• Journal of Information Science Theory and Practice
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• 제7권3호
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• pp.6-20
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• 2019

Learning analytics, or educational data mining, is an emerging field that applies data mining methods and tools for the exploitation of data coming from educational environments. Learning management systems, like Moodle, offer large amounts of data concerning students' activity, performance, behavior, and interaction with their peers and their tutors. The analysis of these data can be elaborated to make decisions that will assist stakeholders (students, faculty, and administration) to elevate the learning process in higher education. In this work, the power of Excel is exploited to analyze data in Moodle, utilizing an e-learning course developed for enhancing the information computer technology skills of school teachers in primary and secondary education in Greece. Moodle log files are appropriately manipulated in order to trace daily and weekly activity of the learners concerning distribution of access to resources, forum participation, and quizzes and assignments submission. Learners' activity was visualized for every hour of the day and for every day of the week. The visualization of access to every activity or resource during the course is also obtained. In this fashion teachers can schedule online synchronous lectures or discussions more effectively in order to maximize the learners' participation. Results depict the interest of learners for each structural component, their dedication to the course, their participation in the fora, and how it affects the submission of quizzes and assignments. Instructional designers may take advice and redesign the course according to the popularity of the educational material and learners' dedication. Moreover, the final grade of the learners is predicted according to their previous grades using multiple linear regression and sensitivity analysis. These outcomes can be suitably exploited in order for instructors to improve the design of their courses, faculty to alter their educational methodology, and administration to make decisions that will improve the educational services provided.

• Steel and Composite Structures
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• 제33권3호
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• pp.445-461
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• 2019

The ultrasonic guided wave-based technique has become one of the most promising methods in non-destructive evaluation and structural health monitoring, because of its advantages of large area inspection, evaluating inaccessible areas on the structure and high sensitivity to small damage. To further advance the development of damage detection technologies using ultrasonic guided waves for the inspection of welded components in structures, the transmission characteristics of the ultrasonic guided waves propagating through welded joints with various types of defects or damage in steel plates are studied and presented in this paper. A three-dimensional (3D) finite element (FE) model considering the different material properties of the mild steel, high strength steel and austenitic stainless steel plates and their corresponding welded joints as well as the interaction condition of the steel plate and welded joint, is developed. The FE model is validated against analytical solutions and experimental results reported in the literature and is demonstrated to be capable of providing a reliable prediction on the features of ultrasonic guided wave propagating through steel plates with welded joints and interacting with defects. Mode conversion and scattering analysis of guided waves transmitted through the different types of weld defects in steel plates are performed by using the validated FE model. Parametric studies are undertaken to elucidate the effects of several basic parameters for various types of weld defects on the transmission performance of guided waves. The findings of this research can provide a better understanding of the transmission behaviour of ultrasonic guided waves propagating through welded joints with defects. The method could be used for improving the performance of guided wave damage detection methods.

• 대한조선학회논문집
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• 제31권2호
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• pp.91-98
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• 1994

대형구조계에 대하여 구조중량의 최소화를 기하면서 고유진동수 제한조건을 만족시키는 동특성 최적화에 효율적인 한 방법을 제안한다. 일련의 근사최적화문제를 형성하는데 있어서는 고유진동수의 설계파라메터에 대한 감도와 설계파라메터의 역에 대한 감도를 병용하는 근사방법을 사용하며, 설계변수의 변화에 따른 고유진동해석 및 감도계산은 저자가 조선학회논문집 제30권 제3호에 발표한 바 있는 부분구조진동형 합성방법에 의거한다. 설계파라메터에 대한 감도와 설계파라메터의 역에 대한 감도를 병용하는 근사방법은 전자만을 사용하는 근사방법에 비해 적은 회수의 재해석으로 고유진동수 제한조건을 만족하는 설계값을 얻을 수 있다. 또한 설계변경에 따른 재해석시 앞서 발표했던 부분구조진동형 합성방법의 장점을 활용하므로써 효율적인 재해석이 가능하다. 제안된 방법의 유용성은 외팔보유추 구조계 및 선체단순화 2-D FEM모델의 상부구조를 대상으로 한 수치예제를 통하여 검증되었다.

