• Advances in nano research
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• 제5권4호
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• pp.337-357
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• 2017

Knowledge of thin films mechanical properties is strongly associated to the reliability and the performances of Nano Electro Mechanical Systems (NEMS). In the literature, there are several methods for micro materials characterization. Bulge test is an established nondestructive technique for studying the mechanical properties of thin films. This study improve the performances of NEMS by investigating the mechanical behavior of Nano rectangular thin film (NRTF) made of new material embedded in Nano Electro Mechanical Systems (NEMS) by developing the bulge test technique. The NRTF built from adhesively-bonded layers of basalt fiber reinforced polymer (BFRP) laminate composite materials in Nano size at room temperature and were used for plane-strain bulging. The NRTF is first pre-stressed to ensure that is no initial deflection before applied the loads on NRTF and then clamped between two plates. A differential pressure is applying to a deformation of the laminated composite NRTF. This makes the plane-strain bulge test idea for studying the mechanical behavior of laminated composite NRTF in both the elastic and plastic regimes. An exact solution of governing equations for symmetric cross-ply BFRP laminated composite NRTF was established with taking in-to account the effect of the residual strength from pre-stressed loading. The stress-strain relationship of the BFRP laminated composite NRTF was determined by hydraulic bulging test. The NRTF thickness gradation in different points of hemisphere formed in bulge test was analysed.

• Advances in Computational Design
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• 제4권1호
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• pp.43-52
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• 2019

Variation Analysis (VA) is used to simulate final product variation, taking into consideration part manufacturing and assembly variations. In VA, all the manufacturing and assembly processes are defined at the product design stage. Process Capability Data Bases (PCDB) provide information about measured variation from previous products and processes and allow the designer to apply this to the new product. A new challenge to this traditional approach is posed by the Industry 4.0 (I4.0) revolution, where Smart Manufacturing (SM) is applied. The manufacturing intelligence and adaptability characteristics of SM make present PCDBs obsolete. Current tolerance analysis methods, which are made for discrete assembly products, are also challenged. This paper discusses the differences expected in future factories relevant to VA, and the approaches required to meet this challenge. Current processes are mapped using I4.0 philosophy and gaps are analysed for potential approaches for tolerance analysis tools. Matching points of simulation capability and I4.0 intents are identified as opportunities. Applying conditional variations, incorporating levels of adjustability, and the un-suitability of present Monte Carlo simulation due to changed mass production characteristics, are considered as major challenges. Opportunities including predicting residual stresses in the final product and linking them to product deterioration, calculating non-dimensional performances and extending simulations for process manufactured products, such as drugs, food products etc. are additional winning aspects for next generation VA tools.

• Steel and Composite Structures
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• 제31권2호
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• pp.149-158
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• 2019

The force-deformation behavior, strain distribution and failure modes of a variable damping self-centering brace (VD-SCB) are theoretically analyzed, experimentally studied, and numerically simulated to guide its design. The working principle of the brace is explained by describing the working stages and the key feature points of the hysteretic curve. A large-scale brace specimen was tested under different sinusoidal excitations to analyze the recentering capability and energy dissipation. Results demonstrate that the VD-SCB exhibits a full quasi-flag-shaped hysteretic response, high ultimate bearing capacity, low activation force and residual deformation, and excellent recentering and energy dissipation capabilities. Calculation equations of the strain distribution in different parts of the brace are proposed and are compared with the experimental data and simulated results. The developments of two failure modes are compared. Under normal circumstances, the brace fails due to the yielding of the spring blocking plates, which are easily replaced to restore the normal operating conditions of the brace. A brief description of the design procedure of the brace is proposed for application.

• Steel and Composite Structures
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• 제38권5호
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• pp.497-521
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• 2021

In this study, an effective numerical method is introduced for nonlinear inelastic analyses of rectangular concrete-filled steel tubular (CFST) frames for the first time. A steel-concrete composite fiber beam-column element model is developed that considers material, and geometric nonlinearities, and residual stresses. This is achieved by using stability functions combined with integration points along the element length to capture the spread of plasticity over the composite cross-section along the element length. Additionally, a multi-spring element with a zero-length is employed to model the nonlinear semi-rigid beam-to-column connections in CFST frame models. To solve the nonlinear equilibrium equations, the generalized displacement control algorithm is adopted. The accuracy of the proposed method is firstly verified by a large number of experiments of CFST members subjected to various loading conditions. Subsequently, the proposed method is applied to investigate the nonlinear inelastic behavior of rectangular CFST frames with fully rigid, semi-rigid, and hinged connections. The accuracy of the predicted results and the efficiency pertaining to the computation time of the proposed method are demonstrated in comparison with the ABAQUS software. The proposed numerical method may be efficiently utilized in practical designs for advanced analysis of the rectangular CFST structures.

