• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.315-324
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• 2012

This paper presents a numerical investigation of the deflagration-to-detonation transition (DDT) of flame acceleration by a shock wave filled with an ethylene/air mixture as the combustible gas, considering geometrical changes by using obstacles and bent tubes. The model used consists of the reactive compressible Navier-Stokes equations and the ghost fluid method (GFM) for complex boundary treatment. Simulations with a variety of bent tubes with obstacles show the generation of hot spots through flame and strong shock-wave interactions, and restrained or accelerated flame propagation due to geometrical effects. In addition, the simulation results show that the DDT occurs with a nearly constant chemical heat-release rate of 20 MJ/($g{\bullet}s$) in our numerical setup. Furthermore, the DDT triggering time can be delayed by the absence of unreacted material together with insufficient pressures and temperatures induced by different flame shapes, although hot spots are formed in the same positions.

• Magazine of the Korean Society of Agricultural Engineers
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• v.32 no.4
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• pp.71-80
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• 1990

Model tests for the ultimate pullout resistance of anchorages and investigation of failure behaviors in cohesionless soil have been conducted. The factors affecting the anchorage are mostly the geometry of the system, and soil properties of sands. The main conclusions of the experimental work were as follows. 1. The load - displacement relationship can be a form of parabolic curve for all plates. 2. The change in ultimate pullout resistance of anchor is mostly affected by embedment ratio and size of anchor, and influenced to a lesser degree by its shape. 3. Critical embedment ratio which is defined as the failure mode changes from shallow to deep mode is increased with increasing height of anchor. 4. For a constant anchor height, as the width of anchor increases the ultimate pullout resistance also increases. However, considering the efficiency of anchor for unit area, width of anchor does not appear to have any sigrnificant contribution on increasing anchor city. 5. Anchor capacity has a linear relation to sand density for any given section and the rate of change increases as the section increases. Critical depth determining the failure patterns of anchor is decreased with a decrease of sand density. 6. With increasing inclination angle, size of anchor, and decreasing embedment ratio, the ultimate pullout resistance of anchor under inclined loading is significantly decreased. 7. The ultimate pullout resistance of double anchor, a method of improving single of anchor capacity, is influenced by the center - to - center spacing adjacent anchors. It is also found that tandem and parallel anchor rigging arrangements decrease the anchor system capacity to less than twice the single anchor capacity due to anchor interference.

• Journal of Microbiology and Biotechnology
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• v.26 no.3
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• pp.503-510
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• 2016

The accumulation (internal and superficial distribution) of magnesium ions (Mg²⁺) by the green freshwater microalga Chlorella vulgaris (C. vulgaris) was investigated under autotrophic culture in a stirred photobioreactor. The concentrations of the three forms of Mg²⁺ (dissolved, extracellular, and intracellular) were determined with atomic absorption spectroscopy during the course of C. vulgaris growth. The proportions of adsorbed (extracellular) and absorbed (intracellular) Mg²⁺ were quantified. The concentration of the most important pigment in algal cells, chlorophyll a, increased over time in proportion to the increase in the biomass concentration, indicating a constant chlorophyll/biomass ratio during the linear growth phase. The mean-average rate of Mg²⁺ uptake by C. vulgaris grown in a culture medium starting with 16 mg/l of Mg²⁺ concentration was measured. A clear relationship between the biomass concentration and the proportion of the Mg²⁺ removal from the medium was observed. Of the total Mg²⁺ present in the culture medium, 18% was adsorbed on the cell wall and 51% was absorbed by the biomass by the end of the experiment (765 h). Overall, 69% of the initial Mg²⁺ were found to be removed from the medium. This study supported the kinetic model based on a reversible first-order reaction for Mg²⁺ bioaccumulation in C. vulgaris, which was consistent with the experimental data.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.3
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• pp.128-134
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• 2016

An analysis of the main factors and its degree of impact on power production is performed against the landfill gas power plant in S landfill site. The number of normal operation (50 MWh & 24 hr) days was 70.9% to the total number of operation days from 2007 to 2014, and the percentage of the actual power production was 79.3% of 3,428,400 MW which is the theoretical maximum estimation. The ratio of factors that accounted for the efficiency of power production are: 44.0% of repairing of the defect and regular servicing, 37.4% of cut-down operation due to hydrogen sulfide, and 18.6% of air pre-heater washing, respectively. Yet, considering that the cut-down operation due to hydrogen sulfide was carried out for only two years, the high concentration of hydrogen sulfide was the most influential factors on landfill gas power production. The long-term power production was analyzed as 35.9 MWh in 2018, and the constant drop is anticipated, resulting in 16.6 MWh by 2028, and under 8.4 MWh in 2038.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.29 no.5
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• pp.282-292
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• 2003

