• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.4
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• pp.409-416
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• 2009

Standard procedures for a fracture toughness testing require very severe restrictions for the specimen geometry to eliminate a size effect on the measured properties. Therefore, the used standard fracture toughness data results in the integrity assessment being irrationally conservative. However, a realistic fracture in general structures, such as in nuclear power plants, may develop under the low constraint condition of a large scale yielding with a shallow surface crack. In this paper, cleavage fracture toughness tests have been made on side-grooved PCVN (precracked charpy V-notch) type specimens (10 by 10 by 55 mm) with various crack depths. The constraint effects on the crack depth ratios were evaluated quantitatively by the developed scaling method using the 3-D finite element method. After the fracture toughness correction from scaling model, the statistical size effects were also corrected according to the standard ASTM E 1921 procedure. The results were evaluated through a comparison with the $T_0$ of the standard CT specimen. The corrected $T_0$ for all of the PCVN specimens showed a good agreement to within $5.4^{\circ}C$ regardless of the crack depth, while the averaged PCVN $T_0$ was $13.4^{\circ}C$ higher than the real CT test results.

• The Korean Journal of Applied Statistics
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• v.17 no.2
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• pp.253-267
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• 2004

In some clinical trials, one may see that a significant fraction of patients are cured and their original disease does not recur even after termination of treatment and pro-longed follow-up. This situation occurs frequently in pediatric cancer trials where there are excellent therapeutic results. In such cases, interest concentrated on the difference of cure rates rather than other types of differences in failure distributions. Various authors have investigated the parametric and nonparametric methods for testing the difference of cure rates. In this study, we compare by simulation the power and size of a parametric test and five nonparametric tests in a various range of the alternatives, censoring rates and cure rates. Our objectives are to determine if any test was preferable on the basis of size and power in various situation, and to investigate the effect of the model misspecification.

• Journal of Forest and Environmental Science
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• v.32 no.2
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• pp.173-181
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• 2016

This study designed a model of the efficient production schemes and raw materials transportation optimization of current South Korean's simple and monolithic distribution system of wood to build a SCM (supply chain management) as a basic level to establish a distribution of future by pellet production of raw materials costs and reduce transport costs, and specifically to forest of pallet to contribute to revitalizing the market. The result of each transportation costs after building the best transportation network from raw material supply area to demand area applying transport law was 964,600 thousands Won from 6 supply areas to 7 demand areas. And the result of each model's analysis to get the pellet's efficient production through production cost reduction showed that it reduced from 325,701 Won/t to 240,106 Won/t, results of existing efficient pellet for the production model 8,233 tons over 20,000 tons annual production capacity from the size of the expanded production capacity when the expansion. However, when the production size expanded to 50,000 Tons of the production, the effect was very small even though production cost decreased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.976-982
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• 2002

In this study, smoke movement in tunnel fire with natural ventilation shaft has been investigated with various size of fire source. Gasoline pool fire with different size of diameter - 73mm, 100mm, 125mm and 154mm - was used to describe fire source. Experimental data is obtained with 1/20 model tunnel test and its results are compared with numerical results. The computation were carried out using FDS 1.0 which is a field model of fire-driven now. Temperature profiles between measured and predicted data are compared along ceiling and near the ventilation shaft. Both results are in good agreement with each other. In order to evaluating a safe egress time in tunnel fire, horizontal smoke front velocity was measured in model tunnel fire tests and those are compared with numerical results. According to the presence or absence of natural ventilation shaft, ventilation effect are estimated quantitatively. Finally, this paper shows that computational fluid dynamics(CFD) is applicable to predict fire-induced flow in tunnel.

• Journal of Power Electronics
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• v.16 no.3
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• pp.849-860
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• 2016

The high-switching-frequency operation of power converters can achieve high power density through size reduction of passive components, such as capacitors, inductors, and transformers. However, a small-output capacitor that has small capacitance and low effective series resistance changes the small-signal model of the converter power stage. Such a capacitor can make the converter unstable by increasing the crossover frequency in the transfer function of the small-signal model. In this paper, the design and implementation of a high-frequency LLC resonant converter are presented to verify the power density enhancement achieved by decreasing the size of passive components. The effect of small output capacitance is analyzed for stability by using a proper small-signal model of the LLC resonant converter. Finally, proper design methods of a feedback compensator are proposed to obtain a sufficient phase margin in the Bode plot of the loop gain of the converter for stable operation at 500 kHz switching frequency. A theoretical approach using MATLAB, a simulation approach using PSIM, and experimental results are presented to show the validity of the proposed analysis and design methods with 100 and 500 kHz prototype converters.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.20 no.3
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• pp.63-67
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• 2012

