• Computers and Concrete
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• 제26권1호
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• pp.75-94
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• 2020

The aim of this research is to investigate free vibration of a novel five layer Timoshenko microbeam which consists of a transversely flexible porous core made of Al-foam, two graphen platelets (GPL) nanocomposite reinforced layers to enhance the mechanical behavior of the structure as well as two piezo-magneto-electric face sheets layers. This microbeam is subjected to a thermal load and resting on Pasternak's foundation. To accomplish the analysis, constitutive equations of each layer are derived by means of nonlocal strain gradient theory (NSGT) to capture size dependent effects. Then, the Hamilton's principle is employed to obtain the equations of motion for five layer Timoshenko microbeam. They are subsequently solved analytically by applying Navier's method so that discretized governing equations are determined in form of dynamic matrix giving the possibility to gain the natural frequencies of the Timoshenko microbeam. Eventually, after a validation study, the numerical results are presented to study and discuss the influences of various parameters such as nonlocal parameter, strain gradient parameter, aspect ratio, porosity, various volume fraction and distributions of graphene platelets, temperature change and elastic foundation coefficients on natural frequencies of the sandwich microbeam.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.59.1-59.1
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• 2015

In the Linford group at Brigham Young University we have recently developed three new sets of materials for three different areas of separations science: thin layer chromatography (TLC), high performance liquid chromatography (HPLC), and solid phase microextraction (SPME). First, via microfabrication we have grown patterned carbon nanotube (CNT) forests on planar substrates that we have infiltrated with inorganic materials such as silicon nitride. The coatings on the CNTs are conformal and typically deposited in a process like low pressure chemical vapor deposition. The resulting materials have high surface areas, are porous, and function as effective separation devices, where separations on our new TLC plates are typically significantly faster than on conventional devices. Second, we used the layer-by-layer (electrostatically driven) deposition of poly (allylamine) and nanodiamond onto carbonized poly (divinylbenzene) microspheres to create superficially porous particles for HPLC. Many interesting classes of molecules have been separated with these particles, including various cannabinoids, pesticides, tricyclic antidepressants, etc. Third, we have developed new materials for SPME by sputtering silicon onto cylindrical fiber substrates in a way that creates shadowing of the incoming flux so that materials with high porosity are obtained. These materials are currently outperforming their commercial counterparts. Throughout this work, the new materials we have made have been characterized by X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, scanning electron microscopy, transmission electron microscopy, etc.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.161-164
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• 2002

In the present study, a passive control method, using the porous wall and cavity system, is applied to the shock wave/boundary layer interactions in transonic moist air flow. The two-dimensional, unsteady, compressible Navier-Stokes equations, which are fully coupled with a droplet growth equation, are solved by the third-order MUSCL type TVD finite difference scheme. Baldwind-Lomax turbulence model is employed to close the governing equations. In order to investigate the effectiveness of the present control method, the total pressure losses of the flow and the time-dependent behaviour of shock motions are analyzed in detail. The computed results show that the present passive control method considerably reduces the total pressure losses due to the shock/boundary layer interaction in transonic moist air flow and suppresses the unsteady shock wave motions over the airfoil, as well. It is also found that the location of the porous ventilation significantly influences the control effectiveness.

• Nuclear Engineering and Technology
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• 제38권2호
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• pp.139-146
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• 2006

An experimental study was performed to evaluate the effects of surface coating and an enhanced insulation structure on the downward facing boiling process and the critical heat flux on the outer surface of a hemispherical vessel. Steady-state boiling tests were conducted in the Subscale Boundary Layer Boiling (SBLB) facility using an enhanced vessel/insulation design for the cases with and without vessel coatings. Based on the boiling data, CHF correlations were obtained for both plain and coated vessels. It was found that the nucleate boiling rates and the local CHF limits for the case with micro-porous layer coating were consistently higher than those values for a plain vessel at the same angular location. The enhancement in the local CHF limits and nucleate boiling rates was mainly due to the micro-porous layer coating that increased the local liquid supply rate toward the vaporization sites on the vessel surface. For the case with thermal insulation, the local CHF limit tended to increase from the bottom center at first, then decrease toward the minimum gap location, and finally increase toward the equator. This non-monotonic behavior, which differed significantly from the case without thermal insulation, was evidently due to the local variation of the two-phase motions in the annular channel between the test vessel and the insulation structure.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2005년도 Proceedings of The 6th korea-china joint workshop on nuclear waste management
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• pp.39-50
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• 2005

