24 results on '"Kyungho Lee"'
Search Results
2. Successful kidney transplantation from a deceased donor with severe COVID-19 respiratory illness with undetectable SARS-CoV-2 in donor kidney and aorta
- Author
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Kyungho Lee, Niraj M. Desai, Jessica Resnick, Maggie Li, Andrew Johanson, Andrew Pekosz, Hamid Rabb, and Joseph L. Mankowski
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Transplantation ,SARS-CoV-2 ,COVID-19 ,Humans ,Immunology and Allergy ,Pharmacology (medical) ,Kidney ,Kidney Transplantation ,Article ,Aorta - Published
- 2022
3. Testing for time stochastic dominance
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Kyungho Lee, Oliver Linton, and Yoon-Jae Whang
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Economics and Econometrics ,Applied Mathematics - Published
- 2022
4. Single-step hydroconversion of triglycerides into biojet fuel using CO-tolerant PtRe catalyst supported on USY
- Author
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Mi-Eun Lee, Kyungho Lee, Minkee Choi, Jae-Kon Kim, and Byeongcheol Shin
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010405 organic chemistry ,Chemistry ,Coke ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Chemical engineering ,Methanation ,Hydrogenolysis ,Physical and Theoretical Chemistry ,Bifunctional ,Zeolite ,Deoxygenation ,Syngas - Abstract
The direct hydroconversion of triglycerides into biojet fuel (i.e., cascade reactions including hydrogenation, deoxygenation, and hydrocracking) is challenging, even though it is beneficial in terms of process intensification. This is because the minute amount of CO produced during deoxygenation can poison the metal component of various metal–acid bifunctional catalysts, causing undesired overcracking and rapid catalyst deactivation through coke formation. To overcome this problem, we synthesized a CO-tolerant catalyst by supporting bimetallic PtRe on ultra-stable Y (USY) zeolite as acidic support. Compared to conventional catalyst (e.g., Pt/USY), PtRe/USY showed markedly enhanced tolerance to CO because it had weakened interaction with CO and also could rapidly convert the chemisorbed CO into less harmful methane and H2O through methanation. Consequently, overcracking and catalyst deactivation were greatly suppressed during the direct triglyceride hydroconversion. It is remarkable that PtRe/USY is intrinsically a much poorer hydrocracking catalyst than Pt/USY under pure H2 atmosphere because of its high hydrogenolysis activity. However, H2O and CO produced in situ during the deoxygenation of triglycerides selectively poisoned the active sites for undesired hydrogenolysis, thereby making PtRe/USY a highly stable and selective catalyst for producing biojet fuel. Under the optimum condition, 41 wt% of biojet fuel with respect to palm oil could be produced through direct hydroconversion, which satisfied all the required fuel specifications.
- Published
- 2019
5. Importance of pore size and Lewis acidity of Pt/Al2O3 for mitigating mass transfer limitation and catalyst fouling in triglyceride deoxygenation
- Author
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Myungwon Oh, Mingyu Jin, Kyungho Lee, Jeong-Chul Kim, Ryong Ryoo, and Minkee Choi
- Subjects
General Chemical Engineering ,Environmental Chemistry ,General Chemistry ,Industrial and Manufacturing Engineering - Published
- 2022
6. Atomic Pd-promoted ZnZrO solid solution catalyst for CO2 hydrogenation to methanol
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Kyungho Lee, Uzma Anjum, Thaylan Pinheiro Araújo, Cecilia Mondelli, Qian He, Shinya Furukawa, Javier Pérez-Ramírez, Sergey M. Kozlov, and Ning Yan
- Subjects
Process Chemistry and Technology ,Catalysis ,General Environmental Science - Published
- 2022
7. Effects of secondary mesoporosity and zeolite crystallinity on catalyst deactivation of ZSM-5 in propanal conversion
- Author
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Youngsun Jun, Kyungho Lee, Minkee Choi, and Songhyun Lee
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Chemistry ,Diffusion ,Inorganic chemistry ,02 engineering and technology ,General Chemistry ,Microporous material ,Coke ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Crystallinity ,Mechanics of Materials ,General Materials Science ,ZSM-5 ,0210 nano-technology ,Zeolite ,Mesoporous material - Abstract
