• Journal of Advanced Marine Engineering and Technology
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• v.30 no.1
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• pp.42-49
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• 2006

In this research. the diesel cycle was thermodynamically interpreted to evaluate the possibility of high efficiency by converting diesel engines to the high expansion diesel cycle, and general cycle features were analyzed after comparing these two cycles. Based on these analyses. an experimental single cylinder a long stroke with high expansion-diesel engine. of which S/B ratio was more than 3, was manufactured. After evaluating the base engine through basic experiments, a diesel engine was converted into the high expansion diesel engine by establish VCR device and VVT system Accordingly, the high expansion diesel cycle can be implemented when the quantity of intake air is compensated by supercharge and the effective compression ratio is maintained at its initial level through the reduction of the clearance volume. In this case, heat efficiency increased by $5.0\%$ at the same expansion-compression ratio when the apparent compression ratio was 20 and the fuel cut off ratio was 2. As explained above, when the atkinson cycle was used for diesel cycle, heat efficiency was improved. In order to realize high expansion through retarding the intake value closing time, the engine needs to be equipped with variable valve timing equipment, variable compression ratio equipment and supercharged pressure equipment. Then a high expansion diesel cycle engine is realized.

• Journal of KSNVE
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• v.10 no.6
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• pp.991-997
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• 2000

The objective of this study is to examine the onset condition and the frequency characteristics of the low-frequency combustion oscillation in a surface burner. For this purpose, extensive parametric studies have been performed experimentally and the effects of size of each section, the equivalence ratio, and the entrance velocity on oscillatory behavior explored. The experimental results were discussed in comparison with the other combustors associated tilth the low-frequency combustion oscillation. The combustion mode is driven at high combustion rate by the lift of unstable flame near the lower limit of the combustible equivalence ratio. The oscillation frequency is dependent not on the burner geometry but on the equivalence ratio and the combustion load. Low-frequency combustion mode was formed to be divided into two different modes, named C1 and C2 respectively. Two modes occurred individually, simultaneously or transitionally according to the equivalence ratio and combustion load. The characteristics of low-frequency oscillation is different from each other depending on the type of combustors. The surface burner has also its own characteristics of low -frequency oscillation.

• Corrosion Science and Technology
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• v.2 no.2
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• pp.93-97
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• 2003

Fatigue crack growth test or low alloy steel was performed in high temperature water. Test parameters were dissolved oxygen content. loading frequency and R-ratio ($P_{min}/P_{max}$). Since the sulfur content or the steel was low, there were no environmentally assisted cracks (EAC) in low dissolved oxygen(DO) water. At high DO, the crack growth rate at R = 0.5 tests was much increased due to environmental effects and the crack growth rate depended on loading frequency and maximized at a critical frequency. On the other hand, R = 0.7 test results showed an anomalous decrease of the crack growth rate as much different behavior from the R = 0.5. The main reason of the decrease may be related to the crack tip closure effect. All the data could be qualitatively understood by effects of oxide rupture and anion activity at crack tip.

• International Journal of Fluid Machinery and Systems
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• v.3 no.3
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• pp.260-270
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• 2010

Reducing the losses of the tip clearance flow is one of the keys in an unshrouded centrifugal compressor design and development because tip clearances are large in relation to the span of the blades and also centrifugal compressors produce a sufficiently large pressure rise in single stage. This problem is more acute for a low flow high-pressure ratio impeller design. The large tip clearance would cause flow separations, and as a result it would drop both the efficiency and surge margin. Thus a design of a high efficiency and wide operation range low flow coefficient centrifugal compressor is a great challenge. This paper describes a recent development of high efficiency and wide surge margin low flow coefficient centrifugal compressor. A viscous turbomachinery optimal design method developed by the authors for axial flow machine was further extended and used in the centrifugal compressor design. The compressor has three main parts: impeller, a low solidity diffuser and volute. The tip clearance is under a special consideration in this design to allow impeller insensitiveness to the clearance. A patented three-dimensional low solidity diffuser design method is used and applied to this design. The compressor test results demonstrated to be successful to extend the low solidity diffusers to high-pressure ratio compressor. The compressor stage performance showed the total to static efficiency of the compressor being about 85% and stability range over 35%. The test results are in good agreement with the design.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.11a
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• pp.65-68
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• 2009

Recycled aggregate by the recycling construction waste has a lot of advantage such as the developing the alternative resource and protecting of environment. However, recycled aggregate is used as the low quality grade, because the technic to remove old mortar from aggregate is low level. To use the recycled aggregate as high quality grade, it is important to develop the technic to produce the high quality recycled aggregate. To manufacture the high quality recycled aggregate, old mortar attached on the aggregates should remove efficiently. Therefore, in this study, we suggested the optimum condition to remove old mortar effectively using sulfuric acid and low speed wet rotary mill for high quality recycled fine aggregate. The results shows that the recycled aggregate satisfy on the standards of KS F 2573 in density, absorption and solid volume when, adequate condition of sulfuric mole ratio and aggregate ratio are make.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.9
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• pp.1410-1419
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• 1989

In this paper, we present a new synthetic high coding method which gives high image compression ratio. Given an image, only its low-pass component is transmitted by DCT coding` the high-pass component is not transmitted but synthesized using edge sharpening on the reconstructed low-pass image at the receiver. For the DCT coding which is used to encode the low-pass image, we used an improved version of Cox's variance estimator. Also, introduced are new image quality measures called GSNR and EPR which emphasize perceptual aspects of image quality. Experimental results show that the performance of the proposed synthetic high coding is better in various quality measures than that of Cox's adaptive transform coding. Also, it yields acceptable image quality with neither apparent block effect nor visible granular noise even at high compression ratio of about 30:1.

