• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.3
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• pp.221-229
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• 1992

A series of experiments on the resuspension of deposited fine-grained sediments were carried out in a recirculating straight flume to investigate the influence of the sediment type, water content and bed shear stress (${\tau}_b$) on the resuspension characteristics of the sediments. The sediments were sampled from Youngkwang coast and Youngdo coast which are located in the western sea and southeastern sea of Korea, respectively. Critical bed shear stress (${\tau}_c$) for resuspension was deduced for each experimental series. For the same sediment, critical bed shear stress for resuspension decreased but suspension mass or rate increased with increasing water content. The resuspension of deposited fine-grained sediments depended strongly on the water content, and the sediment type characterizing the inter-particle bond strength. It has been found that critical bed shear stress for resuspension in the unidirection flow is about 4 times higher than that in the combined wave-current flow, In case of lower bed shear stress, after an initially high suspension, suspension mass approaches a constant value due to the bed hardening with increasing time, but in case of higher bed shear stress, suspension mass increased successively due to the bed softening with time. Initial suspension rate, $E={\alpha}_3({\tau}_b/{\tau}_c-1)^{\beta}$ (where ${\alpha}_3$ and ${\beta}$=empirical constants), was estimated for each experimental series, ${\alpha}_3$ and ${\beta}$ values for the same sediment increased with water content.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.12
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• pp.8637-8642
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• 2015

Typical aging for the rubber using the current military adhesive combat boots was spread with a regular aging caused by heat stress. In this study, the aging test of the rubber for combat boots was carried out and the reaction rate constant, k was calculated at aging temperature $60^{\circ}C$, $80^{\circ}C$ and $100^{\circ}C$, using the Arrhenius equation. The lifetime limit was assumed that the tensile strength of the product is reduced to 30%, the elongation is reduced to 50% and abrasion resistance ratio is 380%. ln($P/P_0$) and the lifetime was predicted with the consideration of the activation energy constant. According to the above, the lifetime of the rubber for combat boots with influenced by aging temperature was predicted. As the result, the estimate lifetime at $20^{\circ}C$ was confirmed more than 10 years.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.708-712
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• 2001

A new phase-shifted parallel-input/series-output (PI SO) dual inductor-fed push-pull converter for high-power step­up applications is proposed. This converter is operated at a constant duty cycle and employs an auxiliary circuit to control the output voltage with a phase-shift between the two modules. It features a voltage conversion characteristic which is linear to changes in the control input, and high step-up ratio with a greatly reduced switch turn-off stress resulting in a significant increase in the converter efficiency. It also shows a low ripple content and low root-mean-square (RMS) current in the output capacitor. The operational principle is analyzed and a comparative analysis with the conventional pulse-width-modulated (PWM) PISO dual inductor-fed push-pull converter is presented. A 50kHz, 800W, 350Vdc prototype with an input of 20-32Vdc has also been constructed to validate the proposed converter. The proposed converter compares favorably with the conventional counterpart and is considered well suited to high-power step-up applications.

• Architectural research
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• v.7 no.1
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• pp.39-48
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• 2005

Main objective of this research is to evaluate performance of high-strength concrete (HSC) columns for ductility and strength. Eight one-third scale columns with compressive strength of 69 MPa were subjected to a constant axial load corresponding to 30 % of the column axial load capacity and a cyclic horizontal load-inducing reversed bending moment. The variables studied in this research are the volumetric ratio of transverse reinforcement (${\rho}_s=1.58$, 2.25 %), tie configuration (Type H, Type C and Type D) and tie yield strength ($f_{yh}=549$ and 779 MPa). Test results show that the flexural strength of every column exceeds the calculated flexural capacity based on the equivalent concrete stress block used in the current design code. Columns with 42 % higher amounts of transverse reinforcement than that required by seismic provisions of ACI 318-02 showed ductile behaviour, showing a displacement ductility factor (${\mu}_{{\Delta}u}$) of 3.69 to 4.85, and a curvature ductility factor (${\mu}_{{\varphi}u}$) of over 10.0. With an axial load of 30 % of the axial load capacity, it is recommended that the yield strength of transverse reinforcement be held equal to or below 549 MPa.

