• Korean Journal of Child Studies
• /
• v.36 no.1
• /
• pp.85-98
• /
• 2015

This study aimed to investigate measures which could reduce the daily stress of 3-5-years-olds who are attending daycare centers, by examining the effects of 3-5-years-olds' time spent in daycare centers and peer competence on daily stress. To this end, two hundred and fifty 3-5-years-olds attending the same daycare for more than 6 months were selected from 5 daycare centers in Daejeon Metropolitan City and tested for their daily stress levels. In addition their teachers completed peer competence tests and a short questionnaire regarding the 3-5-years-olds. In terms of the results, those 3-5-years-olds who spent more than 7 hours or longer in daycare centers were found to have a higher level of daily stress than the 3-5-years-olds who spent less than 7 hours. Additionally, those 3-5-years-olds who returned home after 6 p.m were found to have a higher level of daily stress than the 3-5-years-olds who returned home before 6 p.m. Moreover, it was found that the more time 3-5-years-olds spent in daycare centers and the lower their peer competences were, the more daily stress they seemed to experience.

• Computers and Concrete
• /
• v.6 no.4
• /
• pp.343-356
• /
• 2009

Experiments were designed to investigate the flow behavior of portland cement paste and concrete incorporating superplasticizers. The paste and concrete mixtures were subjected to prolonged mixing for up to 110 min at high temperature. The yield stress values of concrete and that of the corresponding cement paste were measured using a rotating rheometer and viscometer, respectively. The results reveal a weak linear correlation between the yield stress of concrete mixtures and that of the corresponding cement pastes. Results also indicate that the yield stress of concrete varies in a linear fashion with the elapsed time, while its variations with the temperature and superplasticizer dosage follow power and inverse power functions, respectively. In this study, the genetic algorithms (GA) technique was used to predict the yield stress of concrete considering various parameters, such as the mixing time, ambient temperature, and superplasticizer dosage. A sensitivity study was conducted to evaluate the ability of the GA equations thus developed to capture the effects of test parameters on the yield stress of concrete. It was found that the GA equations were sensitive to the effects of test parameters and provided yield stress predictions that compared well with corresponding experimental data.

• Journal of Korean Society for Quality Management
• /
• v.24 no.3
• /
• pp.19-30
• /
• 1996

We treat problems of estimating reliability R(t) = P[Y(t) ＞ X(t)] in the time dependent strength-stress model in which a unit of stress X(t) is subjected to environmental strength Y(t) at time t. In this paper we introduce a special model of R(t) with fixed strength and unaccumulated stress case, and propose a Mann-Whitney-Wilcoxon type estimator of R(t).

• Journal of the Korean Data and Information Science Society
• /
• v.10 no.1
• /
• pp.111-118
• /
• 1999

We treat the problem of estimating reliability R(t) = P[Y(t) < X(t)] in the time dependent strength-stress model in which a unit of strength X(t) is subjected to environmental stress Y(t) at time t. In this paper two nonparametric approaches to estimate of R(t) are analyzed and compared with parametric method by simulation.

• Journal of Physiology & Pathology in Korean Medicine
• /
• v.24 no.5
• /
• pp.877-882
• /
• 2010

This study was designed to investigate job stress, job satisfaction and related factors of oriental medical doctors. The survey used administered questionnaire, was conducted from June 10 to June 30, 2010 in Jeonbuk province. Questionnaire was composed of general characteristics, socioeconomic status perception, job stress scale and job satisfaction scale. Job stress was related to sex, age, marriage, working form, working time, clinical career. Job satisfaction was related to age. Working time, working form and self-status perception influenced job stress. Self-status perception influenced job satisfaction. Especially, it was supposed that working time was most important factor to job stress.

• Geomechanics and Engineering
• /
• v.19 no.5
• /
• pp.369-381
• /
• 2019

The objective of this paper is to study the two dimensional deformation in transversely isotropic thermoelastic medium without energy dissipation due to time harmonic sources using new modified couple stress theory, a continuum theory capable to predict the size effects at micro/nano scale. The couple stress constitutive relationships have been introduced for transversely isotropic thermoelastic medium, in which the curvature tensor is asymmetric and the couple stress moment tensor is symmetric. Fourier transform technique is applied to obtain the solutions of the governing equations. Assuming the deformation to be harmonically time-dependent, the transformed solution is obtained in the frequency domain. The application of a time harmonic concentrated and distributed sources have been considered to show the utility of the solution obtained. The displacement components, stress components, temperature change and couple stress are obtained in the transformed domain. A numerical inversion technique has been used to obtain the solutions in the physical domain. The effects of angular frequency are depicted graphically on the resulted quantities.

