• 대한기계학회논문집B
• /
• 제25권7호
• /
• pp.885-894
• /
• 2001

A large eddy simulation(LES) is performed for turbulent flow in a combustion device. The combustion device is simplified as a cylinder with sudden expansion. To promote turbulent mixing and to accommodate flame stability, a flame holder is attached inside the combustion chamber. Emphasis is placed on the flow details with different geometries of the flame holder. The subgrid scale models are applied and validated. The simulation code is constructed by using a general coordinate system based on the physical contravariant velocity components. The calculated Reynolds numbers are 5000 and 50000 based on the bulk velocity and the diameter of inlet pipe. The predicted turbulent statistics are evaluated by comparing with the LDV measurement data. The agreement of LES with the experimental data is shown to be satisfactory.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1997년도 춘계학술대회 논문집
• /
• pp.670-674
• /
• 1997

Semi-solid forging is a compound forging technology to deventional forging process. Among several steps of semi-solid forging process, the heating step of a billet prior to semi-solid forging step is necessarily required to obtain globular microstructure. For the forming operation to work properly, it is also important to heat the billet uniformly for the uniformity of solid-liquid distribution. To satisfy these requirements, induction heating has been generally used for a long time. This paper presents the method to find heating condition and the temperature distribution inside of a billet with a induction heating apparatus by comparing the computer simulation with experiment for aluminum alloys Al2024 and A356.

• 한국세라믹학회지
• /
• 제38권2호
• /
• pp.112-116
• /
• 2001

고상반응법에 의한 제조한 ZnGa$_2$O$_4$형광체에 Li 및 Tm 원소를 도핑함에 따른 발광특성을 조사하였다. 254nm 여기 하에서, 환원 처리된 ZnGa$_2$O$_4$형광체는 245nm에서 흡수피크와 380nm에서 발광피크를 나타내며, 이는 스피넬 구조에서 Ga$^{3+}$ 이온의 $^4$T$_2$$\longrightarrow$$^4$A$_2$천이에 기인한다. ZnGa$_2$O$_4$형광체에 있어서 Li 및 Tm을 도핑했을 경우가 도핑하지 않은 시료에 비해 발광강도 및 색순도가 개선되었으며, Li 및 Tm을 각각 0.1 mol, 0.01 mol 첨가했을 때 가장 우수한 발광강도 및 색순도 특성을 보였다.

• E2M - 전기 전자와 첨단 소재
• /
• 제1권2호
• /
• pp.152-161
• /
• 1988

Pb(Zr, Ti)O$^{3}$-Pb(Mg, Nb)O$^{3}$계에 MnO$_{2}$첨가량을 변화시켜 소결성, 미세구조, 유전상수, 비저항 및 압전특성에 미치는 영향을 XRD, EDAX 및 SEM을 이용하여 미세구조를 관찰하고 실험을 통하여 전기적 성질에 미치는 영향을 밝혔다. 비저항의 변화없이 그레인 성장이 억제되는 $MnO_{2}$의 첨가량은 0.4wt%이었으며 이때 분말의 합성이 촉진되어 소성된 시편의 밀도가 증가하였다. 그러나 고상반응의 범위를 벗어나는 과잉 $MnO_{2}$는 편석이 되어 그레인 경계상에 모임이 확인되었고 또한 기공을 형성하여 밀도를 낮추었다. $Mn^{+4}$는 $Mg^{+2}$ 와 치환되어 페로브스카이트 구조의 "A" 결핍을 유발하였으며 이것이 비저강을 감소시키는 원인으로 밝혀졌다.감소시키는 원인으로 밝혀졌다.

• 한국정밀공학회지
• /
• 제13권7호
• /
• pp.29-35
• /
• 1996

For semi-solid forging with aluminuim alloys, it is required to develope the globular grain structure. It was studide that cold upsetting ration in SIMA process has effect on the globularization of grain structure. Globular microstructure was generated without cold upsettings for commercial aluminium alloys. In the case of A12024, the range of grain size was 40 .approx. 50 .mu. m. The grain growth in growth in globular microstructure depend on heating time. Spur gear was forged in semi-solid state to investigate the forging condition for A12024 with hydraulic press.

• Journal of Preventive Medicine and Public Health
• /
• 제30권1호
• /
• pp.129-143
• /
• 1997

This study was carried out to assess the relationship between job characteristics(job strain) and psychosocial distress, and to find out the effect of social support on psychosocial distress. The study design was cross-sectional, and included 1,211 industrial workers in middle-sized city. A self-administered questionnaire measured job characteristics(jod demand, job control), and social support(coworker support, supervisor support) at work. Psychosocial distress was measured using PWI(Psychosocial Well-being Index), a 45-item self-administered instrument. Among the 1,211 respondents, the prevalence of psychosocial distress was 24.8% High job stram (high job demand + low job control) was present in 8% of the subjects. The crude odds ratio of high job strain was 4.76 (95% CI : 2.60-8.74), and those of active group and passive group were 3.81(95% CI : 1.82-3.95) and 2.64(95% CI : 1.77-3.94), respectively. The odds ratios of each group adjusted for sex, age, support, and religion were still significant. Our results supported the association between job strain and psychosocial distress. Social support at work, although significantly associated with psychosocial distress, did not modify the association between job strain and psychosocial distress.