Cooperative effects of secondary mesoporosity and zeolite crystallinity on the deactivation of ZSM-5 were investigated during propanal conversion. Varied secondary mesoporosities were introduced into a commercial ZSM-5 by alkaline desilication using solutions with different NaOH concentrations (0.1–0.5 M). The results showed that the mesoporosity gradually increased with the concentration of NaOH, while the intrinsic zeolitic microporosity decreased. This indicated that the alkaline desilication for mesopore generation is a destructive technique that sacrifices the zeolite crystallinity. In propanal conversion, ZSM-5 showed a longer catalyst lifetime as the external surface area increased (or as the zeolite framework thickness decreased) in the mild desilication regime (NaOH concentration ≤ 0.3 M). The enhanced catalyst lifetime could be attributed to the facilitated diffusion of coke precursors out of the zeolite structure. However, when the zeolite crystallinity or microporosity of ZSM-5 was decreased too much from excessively severe alkaline treatments (NaOH concentration > 0.3 M), deactivation of the catalyst became again faster. The result indicates that the crystallinity or the microporosity of ZSM-5 is also important in suppressing coke formation. This is in line with earlier reports showing that coke formation itself is a shape-selective reaction and significantly inhibited in the constrained space of the unique 10-membered micropore channels of ZSM-5. The present results imply that the generation of large mesoporosity (enhancing the diffusion of coke precursors) while keeping the zeolite crystallinity intact (suppressing coke formation by shape-selectivity) is highly desirable for designing a zeolite catalyst with an enhanced catalyst lifetime.
- Published
- 2017
8. Characterization and regulated naproxen release of hydroxypropyl cyclosophoraose-pullulan microspheres
- Author
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Jae-Hyuk Yu, Benel Lee, Seyeon Park, Seunho Jung, Kyeong Hui Park, Eunae Cho, Yong-Joon Jeon, Im-Soon Lee, Kyungho Lee, Sun Hee Do, Bong-Hyun Jun, Someshwar D. Dindulkar, Eun-Ji Choi, Jae Min Choi, and Daham Jeong
- Subjects
Naproxen ,Thermogravimetric analysis ,General Chemical Engineering ,Kinetics ,Pullulan ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,Solid-state nuclear magnetic resonance ,chemistry ,Drug delivery ,Emulsion ,medicine ,Organic chemistry ,Fourier transform infrared spectroscopy ,0210 nano-technology ,Nuclear chemistry ,medicine.drug - Abstract
Hydroxypropyl cyclosophoraose-pullulan (HPCys-Pul) microspheres were designed as a novel hybrid system of biocompatible pullulan matrice and pendant hydroxypropyl cyclosophoraoses with drug complexing ability. The HPCys-Pul microspheres were prepared by emulsion crosslinking method, and characterized using thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, and solid state NMR spectroscopy. By virtue of hydroxypropyl cyclosophoraoses, the developed microspheres can encapsulate 4.2-fold more naproxen than pullulan microspheres. Korsmeyer–Peppas model was introduced for describing release kinetics. In vivo naproxen release analysis was carried out in Sprague-Dawley (SD) rats. From those results HPCys-Pul microsphere will be a promising platform for controlled drug delivery.
- Published
- 2017
9. Cooperative effects of zeolite mesoporosity and defect sites on the amount and location of coke formation and its consequence in deactivation
- Author
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Minkee Choi, Songhyun Lee, Youngsun Jun, and Kyungho Lee
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Chemistry ,Annealing (metallurgy) ,Aromatization ,02 engineering and technology ,Coke ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Pentane ,chemistry.chemical_compound ,Polymerization ,Chemical engineering ,Physical and Theoretical Chemistry ,0210 nano-technology ,Zeolite ,Mesoporous material - Abstract
The cooperative effects of secondary mesoporosity and defects on the coke formation and deactivation of zeolite were investigated in n -pentane aromatization using model Ga/ZSM-5 catalysts. Mesoporosity was introduced to a commercial ZSM-5 by alkaline desilication, while the defects sites ( i.e. , internal silanols) in zeolites were annealed by the treatment with ammonium hexafluorosilicate. Aromatization after supporting Ga showed that the mesopore generation retarded catalyst deactivation via the suppression of internal coke formation while facilitating the external coke formation due to the enhanced diffusion of coke precursors (e.g ., alkylaromatics) out of zeolite micropores. Internal coke can cause a more severe deactivation than external coke because the acid sites are mainly located in the zeolite micropores. However, the mesopore generation alone could not efficiently reduce the total amount of coke deposition (it mainly changed the location of coke). In contrast, the annealing of internal silanols could suppress the overall coke formation. This phenomenon could be explained by the fact that coke precursors are initially generated at the zeolite internal defects, and then deposited as coke at either the internal or the external surfaces of the zeolite depending on the relative kinetics of coke precursor diffusion and its polymerization. Consequently, the catalyst with mesoporosity and annealed internal silanols exhibited the slowest catalyst deactivation due to the suppression of both internal and external coke depositions.
