Bayesian Analysis for Neural Network Models

Chung, Younshik,Jung, Jinhyouk,Kim, Chansoo The Korean Statistical Society 2002 Communications for statistical applications and me Vol.9 No.1

Neural networks have been studied as a popular tool for classification and they are very flexible. Also, they are used for many applications of pattern classification and pattern recognition. This paper focuses on Bayesian approach to feed-forward neural networks with single hidden layer of units with logistic activation. In this model, we are interested in deciding the number of nodes of neural network model with p input units, one hidden layer with m hidden nodes and one output unit in Bayesian setup for fixed m. Here, we use the latent variable into the prior of the coefficient regression, and we introduce the 'sequential step' which is based on the idea of the data augmentation by Tanner and Wong(1787). The MCMC method(Gibbs sampler and Metropolish algorithm) can be used to overcome the complicated Bayesian computation. Finally, a proposed method is applied to a simulated data.

Mesh-type reference Korean phantoms (MRKPs) for adult male and female for use in radiation protection dosimetry

Choi, Chansoo,Nguyen, Thang Tat,Yeom, Yeon Soo,Lee, Hanjin,Han, Haegin,Shin, Bangho,Zhang, Xujia,Kim, Chan Hyeong,Chung, Beom Sun Institute of Physics in association with the Ameri 2019 Physics in medicine & biology Vol.64 No.8

<P>In the present study, to overcome the dosimetric limitations of the previous voxel-type reference Korean computational phantoms due to their limited voxel resolutions (i.e. on the order of millimeters) and the nature of voxel geometry, a pair of new reference Korean phantoms, called mesh-type reference Korean phantoms (MRKPs), were developed for the adult male and female in a high-quality/fidelity mesh format. The developed phantoms include all target and source regions required for effective dose calculation, even micrometer-scale target and source regions of the respiratory and alimentary tract organs, skin, urinary bladder, and eye lens. The developed phantoms, which are in either the polygon-mesh (PM) format or the tetrahedral-mesh (TM) format as necessary, can be directly used in several general-purpose Monte Carlo codes (e.g. Geant4, MCNP6, and PHITS) without voxelization. In order to understand the dosimetric impact of the new phantoms, the dose coefficients (=fluence-to-effective dose conversion coefficients) were calculated for photons and electrons with energies ranging from 10 keV to 10 GeV for the anterior–posterior (AP) irradiation geometry and compared with those of the previous voxel-type reference Korean phantoms. The results demonstrate that the effective dose coefficients of the MRKPs were generally similar to those of the previous voxel-type reference phantoms for photons; however, for electrons, significant differences were observed at energies lower than 1 MeV that were mainly due to the explicit definition of the 50 <I>µ</I>m-thick radiosensitive target layer in the skin of the new mesh phantoms.</P>

Bayesian Approach for Determining the Order p in Autoregressive Models

Kim, Chansoo,Chung, Younshik 한국통계학회 2001 Communications for statistical applications and me Vol.8 No.3

The autoregressive models have been used to describe a wade variety of time series. Then the problem of determining the order in the times series model is very important in data analysis. We consider the Bayesian approach for finding the order of autoregressive(AR) error models using the latent variable which is motivated by Tanner and Wong(1987). The latent variables are combined with the coefficient parameters and the sequential steps are proposed to set up the prior of the latent variables. Markov chain Monte Carlo method(Gibbs sampler and Metropolis-Hasting algorithm) is used in order to overcome the difficulties of Bayesian computations. Three examples including AR(3) error model are presented to illustrate our proposed methodology.

LED 광원에서 잡음 및 돌입전류 방지를 위한 스위칭모드 전원공급 장치 (SMPS) 개발 연구

정찬수,홍규장,위성복,유건수,김미진,Chung, Chansoo,Hong, Gyujang,We, Sungbok,Yu, Geonsu,Kim, Mijin 한국전력공사 2016 KEPCO Journal on electric power and energy Vol.2 No.4

