• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2001년도 춘계학술대회 논문집
• /
• pp.326-331
• /
• 2001

In this study. CT specimens were prepared from ASME SA5l6 which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at $25^{\circ}C$, -3$0^{\circ}C$, -6$0^{\circ}C$, -8$0^{\circ}C$, -10$0^{\circ}C$ and -12$0^{\circ}C$ in the range of stress ratio of 0.1 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range ΔKsub/th/ in the early stage of fatigue crack growth ( Region I) and stress intensity factor range ΔK in the stable of fatigue crack growth ( Region II) was increased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm da.dN -ΔK in RegionII, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It assumed that the fatigue crack growth rate da/dN is rapid in proportion to descend temperature in Region II and the cryogenic-brittleness greatly affect a material with decreasing temperature.

• 한국치위생학회지
• /
• 제17권1호
• /
• pp.27-37
• /
• 2017

Objectives: The purpose of the study is to investigate the correlation between stress and smartphone addiction in some university students. Methods: The subjects were 220 health major students in D area. The study was conducted for 2 weeks, in June, 2016. The questionnaire consisted of general characteristics of the subjects, awareness toward stress, stress-coping pattern, and smartphone addiction. Data was analyzed through SPSS 18.0 program. Results: In the analysis of stress levels according to general characteristics, female group showed higher experience compared to male group (high group 46.10, subgroup 44.38) (p<0.05). Male group and higher stress group showed higher experience in problem solving, social support, and emotional stress coping (p>0.05). Stress and stress coping (r=0.322), stress and smartphone addiction (r=0.299) showed positive correlation. The significant factors of smartphone addiction were average daily using time (${\beta}=0.477$, p<0.001), study stress (${\beta}=0.177$, p<0.05), social stress (${\beta}=0.323$, p<0.01), problem solving (${\beta}=-0.320$, p<0.001), social support (${\beta}=0.064$, p<0.05), and emotional stress coping (${\beta}=0.264$, p<0.001). These factors explained 30.8% of the variance in smartphone addiction. Conclusions: The results from this study indicated that stress had a negative impact on smartphone addictions in subjects. It is necessary to provide smartphone addiction management for stress management.

• Nutrition Research and Practice
• /
• 제6권2호
• /
• pp.155-161
• /
• 2012

Excessive oxidative stress and abnormal blood lipids may cause chronic diseases. This risk can be reduced by consuming an antioxidant- and fiber-rich vegetarian diet. We compared biomarkers of oxidative stress, antioxidant capacity, and lipid profiles of sex- and age-matched long-term vegetarians and omnivores in Korea. Forty-five vegetarians (23 men and 22 women; mean age, $49.5{\pm}5.3$ years), who had maintained a vegetarian diet for a minimum of 15 years, and 30 omnivores (15 men and 15 women; mean age, $48.9{\pm}3.6$ years) participated in this study. Their 1-day, 24-h recall, and 2-day dietary records were analyzed. Oxidative stress was measured by the levels of diacron reactive oxygen metabolites (d-ROM). Antioxidant status was determined by the biological antioxidant potential (BAP) and levels of endogenous antioxidant enzymes such as superoxide dismutase, catalase, and glutathione peroxidase. We observed that vegetarians had a significantly lower body fat percentage ($21.6{\pm}6.4%$) than that of omnivores ($25.4{\pm}4.6%$; $P$ < 0.004). d-ROM levels were significantly lower in vegetarians than those in omnivores ($331.82{\pm}77.96$ and $375.80{\pm}67.26$ Carratelli units; $P$ < 0.011). Additionally, total cholesterol levels in the vegetarians and omnivores were $173.73{\pm}31.42$ mg/dL and $193.17{\pm}37.89$ mg/dL, respectively ($P$ < 0.018). Low-density lipoprotein cholesterol was $101.36{\pm}23.57$ mg/dL and $120.60{\pm}34.62$ mg/dL ($P$ < 0.005) in the vegetarians and omnivores, respectively, indicating that vegetarians had significantly lower lipid levels. Thus, oxidative stress, body fat, and cholesterol levels were lower in long-term vegetarians than those in omnivores.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2010년도 춘계 학술발표회
• /
• pp.730-739
• /
• 2010

Stress history increases in penetration resistance due to the increase in residual horizontal stress of granular soil. This study analyzes the effect of stress history on the results of CPT and DMT from calibration chamber specimen in OC as well as NC state. Test results show that the normalized cone resistance by mean effective stress correlates well with the relative density and the state parameter, whereas the normalized cone resistance with regard to vertical effective stress is a little affected by stress history. The horizontal stress index($K_D$) in DMT more reflects the influence of stress history on granular soil than the dilatometer modulus($E_D$) and cone resistance($q_c$). The $K_D/K_0$, in which the effect of stress history on $K_D$ is compensated by the at-rest coefficient of earth pressure, $K_0$, is related to relative density, state parameter and the normalized cone resistance by mean effective stress. It is also observed that the normalized dilatometer modulus by mean effective stress($E_D/{\sigma_m}'$) is unique correlated with the state parameter, regardless of stress history.

