• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.11
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• pp.1065-1075
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• 2017

In this study, high velocity impact tests along with modeling of material behavior and numerical analyses were conducted to predict the dispersion behavior of the debris resulting from a high velocity impact fracture. For the impact tests, two different materials were employed for both the projectile and the target plate - the first setup employed aluminum alloy while the second employed steel. The projectile impacts the target plate with a velocity of approximately 1 km/s were enforced to generate the impact damages in the aluminum witness plate through the fracture debris. It was confirmed that, depending on the material employed, the debris dispersion behavior as well as the dispersion radii on the witness plate varied. A numerical analysis was conducted for the same impact test conditions. The smoothed particle hydrodynamics (SPH)-finite element (FE) coupled technique was then applied to model the fracture and damage upon the debris. The experimental and numerical results for the diameters of the perforation holes in the target plate and the debris dispersion radii on the witness plate were in agreement within a 5％ error. In addition, the impact test using steel was found to be more threatening as proven by the larger debris dispersion radius.

• Journal of the Korea Society for Simulation
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• v.18 no.4
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• pp.137-148
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• 2009

The purpose of this study is to implement variable selection algorithm which helps construct a reliable linear regression model. If we use all candidate variables to construct a linear regression model, the significance of the model will be decreased and it will cause 'Curse of Dimensionality'. And if the number of data is less than the number of variables (dimension), we cannot construct the regression model. Due to these problems, we consider the variable selection problem as a combinatorial optimization problem, and apply GA (Genetic Algorithm) to the problem. Typical measures of estimating statistical significance are $R^2$, F-value of regression model, t-value of regression coefficients, and standard error of estimates. We design GA to solve multi-objective functions, because statistical significance of model is not to be estimated by a single measure. We perform experiments using simulation data, designed to consider various kinds of situations. As a result, it shows better performance than LARS (Least Angle Regression) which is an algorithm to solve variable selection problems. We modify algorithm to solve portfolio selection problem which construct portfolio by selecting stocks. We conclude that the algorithm is able to solve real problems.

• Progress in Medical Physics
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• v.15 no.4
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• pp.202-209
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• 2004

Flat panel based digital radiography (DR) systems have recently become useful and important in the field of diagnostic radiology. For DRs with amorphous silicon photosensors, CsI(TI) is normally used as the scintillator, which produces visible light corresponding to the absorbed radiation energy. The visible light photons are converted into electric signal in the amorphous silicon photodiodes which constitute a two dimensional array. In order to produce good quality images, detailed behaviors of DR detectors to radiation must be studied. The relationship between air exposure and the DR outputs has been investigated in many studies. But this relationship was investigated under the condition of the fixed tube voltage. In this study, we investigated the relationship between the DR outputs and X-ray in terms of the absorbed energy in the detector rather than the air exposure using SPEC-l8, an X-ray energy spectrum model. Measured exposure was compared with calculated exposure for obtaining the inherent filtration that is a important input variable of SPEC-l8. The absorbed energy in the detector was calculated using algorithm of calculating the absorbed energy in the material and pixel values of real images under various conditions was obtained. The characteristic curve was obtained using the relationship of two parameter and the results were verified using phantoms made of water and aluminum. The pixel values of the phantom image were estimated and compared with the characteristic curve under various conditions. It was found that the relationship between the DR outputs and the absorbed energy in the detector was almost linear. In a experiment using the phantoms, the estimated pixel values agreed with the characteristic curve, although the effect of scattered photons introduced some errors. However, effect of a scattered X-ray must be studied because it was not included in the calculation algorithm. The result of this study can provide useful information about a pre-processing of digital radiography.

• Applied Chemistry for Engineering
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• v.29 no.3
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• pp.283-288
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• 2018

As the use of environmentally friendly and non-disease natural pigments grows, various methods for extracting natural pigments have been studied. The natural color was extracted from parsley, a vegetable ingredient containing natural dyes. Target color codes of green series of natural dyes extracted as variables #50932C (L = 55.0, a = -40.0, b = 46.0) were set with the pH and temperature of extracted natural color coordinates (of the extracted), and the quantitative intensities of natural dyes were analyzed. During the colorimetric analysis predicted by the reaction surface analysis method, a color coordinate analysis was conducted under the optimal conditions of pH 8.0 and extraction temperature of $60.9^{\circ}C$. Under these conditions, predicted figures of L, a, and b were 55.0, -36.3, and 36.8, respectively, while actual experimental ones confirmed were 69.0, -35.9, and 31.4, respectively. In these results, the theory accuracy and actual error rate were confirmed to be 73.0 and 13.8%, respectively. The theoretical optimization condition of the color difference (${\Delta}E$) was at the pH of 9.2 and extraction temperature of $55.2^{\circ}C$. Under these conditions the predicted ${\Delta}E$ figure was 12.4 while the experimental one was 13.0. The difference in color analysis showed 97.5% of the theoretical accuracy and 4.5% of the actual error rate. However, the combination of color coordinates did not represent a desired target color, but rather close to the targeted color by means of an arithmetic mean. Therefore, it can be said that when the reaction surface analysis method was applied to the natural dye extraction process, the use of color coordinates as a response value can be a better method for optimizing the dye extraction process.

