• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2008년도 정기 학술대회
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• pp.39-44
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• 2008

Stress wave propagation plays an important role in many engineering problems for reducing industrial noise and vibrations. In this paper, the dispersion-corrected finite element model is proposed for reducing the dispersion error in simulation of stress wave propagation. At eliminating the numerical dispersion error arising from the numerical simulation of stress wave propagation, numerical dispersion characteristics of the wave equation based finite element model are analyzed and some dispersion control scheme are proposed. The validity of the dispersion correction techniques is demonstrated by comparing the numerical solutions obtained using the present techniques.

• 소성∙가공
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• 제26권5호
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• pp.314-322
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• 2017

In the high-speed forming analysis, dynamic material properties considering a high strain rate are required. The split Hopkinson pressure bar (SHPB) experiment was performed for measuring dynamic material properties under high strain rate. The pulse shaping method was used to improve the accuracy of the SHPB experiment. A pulse shaper attached to the front of the incident bar was used for specimen dynamic stress equilibrium through stress wave control. Numerical analysis and SHPB test were performed to verify whether the pulse shaper affects the dynamic stress equilibrium in copper and Al6061 specimens. The results of SHPB test and numerical analysis show that the pulse shaper contributes to the dynamic stress equilibrium. Based on the improved stress equilibrium using a pulse shaper, the flow stress curves for copper and Al6061 materials were obtained at strain rates of 1344.4/sec and 1291.6/sec, respectively.

• 한국산학기술학회논문지
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• 제13권5호
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• pp.2206-2211
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• 2012

아로마풋스파가 스트레스에 미치는 영향을 알아보기 위해, 스트레스를 가지고 있는 대학생 12명을 대상으로 대조군 6명, 아로마풋스파군 6명으로 나누었다. 대조군은 아무런 처치를 하지 않았으며, 아로마풋스파군은 주니퍼, 라벤더, 레몬 에센셜오일 5%를 이용한 족욕 10분과 마사지크림을 이용한 발마사지 10분을 주 2회 총 4주간 적용하였다. 평가방법은 뇌파를 검사함으로써 스트레스를 변화량을 측정하였다. 실험 전, 후의 뇌파변화를 측정한 결과, 아로마풋스파군의 Alpha파(Z=-2.364, p<.05)와 SMR파(Z=-1.981, p<.05)는 대조군에 비해 더 높은 것으로 나타났다. 또한 아로마풋스파군의 실험 전, 후의 비교에서는 Theta파(Z=-2.366, p<.05)의 수치는 감소하였고, Alpha파(Z=-2.371, p<.05)의 수치는 증가하였다. 즉, 에센셜오일을 이용한 족욕과 발마사지를 실시한 아로마풋스파는 Alpha파의 증가를 일으키고, 이는 근육의 이완으로 인한 혈액순환으로 뇌파에 변화를 주었음을 알 수 있다. 또한 SMR파가 증가함은 Alpha파의 변화와도 관계가 있음을 알 수 있는데 스트레스 완화로 인해 SMR파가 증가되었음 증명해 주고 있다. 따라서 아로마풋스파는 스트레스를 감소시키는데 효과가 있는 것으로 사료된다.

• 한국정밀공학회지
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• 제20권3호
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• pp.157-164
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• 2003

The pulse-echo method is one of the most widely used ultrasonic techniques for application of nondestructive evaluation. Particularly, quantitative nondestructive evaluation of defects has been considered more important to assure the reliability and the safety of structure. Frequency energy in adhesive joints is based on the ultrasonic wave analysis. The attenuation coefficient upon wave amplitude and the frequency energy that is expressed in the term of wave pressure amplitude were utilized for the primary wave experiment. By means of a control experiment, it was confirmed that the variation of the frequency energy in adhesive joints depends on transition by stress variation. In this paper, the ultrasonic characteristics were measured for single lap joint and Double Cantilever Beam specimen with different fracture modes that was subjected to stress. Consequently, the data that was obtained from the adhesive specimen was analytically compared to the fracture mechanics parameter

• 한국응용과학기술학회지
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• 제32권3호
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• pp.394-404
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• 2015

This study investigated the pharmacodynamics of betaine on the blood profile and short chain fatty acid levels in meat ducks exposed to heat wave. 400 heads of Cherry valley (Anasplatyrhynchos) meat ducks were completely randomized to 5 treatments (4 repetitions each), and were raised for 42 days. They were grouped into T1 (heat wave control group without betaine), T2 (betaine 400 ppm), T3 (betaine 800 ppm), T4 (betaine 1200 ppm), and T5 (normal control group without betaine). Compared to T1, the betaine addition groups showed higher body weight gain at shipment, with T3 showing the highest significant difference. For hematological indictors measured (red blood cells and platelets), the betaine addition groups showed significantly higher values than the heat wave control group. The pH of the former was lower but their electrolytes ($K^+$, $P^+$, and $Cl^-$) were significantly higher compared to the latter. For blood gas concentration, the former showed a significantly higher value than the latter. For the total short chain fatty acids, acetic acid, and propionic acid, the betaine addition groups and group fed broiler-high temperature diet showed higher values than the heat wave control group. On the other hand, the former showed significantly lower values in butyric acid, isobutyric acid, valeric acid, and isovaleric acid than the latter group. These results suggest that betaine has the pharmacodynamics that mediate heat stress, via the maintenance and control of the blood profile, osmotic pressure, gas concentration, and short chain fatty acid, of meat ducks under heat wave.

