• Proceedings of the KWS Conference
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• 2002.10a
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• pp.121-126
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• 2002

The railroad cars or the commercial vehicles are generally manufactured by the spot welding. Among various kinds of spot welded lap joints, multi-lap joints are one of popular joints in manufacturing their body structures. But, fatigue strength of these joints are lower than that of base metal due to high stress concentration at the nugget edge of the spot weld and are known to considerably be influenced by welding conditions as well as the mechanical and geometrical factors. Thus, it is necessary to establish a reasonable and systematic fatigue design criterion for spot welded multi-lap joints. In this paper, the $\Delta$P-N$_{f}$ curves has been rearranged in the $\Delta$$\sigma$-N$_{f}$ relation with the maximum stress at the nugget edge of spot welded multi-lap joints subjected to tensile shear load. Consequently, the fatigue data were evaluated in terms of fracture mechanics by plotting on the $\Delta$OP-N$_{f}$ curves. From the results obtained, both of them have been revealed to be applicable to fatigue design of spot welded multi-lap joints. However, the fracture mechanical approach is found to be more effective than the maximum stress approach in the range on N$_{f}$$\geq$2x10$^{5}$ . .

• Korean Journal of Agricultural and Forest Meteorology
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• v.21 no.4
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• pp.261-268
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• 2019

Climate change and drought stress are having profound impacts on crop growth and development by altering crop physiological processes including photosynthetic activity. But finding a rapid, efficient, and non-destructive method for estimating environmental stress responses in the leaf and canopy is still a difficult issue for remote sensing research. We compared the relationships between photochemical reflectance index(PRI) and various optical and experimental indices on soybean drought stress under climate change conditions. Canopy photosynthesis trait, biomass change, chlorophyll fluorescence(Fv/Fm), stomatal conductance showed significant correlations with midday PRI value across the drought stress period under various climate conditions. In high temperature treatment, PRI were more sensitive to enhanced drought stress, demonstrating the negative effect of the high temperature on the drought stress. But high CO₂ concentration alleviated the midday depression of both photosynthesis and PRI. Although air temperature and CO₂ concentration could affect PRI interpretation and assessment of canopy radiation use efficiency(RUE), PRI was significantly correlated with canopy RUE both under climate change and drought stress conditions, indicating the applicability of PRI for tracking the drought stress responses in soybean. However, it is necessary to develop an integrated model for stress diagnosis using PRI at canopy level by minimizing the influence of physical and physiological factors on PRI and incorporating the effects of other vegetation indices.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.1
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• pp.163-171
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• 1996

For the effective analysis of two dimensional plane problems, Treffiz finite elements and cavity elements have been proposed. These element matrix equaitons were formulated on the basis of hybrid variational principle and Treffiz function sets derived consitstently from the complex theoy of plane elasticity. In order to suggest the accuracy chatacteristics of the proposed Treffiz elements typical plane problems were analyzed and these results were compared with ones obtained by using the conveintional displacement type elements. The accuracy of the proposed elements is less sensitive to the element size and shape than the conventional displacement type elements. These elements, being able to be formed with multi-nodes, give the convenient modeling of an analytic domain. The cavity elements give the comparatively exact values of stress concentration factors of stress intensity factors and can be effectively used for the analysis of mechanical stuctures containing various cavities.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.4
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• pp.1-9
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• 2002

There is the high possibility of crack initiation from mechanical joints, which are widely used in aircraft fuselages, due to the development of stress concentration and contact pressure. In this paper, the mixed-mode stress intensity factors at the surface and deepest points of an inclined quarter elliptical corner crack in mechanical joints are analyzed by the weight function method. The coefficients included in the weight function are obtained by finite element analyses for reference loadings. Critical angle at which mode I stress intensity factor becomes maximum is determined by analyzing the variation of stress intensity factors along incline angle of crack and the effects of the amount of clearance and crack depth on the critical angle are investigated.

• Ocean and Polar Research
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• v.32 no.2
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• pp.97-111
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• 2010

Phytoplankton production is affected by various physico-chemical factors of environment. However, one of the most critical factors generally accepted as controlling primary production of phytoplankton is nutrients. It has recently been found that the succession of phytoplankton groups and species are closely related to the chemical properties of ambient water including nutrient limitation and their ratios. In Jangmok Bay, silicate and nitrate are primarily supplied by rainfall, while phosphate and ammonia are supplied by wind stress. Typhoons are associated with rainfall and strong wind stress, and when typhoons pass through the South Sea, such events may induce phytoplankton blooms. When nutrients were supplied by heavy rainfalls during the rainy season and by summer typhoons in Jangmok Bay, the dominant taxa among the phytoplankton groups were found to change successively with time. The dominant taxon was changed from diatoms to flagellates immediately after the episodic seasonal events, but returned to diatoms within 3~10 days. Pseudo-nitzschia spp. were dominant mainly in the presence of low phosphate levels during the first of the survey which included the rainy season, while Skeletonema costatum was dominant when phosphate concentrations were high due to the strong wind stress during the latter half of the survey as a result of the typhoon. The competition between S. costatum and Chaetoceros spp. appeared to be regulated by the silicate concentration. S. costatum preferred high silicate and phosphate concentrations; however, Chaetoceros spp. were able to endure low silicate concentrations. These results implied that, in coastal ecosystems, the input patterns of each nutrient supplied by rainfall and/or wind stress appeared to contribute to the summer succession of phytoplankton groups and species.

