• Smart Structures and Systems
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• 제18권6호
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• pp.1125-1143
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• 2016

Forced vibration analysis of a simple supported viscoelastic nanobeam is studied based on modified couple stress theory (MCST). The nanobeam is excited by a transverse triangular force impulse modulated by a harmonic motion. The elastic medium is considered as Winkler-Pasternak elastic foundation.The damping effect is considered by using the Kelvin-Voigt viscoelastic model. The inclusion of an additional material parameter enables the new beam model to capture the size effect. The new non-classical beam model reduces to the classical beam model when the length scale parameter is set to zero. The considered problem is investigated within the Timoshenko beam theory by using finite element method. The effects of the transverse shear deformation and rotary inertia are included according to the Timoshenko beam theory. The obtained system of differential equations is reduced to a linear algebraic equation system and solved in the time domain by using Newmark average acceleration method. Numerical results are presented to investigate the influences the material length scale parameter, the parameter of the elastic medium and aspect ratio on the dynamic response of the nanobeam. Also, the difference between the classical beam theory (CBT) and modified couple stress theory is investigated for forced vibration responses of nanobeams.

• Geomechanics and Engineering
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• 제30권1호
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• pp.27-44
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• 2022

Gravelly soil is a kind of special geotechnical material, which is widely used in the subgrade engineering of railway, highway and airport. Its mechanical properties are very complex, and will greatly influence the stability of subgrade engineering. To investigate the mechanical properties and failure mechanism of gravelly soils, this paper introduced and verified a new discrete element method (DEM) of gravelly soils in large scale direct shear test, which considers the actual shape and broken characteristics of gravels. Then, the stress and strain characteristics, particle interaction, particle contact force, crack development and energy conversion in gravelly soils during the shear process were analyzed using this method. Moreover, the effects of gravel content (GC) on the mechanical properties and failure characteristics were discussed. The results reveal that as GC increases, the shear stress becomes more fluctuating, the peak shear stress increases, the volumetric strain tends to dilate, the average particle contact force increases, the cumulative number of cracks increases, and the shear failure plane becomes coarser. Higher GC will change the friction angle with a trend of "stability", "increase", and "stability". Differently, it affects the cohesion with a law of "increase", "stability" and "increase".

• 한국식품영양학회지
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• 제30권4호
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• pp.759-770
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• 2017

Stress has been associated with poor eating behavior and diet quality. Yet, the relationship between nutrient and food intake and perceived stress in Korean female adults has not been validated. The purpose of this study is to identify the relationship between nutrient and food intake and perceived stress in Korean female adults. This is a cross-sectional study based on the 2014-2015 Korean National Health and Nutritional Examination Survey data. This study investigated 2,010 female adults age 19~64. In this study, according to subjects' perceived stress, we classified subjects into very low-stress recognition group (VLSRG) (n=211), low-stress recognition group (VSRG) (n=1,223), high-stress recognition group (HSRG) (n=488) and very high-stress recognition group (VHSRG) (n=88). Daily nutrients and food group intake, food groups consumed (Dietary Diversity Score, DDS) were analyzed using data from the 24-recall method. The VHSRG had a larger proportion of subjects that were younger (p<0.0001), single (p<0.0001) and smokers (p<0.0001) compared to the VLSRG. Energy and food intake did not differ between the four groups. Percentage of subjects with protein (p=0.0322), vitamin A (p=0.0364) and vitamin C (p=0.0115) intake lower than the EAR (estimated average requirement) in the VHSRG were significantly lowest in the four groups. Also, food intake percentage from fruits and seaweed groups in the VHSRG were lower than other groups (p=0.0034, p=0.0015). DDS in the VHSRG (3.87) was significantly lowest in the four groups (p=0.0022). Results suggest that perceived stress in Korean female adults may by significant to consider in nutritional education programs.

• 한국터널지하공간학회 논문집
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• 제15권6호
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• pp.547-557
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• 2013

전단응력에 의한 전단강도 및 모드 II 파괴인성은 이산화탄소 지중저장에서의 덮개암 및 주입층의 안정성 평가에 활용되는 중요한 인자들이다. 본 연구에서는 짧은 보 압축시험을 이용하여 코코니노 사암의 전단강도 및 모드 II 파괴인성을 측정하였다. 측정된 평균 전단강도는 23.53 MPa이며, 모드 II 파괴인성은 1.58 MPa${\surd}$m이다. 응력확대계수(stress intensity factor)는 변위외삽법(displacement extrapolation method)을 이용한 유한요소법으로 결정하였다. 또한 이축응력(biaxial stress)과 수분포화(water saturation)가 모드 II 파괴인성에 미치는 영향을 분석하였다. 그 결과 이축응력이 증가할수록 파괴인성도 증가하였고, 완전포화된 시험편의 파괴인성은 건조상태의 파괴인성보다 대략 11.4% 감소하였다.

