• Steel and Composite Structures
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• v.25 no.5
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• pp.545-556
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• 2017

The tubed steel reinforced concrete (SRC) column is a composite column in which the outer steel tube is mainly used to provide confinement on the core concrete. This paper presents experimental and analytical studies on the behavior of circular tubed SRC (TSRC) columns subjected to axial compression. Eight circular TSRC columns were tested to investigate the effects of length-to-diameter ratio (L/D) of the specimens, diameter-to-thickness ratio (D/t) of the steel tubes, and use of stud shear connectors on the steel sections. Elastic-plastic analysis on the steel tubes was used to investigate the mechanism of confinement on the core concrete. The test results indicated that the tube confinement increased the strength and deformation capacity for both short and slender columns, and the effects on strength were more pronounced for short columns. A nonlinear finite element (FE) model was developed using ABAQUS, in which the nonlinear material behavior and initial geometric imperfection were included. Good agreement was achieved between the predicted results using the FE model and the test results. The test and FE results were compared with the predicted strengths calculated by Eurocode 4 and the AISC Standard. Based on the analytical results, a new design method for this composite column was proposed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.2
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• pp.235-243
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• 2001

This paper describes a design study of the cylindrical multi-hole premixed burner to be used for condensing gas boiler which can raise performance and reduce NOx emission. In this study, specifications of the multi-hole burner (hole diameters and arrangement) are investigated using model flat burners in terms of flame stability, and combustion characteristics for stability and NOx emission are examined for cylindrical multi-hole burner. As a result, the equivalence ratio for optimum operation condition of the cylindrical burner is around 0.72(0.7∼0.75). In this condition, turn-down ratio becomes 3 : 1 at least which is suitable for proportional control. The NOx and CO emission is less than 40ppm and 25ppm(0$_2$0% basis), respectively. This burner can be applied LPG as well as NG because there is no difference for stable combustion region.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.351.1-351.1
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• 2014

In this study, we prepared the solution-based In-Ga-Zn oxide thin film transistors (IGZO TFTs) of multistacked active layer and characterized the gate bias instability by measuring the change in threshold voltage caused by stacking. The solutions for IGZO active layer were prepared by In:Zn=1:1 mole ratio and the ratio of Ga was changed from 20% to 30%. The TFTs with multistacked active layer was fabricated by stacking single, double and triple layers from the prepared solutions. As the number of active layer increases, the saturation mobility shows the value of 1.2, 0.8 and 0.6 (). The electrical properties have the tendency such as decreasing. However when gate bias VG=10 V is forced to gate electrode for 3000 s, the threshold voltage shift was decreased from 4.74 V to 1.27 V. Because the interface is formed between the each layers and this affected the current path to reduce the electrical performances. But the uniformity of active layer was improved by stacking active layer with filling the hole formed during pre-baking so the stability of device was improved. These results suggest that the deposition of multistacked active layer improve the stability of the device.

• Journal of Distribution Science
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• v.17 no.12
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• pp.23-32
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• 2019

Purpose As consumer awareness grows, the importance of CSR becomes even more important for long-term growth. In response to this current trend, the purpose of this study is to analyze the effect of CSR activities on business performance for logistics companies. Research design, data, and methodology - Between CSR activities and growth, there was a generally positive(+) relationships between activities such as donation and volunteerism and the growth of the enterprise. In terms of the relationship between environmental factors and growth, negative results were expressed. In case of profitability, improved welfare for workers has had a positive impact on corporate profitability. Results - With respect to stability, a high proportion of equity capital is not considered to be more active in SCR activities. Significant negative results were given between the minimum factors for entry, transportation, and noise generation factors and the ratio of liabilities, which are representative friction factors in the community. Conclusions - With respect to stability, a high proportion of equity capital is not considered to be more active in SCR activities. Significant negative results were given between the minimum factors for entry, transportation, and noise generation factors and the ratio of liabilities, which are representative friction factors in the community.

• Journal of Microbiology and Biotechnology
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• v.14 no.4
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• pp.673-679
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• 2004

A microbial cryoprotectant formulation using a W/O/W multiple emulsion system was developed. The psychrotolerant microorganism, B4, isolated from soil in South Korea, was observed by the drop freezing method, in which the microorganism sample inhibited ice nucleation activity. The antifreeze activity was eliminated when the microorganism sample was treated with protease, indicating that the antifreeze activity was due to the presence of antifreeze protein. The result of the l6S rDNA sequencing indicated the B4 strain was most closely related to a species of the genus Bacillus. Culture broth of B4 strain (Bacillus sp.) and rapeseed oil containing 1 % polyglycerine polyricinolate (PGPR) were used as core and wall material, respectively. The most stable W/O emulsion was prepared at a core/oil ratio of 1:2. The highest W/O/W emulsion stability was achieved when the primary emulsion to external aqueous phase containing 0.5% caster oil polyoxyethylene ether $(COG25^{TM})$ ratio was 1:1. Microcrystalline cellulose showed better W/O/W emulsion stability than other polymer types. The viability of cells in a W/O/W emulsion was higher than free cells during storage at $37^\circ{C}$. An acidic pH and UV exposure decreased the viability of free cells, but cells in W/O/W emulsion were more stable under these conditions.

