• 한국재료학회지
• /
• 제29권5호
• /
• pp.328-335
• /
• 2019

Nb-doped $TiO_2$(NTO) coated NiCrAl alloy foam for hydrogen production is prepared using ultrasonic spray pyrolysis deposition(USPD) method. To optimize the size and distribution of NTO particles based on good physical and chemical stability, we synthesize particles by adjusting the weight ratio of the Nb precursor solution(5 wt%, 10 wt% and 15 wt%). The morphological, chemical bonding, and structural properties of the NTO coated NiCrAl alloy foam are investigated by X-ray diffraction(XRD), X-ray photo-electron spectroscopy(XPS), and Field-Emission Scanning Electron Microscopy(FESEM). As a result, the samples of controlled Nb weight ratio exhibit a common diffraction pattern at ${\sim}25.3^{\circ}$, corresponding to the(101) plane, and have chemical bonding(O-Nb=O) at 534 eV. The NTO particles with the optimum weight ratio of N (10 wt%) show a uniform distribution with a size of ~18.2-21.0 nm. In addition, they exhibit the highest corrosion resistance even in the electrochemical stability estimation. As a result, the introduction of NTO coated NiCrAl alloy foam by USPD improves the chemical stability of the NiCrAl alloy foam by protecting the direct electrochemical reaction between the foam and the electrolyte. Thus, the optimized NTO coating can be proposed for excellent protection of NiCrAl alloy foam for hydrocarbon-based steam methane reforming(SMR).

• 한국전자통신학회논문지
• /
• 제16권4호
• /
• pp.617-624
• /
• 2021

도래각 추정, 간섭제거, 신호 수신 등을 위해 수신신호에 포함되는 신호의 개수를 정확히 파악하는 것이 필요하다. 대표적인 신호 개수 추정 알고리즘으로 AIC(: Akaike Information Criterion)와 MDL(: Minimum Description Length) 알고리즘이 있는데, 이들 알고리즘은 각 기준이 최소화되는 값을 찾아 신호의 개수를 추정한다. 수신기의 배열 안테나 요소 개수가 증가하면 추정 성능이 향상되지만, 최소값을 찾기 위해 모든 안테나 요소에 대한 기준값을 계산하여야 하므로 복잡도가 크게 증가한다. 이러한 문제를 해결하기 위해, 본 논문에서는 빔공간 처리를 통해 차원을 축소시켜 계산량을 줄이면서 효율적으로 신호의 개수를 추정할 수 있는 빔공간 기반의 AIC와 MDL 알고리즘을 제안한다. 또한, 다양한 시나리오 기반의 컴퓨터 시뮬레이션을 통해 제안된 알고리즘의 성능을 평가하고 분석한다.

• 디지털융복합연구
• /
• 제19권3호
• /
• pp.331-344
• /
• 2021

본 연구의 목적은 우리가 일상에서 사용하고 있는 식생활 도구인 젓가락의 디자인에 대해 살펴보고, 획일화되고 한정된 우리의 금속젓가락 디자인을 지양하여 식탁의 미학을 더할 디자인으로의 향상을 꾀하고자 3D 모델링 시스템의 활용 가능성을 모색하는 데 있다. 이를 위해, 연구자는 한국의 문화요소를 디자인의 조형요소로 활용하는 가운데 3D 모델링을 이용한 섬세한 표현을 통해 독창적인 문화콘텐츠가 될 수 있도록 시제품을 제작하였다. 제작 결과, 한국의 특성을 지닌 개성 있는 젓가락 디자인을 도출할 수 있었다. 이러한 시제품의 사례와 같이 3D 모델링과 3D 프린팅은 젓가락 디자인의 새로운 탐색에 도움을 줄 수 있을 것이며, 다양한 시뮬레이션을 통해 디자인의 향상과 품질을 개선시킬 수 있을 것이다. 또한 한국의 문화상품으로서의 역할을 할 수 있는 문화콘텐츠 개발에 도움이 될 것이다.

