• 소성∙가공
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• 제9권1호
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• pp.72-79
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• 2000

Dynamic recrystallization (DRX), which may occur during hot deformation, is important for the microsturctural evolution of 304 stainless steel. Especially, the current interest in modelling hot rolling demands quantitative relationships among the thermomechanical process variables, such as strain, temperature, strain rate, and etc. Thus, this paper individually presents the relationships for flow stress and volume fraction of DRX as a function of processing variables using torsion tests. The hot torsion tests of 304 stainless steel were performed at the temperature range of 900~110$0^{\circ}C$ and the strain rate range of 5x10-2~5s-1 to study the high temperature softening behavior. For the exact prediction of flow stress, the equation was divided into two regions, the work hardening (WH) and dynamic recovery (DRV) region and the DRX region. Especially, The flow stress of DRX region could be expressed by using the volume fraction of DRX (XDRX). Since XDRX was consisted of the critical strain($\varepsilon$c) for initiation of dynamic recrystallization (DRX) and the strain for maximum softening rate ($\varepsilon$*), that were related with the evolution of microstructure. The calculated results predicted the flow stress and the microstructure of the alloy at any deformation conditions well.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.379-395
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• 2021

For the complicated structural details in ships and offshore structures, the traditional hotspot stress approaches are known to be sensitive to the element variables of element topologies, sizes, and integration schemes. This motivated to develop a new approach for predicting reasonable hotspot stresses, which is less sensitive to the element variables and easy to be implemented the real marine structures. The three-point bending tests were conducted for the longitudinal attachments with the round and rectangular weld toes. The tests were reproduced in the numerical simulations using the solid and shell element models, and the simulation technique was validated by comparing the experimental stresses with the simulated ones. This paper considered three hotspot stress approaches: the ESM method based on surface stress extrapolation, the Dong's method based on nodal forces along a weld toe, and the proposed method based on nodal forces perpendicular to an imaginary vertical plane at a weld toe. In order to study the element sensitivities of each method, 16 solid element models and 8 shell element models were generated under the bending and tension loads, respectively. The element sensitivity was analyzed in terms of Stress Concentration Factors (SCFs) in viewpoints of two statistical quantities of mean and bias with respect to the reference SCFs. The average SCFs predicted by the proposed method were remarkably in good agreement with the reference SCFs based on the experiments and the ship rules. Negligibly small Coefficients of Variation (CVs) of the SCFs, which is measure of statistical bias, were drawn by the proposed method.

• 정신신체의학
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• 제1권1호
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• pp.35-44
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• 1993

This study was aimed at investigating the relationship of stress perception and psychopathology with biological variables such as systolic and diastolic blood pressure. serum total cholesterol high density lipoprotein and triglyceride in 50 adult patients with essential hypertension and 50 normotensive individuals. Both of the groups were matched to each other regarding age, sex, the level of education and BMI(body mass index). Stress perception and psychopathology between the two groups were compared using GARS and SCL-90-R scales. Biological variables such as blood pressure(systolic. diastolic), serum total cholesterol, high density lipoprotein and triglyceride were measured in all the subjects. The results were as follows ; 1) Hypertensive patients scored significantly higher than normotensive individuals in stress perception related to unusual happenings, change or no change in routine and overall global area, respectively. 2) Regarding psychopathology, hypertensive patients scored significantly higher than normotensive individuals in depression. hostility and interpersonal sensitivity. respectively. 3) Systolic blood pressure had a significantly positive correlation with scores of stress perception related to sickness and injury, and change or no change in routine, respectively. Diastolic blood pressure had a significantly positive correlation with scores of stress perception related to change or no change in routine. 4) In hypertensive patients. the level of serum total cholesterol had a significantly positive correlation with scores of stress perception related to unusual happenings. However, the level of serum triglyceride had a significantly negative correlation with scores of stress perception related to changes in relationships, sickness or injury, and change or no chang in routine. 5) There were no significant correlations between scores of stress perception and biological factors in the normotensive group. 6) The level of serum triglyceride correlated negatively with phobic anxiety in hypertensive group. whereas it correlated positively with PSDI in normotensive group. In conclusion, these results suggest that hypertensive patients have higher level of stress perception and psychopathology than normal individuals. In hypertensive patients, their stress perception is suggested to be correlated with serum cholesterol.