• Asian-Australasian Journal of Animal Sciences
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• v.31 no.2
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• pp.287-292
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• 2018

Objective: The aim of present study was to assess the anti-oxidant potential of water-soluble peptides (WSPs) extract derived from buffalo and cow milk Cheddar cheeses at different stages of ripening. Methods: The antioxidant potential of WSPs extract was assessed through 2,2'-azinobis-3-ethylbenzothiazoline-6sulfonic acid (ABTS)-radical scavenging activity. In addition, impact of WSPs extract on cell viability and production of reactive oxygen species (ROS) in human colon adenocarcinoma Caco-2 (tert-butylhydroperoxide-induced) cell lines was also evaluated. Results: The ABTS-radical scavenging activity increased progressively with ripening period and dose-dependently in both cheeses. However, peptide extract from buffalo milk Cheddar cheese demonstrated relatively higher activity due to higher contents of water-soluble nitrogen. Intracellular ROS production in Caco-2 cells decreased significantly (p<0.05) till 150th day of cheese ripening and remained constant thereafter. Additionally, dose-dependent response of WSPs extract on antioxidant activity was noticed in the Caco-2 cell line. Conclusion: On the basis of current in vitro study, the Cheddar cheese WSPs extract can protect intestinal epithelium against oxidative stress due to their antioxidant activity.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.53 no.2
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• pp.114-122
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• 2004

This paper presents a novel single-stage active-clamp type high frequency resonant inverter. The proposed topology is integrated full-bridge boost rectifier as power factor corrector and active-clamp type high frequency resonant inverter into a single-stage. The input stage of the full-bridge boost rectifier works in discontinuous conduction mode(DCM) with constant duty cycle and variable switching frequency. So that a boost converter makes the line current follow naturally the sinusoidal line voltage waveform. By adding additional active-clamp circuit to conventional class-E high frequency resonant inverter, main switch of inverter part operates not only at Zero-Voltage-Switching mode but also reduces the switching voltage stress of main switch. Simulation results have demonstrated the feasibility of the proposed high frequency resonant inverter. Characteristics values based on characteristics estimation through circuit analysis is given as basis data in design procedure. Also, experimental results are presented to verify theoretical discussion. This proposed inverter will be able to be practically used as a power supply in the fields of induction heating applications, fluorescent lamp and DC-DC converter etc.

• Journal of Electrical Engineering and Technology
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• v.9 no.3
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• pp.957-963
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• 2014

Converter transformers play important roles in high-voltage direct current transmission systems. This paper presents experimental and analysis results of the combined electrical and thermal aging of oil-impregnated paper at pulsating DC voltages. Breakdown voltages and time-to-breakdown of oil-paper specimens were measured by using short-time and constant-stress tests. The breakdown characteristics of combined electrical and thermal aging on insulation system were discussed. According to the relationship between failure time and aging temperature, the two-parameter Weibull model was improved. On the basis of the competing risk algorithm and the improved Weibull model, the two factors failure model was calculated. And the influence of temperature in the insulation system has been analyzed. This model performs better than the two-parameter Weibull model when both time and temperature are considered as variables in estimating the lifetime of oil-paper insulation.

• Steel and Composite Structures
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• v.42 no.3
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• pp.375-388
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• 2022

In this work, limit elastic speed analysis of functionally graded porous rotating disks has been reported. The work proposes an effective approach for modeling the mechanical properties of a porous functionally graded rotating disk. Four different types of porosity models namely: uniform, symmetric, inner maximum, and outer maximum distribution are considered. The approach used is the variational principle, and the solution has been achieved using Galerkin's error minimization theory. The study aims to investigate the effect of grading indices, aspect ratio, porosity volume fraction, and porosity types on limit angular speed for uniform and variable disk geometries of constant mass. To validate the current study, finite element analysis has been used, and there is good agreement between the two methods. The study yielded a decrease in limit speed as grading indices and aspect ratio increase. The porosity volume fraction is found to be more significant than the aspect ratio effect. The research demonstrates a range of operable speeds for porous and non-porous disk profiles that can be used in industries as design data. The results show a significant increase in limit speed for an exponential disk when compared to other disk profiles, and thus, the study demonstrates a range of FG-based structures for applications in industries that will not only save material (lightweight structures) but also improve overall performance.

