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초소형 비행체용 하이브리드 엔진 냉각을 위한 3D 프린팅 카울 형상 및 재질 연구
이기웅(Kiwoong Lee),김우비(Woo Bee Kim),권혁록(Hyuk Rok Gwon),김대원(Dae Won Kim),정윤식(Yunsik Jung),이현석(Hyeon Seok Lee),조성진(Sung Jin Jo),이선형(Seon Hyeong Lee) 한국추진공학회 2019 한국추진공학회 학술대회논문집 Vol.2019 No.5
본 논문에서는 하이브리드 추진시스템에 사용하는 공랭식 엔진에 3D 프린터로 제작된 카울을 적용하기 위하여 고려되어야 할 형상과 재질 특성에 대해 살펴보았다. 열/유동 해석을 통해 냉각 성능 확인 및 카울에 영향을 줄 수 있는 요소들에 대하여 연구하였으며, 실물 모사 형상의 지상 시험을 통하여 최종적으로 냉각 카울로 적용할 형상 및 재질을 선정하였다. In this paper, we studied shape and material feature which must be considered for appling 3D printing cowls for air cooling hybrid propulsion system engine. Using Heat/Flow analysis, figured the cooling efficiency and factor that can influence to cowl, then confirmed final model by ground test with actual mock-up.
Lee, Seong-Joo,Kim, Kiwoong,Kang, Chan Seok,Hwang, Seong-min,Lee, Yong-Ho IOP Publishing Ltd 2010 Superconductor science & technology Vol.23 No.11
<P>We achieved enhanced pre-polarization in a superconducting quantum interference device (SQUID)-based microtesla nuclear magnetic resonance (NMR) experiment by using dynamic nuclear polarization (DNP). The pre-polarization field is necessary to provide enough signal to noise to perform SQUID-based ultra-low-field (ULF) NMR/magnetic resonance imaging (MRI) experiments. However, it is quite tricky to deal with the strong transient magnetic field when operating the SQUID in a magnetically shielded room (MSR); besides the direct interference with the sensitive SQUID sensor, the strong magnetic field and its abrupt change generate magnetization in local areas in the MSR and eddy currents along the wall, which makes the NMR measurement difficult. The enhanced <SUP>1</SUP>H NMR signals of water in TEMPOL and TEMPO solutions were obtained with a relatively weak radio-frequency (rf) field and double-relaxation oscillation SQUIDs (DROS) at a few mT pre-polarization fields. In our experimental condition, the enhancement factor was near ten in spite of the rf power far below the saturation in both samples.</P>
Pressure-driven spontaneous ion concentration polarization using an ion-selective membrane
Lee, Sang Joon,Lee, Jaehyeon,Kim, Kiwoong Elsevier 2018 Analytical Biochemistry Vol.557 No.-
<P><B>Abstract</B></P> <P>In this study, the spontaneous ion concentration polarization phenomenon induced by pressure via a cation-selective membrane was theoretically and experimentally investigated. Unlike conventional electrokinetic ion concentration polarization, which uses electric current as a driving flux of cations through the membrane, advection caused by pressure is used as a transmembrane driving flux of cations to spontaneously and stably form an ion depletion zone in the present ion concentration polarization technique. The ion depletion zone produced in a simple experimental setup was used to filter electrolyte and preconcentrate ions and microparticles. Different from the general assumption of the negligible thickness of the electric double layer in microchannels, the low concentration in the ion depletion zone considerably increased the length of the electric double layer. This enhanced the formation of the ion depletion zone. The present results can improve the understanding on ion transport in the ion concentration polarization system and can be utilized to develop a portable water desalination device for rural/remote areas and for preconcentrating biomolecules.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Advection caused by pressure generates ion concentration polarization spontaneously. </LI> <LI> Ion depletion zone filters ions and preconcentrates microparticles in a microchannel. </LI> <LI> Electric double layer inside ion depletion zone affects ion distribution in a channel. </LI> </UL> </P>
Lee, Hyun Joon,Lee, Seong-Joo,Shim, Jeong Hyun,Moon, Han Seb,Kim, Kiwoong Elsevier 2019 Journal of magnetic resonance Vol.300 No.-
<P><B>Abstract</B></P> <P>The development of atomic magnetometers has led to nuclear magnetic resonance (NMR) in zero and ultralow magnetic fields without using cryogenic sensors. However, <I>in-situ</I> detection, meaning that a sample locates in the detection space beside a vapor cell, has been conducted only with parahydrogen-induced polarization. Other hyperpolarization techniques remain unexplored yet. In this work, we demonstrate that Overhauser dynamic nuclear polarization allows <I>in-situ</I> NMR detection with an atomic magnetometer at less than 1 μ T. The <SUP> 1 </SUP> H NMR signal of a nitroxide radical solution was observed at 13.83 Hz, which corresponds to 325 nT. Signal-to-noise ratio was 32 after sixteen averages. On the Larmor precession of <SUP> 1 </SUP> H spins, a decaying oscillation was superimposed. We attribute it to a transient <SUP> 87 </SUP> Rb spin precession in response to a non-adiabatic field variation. This work shows a new capability of zero- and ultralow-field NMR.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The first <I>in-situ</I> Overhauser-enhanced nuclear magnetic resonance experiment using an atomic magnetometer at ultra-low field. </LI> <LI> Signal-to-noise ratio was 32 after sixteen averages. </LI> <LI> On the Larmor precession of <SUP> 1 </SUP> H spins, a decaying oscillation was superimposed. </LI> <LI> We attribute it to a transient <SUP> 87 </SUP> Rb spin precession in response to a non-adiabatic field variation. </LI> <LI> Atomic magnetometry technique shows a new capability of zero and ultralow-field NMR. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Lee, Kiwoong,Choi, Hoseop,Kim, Dae Seong,Jang, Min Seok,Choi, Mansoo IOP 2017 Nanotechnology Vol.28 No.47
