• Structural Engineering and Mechanics
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• v.54 no.3
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• pp.433-451
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• 2015

This paper focuses on large deflection static behavior of edge cracked simple supported beams subjected to a non-follower transversal point load at the midpoint of the beam by using the total Lagrangian Timoshenko beam element approximation. The cross section of the beam is circular. The cracked beam is modeled as an assembly of two sub-beams connected through a massless elastic rotational spring. It is known that large deflection problems are geometrically nonlinear problems. The considered highly nonlinear problem is solved considering full geometric non-linearity by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. There is no restriction on the magnitudes of deflections and rotations in contradistinction to von-Karman strain displacement relations of the beam. The beams considered in numerical examples are made of Aluminum. In the study, the effects of the location of crack and the depth of the crack on the non-linear static response of the beam are investigated in detail. The relationships between deflections, end rotational angles, end constraint forces, deflection configuration, Cauchy stresses of the edge-cracked beams and load rising are illustrated in detail in nonlinear case. Also, the difference between the geometrically linear and nonlinear analysis of edge-cracked beam is investigated in detail.

• Bulletin of the Korean Chemical Society
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• v.24 no.5
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• pp.593-599
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• 2003

The nanoparticle magnetite of which diameter was about 3 nm was synthesized in a homogeneous aqueous solution without a template. The synthesized magnetite nanoparticle was easily oxidized to maghemite in an ambient condition. The magnetic properties of the ferrite nanoparticle show superparamagnetism at room temperature and its blocking temperature is around 93 K. Modifying the sequential adsorption method of metal bisphosphonate, we have prepared a multilayer thin film of the ferrite nanoparticle on planar substrates such as glass, quartz and Si wafer. In this multilayer the ferrite nanoparticle layer and an alkylbisphosphonate layer are alternately placed on the substrates by simple immersion in the solutions of the ferrite nanoparticle and 1, 10-decanediylbis (phosphonic acid) (DBPA), alternately. This is the first example, as far as we know, of nanoparticle/alkyl-bisphosphonate multilayer which is an analogy of metal bisphosphonate multilayer. UV-visible absorption and infrared reflection-absorption studies show that the growth of each layer is very systematic and the film is considerably optically transparent to visible light of 400-700 nm. Atomic force microscopic images of the film show that the surface morphology of the film follows that of the substrate in μm-scale image and the nanoparticle-terminated surface is differentiated from the DBPA-terminated one in nm-scale image. The magnetic properties of this ferrite/DBPA thin film are almost the same as those of the ferrite nanoparticle powder only.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.59-59
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• 2007

최근 GaN계 LED를 대체할 만한 물질로 주목받고 있는 ZnO는 단결정 박막성장의 어려움, 동일접합 LED 소자구현을 위한 p-ZnO 성장의 어려움 3원계 합금제작의 어려움 등으로 소자제작에 있어 고전을 하고 있다. 특히 이러한 문제점을 극복하고자 하는 방안으로 양자 제한 효과, 탁월한 결정성, self-assembly, internal stress 등의 새로운 기능성을 지닌 ZnO 나노구조가 제시되었다. 하지만 나노구조를 이용한 다이오드 제작에서도 금속전극의 접합이라는 문제의 벽에 가로막혀 있다. 본 실험에서는 자체 개발된 MOCVD 장비를 이용한 일차원 ZnO 나노선을 성장한 이후 연속적으로 박막을 성장하여 금속전극의 접합을 시도하였다. 이종접합구조 뿐만 아니라 일차원 및 이차원 구조의 복합구조는 일반 다결정 박막보다 결정성에서 우수한 특성을 보였으며, 다이오드 제작시에 높은 효율을 보였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.132.2-132.2
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• 2013

