• 한국융합학회논문지
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• 제10권2호
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• pp.7-11
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• 2019

급격한 전파를 이용하는 기기의 다양화와 대중화로 인해 많은 전파 관련 보안 문제들이 일어나고 있다. 일상적인 생활에서의 전파의 안전은 매우 밀접한데 전파의 방해와 교란은 단순 생활의 불편뿐 아니라 신체의 직접적인 피해를 입힐 수도 있기 때문에 전파보호는 매우 중요한 과제이다. 본 논문에서는 전파 교란과 교섭을 막기 위한 방안으로 백색광 광원, 투영격자와 광원으로 영사식 무아레를 측정 하여 기준격자 및 변형격자의 영사 이미지를 획득한 후 위상도를 알고리즘에 적용하여 화상처리 알고리즘으로 무아레 무늬를 생성하고 무늬 위상도를 3차원 형상도로 생성한다. 이렇게 측정된 얼굴 형상을 이용한 암호화된 토큰을 만들어 토큰링을 통한 정보의 수신여부를 결정 하여 인증 강도, 호출자의 정보 등이 포함된 동적 보안 속성을 가진 수평 전파를 전송하고 java직렬화와 직렬화 해제 기능을 이용하여 토큰의 고유성을 확인 수평전파를 송 수신 하여 문제점을 해결하는 기법을 제안하였다.

• Smart Structures and Systems
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• 제23권2호
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• pp.141-153
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• 2019

This research deals with wave propagation of the functionally graded (FG) nano-beams based on the nonlocal elasticity theory considering surface and flexoelectric effects. The FG nano-beam is resting in Winkler-Pasternak foundation. It is assumed that the material properties of the nano-beam changes continuously along the thickness direction according to simple power-law form. In order to include coupling of strain gradients and electrical polarizations in governing equations of motion, the nonlocal non-classical nano-beam model containg flexoelectric effect is used. Also, the effects of surface elasticity, dielectricity and piezoelectricity as well as bulk flexoelectricity are all taken into consideration. The governing equations of motion are derived using Hamilton principle based on first shear deformation beam theory (FSDBT) and also considering residual surface stresses. The analytical method is used to calculate phase velocity of wave propagation in FG nano-beam as well as cut-off frequency. After verification with validated reference, comprehensive numerical results are presented to investigate the influence of important parameters such as flexoelectric coefficients of the surface, bulk and residual surface stresses, Winkler and shear coefficients of foundation, power gradient index of FG material, and geometric dimensions on the wave propagation characteristics of FG nano-beam. The numerical results indicate that considering surface effects/flexoelectric property caused phase velocity increases/decreases in low wave number range, respectively. The influences of aforementioned parameters on the occurrence cut-off frequency point are very small.

• Metals and materials international
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• 제24권6호
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• pp.1262-1274
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• 2018

The inhibition of gravity segregation has been a long-standing challenge in fabrication and applications of homogeneous immiscible alloys. Therefore, the effect of rare-earth La on the gravity segregation of Al-Bi immiscible alloys was investigated to understand the homogenization mechanism. The results showed that the addition of La can completely suppress the gravity segregation. This is attributed to the nucleation of Bi-rich liquid phase on the in-situ produced $LaBi_2$ phase and the change of the shape of $LaBi_2@Bi$ droplets. In addition, a novel strategy is developed to prepare the homogeneous immiscible alloys through the addition of rare-earth elements. This strategy not only is applicable to other immiscible alloys, but also is conducive to finding more elements to suppress the gravity segregation. This study provided a useful reference for the fabrication of the homogeneous immiscible alloys.

• 한국항행학회논문지
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• 제22권2호
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• pp.57-63
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• 2018

항공기 발사용 유도무기는 자체점검시험(BIT; built in test) 뿐만 아니라 MIL-STD-1760표준을 준수하여 전원, 이산신호, MUX(multiplexer)통신 등 다양한 시험을 수행해야 시스템 안전성 및 신뢰성이 입증된다. 본 사례 연구 목적은 MIL-STD-1760E 기반 항공기-무장간 연동용 테스트 벤치 구축을 통하여 공대지 유도탄 개발 시 유도탄 전원인가부터 표적정보 입력, 전달정렬, 유도탄 분리 절차에 이르기까지 정의된 TIME LINE에 의거 유도탄 발사 시퀀스 구현 방안을 제시하기 위함이고, 추가적으로 오류삽입기능을 통해 비 활성탄에서 시험할 수 없는 항목까지 검증 범위를 극대화하는 참조 방안이 될 수 있다.