• Steel and Composite Structures
• /
• 제37권6호
• /
• pp.711-731
• /
• 2020

This paper deals with free vibration of FG sandwich annular sector plates on Pasternak elastic foundation with different boundary conditions, based on the three-dimensional theory of elasticity. The plates with simply supported radial edges and arbitrary boundary conditions on their circular edges are considered. The influence of carbon nanotubes (CNTs) waviness, aspect ratio, internal pores and graphene platelets (GPLs) on the vibrational behavior of functionally graded nanocomposite sandwich plates is investigated in this research work. The distributions of CNTs are considered functionally graded (FG) or uniform along the thickness of upper and bottom layers of the sandwich sectorial plates and their mechanical properties are estimated by an extended rule of mixture. In this study, the classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler content increases. The core of structure is porous and the internal pores and graphene platelets (GPLs) are distributed in the matrix of core either uniformly or non-uniformly according to three different patterns. The elastic properties of the nanocomposite are obtained by employing Halpin-Tsai micromechanics model. A semi-analytic approach composed of 2D-Generalized Differential Quadrature Method (2D-GDQM) and series solution is adopted to solve the equations of motion. The fast rate of convergence and accuracy of the method are investigated through the different solved examples. Some new results for the natural frequencies of the plate are prepared, which include the effects of elastic coefficients of foundation, boundary conditions, material and geometrical parameters. The new results can be used as benchmark solutions for future researches.

• Tribology and Lubricants
• /
• 제38권3호
• /
• pp.93-100
• /
• 2022

Micro-light emitting diode (micro-LED) displays offer numerous advantages such as high brightness, fast response, and low power consumption. Hence, they are spotlighted as the next-generation display. However, defective LEDs may be created due to non-uniform contact loads or LED alignment errors. Therefore, a repair process involving the replacement of defective LEDs with favorable ones is necessitated. The general repair process involves the removal of defective micro-LEDs, interconnection material transfer, as well as new micro-LED transfer and bonding. However, micro-LEDs are difficult to repair since their size decreases to a few tens of micron in width and less than 10 ㎛ in thickness. The conventional nozzle-type dispenser for fluxes and the conventional vacuum chuck for LEDs are not applicable to the micro-LED repair process. In this study, transfer conditions are determined using a micro stamp for repairing micro-LEDs. Results show that the aging time should be set to within 60 min, based on measuring the aging time of the flux. Additionally, the micro-LEDs are subjected to a compression test, and the result shows that they should be transferred under 18.4 MPa. Finally, the I-V curves of micro-LEDs processed by the laser and hot plate reflows are measured to compare the electrical properties of the micro-LEDs based on the reflow methods. It was confirmed that the micro-LEDs processed by the laser reflow show similar electrical performance with that processed by the hot plate reflow. The results can provide guidance for the repair of micro-LEDs using micro stamps.

• Steel and Composite Structures
• /
• 제44권1호
• /
• pp.65-79
• /
• 2022

The main goal of this paper is to study the vibration of damaged core laminated annular plates with FG face sheets based on a three-dimensional theory of elasticity. The structures are made of a damaged isotropic core and two external face sheets. These skins are strengthened at the nanoscale level by randomly oriented Carbon nanotubes (CNTs) and are reinforced at the microscale stage by oriented straight fibers. These reinforcing phases are included in a polymer matrix and a three-phase approach based on the Eshelby-Mori-Tanaka scheme and on the Halpin-Tsai approach, which is developed to compute the overall mechanical properties of the composite material. In this study the effect of microcracks on the vibrational characteristic of the sandwich plate is considered. In particular, the structures are made by an isotropic core that undergoes a progressive uniform damage, which is modeled as a decay of the mechanical properties expressed in terms of engineering constants. These defects are uniformly distributed and affect the central layer of the plates independently from the direction, this phenomenon is known as "isotropic damage" and it is fully described by a scalar parameter. Three complicated equations of motion for the sectorial plates under consideration are semi-analytically solved by using 2-D differential quadrature method. Using the 2-D differential quadrature method in the r- and z-directions, allows one to deal with sandwich annular plate with arbitrary thickness distribution of material properties and also to implement the effects of different boundary conditions of the structure efficiently and in an exact manner. The fast rate of convergence and accuracy of the method are investigated through the different solved examples. The sandwich annular plate is assumed to have any arbitrary boundary conditions at the circular edges including simply supported, clamped and, free. Several parametric analyses are carried out to investigate the mechanical behavior of these multi-layered structures depending on the damage features, through-the-thickness distribution, and boundary conditions.

