• Smart Structures and Systems
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• 제15권6호
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• pp.1463-1479
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• 2015

Lamb waves have been a promising candidate for quantitative damage identification for various engineering structures, taking advantage of their superb capabilities of traveling for long distances with fast propagation and low attenuation. However, the application of Lamb waves in damage identification so far has been hampered by the fact that the characteristic signals associated with defects are generally weaker compared with those arising from boundary reflections, mode conversions and environmental noises, making it a tough task to achieve satisfactory damage identification from the time series. With awareness of this challenge, this paper proposes a time reversal-based technique to enhance the strength of damage-scattered signals, which has been previously applied to bulk wave-based damage detection successfully. The investigation includes (i) an analysis of Lamb wave propagation in a plate, generated by PZT patches mounted on the structure; (ii) an introduction of the time reversal theory dedicated for waveform reconstruction with a narrow-band input; (iii) a process of enhancing damage-scattered signals based on time reversal focalization; and (iv) the experimental investigation of the proposed approach to enhance the damage identification on a composite plate. The results have demonstrated that signals scattered by delamination in the composite plate can be enhanced remarkably with the assistance of the proposed process, benefiting from which the damage in the plate is identified with ease and high precision.

• 비파괴검사학회지
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• 제31권1호
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• pp.40-46
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• 2011

닫힘균열과 같은 고체-고체의 접촉계면에서 접촉 음향 비선형성을 평가하기 위해 벌크 투과파를 이용하는 기존의 전통적인 음향 비선형 기술의 경우 현장 적용하는데 있어서 송수신 탐촉자를 장착하기 위해 구조물 내부로 접근하는 것은 접근한계성의 어려움이 있다. 본 연구에서, 고체-고체의 접촉계면에서 음향 비선형성을 측정하기 위해 새로운 반사기법을 제안하였고 이는 대상재료의 동일한 면에서 송신과 수신을 하여 현장 적용성에 매우 편리한 기법이다. 이를 위해, 접촉압력에 대한 멱함수 모델를 통한 선형 그리고 비선형 강성을 추정하고 이를 기반으로 계면에서 반사된 초음파의 비선형 파라미터를 이론적으로 계산하였다. A16061-T6 시편에 대한 접촉압력에 따른 접촉계면 실험 결과들은 이론적인 예측과 매우 잘 일치하였으며 따라서 본 연구에서 제안된 반사모드 기술의 유효성을 검증하였다.

• 대한전자공학회논문지SD
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• 제39권4호
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• pp.10-18
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• 2002

본 논문에서는 IPS모드의 액정 셀에서 전압에 따른 액정 거동을 수치 해석적으로 계산하는 방법을 보고한다. 액정 거동을 해석하기 위해 복잡한 구조에 적용이 용이한 3차원 유한 요소법을 사용하여 액정 셀 내부의 전압 분포와 전계 분포를 계산하였다. 전기 에너지와 액정 분자의 탄성 에너지로 이루어지는 액정 셀 내부의 자유에너지 밀도를 고려하였으며, 에릭슨-레슬리(Ericksen-Leslie) 방정식과 라플라스(Laplace) 방정식을 해석함으로서 액정 셀의 스위칭 특성을 계산하였다. 24㎛×12㎛×4.5㎛ 사이즈의 IPS 모드 액정 셀에 대하여 1,859개의 노드와 8,640개의 사면체 요소를 생성하여 16ms까지 과도 해석하였다. 그 결과, 전극 위 부분을 제외한 영역에서 횡방향의 전계가 형성되었고, 전극 위 영역에서 전경선(disclination)이 발생하는 것을 확인하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.199-199
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• 2011

Recently, Thin film transistors (TFTs) with amorphous oxide semiconductors (AOSs) can offer an important aspect for next generation displays with high mobility. Several oxide semiconductor such as ZnO, $SnO_2$ and InGaZnO have been extensively researched. Especially, as a well-known binary metal oxide, tin oxide ($SnO_2$), usually acts as n-type semiconductor with a wide band gap of 3.6eV. Over the past several decades intensive research activities have been conducted on $SnO_2$ in the bulk, thin film and nanostructure forms due to its interesting electrical properties making it a promising material for applications in solar cells, flat panel displays, and light emitting devices. But, its application to the active channel of TFTs have been limited due to the difficulties in controlling the electron density and n-type of operation with depletion mode. In this study, we fabricated staggered bottom-gate structure $SnO_2$-TFTs and patterned channel layer used a shadow mask. Then we compare to the performance intrinsic $SnO_2$-TFTs and doping hafnium $SnO_2$-TFTs. As a result, we suggest that can be control the defect formation of $SnO_2$-TFTs by doping hafnium. The hafnium element into the $SnO_2$ thin-films maybe acts to control the carrier concentration by suppressing carrier generation via oxygen vacancy formation. Furthermore, it can be also control the mobility. And bias stability of $SnO_2$-TFTs is improvement using doping hafnium. Enhancement of device stability was attributed to the reduced defect in channel layer or interface. In order to verify this effect, we employed to measure activation energy that can be explained by the thermal activation process of the subthreshold drain current.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제55권6호
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• pp.297-301
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• 2006