• Structural Engineering and Mechanics
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• 제68권5호
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• pp.603-619
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• 2018

In this research, an effective computational technique is carried out for nonlinear and post-buckling analyses of cracked imperfect composite plates. The laminated plates are assumed to be moderately thick so that the analysis can be carried out based on the first-order shear deformation theory. Geometric non-linearity is introduced in the way of von-Karman assumptions for the strain-displacement equations. The Ritz technique is applied using Legendre polynomials for the primary variable approximations. The crack is modeled by partitioning the entire domain of the plates into several sub-plates and therefore the plate decomposition technique is implemented in this research. The penalty technique is used for imposing the interface continuity between the sub-plates. Different out-of-plane essential boundary conditions such as clamp, simply support or free conditions will be assumed in this research by defining the relevant displacement functions. For in-plane boundary conditions, lateral expansions of the unloaded edges are completely free while the loaded edges are assumed to move straight but restricted to move laterally. With the formulation presented here, the plates can be subjected to biaxial compressive loads, therefore a sensitivity analysis is performed with respect to the applied load direction, along the parallel or perpendicular to the crack axis. The integrals of potential energy are numerically computed using Gauss-Lobatto quadrature formulas to get adequate accuracy. Then, the obtained non-linear system of equations is solved by the Newton-Raphson method. Finally, the results are presented to show the influence of crack length, various locations of crack, load direction, boundary conditions and different values of initial imperfection on nonlinear and post-buckling behavior of laminates.

• 소성∙가공
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• 제27권6호
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• pp.370-378
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• 2018

Cold forging, carried out at room temperature, leads to high dimensional accuracy and excellent surface integrity as compared to other forging methods such as warm and hot forgings. In the cold forging process, WC-Co (Tungsten Carbide-Cobalt) alloy is the mainly used material as a core dies because of its superior hardness and strength as compared to other structural materials. For cold forging, die life is the most significant factor because it is directly related to the manufacturing cost due to periodic die replacement in mass production. To investigate die life of WC-Co alloy for cold forging, mechanical properties such as strength and fatigue are essentially necessary. Generally, uniaxial tensile test and fatigue test are the most efficient and simplest testing method. However, uniaxial tension is not efficiently application to WC-Co alloy because of its sensitivity to alignment of the specimen due to its brittleness and difficulty in thread machining. In this study, shape of specimen, tools, and testing methods, which are appropriate for uniaxial tensile test for WC-Co alloy, are proposed. The test results such as Young's modulus, tensile strength and stress-strain curves are compared to those in previous literature to validate the proposed testing methods. Based on the validation of test results it was concluded that the newly developed testing method is applicable to other cemented carbides like Titanium carbides with high strength and brittleness, and also can be utilized to carry out fatigue tests for further investigation on die life of cold forging.

• 디지털융복합연구
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• 제17권1호
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• pp.295-300
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• 2019

현대 사회는 융합의 시대이며, 스토리텔링에 있어서도 감성적 이야기와 정보라는 두 가지 유형의 데이터 타입 형태가 융합된 스토리텔링의 필요성이 요구되어지고 있다. 특히, VR 콘텐츠의 경우, $360^{\circ}$ 공간을 자유롭게 탐색하는 과정을 통해서 정보를 선택하는 등, 사용자가 콘텐츠에 직접적으로 관여하게 되며, 이에 즉각적으로 대응할 수 있는 인터랙션(Interaction-상호작용)이 이루어져야 한다. 따라서 기존의 스토리텔링 방식으로의 접근으로는 한계가 있으며, 감성과 정보의 두 영역을 충족시키는 '융합형 스토리텔링'의 구현이 절실한 장르라고 판단되어 진다. 본 논문에서는 VR 콘텐츠의 이해에 있어 특히 공간적 특성을 위주로 살펴본 후, VR 콘텐츠에서 '융합형 스토리텔링'을 효과적으로 구현하기 위한 방안으로, 콘텐츠의 스토리 구조 유형에 대한 고찰을 통하여 VR 콘텐츠에 적합한 스토리텔링 유형을 서클(Circle) 구조로 정리하여 맞춤 시스템을 제안한다. 이를 토대로, 향후에는 진정한 4차 산업혁명 시대의 VR 콘텐츠와 인터랙션을 위한 컨텍스트(context) 인식 과정을 활용하여 기술이 감성과 정보의 두 가지 영역을 충족시키는 개인 맞춤형 시스템의 연구로 발전되어질 것을 기대한다.

