• Transactions on Electrical and Electronic Materials
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• 제11권4호
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• pp.170-173
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• 2010

Nanocrystalline cadmium sulfide (CdS) thin films were prepared using chemical bath deposition in a solution bath containing $CdSO_4$, $SC(NH_2)_2$, and $NH_4OH$. The CdS thin films were investigated using X-ray diffraction (XRD), photoluminescence (PL), and Fourier transform infrared spectroscopy (FTIR). The as-deposited CdS thin film prepared at $80^{\circ}C$ for 60 min had a cubic phase with homogeneous and small grains. In the PL spectrum of the 2,900 A-thick CdS thin film, the broad red band around 1.7 eV and the broad high-energy band around 2.7 eV are attributed to the S vacancy and the band-to-band transition, respectively. As the deposition time increases to over 90 min, the PL intensity from the band-to-band transition significantly increases. The temperature dependence of the PL intensity for the CdS thin films was studied from 16 to 300 K. The $E_A$ and $E_B$ activation energies are obtained by fitting the temperature dependence of the PL intensity. The $E_A$ and $E_B$ are caused by the deep trap and shallow surface traps, respectively. From the FTIR analysis of the CdS thin films, a broad absorption band of the OH stretching vibration in the range $3,000-3,600\;cm^{-1}$ and the peak of the CN stretching vibration at $2,000\;cm^{-1}$ were found.

• Nuclear Engineering and Technology
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• 제39권5호
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• pp.637-646
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• 2007

An UET (ultrasound excited thermography) has been used for several years for a remote non-destructive testing in the automotive and aircraft industry. It provides a thermo sonic image for a defect detection. A thermograhy is based On a propagation and a reflection of a thermal wave, which is launched from the surface into the inspected sample by an absorption of a modulated radiation. For an energy deposition to a sample, the UET uses an ultrasound excited vibration energy as an internal heat source. In this paper the applicability of the UET for a realtime defect detection is described. Measurements were performed on two kinds of pipes made from a copper and a CFRP material. In the interior of the CFRP pipe (70mm diameter), a groove (width - 6mm, depth - 2.7mm, and length - 70mm) was engraved by a milling. In the case of the copper pipe, a defect was made with a groove (width - 2mm, depth - 1mm, and length - 110 mm) by the same method. An ultrasonic vibration energy of a pulsed type is injected into the exterior side of the pipe. A hot spot, which is a small area around the defect was considerably heated up when compared to the other intact areas, was observed. A test On a damaged copper pipe produced a thermo sonic image, which was an excellent image contrast when compared to a CFRP pipe. Test on a CFRP pipe with a subsurface defect revealed a thermo sonic image at the groove position which was a relatively weak contrast.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.802-807
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• 2003

International Convention Center Jeju(ICCJ) was planed and built for accommodating a variety of conventional and exhibitional activities. For a better flexibility of operation, almost all rooms in ICCJ are designed to be subdivided Into a couple of small rooms with installation of movable partition walls. Architectural and acoustical design should be deliberatively and cooperatively undertaken to cope with such a complex condition. Conference hall, the largest room in ICCJ, has a capacity of 5000 seats who:1 used as a whole. It could be divided into 3 halls, one with 2000 pre-installed seats on slanted floor, up/down removable stage and its settings above, and the other 2 flat rooms with no seats installed. A devided hall with pre-installed seats and stage is designed for a multi-use auditorium. Almost all surfaces except ceilings adjacent to the stage are sound absorptively treated, in regard to extensive use of sound reinforcement systems. Its reverberation time 1.65 sec without audience, which is roughly correspond to 1.50 sec with fully occupied audience. When there is a need for a larger room, all the partition wail Is removed and the hall could be used as a whole. Exhibition hall is located in the first floor of ICCJ. Absorption and softness are needed for the hat 1 because exhibition behavior has something noisy features. Perforated MDF panels with porous materials and air space in the back groundare adopted for the walls. There are one large, two medium, and several small convention rooms in ICJJ. The room are also acoustically designed for maximum flexibility with no defects soundwisely.

