• Smart Structures and Systems
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• 제6권5_6호
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• pp.731-748
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• 2010

Impact detection and health monitoring are very important tasks for civil infrastructures, such as bridges. Piezoceramic based transducers are widely researched for these tasks due to the piezoceramic material's inherent advantages of dual sensing and actuation ability, which enables the active sensing method for structural health monitoring with a network of piezoceramic transducers. Wireless sensor networks, which are easy for deployment, have great potential in health monitoring systems for large civil infrastructures to identify early-age damages. However, most commercial wireless sensor networks are general purpose and may not be optimized for a network of piezoceramic based transducers. Wireless networks of piezoceramic transducers for active sensing have special requirements, such as relatively high sampling rate (at a few-thousand Hz), incorporation of an amplifier for the piezoceramic element for actuation, and low energy consumption for actuation. In this paper, a wireless network is specially designed for piezoceramic transducers to implement impact detection and active sensing for structural health monitoring. A power efficient embedded system is designed to form the wireless sensor network that is capable of high sampling rate. A 32 bit RISC wireless microcontroller is chosen as the main processor. Detailed design of the hardware system and software system of the wireless sensor network is presented in this paper. To verify the functionality of the wireless sensor network, it is deployed on a two-story concrete frame with embedded piezoceramic transducers, and the active sensing property of piezoceramic material is used to detect the damage in the structure. Experimental results show that the wireless sensor network can effectively implement active sensing and impact detection with high sampling rate while maintaining low power consumption by performing offline data processing and minimizing wireless communication.

• 한국컴퓨터정보학회논문지
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• 제18권8호
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• pp.43-52
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• 2013

본 연구는 서로 다른 두 음원에 대한 표절 여부를 분석하기 위한 음악 요소에 대해서 연구한다. 따라서 본 연구에서는 먼저 음원 분석을 위해서 디지털 음악 요소에 대해서 알아보고, 이 음악 요소를 컴파일러 기법을 활용하여 어떻게 표절 분석에 이용할 것인지 살펴본다. 또한 복잡한 미디 음악 데이터를 간단하게 처리 할 수 있도록 지원하는 오픈소스 자바 API인 JFugue를 활용한다. 따라서 본 논문에서는 JFugue에서 지원하는 포맷인 뮤직스트링 (MusicString)을 이용하여 음악 표절 분석 시스템을 설계하고 음악 표절 분석을 효율적으로 처리하기 위하여 뮤직스트링 문법 처리 요소를 살펴보고 추상구문트리(AST)를 구축하는 하고자 한다. 따라서 본 논문은 지금까지 감성적이고 주관적으로 평가해왔던 두 음원의 표절 분석을 시스템적으로 구축하기 위한 첫걸음이 될 것이며, 이 연구가 잘 활용된다면 차후에 두 음원의 표절 여부를 시스템적으로 정형화할 수 있다는 점에 큰 의의를 둘 수 있다고 판단된다.

• Computers and Concrete
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• 제20권6호
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• pp.635-643
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• 2017

The rehabilitation and strengthening of concrete structures using Fiber-Reinforced Polymer (FRP) materials have been widely investigated. As a priority issue, however, the effect of curing conditions on the bonding behavior between FRP and concrete structures is still elusive. This study aims at developing a prediction model to accurately capture the mode-II interfacial debonding between FRP strips and concrete under different curing conditions. Single shear debonding experiments were conducted on FRP-concrete samples with respect to different curing time t and temperatures T. The J-integral formulation and constrained least square minimization are carried out to calibrate the parameters, i.e., the maximum slip $\bar{s}$ and stretch factor n. The prediction model is developed based on the cohesive model and Arrhenius relationship. The experimental data are then analyzed using the proposed model to predict the debonding between FRP and concrete, i.e., the interfacial shear stress-slip relationship. A Finite Element (FE) model is developed to validate the theoretical predictions. Satisfactory agreements are obtained. The prediction model can be used to accurately capture the bonding performance of FRP-concrete structures.