• Journal of The Korean Society of Grassland and Forage Science
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• v.13 no.4
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• pp.257-267
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• 1993

Optimum pasture management during the summer season is an important factor to maintain good regrowth and persistence of pasture. The field experiment was carried out to investigate the effects of cutting management on growth and reserve carbohydrates in stubble. and on dry matter yield of orchardgrass dominated pasture during the mid-summer season. Three different cutting times(July 15, 25 and August 5) as a main plot and three cutting heights(3, 6 and 10cm) as a sub plot were disigned with three replications. The experiment was done at pasture of Changsung Agricultural High School in 1988. The results obtained were summarized as follows: 1. Temperature of soil surface and underground in the cutting of July 15 and July 25 was not showed significantly different, because of low intensity of radiation with a run of wet weather, and that of August 5 cutting tends to be lowed in high cutting height during the mid-summer season. 2. Amount of soil moisture against cutting height showed that high cutting had a low content. 3. Growth rate against regrowth of plant height, lear length and leaf area showed to be fast in high cutting. 4. Rapid recovery period of carbohydrate content after cutting and large amount of carbohydrate accumulation were showed in the cutting of July 15 and 25 compared with August 5 cutting in the reserve carbohydrate content against cutting of time and height during the mid-summer season. 5. Dry matter yield of the 4th and 5th cutting showed to be remarkable in July 15 cutting compared to those of July 25 and August 5. From the above results, it is suggested that the 10cm cutting height during the mid-summer season is the most effective for good regrowth, reserve carbohydrates and dry matter yield of orchardgrass.

• The Korean Journal of Nuclear Medicine Technology
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• v.13 no.3
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• pp.81-85
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• 2009

Purpose: The examination of nuclear medicine observes the change in accordance with the time elapsed in the same region purposed and there are many examinations to acquire the image during the same term. At this time, the same parameter should be applied. The hepatobiliary scan, lung scan etc, are the acquired examination in the divided time with a regular term. Pre-set time that is applied in continued next image is set in order to acquire the fixed counts. The same scan time should be applied for each image. This study will look for the rational plan and analyze the change of scan time in accordance with the time of the decision of scan time at examination that pre-set time is applied. Methods: The hapatobiliary scan that use the radio pharmaceutical $^{99m}Tc$-mebrofenin is choosed as compensation from Jan. 2009 to Mar. 2009 in the department of nuclear medicine in ASAN MEDICAL CENTER. Scan is started after 5 minutes from when 222 MBq (6 mCi) is injected to patient. We let patient stand up between both detectors, and possibly close to the front of detector. When scan time reach 10%, 25%, 50%, 75% of total scan time, we measured the expected total scan time. After finishing all of scan, we compared the total scan time and the expected total scan time, while image is acquiring. and we observed the change of scan time in accordance with radio activity by using phantom. Results: After starting scan, a difference of when scan time reach 10%, 25%, 50%, 75% of total scan time is that the biggest difference is 5 seconds on 10%. There statistically is difference between 25% (t:2.88, p<0.01) and 50% (t:2.05, p<0.01). Conclusions: When the same the scan time is applied in the examination that acquire the many frame, concluding the same scan time has a important effect on a quantitative analysis. Although method that decide the scan time after finish all of the examinations, there is a few problem to apply practical affairs. This may cause an inaccurate result on the examination that need a quantitative analysis. We think that operator should try to improve it. At least, after reach 50% of total scan time, deciding the total scan time mean that you can minimize error of a quantitative analysis caused by unmatched scan time from a gap of image.

• Journal of Korean Ophthalmic Optics Society
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• v.20 no.2
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• pp.177-186
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• 2015

Purpose: The Purpose of this study is to investigate if the relative legibility of optotypes affects the corrected visual acuity in visual acuity test. Methods: After measuring the relative legibility of 'Landolt ring target', 'arabic number target', 'alphabet target' by showing as a single-letter-target in 24 subjects without specific ocular diseases and ocular surgery experience, the relative legibility of 0.8, 1.0, 1.25 row of vision according to type of target in 7 types of chart were compared. After then we compared by measuring the corrected visual acuity according to type of target by using binocular MPMVA test (#7A) in 60 myopic subjects. Results: In 3 types of target the worst relative legibility target was 'Landolt ring target' with legible distance of $98.97{\pm}4.57cm$ and the best relative legibility target was 'alphabet target' with legible distance of $108.42{\pm}3.46cm$. There was no difference of the relative legibility according to type of chart or visual acuity level in the row of vision if other conditions are the same. In 1.0 and 1.25 row of vision the difference of relative legibility according to type of target was shown the statistically significant difference between 'Landolt ring target' and 'alphabet target' as $-0.07{\pm}0.06$ (p=0.02) and $-0.06{\pm}0.06$ (p=0.04) respectively. In myopia the difference of corrected visual acuity according to type of target was statistically significant difference between 'Landolt ring target' and 'arabic number target' as $-0.04{\pm}0.02$ (p=0.02) and it was especially remarkable in the low myopia. Conclusions: Measuring visual acuity with different optotypes could cause the errors in best vision measurement value because there was difference of the relative legibility according to type of target even though visual acuity level is same in the row of vision.