• Korean Journal of Metals and Materials
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• v.49 no.2
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• pp.145-152
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• 2011

Mechanical and property corrosion resistance of Mg-Zn-Y alloys with an atomic ratio of Zn/Y of 6.8 are investigated using optical microscopy, scanning electron microscopy, transmission electron microscopy, uniaxial tensile test and corrosion test with immersion and dynamic potentiometric tests. The alloys showed an in-situ composite microstructure consisting of ${\alpha}$-Mg and icosahedral phase (I-phase) as a strengthening phase. As the volume fraction of the I-phase increases, the yield and tensile strengths of the alloys increase while maintaining large elongation (26~30%), indicating that I-phase is effective for strengthening and forms a stable interface with surrounding ${\alpha}$-Mg matrix. The presence of I-phase having higher corrosion potential than ${\alpha}$-Mg, decreased the corrosion rate of the cast alloy up to I-phase volume fraction of 3.7%. However further increase in the volume fraction of the I-phase deteriorates the corrosion resistance due to enhanced internal galvanic corrosion cell between ${\alpha}$-Mg and I-phase.

• Journal of the Korean Society of Physical Medicine
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• v.16 no.3
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• pp.55-64
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• 2021

PURPOSE: The purpose of this study was to apply dynamic neuromuscular stabilization (DNS) to subjects with forward head posture (FHP) and to compare its effects on respiratory function as against the conventional neck stabilization exercise and neck stretching and extensor strengthening exercises. METHODS: The whole-body posture measurement system was used to measure the degree of FHP, and a spirometer and a respiratory gas analyzer were used to measure the respiratory function. After the intervention was completed, the changes over time were analyzed in the DNS group, the neck stabilization exercise group, and the neck stretching and extensor strengthening exercise group. The inter-group difference in the changes was also analyzed. A repeated ANOVA was performed to compare the respiratory function according to the period between the three groups, and the least significant difference (LSD) method was used for the post hoc test. RESULTS: After the 6-week exercise period, respiratory functions, such as forced vital capacity (FVC), forced expiratory volume for 1 second (FEV1), forced expiratory volume for 1 sec/forced vital capacity (FEV1/FVC), maximum oxygen intake (VO₂max), and the volume of expired gas (VE), significantly improved according to the period (p < .05), but no inter-group differences were found. CONCLUSION: DNS is an effective training method, and can be applied along with neck stabilization exercise and neck stretching and extensor strengthening exercises, which are widely used in clinical practice, to people with FHP who cannot directly perform neck exercises to improve their respiratory function.

• Journal of Korean Association for Spatial Structures
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• v.23 no.2
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• pp.69-78
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• 2023

This paper investigates the effects of aspect ratio and volume fraction of hooked-end normal-strength steel fibers on the compressive and flexural properties of high-strength concrete with specified compressive strength of 60 MPa. Three types of hooked-end steel fibers with aspect ratios of 64, 67 and 80 were considered and three volume fractions of 0.25%, 0.50% and 0.75% for each steel fiber were respectively added into each high-strength concrete mixture. The test results indicated that the addition of normal-strength steel fibers is effective to improve compressive and flexural properties of high-strength concrete but fiber aspect ratio had little effect on the modulus of elasticity and compressive strength. As steel fiber content and aspect ratio increased, flexural beahvior of notched high-strength concrete beams was effectively improved.

• Transactions of Materials Processing
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• v.16 no.2 s.92
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• pp.126-131
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• 2007

Voids in a large rotor are formed in solidification process of a cast ingot. The voids have to be eliminated from the rotor by a forming process, because they would became stress-intensity factors which suddenly fracture the rotor in the operation. Previous studies on void-elimination of a large rotor have mainly focused on finding the process variables affecting the void-closure. But the study on the amount of void closure in a large rotor has been very rare. This study was performed to obtain an equation which predicts the amount of void-closure in a forging process of a large rotor and to evaluate the availability of the void-closure equation through finite element analyses. Firstly, 2D FE analysis was carried out to find effects of time integral of hydrostatic stress and effective strain on void volume rate of a large rotor in the upsetting process for various diameters and shapes of void, and material temperature. From the 2D FE analysis, we found that effective strain was suitable for predicting the void-closure of a large rotor, because there was a constant relationship between void volume rate and effective strain. And a void-closure equation was proposed fur predicting void-closure of a large rotor in the upsetting process. Finally, ken the 3D FE analysis, the proposed void-closure equation was verified to be useful for upsetting and cogging processes.

