• International Journal of Reliability and Applications
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• v.11 no.2
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• pp.89-106
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• 2010

This paper deals with the reliability and availability characteristics of three different series system configurations with warm standby components and a repairable service station. The failure time of the primary and warm standby are assumed to be exponentially distributed with parameters ${\lambda}$ and ${\alpha}$ respectively. The repair time distribution of each server is also exponentially distributed with parameter ${\mu}$. The breakdown time and the repair time of the service station are also assumed exponentially distributed with parameters ${\gamma}$ and ${\beta}$ respectively. We derive the reliability dependent on time, availability dependent on time, the mean time to failure, $MTTF_i$, and the steady-state availability $A_i$(${\infty}$) for three configurations and perform comparisons. Comparisons are made for specific values of distribution parameters and of the cost of the components. The three configurations are ranked based on: $MTTF_i$, $A_i$(${\infty}$), and $C_i/B_i$ where $B_i$ is either $MTTF_i$ or $A_i$(${\infty}$).

• Journal of the Korean Institute of Telematics and Electronics B
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• v.33B no.3
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• pp.133-141
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• 1996

As the recording density of digital magnetic recording channels increased, the nonlinear distortion caused by inadequate rise-times, demagnetizing field, and overwrite effect during the recording process becomes significant, resulting in limitation on the recording rate. In this paper, a new method for identifying the nonlinear distortion in hihg-density magnetic recording channel using and i.i.d. (independent, identically distributed) inut is described. The proposed method does not require the operatin of large-size matrix inversion which are necessary for the conventional method, and it enables us to estimate nonlinear parameters transition shifts, which can be used to compensate the nonlinear distortion, is demonstrated by computer simulations.

• Journal of Power Electronics
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• v.12 no.4
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• pp.538-547
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• 2012

This paper presents two different robust controllers for boost converters with two stages in a cascade. The first robust controller is monovariable; that is, the duty-cycle is the same for the two switches. The monovariable controller ensures that some prescribed constraints on pole placement and control effort are met, and optimizes the load disturbance rejection, while takes into account the uncertainty in certain parameters. The first controller is then compared with a multivariable robust controller; that is, with independent duty cycles in each switch. The multivariable controller takes into account the same uncertainty, constraints and optimization function. The comparison shows that the multivariable controller performs better at the expense of a slightly more complex implementation; that is, the multivariable controller provides a better rejection of the load disturbance. The paper also describes simulations and experimental results that are in perfect agreement with theoretical derivations.

• Journal of Power System Engineering
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• v.12 no.2
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• pp.12-17
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• 2008

Biodiesel fuel(BDF) which is easily produced from vegetable oils such as soybean oil and rice bran oil can be effectively used as an alternative fuel in diesel engine. But biodiesel fuel can affect the performance and emissions in diesel engine because it has different chemical and physical properties from diesel fuel. To investigate the combustion characteristics of biodiesel fuel as an alternative fuel for D.I. diesel engine, the experiments were carried out at the three-cylinder, four stroke D.I. diesel engine with T/C. Experimental parameters adopted a conventional diesel fuel and a blend of biodiesel fuel derived from soybean. As a result of experiments in a test engine, BSFC with blend of BDF resulted in higher than with diesel fuel. The ignition delay decreased with blend of BDF than with diesel fuel.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.7
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• pp.818-825
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• 2004

