• Applied Chemistry for Engineering
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• v.8 no.3
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• pp.403-409
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• 1997

The equilibrium constants of five deoxyribonucleosides (dDyd, dUrd, dGuo, dThd, dAdo) were estimated by the plate theory and the moment method under isocratic conditions of the Reversed-Phase High Performance Liquid Chromatography (RP-HPLC). The mobile phase in this system was composed of water and organic modifiers(acetonitrile and methanol) The plate theory of linear adsorption isotherm was treated on the basis of continuous flow of eluent through the plates of the column. The moment method was utilized to find the equilibrium constant from the first absolute moment of experimental data. The equilibrium constants of five deoxyribonucleosides in the two methods were very close, and also the equilibrium constants calculated by capacity factor were similar to those by both the plate theory and the moment method. The equilibrium constant was expressed as a semi-log function of the quantity of organic modifier. Excellent agreements between the calculated elusion profile by the plate theory and the experimental data were observed.

• Journal of Energy Engineering
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• v.14 no.1
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• pp.37-45
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• 2005

The fuel cell system is one of very useful energy sources. The system has advantages as renew-able and environmental sources. To obtain AC electricity from fuel cells, inverters are necessary. A multilevel converter is used as an inverter for a high power fuel cell system. Through harmonic analysis, it is shown that the harmonic components and THD increase while fundamental component decreases as voltage sag increases. To solve the voltage sag problems, three different approaches are investigated in this paper; installation of a boost converter at the fuel cell output, control of pulse widths, and use of ultracapacitors. The proposed three approaches are analyzed and compared using simulation and experimental results.

• Transactions of the Korean hydrogen and new energy society
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• v.26 no.4
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• pp.324-330
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• 2015

The electrolyte flow rates of vanadium redox flow battery play very important role in terms of ion transfer to electrolyte, kinetics and pump efficiency in system. In this paper a vanadium redox flow battery single cell was tested to suggest the optimization criteria of electrolyte flow rates on the efficiencies. The compared electrolyte circulation flow rates in this experimental work were 15, 30 and 45 mL/min. The charge/discharge characteristics of the flow rate of 30 mL/min was the best out of all flow rates in terms of charging and discharging time. The current efficiencies, voltage efficiencies and energy efficiencies at the flow rate of 30 mL/min were the best. The IR losses obtained at thd current density of $40mA/cm^2$, at the flow rates of 15, 30 and 45 mL/min were 0.085 V, 0.042 V and 0.115 V, respectively. The charge efficiencies at the current density of $40mA/cm^2$ were 96.42%, 96.45% and 96.29% for the electrolyte flow rates of 15, 30 and 45 mL/min, respectively. The voltge efficiencies at the current density of $40mA/cm^2$ were 77.34%, 80.62% and 76.10% for the electrolyte flow rates of 15, 30 and 45 mL/min, respectively. Finally, the energy efficiencies at the current density of $40mA/cm^2$ were 74.57%, 77.76% and 73.27% for the electrolyte flow rates of 15, 30 and 45 mL/min, respectively. The optimum flow rates of electrolytes were 20 mL/min in most of operating variables of vanadium redox flow battery.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1964-1980
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• 2016

This paper presents a new simplified harmonics extraction algorithm based on the synchronous reference frame (SRF) for an indirect current controlled (ICC) three-level neutral point diode clamped (NPC) inverter-based shunt active power filter (SAPF). The shunt APF is widely accepted as one of the most effective current harmonics mitigation tools due to its superior adaptability in dynamic state conditions. In its controller, the SRF algorithm which is derived based on the direct-quadrature (DQ) theory has played a significant role as a harmonics extraction algorithm due to its simple implementation features. However, it suffers from significant delays due to its dependency on a numerical filter and unnecessary computation workloads. Moreover, the algorithm is mostly implemented for the direct current controlled (DCC) based SAPF which operates based on a non-sinusoidal reference current. This degrades the mitigation performances since the DCC based operation does not possess exact information on the actual source current which suffers from switching ripples problems. Therefore, three major improvements are introduced which include the development of a mathematical based fundamental component identifier to replace the numerical filter, the removal of redundant features, and the generation of a sinusoidal reference current. The proposed algorithm is developed and evaluated in MATLAB / Simulink. A laboratory prototype utilizing a TMS320F28335 digital signal processor (DSP) is also implemented to validate effectiveness of the proposed algorithm. Both simulation and experimental results are presented. They show significant improvements in terms of total harmonic distortion (THD) and dynamic response when compared to a conventional SRF algorithm.