Electrons in graphene make ballistic transport with very high mobility (${\sim}2{\times}105 $cm2V-1s-1), which holds promises for applications in fast electronic devices. However, such expectations have been hampered by the semi-metallicity or zero bandgap of graphene, which makes it impossible to completely turn off graphene transistor devices. Here, we report the observations of local bandgap modulations in Moir$\acute{e}$ patterned graphene on metal substrates using scanning tunneling microscopy and spectroscopy. The Moir$\acute{e}$ patterned graphene was made by combinations of self-assembly processes, and they showed additional electronic states that could be interpreted as sub-band states. Our experimental observations could be explained with orbital transitions of carbon atoms from sp2 to sp3, as supported by our density functional theory calculation results. Our findings will add new poweful components for device applications.

• Transactions of Materials Processing
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• v.7 no.6
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• pp.545-553
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• 1998

The purpose of this paper is to develop a CAD/CAM system for generation of designing and manufacturing information such as total drawing sub-assembly drawing, part drawing detail drawing part list and NC data for machining by CNC lathe were CUT machining center. Through this study the CAD/CAM system for deep drawing transfer die in mechanical press process has been developed The developed CAD system can generate the drawings of transfer die in mechanical press. Using these results from CAD system. it can generate NC data to machine die's elements on the CAD system. This system can reduce design man-hours and human errors. In order to construct the system it is used to automate the design process using knowledge base system. The developed system is based on the knowledge base system which is involved a lot of expert's empirical knowhow in the practice field. Using AutoLISp language under the Auto CAD system. CTK customer language of SmartCAM is used as the overall CAD/CAM environment. Results of this system will be provide effective aids to the designer and manufacturer in this field

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.06a
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• pp.57-64
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• 1998

The purpose of this research is to develop a CAD/CAM system for generation all kind of information such as, total drawing, sub assembly drawing, part drawing, detail drawing, part list, and NC data for machining by CNC lathe, Wire CUT, machining center. Through this study the CAD/CAM System for deep drawing transfer die in mechanical press process has been developed. The developed CAD system can generate the drawing of transfer die in mechanical press. Using these results from CAD system, it can generate the NC data to machine die's elements on the CAD system. This system can reduce design man-hours and human errors. In order to construct the system, it is used to automate the design process using knowledge base system. The developed system is based on the knowledge base system which is involved a lot of expert's technology in the practice field. Using AutoLISP language under the AutoCAD system, CTK customer language of SmartCAM is used as the overall CAD/CAM environment. Results of this system will be provide effective aids to the designer and manufacturer in this field.

• Nuclear Engineering and Technology
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• v.55 no.7
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• pp.2591-2603
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• 2023

Simulating the Corrosion-Related Unidentified Deposit (CRUD) on the surface of fuel assemblies is necessary to predict the axial offset anomaly and the localized corrosion induced by the CRUD during the operation of nuclear power plants. A new CRUD model was developed to predict the formation of the CRUD deposits, considering the deposition and erosion mechanisms. The heat transfer and capillary flow within the CRUD were also considered to evaluate the boiling amount within the CRUD layer. This model predicted a CRUD deposit thickness of 44 ㎛ during a one-cycle operation of the Seabrook nuclear power plant. The CRUD deposition tended to accelerate and decelerate during the simulation, by being related to boiling mechanism on the deposits surface. Additionally, during a three-cycle operation corresponding to the refueling period, the CRUD deposition was saturated at a thickness of 80 ㎛, which was in good agreement with the suggested thickness for CRUD buildupin pressurized water reactors. Surface boiling on the thin CRUD deposits enhanced the acceleration of the deposition, even when the wick boiling properties were not favorable for CRUD deposition. To ensure the certainty of the simulation results, sensitivity analyses were conducted for the porosity, chimney density, and the constants employed in the proposed model of the CRUD.