최근 급속한 녹색환경 정책으로 LED를 이용한 조명 광원들이 설치 운용하고 있으나, 이들 광원의 전원 공급은 안정된 직류 전원 공급을 위해서 스위칭 모드 전원 공급(SMPS) 장치로 전원을 공급하고 있다. 그러나, 이들 전원 공급 장치는 공급 단가 때문에 설계 및 설치과정에서 스위칭에 따른 전력과 변환역률, 전기적 노이즈 및 돌입전류들은 간과하고 있다. 따라서, 본 연구에서는 SMPS는 고품질의 전원을 LED 조명 부하에 공급하기 위하여 스위칭 시에 다음과 같은 3가지 관점에서 회로를 연구하였다. 첫 번째, 역률과 효율을 약 85% 확보하고, 두 번째, 노이즈(고조파 포함) 최소화, 세 번째는 스위치-온 시 3A 돌입전류를 $100{\mu}sec$ 후 최소 0.3 A로 감소하여 돌입 전류 침입을 최소화 하고자 하였다. 본 연구에서는 IC형 구동기(LNK 409)를 적용하여 입력전압과 출력상황을 귀환 형태로 감시하도록 하였으며, 정전류 출력을 위하여 정전압을 유지할 수 있는 제어회로와 시상수를 개발하였다. 그러나, 부하 변동 시 미세한 전류의 불규칙으로 인한 발열 문제는 해결하지 못하고 있다. 이를 증명하고자 LED 조명 부하 46 W급을 대상으로 효과를 검증하였다. This Study focused on the development of SMPS (Switching Mode Power Supply) to supply the constant votage and current nevertheless LED fluorescent Light generated the electric noise (with Harmonics) and Inrush current at instant time of turn-on and off. Recently, according to the Green policy in government, the LED fluorescent Lighter showed the rapidly increasing tend as indoor and outdoor Lighter. But, because of costs, LED fluorescent Light not considered and neglected the following items; power factor, efficiency, Harmonics and Inrush current. So, we are developed the SMPS about 3 key issues as follows: 1st, power factor and efficiency is 85%. 2nd, the switching noisy by harmonic is minimized. 3rd, the Inrush current at turn on and off time is reduced the minimum 0.3 A after $100{\mu}sec$ on turnon time. The proposed SMPS adjusted by LNK 409 driver (included the high frequency modulation function). Although, the developed SMPS maintained the about 85% of power factor and efficiency. but, the SMPS must be generated low heat by the variation of minute load current at switching timing. To improve the above weak point, the developed SMPS have the feedback monitoring circuit between input side and output side to maintain the power factor and efficiency. Also, we are studied the time-constant of control circuit to output the constant voltage and current nevertheless the load disturbance of LED lighting. The LED fluorescent Light of 46W is checked the above items.

Flexible resistive random access memory devices by using NiO_<i>x</i>/GaN microdisk arrays fabricated on graphene films

Lee, Keundong,Park, Jong-woo,Tchoe, Youngbin,Yoon, Jiyoung,Chung, Kunook,Yoon, Hosang,Lee, Sangik,Yoon, Chansoo,Ho Park, Bae,Yi, Gyu-Chul IOP 2017 Nanotechnology Vol.28 No.20

<P>We report flexible resistive random access memory (ReRAM) arrays fabricated by using NiO<SUB> <I>x</I> </SUB>/GaN microdisk arrays on graphene films. The ReRAM device was created from discrete GaN microdisk arrays grown on graphene films produced by chemical vapor deposition, followed by deposition of NiO<SUB> <I>x</I> </SUB> thin layers and Au metal contacts. The microdisk ReRAM arrays were transferred to flexible plastic substrates by a simple lift-off technique. The electrical and memory characteristics of the ReRAM devices were investigated under bending conditions. Resistive switching characteristics, including cumulative probability, endurance, and retention, were measured. After 1000 bending repetitions, no significant change in the device characteristics was observed. The flexible ReRAM devices, constructed by using only inorganic materials, operated reliably at temperatures as high as 180 °C.</P>

Development of Message Gathering System for Digital Electronic Switching System

Shin. Seungsik,Yoo. Bongsun,Kim. Hoonhak,Lee. Seungwhan,Chung. Chansoo 제어로봇시스템학회 2002 제어로봇시스템학회 국제학술대회 논문집 Vol.2002 No.10

Inclusion of thin target and source regions in alimentary and respiratory tract systems of mesh-type ICRP adult reference phantoms

Kim, Han Sung,Yeom, Yeon Soo,Nguyen, Thang Tat,Choi, Chansoo,Han, Min Cheol,Lee, Jai Ki,Kim, Chan Hyeong,Zankl, Maria,Petoussi-Henss, Nina,Bolch, Wesley E,Lee, Choonsik,Qiu, Rui,Eckerman, Keith,Chung, Institute of Physics in association with the Ameri 2017 Physics in medicine & biology Vol. No.