Spaceflight induces a number of cardiovascular physiological alterations. To study adaptations to microgravity on Earth, the tail-suspended, hindlimb-unloaded rat model has been used to simulate the effects of microgravity. Despite the extensive use of this model to infer physiological adaptations of many organs to microgravity, little information has been obtained on the effect of tail suspension(TS) on cardiac adaptations in the rat. This study was aimed to investigate the effects of simulated microgravity on the rat myocardium using the TS model. Twenty-four male Sprague-Dawley rats were randomly assigned to 3 experimental groups(1, 7 and 14 days of TS) and a control group. A microscopic examination was performed to assess histopathological changes in the myocardial morphology. The hearts from the control group, the 1 day-TS rats and the 7 day-TS rats revealed no evident abnormalities in cardiomyocyte size and morphology. At day 14 of TS, in contrast, the ventricular cardiomyocytes appeared more separated from each other and were slightly smaller in size compared with those of the control group. Also seen were scattered areas exhibiting focal disorganization of muscle fibers and some degenerating cardiomyocytes, of which the nuclei had become pyknotic or disappeared. In this study, we demonstrated that the ventricular cardiomyocytes underwent degeneration and atrophy at the microscopic level during exposure to simulated microgravity in TS rats.

• Advances in nano research
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• v.8 no.1
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• pp.13-24
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• 2020

In this paper, for the first time based on the nonlocal strain gradient theory the effect of size dependency in torsional vibration of bi-direction functionally graded (FG) nonlinear nano-cone is study. The material properties were assumed to vary according to the arbitrary function in radial and axial directions. The Navier equation and boundary conditions of the size-dependent bidirectional FG nonlinear nano-cone were derived by Hamilton's principle. These equations were solved by employing the generalized differential quadrature method (GDQM). The presented model can turn into the classical model if the material length scale parameters are taken to be zero. The effects of some parameters, such as inhomogeneity constant, cross-sectional area parameter and small-scale parameters, were studied. As an essential result of this study can be stated that an FG nano-cone model based on the nonlocal elasticity theory behaves softer and based on the strain gradient theory behaves harder.

• Journal of Internet Computing and Services
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• v.25 no.4
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• pp.73-86
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• 2024

With the acceleration of regional economic integration, the agricultural trade network within the RCEP region presents new opportunities and challenges for member countries. This study focuses on agricultural trade among RCEP members from 2011 to 2020, utilizing social network analysis to explore the structural characteristics and evolutionary trends of the trade network. Additionally, an extended gravity model is employed to empirically analyze the key factors influencing South Korea's agricultural trade with other member countries. The findings reveal that: (1) Agricultural trade relationships within the RCEP region are stable and mature, with high interconnectivity in the trade network, indicating a trend towards balanced development. (2) The positions of member countries within the agricultural trade network are characterized by both high density and heterogeneity. (3) South Korea's agricultural trade with RCEP member countries is positively influenced by the economic size, population size, and governance level of its trading partners, while South Korea's own indicators show no significant effect. The trade distance between South Korea and member countries also has a positive impact on agricultural trade. By combining social network analysis with an extended gravity model, this study provides a multi-faceted quantitative analysis of the RCEP agricultural trade network, offering new insights into regional agricultural trade. It also provides empirical evidence for agricultural trade cooperation between South Korea and other RCEP countries.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.44 no.4
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• pp.273-281
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• 2008

In this study, the effect of slope length and angle at the entrance to fishing pots on the size of captured shrimp was examined to determine the optimal design of pots for use in Hokkaido, Japan. The purpose of the current study was to optimize the design of shrimp pots to allow greater control over the size of captured individuals for the purposes of shrimp resource management. Tank experiments were conducted to determine the optimal slope length and slope angle by analyzing the sizes of shrimp entering 10 model pots with combinations of five different slope lengths on slope angle of current shrimp pot, and five different angles on slope length of current shrimp pot. The results showed that, as the slope length of the pot increased, the size of individuals which entered the pot increased. In addition, as the slope angle was elevated in each of the five different slope angle treatments, the size of individuals entering was also increased.

• Journal of the Korean Society of Combustion
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• v.15 no.4
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• pp.65-73
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• 2010

In order to provide fundamental information for developing reaction model in the practical blended coal power plants, effects of particle size and blending ratio on combustion characteristics and thermal reaction in co-firing with bituminous and sub-bituminous coals were experimentally investigated using a TGA and a laboratory-scale burner. Characteristic parameters including ignition, burnout temperature and activation energy were determined from TG and DTG combustion profiles. Distributions of flame length and mean particle temperature were investigated from the visualization of flames in slit-burner system. As coal particle size decreased and volatile matter content increased, characteristic temperatures and activation energy decreased. The ignition/burnout characteristics and activation energy are linearly influenced by a variation in particle size and blending ratio. These results indicated that the control of the coal blending ratio can improve the combustion efficiency for sub-bituminous coals and the ignition characteristics for bituminous coals.