• 한국산업융합학회 논문집
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• 제22권5호
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• pp.467-473
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• 2019

In this study, approached to improve durability of the multi-functional nano-pattern fabricated on the curved lens surface using nanoimprint lithography (NIL) was proposed, and the effects of the proposed methods on functionality after wear test were examined. To improve the mechanical property of ultraviolet(UV)-curable resin, UV-NIL was conducted at the elevated temperature around $60^{\circ}C$. In addition, micro/nano hierarchical structures was fabricated on the lens surface with a durable film mold. Analysis on the worn surfaces of nano-hole pattern and hierarchical structures and measurements on the static water contact angle and critical water volume for roll-off indicated that the UV curing process with elevated temperature is effective to maintain wettability by increasing hardness of resin. Also, it was found that the micro-scale pattern is effective to protect nano-pattern from damage during wear test.

• 한국자기학회지
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• 제5권5호
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• pp.528-532
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• 1995

Ferromagnetic resonance experiments have been used to investigate the magnetic properties of amorphous $Co_{89.5}Zr_{10.5}$ thin films deposited by DC magnetron sputtering method. In the thickness range from $350\;{\AA}$ to $3,200\;{\AA}$, measurements were carried out in a static magnetic field perpendicular and parallel to the film plane and in a conventional 9.44 GHz spectrometer at room temperature. The ferromagnetic resonance spectra by the field perpendicular to the film plane showed standing spin wave. The spacing and the relative intensities between the various spin wave resonance peaks are analysed considering surface magnetic anisotropy. The surface magnetic anisotropy constant ($K_{so},\;K_{sd}$) of amorphous $Co_{89.5}Zr_{10.5}$ thin films are $0.02\;erg/\textrm{cm}^2$ and $0.55\;erg/\textrm{cm}^2$ respectively regardless of the film thickness except for $3,200\;{\AA}$ film. In case of $3,200\;{\AA}$ these values are $0.46\;erg/\textrm{cm}^2$ and $0.55\;erg/\textrm{cm}^2$ respectively.

• Nuclear Engineering and Technology
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• 제47권7호
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• pp.804-813
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• 2015

The electrical-impedance method has been widely used for void-fraction measurement in two-phase flow due to its many favorable features. In the impedance method, the response characteristics of the electrical signal heavily depend upon flow pattern, as well as phasic volume. Thus, information on the flow pattern should be given for reliable void-fraction measurement. This study proposes an improved electrical-conductance sensor composed of a three-electrode set of adjacent and opposite electrodes. In the proposed sensor, conductance readings are directly converted into the flow pattern through a specified criterion and are consecutively used to estimate the corresponding void fraction. Since the flow pattern and the void fraction are evaluated by reading conductance measurements, complexity of data processing can be significantly reduced and real-time information provided. Before actual applications, several numerical calculations are performed to optimize electrode and insulator sizes, and optimal design is verified by static experiments. Finally, the proposed sensor is applied for air-water two-phase flow in a horizontal loop with a 40-mm inner diameter and a 5-m length, and its measurement results are compared with those of a wire-mesh sensor.

• Geomechanics and Engineering
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• 제35권1호
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• pp.1-11
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• 2023

A growing trend of utilizing helical piles for soft soil strata to support infrastructure projects is currently observed in Saemangeum, South Korea. Recognized mainly due to its ease of installation and reusability proves to be far more superior compared to other foundation types in terms of sustainability. This study applies modified p-y springs to characterize the behavior of a laterally loaded helical pile with a shaft diameter of 89.1 mm affixed with 3 helices evenly spaced along its embedded length of 2.5 m. Geotechnical soil properties are correlated from CPT data near the test bed vicinity and strain gauges mounted on the shaft surface. A modification factor is applied on the p-y springs to adjust the simulated data and match it to the bending moment, soil resistance and deflection values from the strain gauge measurements. The predicted lateral behavior of the helical pile through the numerical analysis method shows fairly good agreement to the recorded field test results.

• Geomechanics and Engineering
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• 제37권2호
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• pp.97-107
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• 2024

The accurate prediction of grouting upward diffusion height is crucial for estimating the bearing capacity of tip-grouted piles. Borehole construction during the installation of bored piles induces soil unloading, resulting in both radial stress loss in the surrounding soil and an impact on grouting fluid diffusion. In this study, a modified model is developed for predicting grout diffusion height. This model incorporates the classical rheological equation of power-law cement grout and the cavity reverse expansion model to account for different degrees of unloading. A series of single-pile tip grouting and static load tests are conducted with varying initial grouting pressures. The test results demonstrate a significant effect of vertical grout diffusion on improving pile lateral friction resistance and bearing capacity. Increasing the grouting pressure leads to an increase in the vertical height of the grout. A comparison between the predicted values using the proposed model and the actual measured results reveals a model error ranging from -12.3% to 8.0%. Parametric analysis shows that grout diffusion height increases with an increase in the degree of unloading, with a more pronounced effect observed at higher grouting pressures. Two case studies are presented to verify the applicability of the proposed model. Field measurements of grout diffusion height correspond to unloading ratios of 0.68 and 0.71, respectively, as predicted by the model. Neglecting the unloading effect would result in a conservative estimate.