In this paper, the study of effects of flow parameters on flame structure and NOx emission concentration was performed in co-axial. laminar partially premixed methane/air flames. Such (low parameters as equivalence ratio(${\Phi}$), fuel split percentage($\sigma$), and mixing distance(x/D$\_$i/) were defined as a premixing degree and varied within ${\Phi}$=1.36∼9.52, $\sigma$=50∼100, and x/D$\_$i/=5∼20. The image of OH$\^$*/ and NOx concentration were obtained with an ICCD camera and a NOx analyzer. The flame structure observations show a categorization of partially premixed flames into three distinct flame regimes corresponding to ${\Phi}$<1.7(premixed flame structure), 1.7<${\Phi}$<3.3(hybrid structure), and ${\Phi}$>3.3(diffusion flame structure existing a luminous sooting region) at $\sigma$=75%, and x/D$\_$i/=10. As o decreases from 100% to 50%, and x/D$\_$i/ decreases, nonpremixed flame structure appear at low equivalence ratio relatively. In addition, the measured emissions for NOx rise steeply from ${\Phi}$=1.7, to ${\Phi}$=3.3, then constants ${\Phi}$>4.76. NOx emissions decrease with increase the level of premixing level. In conclusion, the main effect on flame structure and NOx production was at first equivalence ratio(${\Phi}$), and next fuel split percentage($\sigma$), and finally mixing distance(x/D$\_$i/).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.3 s.118
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• pp.341-350
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• 2007

In this paper, the derivation of protection ratio is newly proposed for the detailed planning of frequency coordination in microwave relay networks, and computed results for protection ratio of co-channel and adjacent channel are illustrated over the actual system and its frequency. It is shown that the suggested method based upon availability prediction can be expressed in terms of composite fade margin, interference-to-noise ratio(I/N), net filter discrimination, and system parameters. According to results, for 6.7 GHz, 60 km, 64-QAM, and I/N= -6 dB at BER $10^{-6}$, composite fade margin and co-channel protection ratio provide 25.5 and 50.7 dB, respectively. Also, net filter discrimination and adjacent channel protection ratio are obtained as 26.3 and 24.4 dB, respectively, at the first adjacent channel of 40 MHz. The proposed method provides some merits in computing protection ratio for microwave relay networks in view of an easy extension and practical applications considering more detailed and various system parameters.

• Advances in concrete construction
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• v.5 no.6
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• pp.613-624
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• 2017

In this paper, an experimental investigation was carried out to study the effect of volume fraction of fiber and maximum aggregate size on mode-I fracture parameters of high strength concrete. Total of 108 beams were tested on loading frame with three point loading, the variables in the high strength concrete beams are aggregate size (20 mm, 16 mm and 10 mm) and volume fraction of fibers (0%, 0.5%, 1% and 1.5%). The fracture parameters like fracture energy, brittleness number and fracture process zone were analyzed by the size effect method (SEM). It was found that fracture energy (Gf) increases with increasing the Maximum aggregate size and also increasing the volume of fibers, brittleness number (${\beta}$) decreases and fracture process zone (CF) increases.

• Journal of Biomedical Engineering Research
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• v.35 no.6
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• pp.192-196
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• 2014

Collagen scaffolds were synthesized by cross linking into a solution mixture of 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochlorid(EDC) in ethanol, followed by pressing, cleaning and lyophilization process after the type I atelo-collagen solutions in D.I water(pH3). The experimental conditions are collagen concentration of 1.0 wt%, 3.0 wt%, 5.0 wt% and differential concentration of cross-linker. Then, parametric studies were performed by varying the parameters to investigate the morphology, the porosity, the swelling ratio and the thickness and genotoxicity of the scaffolds. The scaffolds thickness pattern was regular to concentration of the degree of cross-linker and collagen. It was observed that the swelling ratio, the degree of crosslink, and the pore size(thickness of scaffold) can be controlled by adjusting the collagen, crosslinker. Among the parameters investigated, the smallest thickness can be achieved by collagen, crosslinker concentrate condition. The collagen scaffold is induced no genotoxicity. The lowest swelling ratio, as an indication of the highest degree of crosslink, can be obtained by adding crosslink agent.

