• 대한의용생체공학회:의공학회지
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• 제30권2호
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• pp.135-141
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• 2009

Purpose: The aim of present study is to evaluate a possibility of clinical application for the effect of low intensity ultrasound stimulation (LIUS) in mechanical characteristics of bone on osteoporotic fractures prevention. Materials and Methods: Eight virgin ICR mice (14 weeks old, approximate weight 25g) were ovariectomized (OVX) to induce osteoporosis. The right hind limbs were then stimulated with LIDS (US Group), whereas left hind limbs were not stimulated (CON Group). Both hind limbs of all mice were scanned by in-vivo micro-CT to acquire two-dimensional (2D) images at 0 week before stimulation and 3 weeks and 6 weeks after stimulation. Three-dimensional (3D) finite element (FE) models generated by scanned 2D images were used to determine quantitatively the effect of LIUS on strength related to bone structure. Additionally, distributions of Hounsfield units and elastic moduli, which are related to the bone quality, for the bones in the US and CON groups were determined to analyze quantitatively a degree of improvement of bone qualities achieved by LIUS. Results: The result of FE analysis showed that the structural strength in US Group was significantly increased over time (p<0.05), while that in CON Group was statistically constant over time (p>0.05). High values of Hounsfield units obtained from voxels on micro-CT images and high values of elastic moduli converted from the Hounsfield units were dominantly appeared in US Group compared with those in CON Group. Conclusion: These finding indicated that LIUS would improve the mechanical characteristics of osteoporotic bone via the effects of bone structure (bone strength) and quality (Hounsfield unit and elastic modulus). Therefore, the LIUS may decrease effectively the risk of osteoporotic fracture in clinics.

• Journal of Electrochemical Science and Technology
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• 제9권3호
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• pp.229-237
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• 2018

The electrochemical sensing performance of metal-graphene hybrid based sensor may be significantly decreased due to the dissolution and aggregation of metal catalyst during operation. For the first time, we developed a novel large-area high quality three dimensional graphene foam-incorporated gold nanoparticles (3D-GF@Au) via chemical vapor deposition method and employed as free-standing electrocatalysis for non-enzymatic electrochemical glucose detection. 3D-GF@Au based sensor is capable to detect glucose with a wide linear detection range of $2.5{\mu}M$ to 11.6 mM, remarkable low detection limit of $1{\mu}M$, high selectivity, and good stability. This was resulted from enhanced electrochemical active sites and charge transfer possibility due to the stable and uniform distribution of Au NPs along with the enhanced interactions between Au and GF. The obtained results indicated that 3D-GF@Au hybrid can be expected as a high quality candidate for non-enzymatic glucose sensor application.

• 대한기계학회논문집A
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• 제35권9호
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• pp.991-997
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• 2011

본 논문은 EPP 비드폼에 대한 증기실 조형공정의 기본 원리들과 과정들에 대해 다루고 있습니다. 증기실 조형은 EPP 기술을 위한 필수적인 공정입니다. 그러나 증기실 조형의 공정조건에 대해 연구가 거의 이루어져 있지 않습니다. EPP 폼의 특징들은 에너지흡수, 다양한 충격보호, 가벼운 무게, 구조상의 견고성과 내구성 등이다. 본 연구에서는 증기실 조형에서 증기압을 변화시켜 EPP 폼 제작을 위한 최적조건을 찾고자 노력하였으며, 무엇보다 증기조형 제품의 수축을 방지하기 위하여 EPP 폼 조형후 노내 가열을 수행하였다. 다른 노내 가열 온도들에서 시간에 따라 무게가 바뀌는 것을 관찰함으로써 폼수축의 메커니즘을 확인하는 것이 가능하였다. 인장시험과 SEM 해석을 수행하여 이들 실험결과들을 뒷받침할 수 있었고, 다른 증기압들에서 조형된 제품들에 대해 치수안정성을 조사하였다.