- Published
- 2017
10. Hierarchically micro-/mesoporous Pt/KL for alkane aromatization: Synergistic combination of high catalytic activity and suppressed hydrogenolysis
- Author
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Kyungho Lee and Minkee Choi
- Subjects
Alkane ,chemistry.chemical_classification ,Chemistry ,Aromatization ,02 engineering and technology ,Microporous material ,Alkylation ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Hydrogenolysis ,Physical and Theoretical Chemistry ,0210 nano-technology ,Mesoporous material ,Zeolite - Abstract
Pt/KL is a highly active and selective monofunctional catalyst for aromatization of n-alkanes due to its 1-dimensionally connected cage-like micropores. The unique micropore structure of the KL zeolite, however, can also inhibit the diffusion of bulky aromatic products out of the catalyst, which can cause unwanted side reactions that can decrease the aromatic yields. In this work, we investigated the effect of secondary mesoporosity, which can substantially facilitate molecular diffusion in Pt/KL during C6–C8 alkane aromatizations. The results showed that the hierarchically micro-/mesoporous Pt/KL synthesized with a subsequent dealumination/desilication method exhibited enhanced aromatic yields, compared with a conventional Pt/KL. In particular, in C7 and C8 aromatizations, the hierarchical Pt/KL showed substantially less formation of dealkylated aromatic products than the Pt/KL due to suppressed secondary hydrogenolysis. Pt supported on a solely mesoporous γ-Al2O3 also showed significantly suppressed secondary hydrogenolysis (dealkylation), which indicates that fast diffusion of alkylated aromatics out of the catalyst structure is important for suppressing the secondary hydrogenolysis. However, the solely mesoporous Pt/γ-Al2O3 showed markedly lower aromatization activities than the KL-supported catalysts, which indicates that Pt located inside the zeolite micropores is crucial for obtaining high catalytic activity due to the preorganization of n-alkanes in the micropores. The present results showed that the hierarchical Pt/KL provides the synergistically combined benefits of the Pt/KL and the mesoporous Pt catalyst, namely high aromatization activity and suppressed secondary hydrogenolysis, respectively.
- Published
- 2016
11. Revisiting hydrogen spillover in Pt/LTA: Effects of physical diluents having different acid site distributions
- Author
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Kyungho Lee, Minkee Choi, Ju Hwan Im, Songhyun Lee, and Hyungjun Kim
- Subjects
Hydrogen ,Inorganic chemistry ,chemistry.chemical_element ,Diluent ,Catalysis ,Dilution ,Metal ,chemistry.chemical_compound ,chemistry ,visual_art ,visual_art.visual_art_medium ,Lewis acids and bases ,Physical and Theoretical Chemistry ,Hydrogen spillover ,Benzene - Abstract
Historically, Pt/LTA (e.g., Pt/NaA) has often been used as a model catalyst for studying the catalytic functions of hydrogen spillover (H spillover). Notably, none of the works reported appreciable catalytic activities for Pt/LTA alone, while markedly enhanced activities were reported after physical dilution with some acidic oxides. It was often speculated without experimental evidence that activated hydrogen generated from Pt/LTA can migrate to the diluents surface (“inter-particular” H spillover) where organic reactants can react with spilt-over hydrogen. In this work, we carefully studied benzene hydrogenation activities of Pt/NaA and its decationized form (Pt/HA), before and after the physical dilution with various metal oxides possessing different Lewis and Bronsted acidity. The originally negligible activity of Pt/NaA increased significantly after mixing with various acidic oxides. The physical dilutions, however, resulted in a significant alteration of Pt/NaA structure due to solid-state H+ exchange, which made the catalytic interpretation vague. In contrast, Pt/HA structure did not change after the dilutions, and thus could be used as an ideal catalytic model system for studying inter-particular H spillover. The catalytic results showed that Al-rich metal oxides with abundant Lewis acid sites are effective for enhancing the catalytic activity.
