• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2004년도 추계학술대회 논문집
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• pp.92-97
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• 2004

The aim of this study is to estimate the strength of injection molded plastic stepped gear. We considered stepped gear as plate model which are fixed by two edges. While, on the other sides are free. Normal gear is calculated by Lewis formula which can be derived quite simply from the equation for the stress at the root of a cantilever beam. Stress ratio(step factor) is represented for the ratio of the bending stress of normal and the bending stress of stepped gear, and it is plotted by face width factor. This study is propose the step factor added in Dupont equation which are strength estimation of step gear

• 열처리공학회지
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• 제17권6호
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• pp.336-341
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• 2004

The effect of shot peening conditions on the fatigue properties of heat-treated spring steel has been investigated by using residual stress measurement and metallography. The mechanical properties of material did not change so much by shot peening. However, the fatigue strength and fatigue life increased about 20% to 40% by 1-step and 2-step shot peening process. The fatigue strength and life were closely related to the value and position of maximum compressive residual stress by shot peening process. In the case of warm shot peening, compressive residual stress of specimens shot peening processed at $200^{\circ}C$ was higher than those of specimens shot peening processed at room temperature, $100^{\circ}C$ and $300^{\circ}C$.

• 대한기계학회논문집B
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• 제20권5호
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• pp.1661-1670
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• 1996

Incompressible flow over a backward-facing step is computed by low Reynolds number turbulence models in order to compare with direct simulation results. In this study, selected low Reynolds number 1st and 2nd (Algebraic Stress Model : ASM) moment closure turbulence models are adopted and compared with each other. Each turbulence model predicts different flow characteristics, different re-attachment point, velocity profiles and Reynolds stress distribution etc. Results by .kappa.-.epsilon. turbulence models indicate that predicted re-attachment lengths are shorter than those by standard model. Turbulent intensity and eddy viscosity by low Reynolds number .kappa.-.epsilon. models are still greater than DNS results. The results by algebraic stress model (ASM) are more reasonable than those by .kappa.-.epsilon. models. The convective scheme is QUICK (Quadratic Upstream Interpolation for Convective Kinematics) and SIMPLE algorithm is adopted. Reynolds number based on step height and inlet free stream velocity is 5100.

• International Journal of Reliability and Applications
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• 제15권2호
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• pp.125-150
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• 2014

Accelerated life tests (ALTs) are extensively used to determine the reliability of a product in a short period of time. Test units are subject to elevated stresses which yield quick failures. ALT can be carried out using constant-stress, step-stress, progressive-stress, cyclic-stress or random-stress loading and their various combinations. An ALT with linearly increasing stress is ramp-stress test. Much of the previous work on planning ALTs has focused on constant-stress, step-stress, ramp-stress schemes and their various combinations where the stress is generally increased. This paper presents an optimal design of ramp soak-stress ALT model which is based on the principle of Thermal cycling. Thermal cycling involves applying high and low temperatures repeatedly over time. The optimal plan consists in finding out relevant experimental variables, namely, stress rates and stress rate change points, by minimizing variance of reliability function with pre-specified mission time under normal operating conditions. The Burr type XII life distribution and time-censored data have been used for the purpose. Burr type XII life distribution has been found appropriate for accelerated life testing experiments. The method developed has been explained using a numerical example and sensitivity analysis carried out.

• 비파괴검사학회지
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• 제32권1호
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• pp.27-33
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• 2012

광탄성법은 실험역학에서 응력 또는 변형률을 해석하기 위한 여러 실험방법 중의 하나이며, 다양한 종류의 구조물의 응력 분포를 실험적으로 결정하는 기법이다. 광탄성법은 광탄성 영상의 등색 프린지와 등경 프린지로부터 광탄성 시편에 나타나는 전체의 응력장 분포를 정밀하게 측정할 수 있다. 본 논문에서는 여러 가지 광탄성 기법중 8단계 위상이동법(8-step phase-shifting method)에 관한 이론을 살펴보고, 경사균열이 있는 평판 시편에 인장을 가하여 나타난 광탄성 프린지로부터 경사균열 선단주위의 응력분포를 8단계 위상이동법으로 결정한 후, 이들 결과를 유한요소법(FEM)에 의한 결과와 비교하였다. 8단계 위상이동법을 이용한 실험에 의해 측정된 프린지 차수는 유한요소법에 의한 계산된 프린지 차수값에 근접하였다.

• 한국컴퓨터정보학회논문지
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• 제22권6호
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• pp.95-100
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• 2017

Recently, as stress has become a major threat to people's health, there is a growing interest in wearable stress management services for stress relief. In this paper, we developed a wearable device(Care-on) capable of extracting changeable human voice information at each site and a Healthcare App(S-Manager) that enables stress management in real time using the wearable device. It collects and analyzes variable real-time voice information for each part of the person's body. And It also provides the ability to monitor stress conditions in a mobile environment and provide feedback on the analysis results in step by step in the mobile environment. We tested the developed wearable devices and app in a mobile environment and analyzed the results to confirm their usefulness.