• 한국대기환경학회지
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• 제27권3호
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• pp.313-325
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• 2011

From October 2009 to June 2010, major greenhouse gases (GHG: $N_2O$, $CH_4$, $CO_2$) soil emission were measured from upland cabbage field at Kunsan ($35^{\circ}$56'23"N, $126^{\circ}$43'14"E), Korea by using closed static chamber method. The measurements were conducted mostly from 10:00 to 18:00LST during field experiment days (total 28 days). After analyzing GHG concentrations inside of flux chamber by using a GC equipped with a methanizer (Varian CP3800), the GHG fluxes were calculated from a linear regression of the changes in the concentrations with time. Soil parameters (e.g. soil moisture, temperature, pH, organic C, soil N) were also measured at the sampling site. The average soil pH and soil moisture were ~pH $5.42{\pm}0.03$ and $70.0{\pm}1.8$ %WFPS (water filled pore space), respectively. The ranges of GHG flux during the experimental period were $0.08\sim8.40\;mg/m^2{\cdot}hr$ for $N_2O$, $-92.96\sim139.38mg/m^2{\cdot}hr$ for $CO_2$, and $-0.09\sim0.05mg/m^2{\cdot}hr$ for $CH_4$, respectively. It revealed that monthly means of $CO_2$ and $CH_4$ flux during October (fall) were positive and significantly higher than those (negative value) during January (winter) when subsoil have low temperature and relatively high moisture due to snow during the winter measurement period. Soil mean temperature and moisture during these months were $17.5{\pm}1.2^{\circ}C$, $45.7{\pm}8.2$%WFPS for October; and $1.4{\pm}1.3^{\circ}C$, $89.9{\pm}8.8$ %WFPS for January. It may indicate that soil temperature and moisture have significant role in determining whether the $CO_2$ and $CH_4$ emission or uptake take place. Low temperature and high moisture above a certain optimum level during winter could weaken microbial activity and the gas diffusion in soil matrix, and then make soil GHG emission to the atmosphere decrease. Other soil parameters were also discussed with respect to GHG emissions. Both positive and negative gas fluxes in $CH_4$ and $CO_2$ were observed during these measurements, but not for $N_2O$. It is likely that $CH_4$ and $CO_2$ gases emanated from soil surface or up taken by the soil depending on other factors such as background concentrations and physicochemical soil conditions.

• 한국의학물리학회지:의학물리
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• 제15권1호
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• pp.1-8
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• 2004

방사선 치료과정에서 가장 중요한 것은 환자에게 조사된 흡수선량을 검증하는 것이다. IMRT에 사용되는 방사선의 물리적 특성을 결정하고 환자에 조사된 선량분포를 검증할 수 있는 정밀한 선량 측정 장치가 필요하다. 본 연구에서 2차원 광자선의 선량검증을 위해 만들어진 BInS (Beam Intensity Scanner)에 관하여 논의한다. BInS에 있는 Scintillator는 광자선이나 전자선에 조사되면 형광을 발생하는 Gd$_2$O$_2$S:Tb를 주성분으로 한다. Scintillator에서 발생된 형광은 디지털 비디오카메라에 의해 수집되어 디지털 신호로 바뀌고 자체 제작한 소프트웨어에 의해 분석되며 상대적인 선량 분포가 3차원 그림으로 표시된다. BInS가 IMRT에서 사용가능한지를 알아보기 위하여 치료에 관련된 몇 가지 측정을 하였다. IMRT의 주요 작동방식 중의 하나인 SMLC (static multileaf collimator) 방식에서는, leaf들의 동작을 통제하여 만들어지는 여러 개의 정적 조사면적(static portal)을 통하여 IMB (intensity modulated beam)이 만들어진다. 따라서 여러 개의 정적 조사면적이 연달아 맞닿아 있는 경우, 연속된 두 조사면적의 경계면에서 penumbra와 산란된 광자들이 겹쳐지고 따라서 hot spot이 생기게 된다. 이와 같이 SMLC 방식에서 나타나는 inter-step hot spot들의 존재를 BInS를 이용하여 측정하여 가시화하였고 또한 그것들을 제거하는 실험적 방법도 제시하였다. IMRT에서 사용되는 다른 주요한 작동방식인 DMLC (dynamic multileaf collimator)는 광자선이나 전자선을 제어하는 leaf의 작동방식이 다르기 때문에 SMLC 방식과는 다른 특성을 보인다. 따라서 BInS를 이용하여 SMLC와 DMLC 방식에 의해 실제로 target에 투사된 선량을 측정 비교하였다. 비록 같은 선량을 target 부위에 투사하기로 계획했을지라도, 실제로는 산란된 광자와 전자들 때문에 DMLC 방식에 의한 선량이 SMLC 방식에 의한 선량보다 14.8%나 큰 것으로 측정되었다.

