• Geomechanics and Engineering
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• 제29권3호
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• pp.291-300
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• 2022

Tunnel boring machines combined with the earth pressure balanced shield method (EPB shield TBMs) have been adopted in urban areas as they allow excavation of tunnels with limited ground deformation through continuous and repetitive excavation and support. Nevertheless, the expansion of TBM construction requires much more minor and exquisitely controlled surface settlement to prevent economic loss. Several parametric studies controlling the tunnel's geometry, ground properties, and TBM operational factors assuming ordinary conditions for EPB shield TBM excavation have been conducted, but the impact of excessive excavation on the induced settlement has not been adequately studied. This study conducted a numerical evaluation of surface settlement induced by the ground loss from face imbalance, excessive excavation, and tail void grouting. The numerical model was constructed using FLAC3D and validated by comparing its result with the field data from literature. Then, parametric studies were conducted by controlling the ground stiffness, face pressure, tail void grouting pressure, and additional volume of muck discharge. As a result, the contribution of these operational factors to the surface settlement appeared differently depending on the ground stiffness. Except for the ground stiffness as the dominant factor, the order of variation of surface settlement was investigated, and the volume of additional muck discharge was found to be the largest, followed by the face pressure and tail void grouting pressure. The results from this study are expected to contribute to the development of settlement prediction models and understanding the surface settlement behavior induced by TBM excavation.

• Advances in aircraft and spacecraft science
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• 제8권4호
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• pp.345-372
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• 2021

The analysis of nonlinear vibrations, buckling, post-buckling, flutter boundary determination and post-flutter behavior of a homogeneous curved plate assuming cylindrical bending is conducted in this article. Other assumptions include simply-supported boundary conditions, supersonic aerodynamic flow at the top of the plate, constant pressure conditions below the plate, non-viscous flow model (using first- and third-order piston theory), nonlinear structural model with large deformations, and application of mechanical and thermal loads on the curved plate. The analysis is performed with constant environmental indicators (flow density, heat, Reynolds number and Mach number). The material properties (i.e., coefficient of thermal expansion and modulus of elasticity) are temperature-dependent. The equations are derived using the principle of virtual displacement. Furthermore, based on the definitions of virtual work, the potential and kinetic energy of the final relations in the integral form, and the governing nonlinear differential equations are obtained after fractional integration. This problem is solved using two approaches. The frequency analysis and flutter are studied in the first approach by transferring the handle of ordinary differential equations to the state space, calculating the system Jacobin matrix and analyzing the eigenvalue to determine the instability conditions. The second approach discusses the nonlinear frequency analysis and nonlinear flutter using the semi-analytical solution of governing differential equations based on the weighted residual method. The partial differential equations are converted to ordinary differential equations, after which they are solved based on the Runge-Kutta fourth- and fifth-order methods. The comparison between the results of frequency and flutter analysis of curved plate is linearly and nonlinearly performed for the first time. The results show that the plate curvature has a profound impact on the instability boundary of the plate under supersonic aerodynamic loading. The flutter boundary decreases with growing thermal load and increases with growing curvature.

• 한국문헌정보학회지
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• 제56권2호
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• pp.57-82
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• 2022

오늘날 전문적 지식에 대한 시민 요구의 증가, 학계의 시민참여 연구 확대, 전문적 지식에 대한 정보서비스의 제공에도 불구하고, 여전히 비전문적 일반인이 학술정보자원에 접근하는 데에 어려움이 있는 것으로 파악된다. 본 연구는 이에 주목하여 학술정보자원에 대한 일반인의 정보요구와 정보행위를 설문조사를 통해 조사하였다. 학술정보자원의 탐색 및 이용행태, 학술정보자원 활용에 대한 지원 필요성에 관한 인식이 조사되었으며, 이를 통해 학술정보자원이 학술 커뮤니티를 넘어 사회적으로 공유되는 정도와 양상을 분석하였다. 본 연구는 전통적인 학술 커뮤니케이션에서의 이용자 범위를 확대하여, 이들을 위한 학술정보자원에의 접근과 이용 확대 지원의 필요성을 강조한 초기 연구라는 점에서 의의를 찾을 수 있다.