• 한국표면공학회지
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• 제56권4호
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• pp.233-242
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• 2023

In recent years, energy-management studies in buildings have proven useful for energy savings. Typically, during heating and cooling, the energy from a given building is lost through its windows. Generally, to block the entry of ultraviolet (UV) and infrared (IR) rays, thin films of deposited metals or metal oxides are used, and the blocking of UV and IR rays by these thin films depends on the materials deposited on them. Therefore, by controlling the thicknesses and densities of the thin films, improving the transmittance of visible light and the blocking of heat rays such as UV and IR may be possible. Such improvements can be realized not only by changing the two-dimensional thin films but also by altering the zero-dimensional (0-D) nanostructures deposited on the films. In this study, 0-D nanoparticles were synthesized using a sol -gel procedure. The synthesized nanoparticles were deposited as deep coatings on polymer and glass substrates. Through spectral analysis in the UV-visible (vis) region, thin-film layers of deposited zinc oxide nanoparticles blocked >95 % of UV rays. For high transmittance in the visible-light region and low transmittance in the IR and UV regions, hybrid multiple layers of silica nanoparticles, zinc oxide particles, and fluorine-doped tin oxide nanoparticles were formed on glass and polymer substrates. Spectrophotometry in the UV-vis-near-IR regions revealed that the substrates prevented heat loss well. The glass and polymer substrates achieved transmittance values of 80 % in the visible-light region, 50 % to 60 % in the IR region, and 90 % in the UV region.

• Korean Journal of Radiology
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• 제22권5호
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• pp.782-791
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• 2021

Objective: To evaluate the signal intensity of the periosteum using ultrashort echo time pulse sequence with three-dimensional cone trajectory (3D UTE) with or without fat suppression (FS) to distinguish from artifacts in porcine tibias. Materials and Methods: The periosteum and overlying soft tissue of three porcine lower legs were partially peeled away from the tibial cortex. Another porcine tibia was prepared as three segments: with an intact periosteum outer and inner layer, with an intact periosteum inner layer, and without periosteum. Axial T1 weighted sequence (T1 WI) and 3D UTE (FS) were performed. Another porcine tibia without periosteum was prepared and subjected to 3D UTE (FS) and T1 WI twice, with positional changes. Two radiologists analyzed images to reach a consensus. Results: The three periosteal tissues that were partially peeled away from the cortex showed a high signal in 3D UTE (FS) and low signal on T1 WI. 3D UTE (FS) showed a high signal around the cortical surface with an intact outer and inner periosteum, and subtle high signals, mainly around the upper cortical surfaces with the inner layer of the periosteum and without periosteum. T1 WI showed no signal around the cortical surfaces, regardless of the periosteum state. The porcine tibia without periosteum showed changes in the high signal area around the cortical surface as the position changed in 3D UTE (FS). No signal was detected around the cortical surface in T1 WI, regardless of the position change. Conclusion: The periosteum showed a high signal in 3D UTE and 3D UTE FS that overlapped with artifacts around the cortical bone.

• Journal of Radiation Protection and Research
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• 제49권2호
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• pp.68-77
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• 2024

Background: Cone beam computed tomography (CBCT) is essential for correcting and verifying patient position before radiation therapy. However, it poses additional radiation exposure during CBCT scans. Therefore, this study aimed to evaluate radiological safety for the human body through dose assessment for CBCT. Materials and Methods: For CBCT dose assessment, the depth dose was evaluated using a cheese phantom, and the dose in the orbital area was evaluated using a human body phantom self-fabricated with a three-dimensional printer. Results and Discussion: The evaluation of radiation doses revealed maximum doses of 14.14 mGy and minimum doses of 6.12 mGy for pelvic imaging conditions. For chest imaging conditions, the maximum doses were 4.82 mGy, and the minimum doses were 2.35 mGy. Head imaging conditions showed maximum doses of 1.46 mGy and minimum doses of 0.39 mGy. The eyeball doses using a human body phantom model averaged at 2.11 mGy on the left and 2.19 mGy on the right. The depth dose ranged between 0.39 mGy and 14.14 mGy, depending on the change in depth for each imaging mode, and the average dose in the orbit area using a human body phantom was 2.15 mGy. Conclusion: Based on the experimental results, CBCT did not significantly affect the radiation dose. However, it is important to maintain a minimal radiation dose to optimize radiation protection following the as low as reasonable achievable principle.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.181.2-181.2
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• 2014