In the present work, we investigate the characteristics of new composition material, chalcogenide $Ge_1Se_1Te_2$ material in order to overcome the problems of conventional PRAM devices. The Tc of $Ge_1Se_1Te_2$ bulk was measured $231.503^{\circ}C$ with DSC analysis. For static DC test mode, at low voltage, two different resistances are observed. depending on the crystalline state of the phase-change resistor. In the first sweep, the as-deposited amorphous $Ge_1Se_1Te_2$ showed very high resistance. However when it reached the threshold voltage(about 11.8 V), the electrical resistance of device was drastically reduced through the formation of an electrically conducting path. The phase transition between the low conductive amorphous state and the high conductive crystal]me state was caused by the set and reset pulses respectively which fed through electrical signal. Set pulse has 4.3 V. 200 ns. then sample resistance is $80\sim100{\Omega}$. Reset pulse has 8.6 V 80 ns, then the sample resistance is $50{\sim}100K{\Omega}$. For such high resistance ratio of $R_{reset}/R_{set}$, we can expect high sensing margin reading the recorded data. We have confirmed that phase change properties of $Ge_1Se_1Te_2$ materials are closely related with the structure through the experiment of self-heating layers.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.187-187
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• 2013

양자점(Quuantum dot, QD)은 0차원 특성을 가지는 구조로 양자 구속 효과로 인하여 bulk와 는 다른 구조적, 광학적, 전기적 특성을 가지고 있다. InAs QD는 size와 barrier의 bandgap 조절을 이용하여 쉽게 bandgap을 바꿀 수 있는 장점이 있어 solar cell, semiconductor laser diode, infrared photodetector 등으로 많은 연구가 이루어지고 있다. 일반적으로 Stranski-Krastanov (SK) mode로 성장한 InAs QD는 보통 GaAs epilayer와의 lattice mismatch (7%)를 이용하여 성장을 하고 이로 인하여 strain을 가지고 있고 QD의 density와 stack이 높을수록 strain이 커진다. 하지만 sub-monolayer (SML) QD 같은 경우 wetting layer가 생기는 지점인 1.7 ML이하에서 성장되는 성장 방식으로 SK-QD보다는 작은 strain을 가지게 된다. 또 QD의 size가 작아 SK-QD보다 큰 bandgap을 가지고 있다. 본 연구에서는 분자선 에피택시(molecular beam epitaxy, MBE)를 이용하여 semi-insulating GaAs substrate 위에 InAs QD를 0.5/1/1.5/1.7/2/2.5 monolayer로 성장을 하였다. GaAs과 InAs의 성장온도와 성장속도는 각각 $590^{\circ}C$, 0.8 ML/s와 $480^{\circ}C$, 0.2 ML/s로 성장을 하였으며 적층사이의 interruption 시간은 10초로 고정하였고 10주기를 성장하였다. Photoluminescence (PL)측정 결과 SML-QD는 size에 따라서 energy가 1.328에서 1.314 eV로 약간 red shift를 하였고 SK-QD의 경우 1.2 eV의 energy정도로 0.1 eV이상 red shift 하였다. 이는 QD size에 의하여 energy shift가 있다고 사료된다. 또 wetting layer의 경우 1.41 eV의 energy를 가지는 것으로 확인 하였다. SML-QD는 SK-QD 보다 반치폭(full width at half maximum, FWHM)이 작은 것은 확인을 하였고 strain field의 감소로 해석된다. 하지만 SML-QD의 경우 SK-QD보다 상대적으로 작은 PL intensity를 가지고 있었다. 이를 개선하기 위해서는 보다 높은 QD density를 요구하게 되는데 growth temperature, V/III ratio, growth rate 등을 변화주어서 연구할 계획이다.