<P>In this report, we introduce a method utilizing ion-assisted aerosol lithography to stack 3D nanostructures vertically. The stacked 3D nanostructures exhibit extraordinary optical properties: the double layer 3D nanostructures show more than 5-fold increased surface enhanced Raman scattering intensities compared to their single layer counterpart. This unusual enhancement of Raman intensity implies the existence of additional vertical hotspots formed by interlayer cavity effects between the lower and upper nanostructures. Allowing for full three-dimensional control in nanofabrication, this work provides a reliable way to create complex-shaped advanced optical nanostructures with non-intuitive bulk optical properties.</P>
Kiwoong Lee,Soon Jin Yun,Minsoo Kim,Hee Moon Yang,A Reum Kim The Ecological Society of Korea 2024 Journal of Ecology and Environment Vol.48 No.1
Background: The study was carried out to analyze the temporal changes of trade-offs (TOs) between two ecosystem services (ESs) before and after thinning in a Pinus koraiensis plantation on Mt. Gari from 2006 to 2021. As target variables, aboveground carbon (AGC) storage and species richness (SR) were chosen for regulating and supporting services. Thinning was applied from 2007 through 2008 with three treatments: 1) light thinning (LT), 2) heavy thinning (HT), and 3) control (Con). Results: Thinning influenced both AGC and SR. In 2021, AGC in the Con (111.1 t C ha<sup>-1</sup>) was significantly higher compared to the LT (82.0 t C ha<sup>-1</sup>) and HT (60.4 t C ha<sup>-1</sup>) after thinning from 2007 to 2008. Also, SR was marginally higher in the LT (94 species) than in the Con (55 species) and HT (87 species) in 2011. Relative benefits of AGC and SR showed similar trends with the obtained values. In addition, the effects of thinning on TO varied among treatments and over time, demonstrating different degrees of TO between the two ESs. In the LT, TO was 0.13 in 2006 and slightly increased to 0.2 by 2021. TO in the HT exhibited a relatively rapid increase from 0.22 in 2006 to 0.58 by 2021, while To in the Con fluctuated, rising to 0.36 in 2011 from 0.1 in 2006 and decreasing to 0.25 by 2021. Among the three treatments, the degree of TOs between the two ESs was the lowest in the LT. Conclusions: Depending on thinning intensities, the responses of ESs and the degree of TOs vary. Regarding the balance between enhancements and TOs in ESs among treatments, the LT treatment showing intermediate carbon storage, higher SR, and lower TOs will be a proper silvicultural application.
Impact of White Matter Lesions on Depression in the Patients with Alzheimer’s Disease
JungJae Lee,EunYoung Lee,SeokBum Lee,JoonHyuk Park,TaeHui Kim,HyunGhang Jeong,JaeHyoung Kim,JiWon Han,KiWoong Kim 대한신경정신의학회 2015 PSYCHIATRY INVESTIGATION Vol.12 No.4
Objective-Comorbid depression is common in patients with Alzheimer’s disease (AD). An increase in white matter lesions (WMLs) has been associated with depression in both elderly individuals with normal cognition and patients with Alzheimer’s disease. We investigated whether the severity and location of WMLs influence the association between WMLs and comorbid depression in AD. Methods-We enrolled 93 AD patients from Seoul National University Bundang Hospital. We administered both the Mini International Neuropsychiatric Inventory (MINI) and the Korean version of the Consortium to Establish a Registry for Alzheimer’s Disease Assessment Packet (CERAD-K) clinical and neuropsychological battery. Subjects also underwent brain magnetic resonance imaging (MRI). We diagnosed AD according to the criteria of the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer’s Disease and Related Disorders Association. We diagnosed depressive disorders according to the DSM-IV diagnostic criteria, and evaluated the severity of depressive symptoms using the Korean version of the Geriatric Depression Scale (GDS-K). We quantified the WML volumes from the brain MRI using a fully automated segmentation algorithm. Results-The log of the WML volume in the frontal lobe was significantly associated with depressive disorders (odds ratio=1.905, 95% CI=1.027–3.533, p=0.041), but not with the severity of depressive symptoms as measured by the GDS-K. Conclusion-The WML volume in the frontal lobe conferred a risk of comorbid depressive disorders in AD, which implies that comorbid depression in AD may be attributed to vascular causes.