• 비파괴검사학회지
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• 제34권6호
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• pp.419-427
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• 2014

Nonlinear features of ultrasonic waves are more sensitive to the presence of a fatigue crack than their linear counterparts are. For this reason, the use of nonlinear ultrasonic techniques to detect a fatigue crack at its early stage has been widely investigated. Of the different proposed techniques, laser nonlinear wave modulation spectroscopy (LNWMS) is unique because a pulse laser is used to exert a single broadband input and a noncontact measurement can be performed. Broadband excitation causes a nonlinear source to exhibit modulation at multiple spectral peaks owing to interactions among various input frequency components. A feature called maximum sideband peak count difference (MSPCD), which is extracted from the spectral plot, measures the degree of crack-induced material nonlinearity. First, the ratios of spectral peaks whose amplitudes are above a moving threshold to the total number of peaks are computed for spectral signals obtained from the pristine and the current state of a target structure. Then, the difference of these ratios are computed as a function of the moving threshold. Finally, the MSPCD is defined as the maximum difference between these ratios. The basic premise is that the MSPCD will increase as the nonlinearity of the material increases. This technique has been used successfully for localizing fatigue cracks in metallic plates.

• 한국통신학회논문지
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• 제38C권11호
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• pp.990-999
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• 2013

기존의 연구들에서 이론적 근거를 바탕으로 3D 영상 시청에 대해 시각피로도와 연관이 있는 요소와 영향을 주는 요소들에 대해 경험적 데이터를 기반하여 지속적으로 밝혀내고 있다. 하지만, 이러한 영향을 미치는 요소와 맞물려 실제로 시청자가 느끼는 피로감과 연계하여 측정된 자료는 미비한 상태이다. 본 연구에서는 시청자가 느끼는 자각적 피로도에 따른 시기능적 데이터인 IPD, AC/A비, 그리고 사위도와 그 변화량에 미치는 영향 및 상관관계를 알아보고자 하였다. 자각적 피로도의 기술통계량 점수 $6.00{\pm}3.88$점에 기초하여 피로도 점수 합계 0 ~ 6점을 피로 미호소 그룹, 7 ~ 16점을 피로 호소 그룹으로 분류하였다. 실험 결과 자각적 피로도별 영상 만족도, IPD, 원거리 사위도에서는 차이를 나타내지 않았다. 피로 미호소 그룹에서 AC/A비가 높게 나타났고, 피로 호소 그룹에서는 근거리 사위도가 높게 나타났다. 3D 영상 시청 이후에서는 피로 미호소 그룹에서 더 높은 외사위도 증가 경향을 나타냈다. 본 실험에서 나타난 상관관계에서 AC/A비와 근거리 사위도가 3D 영상 시청 시 느끼는 자각적 피로도와 밀접한 관련이 있는 것으로 나타났다. 3D 영상 시청 시 두 데이터에 기반하여 피로도를 예측할 수 있을 것으로 보이며 콘텐츠 제작 시에도 피로도 경감 차원의 주요한 근거 데이터로 사용될 것으로 판단된다.

• 한국운동역학회지
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• 제22권3호
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• pp.349-356
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• 2012

This study aimed to assess the effects of progressive lumbar stability exercises and lumbar stability exercises on changes in the transversus abdominis muscle thickness and lower extremity muscle fatigue index in soccer players. Ten subjects were assigned to undergo training in each of the 2 groups, namely, the progressive lumbar stability exercise group and lumbar stability exercise group. Each intervention session lasted for 30 min, and 4 sessions were conducted in a week for 6 weeks for soccer players of S. University in Jeonnam, Korea. Changes in the transversus abdominis muscle thickness and lower extremity muscle fatigue index were measured using ultrasound and surface electromyogram. The results of the ultrasound measurement for the transversus abdominis muscle thickness indicated that progressive lumbar stability exercises were more effective than lumbar stability exercises. The results of the lower extremity muscle fatigue index measurements using surface electromyogram indicated that the fatigue index decreased in the progressive lumbar stability exercise group. Progressive lumbar stability exercise is believed to have put more workload during the shaking of the limbs, leading to increased stability and increased efficiency of the lower extremity muscle, thereby decreasing the fatigue index. Therefore, progressive lumbar stability exercises can be an effective measure for preventing injuries and improving the game performance of sports players by increasing the transversus abdominis muscle thickness and decreasing the lower extremity muscle fatigue index.

