Simulation of microvascular signal changes used on a gadolinium-chelated contrast agent at 3 T MRI in the presence of amyloid-beta plaques

Yoo Chang Hyun,Goh Junghwan,Jahng Geon-Ho,Jin Seokha,Lee DongKyu,Cho HyungJoon 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.11

It is important to understand microvascular alterations in the brain of Alzheimer disease (AD) patients which usually has amyloid-beta plaques in an imaging voxel, causing a phase dispersion in an MRI signal. The objective of this study was to simulate the changes of transverse relaxation rates and microvascular indexes with and without the presence of amyloid-beta plaques in an imaging voxel with using a clinically available contrast agent. The Monte Carlo simulations with the fnite perturber method were used to calculate microvascular indices of mean vessel diameter (mVD), vessel size index (VSI), mean vessel density (Q), blood volume fraction (BVf), and microvessel-weighted imaging (MvWI) with and without the presence of amyloid-beta plaques in an imaging voxel. The simulation was performed with the conditions of three diferent magnetic feld strengths (1.5 T, 3 T and 7 T), several diferent echo times for gradient-echo (15, 40, and 60 ms) and spin-echo (20, 80, and 100 ms) images, and two diferent contrast agents (gadolinium (Gd)-chelated and superparamagnetic iron oxide nanoparticles (SPION)-based contrast agents). The changes of relaxation rates and microvascular indexes were evaluated with increasing the microvascular vessel sizes and with increasing the amyloid plaque loads. In the microvascular structures without amyloid plaques, ΔR2* and ΔR2 increased as the B0 feld became stronger, the susceptibility diference of the contrast agent became larger, and the echo time was increased. Both mVD and VSI increased with increasing microvessel sizes, but Q decreased with increasing microvessel sizes. In the microvascular structures with amyloid plaques, ΔR2* and ΔR2 were not varied with increasing the vessel radius, but higher in the 3.81% concentration of amyloid plaque than 1.83% of that. BVf and MvWI were increased with increasing the plaque load. The BVf and MvWI indices were sensitive to evaluate the integrity of the microvascular in the AD brain since those values were increased with increasing the plaque load. Therefore, it is worthwhile to evaluate microvascular structure changes in the AD human brain using 3 T MRI with a Gd contrast agent.

Design of a Transverse Flux Linear Motor

Junghwan Chang,Jiwon Kim,Dohyun Kang 한국자기학회 2011 Journal of Magnetics Vol.16 No.1

This paper presents design procedures of a transverse flux linear motor (TFLM). The minimum and maximum flux linkage was determined by the simplified equivalent magnetic circuit and estimated average magnetic flux density at the air gap region by considering the shape of applied magnetomotive force (MMF). With this information, the number of turns of each phase winding was calculated based on the amplitude of applied voltage and speed of a mover. The rated current, coil diameter, and winding area were obtained with the aid of an empirical formula for determining the required MMF. The usefulness of the proposed design method for TFLM is verified by the three-dimensional equivalent magnetic circuit network (EMCN) method and the experimental results of prototyped machine.

p38 MAPK Participates in Muscle-Specific RING Finger 1-Mediated Atrophy in Cast-Immobilized Rat Gastrocnemius Muscle

Junghwan Kim,Kyung-Jong Won,Hwan Myung Lee,Byong-Yong Hwang,Young-Min Bae,Whan Soo Choi,Hyuk Song,Ki Won Lim,Chang-Kwon Lee,Bokyung Kim 대한생리학회-대한약리학회 2009 The Korean Journal of Physiology & Pharmacology Vol.13 No.6