• Computers and Concrete
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• v.18 no.3
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• pp.319-336
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• 2016

In this study, both two- and three-dimensional (2D and 3D) finite-volume-based models were developed to analyze the heat transfer mechanisms through the porous structures of cellular concretes under steady-state heat transfer conditions and to investigate the differences between the 2D and 3D modeling results. The 2D and 3D reconstructed pore networks were generated from the microstructural information measured by 3D images captured by X-ray computerized tomography (X-CT). The computed effective thermal conductivities based on the 2D and 3D calculations performed on the reconstructed porous structures were found to be nearly identical to those evaluated from the 2D cross-sectional images and the 3D X-CT images, respectively. In addition, the 3D computed effective thermal conductivity was found to agree better with the measured values, in comparison with the 2D reconstruction and real cross-sectional images. Finally, the thermal conductivities computed for different reconstructed porous 3D structures of cellular concretes were compared with those obtained from 2D computations performed on 2D reconstructed structures. This comparison revealed the differences between 2D and 3D image-based modeling. A correlation was thus derived between the results of the 3D and 2D models.

• The Journal of Korean Medicine
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• v.23 no.1
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• pp.156-169
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• 2002

Objectives : This experimental study was performed to prove the effect of Ikryung-Tang (yiling-tang; IRT) and Ikryung-tangkamibang (yiling-tangjiaweifang; IRT I, IRT II) on rats with nephrosis induced by a single intravenous injection of puromycin aminonucleoside (PAN). Methods : The effects of IRT, IRT I and IRT II on PAN nephrosis were evaluated by measuring the gene expression of IL-4, $IFN-{\gamma}$ and the concentrations of IgE, albumin, total protein, cholesterol, triglyceride, creatinine, and BUN in the serum and the volume & amount of protein of the 24hrs' urine. Results : In the gene expression linked T cell specialization, IRT II inhibited IL-4 and IgE but IRT and IRT I showed no significant difference compared with control group. On the other hand, IRT, IRT I and IRT II increased $IFN-{\gamma}$ compared with the control group. In the urine protein, serum albumin, total protein, BUN, and creatinine, IRT I especially showed more. significant effect than other groups. In the serum cholesterol and triglyceride, IRT II especially showed more significant effect than other groups. In the urine volume during 24 hrs, IRT especially showed more significant effect than other groups. Conclusions : According to the above results, it is suggested that IRT is effective for the treatment of edema, IRT I is effective for the treatment of hypoproteinemia and kidney dysfunction, IRT II is effective for immune modulation and the treatment of cholesteremia. Therefore IRT, IRT I and IRT II seem to be available for treating nephrosis in clinical practice.

• The Korean Journal of Nuclear Medicine
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• v.16 no.1
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• pp.55-61
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• 1982

Biodistribution studies has been carried out to elucidate the cause of poor bone imagings often encountered in using $methylenediphosphonate(MDP)-^{99m}Tc$ and to establish effective conditions in using the popular bone imaging agent. After 150 minutes from the I.V. injection of $MDP-^{99m}Tc$ to mice, the radioactivities accumulated at bone(B), liver(L), and stomach(S) were counted. The radiochemical purity (RCP), the volume, the radioactivity concentration and the amount of radioactivity of $MDP-^{99m}Tc$ were controlled. Data were expressed either in %cpm/g organ or % cpm/organ. The organ distribution ratios(B/L and B/S) were correlated with the RCP, the volume of injection, the radioactivity concentration etc. Results indicated that the RCP plays a major role in biodistributions. High radioactivity concentration and injection of a small amount is recommended. Negligible effect was observed with the amount of radioactivity. It has been confirmed that the up-to-date methods of RCP determinations cannot sensitively detect the sharply affecting trace impurities. A particular biodistribution pattern of crossed B/L and B/S lines was observed in case of using $MDP-^{99m}Tc$ of low RCP. In such a case, rather a higher dosage would be effective for improving the contrast between bone and liver.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.6 s.165
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• pp.968-978
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• 1999

