which varies depending on deformation history. When the material deforms at several stages, it is not easy to follow up the effect of prior deformation on the final texture of the material. In the present study, the effect of deformation history on texture evolution during equal channel angular pressing (ECAP) of FCC polycrystalline metal like AA1050 is investigated by the finite element method and polycrystal plasticity model based on full constraints Taylor model. The texture evolution during the multi-pass ECAP is simulated with the initial textures determined by three virtual specimens prepared by the fully annealed, extruded, and flat-rolled materials. By comparing the pole figures and orientation distribution functions, the effect of prior deformation histories on the texture evolution is numerically studied according to the routes A and C up to four passes across the thickness of the specimen. For the extruded specimen, it is not enough to wipe out the trace of the initial textures originated from the extrusion even after four passes. For the rolled specimen, strong development of the rotated simple shear texture readily occurred with the rotation about the transverse direction of the ECAP die. This study indicates that it is necessary to control the initial texture properly for achieving a desired mechanical property.
- Published
- 2014
44. Ethanol Production from Glycerol using Pachysolen tannophilus in a Surface-aerated Fermentor
- Author
-
Woon-Yong Choi, Kyung-Hwan Jung, Do-Hyung Kang, Yi-Ok Kim, and Hyeon-Yong Lee
- Subjects
chemistry.chemical_compound ,Ethanol ,chemistry ,Biochemistry ,Glycerol ,Yeast extract ,Ethanol fuel ,Fermentation ,Food science ,Aeration ,Yeast ,Fed-batch culture - Abstract
We investigated ethanol production from glycerol after screening of the yeast Pachysolen tannophilus ATCC 32691. For yeast to produce ethanol form glycerol, it is important that aeration is finely controlled. Therefore, we attempted to produce ethanol using a surface-aerated fermentor. When 880 ml of YPG medium (1% yeast extract, 2% peptone, 2% glycerol) was used to produce ethanol, the optimal aeration conditions for ethanol production were a surface aeration rate and agitation speed of 500 ml/min and 300 rpm, respectively. In a fed-batch culture, the maximum ethanol production and the maximum ethanol yield from glycerol (Ye/g) was 5.74 g/l and 0.166, respectively, after 90 hr using the surface-aerated fermentor.
- Published
- 2013
45. Prediction of the effects of hardening and texture heterogeneities by finite element analysis based on the Taylor model
- Author
-
Yong-Taek Im, Dong-Kyu Kim, Yong-Shin Lee, and Kyung-Hwan Jung
- Subjects
Materials science ,Equal channel angular extrusion ,Mechanical Engineering ,Constitutive equation ,Metallurgy ,Mechanics ,Finite element method ,Simple shear ,Euler angles ,symbols.namesake ,Mechanics of Materials ,Mesh generation ,symbols ,Hardening (metallurgy) ,General Materials Science ,Anisotropy - Abstract
The main objective of this study is to simulate deformation induced anisotropy during the upsetting of commercially available pure aluminum AA1050 after being processed by the equal channel angular extrusion (ECAE) process including the friction effect. A Taylor-type polycrystalline constitutive model was adopted to investigate the effects of texture evolution and deformation heterogeneity during the ECAE and upsetting. In order to save computation time, a decoupled analysis between the crystal plasticity model and finite element method for the multi-pass ECAE and a fully coupled analysis for the subsequent upsetting process were conducted. The rigid-viscoplastic finite element analysis of the ECAE was carried out to determine the history of velocity gradient during the ECAE process in order to identify the effects of the processing routes A and C on texture evolution. The calculated history was applied to the crystal plasticity model to obtain the crystallographic texture distribution. Then, a finite element analysis based on the Taylor model was conducted for prediction of the anisotropic behavior of the three-pass ECAEed specimens which was obtained by applying the ECAE of the aluminum alloy AA1050 with routes A and C, respectively. For this analysis, algorithms for the data transfer of Euler angles and hardness were developed and implemented into the program. The good agreement between the measured and simulated deformed shapes indicates that the proposed simulation technique with the data transfer algorithms can be used effectively to simulate deformation induced heterogeneity during the bulk forming process.