• Metals and materials international
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• 제24권6호
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• pp.1193-1201
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• 2018

Dilatometry is a useful technique to obtain experimental data concerning transformation. In this paper, a dilation conversional model was established to calculate carbides fraction in AISI H13 hot-work tool steel based on the measured length changes. After carbides precipitation, the alloy contents in the matrix changed. In the usual models, the content of carbon atoms after precipitation is considered as the only element that affects the lattice constant and the content of the alloy elements such as Cr, Mo, Mn, V are often ignored. In the model introduced in this paper, the alloying elements (Cr, Mo, Mn, V) changes caused by carbides precipitation are incorporated. The carbides were identified using scanning electron microscope and transmission electron microscope. The relationship between lattice constant of carbides and temperature are measured by high-temperature X-ray diffraction. The results indicate that the carbides observed in all specimens cooled at different rates are V-rich MC and Cr-rich $M_{23}C_6$, and most of them are V-rich MC, only very few are Cr-rich $M_{23}C_6$. The model including the effects of substitutional alloying elements shows a good improvement on carbides fraction predictions. In addition, lower cooling rate advances the carbides precipitation for AISI H13 specimens. The results between experiments and mathematical model agree well.

• Advances in materials Research
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• 제8권1호
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• pp.47-73
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• 2019

Joining of Mg/Ti hybrid structures by welding for automotive and aerospace applications has attracted great attention in recent years due mainly to its potential benefit of energy saving and emission reduction. However, joining them has been hampered with many difficulties due to their physical and metallurgical incompatibilities. Different joining processes have been employed to join Mg/Ti, and in most cases in order to get a metallurgical bonding between them was the use of an intermediate element at the interface or mutual diffusion of alloying elements from the base materials. The formation of a reaction product (in the form of solid solution or intermetallic compound) along the interface between the Mg and Ti is responsible for formation of a metallurgical bond. However, the interfacial bonding achieved and the joints performance depend significantly on the newly formed reaction product(s). Thus, a thorough understanding of the interaction between the selected intermediate elements with the base metals along with the influence of the associated welding parameters are essential. This review is timely as it presents on the current paradigm and progress in welding and joining of Mg/Ti alloys. The factors governing the welding of several important techniques are deliberated along with their joining mechanisms. Some opportunities to improve the welding of Mg/Ti for different welding techniques are also identified.

• 기록학연구
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• 제34호
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• pp.107-163
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• 2012

사회구성원들의 인터넷 사용이 크게 증가하고 있는 만큼 인터넷언론은 우리 시대에 많은 영향을 미치고 있다. 대표적인 국내 인터넷언론인 '오마이뉴스'는 오늘날 국내 독립 인터넷 뉴스를 대표하는 젊은 대안언론으로 평가받고 있으며, 인터넷뉴스의 특징을 보여주는 전형적인 사례이기도 하다. 본 논문은 오마이뉴스 보도기사의 처리과정에서 단계별로 생성되는 기록정보와 그에 해당되는 기술요소를 추출하였고, 메타데이터 설계방안 도출을 위하여 국내외 메타데이터 표준 사례를 분석하였다. 국내 메타데이터 표준은 2010년 10월에 발표된 기록관리 메타데이터 공공표준안을 대상으로 하였으며, 외국 메타데이터 표준 연구는 보존 메타데이터를 위한 PREMIS 데이터 사전으로 하였다. 국내외 사례연구를 바탕으로 이용자 접근의 용이, 연관정보와의 연결, 행위이력의 축적 등에 중점을 두어 메타데이터를 재설계하였다. 오늘날 대중매체의 기록관리 연구에서 인터넷매체를 비롯한 뉴미디어에 대한 연구는 미미한 수준에 있다. 이미 언론정보학, 정보통신학, 커뮤니케이션학 등의 외부 학계에서는 인터넷 매체에 대한 연구가 심도 있게 이루어지고 있다. 인터넷 매체에 대한 다양한 분야의 연구들은 앞으로 이루어질 대중매체 기록관리 연구에 있어서 반드시 고려되어야 할 것이라 예상된다.

• 소성∙가공
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• 제28권3호
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• pp.135-144
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• 2019

Electromagnetic impulse welding (EMIW) is a type of solid state welding using the Lorentz force generated by interaction between the magnetic field of the coil and the current induced in the workpiece. Although many experimental studies have been investigated on the expansion and compression welding of tube using the EMIW process, studies on the EMIW process of lap joint between flat sheets are uncommon. Since the magnetic field enveloped inside the tube can be controlled with ease, the electromagnetic technique has been widely used for tube welding. Conversely, it is difficult to control the magnetic field in the flat sheet welding so as to obtain the required welding velocity. The current study analyzed the effects of coil shape on the impulse velocity for suitable flat one-turn coil for the EMIW of the flat sheets. The finite element (FE) multi-physics simulation involving magnetic and structural field of EMIW were conducted with the commercial software LS-DYNA to evaluate the several shape variables, viz., influence of various widths, thicknesses, gaps and standoff distances of the flat one-turn coil on the impulse velocity. To obtain maximum impulse velocity, the flat one-turn coil was designed based on the FE simulation results. The experiments were performed using an aluminum alloy 1050 sheets of 1.0mm thickness using the designed flat one-turn coil. Through the microscopic interfacial analysis of the welded specimens, the interfacial connectivity was observed to have no defects. In addition, the single lap joint tests were performed to evaluate the welding strength, and a fracture occurred in the base material. As a result, a flat one-turn coil was successfully designed to guarantee welding with bond strength equal to or greater than the base material strength.