• 대한불안의학회지
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• 제18권2호
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• pp.80-91
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• 2022

Objective : Hospital workers' mental health has deteriorated because of the ongoing COVID-19 pandemic. The purpose of this study was to investigate the impact of the prolonged COVID-19 pandemic on the mental health of hospital workers and its determinants. Methods : Two surveys were conducted among employees working in a hospital that received COVID-19 patients from the early phase of the pandemic in South Korea. Data on demographics, perceived threat, workplace evaluation, resilience, and mental health status were collected using the Korean General Health Questionnaire-20 in the initial phase (February 2020) and during the third wave of COVID-19 (December 2020) for 467 and 545 workers, respectively. The mental health of hospital workers in the two phases was compared, and the risk and protective factors during the third wave were investigated. Results : The proportion of patients in the psychiatric high-risk group increased from 2.8% in the initial phase to 11.4% during the third wave. The perceived threat, workplace evaluation, and resilience of respondents deteriorated. Risk factors for mental health during the third wave included the perceived threat items of job stress, loss of control, and considering resignation. Protective factors included presence of children, workplace satisfaction, and hardiness in resilience. Conclusion : Hospital workers' mental health deteriorated as the pandemic progressed. General stress and tension such as job stress, loss of control, considering resignation rather than COVID-19-specific stress had negative effects on mental health of hospital workers. Therefore, care for work stress itself can be helpful to maintain the mental health of hospital workers. Also, governance to improve workplace satisfaction or hardiness in resilience can be a potential protective factor for hospital workers' mental health during the prolonged pandemic.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.860-864
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• 2004

This article discusses the use of pulse-echo ultrasonic testing for the stress analysis of adhesive bonds between metal sheets. The method is based on the measurement of the reflection wave at the metal/adhesive interface. After describing briefly the physical aspects of the phenomenon, an index is defined to detect defective zone of the joint(both for the lack of adhesive and for insufficient adhesion); the influence of the experimental variables(variables stress...) on the measurement is discussed. By means of a control experiment it is shown that Stress Variation in Adhesive Joints are separate to be distingguished. In this paper, Quantitative Nondestructive Evaluation in Adhesive Joints are together with Ultrasonic Testing and Finite Element Method.

• 한국아동복지학
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• 제40호
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• pp.229-253
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• 2012

본 연구는 우리나라 청소년의 학업스트레스와 자기통제의 관계에서 자아존중감의 조절효과를 검증하는데 목적이 있다. 이를 위하여 자기통제 힘 모형을 예방과학적 관점으로 조명하여 연구의 분석틀로 설정하였다. 연구문제 및 가설을 검정하고자 한국청소년패널조사(KYPS)의 중학교 2학년 패널 4차년도 자료를 활용하였으며, 일반 고등학교 2학년에 재학 중인 2,169명의 청소년을 연구참여자로 선정하였다. 분석 결과, 학업스트레스가 자기통제에 미치는 영향에 대하여 자아존중감의 조절효과가 확인되었다. 즉, 학업스트레스는 자아존중감의 수준과 상관없이 청소년의 자기통제를 저하시켰다. 그러나 자아존중감이 높은 청소년의 경우, 자아존중감이 낮은 청소년에 비해 더 높은 수준의 자기통제를 가지고 있었으며, 학업스트레스가 높은 상황에서 자아존중감이 학업스트레스가 자기통제에 미치는 부정적인 영향력을 완화시키고 있었다. 이러한 연구결과에 기반하여 함의를 논하였다.

• 한국산학기술학회논문지
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• 제22권1호
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• pp.585-594
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• 2021

본 연구는 경전 이해를 기반으로 하는 불교와 마음치유 강의에 참여한 수강생들의 스트레스가 강의를 통해 완화됨으로써 심리적 안정과 사고능력을 증진시키고, 이해력을 높이는 효과를 확인하고자 실시한 유사 실험연구이다. 스트레스는 일반적으로 자기보고식 검사를 통해 확인할 수 있으나, 본 연구에서는 보다 객관성을 확보하기 위하여 정량뇌파를 측정하여 스트레스 수준을 평가하였다. 이를 위해 서울특별시 G구에 소재한 S대학교에서 2019년 3월부터 6월까지 진행된 불교와 마음치유 강의를 수강하는 실험군과 수강하지 않는 대조군을 7명씩 표집하여 1주 차 수업 전의 사전과 15주차 수업 후의 사후 정량뇌파 차이를 Mann Whitney U검정과 Wilcoxon 부호순위검정을 통하여 검증하였다. 그 결과, 불교와 마음치유 수업을 수강하는 실험군은 대조군에 비해 Beta파, High Beta파가 높게 나타나 대조군보다 스트레스 혹은 긴장 상태에 있는 것으로 나타났다. 실험군은 Beta파의 F7, T3, T4, T5와 High Beta파의 F7, F8, T3, T4에서 유의한 차이가 발생하였고, Coherence도 좌반구 Fp1-T5, F3-P3, F3-O1, C3-O1, P3-F7, O1-F7에서 개선된 반면, 대조군은 유의한 차이가 없었다. 따라서 불교와 마음치유 강의는 스트레스 개선 효과가 있는 것으로 나타났다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.201-204
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• 2007

This paper proposes a improvement of switching converter's input wave form using VIENNA Rectifier(three-phase three-switch three-level PWM Rectifier). VIENNA Rectifier is based on the combination of a three-phase diode bridge and dc/dc boost converter. It can be available to get sinusoidal mains current, and low-blocking voltage stress on rower transistors. In addition, it can control output voltage.