- Published
- 2015
12. Cooperative effects of secondary mesoporosity and acid site location in Pt/SAPO-11 on n -dodecane hydroisomerization selectivity
- Author
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Minkee Choi, Kyungho Lee, and Myoung Yeob Kim
- Subjects
chemistry.chemical_classification ,Hydrocarbon ,Chemistry ,Yield (chemistry) ,Inorganic chemistry ,Microporous material ,Physical and Theoretical Chemistry ,Brønsted–Lowry acid–base theory ,Mesoporous material ,Selectivity ,Isomerization ,Catalysis - Abstract
Two different methods, organosilane templating and carbon templating, were used to generate secondary mesoporosity within SAPO-11. The former method produced mesoporous SAPO-11 samples with a large amount of external acidity, while the latter produced mesoporous samples containing predominantly internal acid sites. It was shown that, depending on the location of Bronsted acid sites, Pt supported on mesoporous SAPO-11 samples can exhibit widely ranging maximum isomerization yields from 13% to 84%, while solely microporous SAPO-11 showed 44% isomerization yield. The results indicate that the presence of secondary mesoporosity can be either remarkably beneficial or detrimental to hydroisomerization selectivity depending on the spatial location of the acid sites. The present results clearly showed that hydroisomerization selectivity of the catalysts can be significantly enhanced by facilitating the hydrocarbon diffusion via the formation of secondary mesopores while suppressing the formation of external acid sites that can non-selectively catalyze consecutive cracking reactions.
- Published
- 2014
13. Hempseed oil induces reactive oxygen species- and C/EBP homologous protein-mediated apoptosis in MH7A human rheumatoid arthritis fibroblast-like synovial cells
- Author
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Mini Jeong, Sung Joon Lee, Jaewook Cho, Eun-Soo Kim, Jong Il Shin, Kyungho Lee, Jin Hyun Kim, and Yong Joon Jeon
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Cell Survival ,Apoptosis ,Inflammation ,CHOP ,Pharmacology ,medicine.disease_cause ,Cell Line ,Arthritis, Rheumatoid ,Structure-Activity Relationship ,Drug Discovery ,medicine ,Humans ,Plant Oils ,Cytotoxic T cell ,Viability assay ,Cannabis ,Cell Proliferation ,chemistry.chemical_classification ,Reactive oxygen species ,Dose-Response Relationship, Drug ,Synovial Membrane ,Fibroblasts ,Biochemistry ,chemistry ,Seeds ,Unfolded protein response ,medicine.symptom ,Reactive Oxygen Species ,Transcription Factor CHOP ,Oxidative stress - Abstract
Ethnopharmacological relevance The medicinal efficacy of hempseed (Cannabis sativa L.), which is rich in polyunsaturated fatty acids, in atopic dermatitis, inflammation, and rheumatoid arthritis (RA) has been suggested for centuries. Hempseed has been used as a treatment for these diseases in Korean and Chinese folk medicine. The aim of the study is to investigate the effects of hempseed oil (HO) on MH7A human RA fibroblast-like synovial cells. Materials and methods MH7A cells were used to study the anti-rheumatoid effects of hempseed (Cannabis sativa L., cv. Cheungsam/Cannabaceae) oil by investigating cell viability, apoptosis, lipid accumulation, oxidative stress, and endoplasmic reticulum (ER) stress-induced apoptosis. Results HO treatment reduced the survival rate of MH7A cells and promoted apoptotic cell death in a time- and dose-dependent manner. Both lipid accumulation and the level of intracellular reactive oxygen species (ROS) increased in HO-treated MH7A cells. Co-treatment with the antioxidant Tiron effectively abrogated the cytotoxic effects of HO; the ROS level was reduced, cell viability was recovered, and apoptotic cell death was significantly diminished. Moreover, HO-treated cells exhibited increased expression of the major ER stress markers, glucose-regulated protein 78 and C/EBP homologous protein (CHOP). The siRNA-mediated knockdown of CHOP prevented HO-induced apoptosis. Conclusions Our results suggest that HO treatment induced lipid accumulation, ROS production, CHOP expression, and apoptosis in MH7A cells, and that CHOP functions as an anti-rheumatoid factor downstream of HO in MH7A cells.