• 한국정보시스템학회지:정보시스템연구
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• 제26권4호
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• pp.39-62
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• 2017

Purpose The purpose of this study is to investigate the factors which affect users' fatigue and reluctant intention of using a SNS. In particular, this study focused on the fatigue of SNS users, as the recent excessive use of SNS has led to negative effects such as invasion of privacy, addition and social overload. fatigue This research will explain how producing adverse effects by using SNS caused psychological and mental depression. Previous researches explained that mental fatigue associated with SNS is not simple one and it is complicated with various psychological factors. Considering this fact, this study introduced a behavioral economics concept and a social comparison theory in the research model. Design/methodology/approach For research purposes, this study developed research hypotheses in order to empirically examine the factors that affect SNS users' fatigue and reluctant intention. The empirical research was based on a poll done through 800 research candidates in the SNS fields and the final 451 responses were collected and used in statistical data analysis. The adaptability, trust, and validity to measurement model were verified and the structural relationship in the research model was analyzed through these 451 responses. Findings First of all, maintenance fatigue of SNS had a positive significant effect on coupling and fatigue of SNS and information privacy had a non-significant effect on fatigue. Second, coupling had a negative significant effect on rational inattention, however, perceived cost had a non-significant effect on rational inattention. Third, lateral/upward comparison had a positive significant on user's negative emotions. Meanwhile, user's negative emotions did not have a significant effect on rational inattention.

• 대한토목학회논문집
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• 제8권2호
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• pp.167-175
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• 1988

본 연구의 목적은 변동하중을 받는 구조부재의 피로거동을 해석하는 것이다. 이 연구의 해석과정은 다음과 같다. (1) 도로교의 실동응력파측정 및 통계적해석 (2) 등가의 일정진폭하중과, 통계적해석에 의해 모형화된 변동하중하(下)의 피로시험 (3) 등가응력개념의 RMC 모델에 의한 변동하중하(下)의 피로해석 등가응력개념에 의한 변동하중하(下)의 피로해석은 대부분의 구조용강재의 균열성장속도회귀지수가 $m{\fallingdotseq}3$이므로 이론적으로 RMC 모델이 합당하다. 변동하중하(下)의 피로시험해석결과 RMC 모델이 기존의 RMC 모델보다 변동하중에 의한 피로거동치(da/dN-${\Delta}K$, $N_f$)에 더 가까웠다. 또 변동하중하(下)에서 응력범위의 변화로 인한 interaction효과나 응력범위적용순서(sequence)효과 등은 피로수명에 거의 영향을 미치지 않으며, 응력범위변화속도가 클수록 피로균열성장속도가 빨라짐을 알 수 있었다.

• 열처리공학회지
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• 제9권1호
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• pp.69-77
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• 1996

The fatigue crack initiation behavior of plasma ion nitrided SACM645 steel was investigated through the rotary bending fatigue test and residual stress measurement by XRD. It was shown by XRD and EPMA that the plasma ion nitrided surface was composed of ${\gamma}^{\prime}(Fe_4N)$phase and ${\varepsilon}(Fe_{2-3}N)$phase, and that the nitrogen atoms existed in Fe matrix in diffusion layer. The OM, SEM and Auger spectroscopy showed that the depth of compound layer, mixed compound and diffusion layer, and diffusion layer was $8{\mu}m$, $30{\mu}m$ and $300{\mu}m$, respectively. However, the microhardness test showed that the depth of hardened layer was $500{\mu}m$. The tensile strength of the ion nitrided SACM645 was lower than that of the unnitrided SACM645, and the ion nitrided specimen was fractured without plastic deformation. The nitrided SACM645 showed much poorer low cycle fatigue properties than the unnitrided one. In rotary bending fatigue, the fatigue strength of the ion nitrided SACM645 was higher than that of the unnitrided specimen, and the fatigue crack initiation sites changed by applied fatigue stress levels. The XRD result showed that the ion nitrided SACM645 has the compressive residual stress from surface to $600{\mu}m$ deep and the tensile residual stress from $600{\mu}m$ to deeper site. It is thought that crack initiation takes place at the point where the total stress of residual stress and applied stress is maximum.