• 한국재료학회지
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• 제11권9호
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• pp.769-775
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• 2001

High quality PZT piezoelectric thin films were sputter- deposited on$ RuO_2$/$SiO_2$/Si substrates by using 2-step deposition method. As the first step, PZT seed layers were fabricated at a low temperature($475^{\circ}C$ ) to form a pure perovskite phase by reducing the volatility of Pb oxide. and then, as the second step, the PZT films were deposited at high temperatures ($530^{\circ}C$~$570^{\circ}C$) to reduce the defect density in the films. By this method, the pure perovskite phase was obtained at high deposition temperature range ($530^{\circ}C$~$570^{\circ}C$) and the superior electrical properties of PZT films were obtained on $RuO_2$substrate : 2Pr : 60$\mu$C/$\textrm{cm}^2$, $E_c: 60kV/cm, \;J_t: 10^{-6}A/cm^2\; at\; 250kV/cm$. The residual stress of PZT films fabricated by the 2-step deposition method was tensile and below 150MPa. It was attempted to control the residual stress in the PZT films by applying a negative bias to the substrate. As the amplitude of the substrate bias was increased, the residual tensile stress was slightly decreased, however, the ferroelectric properties of PZT films were degraded by ion bombardment.

• 한국응급구조학회지
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• 제21권3호
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• pp.109-120
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• 2017

Purpose: The purpose of the study was to investigate the mediating effects of self-efficacy on the relationship between job stress and turnover intention of paramedics in hospitals. Methods: A self-reported questionnaire was completed by 209 paramedics in hospitals from September 4 to 24, 2015. Data were analyzed by descriptive statistics, t-test, ANOVA, Pearson's correlation coefficients, and multiple regression analysis using Baron & Kenny's 3 step procedure. Indirect effect was confirmed with Sobel test using SPSS/Win 22.0 program. Results: There were negative relationships between job stress, self-efficacy, and turnover intention (r=-.509, p<.001). There was a negative relationship between job stress and self efficacy (r=-.821, p<.001). The self-efficacy and turnover intention showed a positive relationship (r=.636, p<.001) with job stress and turnover intention. Concerning the mediated effect of self efficacy on job stress and turnover intention, the influence of job stress at step 2 on turnover intention was significant (B=1.207, p<.001), while job stress at step 3 had significant influence on turnover intention (B=.474, p<.001). The mediated effect of self-efficacy on job stress and turnover intention showed significant partially mediated effect of self-efficacy (z=7.100, p<.001). Conclusion: Improvement of self-efficacy and job stress was effective at decreasing turnover intention in paramedics in hospitals.

• Geomechanics and Engineering
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• 제30권3호
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• pp.219-231
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• 2022

Geotechnical materials such as silt, fine sand, or coarse granular soils may be unstable under undrained shearing or during rainfall infiltration starting an unsaturated state. Some researches are available describing the instability of coarse granular soils in drained or undrained conditions. However, there is a need to investigate the instability mechanism of unsaturated silty soil considering the effect of degree of compaction and net confining stress under partially and fully drained conditions. The specimens in the current study are compacted at 65%, 75%, & 85% degree of compaction, confined at pressures of 60, 80 & 120 kPa, and tested in partially and fully drained conditions. The tests have been performed in two steps. In Step-I, the specimens were sheared in constant water content conditions (a type of partially drained test) to the maximum shear stress. In Step-II, shearing was carried in constant suction conditions (a type of fully undrained test) by keeping shear stress constant. At the start of Step-II, PWP was increased in steps to decrease matric suction (which was then kept constant) and start water infiltration. The test results showed that soil instability is affected much by variation in the degree of compaction and confining stresses. It is also observed that loose and medium dense soils are vulnerable to pre-failure instability i.e., instability occurs before reaching the failure state, whereas, instability in dense soils instigates together with the failure i.e., failure line (FL) and instability line (IL) are found to be unique.

• 농촌의학ㆍ지역보건
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• 제38권1호
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• pp.39-48
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• 2013

본 연구는 건강취약계층의 건강관리를 위하여 실시되고 있는 방문건강관리을 담당하고 있는 간호사를 대상으로 직무스트레스 및 직무만족도가 조직애착도에 미치는 영향을 파악하기 위해 실시하였다. 조사대상자는 일개 도의 방문건강관리 간호사로 130명의 조사결과를 최종적으로 활용하였다. 단순분석결과에서 직무 스트레스 영역 중 직무 불안정에 해당하는 점수가 69.7점으로 가장 높았으며 다음으로 직무 요구가 64.9점으로 높았다. 직무만족도 및 조직애착도는 각각 2.6점과 2.3점이었다. 직무만족도를 매개변수로 하여 조직애착도에 미치는 직무 스트레스의 관련성을 분석한 결과 직무요구와 직무 불안정은 직무 만족도가 부분 매개하였으며 나머지 스트레스 영역은 직무 만족도가 직무스트레스와 조직애착도간의 관련성을 완전매개하고 있었다. 이상의 결과로 보아, 방문건강관리 간호사들의 조직애착도를 높이기 위해서는 직무 요구도 파악과 직무에 대한 불안정감을 해소하는 것이 우선 실시되어야 할 것이다.