Several agents are in use to promote new bone formation during bone graft procedures in maxillofacial region. Among them, we have used crude BMP, PRP, and P-15 for experimentally created defects with accompanying graft materials in the rabbit model. The aim of this study is to analyze the effect of above mentioned agents on bone formation using histologic and histomorphometrical methods, thus to provide experimental support for clinical application of these agents. Six rabbits were used as experimental animals. Four surgical defects were created on the distal femoral heads of each animal using trephine drill. The defects were filled with each agents with accompaning graft materials as experimental groups and particulate corti-co-cancellous autogenous graft as control. For histomorphometric analysis, fluorescent dye was injected at 2week and 1week before sacrifice. Then, the animals were sacrificed at 2, 4 and 8weeks after surgery and histologic and histomorphometric examinations were achieved. At two weeks after bone graft, bone formation and active remodeling process were examined in all experimental groups and the control. But the intensity of such activities of the experiments were somewhat weaker than that of the control. In BMP group, the amount of newly formed osteoid was increased constantly and the amount was preserved constantly in PRP group. But in P-15 group, the amount of newly formed osteoid was decreased with time to 8week after surgery. Histologic findings showed superior bony quantity and quality in PRP group than that of P-15 group. MAR(Mineralization Apposition Rate) of all experimental groups were slower than that of control group. In P-15 group, constant foreign body reaction was observed at all periods and the graft material showed inwardly destroyed characteristics rather to mature. The data from this study provide the basis for future studies for evaluating the long-term remodeling process and foreign body reactions observed in P-15 group and clinical study for predictable use of these agents.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.9
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• pp.21-25
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• 2008

In this study, to maximize RF performance of MOSFETs, $f_T$ and $f_{max}$ dependent data on $W_u$ are measured and newly analyzed by extracting small-signal model parameters. From the physical analysis results, it is found that a peak value of $f_T$ is generated by $W_u$-independent parasitic gate-bulk capacitance at narrow $W_u$ and the wide width effect of reducing the increasing rate of transconductance at wide $W_u$. In addition, it is revealed that a maximum value of $f_{max}$ is caused by the non-quasi-static effect that the gate resistance is greatly reduced at narrow $W_u$ and becomes constant at wide $W_u$.

• Clean Technology
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• v.17 no.2
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• pp.97-102
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• 2011

The adsorption characteristics of amatanth dye by granular activated carbon were experimently investigated in the batch adsorption. Kinetic studies of adsorption of amaranth dye were carried out at 298, 308 and 318 K, using aqueous solutions with 100, 200 and 300 mg/L initial concentration of amatanth. It was established that the adsorption equilibrium of amaranth dye on granular activated carbon was successfully fitted by Langmuir isotherm equation at 298 K. The pseudo first order and pseudo second order models were used to evaluate the kinetic data and the pseudo second order kinetic model was the best with good correlation. Values of the rate constant ($k_2$) have been calculated as 0.1076, 0.0531, and 0.0309 g/mg h at 100, 200 and 300 mg/L initial concentration of amatanth, respectively. Thermodynamic parameter such as activation energy, standard enthalpy, standard entropy and standard free energy were evaluated. The estimated values for standard free energy were -5.08 - -8.10 kJ/mol over activated carbon at 200 mg/L, indicated toward a spontaneous process. The positive value for enthalpy, 38.89 kJ/mol indicates that adsorption interaction of amatanth dye on activated carbon is an endothermic process.

• Korean Journal of Health Education and Promotion
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• v.29 no.5
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• pp.103-113
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• 2012

Objectives: This study aims to identify the effects of environmental characteristics of the community on adults' drinking problems with held constant effects of characteristics of drinkers themselves. Methods: A multi-level regression analysis was employed to differentiate the variances accounted for by measurements both at individual and group levels. Data on individual demographic, behavioral, and mental health status were obtained from the Community Health Survey conducted in 2009 in the province of Kyunggido, which include 41,376 respondents aged 19 and over. This study included 28,335 adults who were classified as drinkers. They were from 45 communities(si, gun, or gu) for which data on contextual characteristics were collected by secondary data available on local government websites and KOSIS(Korea Statistical Information System). Results: Multi-level analyses showed that the variance of the dependent variable, harmful use of alcohol measured by alcohol use disorder identification test was independently accounted for by variance of independent variables at group level, including number of on-premises alcohol outlet per inhabitant and divorce rate, with held other independent variables of the model controlled. Conclusions: This study confirms that in order to prevent and reduce harms caused by harmful use of alcohol requires restricting physical availability of alcohol in the community where the drinker lives.

• Journal of the Korea Computer Industry Society
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• v.2 no.6
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• pp.859-866
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• 2001

Successful project planning relies on a good estimation of the effort required to complete a project, together with the schedule options that may be available. Despite the extensive research done developing new and better models, existing software effort estimation models are present only the total effort and effort (or manpower： people per unit time) function for the software life-cycle. Also, Putnam presents constant effort rate in each subcycles. However, the size of total efforts are variable according to the software projects under the influence of its size, complexity and operational environment. As a result, the allocated effort in subcycle also differ from project to project. This paper suggests the linear and polynomial effort estimation models in specifying, building and testing phase followed by the project total effort. These models are derived from 128 different projects. This result can be considered as a practical guideline in management of project schedule and effort allocation.

• Korean Chemical Engineering Research
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• v.55 no.4
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• pp.514-519
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• 2017

Adsorption characteristics of acid green 27 dye using activated carbon were investigated as function of adsorbent dose, pH, initial concentration, contact time and temperature. Freundlich isotherm explained adsorption of acid green 27 dye very well and Freundlich separation factors (1/n=0.293~0.387) were found that this process could be employed as effective treatment method. Kinetic studies showed that the kinetic data were well described by the pseudo second-order kinetic model. Pseudo second rate constant ($k_2$) decreased with the increase in initial acid green 27 concentration. Activation energy (10.457 kJ/mol) and enthalpy (79.946 kJ/mol) indicated that adsorption process was physisorption and endothermic. Since Gibbs free energy decreased with increasing temperature, spontaneity of adsorption reaction increased with increasing temperature in the temperature range of 298 K~318 K.