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Ki Young Kim,Ki Young Kim,Ki-Taek Byun,Ho-Young Kwak 한국화학공학회 2009 Korean Journal of Chemical Engineering Vol.26 No.6
With a simple model for a surfactant consisting of a hydrophilic head group and hydrophobic tail groups connected by harmonic springs, the structural change of the association structures of the surfactant in an aqueous solution was studied by using the dissipative particle dynamics (DPD) simulation. The effect of the interaction parameter of DPD particles on the structural change of the association structures was also studied. Simulations show that the proper relative values of these interaction parameters could yield desirable changes for the association structure depending on the concentration of the surfactant. That is, a spherical structure forms at φ=0.15, structural change from a spherical to cylindrical one occurs at φ =0.26, and a hexagonal structure appears at φ =0.30, where φ is the volume fraction of surfactant SDS (sodium dodecyl sulfate), and they are in good agreement with observation.
다중기포 소노루미네센스를 이용한 β<SUB>bc</SUB> 형 수산화니켈의 제조
변기택(Ki-Taek Byun),서국원(Kook Won Seo),심일운(Il-Wun Shim),곽호영(Ho-Young Kwak) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Nanosized nickel hydroxide powder for alkine batteries was synthesized in aqueous or nonaqueous solution of nickel chloride with NaOH under ultrasound radiation at the multibubble sonoluminescence (MBSL) condition. Characterization by X-ray diffraction, transmission electron microscopy, FT-IR spectroscopy, as well as elemental analysis indicates the formation of β<SUB>bc</SUB>-type nickel hydroxide. The β<SUB>bc</SUB>-type nickel hydroxide synthesized in aqueous solution of NiCl₂ is slightly different that formed in nonaqueous solution of NiCl₂. The synthetic process of β<SUB>bc</SUB>-type nickel hydroxide at the MBSL condition was completed within 5 minutes. Coating of nickel hydroxide particles on various oxide particles such as Al₂O₃ and SiO₂ was also prepared at the MBSL condition.
변기택(Ki-Taek Byun),강상우(Sarng Woo Karng),김기영(Ki Young Kim),곽호영(Ho-Young Kwak) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
Sonoluminescence (SL) characteristics such as pulse shape, radiance and spectrum radiance from submicron bubbles were investigated. In this study, a set of analytical solutions of the Navier-Stokes equations for the gas inside bubble and equations obtained from mass, momentum and energy equations for the liquid layer adjacent the bubble wall were used to estimate the gas temperature and pressure at the collapse point, which are crucial parameters to determine the SL characteristics. Heat transfer inside the gas bubble as well as at the liquid boundary layer, which was not considered in the most of previous studies on the sonoluminescence was taken it into account in the calculation of the temperature distribution inside the bubble. It was found that bremsstrahlung is a very possible mechanism of the light emission from either micron or submicron bubbles. It was also found that the peak temperature exceeding 10^6 K in the submicron bubble driven at 1 MHz and 4 atm may be due to the rapid change of the bubble wall acceleration near the collapse point rather than shock formation.
다중기포 소노루미네센스를 이용한 CdS/TiO₂ 나노입자의 제조
변기택(Ki-Taek Byun),이승수(Seung Soo Lee),심일운(Il-Wun Shim),곽호영(Ho-Young Kwak) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
Sonoluminescence (SL) is the light emission associated with the catastrophic bubble collapse of a gas bubble oscillating under an ultrasonic field. At the collapse, the bubble produces high temperature and pressure at liquid layer, where high energy chemical reaction can be possible. In the case of the MBSL, a lot of transient bubbles can be generated by the irradiation of high intensity ultrasound in aqueous solution. In this study, synthesis of cadmium sulfide(CdS) and a preparation of the nanoparticles coated on submicron titanium dioxide particles under ultrasonic field at the multibubble sonoluminescence(MBSL) condition were tried. At the optimal MBSL condition in aqueous solution containing cadium chloride of 8.8 wt%, thioacetamide of 11.5 wt% and TiO₂ of 0.8 wt%, CdS nanoparticles were synthesized first and subsequently nanoparticles of several nanometers of CdS/TiO₂(TiO₂ particles coated with CdS nanoparticles) particles were synthesized within 5 minutes. The prepared particles of CdS/TiO₂ were examined by XRD, EDS, UV-vis spectrophotometer, FE-SEM and TEM. The synthesized CdS/TiO₂ particles may be used for a material to reduce the recombination loss in dye solar cell unit.