• Proceedings of the KWS Conference
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• 2002.05a
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• pp.178-181
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• 2002

This is a partial report of the investigation of fatigue behaviour of hollow section T-joints with circular brace members and rectangular chord members (CRHS). Hot spot stresses and the stress concentration factors (SCFs) were determined experimentally. Fatigue testing was carried out under constant amplitude loading in air. The experimental SCF values for CRHS joints were found to be below those of circular-to-circular (CCHS) and rectangular-to-rectangular (RRHS) hollow section joints. The fatigue strength referred to experimental hot spot stress was in reasonably good agreement with current fatigue design codes for tubular joints.

• Proceedings of the KWS Conference
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• 2001.10a
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• pp.281-284
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• 2001

Fatigue behaviour of eight different hollow section T-joints was investigated experimentally using scaled steel models. The joints had circular brace members and rectangular chords (CRHS). Hot spot stresses and the stress concentration factors (SCFs) were determined experimentally. Fatigue testing was carried out under constant amplitude loading in air. The experimental SCF values for CRHS joints were found to be between those of circular-to-circular (CCHS) and rectangular-to-rectangular (RRHS) hollow section joints. The fatigue strength referred to experimental hot spot stress was in reasonably good agreement with current fatigue design codes for tubular joints.

• Journal of the Korean Society of Radiology
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• v.10 no.2
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• pp.89-99
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• 2016

The purpose of this study is to identify and analyze factors that are affecting radiologists' turnover intention. For the purpose, this researcher surveyed 200 radiologists who were serving at secondary medical institutions located in Busan. For the survey, the researcher used a structured questionnaire. Findings of the study can be summarized as follows. This study show that in order to reduce radiologists' turnover, it is necessary to develop effective personnel management strategies that can make internally motivated radiologists, raise their job satisfaction and organizational concentration and reduce their job stress. Radiologists' turnover rate would not decline if such problems as excessive workload, lack in the number of persons of the same profession and unfair personnel management system are not solved and if no efforts are made to remunerate at reasonable levels, provide more opportunities of promotion and raise job satisfaction. These solutions to prevent radiologists' turnover could be successful only when officially supported by hospitals.

• IMMUNE NETWORK
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• v.5 no.4
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• pp.232-236
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• 2005

Background: A physically active lifestyle and regular exercise training incurs many health benefits. One recently recognized benefit of regular moderate exercise is stress reduction and immune enhancement. Thus, a physical stress such as exercise may act at any number of points in the complex sequence of events collectively termed the immune response. Although exercise causes many propound changes in parameters of immune function, the nature and magnitude of such changes rely on several factors including the immune parameters of interest; type, intensity, and duration of exercise; fitness level or exercise history of the subject; environmental factors such as ambient temperature and humidity. Methods: This study was undertaken to investigate the effect of different type of exercise on superoxide dismutase (SOD), neutrophils, and T lymphocytes of Sprague-Dawley rats. Sprague-Dawley rats were randomly divided into three groups; a non-Trained group (NTG, n=6), a swim-Trained group (STG), and a treadmill-Trained group (TTG). The exercise regimen was designed in a treadmill (5 times/5 days/week) during 8-weeks for TTG, and swim training (5 times/5 days/week) during 8-weeks for STG, and the volume of exercise training was the same in both groups. Results: 8 weeks of regular swim and treadmill training significantly increased liver SOD concentration however, muscle SOD concentration was not statistically significant. In the level of neutrophils, TTG and STG showed significant difference, compared to NTG. TTG was the highest level of neutrophils. In the level of immune cell counts, there was significant difference among TTG, STG, and NTG both in the spleen and thymus. Conculsion: In conclusion, it can be stated that eight weeks swim and treadmill exercise training has beneficial effect in improving immune response and antioxidant defence capacity by augmenting immune cells and SOD activities of SD rats.

• Fire Science and Engineering
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• v.20 no.2 s.62
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• pp.80-86
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• 2006

This study focuses on spalling phenomenon which is the one of the main issues of high strength concrete. The definition, classification and characterization, causes and the reaction mechanism of the spalling were investigated on the basis of previous literatures. The spalling phenomenon occurs when several factors such as sharp temperature increase, high water content, low water/cement ratio and local stress concentration in material combine in the concrete material. On the basis o f the factors, the preventing methods from the spalling are known as decrease of temperature increase, preventing of concrete fragmentation and fast drying of internal moisture. In this study, the controlling method of water content below some critical value was proposed as the most effective spalling-preventing method among the spalling-preventing methods. The spalling phenomenon can be prevented by adjusting the water content in the high strength concrete. Therefore, an enforced drying method is needed to decrease the water content below a critical value. Additional experimental data should be generated to determine the critical value of water content for preventing the spalling.