• Journal of the Korean institute of surface engineering
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• v.48 no.3
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• pp.105-109
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• 2015

We studied emission characteristics of blue fluorescent multi-tandem OLEDs using $Al/MoO_x$ as charge generation layer(CGL). Threshold voltage for 2, 3, 4, and 5 units tandem OLEDs was 8, 11, 14 and 18 V, respectively. The threshold voltage in multi-tandem OLEDs was lower than multiple of 4 V for the single OLED. Maximum current efficiency and maximum quantum efficiency of single OLED were 7.6 cd/A and 5.5%. Maximum current efficiency for 2, 3, 4, and 5 units tandem OLEDs was 22.6, 31.4, 41.2, and 46.6 cd/A, respectively. Maximum quantum efficiency for 2, 3, 4, and 5 units tandem OLEDs was 11.8, 15.8, 21.8, and 25.6%, respectively. The maximum current efficiency and maximum quantum efficiency in multi-tandem OLEDs were higher than multiple of those for the single OLED. The intensity for 508 nm peak was changed and the peak wavelength was red shift by increase of tandem unit in electroluminescent emission spectra. These phenomena can be caused by micro-cavity effect with increasing of organic layer thickness.

• Journal of Korean Society of Water and Wastewater
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• v.24 no.4
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• pp.433-442
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• 2010

BER at different packing ratios of bio-ring media(BRM) was tested to investigate the effect of varying hydraulic retention time (HRT) and current density on the nitrate removal and current efficiency. In the preliminary batch mode experiment of BERs, current density was applied at 2.0 A/$m^2$, 4.0 A/$m^2$, 4.8 A/$m^2$, which correspond to the designation of reactor #1, #2, #3, respectively. The reactor #2 showed a highest nitrate removal rate of 162.0 mg $NO_3{^-}$-N/L/d, and the kinetics of nitrate removal rate was defined as the Zero order reaction. In the primary experiment of BERs, four BERs packed with BRM were operated in varying HRT and current, and the packing ratios of reactor #1, #2, #3 and #4 were 0%, 8%, 16%, 24%. respectively. This results of the experiments indicated that the nitrate removal rate and current efficiency were increased significantly cause of growing of autotrophic denitrification microorganisms on the surface of cathode and media by increasing of the current density and decreasing of HRT. However, The decreasing of nitrate removal rate and current efficiencies were observed in the condition of HRT of 5.25 hr and 4.8 A/$m^2$ of current density. With more increasing current density and decreasing of HRT, the hydrogen inhibition occurred at the surface of cathode. Moreover, nitrate removal rate by autotrophic denitrification microorganisms attached on the media surface was observed to be limited by no longer increasing dissolved hydrogen concentration of each reactor. In conclusion, the highest nitrate nitrogen removal and current efficiency could be achieved when the BER was operated at the conditions of 7 hr HRT, current density of 4.0 A/$m^2$, and 16% packing ratio. And it was found that the amount of nitrate removal by microorganisms attached on the surface of cathode and media (BRM) was 178.2 mg/L and 52.2 mg/L respectively. and the amount of nitrate removal per MLVSS was 0.435 g $NO_3{^-}$-N/g $MLVSS{\cdot}d$ and 0.336 $NO_3{^-}$-N/g $MLVSS{\cdot}d$.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.1
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• pp.36-42
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• 2005

This study examined the feasibility of producing sulfuric acid and ammonia water from ammonium sulfate solution using two-compartment electrodialysis with a bipolar membrane (EDBM). Electrodialysis experiments were carried out with 20 wt% ammonium sulfate at different current densities and sulfuric acid concentrations in a concentrate compartment. The current efficiency increased with the current density from 25 to $100\;mA/cm^2$. Nevertheless, the efficiency was relatively low compared with that of general desalting electrodialysis, owing to the diffusion of sulfuric acid from the concentrate compartment to the diluate. The diffusion rate through the anion exchange membrane increased with the sulfuric acid concentration in the concentrate compartment, which decreased the current efficiency. Conversely, the electrical resistance decreased with increasing current density owing to the Joulian heat generated during water dissociation in the transition region of the bipolar membrane under a high electric field. From the experimental results, we concluded that operating at a higher current density is effective from the perspective of current efficiency and electrical resistance when producing sulfuric acid and ammonia water from ammonium sulfate using a two-compartment EDBM process. Further studies on the effects of increasing the sulfuric acid concentration on current efficiency are required to apply the EDBM process practically.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.5
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• pp.588-593
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• 2014

Current crowding problem can worsen the internal quantum efficiency and the negative-voltage ESD of InGaN-based LEDs. In this paper, by using photon emission microscope and thermal emission microscope measurement, we confirmed that the electric field and the current of the InGaN-based LED sample are crowded in specific regions where the distance between p-type metal contact and n-type metal contact is shorter than other regions. To improve this crowding problem of electric field and current, modified metal contact geometry having uniform distance between the two contacts is proposed and verified by a numerical simulation. It is confirmed that the proposed structure shows better current spreading, resulting in higher internal quantum efficiency and reduced reverse leakage current.