Electrolytic reduction of uranium oxide to uranium metal was studied in a $LiCl-Li_{2}O$ molten salt system. The reduction mechanism of the uranium oxide to a uranium metal has been studied by means of a cyclic voltammetry. Effects of the layer thickness of the uranium oxide and the thickness of the MgO on the overpotential of the cathode and the anode were investigated by means of a chronopotentiometry. From the cyclic voltamograms, the decomposition potentials of the metal oxides are the determining factors for the mechanism of the reduction of the uranium oxide in a $LiCl-3\;wt{\%} Li_{2}O$ molten salt and the two mechanisms of the electrolytic reduction were considered with regards to the applied cathode potential. In the chronopotentiograms, the exchange current and the transfer coefficient based on the Tafel behavior were obtained with regard to the layer thickness of the uranium oxide which is loaded into the porous MgO membrane and the thickness of the porous MgO membrane. The maximum allowable currents for the changes of the layer thickness of the uranium oxide and the thickness of the MgO membrane were also obtained from the limiting potential which is the decomposition potential of LiCl.

• 한국재료학회지
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• 제32권2호
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• pp.94-97
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• 2022

We fabricated 3 types of ETL, mp TiO₂, ZnO, and ZnO coated on mp TiO₂(ZMT) to compare the photoelectric conversion efficiency (PCE) and fill factor (FF) of Perovskite solar cells. The structure of the cells was FTO/ETL/Perovskite (CH₃NH₃PbI₃)/spiro-MeOTAD/Ag. SEM morphology assessment of the ETLs showed that mp TiO₂ was porous, ZnO was flat, and the ZMT porous surface was filled with a thin layer. Via XRD measurements, the crystal structures of mp TiO₂ and ZnO ETL were found to be anatase and wurtzite, respectively. The XPS patterns showing energy bonding of mp TiO₂, ZnO, and ZMT O 1s confirmed these materials to be metal oxides such as ETL. The electrical characteristics of the Perovskite solar cells were measured using a solar simulator. Perovskite solar cells with ZMT ETL showed showed PCE of 10.29 % than that of conventional mp TiO₂ ETL devices. This was considered a result of preventing Perovskite from seeping into the ETL and preventing recombination of electrons and holes.

• 전기화학회지
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• 제4권2호
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• pp.41-46
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• 2001

황산과 황산구리 수용액을 전해질로 사용하여 다공성 그물구조 금속을 전기화학적으로 제조하였으며, 이때 균질 전착에 영향을 미치는 첨가제 PEG, MPS의 영향에 대해 살펴보았다. 분극실험과 기공의 평균 직경이 $250{\mu}m$의 그물구조 전극을 여러장 적층하여 throwing power를 정량화 한 결과, PEG의 경우 분극 초기에 전극에서 탈착됨으로써 오히려 throwing power를 감소시키고 MPS는 500ppm까지 용액 중 첨가량의 증가와 함께 throwing power를 향상시키는 결과를 보였다 또한 MPS와 PEG가 동시에 혼합된 용액에서는 MPS의 효과가 우선적으로 나타나며 PEG의 효과는 무시할 정도였다 그러나 MPS의 첨가는 전착층의 균열을 유도하여 기계적 강도에 좋지 못한 영향을 미치며 균열을 피하려면 50ppm 이하가 적정함을 SEM 관찰을 통해 확인할 수 있었다.