<P>It is not feasible to define very small or complex organs and tissues in the current voxel-type adult reference computational phantoms of the International Commission on Radiological Protection (ICRP), which limit dose coefficients for weakly penetrating radiations. To address the problem, the ICRP is converting the voxel-type reference phantoms into mesh-type phantoms. In the present study, as a part of the conversion project, the micrometer-thick target and source regions in the alimentary and respiratory tract systems as described in ICRP <I>Publications 100</I> and <I>66</I> were included in the mesh-type ICRP reference adult male and female phantoms. In addition, realistic lung airway models were simulated to represent the bronchial (BB) and bronchiolar (bb) regions. The electron specific absorbed fraction (SAF) values for the alimentary and respiratory tract systems were then calculated and compared with the values calculated with the stylized models of ICRP <I>Publications 100</I> and <I>66</I>. The comparisons show generally good agreement for the oral cavity, oesophagus, and BB, whereas for the stomach, small intestine, large intestine, extrathoracic region, and bb, there are some differences (e.g. up to ~9 times in the large intestine). The difference is mainly due to anatomical difference in these organs between the realistic mesh-type phantoms and the simplified stylized models. The new alimentary and respiratory tract models in the mesh-type ICRP reference phantoms preserve the topology and dimensions of the voxel-type ICRP phantoms and provide more reliable SAF values than the simplified models adopted in previous ICRP <I>Publications</I>.</P>

Large-area imaging evolution of micro-scale configuration of conducting filaments in resistive switching materials using a light-emitting diode

Keundong Lee,Youngbin Tchoe,Hosang Yoon,Hyeonjun Baek,Kunook Chung,Sangik Lee,Chansoo Yoon,Bae Ho Park,Gyu-Chul Yi 한국진공학회 2016 한국진공학회 학술발표회초록집 Vol.2016 No.2

New small-intestine modeling method for surface-based computational human phantoms

Yeom, Yeon Soo,Kim, Han Sung,Nguyen, Thang Tat,Choi, Chansoo,Han, Min Cheol,Kim, Chan Hyeong,Lee, Jai Ki,Zankl, Maria,Petoussi-Henss, Nina,Bolch, Wesley E,Lee, Choonsik,Chung, Beom Sun IOP 2016 Journal of radiological protection Vol.36 No.2

<P>When converting voxel phantoms to a surface format, the small intestine (SI), which is usually not accurately represented in a voxel phantom due to its complex and irregular shape on one hand and the limited voxel resolutions on the other, cannot be directly converted to a high-quality surface model. Currently, stylized pipe models are used instead, but they are strongly influenced by developer’s subjectivity, resulting in unacceptable geometric and dosimetric inconsistencies. In this paper, we propose a new method for the construction of SI models based on the Monte Carlo approach. In the present study, the proposed method was tested by constructing the SI model for the polygon-mesh version of the ICRP reference male phantom currently under development. We believe that the new SI model is anatomically more realistic than the stylized SI models. Furthermore, our simulation results show that the new SI model, for both external and internal photon exposures, leads to dose values that are more similar to those of the original ICRP male voxel phantom than does the previously constructed stylized SI model.</P>

Percentile-specific computational phantoms constructed from ICRP mesh-type reference computational phantoms (MRCPs)

Lee, Hanjin,Yeom, Yeon Soo,Nguyen, Thang Tat,Choi, Chansoo,Han, Haegin,Shin, Bangho,Zhang, Xujia,Kim, Chan Hyeong,Chung, Beom Sun,Zankl, Maria IOP 2019 Physics in medicine & biology Vol.64 No.4

<P>Recently, the Task Group 103 of the International Commission on Radiological Protection (ICRP) has developed new mesh-type reference computational phantoms (MRCPs) for adult male and female. When compared to the current voxel-type reference computational phantoms in ICRP Publication 110, the MRCPs have several advantages, including deformability which makes it possible to create phantoms in different body sizes or postures. In the present study, the MRCPs were deformed to produce a set of percentile-specific phantoms representing the 10th, 50th and 90th percentiles of standing height and body weight in Caucasian population. For this, anthropometric parameters for the percentile-specific phantoms were first derived from the anthropometric software and survey data. Then, the MRCPs were modified to match the derived anthropometric parameters. For this, first, the MRCPs were scaled in the axial direction to match the head height, torso length, and leg length. Then, the head, torso, and legs were scaled in the transversal directions to match the lean body mass for the percentile-specific phantoms. Finally, the scaled phantoms were manually adjusted to match the body weight and the remaining anthropometric parameters (upper arm, waist, buttock, thigh, and calf circumferences and sagittal abdominal diameter). The constructed percentile-specific phantoms and the MRCPs were implemented into the Geant4 Monte Carlo code to calculate organ doses for a cesium-137 contaminated floor. The results showed that organ doses of the 50th percentile (both standing height and body weight) phantoms are very close to those of the MRCPs. There were noticeable differences in organ doses, however, for the 10th and 90th percentile phantoms when compared with those of the MRCPs. The results of the present study confirm the general intuition that a small person receives higher doses than a large person when exposed to a static radiation field, and organs closer to the source receive higher doses.</P>