A single-layer graphene has been uniformly grown on a Cu surface at elevated temperatures by thermally processing a poly (methyl methacrylate) (PMMA) film in a rapid thermal annealing (RTA) system under vacuum. The detailed chemistry of the transition from solid-state carbon to graphene on the catalytic Cu surface was investigated by performing in-situ residual gas analysis while PMMA/Cu-foil samples being heated, in conjunction with interrupted growth studies to reconstruct ex-situ the heating process. We found that the gas species of mass/charge (m/e) ratio of 15 ($CH_3{^+}$) was mainly originated from the thermal decomposition of PMMA, indicating that the formation of graphene occurs with hydrocarbon molecules vaporized from PMMA, such as methane and/or methyl radicals, as precursors rather than by the direct graphitization of solid-state carbon. We also found that the temperature for dominantly vaporizing hydrocarbon molecules from PMMA and the length of time, the gaseous hydrocarbon atmosphere is maintained, are dependent on both the heating temperature profile and the amount of a solid carbon feedstock. From those results, we strongly suggest that the heating rate and the amount of solid carbon are the dominant factors to determine the crystalline quality of the resulting graphene film. Under optimal growth conditions, the PMMA-derived graphene was found to have a carrier (hole) mobility as high as ${\sim}2,700cm^2V^{-1}s^{-1}$ at room temperature, which is superior to common graphene converted from solid carbon.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.131-131
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• 2013

A single-layer graphene has been uniformly grown on a Cu surface at elevated temperatures by thermally processing a poly(methyl methacrylate) (PMMA) film in a rapid thermal annealing (RTA) system under vacuum. The detailed chemistry of the transition from solid-state carbon to graphene on the catalytic Cu surface was investigated by performing in-situ residual gas analysis while PMMA/Cu-foil samples being heated, in conjunction with interrupted growth studies to reconstruct ex-situ the heating process. The data clearly show that the formation of graphene occurs with hydrocarbon molecules vaporized from PMMA, such as methane and/or methyl radicals, as precursors rather than by the direct graphitization of solid-state carbon. We also found that the temperature for vaporizing hydrocarbon molecules from PMMA and the length of time the gaseous hydrocarbon atmosphere is maintained, which are dependent on both the heating temperature profile and the amount of a solid carbon feedstock are the dominant factors to determine the crystalline quality of the resulting graphene film. Under optimal growth conditions, the PMMA-derived graphene was found to have a carrier (hole) mobility as high as ~2,700 cm2V-1s-1 at room temperature, superior to common graphene converted from solid carbon.

• 한국진공학회지
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• 제17권1호
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• pp.34-39
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• 2008

