• 공업화학
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• 제20권6호
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• pp.586-592
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• 2009

나노 크기의 배향성을 갖는 구조물의 제작은 자연에 존재하는 여러 가지 형상의 모방을 가능하게 한다. 고분자는 가격이 매우 저렴하며 합성과 가공 그리고 그 구조가 잘 알려져 있는 장점을 갖고 있어 필름(film)의 표면에 이러한 나노 구조물을 제작하고 나노 구조의 특성을 발현하는데 손쉽게 활용할 수 있는 재료이다. 나노 구조물을 제작하는 방법 중 양극산화를 통하여 제작한 다공성 알루미나 템플레이트(porous alumina template)는 매우 규칙적으로 정렬되어 있고 제어하는 공정이 비교적 쉽고 경제적이기 때문에 이를 이용한 연구가 매우 활발하게 진행되고 있다. 본 총설에서는 양극산화 알루미나 템플레이트의 제작과 이를 이용한 나노 구조 고분자 필름의 제작을 설명하고 이러한 나노 구조 필름의 응용범위 및 응용에 필요한 특성에 대하여 기술하였다.

• 설비공학논문집
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• 제25권5호
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• pp.269-278
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• 2013

In this study, in order to examine the applicability of computational fluid dynamics with the porous model to the analysis of APR+ (Advanced Power Reactor Plus) internal flow, simulation was conducted with the commercial multi-purpose computational fluid dynamics software, ANSYS CFX V.14. In addition, among the various reactor internals, the effect of flow skirt geometry on reactor internal flow was investigated. It was concluded that the porous model for some reactor internal structures could adequately predict the hydraulic characteristics inside the reactor in a qualitative manner. If sufficient computation resource is available, the predicted core inlet flow distribution is expected to be more accurate, by considering the real geometry of the internal structures, especially located in the upstream of the core inlet. Finally, depending on the shape of the flow skirt, the flow distribution was somewhat different locally. The standard deviation of the mass flow rate (${\sigma}$) for the original shape of flow skirt was smaller, than that for the modified shape of flow skirt. This means that the original shape of the flow skirt may give a more uniform distribution of mass flow rate at the core inlet plane, which may be more desirable for the core cooling.

• Structural Engineering and Mechanics
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• 제89권3호
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• pp.225-238
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• 2024

In this paper, a quasi-3D hyperbolic shear deformation theory for the bending responses of a functionally graded (FG) porous micro-beam is based on a modified couple stress theory requiring only one material length scale parameter that can capture the size influence. The model proposed accounts for both shear and normal deformation effects through an illustrative variation of all displacements across the thickness and satisfies the zero traction boundary conditions on the top and bottom surfaces of the micro-beam. The effective material properties of the functionally graded micro-beam are assumed to vary in the thickness direction and are estimated using the homogenization method of power law distribution, which is modified to approximate the porous material properties with even and uneven distributions of porosity phases. The equilibrium equations are obtained using the virtual work principle and solved using Navier's technique. The validity of the derived formulation is established by comparing it with the ones available in the literature. Numerical examples are presented to investigate the influences of the power law index, material length scale parameter, beam thickness, and shear and normal deformation effects on the mechanical characteristics of the FG micro-beam. The results demonstrate that the inclusion of the size effects increases the microbeams stiffness, which consequently leads to a reduction in deflections. In contrast, the shear and normal deformation effects are just the opposite.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2001년도 춘계학술대회 논문집
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• pp.172-179
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• 2001

A numelical model has been developed for the permeable coastal structures to simulate hydraulic characteristics on the permeable slopes, which interact with internal flow field of the structures. The model includes hydraulics in the porous medium. Numerical model was calibrated using hydraulic model experiments performed in 2-D wave flume in the Institute of Orean Hydraulics in PKNU. Good agreement were obtained with the model which employed inertia resistance term than with the conventional model, PBREAK.

• 마이크로전자및패키징학회지
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• 제25권4호
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• pp.105-109
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• 2018

본 연구는 구리의 이산화탄소 환원 촉매 특성을 향상시키기 위해 전극 촉매 물질인 다공성 구리에 그래핀을 적용하였다. Thermal Chemical Vapor Deposition(TCVD)법을 이용하여 직접적으로 그래핀이 혼합된 다공성 구리를 제조하였다. 0.1 M $KHCO_3$ 전해액을 사용하여, -1.0 V ~ -1.4 V의 인가전위로 전기화학 실험을 수행한 결과, 그래핀이 혼합된 다공성 구리 전극의 전류 밀도는 다공성 구리에 비해 1.8 배 이상 증가하였다. 생성물을 평가한 결과, 다공성 구리 전극에서 CO와 $H_2$만 생성된 반면 그래핀이 포함된 다공성 구리의 생성물은 CO 뿐만이 아닌 $CH_4$와 $C_2H_4$가 생성되었다. 이는 그래핀으로 인해 이산화탄소 흡착 시간이 길어짐으로써 반응 중 생성된 중간체들이 전극 표면에 머무르는 시간이 길어졌으며, 결과적으로 C2 화합물 생성 반응까지 연속적으로 진행될 수 있었다고 판단된다.