- Published
- 2014
14. Apigenin-induced apoptosis is mediated by reactive oxygen species and activation of ERK1/2 in rheumatoid fibroblast-like synoviocytes
- Author
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Sang-Gyu Lee, Jaewook Cho, Kyungho Lee, Changyoun Kim, Mini Jeong, Wang-Sik Cho, Gu Choul Shin, and Jong-Min Lee
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MAPK/ERK pathway ,Cell Survival ,Immunoblotting ,Arthritis ,Apoptosis ,Inflammation ,Biology ,Toxicology ,Cell Line ,Arthritis, Rheumatoid ,chemistry.chemical_compound ,medicine ,Humans ,Apigenin ,Protein kinase A ,Protein Kinase Inhibitors ,Flavonoids ,Mitogen-Activated Protein Kinase 1 ,chemistry.chemical_classification ,Reactive oxygen species ,Mitogen-Activated Protein Kinase 3 ,General Medicine ,Flow Cytometry ,medicine.disease ,Cell biology ,Enzyme Activation ,Microscopy, Fluorescence ,chemistry ,Cell culture ,Caspases ,Cancer research ,medicine.symptom ,Reactive Oxygen Species - Abstract
Fibroblast-like synovial cells play a crucial role in the pathophysiology of rheumatoid arthritis (RA), as these cells are involved in inflammation and joint destruction. Apigenin, a dietary plant-flavonoid, is known to have many functions in animal cells including anti-proliferative and anticancer activities, but its role in human rheumatoid arthritis fibroblast-like synoviocytes (RA-FLSs) has not been reported. In this study, we investigated the roles of apigenin in RA-FLSs. The survival rate decreased, and apoptotic cell death was induced by apigenin treatment in RA-FLSs. Apigenin treatment resulted in activation of the mitogen-activated protein kinase (MAPK) ERK1/2, and pretreatment with an ERK inhibitor PD98059 dramatically reduced apigenin-induced apoptosis. We found that apigenin-mediated production of a large amount of intracellular reactive oxygen species (ROS) caused activation of ERK1/2 and apoptosis; treatment with the antioxidant Tiron strongly inhibited the apigenin-induced generation of ROS, phosphorylation of ERK1/2, and apoptotic cell death. Apigenin-induced apoptotic cell death was mediated through activation of the effectors caspase-3 and caspase-7, and was blocked by pretreatment with Z-VAD-FMK (a pan-caspase inhibitor). These results showed that apigenin-induced ROS and oxidative stress-activated ERK1/2 caused apoptotic cell death in apigenin-treated RA-FLSs.
- Published
- 2009
15. Design guideline for high-speed InP/InGaAs SHBT using a practical scaling law
- Author
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P. Pinsukanjana, J.M. Kuo, Daekyu Yu, K. Vargason, Bumman Kim, Kyungho Lee, H. Zhu, Kwangsik Choi, and Y.C. Kao
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Engineering ,Scaling law ,business.industry ,Bipolar junction transistor ,Condensed Matter Physics ,Capacitance ,Engineering physics ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,Scaling limit ,chemistry ,Materials Chemistry ,Miniaturization ,Electronic engineering ,Indium phosphide ,Electrical and Electronic Engineering ,business ,Scaling ,Common emitter - Abstract
For many years, HBTs have been vertically and laterally scaled down to improve high-frequency performance. For the very small devices of recent process, some parameters cannot be scaled down properly and an alternative scaling-law is required. In this paper, we describe the optimization issues for high-speed InP/InGaAs SHBTs and offer a design guideline to accommodate the scaling limit. From a 0.25 μm SHBT designed by the scaling law, the maximum extrapolated f max of about 687 GHz with f T of 215 GHz can be achieved. We also investigate the effect of key geometrical parameters such as emitter geometry and base/collector layer thicknesses on the device RF performance.
