• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.1
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• pp.39-45
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• 2016

Thermal management of a fuel cell is important to satisfy the requirements of durability and efficiency under varying load conditions. In this study, a linear state feedback controller was designed to maintain the temperature within operating conditions. Due to the nonlinearity of automotive fuel cell system, the state feedback controller results in marginal stable under load condition from $0.5A/cm^2$ to $0.7A/cm^2$. A PWM (Pulse Width Modulation) and the modified state feedback controller are applied to control the temperature under the load condition from $0.5A/cm^2$ to $0.7A/cm^2$. The cooling system model is composed of a reservoir, radiator, bypass valve, fan, and a water pump. The performance of the control algorithm was evaluated in terms of the integral time weighted absolute error (ITAE). Additionally, MATLAB/SIMULINK$^{(R)}$ was used for the development of the system models and controllers. The modified state feedback controller was found to be more effective for controlling temperature than other algorithms when tested under low load conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.10
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• pp.1029-1037
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• 2015

Recently, the importance of rotordynamic stability has been increased because of the tendency to employ ultra-high speeds in rotating machinery. In particular, the dynamic characteristics of gas bearings for high-speed rotating machinery need to be identified at various excitation frequencies to predict the rotor's behavior. In this study, we perform dynamic loading tests for gas-foil bearings (GFBs) to determine the bump foil structure and an air-film combined bump-foil structure for varying excitation frequencies. We calculate the dynamic characteristics from the measured force and displacement data. The air film is generated by a pressurized air supply. Based on the results, the stiffness coefficients of the bump structure and the air-film combined bump structure increased, while the damping coefficients decreased at increasing excitation frequencies. Further, the stiffness and damping coefficients of the air-film combined structure show lower values than those of the bump structure. Consequently, we identify the frequency-dependent dynamic characteristics of the bump structure and the effect of gas film on the dynamic characteristics of GFBs. Furthermore, to reveal the effectiveness of the proposed method, we perform experiments and discuss two methods of extracting the dynamic characteristics from the measured data.

• Korean journal of food and cookery science
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• v.21 no.5
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• pp.669-676
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• 2005

The effect of chlorella addition on the quality characteristics of pound cake was investigated. Chlorella pound cake was prepared with in different ratios of chlorella powder (0, 2, 4, 6 %). The pH of the dough made with chlorella powder were ranged from 7.10 to 7.13 and the pH of the control was 7.08. The weight of the pound cake prepared by adding $2{\sim}6\;%$ chlorella powder decreased from 392.4 to 384.2 g. The volume of the pound cake prepared by adding $2{\sim}6\;%$ chlorella powder increased from 801.8 to 839.2 mL. Loaf volume index increased by $3.12{\sim}3.22$ and that of control by 2.96. Baking loss rate of pound cake prepared by adding $2{\sim}6\;%$ chlorella powder increased by $12.80{\sim}14.97\;%$ and that of control by was 12.88 %. The lightness, redness and yellowness values of the bread decreased with the increase of chlorella powder. There were no significant differences in hardness and penetration by adding $2{\sim}6\;%$ chlorella powder for 1 hour and 72 hours. The sensory quality of the pound cake with addition of 4 % chlorella powder, as estimated by taste, moistness and overall acceptability, was better than that of the others. Consequently, pound cake quality with addition of 4 % chlorella powder was considered the best.

• Korean Journal of Plant Resources
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• v.18 no.3
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• pp.433-440
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• 2005