• 대한조선학회지
• /
• 제21권1호
• /
• pp.43-47
• /
• 1984

The purpose of this paper is to investigate theoretically the effect of residual stress due to welding in stress intensity factor of a plate containing the Model I Crack in different crack size and location, and on fatigue crack growth rate. The initiation of crack is found to be possible only in the region of tensile residual stress. The most dangerous crack has the values of d/b and a/b equal to about 0.6 and 1.0, respectively, where d/b is the ratio of distance from the crack to welding bead and the width of tensile residual stress region and a/b is the ratio of crack length and tensile residual stress region. The crack perpendicular to and on the line of welding bead and with a/b equal to about 0.6 has maximum stress intensity factor. The theoretical fatigue crack growth rate under residual stress and applied stress, which is obtained from Forman's Law by stress superposition, is relatively in good agreement with Glinka's[8] experimental value. The fatigue crack growth is shown to be retarded due to residual stress distribution.

• 한국산학기술학회논문지
• /
• 제22권2호
• /
• pp.496-506
• /
• 2021

본 연구는 소방공무원들의 직무스트레스와 피로수준과의 관련성을 규명하는 것을 목적으로 실시하였다. 조사대상은 D광역시의 5개 소방서에 근무하고 있는 소방공무원 330명을 대상으로 2019년 9월 1일부터 10월 31일까지의 기간 동안에 구조화된 무기명 자기기입식 설문조사를 실시하였다. 연구결과, 조사대상자의 피로수준은 직무스트레스 총점이 높을수록 유의하게 높았으며(p<0.001), 하위영역별로는 업무요구도가 높을수록(p=0.046), 업무의 자율성이 낮을수록(p=0.006), 상사의 지지가 낮을수록(p<0.001), 동료의 지지가 낮을수록(p<0.001) 유의하게 높았다. 조사대상자의 피로수준과 직무스트레스 내용 간의 상관관계를 보면, 피로수준은 직무스트레스 총점(r=0.348, p<0.05) 및 업무의 요구도(r=0.301, p<0.05)와는 유의한 양의 상관관계를 보인 반면, 업무의 자율성(r=-0.306, p<0.05), 상사의 지지(r=-0.340, p<0.05) 및 동료의 지지(r=-0.355, p<0.05)와는 유의한 음의 상관관계를 보였다. 피로수준에 대한 직무스트레스의 관련성을 파악하기 위해 다변량 로지스틱 회귀분석을 실시한 결과, 직무스트레스 총점이 낮은 집단(Q1)에 비해 매우 높은 집단(Q4)에서 「고위험 피로군」에 속할 위험비가 유의하게 상승하였다(ORs=3.03, 95% CI=1.13~8.12). 위와 같은 연구결과는 소방공무원들의 피로수준은 직무스트레스와 유의한 관련성이 있음을 시사하고 있다. 따라서 직장에서의 직무스트레스 요인들을 줄일 수 있는 구체적인 방안이 마련될 필요가 있다고 생각된다.

• 대한기계학회논문집
• /
• 제4권3호
• /
• pp.113-118
• /
• 1980

Stresses were calculated for finite-width orthotropic laminates with a circular hole and remote uniaxial loading using a two-dimensional finite-element analysis with both uniform stress and uniform displacement boundary conditions. Five different laminates were analyzed: quasi-isotropic [0.deg./.+-.45.deg./90.deg.].$\_$s/, 0.deg., 90.deg., [0.deg./90.deg.]$\_$s/, and [.+-.45.deg.]$\_$s/, Computed results are presented for selected combinations of hole diameter-sheet-width ratio d/w and length-to width ratio L/w. For small L/w values, the stress-concentration factors K$\_$tn/ were significantly different for the uniform stress and uniform displacement boundary conditions. Typically, for the uniform stress conditions, the K$\_$tn/ values were much larger than for the infinite-strip reference conditions; however, for the uniform displacement conditon, they were only slighty smaller than for this reference. The results for long strips are also presented as width-correction factor. For d/w.leg.33, these width-correction factors are nearly equal for all five laminates.

