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An HBT Saturated Power Amplifier With Minimized Knee Effect for Envelope Tracking Operation
Kyunghoon Moon,Yunsung Cho,Jooseung Kim,Sangsu Jin,Seokhyeon Kim,Bumman Kim THE INSTITUTE OF ELECTRICAL ENGINEERS 2015 IEEE Microwave and Wireless Components Letters Vol. No.
<P>In this letter, a highly efficient saturated power amplifier (PA) based on a heterojunction bipolar transistor (HBT) is employed to maximize the efficiency of an envelope tracking (ET) PA. In this PA, output voltage waveform of the PA is shaped as a half-sinusoidal voltage waveform peaked by a second harmonic. The knee voltage effect is minimized in this voltage waveform due to the large fundamental voltage for a given supply voltage, which is very important for an ET PA with a low average supply voltage. Based on the saturated PA, the ET PA is tested at 1.85 GHz using a long term evolution signal. The ET PA delivers a power-added efficiency of 46.5%, an E- UTRAACLR of -33.4 dBc, and an error vector magnitude of 3.0% at an average output power of 27 dBm.</P>
Understanding carbon nanotube channel formation in the lipid membrane
Choi, Moon-ki,Kim, Hyunki,Lee, Byung Ho,Kim, Teayeop,Rho, Junsuk,Kim, Moon Ki,Kim, Kyunghoon IOP Pub 2018 Nanotechnology Vol.29 No.11
<P>Carbon nanotubes (CNTs) have been considered a prominent nano-channel in cell membranes because of their prominent ion-conductance and ion-selectivity, offering agents for a biomimetic channel platform. Using a coarse-grained molecular dynamics simulation, we clarify a construction mechanism of vertical CNT nano-channels in a lipid membrane for a long period, which has been difficult to observe in previous CNT-lipid interaction simulations. The result shows that both the lipid coating density and length of CNT affect the suitable fabrication condition for a vertical and stable CNT channel. Also, simulation elucidated that a lipid coating on the surface of the CNT prevents the CNT from burrowing into the lipid membrane and the vertical channel is stabilized by the repulsion force between the lipids in the coating and membrane. Our study provides an essential understanding of how CNTs can form stable and vertical channels in the membrane, which is important for designing new types of artificial channels as biosensors for bio-fluidic studies.</P>
Dynamic characteristics of a flagellar motor protein analyzed using an elastic network model
Choi, Moon-ki,Jo, Soojin,Lee, Byung Ho,Kim, Min Hyeok,Choi, Jae Boong,Kim, Kyunghoon,Kim, Moon Ki Elsevier 2017 Journal of molecular graphics & modelling Vol.78 No.-
<P><B>Abstract</B></P> <P>At the base of a flagellar motor, its rotational direction and speed are regulated by the interaction between rotor and stator proteins. A switching event occurs when the cytoplasmic rotor protein, called C-ring, changes its conformation in response to binding of the CheY signal protein. The C-ring structure consists of FliG, FliM, and FliN proteins and its conformational changes in FliM and FliG including Helix<SUB>MC</SUB> play an important role in switching the motor direction. Therefore, clarifying their dynamic properties as well as conformational changes is a key to understanding the switching mechanism of the motor protein. In this study, to elucidate dynamic characteristics of the C-ring structure, both harmonic (intrinsic vibration) and anharmonic (transition pathway) analyses are conducted by using the symmetry-constrained elastic network model. As a result, the first three normal modes successfully capture the essence of transition pathway from wild type to CW-biased state. Their cumulative square overlap value reaches up to 0.842. Remarkably, it is also noted from the transition pathway that the cascade of interactions from the signal protein to FliM to FliG, highlighted by the major mode shapes from the first three normal modes, induces the reorientation (∼100° rotation of FliG<SUB>C5</SUB>) of FliG C-terminal that directly interacts with the stator protein. Presumably, the rotational direction of the motor protein is switched by this substantial change in the stator-rotor interaction.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Dynamic characteristics of cytoplasmic ring are investigated using normal mode analysis based on elastic network model. </LI> <LI> Transition of FliG protein from wild type to CW-biased provides insights into the structural change switching event. </LI> <LI> Structural dynamics of motor protein implies that the reorientation of important domains makes rotation of motor effective. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Moon Hui jeong,Kim Kyunghoon,Kang Eun Kyeong,Yang Hyeon-Jong,Lee Eun 대한의학회 2021 Journal of Korean medical science Vol.36 No.35
Background: Prediction of mortality in patients with coronavirus disease 2019 (COVID-19) is a key to improving the clinical outcomes, considering that the COVID-19 pandemic has led to the collapse of healthcare systems in many regions worldwide. This study aimed to identify the factors associated with COVID-19 mortality and to develop a nomogram for predicting mortality using clinical parameters and underlying diseases. Methods: This study was performed in 5,626 patients with confirmed COVID-19 between February 1 and April 30, 2020 in South Korea. A Cox proportional hazards model and logistic regression model were used to construct a nomogram for predicting 30-day and 60-day survival probabilities and overall mortality, respectively in the train set. Calibration and discrimination were performed to validate the nomograms in the test set. Results: Age ≥ 70 years, male, presence of fever and dyspnea at the time of COVID-19 diagnosis, and diabetes mellitus, cancer, or dementia as underling diseases were significantly related to 30-day and 60-day survival and mortality in COVID-19 patients. The nomogram showed good calibration for survival probabilities and mortality. In the train set, the areas under the curve (AUCs) for 30-day and 60-day survival was 0.914 and 0.954, respectively; the AUC for mortality of 0.959. In the test set, AUCs for 30-day and 60-day survival was 0.876 and 0.660, respectively, and that for mortality was 0.926. The online calculators can be found at https://koreastat.shinyapps.io/RiskofCOVID19/. Conclusion: The prediction model could accurately predict COVID-19-related mortality; thus, it would be helpful for identifying the risk of mortality and establishing medical policies during the pandemic to improve the clinical outcomes.