• 전기화학회지
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• 제2권3호
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• pp.130-133
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• 1999

본 연구에서는 음주 측정에 적용할 수 있는 다공질 실리콘층으로 된 저농도의 캐퍼시턴스형 알코올 가스 측정용 센서를 제작하고, 상온에서 그 특성을 측정하였다. 기존의 $SnO_2$등의 금속 산화물 반도체를 이용한 센서는 저농도의 알코올을 정확하게 검지하기에 어려울 뿐만 아니라 감도를 높이기 위해 $200\~400^{\circ}C$로 가열이 필요하였다. 이에 비해 다공질 실리콘층을 이용한 센서는 넓은 표면적을 갖고 있어 상온에서도 감도가 양호할 뿐만 아니라 집적화 센서로 제작이 용이한 점을 갖고 있다. 실험은 증류수에 희석한 알코올 수용액을 체온과 같은 $36^{\circ}C$를 비롯하여 25와 $45^{\circ}C$로 유지한 상태에서 0에서 $0.5\%$의 농도범위에 대해서 $0.05\%$의 간격으로 120 Hz와 1 kHz의 두 주파수에서 측정하였다. 그 결과, 양호한 선형성과 함께 120 Hz의 주파수에서 측정하였을 때, $0.1\%$의 알코올 농도의 증분마다 $25,\;36,\;45^{\circ}C$의 알코올 수용액의 온도에 대해 각각 1.1, 2.6 및 $4.6\%$로 캐퍼시턴스의 증가율을 보였다.

• 열처리공학회지
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• 제12권2호
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• pp.136-144
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• 1999

The study on the wear characteristics of compound layers formed during gaseous nitrocarburising in the medium carbon boron steels and the plain carbon steel has been carried out by using a pin-on-disc type wear test machine under the oil lubricating condition at room temperature and by varying applied loads, sliding speeds and wear distances. Values of friction coefficient measured at the sliding speed of 0.4m/sec under the oil lubricating condition have been shown to decrease considerably with increasing applied load and become gradually a constant value as load is increased to a higher value, showing that the transition load for friction coefficient appears at an applied load of 247.2N. The length and volume wear rates of compound layer have been revealed to relatively constantly increase, also showing that the wear life per unit thickness of compound layer turns out to be superior as porous layer has a denser and thinner appearance. As the sliding speed increases during wear test performed by varying sliding speed at a load of 63.2N under the oil lubricating condition for medium carbon boron steel nitrocarburised in gas atmosphere, the wear rate has been found to increase, the friction coefficient to decrease and the wear life per unit thickness of compound layer to decrease considerably.

• 한국산학기술학회논문지
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• 제21권10호
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• pp.55-63
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• 2020

도로교통 소음은 주요 민원의 대상이 되고 있다. 다공성 포장은 도로교통 소음에 효과적인 방안으로 제안되었지만 정량적인 평가의 부족으로 인해 많이 적용되지는 않았다. 본 연구에서는 단층 다공성 포장과 복층 다공성 포장의 소음저감 성능을 평가하였다. 소음은 CPX 방법으로 측정되었으며, 주행 속도는 50km/h부터 80km/h까지 10km/h마다 측정하였다. 분석을 통해 복층 다공성 포장과 단층 다공성 포장의 소음 수준은 통계적으로 유의한 차이를 나타내었다. 도로포장 소음수준은 포장 유형에 관계없이 주행 속도에 비례했으며, 주행 속도는 두 포장의 소음 차이에 통계적으로 유의한 영향을 미치지 않는 것으로 나타났다. 복층 다공성 포장은 단층 다공성 포장에 비해 평균 6.6dB (A), 95% 신뢰수준에서 6.3dB(A) 감소하는 것으로 나타났다. 도로교통 소음을 5dB(A) 저감한다는 것은 교통량을 1/3로 줄이거나 차량의 속도를 1/2로 낮추는 것에 상당한다. 감각적으로도 3dB(A)의 차이에서 변화의 인지가 가능하고 5dB(A)의 차이에서는 명확한 변화인지가 가능하다. 일반포장에 비해 3dB(A)의 교통소음을 저감하는 단층 다공성 포장보다도 6dB(A) 이상을 추가로 저감하는 복층 다공성 포장은 교통소음 저감에 매우 효과적인 공법이다.