• Korean Journal of Veterinary Research
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• v.36 no.2
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• pp.305-312
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• 1996

Cell volume regulatory mechanisms are usually disclosed by exposure of cell to anisotonic media. If a cell is suddenly exposed to hypotonic media, it swells initially like an osmometer but within minutes regains its original cell volume. This behavior has been labelled as regulatory cell volume decrease(RVD). RVD is believed to result from the loss of permeable ions through the membrane. In this study, we examined hypotonically induced changes in the membrance currents involved in RVD by using whole cell voltage clamp technique in the unfertilized hamster egg. At -40mV of the holding potential, the stationary current was maintained in the hamster egg exposed to isotonic solution composed of, mainly, 115mM NaCl and 40mM mannitol. Hypotonic solution was prepared by removing mannitol. Therefore, the concentrations of $Na^+$ and $Cl^-$ in this hypotonic media were the same as those in the isotonic solution. Following 30 to 60 sec after applying the hypotonic media to the egg, the inward current was evoked. This inward current was eliminated by $100{\mu}M$ 4-acetamido-4'-isothiocyanostil-bene-2,2'-disulfonic acid(SITS), an anion channel blocker, leaving the small outward current component. Further addition of 2mM $Ba^{2+}$, a broad $K^+$ channel blocker, completely abolished the small outward current left even in the presence of SITS during hypotonic stress. These results suggest that $K^+$ and $Cl^-$ move out of cells, resulting in RVD. To test the involvement of $Na^+$ in RVD, 20mM Na-isethionate was substituted for mannitol in isotonic media(135mM $Na^+$) and Na-isethionate (20mM) was freed the hypotonic solution. Only $Cl^-$ concentration in both isotonic and hypotonic media was kept constant at 115mM, whereas concentration of $Na^+$ was lowered in hypotonic solution to 115mM from 135mM in isotonic solution. Hypotonic medium induced the outward current in the egg equilibrated isotonically. This current was reduced by $100{\mu}M$ SITS but was augmented by 2 mM $Ba^{2+}$. In terms of RVD, these results imply that $Cl^-$ efflux is coupled with $K^+$, maybe for electroneutrality during hypotonic stress and/or with $Na^+$ via unknown transport mechanism(s). From the overall results, the hypotonic stress facilitates the movement of $Cl^-$ and $K^+$ out of the hamster egg to regain cellular volume with electroneutrality. If there exist a difference in $[Na^+]_0$ between isotonic and hypotonic solution, another transport mechanism concerned with $Na^+$ may, at least partly, participate in regulatory volume decrease.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.7
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• pp.23-31
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• 2008

Experiment results are presented for gate oxide degradation under the constant voltage stress conditions using MOSFETs with 3-nm-thick gate oxides that are treated by deuterium gas. Two kinds of methods, annealing and implantation, are suggested for the effective deuterium incorporation. Annealing process was rather difficult to control the concentration of deuterium. Because the excess deuterium in gate oxide could be a precursor for the wear-out of gate oxide film, we found annealing process did not show improved characteristics in device reliability, compared to conventional process. However, deuterium implantation at the back-end process was effective method for the deuterated gate oxide. Device parameter variations as well as the gate leakage current depend on the deuterium concentration and are improved by low-energy deuterium implantation, compared to those of conventional process. Especially, we found that PMOSFET experienced the high voltage stress shows a giant isotope effect. This is likely because the reaction between "hot" hole and deuterium is involved in the generation of oxide trap.