• Journal of the Korean Society of Radiology
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• v.2 no.4
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• pp.5-9
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• 2008

Antiscatter grids are widely used in radiography to remove scattered X-rays and thus improve the image contrast. However, the use of grids makes moir$\acute{e}$ artifact in the digital image, and this can be a critical reason for a mistaken diagnosis. In this paper, we examined that moire artifacts are how to relate with grid frequency, pixel pitch and grid rotation angle. To experiment we prepared 6 grids having different line frequencies (4.0 to 8.5lines/mm) and tested with a DR imager having a $139{\mu}m{\times}139{\mu}m$ pixel size. In the result of this experiment, we could get data about moir$\acute{e}$ artifact that could be make solution to remove the line artifact for the successful use of the grid in digital radiography. The acquired data and theory through this experiment, are expected to make contribution to the elimination of moir$\acute{e}$ artifact in the DR system.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.6
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• pp.375-382
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• 2016

In the present study, the wave hindcasting has been performed, and then the characteristics of storm waves at Gangnueng port was investigated, in which the high waves are observed. Comparing the numerical results with the wave measurements at Gangneung port, Niigata, and Hamada, there were good agreements between them. In particular, the Pearson correlation coefficients of significant wave heights and peak periods at Gangneung port were 0.92 and 0.72, respectively. Then the extreme wave analysis on the significant wave heights was carried out for the estimation of the frequency of storm waves. In this analysis, the storm waves over the threshold were fitted to GPD(Generalized Pareto Distribution). According to this analysis, the return period of the storm wave on February, 24, 2008, one of the large storm waves at Gangneung port, was 8.2 months. Among the computed significant wave heights larger than one-year wave, 58.3% of them were resulted from the storm, while the others were from the typhoon. Additionally, the regression analysis on the waves larger than one-month wave has been conducted, and then the relationship between the computed significant wave heights and the significant wave period, $T_{1/3}=7H_s^{0.25}$ was obtained.

• Journal of the Korea Concrete Institute
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• v.20 no.5
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• pp.583-592
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• 2008

Recently, the effects of high temperature on compressive strength, elastic modulus and strain at peak stress of high strength concrete were experimentally investigated. The present study is aimed to study the effect of elevated temperatures ranging from 20 to 700 on the material mechanical properties of high strength concrete of 40, 60, 80 MPa grade. In this study, the types of test were the stressed test and stressed residual test that the specimens are subjected to a 25% of ultimate compressive strength at room temperature and sustained during heating and when target temperature is reached, the specimens are loaded to failure. And another specimens are loaded to failure after 24 hour cooling time. Tests were conducted at various temperatures ($20{\sim}700^{\circ}C$) for concretes made with W/B ratios 46%, 32% and 25%. Test results showed that the relative values of compressive strength and elastic modulus decreased with increasing compressive strength grade of specimen and the axial strain at peak stress were influenced by the load before heating. Thermal strain of concrete at high temperature was affected by the preload level as well as the compressive strength. Finally, model equation for compressive strength and elastic modulus of heated high strength concrete proposed by result of this study.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.3
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• pp.22-30
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• 2010

This paper proposes a combination system of Adaptive Modulation and Coding (AMC) and Multiple Input Multiple Output (MIMO), which improves the throughput and has a better reliability. In addition, the system includes Precoding, Antenna Subset Selection and MIMO Mode Selection scheme. Finally, we make a performance analysis of the proposed system. The principal environmental parameters for the simulation experiment consist of a frequency non-selective rayleigh fading channel and a Spreading Factor (SF) of 16. Other parameters may be included in order to fulfill the requirements of the HSDP A Standard. The proposed system has a higher throughput and more reliability than the conventional system, which does not include MIMO Mode Selection scheme, Precoding or Antenna Subset Selection. According to the simulation results, the proposed system reaches the maximum throughput at 8dB, presentlng an improvement of 6dB and twice higher throughput, respect to the conventional system. Specifically, at the point of -6dB, the conventional system reaches 2.5Mbps, while the proposed system reaches 6.4Mbps at the same SNR. Also, at the point of 2dB, each system reaches 7.5Mbps (conventional system) and 15.3Mbps (proposed system), with near twice the difference. According to the results exposed above, we can conclude that the system proposed in this paper has, as the greatest contribution, the improvement of the throughput, especially, the average throughput.