• Steel and Composite Structures
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• 제33권4호
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• pp.489-507
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• 2019

In order to obtain high bearing capacity and good ductility simultaneously, a structural column with hybrid normal and high strength steel (HNHSS) welded box section has been developed. Residual stress is an important factor that can influence the behaviour of a structural member in steel structures. Accordingly, the magnitudes and distributions of residual stresses in HNHSS welded box sections were investigated experimentally using the sectioning method. In this study, the following four box sections were tested: one normal strength steel (NSS) section, one high strength steel (HSS) section, and two HNHSS sections. Based on the experimental data from previous studies and the test results of this study, the effects of the width-to-thickness ratio of plate, yield strength of plate, and the plate thickness of the residual stresses of welded box sections were investigated in detail. A unified residual stress model for NSS, HSS and HNHSS welded box sections was proposed, and the corresponding simplified prediction equations for the maximum tensile residual stress ratio (${\sigma}_{rt}/f_y$) and average compressive residual stress ratio (${\sigma}_{rc}/f_y$) in the model were quantitatively established. The predicted magnitudes and distributions of residual stresses for four tested sections in this study by using the proposed residual stress model were compared with the experimental results, and the feasibility of this proposed model was shown to be in good agreement.

• Restorative Dentistry and Endodontics
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• 제33권5호
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• pp.457-462
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• 2008

중합수축이 일어난 후 복합 레진 내에는 중합수축에서 기원한 응력이 내부에 남아있을 수 있는데 이를 "잔류응력"이라 한다. 수복물에 가해지는 총힘은 외부에서 가해지는 힘과 내부에 남아있는 응력의 합으로 결정이 되며 수복물의 실패를 이해하기 위해서 이 두 가지 요소가 반드시 고려되어야 한다. 본 연구에서는 ring slitting방법을 이용하여 최근 임상에 소개된 나노충진형 복합레진간의 잔류응력을 비교하였다. 실험에 사용한 복합레진은 대조군으로 microhybrid-type인 Z250과 nanofiller를 함유한 Grandio, Filtek Supreme, Ceram-X를 이용하여 복합레진 링을 제작하고 2개의 기준점을 표시한 후 이 사이의 거리를 링 절단 전과 후에 각각 측정하여 거리 변화를 측정하였다. 거리의 변화로부터 average circumferential residual stress $({\sigma}{\theta})$를 계산하였다. 10분과 1시간 경과 후 측정한 군에서는 Filtek Supreme이 Z250이나 Ceram-X보다 높은 잔류응력을 보여 주었고, 24시간 경과한 군에서는 Filtek Supreme이 나머지 군보다 높은 잔류응력을 보여주었다. 본 실험 결과에 의하면 nanofiller를 함유한 복합레진의 잔류응력은 대조군으로 사용한 Z250보다 높거나 같은 값을 나타냈으며 거의 비슷한 기질조성을 가진 Z250과 Filtek Supreme을 비교했을 때 Filtek supreme이 모든 측정시간대에서 높은 잔류응력을 보여주었다.

• 한국자연치유학회지
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• 제10권1호
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• pp.10-18
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• 2021

목적: 본 연구의 목적은 새로 개발한 '전인 치유 프로그램'을 행복힐링모임을 통해 수행한 대상자 62명의 스트레스 변화'에 대한 연구를 하는 것이었다. 방법: 전인치유 프로그램을 행복힐링모임에 주당 1회(90분)씩 6회기를 수행하였고, 회기 및단 계별내용을 기록하였다. 결과: 일반인에게 적용할 수 있도록 개발한 전인치유프로그램은 회기별로 '도입-전개-마무리'의 세부적 3단계로 구성되었다. 전인치유요법으로 행복힐링모임 수행 후에 스트레스에 미치는 요인은 사전 평균치에 비해 사후의 평균치는 26.371점으로 유의성이 있게 감소하였다(p < .000). 사회심리적 스트레스의 변화는 사전에서는 34.306점, 사후에는 9.096점으로유의하게감소하였다. 스트레스 대처방식의 변화는 사전에 비해서사후에는 201.661점으로 유의하게 높게 나타났다. 기분 상태 변화는 사전에는 69.451점이었고사후에는 123.983점으로 높게 증가하여 유의한 차이를 보이었다(p < .000). 결론: 전인치유 프로그램을 행복힐링모임에 적용한 대상자에게서는 일반 또는 사회적심리적 스트레스에는 유의하게 감소하였고, 스트레스 대처방식과 기분상태의 변화는 높게 증가하는 경향을 보이었다. 이 결과로 평가할 때에 새 전인 치유요법이 행복힐링모임에 매우 유용한 자연치유적 요법 중의 하나라고 판단되었다.