• 한국컴퓨터정보학회논문지
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• 제27권2호
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• pp.25-32
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• 2022

본 논문에서는 활동 인식장치를 이용한 딥러닝 기반의 반려동물 모니터링 시스템을 제안한다.이 시스템은 반려동물의 활동 인식장치와 반려인의 스마트 기기, 서버로 구성된다. 아두이노 기반 활동 인식 장치로부터 가속도와 자이로 데이터를 수집하고, 이로부터 반려동물의 걸음 수를 연산하였다. 수집된 데이터는 전처리 과정을 거쳐 CNN과 LSTM을 하이브리드한 딥러닝 모델을 통해 5가지 형태(앉기, 서기, 눕기, 걷기, 뛰기)로 활동을 인식함으로써 활동량을 측정한다. 마지막으로, 반려인의 스마트 기기에 일일 및 주간 브리핑 차트 등 활동 변화에 대한 모니터링을 제공한다. 성능 평가 결과, 반려동물의 구체화된 활동 인식 및 활동량 측정이 가능함을 확인하였다. 향후 데이터 축적을 통해 반려동물의 이상행동 탐지 및 헬스 케어 서비스의 확장을 기대할 수 있다.

• 한국분말재료학회지
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• 제29권6호
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• pp.468-476
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• 2022

Yttria-stabilized zirconia (YSZ) has a low thermal conductivity, high thermal expansion coefficient, and excellent mechanical properties; thus, it is used as a thermal barrier coating material for gas turbines. However, during long-time exposure of YSZ to temperatures of 1200℃ or higher, a phase transformation accompanied by a volume change occurs, causing the YSZ coating layer to peel off. To solve this problem, YSZ has been doped with trivalent and tetravalent oxides to obtain coating materials with low thermal conductivity and suppressed phase transformation of zirconia. In this study, YSZ is doped with trivalent oxides, Nd₂O₃, Yb₂O₃, Al₂O₃, and tetravalent oxide, TiO₂, and the thermal conductivity of the obtained materials is analyzed according to the composition; furthermore, the relative density change, microstructure change, and m-phase formation behavior are analyzed during long-time heat treatment at high temperatures.

• Composites Research
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• 제20권3호
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• pp.37-42
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• 2007

금속복합재료에서는 강화재와 기지재 사이의 열팽창계수 차이에 의해 복합재료 내부에 잔류응력이 남아있어 복합재료 전체의 강도저하를 가져온다. 본 연구에서는 TiNi 형상기억합금을 강화재료로써 이러한 잔류응력 문제를 해결하기 위하여 이용하였다. TiNi 형상기억합금은 형상기억효과를 이용하여 복합재료의 잔류응력문제를 해결할 뿐만 아니라 복합재료의 인장강도를 증가시키는 역할을 한다. 핫프레스 방법에 의해 제작된 형상기억복합재료의 강도증가를 위하여 냉간압연을 실시하여 실험을 실시하였다. 이와 같이 제작된 형상기억복합재료의 저온에서의 미시적 손상거동을 평가하기 위하여 음향방출기법을 이용하였다. 또한 열충격을 받은 시험편의 손상에 대한 연구도 이루어졌다.

• 한국융합학회논문지
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• 제13권1호
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• pp.387-398
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• 2022

본 논문은 독거노인의 복합적 행태를 이종 사물인터넷 센서들과 딥러닝 기법을 활용하여 인지하고 낙상, 잦은 기침, 수면의 질 감소, 발열 및 비정상적 생활 동선의 발생 등 위급하거나 건강이 저하되는 상황을 적시에 보호자 및 의료복지 담당자에게 알리고 적정한 후속 서비스를 추천 및 수행할 수 있는 시스템을 논한다. 독거노인들의 생활을 최대한 방해하지 않기 위하여 전면 비접촉식 상황 인식 기술을 선보인다. 본 논문은 센서 데이터의 수집 및 분석 체계의 설계와 구현 방법은 물론, 서울시 총 5개구 거주 독거노인들을 대상으로 실증한 경험을 통해 설치, 설정, 운영 및 유지 보수 측면에서의 다양한 문제점들을 서술하고 해당 시스템의 전국 확산에 대비한 향후 발전 방향을 제언한다.

