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Characteristics of Nano-Laminated Al-Doped ZnO (AZO) Multilayers
Choi, Moonsuk,Lim, Donghwan,Kim, Jinok,Park, Jin-Hong,Choi, Changhwan American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.11
<P>The structural, morphological, optical, and electrical properties of Al-doped ZnO (AZO) single layer and AZO/metal (Ag and Au: 3 nm)/AZO multilayer thin films prepared via sputtering processes were characterized. Additionally, the effect of post-annealing on the properties of films was investigated. X-ray diffraction revealed that the crystal properties of hexagonal wurtzite crystal structures and the preferred orientation of ZnO (002), with c-axis growth for both AZO single layer and AZO multilayer films. Surface roughness was not degraded by inserting metals into the AZO films. Post air annealing at 300 degrees C improved the crystallinity and surface roughness of the films. AZO multilayer films exhibited lower transmittance values compared with AZO single layer films, but improved after post-annealing. The energy band gap was about 3.5 eV for the AZO multilayer films. Compared to AZO single layer films, AZO multilayer films exhibited lower sheet resistance and resistivity values. Additionally, high carrier concentrations and electron mobilities were attained by inserting metals into AZO. Post-annealing further improved the electrical properties. The post-annealed AZO/Ag/AZO thin films exhibited the best properties (4.26 x 10(-3) Omega(-1)) as Haccke figure of merit (FOM) parameters, due to low sheet resistance (6.75 Omega/sq) and moderate transmittance (70.12%) within the visible light region.</P>
( Changhwan Choi ),( Tamar Ringel Kulka ),( Daniel Temas ),( Ari Kim ),( Yehuda Ringel ) 대한내과학회 2014 대한내과학회 추계학술대회 Vol.2014 No.1
Background: Dysbiosis leading to abnormal intestinal fermentation has been suggested as a possible etiological mechanism in Irritable bowel syndrome (IBS). We aimed to investigate the location and magnitude of altered intestinal bacterial fermentation in IBS and its clinical subtypes. Methods: 114 IBS patients who satisfi ed Rome III criteria and 33 healthy controls (HC) were investigated. Intestinal fermentation was assessed using two surrogate measures: Intestinal intraluminal pH and fecal short chain fatty acids (SCFAs). Intraluminal pHs were measured at four quartiles (Q1-4) in each small and large bowel using a wireless motility capsule (SmartPill™). Fecal SCFAs including acetate, propionate, butyrate and lactate were analyzed by capillary gas chromatography. Correlations between intestinal pH, fecal SCFAs, intestinal transit time and IBS symptom scores were analyzed. Results: Intraluminal pH levels in Q1, Q4, and total colon were signifi cantly lower in IBS compared to those in HC (6.83 for IBS vs. 7.29 for HC, P = 0.042). There were no differences in total and segmental pH levels in the small bowel between IBS and HC (6.84 vs. 6.83, P = NS). The intraluminal colonic pH differences were consistent in all IBS subtypes. Total SCFAs level was signifi cantly lower in C-IBS than in D-IBS and M-IBS. The total SCFAs level in all IBS was similar with that in HC. Colonic pH levels correlated positively with colon transit time (CTT) and IBS symptom severities. Total SCFAs levels correlated negatively with CTT, and positively with stool frequency. Conclusions: Bacterial fermentation is increased in IBS across all subtypes compared with HC. The altered intestinal fermentation in IBS appeared to be in the colon but not in the small bowel. Fecal SCFAs negatively correlated with CTT and may not be a sensitive marker to estimate intraluminal bacterial fermentation.
