• Korean Journal of Clinical Laboratory Science
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• v.49 no.3
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• pp.308-315
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• 2017

Carotid artery intima-media thickness (CIMT) test is a standardized ultrasound procedure that screens for and monitors atherosclerosis in a safe and non-invasive manner, even in individuals with no symptoms of heart disease. The purpose of this study was to research the relationship between CIMT, as measured by ultrasonography, and the degree of individual perceived stress. There was a total of 168 (male: 46, female: 122) university students in Suwon-si, Gyeonggi-do, Korea, without other diseases. Written informed consent was obtained from all participants. CIMT was measured in the right and left common carotid arteries 1 cm below the bifurcation, and internal carotid artery, using non-invasive high-resolution Medison Accuvix V20 prestige ultrasound equipment and perceived stress, was measured with the 10-item PSS (Perceived Stress Scale) questionnaire. This study indicates that PSS may be appropriate to estimate perceived stress levels and weight. Failure to control stress anxiety could lead to weight and CIMT soaring to dangerous levels, resulting in a myocardial infarction or cerebrovascular accident. There was a statistically significant difference between left CIMT (p<0.05) and weight (p<0.05) according to each stress classification. The results of this study suggest that the weight measurement is influenced in part by one's generalized stress levels. Future continuous studies should be conducted to test the influences of perceived stress and generalized anxiety on CIMT when these are many continuous variables.

• International Journal of Highway Engineering
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• v.9 no.2 s.32
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• pp.141-151
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• 2007

The current standards and specifications for the road pavement construction have been developed based on materials and construction methods. The pavements constructed in accordance with those specifications do not guarantee high performance of pavements since they do not consider long-term performance of pavements. Therefore, as part of the study to develop performance-based construction standards for pavements, the payment adjustment methods based on the pavement performance are currently being developed. This paper presents preliminary studies performed to develop the payment adjustment methods when there is deficiency in the concrete slab thickness that is one oi the most important factors for the pavement design and construction. First, the payment adjustment methods in USA were investigated. Then, the AASHTO failure equation, the relationship between slab thickness and stress, and the relationship between stress level and pavement life were employed to propose the payment adjustment concepts based on the pavement performance for the deficient slab thickness. The variation in the slab thickness according to measurement locations was investigated by taking cores. In addition, the measurement methods of slab thickness and the variation of measured thicknesses depending on performers were analyzed, and finally the methodology to develop the thickness deficiency ranges for the use in the payment adjustment methods was proposed.

• Restorative Dentistry and Endodontics
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• v.33 no.5
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• pp.457-462
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• 2008

"Residual stress" can be developed during polymerization of the dental composite and it can be remained after this process was completed. The total amount of the force which applied to the composite restoration can be calculated by the sum of external and internal force. For the complete understanding of the restoration failure behavior. these two factors should be considered. In this experiment. I compared the residual stress of the recently developed nanofilled dental composite by ring slitting methods. The composites used in this study can be categorized in two groups. one is microhybrid type-Z250, as control group, and nanofilled type-Grandio, Filtek Supreme. Ceram-X, as experimental ones. Composite ring was made and marked two reference points on the surface. Then measure the change of the distance between these two points before and after ring slitting. From the distance change, average circumferential residual stress $({\sigma}{\theta})$ was calculated. In 10 minutes and 1 hour measurement groups, Filtek Supreme showed higher residual stress than Z250 and Ceram-X. In 24 hour group, Filtek showed higher stress than the other groups. Following the result of this experiment, nanofilled composite showed similar or higher residual stress than Z250, and when comparing the Z250 and Filtek Supreme, which have quite similar matrix components. Filtek Supreme groups showed higher residual stress.

• Tunnel and Underground Space
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• v.12 no.4
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• pp.248-258
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• 2002

The sixth underground pumped powerhouse cavern is now under construction in Korea. For the stability analysis for the caverns of the five underground powerhouses, finite element method was used. For the analysis, in-situ rock stress were measured by overcoring method. The stress measurement showed that initial horizontal to vertical stress ratio was 1.07-1.32 in low powerhouse sites. Rock mass strength and elasticity were assumed from rock core properties through engineering processes. So the ratio of input elasticity fur the analysis were about 0.16-0.55 to rock core elasticity. In most of the analysis, elasto-plastic condition with Mohr-Coulomb failure criteria were applied. But in one case, viscoelastic condition was applied, too. The input cohesion and internal friction angle were approximately 0.12-0.22, 0.6-0.87 to rock core strength parameters, respectively.

• Composites Research
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• v.17 no.5
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• pp.15-24
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• 2004

Longitudinal strains (${\varepsilon}_x$) of the core and skin layers in glass fiber reinforced plastic (GFRP) cross-ply composite laminates have been measured using the embedded optical fiber sensor of absolute extrinsic Fabry-Perot interferometer (A-EFPI). Transmission optical microscopy was used to investigate the damage behavior around the A-EFPI sensor. Foil-type strain gauges bonded on both the upper and lower surfaces were used for the measurement of the surface strains. It was shown that values of ${\varepsilon}_x$ in the interior of the skin layer and the core layer measured by embedded A-EFPI sensor were significantly higher than that of the specimen surface measured by strain gauges. The experimental results agreed well with those from finite element analysis on the basis of uniform stress model. Large strains in the core layer led to the occurrence of many transverse cracks which drastically reduced the strain at failure of optical fiber sensor embedded in the core layer.