• 한국의류산업학회지
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• 제25권2호
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• pp.185-198
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• 2023

The purpose of this study is to obtain information necessary for the development of patient clothes that can reduce physical fatigue of caregivers by quantitatively measuring the muscle load and fatigue. The patient clothes used in this study can be broken down into three types: A type (back center zipper open suit), B type (top-to bottom separated patient clothes), and C type (front zipper open suit). The EMG measurement sites are as follows: hand muscle (brachioradialis), upper arm (biceps, triceps), shoulder (anterior deltoid, medial deltoid, posterior deltoid, upper trapezius), and waist (erector spinae); additionally, the EMG signals were measured. Through this experiment, muscle load, muscle energy consumption, and muscle fatigue generation tendency were analyzed. The results of the study revealed that the C type patient clothes required the most strength in the muscles of the shoulders, upper arms, hands, and back when being put on and taken off compared to other patient clothes. The A type clothes required a relatively large force in opening the zipper. In terms of muscle energy consumption, B type generally called for more strength when it came to the zip-up and putarmsup motions. With regard to the cover the body and put legs/hips up motions, C type used the highest amount of muscle energy, whereas A type used relatively little energy. In terms of the occurrence of muscle fatigue during the putting on and taking off of the patient's clothing, there was a difference in the area and degree of muscle fatigue in the A, B, and C types, and there was also a tendency for muscle fatigue to occur when performing repetitive movements.

• 제어로봇시스템학회논문지
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• 제13권3호
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• pp.218-223
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• 2007

The dissipation of high-power ultrasonic energy at the faces of the defect causes an increase in temperature. It is resulted from localized selective heating in the vicinity of cracks because of the friction effect. In this paper the measurement of size and direction of crack using UET(Ultrasound Excitation Thermography) is described. The ultrasonic pulse energy is injected into the sample in one side. The hot spot, which is a small area around the crack tip and heated up highly, is observed. The hot spot, which is estimated as the starting point of the crack, is seen in the nearest position from the ultrasonic excitation point. Another ultrasonic pulse energy is injected into the sample in the opposite side. The hot spot, the ending point of the crack, is seen in the closest distance from the injection point also. From the calculation of the coordinates of both the first hot spot and the second hot spot observed, the size and slope of the crack is estimated. In the experiment of STS fatigue crack specimen(thickness 14mm), the size and the direction of the crack was measured.

• 한국소음진동공학회논문집
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• 제21권8호
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• pp.708-713
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• 2011

U.S. nuclear regulatory commission(NRC) regulatory guide(RG) 1.20 requires a comprehensive vibration assessment program(CVAP) for use in verifying the structural integrity of reactor vessel internals(RVI) for flow-induced vibrations prior to commercial operation. The CVAP program consist of vibration and fatigue analysis, a vibration measurement program, an inspection program, and a correlation of their results. One of the main purposes of the analysis program is to select measurement locations, however measurement locations can not be determined by only analysis results, therefore we developed selection criteria of measurement locations for advanced power reactor 1400(APR1400) RVI CVAP, It will be used to select measurement locations and instrument types for APR1400 RVI CVAP.

• 방송공학회논문지
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• 제19권2호
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• pp.215-226
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• 2014

3D 기술은 초기의 붐 이후 점차 느리게 확산되고 있다. 그 원인 중 하나로 현재 3D 입체 영상을 시청할 수 있는 디스플레이가 주로 안경을 사용하며 그 때문에 사용 환경이 제한적이라는 점을 들 수 있다. 이런 측면에서 본 연구에서는 기존에 주로 연구되었던 안경식 디스플레이가 아닌 휴대용 무안경식 3D 디스플레이를 대상으로 기존에 잘 연구되지 않았던 지각적 크로스톡과 입체 시각 피로를 측정하고 그 결과를 모형화 하였다. 그 결과 휴대용 무안경식 3D 디스플레이의 수평 위치에 따라 지각되는 크로스톡이 체계적으로 변화한다는 것을 확인하였다. 측정된 크로스톡은 화면 중심부에서 상대적으로 낮았으나 좌/우측으로 이동함에 따라 급격하게 증가하는 현상을 보였으며, 이런 변화 경향성은 입체 시각 피로 및 불편감 측정 과정에서도 나타났다. 본 연구의 결과는 무안경식 디스플레이를 설계하고 평가하는 과정에서 지각적 요소를 고려하는 것이 필요함을 시사한다.