• 대한기계학회논문집A
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• 제25권12호
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• pp.2056-2061
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• 2001

Non-proportional loading tests of Nylon 66 at room temperature exhibit path dependent behavior and plasticity-relaxation interactions. The uniaxial formulation of the viscoplasticity theory based on overstress (VBO), which has been used to reproduce the nonlinear strain rate sensitivity, relaxation, significant recovery and cyclic softening behaviors of Nylon 66, is extended to three-dimensions to predict the response in strain-controlled, comer-path tests. VBO consists of a flow law that is easily written for either the stress or the strain as the independent variable. The flow law depends on the overstress, the difference between the stress and the equilibrium stress that is a state variable in VBO. The evolution law of the equilibrium stress in turn contains two additional state variables, the kinematic stress and the isotropic stress. The simulations show that the constitutive model is competent at modeling the deformation behavior of Nylon 66 and other solid polymers.

• 대한간호학회지
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• 제48권3호
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• pp.298-310
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• 2018

Purpose: The purpose of this study was to examine the effects of the laughter therapy program on perceived stress and psycho-neuro-endocrine-immune responses in obese women. Methods: A nonequivalent control group with a pretest-posttest design was used. The participants (n=60), whose age ranged from 30 to 50 years (pre-menopausal and body mass index of over $25kg/m^2$), were assigned to the experimental group (n=24) or control group (n=26). The experimental group was provided with the laughter therapy program (12 sessions) for 6 weeks. Results: There were significant differences in perceived stress, psychological stress response, fasting blood sugar, interleukin-6, and tumor necrosis factor alpha between the two groups after the program. However, there were no significant differences in normalized low frequency (norm LF), normalized high frequency (norm HF), LF/HF ratio, and cortisol between the two groups after the program. Conclusion: It was found that the laughter therapy program had positive effects on some variables in terms of perceived stress and psycho-neuro-endocrine-immuno responses. It is suggested that the laughter therapy in this study can provide the direction for developing a program for obese women.

• 가족자원경영과 정책
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• 제14권2호
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• pp.153-176
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• 2010

The purpose of this study was to investigate the relationship between marriage migration females' acculturative stress and marital adjustment, especially the mediating and moderating effects of ego-resilience. The structural equation models were tested by setting marriage migration females' acculturative stress as a prediction variable, their marital adjustment as an outcome variable and their ego-resilience as mediator and moderator variables. The sample consisted of 172 marriage migration females from Busan. I analyzed the data using correlation analysis in order to discover the correlation coefficient of those variables among acculturative stress, ego-resilience and marital adjustment. I used the structural equation model (SEM) for investigating the relationship among acculturative stress, ego-resilience and marital adjustment and for investigating the mediating effects of ego-resilience. I also used multiple group analysis and two way ANOVA to investigate the moderating effects of ego-resilience. The results of structural equation modeling were as follows: first, it was proved that ego-resilience was exerted as a mediating variable, because acculturative stress appeared to affect marital adjustment in relation to ego-resilience. Therefore, marital adjustment was evident when ego-resilience was low. Second, it was proved that ego-resilience was exerted as a moderating variable, because those with low ego-resilience experienced high acculturative stress and low marital adjustment, and those with high ego-resilience experienced low acculturative stress and high marital adjustment. Such findings point out the importance of considering personal characteristics, like ego-resilience, in the relationship between acculturative stress and marital adjustment.