• 소성∙가공
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• 제28권3호
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• pp.145-153
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• 2019

The objective of this study is to analyze the mechanical splicing characteristic of the threaded bar according to the contact conditions of the transverse rib. In order to consider the contact conditions of the rib, selection of the main variables including the gap of the core diameter ($l_c$), rib angle (${\theta}$), and the number of contacts ($C_N$) of transverse rib was done. So as to analyze the splicing characteristic of the D51 threaded bar, a finite element (FE) simulation of the tensile test was conducted using the designed D51 threaded bar and coupler. Through FE simulation results, it was verified that the mechanical slicing characteristics varied based on the main design variables ($l_c$, ${\theta}$, and $C_N$). It was further confirmed that it was important to determine the $C_N$ in consideration of $l_c$. Additionally, the tensile test results of the D25 and D51 threaded bar combined with the couplers were similar to FE simulation results. Furthermore, to quantitatively evaluate FE simulation and test results, the calculation equation for the contacted projection area ratio (R) of the transverse rib was proposed. To secure a mechanical splicing joint of the threaded bar, it was established that the R calculated using the proposed equation had to be greater or equal to 40%.

• 소성∙가공
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• 제30권1호
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• pp.5-15
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• 2021

The effects of heat treatments (T6 and T73) on the microstructure, mechanical properties, and high cycle fatigue behavior of modified AA7075 alloys were investigated. A modified 7075 alloy was manufactured using modified-Mg (Mg-Al2Ca) instead of the conventional element Mg. Based on the microstructure, the average grain size was 4.5 ㎛ (T6) and 5.2 ㎛ (T73). Regardless of heat treatment, the modified AA7075 alloys consisted of Al matrix containing homogeneously distributed Al2CuMg and MgZn2 phases with reduced Fe-intermetallic compound. Room temperature tensile tests showed that the properties of modified 7075-T6 (Y.S.: 622MPa, T.S: 675MPa, elongation: 15.4%) were superior to those of T73 alloy (Y.S.: 492MPa, T.S: 548MPa, elongation: 12.8%). Experimental data show that the fatigue life of T6 was 400 MPa, about 64% of its yield strength. However, the fatigue life of T73 alloy was 330 MPa and 67%. Irrespective of the stress level, all crack initiation points were located on the specimen surface, and no inclusions acting as stress concentrators were seen. Superior mechanical properties and high cycle fatigue behavior of modified AA7075-T6 alloy are attributed to the fine grains and homogeneous distribution of small second phases such as MgZn2 and Al2CuMg, in addition to reduced Fe-intermetallic compounds.

• 한국정보통신학회논문지
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• 제25권5호
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• pp.659-666
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• 2021

본 연구는 현실에 존재하지 않는 디지털 미디어에 실질적인 물질성을 부여하는 개념을 가지고 있는 피지컬 컴퓨팅의 환경적 특징을 게임 개발에 적용해보고자 한다. 피지컬 컴퓨팅의 처리 과정은 디지털 입력과 디지털 출력 그리고 아날로그 입력과 아날로그 출력으로 이루어져 있으며 마이크로 컨트롤러를 중심으로 입력과 출력이 이루어져 있다. 본 논문은 피지컬 컴퓨팅이 많이 연구되고 있는 디지털 아트와 정보교육 분야의 연구 사례 분석과 피지컬 컴퓨팅 요소를 일부 차용한 게임들을 분석해서 개발적 요소를 선별했다. 도출된 요소들은 델파이 조사방법으로 전문가와의 합의를 통해 검증했다. 본 논문에서 12개의 요소를 선정했으며 가상세계의 물리적 성질부여, 구현 기술의 적합성, 현실의 플레이이어와 가상의 플레이어와의 일치성 순으로 중요도가 나타났다.