- Published
- 2006
16. ER stress signaling by regulated splicing: IRE1/HAC1/XBP1
- Author
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Randal J. Kaufman, Kyungho Lee, Martin Schröder, Kezhong Zhang, and Sung Hoon Back
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X-Box Binding Protein 1 ,Protein Folding ,Saccharomyces cerevisiae Proteins ,XBP1 ,RNA Splicing ,Molecular Sequence Data ,Regulatory Factor X Transcription Factors ,Protein Serine-Threonine Kinases ,Biology ,Endoplasmic Reticulum ,General Biochemistry, Genetics and Molecular Biology ,Mice ,Genes, Reporter ,Methods ,Animals ,Humans ,RNA, Messenger ,Molecular Biology ,Transcription factor ,Membrane Glycoproteins ,Base Sequence ,Endoplasmic reticulum ,Nuclear Proteins ,Cell biology ,DNA-Binding Proteins ,Repressor Proteins ,Basic-Leucine Zipper Transcription Factors ,Secretory protein ,RNA splicing ,Unfolded protein response ,Signal transduction ,Signal Transduction ,Transcription Factors - Abstract
The endoplasmic reticulum (ER) serves many specialized functions in the cell including calcium storage and gated release, biosynthesis of membrane and secretory proteins, and production of lipids and sterols. Therefore, the ER integrates many internal and external signals to coordinate downstream responses, although the mechanism(s) that maintain homeostasis are largely unknown. When misfolded or unfolded proteins accumulate in the ER, an intracellular signaling pathway termed the unfolded protein response (UPR) is activated. Identification of IRE1 in the yeast Saccharomyces cerevisiae as a proximal sensor in the UPR pathway was a milestone in understanding how the ER responds to the accumulation of unfolded protein and signals transcriptional activation through regulated nonconventional splicing of its substrate mRNA encoding the transcription factor Hac1p. Subsequent studies identified IRE1 and HAC1 homologues in mammalian cells. Here, we summarize various approaches to study the IRE1–Hac1 pathway in yeast and the homologous IRE1–XBP1 pathway in mammalian cells. We present microbiological growth assays for the UPR, reporter assays for UPR signaling, direct techniques to measure UPR activation in vivo, methods to study translation of HAC1 mRNA, and in vitro cleavage and ligation of HAC1 and XBP1 mRNA. Especially we think the newly developed quantitative and qualitative methods to detect IRE1 activity-dependent XBP1 mRNA splicing will be fast and accurate tools to show the activation of the UPR.
- Published
- 2005
17. An X-band InGaP GaAs HBT MMIC oscillator
- Author
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Jung Hyung Bae, Byoung-Gue Min, Cheol Park, Jongmin Lee, Kyungho Lee, Sungil Kim, Chang Woo Kim, Hong Ju Kim, and Young-Gi Kim
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Materials science ,business.industry ,General Physics and Astronomy ,Variable-frequency oscillator ,law.invention ,Vackář oscillator ,Voltage-controlled oscillator ,law ,RC oscillator ,Phase noise ,Optoelectronics ,General Materials Science ,Colpitts oscillator ,Pierce oscillator ,business ,Hartley oscillator - Abstract
This paper addresses the performance of a fully integrated low phase noise X-band oscillator fabricated by using an InGaP/GaAs HBT process with f t of 53.2 GHz. The oscillator circuit consists of a negative resistance generating circuit with base inductors, a resonating emitter circuit with micro-strip lines and a buffing resistive collector circuit with tuning diodes. The oscillator achieves 4.33 dBm output power and exhibits −121.17 dBc/Hz phase noise at 100 KHz away from 10.38 GHz oscillating frequency. This phase noise is, to our knowledge, the lowest reported for monolithic oscillators with oscillation frequencies higher than 10 GHz. The oscillator draws 36 mA current from a 6.19 V supply and occupies 0.8 mm by 0.8 mm die area.