• Animal Bioscience
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• 제34권2호
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• pp.163-171
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• 2021

Objective: Considering the importance of dairy farming and the negative effects of heat stress, more tolerant genotypes need to be identified. The objective of this study was to investigate the effect of heat stress via temperature-humidity index (THI) and diurnal temperature variation (DTV) in the genetic evaluations for daily milk yield of Holstein dairy cattle, using random regression models. Methods: The data comprised 94,549 test-day records of 11,294 first parity Holstein cows from Brazil, collected from 1997 to 2013, and bioclimatic data (THI and DTV) from 18 weather stations. Least square linear regression models were used to determine the THI and DTV thresholds for milk yield losses caused by heat stress. In addition to the standard model (SM, without bioclimatic variables), THI and DTV were combined in various ways and tested for different days, totaling 41 models. Results: The THI and DTV thresholds for milk yield losses was THI = 74 (-0.106 kg/d/THI) and DTV = 13 (-0.045 kg/d/DTV). The model that included THI and DTV as fixed effects, considering the two-day average, presented better fit (-2logL, Akaike information criterion, and Bayesian information criterion). The estimated breeding values (EBVs) and the reliabilities of the EBVs improved when using this model. Conclusion: Sires are re-ranking when heat stress indicators are included in the model. Genetic evaluation using the mean of two days of THI and DTV as fixed effect, improved EBVs and EBVs reliability.

• 대한가정학회지
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• 제47권10호
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• pp.51-61
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• 2009

The purpose of this research is to verify the impact of job stress on depression among married workers and to examine mediation effect of work-family conflict between the two variables. 356 married workers in Seoul and Gyonggi Province were selected to analyze. The results indicate that job stress was statistically influential on depression and work-family conflict. And job stress implied the partial mediation effect of work-family conflict, with both direct and indirect impacts on depression. These findings indicated that maltreatment of job stress and workfamily conflict would negatively impact on depression. Therefore, work organizations must launch and activate EAP(employee assistance programs) or family friendly welfare programs in order to increase the overall mental health of the employees.

• 한국보육지원학회지
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• 제12권6호
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• pp.19-39
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• 2016

The present study examined differences in children's behavior problems and peer interaction, and parental factors including self-esteem, depression and childrearing stress between atopic dermatitis(AD) and normal(non-AD) children in each gender, and analyzed the effects of the parental factors on the two variables of AD children. 165 AD and 1176 non-AD children of age 5 were selected from the 6th year data of the Panel Study on Korean Children. The results from t-test and multiple regression are as follows. First, only AD boys showed a higher level of behavior problems than non-AD boys, but peer interaction showed no difference between AD and non-AD groups. Compared with non-AD children's parents, mothers of AD children showed a higher stress level and mothers of AD boys had a higher depression level. But there were no differences in maternal self-esteem and paternal factors between the groups. Second, AD boys' behavior problems were related to maternal factors and paternal stress, and some characteristics of AD girls' behavior problems were related with some parental variables. But peer interaction of AD children had no relation with parental factors. Third, behavior problems were influenced by maternal stress in AD boys and influenced by maternal depression and parental self-esteem in AD girls.

• Journal of Welding and Joining
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• 제19권4호
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• pp.413-422
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• 2001

In this study. two-dimensional heat flow and residual stress in arc brazing to join the pipe and plate structure were analyzed by using a commercialized FEM package. Advantages offered by arc brazing are that strong joints can be produced with lower heat input than that of previous gas metal arc welding and narrower heat affected zone can usually be obtained than that in the case of torch brazing. To investigate the effects of process variables and minimize the thermal effects on the structure, this study presents a method for analyzing the heat flow and residual stress in arc brazing process according to variables such as traveling speed, torch angle and position. The simulation results were compared with the experimental ones to verify the numerical analysis method. The experiments include the measurement of HAZ size from the section of joints and residual stresses by using strain gages named 'section method'. A comparatively good agreement between the results of numerical analysis and experimental ones could be obtained in both of the temperature distribution and residual stress of the brazed structure. Using the proposed numerical analysis method, the process parameters were evaluated to get proper arc brazing conditions.