• 한국응급구조학회지
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• 제13권3호
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• pp.91-105
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• 2009

Purpose : The purpose of this study was to describe the current status of 119 EMT to violence experiences in Korea. Method : The number of 119 EMT in this study 2522. Self-administering questionnaire data were collected from April 27 to March 8 in 2009. Collected data were analyzed using SPSS 14.0 program. Real number, percentage, mean and standard deviation were calculated. Pearson correlation coefficient was analyzed. Result : 119 EMTs experienced 95.32%-verbal insults, 61.54%-violence aggression, 60.51%- potential violence, 38.70%-physical assault. Within 30 days from the most recent period of violence experienced verbal insults and violence aggression-51.07%, potential violence and physical assault-48.41%. The patients(50.59%) and the patients and patient's carers(38.26%) proved to be violent offender. The main reason of violent act was drug or alcohol addiction(56.15%). Recent exposure to violence was 34.82% by 7 point reward of stress level. 5-point scale showed the average of experiences of violence. Response average of emotional reactions was 2.66 points and that of physical reaction was 2.18 points. Social reaction was 2.06 points. Conclusion : This study was based on the violence experience of 119 EMT. It is necessary to prevent the violence from emergency scene. So we proposed the preventive measure against violence as well as critical incident stress debriefing(CISD). Policy for CISD and stress management will be implemented in the near future in Korea.

• 대한족부족관절학회지
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• 제8권1호
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• pp.81-85
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• 2004

Purpose: The purpose of this study is to evaluate the surgical results of modified $Brostr{\ddot{o}}m$ procedure for chronic lateral ankle instability and to assess whether or not associated injuries may affect postoperative satisfaction. Materials and Methods: Twenty- four patients with chronic lateral ankle instability were evaluated retrospectively from August 1998 to March 2002. Average age was 29.3 years. All patients were performed pre & postoperative ankle anteroposterior and lateral view, stress anterior drawer and varus test using Telos device, MRI and intraoperative arthroscopic evaluations before ligament reconstruction. Results: Of the 24 cases, 23 cases was improved more than average 12 points on AOFAS scales. On modified scales of Hamilton, 3 excellent, 20 good, 1 fair results. On stress view, average 2.2 mm difference was improved on anterior drawer test and average 1.7 degree on varus test. Associated injuries were 8 osteochondral defects, 4 anterior impingements, 2 loose bodies, 2 os subfibulare, 2 os submalleolare and 2 partial ruptures of peroneus brevis. 8 cases with no associated injuries rated excellent or good. Conclusion: The modified $Brostr{\ddot{o}}m$ procedure is believed to be an effective and successful method for chronic lateral ankle instability that didn't respond to conservative treatment. Because associated injuries in chronic lateral ankle instability may affect postoperative satisfaction, appropriate detection and treatment may need for postoperative satisfaction.

• 보건교육건강증진학회지
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• 제25권3호
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• pp.125-138
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• 2008

Purpose: This study was attempted to find out female smoking behavior and the smoking related factors. Method: Study subjects were 226 female smokers who have visited temporary clinic or smoking cessation clinic run by 10 public health centers in Incheon. The data were collected through the questionnaire specially designed for this study from April 1 to June 30, 2008. The data were analyzed by the SPSS 12.0 program. Result: 68.0% of feale smokers have smoked habitually. The average daily smoking amount of the subjects was $12.0{\pm}8.7$ ea, average rate of nicotine dependence was $4.2{\pm}2.2$ points, the mean smoking duration was $12.7{\pm}9.3$ years, and the smoking start age was $23.1{\pm}8.5$ year old. The smoking behavior by the drinking frequency showed significant difference in average daily smoking amount and rate of nicotine dependence(p<.05). Also the smoking behavior by exercise showed significant difference in current smoking frequency(p<.05). There was positive relation between female smoking behavior and monthly income, frequency of drinking, exercise, and stress respectively(p<.05, p<.01). Conclusion: Compared to a male smoker, the average daily smoking amount of a female smoker was less and the duration of smoking was longer. This study suggests that not only a social movement about a female smoking cessation is imperative but also smoking cessation programs should be combined with reduced drinking consumption, exercise and stress relief programs. Moreover, early intervention for preventing teenager smoking should be added to smoking cessation programs.