• Proceedings of the KIEE Conference
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• 2006.04a
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• pp.288-290
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• 2006

An efficiency improving method for Uninterruptible Power Supply System(UPS) was developed by using OP-AMP based application circuits such as voltage detection device, current detection device and static switch control device. The efficiency improving algorithm was made by mixing the operating concepts of On-Line type UPS with the operating concepts of Off-Line type UPS. The UPS' inverter does not work if the UPS' output load current is not higher than the low load operating current which is about 0-30(%) of the UPS' output load capacity. The low load operating current is adjustable within the half of the UPS' output load capacity. If the UPS' output load current is rising over than the low load operating current, the UPS' inverter starts working and the inverter output power feeds to the loads of UPS. If UPS' input power breaks out while UPS' inverter does not operate because the load current is low, the inverter starts working within 4(ms) with excessive output voltage which is ${\pm}$8(%) of normal UPS' output voltage. Like these. UPS can continuously feeds power to it's load device and reduce power consumptions.

• Journal of the Korean institute of surface engineering
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• v.36 no.2
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• pp.155-160
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• 2003

The effect of the temperature, current density and deposit time on hard chromium deposition in trivalent chromium bath was investigated. Cathode current efficiency increased with increasing current density. Increasing bath temperature from $20^{\circ}C$ to $50^{\circ}C$, chromium deposits were produced in higher current density and the maximum current efficiency was increased. At the plating conditions of $40^{\circ}C$, $30A/dm\m^2$, the deposition thickness increased in proportion to increasing electrolysis time The rate is$ 90\mu\textrm{m}$/hrs. for 2 hours. Microhardness of chromium deposits increased with increasing bath temperature and decreasing current density, and it was constant with electrolysis time. All of bath conditions, microstructure of chromium deposits has nodular structure with some cracking pattern and nodule size increased with increasing deposit thickness.

• Journal of Korea Society of Waste Management
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• v.35 no.7
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• pp.653-659
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• 2018

In the industrial wastewater that occupies a large proportion of river pollution, the wastewater generated in textile, leather, and plating industries is hardly decomposable. Though dyeing wastewater has generally been treated using chemical and biological methods, its characteristics cause treatment efficiencies such as chemical oxygen demand (COD) and suspended solids (SS) to be reduced only in the activated sludge method. Currently, advanced oxidation technology for the treatment of dyeing wastewater is being developed worldwide. Electro-coagulation is highly adapted to industrial wastewater treatment because it has a high removal efficiency and a short processing time regardless of the biodegradable nature of the contaminant. In this study, the effects of the current density and the electrolyte condition on the COD removal efficiency in dyeing wastewater treatment by using electro-coagulation were tested with an aluminum anode and a stainless steel cathode. The results are as follows: (1) When the current density was adjusted to $20A/m^2$, $40A/m^2$, and $60A/m^2$ under the condition without electrolyte, the COD removal efficiency at 60 min was 62.3%, 72.3%, and 81.0%, respectively. (2) The removal efficiency with NaCl addition was 7.9% higher on average than that with non-addition at all current densities. (3) The removal efficiency with $Na_2SO_4$ addition was 4.7% higher on average than that with non-addition at all current densities.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.6
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• pp.539-545
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• 2012

Due to merits cost and efficiency, the transformer-less type photovoltaic (PV) inverters have been popularized in the solar market. However, the leakage current flowing through a parasitic capacitor between PV array and ground can cause adverse effect in the transformer-less PV system. In this paper, a bi-directional PV inverter with high efficiency and low noise is proposed for the PV system with an energy storage device. The proposed inverter is a transformer-less type and performs the bi-directional power control between dc sources and grid with high efficiency. In addition, the proposed inverter can suppress the leakage current and obtain low noise characteristic. Finally, 3-kW prototype was implemented to confirm validity of the proposed inverter.

• KIEE International Transactions on Electrophysics and Applications
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• v.2C no.5
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• pp.253-257
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• 2002

A new Current-Controlled Driving Method that can drive AC PDPs with low voltage and high luminous efficiency for the sustaining period is presented. In this driving method, the voltage source is connected to a storage capacitor and the stored voltage is delivered to the panel through LC resonance. Thus, this driving method can drive the panel with a voltage source as low as about half of the voltage necessary in the conventional driving methods. The discharge current flowing into the AC PDP is limited in this method. Thus, the power consumption for the discharge is reduced and the discharge input power to output luminance efficiency is improved. Experimental results using this driving method showed that we could drive an AC PDP with a voltage source as low as 146V and that high luminous efficiency of 1.33 1m／W can be achieved.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.351-352
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• 2008

A new high efficient red PhOLED using a host of $Bebq_2$ and double dopants of $(pq)_2$Ir(acac) and SEC-R411 have been fabricated and evaluated. The device doubly doped with $(pq)_2$Ir(acac) and SFC-R411 showed the current efficiency improvement of 22% under a luminance of 10000 cd/$m^2$ in comparision with the device singly doped with SFC-R411. The luminance, current efficiency and central wavelength of the doubly doped device were 9300 cd/$m^2$ at 7V, 11.1 cd/A under a luminance of 10000 cd/$m^2$ and 625 nm, respectively.