• 전기전자학회논문지
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• 제27권4호
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• pp.439-449
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• 2023

In an era marked by the increasing use of drones and the growing demand for indoor surveillance, the development of a robust application for detecting and tracking both drones and humans within indoor spaces becomes imperative. This study presents an innovative application that uses FMCW radar to detect human and drone motions from the cloud point. At the outset, the DBSCAN (Density-based Spatial Clustering of Applications with Noise) algorithm is utilized to categorize cloud points into distinct groups, each representing the objects present in the tracking area. Notably, this algorithm demonstrates remarkable efficiency, particularly in clustering drone point clouds, achieving an impressive accuracy of up to 92.8%. Subsequently, the clusters are discerned and classified into either humans or drones by employing a deep learning model. A trio of models, including Deep Neural Network (DNN), Residual Network (ResNet), and Long Short-Term Memory (LSTM), are applied, and the outcomes reveal that the ResNet model achieves the highest accuracy. It attains an impressive 98.62% accuracy for identifying drone clusters and a noteworthy 96.75% accuracy for human clusters.

• Computers and Concrete
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• 제33권6호
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• pp.671-688
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• 2024

The modeling efficiency of concrete meso-models close to real concrete is one of the important issues that limit the accuracy of mechanical simulation. In order to improve the modeling efficiency and the closeness of the numerical aggregate shape to the real aggregate, this paper proposes a method for generating a two-dimensional concrete meso-model based on pixel matrix and skeleton theory. First, initial concrete model (a container for placing aggregate) is generated using pixel matrix. Then, the skeleton curve of the residual space that is the model after excluding the existing aggregate is obtained using a thinning algorithm. Finally, the final model is obtained by placing the aggregate according to the curve branching points. Compared with the traditional Monte Carlo placement method, the proposed method greatly reduces the number of overlaps between aggregates by up to 95%, and the placement efficiency does not significantly decrease with increasing aggregate content. The model developed is close to the actual concrete experiments in terms of aggregate gradation, aspect ratio, asymmetry, concavity and convexity, and old-new mortar ratio, cracking form, and stress-strain curve. In addition, the cracking loss process of concrete under uniaxial compression was explained at the mesoscale.

• 환경생물
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• 제32권4호
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• pp.311-318
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• 2014

PFOS (Perfluorooctane sulfonate) 노출에 따른 Macrophthalmus japonicus의 생태독성학적 판정점을 탐색하고자 생존율, 부속지 탈락 수, 갑각 및 내장 색의 변화를 관찰하였다. 그 결과, PFOS 노출에 따른 생존율의 감소는 농도 의존적 패턴을 보여 상대적 고농도인 PFOS $30{\mu}gL^{-1}$에서 168시간 노출시 24%의 가장 낮은 생존율을 나타내었다. 부속지 탈락은 대조군에 비해 PFOS 노출군에서 탈락빈도가 증가하였다. 또한 대조군에서는 갑각색의 변화가 관찰되지 않았으나, PFOS 노출군에서는 백화현상이 농도의존적 패턴으로 관찰되었다. 내부 장기의 색 선명도도 PFOS 노출군에서 대조군에 비해 변화가 나타났다. 이러한 결과는 해양 저서환경의 모니터링을 위한 생물적 주요한 정보를 제공해 줄 것이다.

• 대한환경공학회지
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• 제28권4호
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• pp.447-452
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• 2006

대형 수체의 수질 모델 검증 효과를 향상시키기 위하여 원격탐사 기술이 적용되었다. 인공위성 영상은 대형 수체의 넓은 표면을 한꺼번에 파악할 수 있으므로 모델의 보정 및 검증에 사용되는 관측 자료의 부족함을 보완할 수 있다. 이 논문은 2000년 4월 29일과 9월 4일에 촬영된 Landsat FTM+영상을 분석하여 팔당호 표층 수온 검증 연구를 제시하고 있다. 영상으로부터 계산된 수온과 모델의 표층 수온의 자료를 획득하여 3가지 방법으로 영상에 의한 수온과 모델의 결과를 비교하였다. 4월 29일 영상의 경우 모델 결과를 기준으로 오차율이 0.13이며 9월 4일에는 오차율이 0.04로 모델의 표층 수온이 영상으로부터 계산된 수온과 잘 일치함을 알 수 있다. 그러나 영상촬영 시점의 대기의 간섭을 고려하지 못한 것이 4월 29일 결과의 오차를 발생시킨 주요 원인으로 사료된다. 그러므로 정확한 수질자료를 얻기 위해서는 영상촬영 시점의 대기의 효과를 고려한 대기보정이 필요할 것이라 사료된다.