Four varieties of perilla(Perilla ocimoids L.) were tested to investigate the ecological adaptation of the crop to variations in sowing time extending from April 25 to July 25 with an interval of 30 days between each of the four sowing. As sowing time was delayed, the plant height, the number of first branches and cluster, the weight of fresh and dried stems, the day to germination and flowering decreased, showing a highly negative correlation between the showing dates and these characteristics, but a highly positive correlation between days to flowering and the required accumulated temperature. With early sowing under low temperature and long day conditions, it took about 132 days from sowing to flowering due to the long period of vegetative growth, but as sowing was delayed, the days to flowering decreased with a minimum period of 57 days. The yield of seeds in each case varied with each variety. Type A(Nonsan var.) and type B(Jinchon var.) had higher yields when sowed earlier. But type C(Namyang var. and Wooljin var.) had its highest yield in the plot sowed on May 25 and the 1000 grain weight showed a tendency to increase as sowing was delayed. In conclusion, the perilla was preyed to be a short-day plant that flowers from the begining to the middle of Sep. regardless of sowing time, so that the sowing time should be decided after due consideration of the length of the vegetative growth periods of the varieties.

• Journal of Nutrition and Health
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• v.47 no.5
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• pp.321-329
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• 2014

Purpose: The aim of this study was to determine the relationship between serum concentrations of 25-hydroxyvitamin D [25(OH)D] and chronic obstructive pulmonary disease (COPD) prevalence. Methods: The analysis was performed using data from the Fifth Korean National Health and Nutrition Examination Survey, a cross-sectional survey of the Korean civilian population conducted from 2010 to 2012. The analyses were restricted to males who were 40 years of age and above. Complex sample multiple logistic regression analyses were used to examine the associations of COPD prevalence with 25(OH)D and other factors. Results: $FEV_1/FEV_6$ varied significantly with smoking status, age, household income, education level, occupation, body mass index (BMI), and physical activity (p < 0.05). In univariate analysis, smoking status, BMI, household income, education level, and occupation showed association with COPD (p < 0.05), but vitamin D was not associated with COPD (p = 0.078). However, when adjusted with smoking status, household income, education level, occupation, BMI, age, and smoking index, the lowest quartile of 25(OH)D showed OR 1.643 (95% CI 1.161-2.236) compared to 3rd quartile (p = 0.024). Conclusion: A significant relationship was observed between serum concentration of 25(OH)D and COPD.

• Journal of the Mineralogical Society of Korea
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• v.14 no.2
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• pp.128-136
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• 2001

The K-Ba complete solid solution of 7 synthetic hollandite-type minerals ($K_{2x}$ $Ba_{1-x}$ $Cr_2$/$Ti_{6}$ $O_{16}$ , x=0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0, respectively) are studied by the X-ray powder diffraction and Rietveld refinement to find structural transformation during substitution of $Ba^{2+}$ by $K^{+}$ in A site of the tunnel structure of hollandite. Rietveld indices indicate that $R_{wp}$ with respect to $R^{exp}$ ($R_{wp}$ $R_{exp}$ ) are in the range of 15.66%/20.90% and 14.74%/l9.37%, $R_{B}$ and S(Goodness of Fitness) are 6.45~8.97%, 1.45~1.63, respectively. Unit cell parameters of synthetic hollandites, space group 14/m, are a=10.1194(2)~10.0599(2)$\AA$, c=2.9572(6)~2.9512(7)$\AA$, and V=302.75~298.66$\AA^{3}$. Rutile formed as an impurity in those with more than 50% K contents in hollandite series. Substitution of Ba by K ion in a tunnel structure results in constant decrease of cell parameters, but is not sufficient enough to change the hollandite structure. Our data indicate that transformation of tetragonal 14/m to lower symmetry of monoclinic 12/m in hollandite structure may at least be affected by other cation substitution in same A site and/or by cation substitution in B site.

• Journal of the Korean Society of Food Science and Nutrition
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• v.13 no.4
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• pp.451-458
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• 1984

The effects of branched chain amino acids added to a diet on changes in the body weight with or without liver, moist and dry liver weight, protein, DNA, $^3H-thymidine$ incorporation into DNA, ana mitotic index of regenerating liver were studied in partial hepatectomized rat. Experimental diet was a 14.63% casein diet supplemented with 1.49% L-leucine, 0.90% L-isoleucine and 0.98% L-Valine, and control diet was an 18.0% casein. In both diets, 2.54% nitrogen were included. Rats fed experimental diet were significantly increased body weight with or without liver 7 days, and regenerated weight of dry liver and an index of liver regeneration 5 days after partial hepatectomy. Mitotic index, contents of protein and DNA increased in regenerating liver after partial hepatectomy was higher in experimental diet group. This results suggest that branched chain amino acids have an benefitial effect on whole body as well as liver regeneration after partial hepatectomy in rat.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.42 no.3
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• pp.292-298
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• 1997