• 한국정보통신학회논문지
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• 제25권5호
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• pp.677-684
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• 2021

본 논문은 절대 시간 측정 가능한 시간 디지털 변환기에 대한 논문으로 제안하는 시간 디지털 변환기는 0.18-um CMOS 공정을 이용하여 설계 되었고 IC로 제작하여 검증하였다. 설계된 시간 디지털 변환기는 라이다 시스템에 적용하기 위하여 긴 측정시간과 절대적인 50ps를 측정할 수 있어야하는데 위상고정루프의 625MHz 클록을 기준클록으로 사용하기 때문에 절대시간의 측정이 가능하며 디지털 보정회로를 이용하여 어떤 상황에서 든 50ps의 분해능을 가질 수 있다. 기준클록을 카운터하여 큰 시간 단위의 측정을 할 수 있어 최대 800ns의 시간이 측정가능하고 딜레이 체인을 이용하여 정밀한 시간 값을 측정 할 수 있다. 결과적으로 제작된 시간 디지털 변환기는 50ps 단위로 시간을 측정할 수 있는데 최대 오차는 INL 0.8-LSB정도이며 1.8V 인가전압에 전력 소모는 약 70mW 정도이다.

• 한국기록관리학회지
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• 제23권1호
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• pp.47-61
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• 2023

본 연구에서는 대구 근현대 출판문화를 기록화하여 보존, 이용할 수 있는 기반을 마련하기 위한 도큐멘테이션 전략의 방향성을 제시하고자 하였다. 이를 위해 Hackman의 실행모델 중 도큐멘테이션 '영역의 정의와 예비분석 단계'를 적용하였다. 예비분석 단계에서는 특정 주제를 기록화한 사례를 조사하고 대구 출판문화 기록화 관계자(연구자, 현장관계자, 기록관리요원)를 대상으로 면담을 실시하였다. 조사 내용은 국내 사례와 해외 사례를 '수집영역', '참여집단', '수집방법'으로 나누어 분석하였고, 면담 내용은 '대구 근현대 출판문화의 가치', '수집 대상과 방법', '도큐멘테이션 집단','어려움과 한계점'으로 구분하여 제시하였다. 이를 기반으로 도큐멘테이션 전략 요소를 제안한 뒤, 기록관리 전문요원의 의견을 수렴하여 이를 수정, 보완하였다. 전략 요소는 도큐멘테이션 목적, 시기적·지리적·형태적 영역, 집단별 역할, 참고정보원, 선행작업과 수집 및 운영의 주요 고려사항으로 구성하였다. 본 연구에서 실시한 예비분석이 대구의 출판문화를 보존하고 전승하는 기초자료가 되길 기대한다.

• 공학교육연구
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• 제26권6호
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• pp.19-29
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• 2023

This study aims to develop and apply a metaverse-based instructional design model for the education in science and technology. It analyzed the concept and characteristics of metaverse, existing non-contact education models, and major teaching strategies systematically. Based on the prior researches, an instructional design model using metaverse is developed that presents metaverse-related teaching strategies and design principles for the before-, during-, and after-lesson phases. Then, this model was applied to a project-based learning program, conducted a perception survey on instructors and learners, and revised the metaverse instructional design model based on the results of the survey. In the Metaverse Instructional Design Model, before-lesson phase is a physical and psychological preparation stage for class participation, which includes familiarization with the Metaverse learning environment, formation of expectations for education, and self-directed pre-learning. During the lesson, to effectively deliver the lesson content, it is necessary to build confidence in the learning environment, promote learning participation, provide reference materials, perform team projects and provide feedback, digest learning content, and transfer learning content. The after-lesson phase provides strategies for ongoing interaction between learners and mentors. This study introduces a new instructional design model that utilizes metaverse and shows the potential of metaverse-based education in science and technology. It also has important implications in that it provides practical guidelines for the effective design and implementation of metaverse-based education.

