• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2004.11a
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• pp.323-329
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• 2004

The electrical and rheological properties pertaining to the electrorheological (ER) behavior of chitosan derivatives, chitosan, chitosan ammonium salt and chitosan phosphate suspensions in silicone oil were investigated. Chitosan derivative suspensions showed a typical ER response (Bingham flow behavior) upon application of an electric field. However, chitosan phosphate suspension exhibited an excellent shear yield stress compared with chitosan and chitosan ammonium salt suspensions. The difference in behavior results from the difference in the conductivity of the disperse phases due to the difference of their polarizability. The shear stress for the chitosan, chitosan ammonium salt and chitosan phosphate suspensions exhibited a linear dependence on the volume fraction of particles and 1.18 ,1.41 and 1.67 powers of the electric field. On the basis of the experimental results, the newly synthesized chitosan derivative suspensions found to be an ER fluid.

• Journal of Korean Home Economics Education Association
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• v.31 no.1
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• pp.59-75
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• 2019

The purpose of this study was to explore ways to help reduce adolescents' academic stress by exploring the influences of parental learning involvement and family strengths on academic stress. The research participants were 445 middle school students living in Gwangju. Data were collected from self-reported questionnaires and analyzed with SPSS 23.0 program. The major findings were as follows: First, the parental learning involvement(provision of learning option, democratic rules, encouragement of academic progress) and academic stress showed significant differences according to gender. There was a significant difference in academic stress depending on school year, but there was no significant difference in parental learning involvement. The family strengths did not show significant difference according to gender or school year. The parental learning involvement(provision of learning option, democratic rules, pursuit of adequate performance, academic information, total), family strengths, and academic stress showed significant differences according to economic status. Second, the adolescents' academic stress was influenced by parental learning involvement(encouragement of academic progress, democratic rules, pursuit of adequate performance) and family strengths. Approximately 30 percent of the adolescents' academic stress was explained by these variables.

• Journal of Welding and Joining
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• v.5 no.2
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• pp.9-16
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• 1987

Post weld heat treatment (PWHT) is carried out to increase the fracture toughness in heat affected zone(HAZ) and remove the residual stress. There occur some problems such as toughness decreement and stress relief cracking(SRC) in the coarse grained HAZ subjected to the effect of tempering treatment. Especially, embitterment of structure directly relates to the mode of fracture and is appeared as the difference of fracture surface, that is, grain boundary failure. Therefore, in this paper, PWHT was carried out under the stress of 0, 10, 20 and $30kg/cm^2$ to simulate residual stress in HAZ welded by heat input of 10, 30 and 40KJ/cm. Applied stress in weld HAZ during PWHT assisted precipitin of over saturated alloying element in the structure, and grain boundary failure according to welding heat input didn't almost appear at the heat input of 10 KJ/cm, but it appeared from being the applied stress of $30kg/cm^2$ at $30KJ/cm and 20kg/mm^2$ at 40KJ/cm.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.12
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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.

• KSTLE International Journal
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• v.5 no.2
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• pp.49-51
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• 2004

The electrical and rheological properties pertaining to the electrorheological (ER) behavior of chitosan derivatives, chitosan, chitosan ammonium salt and chitosan phosphated suspensions in silicone oil were investigated. Chitosan derivative suspensions showed a typical ER response (Bingham flow behavior) upon application of an electric field. However, chitosan phosphate suspension exhibited an excellent shear yield stress compared with chitosan and chitosan ammonium salt suspensions. The difference in behavior results from the difference in the conductivity of the disperse phases due to the difference of their polarizability. The shear stress for the chitosan, chitosan ammonium salt and chitosan phosphate suspensions exhibited a linear dependence on the volume fraction of particles and 1.18, 1.41 and 1.67 powers of the electric field. On athe basis of the experimental results, the newly synthesized chitosan dervative suspensions found to be an ER fluid.