- Published
- 2005
18. Low-frequency noise characteristics of metamorphic In0.52Al0.48As/In0.60Ga0.40As double-heterostructure pseudomorphic high electron mobility transistors grown on a GaAs substrate
- Author
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Jeong Hoon Kim, Jin-Hee Lee, Hyung-Sup Yoon, Kyungho Lee, Jae Yup Shim, Jong-In Song, and Woo Jin Chang
- Subjects
Materials science ,business.industry ,Noise spectral density ,Transconductance ,Infrasound ,Substrate (electronics) ,High-electron-mobility transistor ,Double heterostructure ,Condensed Matter Physics ,Noise (electronics) ,Electronic, Optical and Magnetic Materials ,Materials Chemistry ,Optoelectronics ,Flicker noise ,Electrical and Electronic Engineering ,business - Abstract
Low-frequency noise characteristics of metamorphic In0.52Al0.48As/In0.60Ga0.40As double-heterostructure pseudomorphic high electron mobility transistors (p-HEMTs) grown on a GaAs substrate are investigated. Low-frequency noise spectral density of the In0.52Al0.48As/In0.60Ga0.40As metamorphic HEMT (MM-HEMT) having two 0.5×50 μm2 gates was measured for temperatures between 200 and 400 K and frequencies between 1 Hz and 53 kHz. Dependence of input noise spectral density on gate–source and drain–source bias voltages and transconductance frequency dispersion characteristics were also characterized. The low-frequency input noise spectra of the MM-HEMT showed pure 1/f noise characteristics for the temperature and the frequency ranges investigated, indicating that there exists insignificant level of deep traps associated with the metamorphic epitaxial layer growth. The MM-HEMT showed a very low-noise spectral density (0.8×10−13 V2/Hz at 1 kHz) and the Hooge parameter (3.7×10−5) that are comparable to those of the state-of-the-art In0.52Al0.48As/In0.53Ga0.47As HEMT grown on an InP substrate and an extremely small transconductance frequency dispersion (Δgm/gm0
- Published
- 2002
19. The base contact recombination current and its effect on the current gain of surface-passivated InGaP/GaAs HBTs
- Author
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Lee Tae-Woo, Moon-Pyung Park, In-Hoon Choi, Sung Ho Park, Kyungho Lee, Byoung-Gue Min, and Jongmin Lee
- Subjects
Materials science ,Passivation ,business.industry ,Mechanical Engineering ,Heterojunction bipolar transistor ,Nitride ,Condensed Matter Physics ,chemistry.chemical_compound ,chemistry ,Mechanics of Materials ,Ternary compound ,Gallium phosphide ,Indium phosphide ,Optoelectronics ,General Materials Science ,Current (fluid) ,business ,Diode - Abstract
In this study, the effect of the emitter-base contact spacing on the current gain of InGaP/GaAs HBTs has been described and the base contact recombination current has been experimentally studied. When devices were passivated by nitride, the current gain of InGaP/GaAs HBTs showed no variation with the perimeter to area ratio, which suggested that the surface recombination current of InGaP/GaAs HBTs was negligible, leading the base contact recombination current to affect the current gain. It was found that the base contact recombination current significantly degraded the current gain when the emitter-base contact spacing was reduced to below 0.5 μm. The diode equation was used to model the base contact recombination current, and an ideality factor of 1.76 was obtained.
- Published
- 2001
20. A new approach to highly conductive polymer electrolytes: synthesis of gelling fluoroalkylated end-capped 2-acrylamido-2-methylpropanesulfonic acid copolymers containing poly(oxyethylene) units
- Author
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Jun Kyokane, Tokuzo Kawase, Kyungho Lee, Yukiko Ariyoshi, and Hideo Sawada
- Subjects
Conductive polymer ,Materials science ,Polymers and Plastics ,Organic Chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,Electrolyte ,Macromonomer ,Polyelectrolyte ,End-group ,chemistry ,Polymer chemistry ,Materials Chemistry ,Copolymer ,Ionic conductivity ,Lithium - Abstract
New fluoroalkylated end-capped 2-acrylamido-2-methylpropanesulfonic acid copolymers containing poly(oxyethylene) units were prepared by the use of fluoroalkanoyl peroxides. It was demonstrated that these fluorinated copolymers can form gels in DMSO under non-crosslinked conditions, and these fluorinated polymeric gelling electrolytes containing lithium salts exhibit a considerably high ionic conductivity of 10 −3 S/cm level at room temperature.