To compare the growth pattern of ginseng plant under between conventional shading(light transmittance rate 3％) and polyethylene net shading(light transmittance rate 10％), the distribution of leaf area, specific leaf weight (S. L. W), leaf and stem dry weight and changes in light intensity were investigated in 2, 4 and 6 year old ginseng plant populations. Light transmittance rate(L.T.R.) was 3％ at front line, 2％ at middle line and 1.5％ at rear line under conventional shading but it was 12, 10 and 8％ under polyethylene net(P.E) shading, respectively. In 2 year old population, there was a little difference in the growth characteristics investigated between conventional and P.E. shading. In 4 year old field, the leaf area, stem and leaf dry weight decreased in large amount in the order of middle, and rear line on ridge under conventional shading, but with a little difference under P.E. shading. And these trends enlarged in 6 year old field with appearance of a large part of shoot over furrow from ridge planted ginseng. Root yield index was much lowered at the rear 3rd, 4th and 5th line of the conventional shading bed, but there was no yield difference among lines except 5th lines under the P.E. shading with higher yield by 28％ than conventional shading.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.32 no.3
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• pp.357-368
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• 1987

The productivity of cropping systems with corn and soybean were tested in field layouts such as monocultures of each, I-row alternation(l：1), 1-row corn with 2-rows soybean(l：2), and 1-row corn with 3 rows soybean(l : 3). Increasing soybean rows in alternative row croppings modified corn plant short and thick stalk. Decreasing soybean rows induced lodging of soybean plants because of lengthy stem. Although LAI in alternative row croppings increased by 2-8% over monocultures, light transmition into canopy was improved in alternative rows with rearrangement of leaf area and top dry wt.. Top/root ratio of corn plants in alternative rows was decreased as increasing soybean rows. The amount of total nitrogen uptake was increased by 4-22% in alternative row croppings over monocultures. Grain yield of corn plants was increased and that of soybean was decreased as rows of soybean increased in alternative row croppings. Land equivalent ratios were ranged from 0.96 to 1.01, but grain yields, amount of total nitrogen, and dry matter yields were increased by 17-20, 10-25, and 17-20%, respectively, in alternative rows. The 1 : 1 alternative row of corn and soybean was concluded the best cropping system for production of grain and dry matter.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.18 no.6
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• pp.571-580
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• 1985

Based on the data collected by R/V "Shinkai Maru" of the Japan Marine Fishery Resources Research Center during the period from April 1978 to April 1979, seasonal migration of Merluccius hubbsi was studied using the catch per fishing effort (tons/30 min. haul) and gonad maturity index (gonad weight /body weight X $10^3$). Merlurccius hubbsi are found in the area between $36^{\circ}S\;and\;54^{\circ}S$ along the coast of Arzentine and are abundant especially above the 100 fathoms in northern offshore of $48^{\circ}S$. It was observed that critical maturity body lengths (spawning minimum body length) in terms of gonad maturity index are 40 cm and 30cm in female and male respectively, while spawning seasons are from December to January and from November to December for female and male respectively. It was assumed that while the group which distrbutes in the north ($36^{\circ}S{\sim}39^{\circ}S$) in spring moves down south to $42^{\circ}{\sim}46^{\circ}S$ for spawning in summer (from December to January), the group which does not move or a part of this group which comes back to the north spawn in the area north of $42^{\circ}S$ throughout the long period except winter time (from July to August). Southern group as well might move north and spawn after mixing together with northern group at $42^{\circ}{\sim}46^{\circ}S$ area around the period of December to January,