• Journal of Power Electronics
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• v.18 no.3
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• pp.931-943
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• 2018

Wireless power transfer (WPT) technology has been the focus of a lot of research due to its safety and convenience. The Z-source inverter (ZSI) was introduced into WPT systems to realize improved system performance. The ZSI regulates the dc-rail voltage in WPT systems without front-end converters and makes the inverter bridge immune to shoot-through states. However, when the WPT system is combined with a ZSI, the system parameters must be configured to prevent the ZSI from entering an "accidental shoot-through" (AST) state. This state can increase the THD and decrease system power and efficiency. This paper presents a mathematical analysis for the characteristics of a WPT system and a ZSI while addressing the causes of the AST state. To deal with this issue, the impact of the system parameters on the output are analyzed under two control algorithms and the primary compensation capacitance range is derived in detail. To validate the analysis, both simulations and experiments are carried out and the obtained results are presented.

• Tribology and Lubricants
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• v.33 no.6
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• pp.288-295
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• 2017

In order to improve the efficiency and reliability of the machine, the friction should be minimized. The most widely used method to minimize friction is to maintain the fluid lubrication state. However, we can reduce friction only up to a certain limit because of viscosity. As a result of several recent studies, surface texturing has significantly reduced the friction in highly sliding machine elements, such as mechanical seals and thrust bearings. Thus far, theoretical studies have mainly focused on isothermal/iso-viscous conditions and have not taken into account the heat generation, caused by high viscous shear, and the temperature conditions on the bearing surface. In this study, we investigate the effect of dimple depth and film-temperature boundary conditions on the thermohydrodynamic (THD) lubrication of textured parallel slider bearings. We analyzed the continuity equation, the Navier-Stokes equation, the energy equation, and the temperature-viscosity and temperature-density relations using a computational fluid dynamics (CFD) code, FLUENT. We compare the temperature and pressure distributions at various dimple depths. The increase in oil temperature caused by viscous shear was higher in the dimple than in the bearing outlet because of the action of the strong vortex generated in the dimple. The lubrication characteristics significantly change with variations in the dimple depths and film-temperature boundary conditions. We can use the current results as basic data for optimum surface texturing; however, further studies are required for various temperature boundary conditions.

• 한국해양학회지
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• v.13 no.1
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• pp.1-8
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• 1978

A seismic reflection Survey was carried out in the offshere area between Geoje Island and Namhae Island, utilizing the echosounder with the frequency 28KHz and thd Uniboom with the filter band 800∼2000Hz. The results show the submarine topography, sedimentary layer structure and the depth distribution of the base rock. The water depth of the sea in the survey area is less than 80m; up to 40m contour line the sea bottom surface has a slight dip(about 1/1000), while in the zone deeper than 40m the bottom topography has a irregular relief. The thickness of the whole sedimentary deposit is about 20∼70m and divided into 3 layers: Upper layer(A layer) with horizontal laminae, intermediate layer(B layer) with cross-bedding and groove structure, and lower layer(C layer) not showing any sedimentary structure on the seismic reflection profile. The surface of the base rock is deeper gradually in the south-eastern part of the survey area and extends to 140m depth. The vertical sediments sequences, composed of B layer and A layer, show the type of transgressive sequences. It is interpreted that B layer was formed at one period when the sea level was lower 40∼60 than the present and ince then, following the rising of the sea level, A layer was deposited.

