• Tribology and Lubricants
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• 제35권4호
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• pp.222-228
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• 2019

As rubber products such as O-rings, which are also known as packings or toric joints, come in regular, long term contact with liquid fuel, they can eventually swell, become mechanically weakened, and occasionally crack; this diminishes both their usefulness and intrinsic lifetime and could cause leaks during the steady-state flow condition of the fuel. In this study, we evaluate the lifetime of such products through compression set tests of FKM, a family of fluorocarbon elastomer materials defined by the ASTM international standard D141; these materials have great compression, sunlight, and ozone resistance as well as a low gas absorption rate. In this process, O-rings are immersed in the liquid fuel of airtight containers that can be expressed as a compression set, and the liquid fuel leakage in a flow rig tester at variable temperatures over 12 months is investigated. Using the Power Law model, our study determined a theoretical O-ring lifetime of 2,647 years, i.e. a semi-permanent lifespan, by confirming the absence of liquid fuel leakage around the O-ring assembled fittings. These results indicate that the FKM O-rings are significantly compatible for fuel tests to evaluate long-term sealing conditions.

• Smart Structures and Systems
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• 제23권3호
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• pp.307-318
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• 2019

The frequently excessive vibrations presented in civil structures during seismic events or service conditions may result in users' discomfort, or worst, in structures failure, producing economic and even human casualties. This work contributes in proposing the synthesis of a nonlinear optimal control strategy for semiactive structural control, with the main characteristic that the synthesis considers both the structure model and the semiactive actuator nonlinear dynamics, which produces a nonlinear system that requires a nonlinear controller design. The aim is to reduce the unwanted vibrations in the response of civil structures, by means of intelligent fluid semiactive actuator such as the Magnetorheological Damper (MRD), which is a device with a low level of power consumption. The civil structures for which the proposed control methodology can be applied are those admitting a state-dependent coefficient factorized representation model, such as buildings, bridges, among others. A scaled model of a three storey building is analyzed as a case study, whose dynamical response involves displacement, velocity and acceleration of each one of the storeys, subjected to the North-South component of the September 19th., 2017, Puebla-Morelos (7.1M), Mexico earthquake. The investigation rests on comparing the structural response over time for two different conditions: with no control device installed and with one MRD installed between the first floor and the ground, where a nonlinear optimal signal for the MRD input voltage is determined. Simulation results are presented to show the effectiveness of the proposed controller for reducing the building's dynamical response.

• 미생물학회지
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• 제55권1호
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• pp.1-8
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• 2019

Due to the major role played by several species of Streptococcus in the etiology of periodontitis, it is important to assess the pattern of Streptococcus pathogenic pathways within the infected subgingival pockets using a bacterial specific 16S rRNA fragment. From the total of 50 patients with periodontitis included in the study, only 23 Streptococcal isolates were considered for further analyses, in which their 16S rRNA fragments were amplified and sequenced. Then, a comprehensive phylogenetic tree was constructed and in silico prediction was performed for the observed Streptococcal species. The phylogenetic analysis of the subgingival Streptococcal species revealed a high discrimination power of the 16S rRNA fragment to accurately identify three groups of Streptococcus on the species level, including S. salivarius (14 isolates), S. anginosus (5 isolates), and S. gordonii (4 isolates). The employment of state-of-art in silico tools indicated that each Streptococcal species group was characterized with particular transcription factors that bound exclusively with a different 16S rRNA-based secondary structure. In conclusion, the observed data of the present study provided in-depth insights into the mechanism of each Streptococcal species in its pathogenesis, which differ in each observed group, according to the differences in the 16S rRNA secondary structure it takes, and the consequent binding with its corresponding transcription factors. This study paves the way for further interventions of the in silico prediction, with the main conventional in vitro microbiota identification to present an interesting insight in terms of the gene expression pattern and the signaling pathway that each pathogenic species follows in the infected subgingival site.

• 한국정보기술학회논문지
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• 제16권12호
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• pp.57-68
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• 2018

도시철도 중 하나인 트램 건설시 노면의 상태를 지속적으로 모니터링 하여 도로의 노면 침화, 싱크 홀, 교량 붕괴 위험, 트램역 주변 온 습도 등 환경정보를 수집과 분석을 통해 재난을 예방하는 시스템이 구축되어야 한다. 본 논문에서는 무가선 트램의 노면, 교량 및 트램역의 위험요인을 사전에 인지하고 위험을 예방할 수 있는 저전력 장거리 통신망(LPWA) 기반 트램 노면의 무선통신망 안전관리 시스템을 제안한다. 제안하는 시스템은 트램 노면의 상태를 감지하는 센서 노드와 센서의 정보를 수집하는 게이트웨이 그리고 트램 노면의 안전 및 환경상황을 모니터링 하는 안전관리 시스템으로 구성되며, 저전력 장거리 통신 기술(LoRa)을 적용하였다. 현장 시험에 제안한 시스템과 LTE를 적용한 시스템을 비교 분석한 결과 모니터링 시스템에서 센서 정보 값과 위험신호 임계값 이상 시 위험 알람 상태에 큰 차이가 없음을 확인하였다.