Moon, Dong Gwon,Yun, Jae Ho,Gwak, Jihye,Ahn, SeungKyu,Cho, Ara,Shin, Keeshik,Yoon, Kyunghoon,Ahn, SeJin The Royal Society of Chemistry 2012 ENERGY AND ENVIRONMENTAL SCIENCE Vol.5 No.12
<P>We report a new approach to fabricating Cu(In,Ga)Se<SUB>2</SUB> (CIGSe) light absorbing layers for thin film solar cells without Ga segregation using a sputtering and single-step selenization process. To mitigate Ga segregation at the CIGSe/back-contact region, which has frequently been observed in the selenization of metal/alloy precursor layers, we used Se-containing precursor layers (Cu-In-Ga-Se) to capture Ga in covalently bonded structures and investigated the effects of Se content in the precursor layers on the properties of the selenized CIGSe films and the devices. As the Se content in the precursor layer increased, Ga segregation was significantly mitigated, resulting in a completely homogenized Ga distribution when the Se/metal ratio of the precursor films is over 0.8. Finally, a thin CIGSe film (∼670 nm) with a uniform Ga distribution was processed to fabricate a solar cell, and the device exhibited a conversion efficiency of 11.7% with an open circuit potential of 0.6 V. An increase of the CIGSe film thickness to 1.55 μm resulted in a device efficiency of up to 13.16%.</P> <P>Graphic Abstract</P><P>A new approach to fabricating Cu(In,Ga)Se<SUB>2</SUB> thin films without Ga segregation using a sputtering and single-step selenization process. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2ee22804a'> </P>
Mi-Gil Moon,Chang-Hwan Yoon,Kyunghoon Lee,강시혁,Tae-Jin Youn,In-Ho Chae 대한의학회 2021 Journal of Korean medical science Vol.36 No.8
Background: Although electrocardiography and cardiac troponin play important roles in the diagnosis of acute coronary syndrome (ACS), there remain unmet clinical needs. Heart-type fatty acid-binding protein (H-FABP) has been identified as an early diagnostic marker of acute myocardial infarction (AMI). In this study, we examined the diagnostic and prognostic value of H-FABP in patients suspected with ACS. Methods: We conducted an observational single-center cohort study, including 89 adults aged 30 years or older, who presented to the emergency room (ER) within 24 hours after the onset of chest pain and/or dyspnea. We performed laboratory analysis and point-of-care testing (POCT) for cardiac markers, including H-FABP, troponin I, and creatine kinase-myocardial band. We also evaluated the correlation between cardiac markers and left ventricular (LV) dysfunction and extent of coronary artery disease (CAD). Results: In patients presented to ER within 4 hours after symptom onset (n = 49), the diagnostic accuracy of H-FABP for AMI, as quantified by the area under the receiver operating characteristic curve, was higher (0.738; 95% confidence interval [CI], 0.591–0.885) than other cardiac markers. In POCT, the diagnostic accuracy of H-FABP (56%; 95% CI, 45–67) was significantly higher than other cardiac markers. H-FABP was correlated with not extent of CAD but post-AMI LV dysfunction. Conclusion: H-FABP is a useful cardiac marker for the early diagnosis of AMI and prediction of myocardia injury. Difference in the circulatory release timeline of cardiac markers could explain its utility in early-stage of myocardial injury.