• Archives of Pharmacal Research
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• 제28권7호
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• pp.839-847
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• 2005

The aim of this study was to provide the basis to further examine the mode of action of ethanol. Fluorescent probes reported to have different membrane mobilities were used to evaluate the effect of dimyristoylphosphatidylethanol (DMPEt) on the lateral and rotational mobilities of liposome lipid bilayers. An experimental procedure, based on the selective quenching of 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1,3-di(1-pyrenyl)propane (Py-3-Py) by trinitrophenyl groups, was used. DMPEt increased the bulk lateral and rotational mobilities, and had a greater fluidizing effect on the outer than the inner monolayer. These effects of DMPEt on liposomes may be responsible for some, but not all, of the general anesthetic actions of ethanol.

• International Journal of Naval Architecture and Ocean Engineering
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• 제7권3호
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• pp.580-594
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• 2015

Liquid sloshing in two-dimensional (2-D) and three-dimensional (3-D) rectangular tanks is simulated by using a level set method based on the finite volume method. In order to examine the effect of natural frequency modes on liquid sloshing, we considered a wide range of frequency ratios ($0.5{\leq}fr{\leq}3.2$). The frequency ratio is defined by the ratio of the excitation frequency to the natural frequency of the fluid, and covers natural frequency modes from 1 to 5. When fr = 1, which corresponds to the first mode of the natural frequency, strong liquid sloshing reveals roof impact, and significant forces are generated by the liquid in the tank. The liquid flows are mainly unidirectional. Thus, the strong bulk motion of the fluid contributes to a higher elevation of the free surface. However, at fr = 2, the sloshing is considerably suppressed, resulting in a calm wave with relatively lower elevation of the free surface, since the waves undergo destructive interference. At fr = 2, the lower peak of the free surface elevation occurs. At higher modes of $fr_3$, $fr_4$, and $fr_5$, the free surface reveals irregular deformation with nonlinear waves in every case. However, the deformation of the free surface becomes weaker at higher natural frequency modes. Finally, 3-D simulations confirm our 2-D results.

• Elastomers and Composites
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• 제33권4호
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• pp.267-273
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• 1998

MDI와 에스테르타입의 폴리올인 EBA, NBA, HA를 각각 반응시켜 이소시아네이트 말단기를 갖는 다양한 우레탄 프리폴리머를 합성하였다. 합성된 프리폴리머는 상온에서는 100% 고형분이었으며, 약 $80^{\circ}C$로 가열하면 용융되어 도포에 적당한 흐름성을 나타내었고, 냉각하면 고화되고 습기와 반응하면서 서서히 경화되었다. 대기중의 습기와 반응하여 경화된 우레탄수지의 인장물성은 폴리올의 구조에 따라 특징적인 거동을 나타내었다. 접착력은 EBA, NBA, HA순의 큰 값을 나타내었으며, 이는 동일한 조건에서 가교된 우레탄수지의 파단에너지와 같은 경향을 나타내었다. 또한, 접착조인트의 파괴는 모두 접착제 자체에서 일어났으며, 시험속도가 증가함에 따라 증가하였다. 이로 미루어, 우레탄 핫멜트 접착제 자체의 강인성이 접착력을 결정하는 주요 요인임을 알 수 있었다.

• 한국동물위생학회지
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• 제45권1호
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• pp.39-45
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• 2022

The total bacteria count is significantly important factor for hygienic quality in raw milk. BactoScan FM^TM and BactoCount IBC^TM are the automated instruments for the determination of the total bacterial count in raw milk. They have been used after calibration by standard plate count (SPC) method in South Korea since 2000. It is necessary to re-evaluate for total bacterial counter according to the improvement of milk quality and the change of milk quality grade. Therefore, this study was evaluated the conversion mode of the two machines by SPC method. We collected 921 bulk-tank milk samples throughout the concentration range of 1,000~1,000,000 CFU/mL from June 2020 to October 2021. As a result, when compared by the SPC value, there was a slight difference in total bacterial count in BactoScan below 10,000 CFU/mL and above 200,000 CFU/mL and in BactoCount above 100,000 CFU/mL, respectively. Therefore, the conversion factor for BactoScan and the conversion equation for BactoCount were newly adjusted based on SPC value, and then the correlation coefficients (R²) was 0.85 or higher. In addition, the correlation (R²) between BactoScan and BactoCount was 0.91, which means the results were high positive correlation. These results are expected to contribute to improving the accuracy of the automated instruments for determining of total bacterial count in raw milk.