• Steel and Composite Structures
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• 제45권3호
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• pp.409-423
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• 2022

Nowadays, there is a high demand for great structural implementation and multifunctionality with excellent mechanical properties. The porous structures reinforced by graphene platelets (GPLs) having valuable properties, such as heat resistance, lightweight, and excellent energy absorption, have been considerably used in different engineering implementations. However, stiffness of porous structures reduces significantly, due to the internal cavities, by adding GPLs into porous medium, effective mechanical properties of the porous structure considerably enhance. This paper is relating to vibration analysis of fluidconveying cantilever porous graphene platelet reinforced (GPLR) pipe with fractional viscoelastic model resting on foundations. A dynamical model of cantilever porous GPLR pipes conveying fluid and resting on a foundation is proposed, and the vibration, natural frequencies and primary resonant of such a system are explored. The pipe body is considered to be composed of GPLR viscoelastic polymeric pipe with porosity in which Halpin-Tsai scheme in conjunction with the fractional viscoelastic model is used to govern the construction relation of nanocomposite pipe. Three different porosity distributions through the pipe thickness are introduced. The harmonic concentrated force is also applied to the pipe and the excitation frequency is close to the first natural frequency. The governing equation for transverse motions of the pipe is derived by the Hamilton principle and then discretized by the Galerkin procedure. In order to obtain the frequency-response equation, the differential equation is solved with the assumption of small displacement, damping coefficient, and excitation amplitude by the multiple scale method. A parametric sensitivity analysis is carried out to reveal the influence of different parameters, such as nanocomposite pipe properties, fluid velocity and nonlinear viscoelastic foundation coefficients, on the primary resonance and linear natural frequency. Results indicate that the GPLs weight fraction porosity coefficient, fractional derivative order and the retardation time have substantial influences on the dynamic response of the system.

• 한국포장학회지
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• 제21권2호
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• pp.55-60
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• 2015

수출 절화 백합에서의 포장은 품질 유지 및 신선도에 직접적인 영향을 끼칠 수 있기 때문에 어느 포장재를 선정해야 하는가에 대한 연구가 필요하다. 이 연구에서는 무처리 신문지, OPP천공필름, 연신나이론필름(ON), OPP펀칭필름 그리고 무처리 OPP필름을 이용하여 실험하였다. $25^{\circ}C$에 저장한 백합은 $5^{\circ}C$에 비하여 노화가 급격하게 일어났음을 알 수 있었으며 $25^{\circ}C$에 저장한 백합이 $5^{\circ}C$에 저장한 것보다 수분 흡수와 생체중의 변화폭이 작았다. 뿐만 아니라 생체중은 $5^{\circ}C$가 $25^{\circ}C$ 비하여 OPP필름을 제외한 모든 포장재에서 높게 나타났는데 이는 $5^{\circ}C$가 $25^{\circ}C$에 비해 수분 흡수량이 높게 나타나 생체중 감소를 억제하였기 때문이다. 또한 $5^{\circ}C$일 때 포장재 형태가 백합의 생리활성에 미치는 영향이 $25^{\circ}C$때보다 높게 나타났다. 포장재를 비교하였을 때에는 신문지 포장재만이 저장온도에 따른 절화백합의 생리활성 변화에 영향이 가장 작게 나타났다는 사실로 미루어 보아 개화일은 포장재 형태보다 온도에 의한 영향을 많이 받는다는 사실을 알 수 있었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.272.1-272.1
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• 2016

In a three-dimensional topological insulator Bi2Se3, a stress control for band gap manipulation was predicted but no systematic investigation has been performed yet due to the requirement of large external stress. We report herein on the strain-dependent results for Bi2Se3 films of various thicknesses that are grown via a self-organized ordering process. Using small angle X-ray scattering and Raman spectroscopy, the changes of d-spacings in the crystal structure and phonon vibration shifts resulted from stress are clearly observed when the film thickness is below ten quintuple layers. From the UV photoemission/inverse photoemission spectroscopy (UPS/IPES) results and ab initio calculations, significant changes of the Fermi level and band gap were observed. The deformed band structure also exhibits a Van Hove singularity at specific energies in the UV absorption experiment and ab initio calculations. Our results, including the synthesis of a strained ultrathin topological insulator, suggest a new direction for electronic and spintronic applications for the future.