• Water for future
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• v.22 no.1
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• pp.81-90
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• 1989

A numerical simulation technique of three-dimensional finite difference model is developed to study the groundwater flow system in Dejima, an upland area which faces Kasumigaura Lake. For general perspectives of the groundwater flow system, a steady state three-dimensinal model is simulated. For the sedimentary mud formations which are found in the representative formation, three situations where the horizontal permeability is equal to 10 times and 100 times of the vertical one. The finite difference grid used in the simulation has 60$\times$50$\times$30=90,000 nodes. A converged solution with a tolerance of 0.001 meter of hydraulic head is set. Having determined the flow net by using a steady state three-dimensional model, the results for the three cases of hydraulic conductivity are compared with the results of the tracer methods (Bae and Kayane, 1987). With the aid of four representative vertical cross-sections, groundwater flow systems in the study area are assumed. The results of these are reasonally good comparable with the results of the basin yield and thd recharge-discharge distribution 8.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 1997.11a
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• pp.75-79
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• 1997

The present study was designed to investigate whether there is a consistint changes in the signals from the central and autonomic nervous systim due to olfactory stimulation. The olfactory stimuli were 0.6% orange and 2.5% valeric acid and the stimuli through the olfactory stimulator soth controlled consistint flow, controlled concentration, and saturated with vapour to prevent drying the nasal mucosa. A room air blunk served as the control stimulus, EEG was recorede from 4channels according to the international 10-20 systim. Additionally, ECG, EOG, heart rate, skin conductance and resputation were recorded comtinuously. The fast Fourier transform analysis of EEG waves was analysed with the power spectra. Averaged power spectra were computed for the following frequency bands ; delta(0-4.5Hz), theta (4.5-7Hz), alphal(7-9.5Hz), alpha2 (9.5-12.5Hz) and beta(12.5-30Hz). Withthe results of the subjective sensibility test for the ordor, the orange was related to pleasant and familiar and the valeric acid was realted to snpleasant and bothersome. There is the difference between orange and valeric acid in alphal at PG2-A2 channel. While the unpleasant stimuli seem to be increased in alphal, alpha2 and beta waves at all channels. Also, the heart rate, galvaric skin resistance seem to be decreased by pleasant stimuli and thd unpleasant stimuli shdwed the opposite. In respiration, respiration rate had been declinig tendency, and input/output ampoitued and duration showed an upward trend by olfactory stimulation with orange, while opposite by valeric acid. In conclusion, the consistent EEG changes and the autonomic responses suggests the possibilities of the subjective signal of human sensibility.

• Journal of Power Electronics
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• v.16 no.6
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• pp.1991-2004
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• 2016

An LC filter is required to reduce the output current ripple in the auxiliary resonant snubber inverter (ARSI) for high-performance applications. However, if the traditional control method is used in the ARSI with LC filter, then unnecessary current flows in the auxiliary circuit. In addressing this problem, a novel load-adaptive control that fully uses the filter inductor current ripple to realize the soft-switching of the main switches is proposed. Compared with the traditional control implemented in the ARSI with LC filter, the proposed control can reduce the required auxiliary current, contributing to higher efficiency and DC-link voltage utilization. In this study, the detailed circuit operation in the light load mode (LLM) and the heavy load mode (HLM) considering the inductor current ripple is described. The characteristics of the improved ARSI are expressed mathematically. A prototype with 200 kHz switching frequency, 80 V DC voltage, and 8 A maximum output current was developed to verify the effectiveness of the improved ARSI. The proposed ARSI was found to successfully operate in the LLM and HLM, achieving zero-voltage switching (ZVS) of the main switches and zero-current switching (ZCS) of the auxiliary switches from zero load to full load. The DC-link voltage utilization of the proposed control is 0.758, which is 0.022 higher than that of the traditional control. The peak efficiency is 91.75% at 8 A output current for the proposed control, higher than 89.73% for the traditional control. Meanwhile, the carrier harmonics is reduced from -44 dB to -66 dB through the addition of the LC filter.