- Published
- 2013
46. Stable Isolation of Phycocyanin from Spirulina platensis Associated with High-Pressure Extraction Process
- Author
-
Hyeon Yong Lee, Woo Seok Choi, Yong Chang Seo, Jong Ho Park, Jin Oh Park, and Kyung-Hwan Jung
- Subjects
DPPH ,Spirulina platensis ,macromolecular substances ,Catalysis ,Article ,Inorganic Chemistry ,Absorbance ,lcsh:Chemistry ,chemistry.chemical_compound ,Bacterial Proteins ,Chromoprotein ,Phycocyanin ,Pressure ,Spirulina ,Physical and Theoretical Chemistry ,high-pressure extraction process ,Molecular Biology ,lcsh:QH301-705.5 ,Spectroscopy ,Spirulina (genus) ,Chromatography ,biology ,Organic Chemistry ,Extraction (chemistry) ,phycocyanin ,General Medicine ,biology.organism_classification ,Computer Science Applications ,Solvent ,chemistry ,lcsh:Biology (General) ,lcsh:QD1-999 ,Yield (chemistry) - Abstract
A method for stably purifying a functional dye, phycocyanin from Spirulina platensis was developed by a hexane extraction process combined with high pressure. This was necessary because this dye is known to be very unstable during normal extraction processes. The purification yield of this method was estimated as 10.2%, whose value is 3%–5% higher than is the case from another conventional separation method using phosphate buffer. The isolated phycocyanin from this process also showed the highest purity of 0.909 based on absorbance of 2.104 at 280 nm and 1.912 at 620 nm. Two subunits of phycocyanin namely α-phycocyanin (18.4 kDa) and β-phycocyanin (21.3 kDa) were found to remain from the original mixtures after being extracted, based on SDS-PAGE analysis, clearly demonstrating that this process can stably extract phycocyanin and is not affected by extraction solvent, temperature, etc. The stability of the extracted phycocyanin was also confirmed by comparing its DPPH (α,α-diphenyl-β-picrylhydrazyl) scavenging activity, showing 83% removal of oxygen free radicals. This activity was about 15% higher than that of commercially available standard phycocyanin, which implies that the combined extraction method can yield relatively intact chromoprotein through absence of degradation. The results were achieved because the low temperature and high pressure extraction effectively disrupted the cell membrane of Spirulina platensis and degraded less the polypeptide subunits of phycocyanin (which is a temperature/pH-sensitive chromoprotein) as well as increasing the extraction yield.
- Published
- 2013
47. Mesoscopic Modeling of Primary Recrystallization of AA1050 with Curvature-Driven Interface Migration Effect
- Author
-
Kyung-Hwan Jung, Ho Won Lee, Yong-Taek Im, and Dong-Kyu Kim
- Subjects
Materials science ,Misorientation ,Mechanical Engineering ,Nucleation ,Thermodynamics ,Recrystallization (metallurgy) ,Condensed Matter Physics ,Microstructure ,Crystallography ,Mechanics of Materials ,Dynamic recrystallization ,General Materials Science ,Grain boundary ,Anisotropy ,Electron backscatter diffraction - Abstract
Primary recrystallization is an important phenomenon involved with cold deformation and heat treatment process. In the presentinvestigation, a two dimensional probabilistic cellular automata model is used to simulate primary recrystallization of cold rolled AA1050,commercially pure aluminum. Electron backscatter diffraction measurement data was used as an input for the simulation to consider highlyheterogeneous distribution of the stored energy and orientations compared to the randomly-distributed initial microstructure. Nucleation processwas assumed to be site-saturated. Once a nucleus is formed, its recrystallization front will sweep the deformed regions by dissipating the storeddeformation energy. In an attempt to contemplate anisotropic property of grain boundary migration, the grain boundary mobility was representedas a function of misorientation and the pressure was expressed as a function of dislocation density difference, curvature, and misorientation. Theresults of CA simulations were compared well with the JMAK theory in order to investigate the effects of nucleation criteria and curvature-driven pressure on the microstructure and the kinetics of primary recrystallization. This study revealed that local interface migration bycurvature-driven pressure could significantly affect the recrystallization kinetics and microstructure morphology depending on the nucleationcriteria. [doi:10.2320/matertrans.M2012267](Received July 31, 2012; Accepted October 10, 2012; Published December 25, 2012)Keywords: primary recrystallization, cellular automata, curvature-driven pressure, microstructure, kinetics
- Published
- 2013
48. Crystal Plasticity Finite Element Analysis of Texture Evolution during Rolling of fcc Polycrystalline Metal
- Author
-
Dong-Kyu Kim, Yong-Taek Im, Yong-Shin Lee, and Kyung-Hwan Jung
- Subjects
Materials science ,Mechanical Engineering ,Constitutive equation ,Metallurgy ,Pole figure ,Condensed Matter Physics ,Finite element method ,Distribution function ,Mechanics of Materials ,Orientation (geometry) ,General Materials Science ,Texture (crystalline) ,Crystallite ,Composite material ,Deformation (engineering) - Abstract