• Journal of Power System Engineering
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• v.14 no.3
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• pp.33-38
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• 2010

Technology of vehicle industry has been developing and it is required a better vehicle performance than before. Therefore, the consumers are asking not only an economic efficiency, functionality, polished design, ride comfort and silence but also a driving stability. The ride comfort, silence and driving stability are influenced by the size of vehicle and various facilities. But the principal factor is a room noise and vibration sensed by a driver and passenger. Thus, the NVH of vehicle has been raised and used as a principal factor for evaluation of vehicle performance. The primary objective of this study is an optimized design of powertrain mounting system. To optimized design was applied MSC.Nastran optimization modules. Results of dynamic analysis for powertrain mounting system was investigated. By theses results, design variables was applied 12 dynamic spring constant. And the weighting factor according to translational displacement and rotational displacement applied 3 cases. The objective function was applied to minimize displacement of powertrain. And the design variable constraint was imposed dynamic spring constant ratio. The constraint of design variable for objective function was imposed bounce displacement for powertrain.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.264-270
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• 2011

This paper reports a filtered velocity feedback (FVF) controller, which is an alternative to direct velocity feedback (DVFB) controller. The instability problems due to high frequency response under DVFB can be alleviated by the suggested FVF controller. The FVF controller is designed to filter out the unstable high frequency response. The FVF controller and the dynamics of clamped beams under forces and moments are first formulated The effects of the design parameters (cut-off frequency, gain, and damping ratio) on the stability and the performance are then investigated. The cut-off frequency should be selected not to affect the system stability. The magnitude of the open loop transfer function (OLTF) at the cut-off frequency should be small. As increasing the gain of the FVF controller, the magnitude of the OLTF is increased, so that the closed loop response can be reduced more. The enhancement of the OLTF at the cut-off frequency is reduced but the phase behavior around the cut-off frequency is distorted, as the damping ratio is increased The control performance is finally estimated for the clamped beam. More than 10dB reductions in velocity response can be achieved at the modal frequencies from the first to eighth modes.

• Steel and Composite Structures
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• v.35 no.4
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• pp.555-566
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• 2020

This paper aims to present an analytical methodology to investigate influences of nanoscale and surface energy on buckling stability behavior of perforated nanobeam structural element, for the first time. The surface energy effect is exploited to consider the free energy on the surface of nanobeam by using Gurtin-Murdoch surface elasticity theory. Thin and thick beams are considered by using both classical beam of Euler and first order shear deformation of Timoshenko theories, respectively. Equivalent geometrical constant of regularly squared perforated beam are presented in simplified form. Problem formulation of nanostructure beam including surface energies is derived in detail. Explicit analytical solution for nanoscale beams are developed for both beam theories to evaluate the surface stress effects and size-dependent nanoscale on the critical buckling loads. The closed form solution is confirmed and proven by comparing the obtained results with previous works. Parametric studies are achieved to demonstrate impacts of beam filling ratio, the number of hole rows, surface material characteristics, beam slenderness ratio, boundary conditions as well as loading conditions on the non-classical buckling of perforated nanobeams in incidence of surface effects. It is found that, the surface residual stress has more significant effect on the critical buckling loads with the corresponding effect of the surface elasticity. The proposed model can be used as benchmarks in designing, analysis and manufacturing of perforated nanobeams.

• The KSFM Journal of Fluid Machinery
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• v.7 no.6 s.27
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• pp.21-27
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• 2004

The floating ring seal has an advantage to find the optimum position by itself, which is used in the turbo pump of a liquid rocket. The main purpose of seals is to reduce the leakage. Especially, seals of the turbo pump for the liquid rocket engine are operated under the serious conditions such as high pressure above 10 MPa, very low temperature about $-180^{\circ}C$ and high rotating speed above 25,000 rpm. So, rotordynamic stability is very important for the system stability. In this paper, the leakage and dynamic characteristics of floating ring seals were investigated by a experimental and analytical method. The theoretical results of the leakage performance for the floating ring seal showed much higher than that of experimental results. On the other hand, the results of stiffness and damping characteristics showed similarity each other. As the shaft speed was increasing, the whirl frequency ratio was increased in the experimental results.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.11a
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• pp.67-70
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• 2006

This study investigates the properties of light weight foamed concrete designed with various incorporating ratios of CKD and adding ratios of PS. Test showed that increase of CKD and PS decreased fluidity of fresh concrete, which need more addition of superplasticizer to secure proper fluidity. As for the sinking depth of specimens, using more CKD or PS decreased the value, due to the improvement of viscosity by micro particles of CKD and reduction of air loss by PS. Those methods are very effective to solve the sinking problem of light weight foamed concrete, which has been highly concerned. For the hardened concrete, compressive strength of specimens exhibited that using around 10% of CKD or 0.02% of PS increased the strength value, but decreased when incorporated or added more amounts of that, due to reduction of the sinking depth, caused by filling effect of the micro particle and improvement of the viscosity.