저온에서 성장된 AlN (LT-AlN)층이 삽입된 $Al_xGa_{1-x}N/LT$-AlN/GaN 이종접합 구조를 금속유기 화학기상 증착법 (metal-organic chemical vapor deposition)을 사용하여 사파이어 기판 위에 제작하였다. Rutherford backscattering spectroscopy 실험을 통하여 $Al_xGa_{1-x}N$층의 Al의 조성비 x가 55% 임을 확인하였고, X-선 역격자 공간 mapping을 통하여 층간 변형력을 조사하였다. LT-AlN층의 삽입 여하에 따른 $Al_{0.55}Ga_{0.45}N$ 층의 깨짐 현상을 광학현미경과 주사전자현미경을 통하여 조사하였는데, LT-AlN 층이 삽입된 시료의 경우에 깨짐 현상이 현저히 줄어든 $Al_{0.55}Ga_{0.45}N$ 층을 얻을 수 있었다. 뿐만 아니라 LT-AlN 층이 삽입된 $Al_{0.55}Ga_{0.45}N$/LT-AlN/GaN 이종접합 구조에 대하여 이차원 전자가스 (two-dimensional electron gas, 2DEG) 관련된 photoluminescence (PL) 신호를 관찰하였다. 이 시료에 대하여 온도 변화에 따른 PL 실험을 수행하여 100 K 근방까지 2DEG 관련된 PL 신호를 관찰하였다. 여기광 세기에 따른 PL 실험을 통하여 ~3.411 eV에서 나타난 2DEG PL 신호와 함께 ${\sim}3.437eV$에서도 PL 신호가 관측되었는데, 이는 AlGaN/LT-AlN/GaN 계면에 형성된 2DEG 버금띠와 Fermi 에너지 준위에서의 재결합 특성으로 각각 해석되었다.

• 자원환경지질
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• 제36권4호
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• pp.305-312
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• 2003

본 연구는 중력자료를 이용하여 팔공산화강암체의 분포양샹, 인근지역의 지하 지질 및 지질구조, 경상분지와 영남 육괴와의 관계규명 등을 밝히는데 그 목적이 있다. 연구지역은 북위 35$^{\circ}$45'-36$^{\circ}$21', 동경 128$^{\circ}$15'-129$^{\circ}$00'에 해당한다. 중력자료는 서울대학교, 한국지질자원연구원, 부산대학교 및 연세대학교에서 측정한 기존의 중력자료 826개와 팔공산 화강암체를 포함하는 주변지역에서 금번에 측정된 중력자료 140개에 대해 계기보정, 조석보정, 위도보정, 푸리에어보정, 부게보정, 대기보정, 지형보정을 실시하여 부게중력이상을 구하였다. 연구지역의 부게중력이상은 -12.88∼26.01 mgal의 분포를 보이며, 평균치는 11.27mgal이다. 연구지역의 서쪽에 위치한 영남육괴에서는 평균에 비해 상당히 낮은 저 이상대를 보이며, 연구지역의 서쪽에서 동쪽으로 갈수록 이상값이 높아진다. 팔공산화강암체와 영남육괴 분포지역에서 부게중력이상이 낮게 나타나는 것은 이들의 밀도가 경상분지의 퇴적암보다 낮기 때문인 것으로 해석된다. 부게중력이상으로부터 지하에 존재하는 밀도 불연속면의 평균심도를 구하기 위해 진폭스펙트럼과 공간주파수를 이용한 파워스펙트럼분석을 실시한 결과, 밀도 불연속면의 평균 심도는 4.9 km와 10.4 km이며, 이는 각각 분지기반암과 콘라드면의 평균심도로 해석된다. 연구지역의 동쪽에서 갑자기 낮아지는 저이상대는 신령단층과 노고산 환상단층의 영향으로 해석된다 2차원 모델링에 의한 팔공산화강암체의 심도는 연구지역의 중앙을 기준으로 서쪽에서 동쪽으로 갈수록 감소한다. 각 측선의 2차원 모델링에 의한 팔공산화강암체의 분포 심도가 두 지점에서 첨예하게 깊게 나타나며, 각자의 심도는 측선 AAl에서는 5.3 km, 측선 BBl에서는 팔공산화강암체의 최대심도인 약 7 km이다. 또한, 팔공산화강암체 주변의 천부지역에는 작은 화강암체들이 관입해 있음을 알 수 있다. 각 측선별 2차원 모델링에 의해 얻어진 자료의 보간을 통해 구현한 3차원 해석으로부터 팔공산화강암체의 뿌리는 지표에 나타나는 팔공산화강암체를 중심으로 남서쪽부근에 위치하며, 지하에 분포하는 팔공산화강암체의 전체 부피는 약 31.211$Km^3$으로 추정된다.