Localized strain and crystallographic orientation distribution during rolling process have a significant effect on anisotropic flow behavior in sheet forming of aluminum alloy, resulting in local thinning. In this study, crystal plasticity finite element method (CPFEM), which incorporates a crystal plasticity constitutive law into the three-dimensional finite element method, was used to investigate strain localization and textural evolution during the flat rolling process of the face-centered-cubic material. A rate-dependent polycrystalline theory based on the Taylor model was fully implemented into an in-house program, CAMProll3D. The through-thickness texture evolution depending on the degree of draught was predicted by using the developed CPFEM program and compared well with the experimental data available in the literature. The orientation distributions not only in the thickness direction but also in the width direction of the flat rolled sheet were investigated depending on the amount of reduction during the multi-pass flat rolling in terms of pole figure, orientation distribution function and flow potential surface in the 3-plane. Finally, the effect of friction condition between the rolls and the material on rotation about the transverse direction was found to be important to determine the texture evolution at the surface of the rolled sheet. [doi:10.2320/matertrans.M2012346]
- Published
- 2013
49. Preparation of Corncob Grits as a Carrier for Immobilizing Yeast Cells for Ethanol Production
- Author
-
Choon Geun Lee, Sang-Eun Lee, Kyung-Hwan Jung, Hyeon-Yong Lee, and Do-Hyung Kang
- Subjects
Chromatography ,Ethanol ,biology ,Chemistry ,Saccharomyces cerevisiae ,Biosorption ,General Medicine ,Cells, Immobilized ,Corncob ,biology.organism_classification ,Zea mays ,Applied Microbiology and Biotechnology ,Yeast ,Hydrolysate ,chemistry.chemical_compound ,Bioreactors ,Adsorption ,Ethanolamines ,Biofuels ,Ethanol fuel ,Biotechnology - Abstract
In this study, DEAE-corncobs [delignified corncob grits derivatized with 2-(diethylamino)ethyl chloride hydrochloride (DEAE·HCl)] were prepared as a carrier to immobilize yeast (Saccharomyces cerevisiae) for ethanol production. The immobilized yeast cell reactor produced ethanol under optimized DEAE·HCl derivatization and adsorption conditions between yeast cells and the DEAE-corncobs. When delignified corncob grit (3.0 g) was derivatized with 0.5M DEAE·HCl, the yeast cell suspension (OD600 = 3.0) was adsorbed at >90% of the initial cell OD600. This amount of adsorbed yeast cells was estimated to be 5.36 mg-dry cells/g-DEAE corncobs. The Qmax (the maximum cell adsorption by the carrier) of the DEAE-corncobs was estimated to be 25.1 (mg/g), based on a Languir model biosorption isotherm experiment. When we conducted a batch culture with medium recycling using the immobilized yeast cells, the yeast cells on DEAE-corncobs produced ethanol gradually, according to glucose consumption, without cells detaching from the DEAE-corncobs. We observed under electron microscopy that the yeast cells grew on the surface and in the holes of the DEAEcorncobs. In a future study, DEAE-corncobs and the immobilized yeast cell reactor system will contribute to bioethanol production from biomass hydrolysates.
- Published
- 2012
50. Long-term Repeated-Batch Operation of Immobilized Escherichia coli Cells to Synthesize Galactooligosaccharide
- Author
-
Kyung Hwan Jung, Sang-Eun Lee, and Ji Hyeon Yeon
- Subjects
Inclusion Bodies ,Chromatography ,Galactooligosaccharide ,Escherichia coli Proteins ,Thermophile ,Galactose ,Oligosaccharides ,General Medicine ,Cells, Immobilized ,beta-Galactosidase ,medicine.disease_cause ,Applied Microbiology and Biotechnology ,chemistry.chemical_compound ,Bioreactors ,chemistry ,Biochemistry ,Reactor system ,Microbial enzymes ,Escherichia coli ,medicine ,Glutaraldehyde ,Batch operation ,Operational stability ,Biotechnology - Abstract
In this study, we investigated whether galactooligosaccharide (GOS) can be stably and steadily synthesized using immobilized beta-galactosidase (β-gal) inclusion body (IB)- containing E. coli cells during long-term repeated-batch operation. To improve the operational stability of this enzyme reactor system, immobilized E. coli cells were crosslinked with glutaraldehyde (GA) after immobilization of the E. coli. When we treated with 2% GA for E. coli crosslinking, GOS production continued to an elapsed time of 576 h, in which seven batch runs were operated consecutively. GOS production ranged from 51.6 to 78.5 g/l (71.2 ± 10.5 g/l, n = 7) during those batch operations. In contrast, when we crosslinked E. coli with 4% GA, GOS production ranged from 31.5 to 64.0 g/l (52.3 ± 10.8, n = 4), and only four consecutive batch runs were operated. Although we did not use an industrial β-gal for GOS production, in which a thermophile is used routinely, this represents the longest operation time for GOS production using E. coli β-gal. Improved stability and durability of the cell immobilization system were achieved using the crosslinking protocol. This strategy could be directly applied to other microbial enzyme reactor systems using cell immobilization to extend the operation time and/or improve the reactor system stability.
- Published
- 2012
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