• Journal of The Korean Association For Science Education
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• v.27 no.6
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• pp.529-545
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• 2007

Questioning forms an integral part of most strategies for effective teaching when the class consists of difficult content. Science including chemistry is usually content-rich, but difficult to understand without supporting lab experiments, subsidiary visual materials and model kits. Engaging the attention and interest of students in such a subject, therefore, is the key to the success of a daily lesson in the classroom. However, generating meaningful questions requires a certain level of information and metacognitive skills on the part of the teacher. The purpose of this study was to find out the framework of effective teachers' questioning with a large group in chemistry class: how teachers used questioning to engage their students in such a big class, to identify a variety of forms of feedback provided by students and to develop a model of question-inducing strategies. We investigated the teachers' recognition of their questioning and the students' recognition of teachers' questioning by surveying over 82 teachers and 434 students in Korea. The survey findings show that the questionnaire can be categorized into four elements: the theme of the teachers' questions (T), students' inquiries (I), methods of teachers' questioning (M) and encouragement of students (E). These elements can be analyzed and sub-categorized to find out which elements are effective in good questioning, even though the elements are interwoven tetrahedrally.

• Korean Journal of Construction Engineering and Management
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• v.22 no.6
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• pp.120-130
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• 2021

Recently, the government is reinforcing safety management at construction sites to prevent safety accidents in construction works, and the safety management plan of workers is an important situation. Meanwhile, modular construction is expected to be gradually expanded to middle and high-rise buildings, but active measures to ensure worker safety are insufficient. This study is a preliminary study of the development of a checklist for preventive worker safety management. The purpose of this study is to derive a checklist classification system for the safety management of workers in the field of modular construction by preceding studies, case analysis, and expert advisory opinions. The classification system consists of large categories of factory manufacturing, transportation, and on-site construction, and the sub-system consists of six sub-classes: foundation work, frame work, modular frame installation work, finishing work, and facility work. Among them, the sub-classification of modular frame installation work consists of 12 unit works, centering on module lifting and assembly module work, which are the main construction processes. And the classification system reflects the three main management factors and contents for defined safety management. It is expected that the research results of this study can contribute to efficient safety management at the modular construction site.

• Nuclear Engineering and Technology
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• v.46 no.3
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• pp.439-446
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• 2014

An amphibious inspection robot system (hereafter AIROS) is being developed to visually inspect the in-containment refueling storage water tank (hereafter IRWST) strainer in APR1400 instead of a human diver. Four IRWST strainers are located in the IRWST, which is filled with boric acid water. Each strainer has 108 sub-assembly strainer fin modules that should be inspected with the VT-3 method according to Reg. guide 1.82 and the operation manual. AIROS has 6 thrusters for submarine voyage and 4 legs for walking on the top of the strainer. An inverse kinematic algorithm was implemented in the robot controller for exact walking on the top of the IRWST strainer. The IRWST strainer has several top cross braces that are extruded on the top of the strainer, which can be obstacles of walking on the strainer, to maintain the frame of the strainer. Therefore, a robot leg should arrive at the position beside the top cross brace. For this reason, we used an image processing technique to find the top cross brace in the sole camera image. The sole camera image is processed to find the existence of the top cross brace using the cross edge detection algorithm in real time. A 5-DOF robot arm that has multiple camera modules for simultaneous inspection of both sides can penetrate narrow gaps. For intuitive presentation of inspection results and for management of inspection data, inspection images are stored in the control PC with camera angles and positions to synthesize and merge the images. The synthesized images are then mapped in a 3D CAD model of the IRWST strainer with the location information. An IRWST strainer mock-up was fabricated to teach the robot arm scanning and gaiting. It is important to arrive at the designated position for inserting the robot arm into all of the gaps. Exact position control without anchor under the water is not easy. Therefore, we designed the multi leg robot for the role of anchoring and positioning. Quadruped robot design of installing sole cameras was a new approach for the exact and stable position control on the IRWST strainer, unlike a traditional robot for underwater facility inspection. The developed robot will be practically used to enhance the efficiency and reliability of the inspection of nuclear power plant components.