Byun, Jung-Ick,Jung, Ki-Young,Lee, Gwan-Taek,Kim, Choong-Ki,Kim, Beop-Min 대한신경과학회 2016 Journal of Clinical Neurology Vol.12 No.1
<P><B>Background and Purpose</B></P><P>Periodic limb movements (PLM) during sleep (PLMS) are associated with cortical and cardiovascular activation. Changes in cerebral hemodynamics caused by cortical activity can be measured using near-infrared spectroscopy (NIRS). We investigated oscillatory components of cerebral hemodynamics during PLM and different sleep stages in restless legs syndrome (RLS) patients with PLMS.</P><P><B>Methods</B></P><P>Four female RLS patients with PLMS, and four age- and sex-matched normal controls were included. PLM and sleep stages were scored using polysomnography, while the spontaneous cerebral hemodynamics was measured by NIRS. The phase and amplitude of the cerebral oxyhemoglobin concentration [HbO] and the deoxyhemoglobin concentration [Hb] low-frequency oscillations (LFOs) were evaluated during each sleep stage [waking, light sleep (LS; stages N1 and N2), slow-wave sleep (stage N3), and rapid eye movement (REM) sleep]. In RLS patients with PLMS, the cerebral hemodynamics during LS was divided into LS with and without PLM.</P><P><B>Results</B></P><P>The cerebral hemodynamics activity varied among the different sleep stages. There were changes in phase differences between [HbO] and [Hb] LFOs during the different sleep stages in the normal controls but not in the RLS patients with PLMS. The [HbO] and [Hb] LFO amplitudes were higher in the patient group than in controls during both LS with PLM and REM sleep.</P><P><B>Conclusions</B></P><P>The present study has demonstrated the presence of cerebral hemodynamics disturbances in RLS patients with PLMS, which may contribute to an increased risk of cerebrovascular events.</P>
Ki Young Kim(김기영),Ki-Taek Byun(변기택),Ho-Young Kwak(곽호영) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
A set of solutions of the Navier-Stokes equation for the gas inside a spherical bubble with heat transfer through the bubble wall permits to predict correctly behavior of an ultrasonically driven bubble in aqueous solutions of sulfuric acid. Calculation results of the minimum velocity of bubble wall and the peak temperature and pressure are in excellent agreement with the observed ones. Further the calculated bubble radius-time curve displays alternating pattern of bubble motion as observed in experiment.
소산적 입자동력학을 이용한 계면활성제 수용액의 미셀 구조에 대한 메조스코픽 시뮬레이션
김기영(Ki Young Kim),변기택(Ki Taek Byun),곽호영(Ho-Young Kwak) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
Surfactant molecules which possess polar (head) and non-polar (tail) parts, spontaneously aggregate to form association structures such as micelles and vesicles in solutions. The association structures formed by the surfactant molecules play very important role in biological system. It is also known that the shape of micelles changes with increasing concentration from spherical to cylindrical and to lamellar. With a simple model surfactant which consists of hydrophilic head group and hydrophobic tail groups connected by harmonic springs. The structural change of the association structures in an aqueous surfactant solution has been studied using the dissipative particle dynamics (DPD) simulation. The effect of the hydrophilic interaction between the head and water molecules and the hydrophobic interaction between the tail and water molecules and between the head and tail on the structural change of the association structures was studied. For example, the change of the interaction parameters yields the various structures such as spherical micelle, cylindrical micelle and vesicle in the surfactant volume fraction of 20 %. Simulation results show that proper value of these interaction parameters could yield desirable change of the association structure depending on the concentration.