• Current Optics and Photonics
• /
• v.8 no.3
• /
• pp.225-229
• /
• 2024

This paper introduces a rapid measurement technique for the stress-optic coefficient, using terahertz time-domain spectroscopy. First we propose a design combining a four-point bending device with a scanning stage to streamline the loading process. Then we detail the measurement principle and outline the signal-processing algorithm. The experiments are carried out on Al₂O₃, a representative ceramic material. The experimental data reveal that the refractive index of Al₂O₃ exhibits a linear decrease with increasing stress. This work supplies an efficient method for stress measurement rooted in the stress-optic effect.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.12
• /
• pp.3369-3376
• /
• 1994

A finite element program for elastic stress wave propagation is developed in order to investigate the shape of stress field and analysis the magnitude of stress wave intensity at time increment. Accuracy and reliance of the finite element analysis are acquired when the element size is smaller than the product of the stress wave speed and the critical value of increasing time step. In the finite element analysis and theoretical solution, the longitudinal stress wave is propagated to the similar direction of impact load, and the stress wave intensity is expressed in terms of the ratio of propagated area. The direction of shear wave is declined at an angle of 45 degrees compared with longitudinal stress wave and the speed of shear wave is half of the longitudinal stress wave.

• Journal of the Korean institute of surface engineering
• /
• v.38 no.1
• /
• pp.14-20
• /
• 2005

The control of internal stress is extremely important in electroforming because of the deliberately low adhesion between the electro form and the mandrel. Excessive tensile or compressive stress can cause distortion, separation problem, curling, peeling or separation of electroform prematurely from the mandrel, buckling and blistering. Nickel sulfamate bath has been widely used in electroforming because of its low internal stress and moderate hardness. In this study, real-time stress sensor has been used for stress control in chloride-free nickel sulfamate bath for 400 mm x 300 mm x 500 ㎛ nickel electroform. It was found that compressive stress found at low current density indicated the contamination of electrolyte, which is very useful in procuring buckling and peeling of electroform. No compressive stress is allowed for plate electroform. The real-time stress can also be used for accurate stress control of nickel electroform. The tensile stress was found to be increased slightly with increase in nickel electroform thickness, i.e., from initial 1.47 ksi to 2.02 ksi at 320 ㎛.

• Journal of Preventive Medicine and Public Health
• /
• v.34 no.2
• /
• pp.141-148
• /
• 2001

Objective : To investigate the sources, extent and related factors in South Korean doctors. Methods : The study subjects were 934 doctors in Taegu, Kyungpook Province, Korea(540 independent practitioners, 105 employed at hospitals and 289 residents in training). Information concerning job stress was obtained using a 9-item questionnaire. Information regarding related factors such as demographic characteristics(age, sex, marital status), perceptions on the socioeconomic status of doctors and working conditions(work time, on-call days per week) was also obtained by self-administered questionnaire during April and May, 2000. Results : Major sources of job stress included clnical responsibility/judgement factor, patient factor and work loading factor. The job stress score of residents was the highest among three groups. The score was lower in older doctors. The score was low among those who thought doctors' socioeconomic status was not good. The longer the work time, the higher the job stress score was. Multiple regression analysis was conducted to control for the mutual influence of independent variables. In regression analysis, the score of residents was higher than practitioners. Work time and socioeconomic status perception had negative effects on job stress score. Conclusion : The average job stress score of the doctors was high. Age, work type, working conditions and perceptions of socioeconomic status were found to besignificantly related to job stress score. Although the job stress of doctors is somewhat inevitable due to the nature of the doctor's job, control of work time, development of coping tools and other intervention methods are needed to reduce job stress of doctors. Further studies are required to understand the characteristics of iob stress and reduce the job stress of doctors.