• 한국기계가공학회지
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• 제20권4호
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• pp.39-48
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• 2021

In this paper, an in-plane deformation measuring system using a dual-beam shear interferometer was constructed to measure the in-plane deformation of the measuring object. The in-plane deformation of the object was quantitatively measured according to the load and surface treatment conditions of the object. We also verified the reliability of the proposed technique by simultaneously performing the technique with an electronic speckle pattern interferometry system (ESPI), which is another laser application measurement technology. Digital shearography directly measures the deformation gradient or strain components and has the advantages of being full-field, noncontact, highly sensitive, and robust. It offers a much higher measurement sensitivity compared with noncoherent measurement methods and is more robust and applicable to in-field tests.

• Structural Engineering and Mechanics
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• 제77권2호
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• pp.167-177
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• 2021

Due to various benefits such as unlimited degrees of freedom, environment adaptability, and safety for humans, engineers have used soft materials with hyperelastic behavior in various industrial, medical, rescue, and other sectors. One of the applications of these materials in the fabrication of bending soft actuators (SA) is that they have eliminated many problems in the actuators such as production cost, mechanical complexity, and design algorithm. However, SA has complexities, such as predicting and monitoring behavior despite the many benefits. The first part of this paper deals with the prediction of SA behavior through mathematical models such as Ogden and Darijani, and its comparison with the results of experiments. At first, by examining different geometric models, the cubic structure was selected as the optimal structure in the investigated models. This geometrical structure at the same pressure showed the most significant bending in the simulation. The simulation results were then compared with experimental, and the final gripper model was designed and manufactured using a 3D printer with silicone rubber as for the polymer part. This geometrical structure is capable of bending up to a 90-degree angle at 70 kPa in less than 2 seconds. The second section is dedicated to monitoring the bending behavior created by the strain sensors with different sensitivity and stretchability. In the fabrication of the sensors, silicon is used as a soft material with hyperelastic behavior and carbon fiber as a conductive material in the soft material substrate. The SA designed in this paper is capable of deforming up to 1000 cycles without changing its characteristics and capable of moving objects weigh up to 1200 g. This SA has the capability of being used in soft robots and artificial hand making for high-speed objects harvesting.

• 한국환경복원기술학회지
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• 제24권4호
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• pp.61-75
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• 2021

Roadside greenery in the city is not only a means of reducing fine dust, but also an indispensable element of the city in various aspects such as improvement of urban thermal environment, noise reduction, ecosystem connectivity, and aesthetics. However, in studies dealing with the effect of reducing fine dust through trees in existing urban spaces, microscopic aspects such as the adsorption effect of plants were dealt with, structural changes such as the width of urban buildings and streets, and the presence or absence of trees, Impact studies that reflect the actual form of In this study, the effect of greenery composition applicable to urban space on PM2.5 was simulated through the microclimate epidemiologic model ENVI-met, and field measurements were performed in parallel to verify the results. In addition, by analyzing the results of fine dust background concentration, wind speed, and leaf area index, the sensitivity to major influencing variables was tested. As a result of the study, it was confirmed that the fine dust reduction effect was the highest in the case with a high planting amount, and the reduction effect was the greatest at a low background concentration. Based on this, the cost of planting street green areas and the effect of reducing PM2.5 were compared. The results of this study can contribute as a basis for considering the effect of pedestrian space on air quality when planning and designing street green spaces.

• 한국인터넷방송통신학회논문지
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• 제21권4호
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• pp.143-148
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• 2021

격자 구조로 구성된 유전체 다층 구조의 GMR 특성에 의하여 생성되는 Bloch 표면파 (BSW)의 체계적인 연구가 바이오 센서의 감지 성능을 분석하기 위하여 제시되었다. 그 광학적 반응 현상에 대한 구조적 매개 변수의 영향을 Babinet의 원리와 모드 전송선 이론 (MTLT)을 사용하여 평가하였다. 설계된 바이오 센서의 감도는 파장 스펙트럼에서는 격자 상수에 비례하였으며, 각도 스펙트럼에서는 입사 전자기파의 정상 파동 벡터에 반비례하였다. SiO/SiO₂와 TiO₂/SiO₂ 다층 유전체 스택으로 구성된 두 개의 소자에 대한 수치해석 결과를 제시하여, BSW가 적외선에서 가시 영역에 이르는 대역에서 효율적인 회절 기반 바이오 센서를 실현하는 데 활용 될 수 있음을 보여주었다.