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Park, Young-Jun,Park, Ju-Hyun,Kim, Hong-Jin,Ryu, Hocheol,Kim, SangYun,Pu, YoungGun,Hwang, Keum Cheol,Yang, Youngoo,Lee, Minjae,Lee, Kang-Yoon IEEE 2017 IEEE TRANSACTIONS ON POWER ELECTRONICS - Vol.32 No.9
<P>This paper presents a retention/pulse frequency modulation (PFM)/pulse width modulation (PWM) mode dc-dc buck converter with adaptive zero current detector (AZCD) and spread spectrum clock generation (SSCG) for IoT/Wearable systems. The proposed dc-dc buck converter is capable of handling loads from 10 mu A to 20 mA with high efficiency by applying triple mode (retention mode, PFM mode, and PWM mode), gate split technique, and AZCD. Retention mode is proposed to extend wide load range at ultralight load. Gate split technique adjusts the conduction loss and switching loss. AZCD reduces the operation duty of the high-speed comparator and avoid reverse current below light load. In IoT applications, each node communicates with other nodes through a Bluetooth low energy transceiver, which consumes very low current and is highly sensitive to supply noise. Therefore, the proposed dc-dc buck converter adopts the SSCG technique to reduce electromagnetic interference by up to 18 dB. This chip is implemented using 0.13 mu m CMOS technology with an active area of 820 x 800 mu m(2). The maximum power efficiency of the proposed dc-dc buck converter is 92.4% at a switching frequency of 2.5 MHz when the load current range is 10 to 20 mA. The input voltage range and the regulated output voltage are 2.2-3.3 and 1.7 V, respectively. In addition, the proposed dc-dc buck converter achieves over 74.2% efficiency in retention mode when the load current range is from 10 to 500 mu A.</P>
Park Sang Won,김성헌,Park Jeonghoon,장재원,Kim SangYun 대한치매학회 2020 Dementia and Neurocognitive Disorders Vol.19 No.4
Background and Purpose: To identify biomarkers for prediction of the progression to dementia in mild cognitive impairment (MCI) patients, evaluation of brain structure changes has been validated by a comprehensive visual grading scale (CVRS) through magnetic resonance imaging (MRI). In this study, we specifically elucidated for the cognitive change of MCI patients classified based on AT(N) pathological status classification during the follow-up period of 3 years through the CVRS. Methods: The 301 patients with initial MCI visited at least once for follow-up period. The data used in this study were obtained from the Alzheimer's disease (AD) Neuroimaging Initiative study. Brain atrophy was assessed by CVRS using MRI. AT(N) profiles were classified by cerebrospinal fluid abnormality. Based on the AT(N) assessment, all individuals in this study were divided into 3 groups (normal state biomarker, suspected non-Alzheimer's pathology [SNAP], or Alzheimer's continuum). The cox regression was used to analyze the hazard ratios of CVRS for progression to dementia. Results: Sixty-three progressed and 238 remained stable to dementia and the CVRS (mean±standard deviation) had significant difference between progressive MCI and stable MCI (p<0.001). Univariate and multivariate cox regression results (p<0.001) showed the independence of initial CVRS as a predictor for the progression to dementia. Moreover, comparing the classified AT(N) pathology group, SNAP and AD, effectiveness of CVRS as a predictor was verified only in Alzheimer's continuum. Conclusions: The initial CVRS score as a predictor of dementia progression was independently validated at the stage of Alzheimer's progression among AT(N) pathologically differentiated MCI.
Electrochemical analysis based on nanoporous structures
Park, Sangyun,Kim, Hee Chan,Chung, Taek Dong The Royal Society of Chemistry 2012 The Analyst Vol.137 No.17
<P>Analytical applications and the underlying principles of unique electrochemistry in nanoporous structures are reviewed and discussed. In addition to the conventional concept of enlarged surface area, the structural effects of nanoporous materials can play significant roles such as discriminative electrokinetics, the nano-confinement effect, electrical double layer overlapping, ion-selective impedance, <I>etc.</I> The applications described in this review article include solid-state pH sensors, miniaturized pseudo-reference electrodes, nonenzymatic glucose monitoring, ion diodes, transistors, extracellular neural probes, and a few more. Further intensive research is required to develop creative analytical tools based on nanoporous structures and to unravel the underlying physicochemical principles.</P> <P>Graphic Abstract</P><P>Analytical applications and the underlying principles of unique electrochemistry in nanoporous structures are reviewed and discussed. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2an35294j'> </P>
Park, Eunsung,Lee, Sangyun,Ronning, Filip,Thompson, Joe D,Zhang, Qiu,Balicas, Luis,Lu, Xin,Park, Tuson IOP 2018 Journal of Physics, Condensed Matter Vol.30 No.16
<P>Low-dimensional electronic systems with confined electronic wave functions have attracted interest due to their propensity toward novel quantum phases and their use in wide range of nanotechnologies. The newly discovered chalcogenide Nb<SUB>2</SUB>PdS<SUB>5</SUB> possesses a quasi-one-dimensional electronic structure and becomes superconducting. Here, we report spectroscopic evidence for two-band superconductivity, where soft point-contact spectroscopic measurements in the superconducting (SC) state reveal Andreev reflection in the differential conductance <I>G</I>. Multiple peaks in <I>G</I> are observed at 1.8 K and explained by the two-band Blonder–Tinkham–Klapwijk model with two gaps Δ<SUB>1</SUB> = 0.61 meV and Δ<SUB>2</SUB> = 1.20 meV. The progressive evolution of <I>G</I> with temperature and magnetic field corroborates the multiple nature of the SC gaps.</P>
Three-dimensional Refractive-index Distributions of Individual Angiosperm Pollen Grains
Chansuk Park,SangYun Lee,Geon Kim,SeungJun Lee,Jaehoon Lee,Taehyun Heo,Yoonjeong Park,YongKeun Park 한국광학회 2018 Current Optics and Photonics Vol.2 No.5
Three-dimensional (3D) refractive-index (RI) imaging and quantitative analyses of angiosperm pollen grains are presented. Using optical diffraction tomography, the 3D RI structures of individual angiosperm pollen grains were measured without using labeling or other preparation techniques. Various physical quantities including volume, surface area, exine volume, and sphericity were determined from the measured RI tomograms of pollen grains. Exine skeletons, the distinct internal structures of angiosperm pollen grains, were identified and systematically analyzed.