• Journal of Animal Science and Technology
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• v.48 no.1
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• pp.29-38
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• 2006

The objective of this study was to estimate genetic variances of growth curve parameters in Hanwoo cows. The data used in this study were records from 1,083 Hanwoo cows raised at Hanwoo Experiment Station, National Livestock Research Institute(NLRI). First evaluation model(Model I) fit year-season of birth and age of dam as fixed effects and second model(Model II) added age at the final weight as a linear covariate to Model I. Heritability estimates of A, b and k from Gompertz model were 0.22, 0.11 and 0.07 using modelⅠ and 0.28, 0.11 and 0.12 using modelⅡ. Those from Von Bertalanffy model were 0.22, 0.11 and 0.07 using modelⅠ, 0.28, 0.11 and 0.12 using modelⅡ. Heritability estimates of A, b and k from Logistic model were 0.14, 0.07 and 0.05 using modelⅠ, 0.18, 0.07 and 0.12 using modelⅡ. Heritability estimates of A from Gompertz model were higher than those from Von Bertalanffy model or Logistic model in both model Ⅰand model Ⅱ. Heritability estimates of b from Logistic model were higher than those from Gompertz model or Von Bertalanffy model in both modelⅠand model Ⅱ. Heritability estimates of birth weight, weaning weight, 3 month weight, 6 month weight, 9 month weight, 12 month weight, 18 month weight, 24 month weight, 36 month weight were after linear age adjustment 0.27, 0.11, 0.19, 0.14, 0.16, 0.23, 0.52 and 0.32, respectively. Heritability estimates of birth weight, weaning weight, 3 month weight, 6 month weight, 9 month weight and 24 month weight fit by Gompertz model were larger than those estimated from linearly adjusted data. Heritability estimates of 12 month weight, 18 month weight and 36 month weight fit by Von Bertalanffy model were larger than those estimated from linearly adjusted data. In the multitrait analyses for parameters from Gompertz model, genetic and phenotypic correlations between A and k parameters were －0.47 and －0.67 using modelⅠand －0.56 and －0.63 using model Ⅱ. Those between the A and b parameters were 0.69 and 0.34 using modelⅠand 0.72 and 0.37 using model Ⅱ. Those between the b and k parameters were －0.26 and 0.01 using modelⅠand －0.30 and 0.01 using model Ⅱ. In the multitrait analyses for parameters from Von Bertalanffy model, genetic and phenotypic correlations between A and k parameters were －0.49 and －0.67 suing model Ⅰ and －0.57 and －0.70 using modelⅡ. Those between the A and b parameters were 0.61 and 0.33 using modelⅠ and 0.60 and 0.30 using model Ⅱ. Those between the b and k parameters were －0.20 and 0.02 using modelⅠ and 0.16 and 0.00 using modelⅡ. In the multitrait analyses for parameters from Logistic model, genetic and phenotypic correlations between A and k parameters were －0.43 and －0.67 using model Ⅰ and －0.50 and －0.63 using modelⅡ. Those between the A and b parameters were 0.47 and 0.22 using modelⅠ and 0.38 and 0.24 using modelⅡ. Those between the b and k parameters were －0.09 and 0.02 using model Ⅰ and －0.02 and 0.13 using model Ⅱ.

• Journal of Nutrition and Health
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• v.29 no.7
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• pp.758-771
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• 1996

This study attempted to define reference data for the distribution of vitamin d status and to explore the relationship between vitamin D status and related biochemical indices in Korean women. The vitamin D status of 179 Korean women aged from 20 to 75 years was analyzed by using HPLC(High Pressure Liquid Chromatography). Related biochemical indices such as iPTH, alkaline phosphatase, creatinine, albumin, Ca, Mg and P were also measured. The mean serum level of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D were s25.8ng/ml and 89.8pg/ml, respectively. Low 25-hydroxyvitamin D (<25nmol/L) was found in 29 subjects(16.5%). There was a significantly progressive decrease in serum 25-hydroxyvitamin D with increasing age(p<0.05). After in their, there was a dramatical reduction in 25-hydroxyvitamin D(p<0.05). It was also significant in post-menopasusal women compared with pre-menopausal women(p<0.000). Serum alkaline phosphatase levels increased significantly with age(p<0.001). Whereas serum calcium and phosphorus levels remained constant with age. Serum 250-hydroxyvitamin D was invesely related to iPTH (p<0.05) and alkaline phophatase (p<0.001).