• 소성∙가공
• /
• 제11권1호
• /
• pp.69-74
• /
• 2002

In addition to lightweight and moldable characteristics, polymeric foams possess an excellent energy absorbing capability that can be utilize for a wide range of commercial applications, especially in the crashworthiness of the automobiles. The purpose of the present study is to develop experimental methodology to characterize the pressure dependent yield behavior of the energy absorbing polymeric foams. For the compression test in a triaxial stress sate, a specially designed device was placed in a hydraulic press to produce and control oil pressure. For the test material, the polyurethane foams of two different densities were used. The displacement of the specimen, the load subjected to the specimen, and oil pressure applied to the specimen were measured and controlled. Stress strain curves and yield stresses for the four different oil pressure were obtained. It was found from the present experiments that the polyurethane foams exhibited significant increases in yield stress with applied pressure or mean normal stress. Based on this observation, a yield criteria which included the effect of the stress invariant were established for the polymeric foams. The obtained experimental constants which constituted the pressure-dependent yield criterion were verified.

• 간호행정학회지
• /
• 제21권4호
• /
• pp.417-425
• /
• 2015

Purpose: The purpose of this study was to identify factors in the clinical learning environment that affect clinical practice stress and anxiety in nursing students. Methods: Participants were 210 senior nursing students from two universities who had completed their clinical experience. Data were collected from self-report questionnaires and analyzed using t-test, ANOVA, and hierarchical multiple regression analysis with the SPSS/WIN 21.0 Program. Results: The mean scores for the clinical learning environment, the clinical practice stress, and anxiety were $3.16{\pm}0.68$, $2.98{\pm}0.66$, and $43.74{\pm}10.18$ points, respectively. The regression analysis showed that the clinical learning environment contributed to 13% of the stress and 20% of the anxiety in the nursing students with the conditions controlled for general characteristics, department satisfaction and social support. Conclusion: The results of this study suggest that the clinical learning environment should be carefully assessed to reduce nursing students' stress and anxiety from clinical practice. Therefore, collaboration between nursing universities and teaching hospitals is necessary to optimize clinical learning environment.

• 기본간호학회지
• /
• 제8권2호
• /
• pp.199-209
• /
• 2001

The purpose of this study was to examine the relationship between life stress and depression, and the effect of social support in postpartal $4{\sim}6$ week women. Theoretically social support is thought to mediate the relationship between life stress and depression. Data were collected from June 1 to July 30, 1999. The data were analysed by use of SPSS. Two hypotheses were tested using Gamma, a measure of association for ordinal variables. Partial gamma was used to test the third hypothesis. Patterns of elaboration described by Babbie(1986) were selected to interpret the relationship of the three variables in the analyses. The results of this study are summarized as follows ; There was a positive relationship between life stress and depression (Gamma=.45, P=.017), and an inverse relationship between social support and depression (Gamma=-.49, P=.009). Thus the first, two hypotheses were supported. 2. When social support was controlled, the relationship between life stress and depression increased under the condition of low social support, but with high social support, the relationship decreased. It can be interpreted that life stresses are positively related to depression under the condition of low social support, however this relationship cannot be expected with high social support.

• International Journal of Precision Engineering and Manufacturing
• /
• 제9권4호
• /
• pp.57-62
• /
• 2008

The aim of this investigation was to extract the fatigue properties at the designated fatigue life of copper foil and observe the mean stress and stress amplitude effects on both the fatigue life and the corresponding surface morphology. Tensile tests were performed to determine the baseline monotonic material properties of the proportional limit and ultimate tensile strength. Constant amplitude fatigue tests were carried out using a feedback-controlled fatigue testing machine. The mean stress and the stress amplitude were changed to obtain the complete nominal stress-life curves. An atomic force microscope was utilized to observe the relationship between the fatigue damage and the corresponding changes in surface morphology. A Basquin's exponent of-0.071 was obtained through the fatigue tests. An endurance limit of 122 MPa was inferred from a Haigh diagram. The specimen surface became rougher as the number of fatigue cycles increased, and there was a close relationship between the fatigue damage and the surface roughness evolution.