• Korean Journal of Occupational Health Nursing
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• v.19 no.2
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• pp.268-277
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• 2010

Purpose: To examine the relations among occupational satisfaction, stress, and customer orientation of upper-scale general hospital nurses. Method: We studied with structured questionnaires with total 66 questions for 218 nurses working at university hospitals in Gangwon-do from February 2 to 22, 2010. Result: Occupational satisfaction and customer-oriented character increased when nurses' ages and career experiences were higher, married, working in daytime without shift and in higher positions. Occupational stress increased when nurses were younger, not married, with three shifts, and when they were general nurses. However, there was no statistical difference. Customer-oriented character had positive correlation with occupational satisfaction and stress while occupational satisfaction had negative correlation(r=-0.358) with occupational stress. Conclusion: As occupational stress and satisfaction of nurses in university hospitals showed significant relations with customer-oriented character, t is necessary to reduce occupational stress of nurses, and strengthen occupational satisfaction of them.

• Journal of People, Plants, and Environment
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• v.23 no.3
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• pp.363-375
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• 2020

Background and objective: Recreation or activities in forest are regarded as therapy. Many forest therapy programs have been developed and assessed in the domestic. This study was conducted to investigate the effect of the forest therapy program on academic and job-seeking stress in college students. Methods: Thirty five subjects were selected as the experimental group and 25 as the control group, and 29 subjects in the experimental group and 11 in the control group participated in the follow-up test to verify the persistence of stress reduction effects. The forest therapy program was carried out once a week for 2 hours each from September 4 to December 4, 2018, adding up to total eight sessions. Results: The experimental group showed statistically significant reduction in both academic stress and job-seeking stress, whereas the control group did not. For the persistence of the forest therapy program, the experimental group did not show a statistically significant difference between the posttest and the follow-up test, and thus the stress reduction effect was maintained. Conclusion: This study proved the reduction of academic and job-seeking stress in forest therapy programs and the persistence of the stress reduction effect of the forest therapy program. The result is consistent with the Stress Recovery Theory (SRT) that shows the stress reduction effect of nature. In addition, it has significance in that it has verified that the program using the forest on campus can reduce stress of most college students.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.129-138
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• 2010

Technical ceramics, due to their unique physical properties, are excellent candidate materials for engineering applications involving extreme thermal and chemical environments. When ceramics are rapidly cooled, they receive thermal shock. The thermal shock parameter is defined as the critical temperature difference. The critical temperature difference for ceramic parts is influenced by its size, the convective heat transfer coefficient, etc. The thermal shock for a component is analyzed by using the transient thermal stress. If the transient thermal stress exceeds the modulus of rupture (MOR), cracking by thermal shock is initiated. The critical temperature difference for water is less than the critical temperature difference for air. The three-way catalyst substrate used in this study has an adequate performance against thermal shock because its radial and axial temperature differences existed below the critical temperature differences.

• International journal of advanced smart convergence
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• v.12 no.4
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• pp.386-394
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• 2023

This study investigated changes in salivary cortisol, lactic acid, and heart rate along the route during walking exercise in a forest environment for the purpose of reducing stress. Walking exercise in a forest environment was conducted on a Hill Type (Distance: 800m, Average slope 25°, Altitude 112m) and Step Type (Distance: 800m, Average slope 25°, Altitude 114m) routes for 10 female college students in their 20s. The subjects were asked to walk at a speed of 60 bpm. The resulting changes in salivary cortisol, lactate, and average heart rate during exercise were compared and analyzed using Repeated Measurement two-way ANOVA, and the maximum heart rate during exercise and average heart rate at rest were compared and analyzed using paired t-test, and the following results were obtained. First, there was no significant difference in salivary cortisol depending on the type and period of the forest, but it tended to gradually decrease. Second, there was a significant difference in lactic acid depending on the type and period, and it was higher in Step Type. Third, there was a significant difference in the average heart rate during exercise, and it was higher in Step Type. Fourth, there was a significant difference in maximum heart rate during exercise, and it was higher in Step Type. Fifth, there was no significant difference in average heart rate during rest. In summary, walking exercise in a forest environment can be effective for stress reduction for female college students in their 20s, but it appears that forest routes should be selected according to physical strength level, and walking exercise in a forest environment for long periods of time is not recommended. For this purpose, it is suggested that it is appropriate to select the Hill Type route.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.04a
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• pp.152-162
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• 2001

Comparison of results from two different methods of soil-structure dynamic interaction analysis is presented. Two methods include transfromed static and seismic response analyes. In seismic response analysis, the difference in result of total stress analysis relative to effective stress analysis is investigated.