• 한국재료학회지
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• 제34권6호
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• pp.283-290
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• 2024

The aggressive scaling of dynamic random-access memory capacitors has increased the need to maintain high capacitance despite the limited physical thickness of electrodes and dielectrics. This makes it essential to use high-k dielectric materials. TiO₂ has a large dielectric constant, ranging from 30~75 in the anatase phase to 90~170 in rutile phase. However, it has significant leakage current due to low energy barriers for electron conduction, which is a critical drawback. Suppressing the leakage current while scaling to achieve an equivalent oxide thickness (EOT) below 0.5 nm is necessary to control the influence of interlayers on capacitor performance. For this, Pt and Ru, with their high work function, can be used instead of a conventional TiN substrate to increase the Schottky barrier height. Additionally, forming rutile-TiO₂ on RuO₂ with excellent lattice compatibility by epitaxial growth can minimize leakage current. Furthermore, plasma-enhanced atomic layer deposition (PEALD) can be used to deposit a uniform thin film with high density and low defects at low temperatures, to reduce the impact of interfacial reactions on electrical properties at high temperatures. In this study, TiO₂ was deposited using PEALD, using substrates of Pt and Ru treated with rapid thermal annealing at 500 and 600 ℃, to compare structural, chemical, and electrical characteristics with reference to a TiN substrate. As a result, leakage current was suppressed to around 10^-6 A/cm² at 1 V, and an EOT at the 0.5 nm level was achieved.

• Advances in materials Research
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• 제13권3호
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• pp.161-171
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• 2024

This study aimed to investigate the effect of physicochemical properties and mix ratios of iron ore (oxide feed): coke (reductant) on the carbothermic reductions of iron ore. Coke size was fixed at ≤63 ㎛ while iron ore size varied between 150-63 ㎛ and ≤63 ㎛ respectively. Mix ratios were changed from 100:0 (reference) to 80:20 and 60:40 while the temperature, heating rate and soaking duration in muffle furnace were fixed at 1100 ℃, 10 ℃/min and 1 hour. Particle size analyzer, XRF, CHNS and XRD analyses were used for determination of raw feed characteristics. The occurrence of phase transformations from various forms of iron oxides to iron during the carbothermal reductions were identified through XRD profiles and supported with weight loss (%). XRF analysis proved that iron ore is of high grade with 93.4% of Fe₂O₃ content. Other oxides present in minor amounts are 2% Al₂O₃ and 1.8% SiO₂ with negligible amounts of other compounds such as MnO, K₂O and CuO. Composite pellet with finer size iron particles (≤63 ㎛) and higher carbon content of 60:40 exhibited 45.13% weight lost compared to 32.30% and 3.88% respectively for 80:20 and 100:0 ratios. It is evident that reduction reactions can only occur with the presence of coke, the carbon supply. The small weight loss of 3.88% at 100:0 ratio occurs due to the removal of moisture and volatiles and oxidations of iron ore. Higher carbon supply at 60:40 leads into better heat and mass transfer and diffusivity during carbothermic reductions. Overall, finer particle size and higher carbon supply improves reactivity and gas-solid interactions resulting in increased reductions and phase transformations.

• Korean Journal of Radiology
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• 제20권1호
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• pp.102-113
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• 2019

Objective: To assess the accuracy and potential bias of computed tomography (CT) ventricular volumetry using semiautomatic three-dimensional (3D) threshold-based segmentation in repaired tetralogy of Fallot, and to compare them to those of two-dimensional (2D) magnetic resonance imaging (MRI). Materials and Methods: This retrospective study evaluated 32 patients with repaired tetralogy of Fallot who had undergone both cardiac CT and MRI within 3 years. For ventricular volumetry, semiautomatic 3D threshold-based segmentation was used in CT, while a manual simplified contouring 2D method was used in MRI. The indexed ventricular volumes were compared between CT and MRI. The indexed ventricular stroke volumes were compared with the indexed arterial stroke volumes measured using phase-contrast MRI. The mean differences and degrees of agreement in the indexed ventricular and stroke volumes were evaluated using Bland-Altman analysis. Results: The indexed end-systolic (ES) volumes showed no significant difference between CT and MRI (p > 0.05), while the indexed end-diastolic (ED) volumes were significantly larger on CT than on MRI (93.6 ± 17.5 mL/m² vs. 87.3 ± 15.5 mL/m² for the left ventricle [p < 0.001] and 177.2 ± 39.5 mL/m² vs. 161.7 ± 33.1 mL/m² for the right ventricle [p < 0.001], respectively). The mean differences between CT and MRI were smaller for the indexed ES volumes (2.0-2.5 mL/m²) than for the indexed ED volumes (6.3-15.5 mL/m²). CT overestimated the stroke volumes by 14-16%. With phase-contrast MRI as a reference, CT (7.2-14.3 mL/m²) showed greater mean differences in the indexed stroke volumes than did MRI (0.8-3.3 mL/m²; p < 0.005). Conclusion: Compared to 2D MRI, CT ventricular volumetry using semiautomatic 3D threshold-based segmentation provides comparable ES volumes, but overestimates the ED and stroke volumes in patients with repaired tetralogy of Fallot.