• 국제초고층학회논문집
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• 제4권1호
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• pp.1-8
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• 2015

A team of researchers and practitioners were recently assembled to prepare a monograph on "Wind-Induced Motion of Tall Buildings: Designing for Habitability". This monograph presents a state-of-the-art report of occupant response to wind-induced building motion and acceptability criteria for wind-excited tall buildings. It provides background information on a range of pertinent subjects, including: ${\bullet}$ Physiological, psychological and behavioural traits of occupant response to wind-induced building motion; ${\bullet}$ A summary of investigations and findings of human response to real and simulated building motions based on field studies and motion simulator experiments; ${\bullet}$ A review of serviceability criteria to assess the acceptability of wind-induced building motion adopted by international and country-based standards organizations; ${\bullet}$ General acceptance guidelines of occupant response to wind-induced building motion based on peak acceleration thresholds; and ${\bullet}$ Mitigation strategies to reduce wind-induced building motion through structural optimization, aerodynamic treatment and vibration dissipation/absorption. This monograph is to be published by the American Society of Civil Engineers (ASCE) and equips building owners and tall building design professionals with a better understanding of the complex nature of occupant response to and acceptability of wind-induced building motion. This paper is a brief summary of the works reported in the monograph.

• 한국주조공학회지
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• 제30권1호
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• pp.22-28
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• 2010

Metal foam is a porous or cellular structure material and representative property is a very high porosity. Foamed materials have very special properties such as sound, vibration, energy and impact absorption capacity. Especially this properties are widely used for safety demands of architecture, auto and aircraft industry. But metal foam need to increased its compression strength and hardness. This study were researched about Al-Si alloy foams with variation amount of Si contents for their fabrication and properties such as porosity, cell structure, microstructure and mechanical properties. The result are that the range of pore size is 2~4 $mm{\phi}$, the high porosity are 88%, high yield strength is 1.8MPa, the strain ratio is 60~70% and vickers hardness is 33.1~50.6.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.6-12
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• 2010

철도소음은 공기역학적 소음, 차륜과 레일의 상호작용에 의한 전동소음과 고가구조음으로 나눌 수 있다. 열차의 속도한계에 의해 재래철도의 주소음원은 전동음이라고 알려져 있으며, 전동음에 대한 많은 연구가 이루어졌다. 또한 전동음을 주소음원으로 하여 철도소음에 대한 예측모델을 제시하고, 철도소음의 전파특징에 대한 연구가 다수 이루어졌다. 또한 근래에는 고가선로에 대한 고가진동음에 대한 연구가 진행되고 있다. 한편, 본 연구에서는 국내 고가철교에 거의 설치되어 있지 않은 방음터널에 대한 효과를 파악하고 앞으로 설치가 예상되는 고가철교 방음터널에 대한 설계 자료를 확보하기 위한 기초연구를 수행하였다.

• 열처리공학회지
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• 제25권5호
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• pp.227-232
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• 2012

Magnesium alloy have good physical properties such as good castability, good vibration absorption, high strength/weight ratios. Despite the desirable properties, the poor resistance of Mg alloy impedes their use in many various applications. Therefore, magnesium alloy require surface treatment to improve hardness, corrosion and wear resistance. Plasma Electrolytic Oxidation (PEO) is one the surface treatment methods to form oxide layer on Mg alloy in alkali electrolyte. In comparison with Anodizing, there is environmental process having higher hardness and faster deposition rate. In this study, the characteristics of oxide film were examined after coating the AZ31 Mg alloy through the PEO process. We changed concentration of sodium aluminate into $K_2ZrF_6$, KF base electrolyte. The morphologies of the coating layer were characterized by using scanning electron microscopy (SEM). Corrosion resistance also investigated by potentiodynamic polarization analysis. As a result, propertiy of oxide layer were changed by concentration of sodium aluminate. Increasing with concentration of sodium aluminate in electrolyte, the oxidation layer was denser and the pore size was smaller on the surface.