• 한국전기전자재료학회논문지
• /
• 제16권12호
• /
• pp.1071-1076
• /
• 2003

The nonlinear properties and their stability of ZPCCD- based varistors, which are composed of ZnO P $r_{6}$ $O_{ll}$ - CoO-C $r_2$ $O_3$-D $y_2$ $O_3$-based ceramics, were investigated in the D $y_2$ $O_3$ content range of 0.0∼2.0 mol%. The incorporation of D $y_2$ $O_3$ greatly affected the nonlinear properties and the best nonlinearity was obtained from 0.5 mol% D $y_2$ $O_3$ with nonlinear exponent of 66.6 and leakage current of 1.2 $\mu$A. Further addition of D $y_2$ $O_3$ deteriorated the nonlinear properties. In stability against DC accelerated aging stress state: 0.95 $V_{1mA}$/15$0^{\circ}C$/24 h, the 0.5 mol％ D $y_2$ $O_3$-doped varistor exhibited the highest stability, in which the variation rate of varistor voltage and nonlinear exponent are -1.9% and 10.5%, respectively. The remainder varistors resulted in thermal runaway due to low density of ceramics.s.s.

• Animal Bioscience
• /
• 제37권1호
• /
• pp.142-150
• /
• 2024

Objective: This study was conducted to assess effects of heat stress on growth performance, physiological parameters, and blood profiles of Hanwoo steers during early-fattening period in climate chambers. Methods: Four Hanwoo steers (body weight, 454.3±10.9 kg; age, 14±0.1 month) were allocated into four levels of temperature-humidity index (THI) in a 4×4 Latin square design for 21 days (pre-adaptation, 7 d; heat stress, 7 d; post-adaptation, 7 d) per period. Experimental treatments were assigned according to THI chart based on National Institute Animal Science (NIAS, 2022): Comfort (25.5℃ to 26.5℃, 60%; THI 73 to 75), Mild (28℃ to 29℃, 60%; THI 77 to 79), Moderate (29.5℃ to 30.5℃, 80%; THI 82 to 84), and Severe (31℃ to 32℃, 80%; THI 85 to 86) in separate climatic controlled chambers. Results: The dry matter intake (DMI) of the formula feed was lower in Severe compared to Mild and Comfort (p<0.05). The DMI of rice straw was the lowest in Severe and lower in Moderate than Comfort and Mild (p<0.05). Both average daily gain and feed conversion ratio of Severe and Moderate were lower than those of Mild and Comfort (p<0.05). Water intake was the highest in Severe and lower in Moderate compared with Comfort and Mild (p<0.05). Heart rate and rectal temperature increased as THI level increased (p<0.05). Glucose was the lowest in Severe and lower in Moderate compared to Comfort (p<0.05). On the contrary, non-esterified fatty acid was the highest in Severe and lower in Moderate compared with Comfort (p<0.05). Blood urea nitrogen of Moderate and Severe were higher than those of Comfort and Mild (p<0.05). Cortisol increased as THI increased (p<0.05). Conclusion: This study demonstrated the negative effects of heat stress on the performance and physiological responses of Hanwoo steers during the early-fattening period. In addition, it is judged that the THI chart for Hanwoo steers of National Institute of Animal Science (2022) was properly calculated.

• Asian-Australasian Journal of Animal Sciences
• /
• 제31권2호
• /
• pp.263-269
• /
• 2018

Objective: Heat stress (HS) triggers oxidative stress and respiratory alkalosis in pigs. The objective of this experiment was to study whether a short-term supranutritional amount of dietary vitamin E (VE) can mitigate oxidative stress and respiratory alkalosis in heat-stressed pigs. Methods: A total of 24 pigs were given either a control diet (17 IU/kg VE) or a high VE (200 IU/kg VE; HiVE) diet for 14 d, then exposed to thermoneutral (TN; $20^{\circ}C$, 45% humidity) or HS ($35^{\circ}C$, 35% to 45% humidity, 8 h daily) conditions for 7 d. Respiration rate and rectal temperature were measured three times daily during the thermal exposure. Blood gas variables and oxidative stress markers were studied in blood samples collected on d 7. Results: Although HiVE diet did not affect the elevated rectal temperature or respiration rate observed during HS, it alleviated (all p<0.05 for diet${\times}$temperature) the loss of blood $CO_2$ partial pressure and bicarbonate, as well as the increase in blood pH in the heat-stressed pigs. The HS reduced (p = 0.003) plasma biological antioxidant potential (BAP) and tended to increase (p = 0.067) advanced oxidized protein products (AOPP) in the heat-stressed pigs, suggesting HS triggers oxidative stress. The HiVE diet did not affect plasma BAP or AOPP. Only under TN conditions the HiVE diet reduced the plasma reactive oxygen metabolites (p<0.05 for diet${\times}$temperature). Conclusion: A short-term supplementation with 200 IU/kg VE partially alleviated respiratory alkalosis but did not reduce oxidative stress in heat-stressed pigs.