• 가정간호학회지
• /
• 제24권3호
• /
• pp.316-324
• /
• 2017

Purpose: This study was conducted to investigate the effect of white noise on sleep quality, depression, and stress in college students. Method: This study was designed a randomized controlled design to measure the effect of white noise on college students' sleep quality, depression, and stress. Data collection was conducted from May 15, 2017 to June 5, 2017. The subjects were randomly assigned to 27 college students and 28 control volunteers. Data analysis was done using SPSS 23.0 Windows program. Results: The experimental and control groups were homogeneous in general characteristics and study variables. The white noise group showed statistically significant effects on stress(t=-2.25, p=.015) and sleep quality(t=0.65, p<.001). Conclusion: This study confirms that white noise has a positive effect on stress and sleep of college students. Based on these results, it is expected that further research will be conducted on systematic and differentiated white noise mediation.

• Molecules and Cells
• /
• 제40권2호
• /
• pp.143-150
• /
• 2017

Homologous recombination (HR) is necessary for maintenance of genomic integrity and prevention of various mutations in tumor suppressor genes and proto-oncogenes. Rad51 and Rad54 are key HR factors that cope with replication stress and DNA breaks in eukaryotes. Rad51 binds to single-stranded DNA (ssDNA) to form the presynaptic filament that promotes a homology search and DNA strand exchange, and Rad54 stimulates the strand-pairing function of Rad51. Here, we studied the molecular dynamics of Rad51 and Rad54 during the cell cycle of HeLa cells. These cells constitutively express Rad51 and Rad54 throughout the entire cell cycle, and the formation of foci immediately increased in response to various types of DNA damage and replication stress, except for caffeine, which suppressed the Rad51-dependent HR pathway. Depletion of Rad51 caused severe defects in response to postreplicative stress. Accordingly, HeLa cells were arrested at the G2-M transition although a small amount of Rad51 was steadily maintained in HeLa cells. Our results suggest that cell cycle progression and proliferation of HeLa cells can be tightly controlled by the abundance of HR proteins, which are essential for the rapid response to postreplicative stress and DNA damage stress.

• 대한예방한의학회지
• /
• 제25권2호
• /
• pp.45-60
• /
• 2021

Objective : This study was aimed to review randomized controlled trials (RCTs) about whether aromatherapy relieves stress. Method : We searched document about criteria to use words like 'Aroma', 'Oil' and 'Stress'. The study included 24 RCTs which were selected by total 167 studies searched in Korean Journal by searching OASIS, ScienceON, KISS, RISS. Cases that cannot be performed alone are excluded. Results : We got 24 domestic standard documents. Of the 24 studies, 14 were for students, and 6 were for patients receiving hospital treatment. Among the 7 treatments, dry-inhalation was used 13 times, and necklace-inhalation was used 9 times. Of the 24 Studies, lavender oil was used 19 times and sweet orange was used 4 times. Among the 28 types of measuring instruments used, 10 related to the autonomic nervous system and 8 STAIs and VASs were used respectively. Conclusion : It was possible to conclude that aromatherapy was effective in relieving stress. Through further research, it is necessary to study effective oil mixing methods, methods for measuring subjective stress, multimodal intervention, and effective intervention periods.

• 대한통합의학회지
• /
• 제11권3호
• /
• pp.11-23
• /
• 2023

Purpose : The stress of job-seeking college students is gradually worsening due to the continuing recession in the job market. Therefore, this study aims to verify whether intervention with an 'aromatherapy education program,' which combines theory and practice, has greater effect on stress, self-efficacy, and autonomic nervous system function than simple inhalation of essential oils in female college students preparing for employment. Methods : A single-blind, randomized controlled trial was conducted once a week for a total of 4 weeks with 29 female college students preparing for employment. Interventions included essential oil inhalation combined with an aromatherapy education program (experimental group(EG), n=14) and essential oil inhalation alone (control group(CG), n=15); measurements were taken before, immediately after, and 2 weeks after completion of the intervention. Evaluations were conducted using the job-seeking stress scale, stress VAS, self-efficacy scale, and a pulse-wave measuring instrument. Results : There were significant differences between the CG and EG groups with repeated measurements of job-seeking stress (p=.003), cognitive stress (p<.001), and self-efficacy (p<.001). There was a significant interaction between group and time. There were also significant differences between the CG and EG in terms of autonomic nervous system changes stress index(p=.047), total power(p=.029), high frequency(p=.036), and low frequency/high frequency ratio(p=.049). However, there was no significant difference in low frequency between the groups. Conclusion : The aromatherapy education program was more effective in improving job-seeking stress, cognitive stress, self-efficacy, and autonomic nervous system function than simple essential oil inhalation. For the aromatherapy education program to be useful as a complementary intervention for stress management in job seekers, it will be necessary to gather additional evidence of its efficacy by conducting follow-up studies with diverse participants and expanding the numbers, and durations, of the interventions.