• 반도체디스플레이기술학회지
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• 제22권4호
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• pp.124-130
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• 2023

Recently, fan out wafer level packaging, which enables high integration, miniaturization, and low cost, is being rapidly applied in the semiconductor industry. In particular, FOWLP is attracting attention in the mobile and Internet of Things fields, and is recognized as a core technology that will lead to technological advancements such as 5G, self-driving cars, and artificial intelligence in the future. However, as chip density and package size within the package increase, FOWLP warpage is emerging as a major problem. These problems have a direct impact on the reliability and electrical performance of semiconductor products, and in particular, cause defects such as vacuum leakage in the manufacturing process or lack of focus in the photolithography process, so technical demands for solving them are increasing. In this paper, warpage simulation according to the thickness of FOWLP material was performed using finite element analysis. The thickness range was based on the history of similar packages, and as a factor causing warpage, the curing temperature of the materials undergoing the curing process was applied and the difference in deformation due to the difference in thermal expansion coefficient between materials was used. At this time, the stacking order was reflected to reproduce warpage behavior similar to reality. After performing finite element analysis, the influence of each variable on causing warpage was defined, and based on this, it was confirmed that warpage was controlled as intended through design modifications.

• Composites Research
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• 제36권5호
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• pp.369-376
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• 2023

본 연구에서는 복합소재의 기지재로 활용되고 있는 에폭시 고분자의 가교율이 항복표면에 미치는 영향을 분자동역학 해석을 통해 평가하고자 한다. 분자동역학 해석을 활용하여 가교율에 따른 에폭시 모델을 형성한 후, 상온-대기압 조건하에서 단축 변형 해석 및 평면응력 조건을 고려한 다축 변형 해석을 수행하였으며, 해석 데이터를 통하여 가교율에 따른 영률, 항복점, 항복표면, 그리고 경화지수를 도출하였다. 해석 결과, 영률 및 응력은 기존 선행 연구들에서 조사되었듯이, 가교율에 따라 증가하는 경향을 확인하였다. 다축 변형 시에는, 이러한 가교율과 도출된 응력간의 관계가 하중의 방향에 따라 의존적임을 확인하였는데, 가교율이 증가할수록 단축 인장 영역에 비해, 이축 압축 영역의 항복표면은 빠른 속도 팽창하였으며, 이로 인한 항복표면의 상이함을 관측하였다. 이를 통해, 고분자 소재의 항복 표면의 압력의존성은 소재의 가교 정도에 의존적이며, 항복이 진행될수록, 압력의 존성은 동일 소재 하에서도 변할 수 있음을 확인하였다.

• 한국전기전자재료학회논문지
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• 제37권4호
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• pp.445-450
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• 2024

The expansion of lithium-ion battery usage beyond portable electronic devices to electric vehicles and energy storage systems is driven by their high energy density and favorable cycle characteristics. Enhancing the stability and performance of these batteries involves exploring solid electrolytes as alternatives to liquid ones. While sulfide-based solid electrolytes have received significant attention for commercialization, research on amorphous-phase glass solid electrolytes in oxide-based systems remains limited. Here, we investigate the glass transition temperatures and sintering behaviors by changing the molecular ratio of Li₂O/B₂O₃ in borate glass comprising Li₂O-B₂O₃-Al₂O₃ system. The glass transition temperature is decreasing as increasing the amount of Li₂O. When we sintered at 450℃, just above the glass transition temperature, the samples did not consolidate well, while the proper sintered samples could be obtained under the higher temperature. We successfully obtained the borate glass ceramics phases by melt-quenching method, and the sintering characteristics are investigated. Future studies could explore optimizing ion conductivity through refining processing conditions, adjusting the glass former-to-modifier ratio, and incorporating additional Li salt to enhance the ionic conductivity.