The Design and Analysis of a Feeder Pipe Inspection Robot With an Automatic Pipe Tracking System
Changhwan Choi,Byungsuk Park,Seungho Jung IEEE 2010 IEEE/ASME transactions on mechatronics Vol.15 No.5
<P>The feeder pipes in a pressurized heavy water reactor (PHWR) suffer from flow-assisted corrosion (FAC), which makes the wall thickness of the pipes thin. This effect is a well-known degradation mechanism of a carbon pipe with high pressure and high flow rate. Therefore, the weak parts of the pipe should be measured to guarantee the safety. This paper describes a mobile out-pipe inspection robot with an automatic pipe tracking system for a feeder pipe inspection in a PHWR. The robot is composed of dual inch worm mechanisms. One is for a longitudinal motion along a pipe, and the other is for a rotational motion in a circumferential direction to access all of the outer surfaces of a pipe. A design method for a gripper actuator is proposed by using a kinematic and force analysis. The proposed mechanism shows a more stable gripping capability than the conventional ones. An automatic pipe tracking system is proposed based on machine vision techniques to make the mobile robot follow the exact outer circumference of a curved feeder pipe as closely as possible, which is one of the requirements of a thickness measurement system for a feeder pipe. The proposed sensing technique is analyzed to verify its feasibility and to develop a calibration method for an accurate measurement. A mobile robot and control system are developed, and the automatic pipe tracking system is tested in a mockup of a feeder pipe.</P>
The Post Annealing to Control the Number of Layers of 2D MoS<sub>2</sub> and SnS<sub>2</sub>
Choi, Moonsuk,Lim, Donghwan,Sergeevich, Andrey Sokolov,Son, Seok Ki,Kim, Young Jin,Han, Hoon Hee,Choi, Changhwan American Scientific Publishers 2016 Journal of nanoscience and nanotechnology Vol.16 No.11
<P>We have demonstrated that post annealing could control the layer thickness of 2D MoS2 and SnS2 films transferred on a SiO2/Si substrate by varying the annealing temperature and time. Atomic force microscopy and Raman spectroscopy characterizations revealed that higher annealing temperature and longer treatment time led to thinner films, lower residues and fewer impurities on the surface of 2D materials. In addition, a higher possibility to attain few-layers on both 2D films was achieved using post annealing. The multiple layers of pristine films having the thickness over 15 nm were reduced down to bi-layers after annealing. We observed that the moderate annealing temperature of 450 degrees C on led to effective layer-thinning compared to the films annealed at 340 degrees C. The post annealing at 450 degrees C produced very smooth few-layers (<= 4 nm thickness, >1 mu m size) of 2D MoS2 and SnS2. However, the 2D films decomposed or disappeared at temperature greater than 650 degrees C. In addition, process time also affected the number of layers and the sweet spot turned out to be 2 to 3 hours in our experiment.</P>
Model-based inverse regression for mixture data
Choi, Changhwan,Park, Chongsun The Korean Statistical Society 2017 Communications for statistical applications and me Vol.24 No.1
This paper proposes a method for sufficient dimension reduction (SDR) of mixture data. We consider mixture data containing more than one component that have distinct central subspaces. We adopt an approach of a model-based sliced inverse regression (MSIR) to the mixture data in a simple and intuitive manner. We employed mixture probabilistic principal component analysis (MPPCA) to estimate each central subspaces and cluster the data points. The results from simulation studies and a real data set show that our method is satisfactory to catch appropriate central spaces and is also robust regardless of the number of slices chosen. Discussions about root selection, estimation accuracy, and classification with initial value issues of MPPCA and its related simulation results are also provided.
Fabrication, structure, and photoluminescence of GeO2/ ZnO core-shell nanorods
Changhwan Choi 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.4
We have fabricated GeO2-core/ZnO-shell nanorods using the atomic layer deposition technique to shell-coat the GeO2 nanorods. The samples were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and photoluminescence spectroscopy (PL). The coated product showed a rod-like morphology, in which the shell layer comprised a hexagonal ZnO phase. PL measurement of GeO2-core/ZnO-shell nanorods exhibited emissions from the ZnO shell layer, in addition to those form the GeO2-core nanorods.
Feeder Pipe Inspection Robot with an Inch-Worm Mechanism Using Pneumatic Actuators
Changhwan Choi,Seungho Jung,Seungho Kim 대한전기학회 2006 International Journal of Control, Automation, and Vol.4 No.1
The outlet feeder pipe thinning in a PHWR (Pressurized Heavy Water Reactor) is caused by a high pressure steam flow inside the pipe, which is a well known degradation mechanism called a FAC (Flow Assisted Corrosion). In order to monitor the degradation, the thickness of the outlet bends close to the exit of the pressure tube should be measured and analyzed at every official overhaul. This paper describes a mobile feeder pipe inspection robot that can minimize the irradiation dose to human workers by automating the measurement process. The robot can move by itself on the feeder pipe by using an inch worm mechanism, which is constructed by two gripper bodies that can fix the robot body on to the pipe, one extendable and contractible actuator, and a rotation actuator connected to the two gripper bodies to move forward and backward, and to rotate in a circumferential direction.