• 한국자동차공학회논문집
• /
• 제13권3호
• /
• pp.186-192
• /
• 2005

The apparent activation energy Qc, the applied stress exponent n, and rupture life have been determined from creep test results of AZ31 Mg alloy over the temperature range of 200$^{\circ}C$ to 300$^{\circ}C$ and the stress range of 23.42 MPa to 93.59 MPa, respectively, in order to investigate the creep behavior. Constant load creep tests were carried out in the equipment including automatic temperature controller with data acquisition computer. At the temperature of $200^{\circ}C{\sim}220^{\circ}C$ and under the stress level of 62.43~93.59 MPa, and at around the temperature of $280^{\circ}C{\sim}300^{\circ}C$ and under the stress level of 23.42~39.00 MPa, the creep behavior obeyed a simple power-law relating steady state creep rate to applied stress and the activation energy fur the creep deformation was nearly equal to that of the self diffusion of Mg alloy including aluminum From the above results, at the temperature of $200^{\circ}C{\sim}220^{\circ}C$ the creep deformation for AZ31 Mg alloy seemed to be controlled by dislocation climb but controlled by dislocation glide at $280^{\circ}C{\sim}300^{\circ}C$ .And relationship beween rupture time and stress at around the temperature of $200^{\circ}C{\sim}220^{\circ}C$ and under the stress level of 62.43~93.59 MPa, and again at around the temperature of $280^{\circ}C{\sim}300^{\circ}C$ and under the stress level of 23.42~39.00 MPa, respectively, appeard as fullow; log$\sigma$=-0.18(T+460)(logtr+21)+5.92, log$\sigma$ = -0.25(T+460)(logtr+21)+8.02 Also relationship beween rupture time and steady state creep rate appears as follow; ln$\dot$ =-0.881ntr-2.45

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• 제33권5호
• /
• pp.485-493
• /
• 2007

Purpose: Heart rate variability(HRV) is the clinical consequence of various influences of the autonomic nervous system(ANS) on heart beat. HRV can estimate the potential physiologic rhythm from the interval between consecutive beats(RR interval or HRV data). It is known as RSA which represents respiration-related HR rhythmic oscillation. Previous studies demonstrated a specific breathing pattern(0.1Hz, 6breaths/min) to improve a physiological body condition related to the stress. In this paper, the level of stress would be evaluated in terms of three phases of the dental treatment, combined with 6breaths/min. Methods: These phases include before, during and after tooth extraction or anesthesia or something.36 patients' stresses were assessed using HRV stress analyzer in each phase in Kangdong Sacred Heart Hospital, and Chuncheon Sacred Heart Hospital, Hallym University Medical Center from Jun. to Sept. of 2007. HRV 5-min data collected were analyzed in time-domain and frequency-domain to evaluate the activity of autonomic nervous system(ANS) which represents the level of stress. Results: All HRV parameters including HF(high frequency), LF(low frequency) and LF/HF ratio showned a significant change affecting the ANS balance. There was a 6.4% difference between R(LF/HF)s on general breathing pattern for balance of Autonomic nervous system, but on controlled breathing pattern, 0.1Hz, was made narrow till 1.4%. The activity of ANS has increased by 1.4% on general breathing pattern, and by 2.9% on controlled breathing pattern, 0.1Hz. Conclusion: After analysis of preoperative stress changes and effect of breathing pattern of 0.1 Hz on the stress in 36 patients who have undergone third molar extraction, following was concluded. In the preoperative stage, the sympathetic change was the greatest?after the?anesthetic injection, and stress was relieved by controlling the breathing pattern to a frequency of 0.1Hz.