• Journal of Biosystems Engineering
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• v.41 no.3
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• pp.153-160
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• 2016

Purpose: This study was conducted to experimentally investigate the structural safety of and identify critical locations in a front-end loader under impact loads. Methods: Impact and static tests were conducted on a commonly used front-end loader mounted on a tractor. In the impact test, the bucket of the front-end loader with maximum live load was raised to its maximum lift height and was allowed to free fall to a height of 500 mm above the ground where it was stopped abruptly. For the static test, the bucket with maximum live load was raised and held at the maximum lift height, median height, and a height of 500 mm from the ground. Strain gages were attached at twenty-three main locations on the front-end loader, and the maximum stresses and strains were measured during respective impact and static tests. Results: Stresses and strains at the same location on the loader were higher in the impact test than in the static test, for most of measurement locations. This indicated that the front-end loader was put under a severe environment during impact loading. The safety factors for stresses were higher than 1.0 at all locations during impact and static tests. Conclusions: Since the lowest safety factor was higher than 1.0, the front-end loader was considered as structurally safe under impact loads. However, caution must be exercised at the locations having relatively low safety factors because failure may occur at these locations under high impact loads. These important design locations were identified to be the bucket link elements and the connection elements between the tractor frame and front-end loader. A robust design is required for these elements because of their high failure probability caused by excessive impact stress.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5956-5963
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• 2013

By the activation of environment-friendly river works, application of vegetation mats is increasing, however, evaluation techniques for hydraulic stability of vegetation mats are not presented. This study is conducted to develop the objective test method for vegetation mats. Two kind of vegetation mats are tested by the real scale experiments, and hydraulic quantities are measured and analyzed to evaluate acting shear stresses. To evaluate soil loss, Terrestrial 3D LiDAR measurement is conducted and soil loss index are calculated from changes of bed elevation. Quantified evaluation for permissible shear stresses is conducted by graphical method for acting shear stresses and soil loss index. By the results of precision survey, changes of sub soil are limited to local range in stable cases and relatively large changes of sub soil which is similar to natural river bed are detected in unstable cases. From the study, evaluation of permissible shear stresses by ASTM D 6040 is avaliable in the failure mechanism and failure criteria by soil loss index.

• Journal of The Korean Society of Agricultural Engineers
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• v.64 no.3
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• pp.45-52
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• 2022

Prediction of soil behavior should be interpreted based on the level of axial strain in the actual ground. Recently numerical methods have been carried out focus on the state of soil failure. However considered the deformation of soil the prior to failure, mostly the small strain occurring in the elastic range is considered. As a result of calculating the deformation modulus to 50% of the maximum unconfined compression strength, Deformation modulus (E50) showed a tendency to increase according to the degree of compaction by region. The Poisson's ratio during loading-unloading was 0.63, which was higher than the literature value of 0.5. For the unconfined compression test under cyclic loading for the measurement of permanent strain, the maximum compression strength was divided into four step and the test was performed by load step. Changes in permanent strain and deformation modulus were checked by the loading-unloading test for each stage. At 90% compaction, the permanent deformation of the SM sample was 0.21 mm, 0.37 mm, 0.6 mm, and 1.35 mm. The SC samples were 0.1 mm, 0.17 mm, 0.42 mm, and 1.66 mm, and the ML samples were 0.48 mm, 0.95 mm, 1.30 mm, and 1.68 mm.

• Macromolecular Research
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• v.15 no.1
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• pp.44-50
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• 2007

This study investigated the effect of ultrasound irradiation on the blend of poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT). The blends of PLA/PBAT(50/50) (PBAT50) were prepared in a melt mixer with an ultrasonic device attached. Thermal, rheological, and mechanical properties, morphology, and biodegradability of the sonicated blends were analysed. The viscosity of the sonicated blends was increased by the ultrasound irradiation owing to the strong interaction. The morphology of the sonicated blends was significantly dependent on the duration o the ultrasound irradiation. For PBAT50, the phase size reduction was maximized when the blends were ultrasonically irradiated for 30 sec. At longer duration of ultrasound irradiation, the PBAT phase underwent flocculation. Measurement of the tensile properties showed an increased breakage tensile stress and an enhanced Young's modulus when the blends were properly irradiated. This improvement was ascribed to better adhesion between the PLA matrix and the PBAT domain and to better dispersion of the PBAT phase. However, the tensile properties were maximized after excessive energy irradiation, which was ascribed to an emulsifying effect leading to coalescence of the PBAT phase. Impact strength was increased to reach a peak with the ultrasound irradiation, and was higher than the untreated sample for all sonicated samples due to the difference of failure mechanism between the tensile test and the impact test.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.4
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• pp.460-469
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• 2000

A study on the corrosion behavior of RE36 steel for marine structure was investigated with parameters such as micro-Vickers hardness, corrosion potential and corrosion current density measurement of weld metal(WM), base metal (BM) and heat affected zone(HAZ), Al anode generating current and Al anode weight loss quantity in case of cathodic protection. And we carried out slow strain rate test(SSRT) in order to research mechanical properties such as stress at maximum load, percent strain, time to fracture and strain to failure ratio etc and to find out limiting cathodic polarization potential for hydrogen embrittlement with applied cathodic polarization potential. Hardness of HAZ part was the highest among those three parts and also galvanic corrosion susceptibility was the highest in HAZ part among those three parts due to the lowest corrosion potential than other parts. However corrosion current density was the highest in WM part among those three parts. And the optimum cathodic polarization potential showing the best mechanical properties obtained by SSRT method with applied constant cathodic potential was from - 770mV to - 875mV(SCE). However it is suggested that limiting cathodic polarization potential indicating hydrogen embrittlement on the mechanical properties was under - 900mV(SCE).