- Published
- 2000
21. Optimization study of halo doped MOSFETs
- Author
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Young June Park, Duheon Song, Kyungho Lee, Junhee Lim, and Hong-Shick Min
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Materials science ,business.industry ,Doping ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Hot carrier stress ,Electronic, Optical and Magnetic Materials ,Threshold voltage ,Saturation current ,Materials Chemistry ,Electronic engineering ,Optoelectronics ,Halo ,Electrical and Electronic Engineering ,Hot carrier reliability ,business ,Astrophysics::Galaxy Astrophysics ,Hot carrier degradation - Abstract
In this work, the hot carrier degradation behavior of the halo doped MOSFETs is investigated and an optimized halo design, taking into account the hot carrier reliability, is proposed. Conventional LDD MOSFETs and halo MOSFETs with the variations in LDD n -dose and halo dose are fabricated. The degradations of the threshold voltage and the drain saturation current under hot carrier stress (DAHC and CHC) conditions are measured and analyzed. Device simulations are also carried out to cover a wider range than the experiments. In order to obtain the improved device characteristics in hot carrier effects as well as short channel effects, the halo design should be carefully optimized.
- Published
- 1996
22. Corrigendum to 'Cooperative effects of secondary mesoporosity and acid site location in Pt/SAPO-11 on n-dodecane hydroisomerization selectivity' [J. Catal. 319 (2014) 232–238]
- Author
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Kyungho Lee, Minkee Choi, and Myoung Yeob Kim
- Subjects
Site location ,Chemistry ,N-dodecane ,Organic chemistry ,Physical and Theoretical Chemistry ,Selectivity ,Catalysis - Published
- 2015
23. The role of LH receptor in human IVF-ET program
- Author
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Hyun-Soo Yoon, Eun-Soo Kim, Lee Jung-Bok, Kyungho Lee, Sung-Il Roh, and B. Do
- Subjects
medicine.medical_specialty ,Endocrinology ,Reproductive Medicine ,business.industry ,Internal medicine ,luteinizing hormone/choriogonadotropin receptor ,medicine ,Obstetrics and Gynecology ,business - Published
- 2002
24. The unfolded protein response is required for haploid tolerance in yeast
- Author
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Lenore Neigeborn, Kyungho Lee, and Randal J. Kaufman
- Subjects
Protein Folding ,Saccharomyces cerevisiae Proteins ,Saccharomyces cerevisiae ,Mutant ,Haploidy ,Protein Serine-Threonine Kinases ,Biochemistry ,Fungal Proteins ,Meiosis ,Gene Expression Regulation, Fungal ,HSP70 Heat-Shock Proteins ,DNA, Fungal ,Gene ,Transcription factor ,Molecular Biology ,Genetics ,Membrane Glycoproteins ,biology ,fungi ,Fungal genetics ,Cell Biology ,Spores, Fungal ,biology.organism_classification ,Diploidy ,Repressor Proteins ,Basic-Leucine Zipper Transcription Factors ,Phenotype ,Mutagenesis ,Unfolded protein response ,Ploidy ,Transcription Factors - Abstract
HAC1 encodes a transcription factor that mediates the unfolded protein response (UPR) in Saccharomyces cerevisiae. We characterized hac1Delta mutants in the sporulation-proficient SK1 genetic background and found a novel function for HAC1 in haploid tolerance. hac1Delta spore clones contain a diploid DNA content as determined by fluorescence-activated cell sorting and genetic analyses. Autodiploidization of hac1 spore clones occurred after germination; hac1 spores were born haploid, but efficiently generated diploid progeny during the subsequent mitotic division. Once the hac1 mutant acquired a diploid DNA content, no further ploidy increase was observed. Interestingly, the increase in genome content following meiosis was not a general property associated with hac1 spore clones; instead, it was restricted to an inability to tolerate the haploid state. Genetic analyses involving the UPR target gene KAR2 and the UPR regulator IRE1 revealed that autodiploidization associated with hac1 mutants is a consequence of its role in the UPR pathway. Inhibition of the UPR pathway induces autodiploidization, and constitutive activation of UPR target genes suppresses this response.
- Published
- 2003
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