• Bulletin of the Society of Naval Architects of Korea
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• v.25 no.4
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• pp.69-80
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• 1988

This paper proposes simple formulae for buckling and ultimate strength estimation of plates subjected to water pressure and uniaxial compression. For the construction of a formula for elastic buckling strength estimation, parametric study for actual ship plates with varying aspect ratios and the magnitude of water pressure is carried out by means of principle of minimum potential energy. Based on the results by parametric study, a new formula is approximately expressed as a continuous function of loads and aspect ratio. On the other hand, in order to get a formula for ultimate strength estimation, in-plane stress distribution of plates is investigated through large deflection analysis and total in-plane stresses are expressed as an explicit form. By applying Mises's plasticity condition, ultimate strength criterion is then derives. In the case of plates under relatively small water pressure, the results by the proposed formulae are in good agreement compared with those by other methods and experiment. But present formula overestimates the ultimate strength in the range of large water pressure. However, actual ship plates are subjected to relatively small water pressure except for the impact load due to slamming etc.. Therefore, it is considered that present formulae can be applied for the practical use.

• Journal of Nutrition and Health
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• v.41 no.5
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• pp.381-390
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• 2008

Present study was conducted to investigate the effects of exercise and cholesterol diet on plasma and liver lipids, platelet aggregation, erythrocyte Na efflux and liver index such as GOT and GPT using Sprague Dawley rats. Forty rats were divided into four groups and fed control or 0.5% cholesterol diet with and without treadmill for six weeks. The final body weight of group fed cholesterol diet with exercise was somewhat decreased compared with group fed cholesterol diet without exercise. L.W/B.W ratio was significantly increased in groups fed cholesterol diet (p < 0.01), but exercise tended to decrease this ratio. Plasma total cholesterol was significantly increased and HDL-cholesterol was decreased in groups fed cholesterol diet (p < 0.01). Plasma triglyceride was significantly decreased in groups fed cholesterol diet compared with groups fed control diet (p < 0.01). Plasma triglyceride of groups with exercise was significantly decreased compared with their non exercising counterparts regardless diet (p < 0.05). Liver total cholesterol and triglyceride was significantly increased in groups fed cholesterol diet (p < 0.01), but exercise did not affect on these levels. Na-K ATPase was somewhat decreased in groups fed cholesterol diet, and exercise tended to recover the reduced Na-K ATPase. Na passive transport was significantly decreased in group fed control diet without exercise and significantly increased in group fed cholesterol diet with exercise, there were significant differences between groups (p < 0.05). There were no differences in total Na efflux and intracellular Na among groups, and total Na efflux was not correlated with intracellular Na. Hematocrit was significantly lower (p < 0.05) in group fed cholesterol diet without exercise compared with other groups. Platelet aggregation in the initial slope and the maximum was increased in groups fed cholesterol diet, but not statistically significant. Exercise especially increased the initial slope of aggregation. Plasma GOT and GPT was significantly increased in groups fed cholesterol diet (p < 0.01), and exercise in group fed cholesterol diet significantly decreased both GOT and GPT compared with the non exercising counterpart (p < 0.01). This study showed that cholesterol diet increases plasma and liver lipids and GOT and GPT, and exercise improves plasma and liver lipid profile and liver index of GOT and GPT preventing fatty liver.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.5
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• pp.481-486
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• 2011

It is important to predict the behavior of a liquid film around a rotating cylinder in the film coating process of the steel industry. When the cylinder rotates, the behavior of the liquid film on the rotating cylinder surface is influenced by the cylinder diameter, the rotation speed, the gravitational force, and the fluid properties. These parameters determine the liquid film thickness and the rise of the film on the cylinder surface. In the present study, the two-phase interfacial flow of the liquid film on the rotating cylinder were numerically investigated by using a VOF method. For various rotation speeds, cylinder diameters and fluid viscosities, the behavior of liquid film on the rotating cylinder were predicted. Thicker film around the rotating cylinder was observed with an increase in the rotation speed, cylinder diameter, and fluid viscosity. The present results for the film thickness agreed well with available experimental and analytical results.