• 융합정보논문지
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• 제9권7호
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• pp.41-47
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• 2019

본 연구는 요양보호사의 감정노동과 소진이 노인 돌봄 태도에 미치는 영향요인 파악하기 위한 서술적 조사이다. 2018년 12월 1일부터 30일까지 D시, K도에서 6개월 이상 노인 돌봄으로 근무한 요양보호사 142명으로 구조화된 설문지로 자가기입방식의 설문 조사를 시행하였다. 수집된 자료는 SPSS 21.0을 이용하여 t-test, ANOVA, Pearson 상관분석 및 다중회귀분석을 시행하였다. 본 연구결과는 요양보호사의 노인 돌봄 태도에 영향을 미치는 변수로 감정노동의 주의 정도, 건강상태, 근무형태이며, 설명력은 31%였다. 즉, 요양보호사는 노인의 행동을 그대로 이해하며 받아들여야 하는 감정표현의 주의 정도에 관한 요구가 높을수록, 자가건강상태가 좋지 않을수록, 근무형태가 불안정할수록 노인 돌봄 태도에 부정적인 영향을 미치는 것으로 확인되었다. 따라서 요양보호사의 노인 돌봄 태도를 높이기 위하여 요양보호사의 안정적인 근무 환경과 더불어 사회적 인식 개선을 위한 교육프로그램의 적용이 필요하다.

• 정보교육학회논문지
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• 제23권4호
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• pp.303-314
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• 2019

2015개정 교육과정에 의해 2019년부터 초등학교 5, 6학년을 대상으로 실과과목에서 정보교육이 진행되고 있지만, 국외에서는 초등학교 저학년부터 정보교육을 시행하는 경우가 많다. 이에 본 연구는 초등학교 저학년의 특성을 고려한 프로그래밍 언어의 선택 방향성을 제시하기 위한 목적이 있다. 목적 달성을 위해 저학년의 발달특징과 교육용 프로그래밍 언어의 필요요소를 고려하여 평가 준거를 개발하였다. 준거에 근거하여 두 언어의 사용성을 분석한 결과는 다음과 같다. 첫째, 비스킷은 학령이 낮은 학생의 표현력 고려, 프로그래밍의 개념에 대한 학습 없이 알고리즘 익히기 등에 활용할 수 있으며, 둘째, 스크래치 주니어는 알고리즘이나 프로그래밍에 대한 개념 학습에 용이한 것으로 나타났다. 본 연구는 향후, 초등학교 저학년 대상의 프로그래밍 교육을 대비하여 학생들의 발달 상태를 고려한 시사점을 제시했다는데 의의가 있다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2019년도 전력전자학술대회
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• pp.230-232
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• 2019

Light Triggerd Thyristor (LTT)는 HVDC 및 산업용 스위치 등에 사용되는 대전력 반도체소자이다. 일반적인 Thyristor가 전기적 신호에 의해 trigger 되는 것과는 다르게 LTT는 광신호에 의해 동작하는 소자이다. 본 논문에서는 5,000V, 2,200A 급의 4인치 LTT 소자의 제작 및 전기적인 특성평가 결과를 기술하였다. 4인치 LTT의 구조적인 특징은 전면부 중앙에 광신호가 주입되는 수광부가 위치해 있으며 입력 전류 증폭을 위한 4-단계 증폭 게이트 (gate) 구조를 가지도록 설계하였다. $400{\Omega}{\cdot}cm$ 비저항을 갖는 1mm 두께의 n-형 실리콘 웨이퍼에 boron 이온주입과 열처리 공정으로 약 $30{\mu}m$ 깊이의 p-base를 형성하였으며, 고내압 저지를 위한 edge termination은 VLD (variable lateral doping) 기술을 적용하였다. 제작된 4인치 LTT는 6,500 V의 순방향 항복전압 ($V_{DRM}$) 특성을 나타내었으며, 100V의 어노드전압 ($V_A$)과 20 mA의 게이트전류 ($I_G$)에 의하여 thyristor가 trigger 됨을 확인하였다. 제작한 LTT 소자는 disk형 press-pack 패키지를 진행한 후, LTT의 수광부에 $10{\mu}s$, 50 mW의 900 nm 광 펄스를 조사하여 전류 특성을 평가하였다. LTT 패키지 샘플에 60 Hz 주파수의 광 펄스를 조사한 경우 2,460 A의 순방향 평균전류 ($I_T$)와 $336A/{\mu}s$의 반복전류상승기울기 (repetitive di/dt)에 안정적으로 동작함을 확인하였다. 또한, 펄스 전류 시험의 경우 61.6 kA의 최대 통전 전류 (ITSM, surge current)와 $1,050A/{\mu}s$의 펄스전류 상승 기울기 (di/dt of on-state pulse current)에도 LTT의 손상 없이 동작함을 확인하였다.