• 대한치과교정학회지
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• 제36권2호
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• pp.161-169
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• 2006

이 연구의 목적은 훼이스마스크로 상악 전방견인치료를 받은 성장기 골격성 III급 부정교합자 25명(남 10, 여 15, 평균나이 9.9세)에서 단기간의 정적인 구개범인두 변화를 측모두부방사선 계측사진상에서 선 계측, 각도 계측 및 비율 계측을 시행하여 평가하는 것이다. 경구개 평면각의 변화량은 maxillary depth 또는 N-perp to A의 변화량과 음의 상관관계를 보였다 (p<0.01). 경-연구개 각의 증가는 유의성이 있었으며, 이는 경구개 평면각의 변화보다 연구개 평면각의 변화의 영향을 더 받았다 (p<0.001). 연조직- 과 경조직- 비인두 깊이의 증가는 유의성 있었으며 (p<0.001), 이들의 변화량과 연구개 평면각의 변화량간에는 양의 상관관계를 보였다 (p<0.05). 경구개 길이의 증가는 유의성이 있었으며 (p<0.001), 이는 연조직 비인두 깊이의 증가량과 음의 상관관계를 보였다. (p<0.05). Need 비율 S (C)의 증가는 유의성이 있었으나 (p<0.001), 이러한 증가는 이전 연구에서 보고된 Need 비율 S (C)의 정상 범위 내에 있었다. 이 연구로 상악골의 전방견인 후에 정적인 구개범인두 부위에 변화가 있을지라도 구개범인두의 적격성이 유지됨을 알 수 있었다.

• 대한물리의학회지
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• 제6권4호
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• pp.369-379
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• 2011

Purpose : The purpose of this study is to compare the initial effect of nerve mobilization (NM), static stretching (SS), and contract-relax (CR) techniques to find the best method in improving hamstring flexibility and gait function in patients with hemiplegia. Methods : Eleven patients with hemiplegia were included in this study. Passive knee extension (PKE) range of motion and the sit and reach (SR) test were used to measure hamstring flexibility, while timed up and go (TUG) and the 10m walking (10MW) test were used to measure the subject's gait. Measurements on each test were assessed prior to the experiment, immediately following the experiment, and 30 minutes after the experiment. Analysis of the results utilized a repeated measures analysis of variance to examine hamstring flexibility and the difference in walking ability. Results : The results suggest significant increases in NM, SS, and CR techniques as they relate to hamstring flexibility (p<.05) following (both immediate and 30 minutes post experiment) PKE range of motion and the SR test, but post-hoc showed no significant difference between the three techniques (p>.05). Additionally, the results suggest significant increases in NM, SS, and CR techniques as they relate to gait function (p<.05) following the TUG test, but found no significant difference in the 10MW test (p>.05). Post-hoc analysis between the three techniques suggests that only the NM technique significantly changed gait function. The time of TUG and 10MW test showed no significant difference between the three techniques before an experiment, just after an experiment, and 30 minutes following the experiment according to the measurement points in time (p>.05). Conclusion : This study suggests NM, SS, and CR techniques immediately improve hamstring length and flexibility while improving gait function in patients with hemiplegia.

• Smart Structures and Systems
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• 제3권3호
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• pp.281-298
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• 2007

The load carrying capacity of a bridge needs to be properly assessed to operate the bridge safely and maintain it efficiently. For the evaluation of load carrying capacity considering the current state of a bridge, static and quasi-static loading tests with weight-controlled heavy trucks have been conventionally utilized. In these tests, the deflection (or strain) of the structural members loaded by the controlled vehicles are measured and analyzed. Using the measured data, deflection (or strain) correction factor and impact correction factor are calculated. These correction factors are used in the enhancement of the load carrying capacity of a bridge, reflecting the real state of a bridge. However, full or partial control of the traffic during the tests and difficulties during the installment of displacement transducers or strain gauges may cause not only inconvenience to the traffic but also the increase of the logistics cost and time. To overcome these difficulties, an alternative method is proposed using an excited response part of full measured ambient acceleration data by ordinary traffic on a bridge without traffic control. Based on the modal properties extracted from the ambient vibration data, the initial finite element (FE) model of a bridge can be updated to represent the current real state of a bridge. Using the updated FE model, the deflection of a bridge akin to the real value can be easily obtained without measuring the real deflection. Impact factors are obtained from pseudo-deflection, which is obtained by double-integration of the acceleration data with removal of the linear components on the acceleration data. For validation, a series of tests were carried out on a steel plategirder bridge of an expressway in Korea in four different seasons, and the evaluated load carrying capacities of the bridge by the proposed method are compared with the result obtained by the conventional load test method.