• Macromolecular Research
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• v.8 no.6
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• pp.268-275
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• 2000

After imposing a large pre-strain, anisotropy increases with increasing residual extension ratio. Gums have very low residual extension ratio and exhibit little anisotropy, while black filled SBR and especially sulfur-cured carbon black filled NR have large set and anisotropy. For carbon black filled rubber, samples subjected to tensile loading in perpendicular to the pre-strain direction have the same stress-strain curves shape as the sample without pre-strain (=isotropic samples), but slightly lower modulus. However, compared to isotropic or perpendicular directional samples to pre-strain direction, samples subjected to tensile loading in parallel to the pre-strain direction show low stress at low deformation, but have high stiffness at high deformation. Normalized anisotropy changes with strain. The normalized anisotropy for various deformations is a linear function of residual extension ratio.

• Journal of Nutrition and Health
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• v.33 no.8
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• pp.864-872
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• 2000

This study intended to evaluate the validity of the simple nutrition screening test that had been developed with the elderly living in Cheongju as a subject. Nutrition screening score(NSS) and reference standards for nutritional and health status(nutrient intakes, mean adequacy ratio, perceive health, and serum albumin, hematocrit, and hemoglobin) were estimated by using the date obtained in 1996 from the 174 elderly living in Taejon, Statistical analysis showed significant correlations between mean adequacy ratio(MAR) and NSS(r=0.341) and also between NSS and biological indices such as albumin and hematocrit, Around 65-75% of the elderly with perceive health and low level of serum albumin, hemoglobin and hematocrit had NSS$\leq$ll. Sensitivity, specificity, and positive predictive values(PPV) were calculated from the crosstabulation of the three categories of NSS(high, moderate, and low nutritional risk) and low categories MAR(< 0.75, undernutrition;$\geq$0.75, normal) to validate the cut-off point for high or low nutritional risk by NSS. It was suggested that point l1 was appropriate as a criterion to determine high risk of undernutrition, but point 16 was better than 17 as criterion to determine low nutritional risk in the Taejon elderly. When point ll was used as a criterion of high nutritional risk, sensitivity, specificity, and PPV are 59.5, 60.5 and 82.1 respectively. When point 16 was used as a criterion of low nutritional risk, sensitivity, specificity, and PPV are 25.6, 95.4, and 64.7%, respectively. In conclusion, nutrition screening test that had been developed can be a simple, easy, and proper instrument to classify the high risk group of undernutrition. A further validation study seems to be required among other groups of individuals for the screening test to the finalized as a more valid instrument identifying Korean elderly at nutrition and health risk(Korean J Nutrition 33(8) : 864-872, 2000)

• Structural Engineering and Mechanics
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• v.53 no.4
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• pp.645-659
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• 2015

This research investigates the thermoelastic transient behavior of a thermally loaded slab made of a thermal diode-like material which has two directional thermal conductivity values (low and high). Finite difference analysis is used to obtain the elastic response of the slab based on the temperature solutions. It is found that the rate of heat transfer through the thickness of the slab decreases with reducing the ratio between the low and high thermal conductivity values (R). In addition, reducing R makes the slab less responsive to the thermal load when heated from the direction associated with the low thermal conductivity value.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.6
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• pp.835-842
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• 2009

The present thesis carried out a research on a compression pressure's reduction phenomenon and its countermeasure according to the thermal efficiency improvement method by a Miller method in 4-cycle low speed diesel engine. In case of retardation of intake valve closing time in a engine, the theoretical heat efficiency shows a remarkably reducing trend when a compression ratio is not compensated. Accordingly, the thermal efficiency showed an increasing trend in case of compensating the compression ratio. Especially, it could be understood that the theoretical heat efficiency at near ABDC $100^{\circ}$ of intake valve closing time in case of compensation of the compression ratio was improved by around 25.1%, and the mean effective pressure was also increased by around 18.6%. Also, as the retardation of intake valve closing time increases, air quantity becomes insufficient due to a backflow phenomenon of intake air and thus thermal efficiency was decreased in a high load operation domain. The solving method of this problem is possible by supercharge. Therefore, in order to improve thermal efficiency by retardation of ntake valve closing time, the thermal efficiency improvement according to low compression is possible when there are a compensation device of a compression ratio and a supercharge device. This is a problem-solving method of low compression and high expansion cycle.