• Nuclear Engineering and Technology
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• 제51권6호
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• pp.1696-1707
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• 2019

This paper conducts a qualitative policy analysis of current challenges to safety culture and security culture in Southeast Asia and emerging best practices in Northeast Asia that are aimed at strengthening both cultures. It analyses lessons, including strengths and limitations, that can be derived from Northeast Asian states, given the long history of nuclear energy in South Korea, China and Japan. It identifies and examines best practices from Northeast Asia's Nuclear Security Centres of Excellence in terms of boosting nuclear security culture and their relevance for Southeast Asia. The paper accentuates the important role of the State in adopting policy and regulatory frameworks and in institutionalising nuclear education and training programmes to deepen the safety-security cultures. Best practices in and challenges to developing a nuclear safety culture and a security culture in East Asia are examined using three frameworks of analysis (i) a comprehensive nuclear policy framework; (ii) a proactive and independent regulatory body; and (iii) holistic nuclear education and training programmes. The paper argues that Southeast Asian states interested in harnessing nuclear energy and/or utilising radioactive sources for non-power applications must develop a comprehensive policy framework on developing safety and security cultures, a proactive regulatory body, and holistic nuclear training programmes that cover both technical and human factors. Such measures are crucial in order to mitigate human errors that may lead to radiological accidents and nuclear security crises. Key lessons from Japan, South Korea and China such as best practices and challenges can inform policy recommendations for Southeast Asia in enhancing safety-security cultures.

• Wind and Structures
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• 제29권4호
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• pp.247-270
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• 2019

Wind-resistant design of existing cooling tower structures overlooks the impacts of rainfall. However, rainstorm will influence aerodynamic force on the tower surface directly. Under this circumstance, the structural response of the super-large cooling tower (SLCT) will become more complicated, and then the stability and safety of SLCT will receive significant impact. In this paper, surrounding wind fields of the world highest (210 m) cooling tower in Northwest China underthree typical wind velocities were simulated based on the wind-rain two-way coupling algorithm. Next, wind-rain coupling synchronous iteration calculations were conducted under 9 different wind speed-rainfall intensity combinations by adding the discrete phase model (DPM). On this basis, the influencing laws of different wind speed-rainfall intensity combinations on wind-driving rain, adhesive force of rain drops and rain pressure coefficients were discussed. The acting mechanisms of speed line, turbulence energy strength as well as running speed and trajectory of rain drops on structural surface in the wind-rain coupling field were disclosed. Moreover, the fitting formula of wind-rain coupling equivalent pressure coefficient of the cooling tower was proposed. A systematic contrast analysis on its 3D distribution pattern was carried out. Finally, coupling model of SLCT under different working conditions was constructed by combining the finite element method. Structural response, buckling stability and local stability of SLCT under different wind velocities and wind speed-rainfall intensity combinations were compared and analyzed. Major research conclusions can provide references to determine loads of similar SLCT accurately under extremely complicated working conditions.

• 대한치과기공학회지
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• 제41권3호
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• pp.221-232
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• 2019

Purpose: This experiment aims to provide the fundamental resources in developing a programme intended to prevent students from dropping out of their academics by promoting students to develop an optimistic psychological state, through analysis of the factors that influence students' commitment to their major. Methods: A self-administered questionnaire was conducted from $19^{th}$ of November of the year 2018, till $1^{st}$ of December of the same year, with dental technology students located in W city as the subject. 261(93.2%) of the participants' responses were used for the final analysis. Results: A negative association between factors of commitment to major and factors of academic dropout decision were portrayed to be of statistical significance (p<.01), and factors of commitment to major that influence dropping out of their academics were shown to be that of 'autotelic experience' (p<.001) with a negative ( - ) relationship, and 'change in a sense of time' (p<.01) with a positive ( + ) relationship of statistical significance, while the explanatory power of the model was shown to be 33.6%. Conclusion: In order to prevent dental technology students from dropping out of their academics, following their entrance, To achieve this, the department must consider the implementation of, aside from subject matters of the major, other various extra-curricular programmes, and programmes in which the supervisor is consistently providing consultations that are tailored to each individual student.