The effective elastic properties of materials containing spherical inclusions were calculated by the elastic wave scattering theory. In the formulation additional scattering fields by the presence of random multiple scatterers that affects the effective properties were found by the single scattering approximation. In calculating the scattering fields the ensemble average on the displacements and strains inside the scatterer was found from the static approximation at long wavelength limit. The displacements were assumed to be equal to the incident field, while the strains were calculated by Eshelby's equivalent inclusion principle on the single inclusion problem. Four different models were considered and they reflected different degrees of multiple scattering effects based on the approximation introduced in the process of embedding the inclusion in the matrix. The expressions for the effective elastic constants were given in each model, and their relations to the results obtained from other scattering theory and elasticity theory were discussed. The theoretical predictions were compared with experimental results on the epoxy matrix composites containing tungsten particles of different sizes and volume fractions

• The Journal of Korean Society for Radiation Therapy
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• v.26 no.1
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• pp.11-19
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• 2014

Purpose : To derive the most appropriate factors by considering the effects of the major factors when applied to the optimization algorithm, thereby aiding the effective designing of a ideal treatment plan. Materials and Methods : The eclipse treatment planning system(Eclipse 10.0, Varian, USA) was used in this study. The PBC (Pencil Beam Convolution) algorithm was used for dose calculation, and the DVO (Dose Volume Optimizer 10.0.28) Optimization algorithm was used for intensity modulated radiation therapy. The experimental group consists of patients receiving intensity modulated radiation therapy for the head and neck cancer and dose prescription to two planned target volume was 2.2 Gy and 2.0 Gy simultaneously. Treatment plan was done with inverse dose calculation methods utilizing 6 MV beam and 7 fields. The optimal algorithm parameter of the established plan was selected based on volume dose-priority(Constrain), dose fluence smooth value and the impact of the treatment plan was analyzed according to the variation of each factors. Volume dose-priority determines the reference conditions and the optimization process was carried out under the condition using same ratio, but different absolute values. We evaluated the surrounding normal organs of treatment volume according to the changing conditions of the absolute values of the volume dose-priority. Dose fluence smooth value was applied by simply changing the reference conditions (absolute value) and by changing the related volume dose-priority. The treatment plan was evaluated using Conformal Index, Paddick's Conformal Index, Homogeneity Index and the average dose of each organs. Results : When the volume dose-priority values were directly proportioned by changing the absolute values, the CI values were found to be different. However PCI was $1.299{\pm}0.006$ and HI was $1.095{\pm}0.004$ while D5%/D95% was $1.090{\pm}1.011$. The impact on the prescribed dose were similar. The average dose of parotid gland decreased to 67.4, 50.3, 51.2, 47.1 Gy when the absolute values of the volume dose-priority increased by 40,60,70,90. When the dose smooth strength from each treatment plan was increased, PCI value increased to $1.338{\pm}0.006$. Conclusion : The optimization algorithm was more influenced by the ratio of each condition than the absolute value of volume dose-priority. If the same ratio was maintained, similar treatment plan was established even if the absolute values were different. Volume dose-priority of the treatment volume should be more than 50% of the normal organ volume dose-priority in order to achieve a successful treatment plan. Dose fluence smooth value should increase or decrease proportional to the volume dose-priority. Volume dose-priority is not enough to satisfy the conditions when the absolute value are applied solely.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.2
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• pp.197-204
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• 2004

An accumulator in hydraulic systems stores kinetic energy during braking action, and then that controls hasty surge pressure. An energy recovery system using accumulator seems to be advantageous for ERBS due to its high energy density. This study suggests a method to decide suitable accumulator volume for ERBS. The method is based upon energy conservation between kinetic energy of moving inertia and elastic energy of accumulator. The energy conversion was analyzed and a simple formula was derived. Also accumulator tests were conducted for different load mass and motor speed. A series of test work were carried out in the laboratory and the dynamic characteristics of the hydraulic motor system, such as the surge pressure and response time, were investigated in both brake action and acceleration action and these results show that the proposed design is effective for decision accumulator volume in ERBS.