• 웰빙융합연구
• /
• 제6권3호
• /
• pp.13-18
• /
• 2023

Purpose: The small-scale environmental impact assessment has been in operation since its implementation in August 2000, and is a system that meets the purpose of sustainable development in consideration of the environment in areas requiring conservation. However, when preparing a small environmental impact assessment report, the contents of the reduction measures are too qualitative, or reports are prepared to simply list the compliance stipulated by individual laws, and the contents of consultations prepared by consultative agencies and review agencies are not much different. In addition, the direction of consultation on development projects for similar locations of the same project type is frequently changed by reflecting the subjective judgment of the consultative officer of the Ministry of Environment (Environment Agency). Therefore, this study attempted to improve the establishment of measures to reduce the existing simple listing of qualitative contents and the inconsistent presentation of review opinions by consultative agencies and review agencies. Research design, data and methodology: The research method extracted absolute evaluation items and relative evaluation items among small environmental impact assessment items, analyzed and presented detailed items, and prepared a distribution table for each section according to the details of the relative evaluation items, and presented them as a table. Results: This study was conducted to derive uniform results with objective indicators in the preparation and consultation process of a small-scale environmental impact assessment. Conclusions: Once a quantitative evaluation is established, the consultant can objectively determine and process the environmental impact.

• 문화기술의 융합
• /
• 제9권1호
• /
• pp.347-353
• /
• 2023

현재 軍(육군) 입대 장병은 신병훈련소에서 신체에 대한 치수 측정(자동, 수동) 및 샘플 피복을 착용해 본 후, 희망하는 치수로 피복을 지급받고 있다. 하지만, 민간 평상복보다 상대적으로 매우 세분화된 치수 체계를 적용하고 있는 軍에서는 이와 같은 치수 측정 과정에서 발생하는 측정된 치수의 낮은 정확도로 인해 지급받은 피복이 제대로 맞지 않아 피복을 교체하는 빈도가 매우 빈번히 발생하고 있다. 뿐만 아니라 서구적으로 변화된 MZ 세대의 체형변화를 반영하지 않고, 10여 년 전(前)에 수집된 구세대 체형 데이터 기반의 치수 체계를 적용함으로써 재고량이 비효율적으로 관리되는 문제점이 있다. 즉, 필요한 규격의 피복은 부족하고 불필요한 규격의 피복재고는 다수 발생하고 있다. 따라서, 피복 교체빈도를 감소시키고 재고관리의 효율성을 향상하기 위해 딥러닝 기반의 신체 치수 자동측정과 빅데이터 분석 및 머신러닝 기반의 "입대 장병 개인 맞춤형 피복 자동 추천 시스템"을 제안한다.

• 문화기술의 융합
• /
• 제9권3호
• /
• pp.619-624
• /
• 2023

본 논문에서는 2중 유전체층 사이의 저항띠 격자구조에 의한 TE(transverse electric) 산란 문제를 전자파 수치해석 방법으로 알려진 FGMM(fourier galerkin moment method)를 이용하여 해석하였다. 경계조건들은 미지의 계수를 구하기 위하여 이용하였고, 산란 전자계는 Floquet 모드 함수의 급수로 전개하였고, 저항띠의 해석을 위해 저항 경계조건을 적용하였다. 2중 유전체층의 문제를 취급하기 위하여 유전체층들의 두께와 비유전율을 동일한 값을 가지는 경우에 대해서만 수치계산하였다. 전반적으로, 저항띠 균일 저항율이 증가하면 저항띠에 유도되는 전류밀도는 감소하였고 반사 전력은 감소하였으며, 상대적으로 투과전력은 증가하였다. 본 논문에서 제안된 구조에 대한 수치결과들은 기존 논문의 수치해석 방법인 PMM의 결과들과 비교하여 매우 잘 일치하였다.

• 문화기술의 융합
• /
• 제9권3호
• /
• pp.641-646
• /
• 2023

본 논문에서는 2중 유전체층 사이의 저항띠 격자구조에 의한 TM(transverse magnetic) 산란 문제를 전자파 수치해석 방법으로 알려진 FGMM(fourier galerkin moment method)를 이용하여 해석하였다. 경계조건들은 미지의 계수를 구하기 위하여 이용하였고, 산란 전자계는 Floquet 모드 함수의 급수로 전개하였고, 저항띠의 해석을 위해 저항 경계조건을 적용하였다. 전반적으로, 저항띠의 균일저항율이 증가하면 저항띠에 유도되는 전류밀도의 크기는 감소하였고 반사 전력은 감소하였으며, 상대적으로 투과전력은 증가하였다. 또한 유전체 층의 두께가 증가할수록 반사전력은 증가하였고 상대적으로 투과전력은 상대적으로 감소하였다. 본 논문에서 제안된 구조에 대한 수치결과들은 기존 논문의 수치해석 방법인 PMM의 결과들과 비교하여 매우 잘 일치하였다.