• 대한치과보철학회지
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• 제35권4호
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• pp.706-718
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• 1997

Ceramometal crowns are common restorations in fixed prosthodontics because of their casting accuracy, the high strength properties of the metal, and the cosmetic appearance of porcelain. However, deterioration of the initial fit of the metal coping has been observed after the porcelain firing cycle. The distortion due to repeated firing makes it difficult to fit crown margin and elicits microleakage. The major causes of distortion are the residual stress that accumulate during wax-up, casting, cold work and the induced stress caused by the mismatch of porcelain-metal thermal contraction. This study examined the marginal fit changes of metal copings in relation to repeated firing and the effects of heat treatment that reduce the distortion resulted from residual stress. The marginal changes of the copings that were treated with conventional method and those treated with heat before repeated firing, were evaluated. The metal die which represented preparations of a maxillary central incisor was fabricated, and 45 wax patterns were cast with nonprecious metal alloys. The heat treatment of each group was performed as follows. Group 1(control) : Casting - Devesting - Cold work - Firing Group 2 : Casting - Heat treatment - Devesting - Cold work - Firing Group 3 : Casting - Devesting - Cold work - Reinvesting - Heat treatment - Devesting - Firing The copings were fired 3 times. After each firing, the marginal fit changes were measured with inverted metallurgical microscope at the 4 reference points located at labial, lingual, and both proximal surface. Measurements were compared, and statistically analyzed. The results were as follows ; 1. In all groups, the highest value of marginal fit changes of the copings studied were found after the first firing cycle. 2. When the distortion of each experimental group at the first firing cycle were compared, group 1 exhibited the greatest changes($20-27{\mu}m$), followed by group 2($9-13{\mu}m$), and group 3($8-10{\mu}m$). 3. The copings treated with heat before devesting(group 2) revealed significantly smaller marginal fit changes than the copings treated with conventional method(group 1). (p<0.01) 4. The copings treated with heat after reinvesting(group 3) revealed significantly smaller marginal fit changes than the copings treated with conventional method(group 1). (p<0.01) 5. No siginificant differences in marginal fit changes were found between the copings treated with heat before devesting(group 2) and the copings treated with heat after reinvesting(group 3). (p>0.01)

• 대한치과보철학회지
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• 제32권4호
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• pp.526-552
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• 1994

The extent and direction of movement of removable partial dentures during function are influenced by the nature of the supporting structures and and the design of the prosthesis. Since forces are transmitted to the abutment teeth through occlusal rests, guide planes and direct retainers during functional movements, proper design based on the avaialble research data will maintain the health of abutment teeth and their supporting structures. The purpose of this in vitro study is evaluating stress distribution clinically around the abutment teeth prepared following 4-type clasping systems for unilateral free-end removable partial dentures. Three-Dimensional Photoelastic Stress Analysis method was used because it shows a visual display of stresses of the simulated abutment teeth and residual ridges and reveals stress concentration that can be read at any given points in terms of direction and magnitude. For this study, the author fabricated 4 mandibular photoelastic epoxy models missing left 1st and End molar. Epoxy models were duplicated and 4 unilateral removable partial dentures were construe- ted in accordance with 4-type direct retainers. Unilateral free-end removable partial dentures were positioned on their own models. 6kg force was loaded on the every removable partial dentures of the epoxy model on the central fossa of mandibular left 1st molar vertically by the loading device. After the stress was frozen in a stress freezing furnace, 6 specimens of 6-mm thickness were made from every epoxy model and examined with the circular polariscope. The results were as follows : 1. Generally I-bar clasp revealed the most favorable stress distribution around the abutment teeth. 2. At the end portion of the free-end ridge, Back action clasp showed the highest stress concentration at the bucco-lingual and top portions of the residual alveolar ridge. 3. At the distal area of the abutment teeth, Akers clasp and Roach clasp showed higher stress concentration bucco-lingually and apically than the others. 4. To the abutment tooth, I-bar clasp showed the least stress distribution bucco-lingually but the others showed irregular stress distribution. 5. At the mesial area of the abutment teeth, the order of effective stress distribution was I-bar clasp, Back-action clasp, Akers clasp and Roach clasp. There was big difference of stress distribution between them. 6. At the right 2nd premolar and 1st molar, the stress concentration of Akers clasp was a little high but that of I-bar clasp was low.