• Journal of Korean Biological Nursing Science
• /
• 제16권2호
• /
• pp.123-132
• /
• 2014

Purpose: The purpose of this study was to compare and analyze the effects of gargling using normal saline or essential oil on oral bacterial colonization of the subjects who did transoral endotracheal intubation for general anesthesia. Methods: A repeated measures, non-equivalent control group pretest-posttest design was used in this study. The subjects of the study included 58 people; the gargling group with normal saline (n=19); the gargling group with essential oil (n=20); and the control group (n=19). Data were collected from University hospitals in a Korean province from August 13-31, 2012. The collected data were analyzed with $X^2$-test, t-test, ANOVA and Scheff$\acute{e}$ test using SPSS 19.0. Results: Although statistically significant differences among the three groups did not appear in the change of the aerobic bacterial colony before and after the experiments, the aerobic bacterial colony of the gargling group with normal saline ($71.58{\pm}143.39$) and the group with essential oil ($6.95{\pm}332.07$) have increased less compared to the control group ($145.42{\pm}385.01$). The change of the anaerobic bacterial colony before and after the experiments, the control group was ($167.58{\pm}483.58$) and the gargling group with essential oil was ($169.70{\pm}291.60$) and increased, while the gargling group with normal saline ($-42{\pm}331.09$) reduced, but statistically significant differences have not appeared. Conclusion: These findings indicated that oral gargling with normal saline is effective in reducing anaerobic bacterial colonization.

• Journal of Korean Biological Nursing Science
• /
• 제19권1호
• /
• pp.48-54
• /
• 2017

Purpose: This study was done to identify the influence of severity of drinking problem, circadian rhythm and sleep quality in patients with alcohol use. Methods: A descriptive study design was utilized. Data were collected using self-report questionnaires from 139 patients with alcohol use disorder who were admitted to a psychiatric hospital in D city, Korea. The questionnaires included Alcohol Use Disorders Identification Test (AUDIT), Composite Scale of Morningness (CMS), Pittsburgh Sleep Quality Index (PSQI), and Korea sleep scale A. Data were analyzed using descriptive statistics, Pearson's correlation coefficients, and multiple regressions using the SPSS 20.0 program. Results: There was significant correlations among severity of problem drinking, circadian rhythm, sleep quality and sleep disorder. The significant factors influencing sleep disorder were severity of problem drinking(${\beta}=.12$, p= .042), circadian rhythm(${\beta}=-.14$, p= .039) and sleep quality(${\beta}=.63$, p= < .001). This model explained 56% of variance in sleep disorder(F = 57.34, p= < .001). Conclusion: The results of this study suggest that the development of sleep intervention programs for alcohol use disorder patients needs to consider severity of alcohol use, circadian rhythm and sleep quality, and sleep assessment and intervention are needed the early stage of the treatment and recovery process.

• 동아시아식생활학회지
• /
• 제24권6호
• /
• pp.883-895
• /
• 2014

This study investigated quality characteristics of pan breads prepared with 0, 10, 20, 30 and 40% purple rice flour and naturally fermented blueberry-rice starters. RVA (Rapid Visco Analyzer) analysis showed that wheat flour retrogradation was not retarded by addition of purple rice flour. Using amylography, gelatinization tem. perature of purple rice flour samples was higher than that of the control, whereas maximum viscosity temperature. and maximum viscosity of purple rice flour samples were lower than those of the control. Weights of pan breads containing purple rice flour were lower than that of the control, whereas volume, specific volume and baking loss rate were higher than those of the control. The anthocyanin contents and antioxidative activites as measured by DPPH radical scavenging activity of breads increased as the concentration of purple rice flour increased. The moisture content of pan breads containing purple rice flour decreased as storage time increased. The pH of breads containing purple rice flour was higher than that of the control. Color L value decreased, whereas a and b values increased significantly, as storage time increased. In texture analyzer measurement, hardness of breads containing purple rice flour significantly increased as storage time increased. Breads containing 10~20% purple rice flour showed acceptable sensory properties, such as mouth feel, appearance, flavor, texture, taste and overall acceptability.

• 한국구조물진단유지관리공학회 논문집
• /
• 제18권6호
• /
• pp.21-29
• /
• 2014

본 연구에서는 모노파일지지구조의 고성능 그라우트연결부의 부착거동을 다루고 있다. 강관파일 연결부의 일체화를 위하여 섬유보강 고성능 그라우트를 개발하였으며, 재령 7일 압축강도 125MPa와 직인장강도 7.5MPa를 나타내었다. 축하중을 받는 상태에서의 그라우트의 부착거동을 평가하기 위하여 강관파일에 그라우트를 충진하여 부착실험을 수행하였으며, 그 결과를 기존의 설계기준과 분석하였다. 실험변수는 섬유혼입율 (0%, 0.5% and 0.9%), 섬유의 형상비 (60 and 80)와 전단키의 높이와 간격의 비 (0.013 and 0.056)로 선정하였다. 실험결과 최대부착강도는 30.8MPa로 관찰되었으며, 섬유 혼입율보다는 전단키의 높이와 간격의 비가 부착강도에 영향을 미치는 것으로 분석되었다.