• Korean Journal of Environmental Agriculture
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• v.17 no.3
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• pp.215-219
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• 1998

This experiment was conducted to investigate effects of NaCl concentration on photosynthetic rate, free proline content and ion content in tobacco. As NaCl concentration was increased growth was retarded. The decrease growth characteristics(shoot/root ratio was 2.0) at 90mM NaCl indicated that this concentration could be a limiting level. As NaCl concentration was increased photosynthetic rate, transpiration rate, and water use efficiency were decreased. Photosynthetic rate was highly decreased at 60mM NaCl. There was no significant difference between transpiration rate and water use efficiency. Leaf water potential was decreased as NaCl concentration was increased, in that twice lower at 30mM than that of control and drop largely at 120mM NaCl. Free proline content was increased as NaCl increased until 120mM NaCl and drop at 150mM NaCl. The $Ca^{2+}$, $Mg^{2+}$, and $K^+$ contents were increased until NaCl concentration was 120mM. The $Na^{2+}$ content was slowly increased as NaCl concentration increased until 120mM NaCl, and largely increased at 150mM NaCl. There was no significant difference between $Cl^-$ and NaCl treatments except 30 mM NaCl in which $Cl^-$ content was higher than that of control. As NaCl concentration was increased $K^+/Na^+$ ratio was decreased. The negative correlation between $K^+$ and $Na^+$, and positive correlation between $K^+/Na^+$ and protein content were found.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.23-27
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• 2013

The risks of debris flows caused by climate change have increased significantly around the world. Recently, landslide disaster prevention technology is more focused on the failure and post-failure dynamics to mitigate the hazards in flow-prone area. In particular, we should define the soil strength and flow characteristics to estimate the debris flow mobility in the mountainous regions in Korea. To do so, we selected known ancient landslides area: Inje, Pohang and Sangju debris flows. Firstly we measured physical and mechanical properties: liquidity index and undrained shear strength by fall cone penetrometer. From the test results, we found that there is a possible relationship between liquidity index and undrained shear strength, $C_{ur}=(1.2/I_L)^{3.3}$, in the selected areas, even though they were different in geological compositions. Assuming that the yield stress is equal to the undrained shear strength at the initiation of sliding, we examined the flow characteristics of weathered soils in Korea. When liquidity index is given as 1, 1.5 and 3.0, the debris flow motion of weathered soils is compared with that of mud-rich sediments, which are known as low-activity clays. At $I_L=1$, it seems that debris flow could reach approximately 250m after 5 minutes. As liquidity index increased from 1 to 3, the debris flow propagation of weathered soils is twice than that of low-activity clays. It may be due to the fact that soil masses mixed with the ambient water and then highly fragmented during flow, thereby leading to the high mobility. The results may help to predict the debris flow propagation and to develop disaster prevention technology at similar geological settings, especially for the weathered soils, in Korea.

• Journal of Korea Soil Environment Society
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• v.4 no.2
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• pp.137-147
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• 1999

Fluidized-bed thermal desorber coupled with a heat pipe was investigated for the remediation of soil contaminated with diesel oils. Thermal gravimetric analysis by Cahn-balance indicated that the desorption of diesel oils from the soil particles was mainly governed by the internal diffusion at low concentration of less than 0.5 wt. % of oils in the soil particles. In fluidized-bed experiments. increase of fluidizing gas velocity reduced the residual oils of the contaminated soils, the increase of soil feed rate decreased efficiency of fluidized-bed desorber. A mathematical model was developed by incorporating Fickian diffusion kinetics into the Kunii-Levenspiel model Simulation results showed reasonable agreement for the performance of fluidized-bed thermal desorber.