Skeletal muscle atrophy is a common phenomenon during the prolonged muscle disuse caused by cast immobilization, extended aging states, bed rest, space flight, or other factors. However, the cellular mechanisms of the atrophic process are poorly understood. In this study, we investigated the involvement of mitogen-activated protein kinase (MAPK) in the expression of muscle-specific RING finger 1 (MuRF1) during atrophy of the rat gastrocnemius muscle. Histological analysis revealed that cast immobilization induced the atrophy of the gastrocnemius muscle, with diminution of muscle weight and cross-sectional area after 14 days. Cast immobilization significantly elevated the expression of MuRF1 and the phosphorylation of p38 MAPK. The starvation of L6 rat skeletal myoblasts under serum-free conditions induced the phosphorylation of p38 MAPK and the characteristics typical of cast-immobilized gastrocnemius muscle. The expression of MuRF1 was also elevated in serum-starved L6 myoblasts, but was significantly attenuated by SB203580, an inhibitor of p38 MAPK. Changes in the sizes of L6 myoblasts in response to starvation were also reversed by their transfection with MuRF1 small interfering RNA or treatment with SB203580. From these results, we suggest that the expression of MuRF1 in cast-immobilized atrophy is regulated by p38 MAPK in rat gastrocnemius muscles.

Transverse Flux Linear Machine with High Thrust for Direct Drive Applications

Junghwan Chang,Jiwon Kim,Dohyun Kang,Deokje Bang 한국자기학회 2010 Journal of Magnetics Vol.15 No.2

This paper describes the development of a novel transverse flux linear motor (TFLM) excited by permanent magnets (PMs). It combines the advantage of two different TFLMs and produces high thrust with reduced normal force. The magnetic field is analyzed by combining the three-dimensional (3D) equivalent magnetic circuit network (EMCN) method with 2D finite element analysis. The experimental findings of the prototype motors are in good agreements with the analysis results, and demonstrate the potential of the proposed motor as a direct drive requiring relatively long displacement of a mover.

Contribution of Microbleeds on Microvascular Magnetic Resonance Imaging Signal

Chang Hyun Yoo,Junghwan Goh,Geon-Ho Jahng Korean Society of Medical Physics 2022 의학물리 Vol.33 No.4

Purpose: Cerebral microbleeds are more susceptible than surrounding tissues and have been associated with a variety of neurological and neurodegenerative disorders that are indicative of an underlying vascular pathology. We investigated relaxivity changes and microvascular indices in the presence of microbleeds in an imaging voxel by evaluating those before and after contrast agent injection. Methods: Monte Carlo simulations were run with a variety of conditions, including different magnetic field strengths (B₀), different echo times, and different contrast agents. ΔR2^* and ΔR2 and microvascular indices were calculated with varying microvascular vessel sizes and microbleed loads. Results: As B₀ and the concentration of microbleeds increased, 𝜟R2^* and 𝜟R2 increased. 𝜟R2^* increased, but 𝜟R2 decreased slightly as the vessel radius increased. When the vessel radius was increased, the vessel size index (VSI) and mean vessel diameter (mVD) increased, and all other microvascular indices except mean vessel density (Q) increased when the concentration of microbleeds was increased. Conclusions: Because patients with neurodegenerative diseases often have microbleeds in their brains and VSI and mVD increase with increasing microbleeds, microbleeds can be altered microvascular signals in a voxel in the brain of a neurodegenerative disease at 3T magnetic resonance imaging.

벽면 녹화가 실내 온열환경 및 이산화탄소 농도 조절에 미치는 영향

신정환(Junghwan Sin),김환이(Hwanyi Kim),김석환(Sughwan Kim),김수민(Sumin Kim),Jae D. Chang 한국가구학회 2014 한국가구학회지 Vol.25 No.2

Importance of energy consumptions has being emphasized because of problems of the energy and environment. So, recently, green wall systems have been installed to reduce building energy consumptions. The green wall systems provide several benefits; they make it possible to maintain moderate thermal comforts by greenery. Greening such a surface wall in the building by plants, the temperature of the wall can be properly controlled that purifies the air and improves the view spanning over the space. This study evaluated the effects of green wall systems on reducing room temperature quantitatively, changing of humidity, decreasing of CO₂. Test results were confirmed; first, the space installed by green walls showed that temperature and CO₂ decreased and humidity was increased. Second, two structures were compared with the solar radiation, and green wall systems controlled the temperature and humidity stably near the wall regardless of the amount solar radiation. In conclusion, the green wall systems can contribute to thermal comforts and indoor air quality in the buildings.