• Steel and Composite Structures
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• 재36권6호
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• pp.671-687
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• 2020

The aim of this research is to analyze buckling and bending behavior of a sandwich Reddy beam with porous core and composite face sheets reinforced by boron nitride nanotubes (BNNTs) and shape memory alloy (SMA) wires resting on Vlasov's foundation. To this end, first, displacement field's equations are written based on the higher-order shear deformation theory (HSDT). And also, to model the SMA wire properties, constitutive equation of Brinson is used. Then, by utilizing the principle of minimum potential energy, the governing equations are derived and also, Navier's analytical solution is applied to solve the governing equations of the sandwich beam. The effect of some important parameters such as SMA temperature, the volume fraction of SMA, the coefficient of porosity, different patterns of BNNTs and porous distributions on the behavior of buckling and bending of the sandwich beam are investigated. The obtained results show that when SMA wires are in martensite phase, the maximum deflection of the sandwich beam decreases and the critical buckling load increases significantly. Furthermore, the porosity coefficient plays an important role in the maximum deflection and the critical buckling load. It is concluded that increasing porosity coefficient, regardless of porous distribution, leads to an increase in the critical buckling load and a decrease in the maximum deflection of the sandwich beam.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 추계학술발표대회
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• pp.16.1-16.1
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• 2011

Gas sensor properties of $WO_3$ nanowire structures have been studied. The sensing layer was prepared by deposition of tungsten metal on porous single wall carbon nanotubes followed by thermal oxidation. The morphology and crystalline quality of $WO_3$ material was investigated by SEM, TEM, XRD and Raman analysis. A highly porous $WO_3$ nanowire structure with a mean diameter of 82 nm was obtained. Response to CO, $NH_3$ and $H_2$ gases diluted in air were investigated in the temperature range of $100{\sim}340^{\circ}C$ The sensor exhibited low response to CO gas and quite high response to $NH_3$ and $H_2$ gases. The highest sensitivity was observed at $250^{\circ}C$ for $NH_3$ and $300^{\circ}C$ for $H_2$. The effect of the diameters of $WO_3$ nanowires on the sensor performance was also studied. The $WO_3$ nanowires sensor with diameter of 40 nm showed quite high sensitivity, fast response and recovery times to $H_2$ diluted in dry air. The sensitivity as a function of detecting gas concentrations and gas sensing mechanism was discussed. The effect of dilution carrier gases, dry air and nitrogen, was examined.

• Steel and Composite Structures
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• 제29권1호
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• pp.53-66
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• 2018

A high-order nonlocal strain gradient model is developed for wave propagation analysis of porous FG nanoplates resting on a gradient hybrid foundation in thermal environment, for the first time. Material properties are assumed to be temperature-dependent and graded in the nanoplate thickness direction. To consider the thermal effects, uniform, linear, nonlinear, exponential, and sinusoidal temperature distributions are considered for temperature-dependent FG material properties. On the basis of the refined-higher order shear deformation plate theory (R-HSDT) in conjunction with the bi-Helmholtz nonlocal strain gradient theory (B-H NSGT), Hamilton's principle is used to derive the equations of wave motion. Then the dispersion relation between frequency and wave number is solved analytically. The influences of various parameters (such as temperature rise, volume fraction index, porosity volume fraction, lower and higher order nonlocal parameters, material characteristic parameter, foundations components, and wave number) on the wave propagation behaviors of porous FG nanoplates are investigated in detail.

• The Journal of the Acoustical Society of Korea
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• 제21권2E호
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• pp.81-90
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• 2002

Single absorbing materials and Helmholtz resonators have limited absorption characteristics over limited frequency ranges due to their structures and properties. Porous materials are highly absorptive for mid and high frequency ranges, while they have little sound absorption for low frequency sounds. Helmholtz resonators are generally used to absorb sound energy for a specified frequency range. Hence they have limited capability in controlling the overall acoustic properties of a space. Not much has been known about useful finishing materials which have enough rigidity and absorption over broad frequency range, in spite of wide demands from acoustic designers and consultants. The present work measured and analyzed absorption characteristics of a slit absorber by varying surface materials, depths of air gap, dimensions of slat and slit widths. It was found that the narrower the slit width, the larger the absorptions over the wide frequency ranges and the pattern was dependent on the presence of porous material. Narrower slat's width tend to increase the slit absorber's absorption more or less. Absorption coefficients at low frequency ranges were dramatically improved (from 0.23 to 0.56) by increasing air gap when porous materials were present.

• Macromolecular Research
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• 제14권4호
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• pp.430-437
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• 2006

The ultra-drawing process of an ultra high molecular weight polyethylene (UHMWPE) gel film was examined by incorporating linear low-density polyethylene (LLDPE) and $BaTiO_3$ nanoparticles. The effects of LLDPE and the draw ratios on the morphological development and mechanical properties of the nanocomposite membrane systems were investigated. By incorporating $BaTiO_3$ nanoparticles in the UHMWPE/LLDPE blend systems, the ultra-drawing process provided a highly extended, fibril structure of UHMWPE chains to form highly porous, composite membranes with well-dispersed nanoparticles. The ultra-drawing process of UHMWPE/LLDPE dry-gel films desirably dispersed the highly loaded $BaTiO_3$ nanoparticles in the porous membrane, which could be used to form multi-layered structures for electronic applications in various embedded, printed circuit board (PCB) systems.