해석적 방법에 의한 횡자속형 전동기 특성 분석

장정환(Junghwan Chang),김지원(Jiwon Kim),강도현(Dohyun Kang),I.A. Viorel 대한전기학회 2006 대한전기학회 학술대회 논문집 Vol.2006 No.7

횡자속형 전동기는 3차원적인 자속의 흐름 때문에 기존의 전동기와는 달리 2차원적인 수치해석이 용이하지 않으며 특성 분석에 상대적으로 많은 계산 시간을 필요로 한다. 본 논문에서는 퍼미언스법과 철심의 포화를 고려하기 위한 최소한의 유한 요소 해석을 결합하여 횡자속형 전동기의 특성을 분석하기 위한 해석적인 방법을 제시하고자 한다. 본 논문에서 제시하고 있는 추력 및 쇄교 자속량을 표현하는 수식들은 향후 전동기 제어 알고리즘 개발이나 최적 설계에 응용될 수 있을 것으로 판단된다.

영구자석 여자 횡자속 선형 전동기를 적용한 스토크 시스템 개발

장정환(Junghwan Chang),박건우(Gunwoo Park),김지원(Jiwon Kim),강도현(Dohyun Kang),방덕제(Deokje Bang) 대한전기학회 2005 대한전기학회 학술대회 논문집 Vol.2005 No.7

Phorbol Ester-induced Contraction Through p38 Mitogen-activated Protein Kinase is Diminished in Aortas from DOCA-Salt Hypertensive Rats

Chang-Kwon Lee,Junghwan Kim,원경종,Hwan Myung Lee,Hyo Jin Kim,Hui Yul Roh,Hyo-Jun Park,신화섭,박태규,Bokyung Kim,이상목 대한약학회 2006 Archives of Pharmacal Research Vol.29 No.11

The role of mitogen-activated protein kinase (MAPK) in the decreased contractile response to phorbol ester in aortic smooth muscle strips from deoxycorticosterone acetate (DOCA)-salt hypertensive rats was examined. Norepinephrine (NE) evoked greater contractility in aortic strips from DOCA rats than in those of sham-operated rats. 12-Deoxyphorbol 13-isobutyrate (DPB) induced contraction in Ca2+-free medium, which was diminished in strips from DOCA rats compared to sham-operated rats. Vasoconstrictions induced by these stimulants were inhibited by SB203580 and PD098059, inhibitors of p38 MAPK and extracellular signalregulated kinase (ERK) 1/2, respectively, in both strips. The phosphorylation of p38 MAPK and ERK1/2 induced by NE was greater in strips from DOCA rats compared to those from shamoperated rats, and this phosphorylation was inhibited by the kinase inhibitors. DPB increased the phosphorylation of p38 MAPK and ERK1/2 in strips from both animals, and the increment of p38 MAPK phosphorylation by the stimulant was diminished in strips from DOCA rats compared to sham-operated rats. These findings suggest that the Ca2+-independent contraction evoked by DPB results from the activation of MAPKs in rat aortic smooth muscle and that the attenuated contractility by DPB in DOCA rat appears to be associated with diminished p38 MAPK activity.

Effect of atomic passivation at Ni-MoS2 interfaces on contact behaviors

Junghwan Kim,Chang-Gyu Choi,Kyung-Ah Min,Kyeongjae Cho,SuklyunHong 한국물리학회 2020 Current Applied Physics Vol.20 No.1

Recently, spintronics devices using MoS2 and ferromagnetic electrode have been in the spotlight. However, strong Fermi level pinning (FLP) is known to occur between MoS2 and ferromagnetic electrode, resulting in a large Schottky barrier height (SBH), which makes it difficult to inject electron from ferromagnetic electrode to semiconductor. To resolve this problem, we study the reduction of FLP occurring between two materials by investigating the effect of atomic passivation at Ni-MoS2 interfaces on contact behaviors. Such atomic passivation can reduce the FLP and magnetic moments induced at S atoms of MoS2. Especially, the largest decrease in the FLP occurs in the case of H atom passivation. Besides, the N, O, and F atom passivation confirms the possibility of ohmic contact, indicated from small SBHs (~0.2 eV). As a result, the SBH and thus the efficiency of the device can be controlled by atomic passivation at metal-semiconductor interfaces.