• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.73-73
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• 2011

We will report a few methods to improve the efficiency and stability in small molecule based organic solar cells, including the formation of bulk heterojunctions (BHJs) through alternative thermal deposition (ATD), the use of a micro-cavity structure and interface modifications. By ATD which is a simple modification of conventional thermal evaporation, the thicknesses of alternative donor and acceptor layers were precisely controlled down to 0.1 nm, which is critical to form BHJs. The formation of a BHJ in copper(II) phthalocyanine (CuPc) and fullerene (C60) systems was confirmed by AFM, GISAXS and absorption measurements. From analysis of the data, we found that the CuPc|C60 films fabricated by ATD were composed of the nanometer sized disk shaped CuPc nano grains and aggregated C60, which explains the phase separation of CuPc and C60. On the other hand, the co-deposited CuPc:C60 films did not show the existence of separated CuPc nano grains in the CuPc:C60 matrix. The OPV cells fabricated using the ATD method showed significantly enhanced power conversion efficiency compared to the co-deposited OPV cells under a same composition [1]. We will also present by numerical simulation that adoption of microcavity structure in the planar heterojunction can improve the short circuit current in single and tandem OSCs [2]. Interface modifications also allowed us to achieve high efficiency and high stability OSCs.

• Journal of The Korean Astronomical Society
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• v.37 no.4
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• pp.151-157
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• 2004

It is investigated quantitative relations between the magnetic storm magnitude and the solar wind parameters such as the Interplanetary Magnetic Field (hereinafter, IMF) magnitude (B), the southward component of IMF (Bz), and the dynamic pressure during the main phase of the magnetic storm with focus on the role of the interplanetary shock (hereinafter, IPS) in order to build the space weather fore-casting model in the future capable to predict the occurrence of the magnetic storm and its magnitude quantitatively. Total 113 moderate and intense magnetic storms and 189 forward IPSs are selected for four years from 1998 to 2001. The results agree with the general consensus that solar wind parameter, especially, Bz component in the shocked gas region plays the most important role in generating storms (Tsurutani and Gonzales, 1997). However, we found that the correlations between the solar wind parameters and the magnetic storm magnitude are higher in case the storm happens after the IPS passing than in case the storm occurs without any IPS influence. The correlation coefficients of B and $BZ_(min)$ are specially over 0.8 while the magnetic storms are driven by IPSs. Even though recently a Dst prediction model based on the real time solar wind data (Temerin and Li, 2002) is made, our correlation test results would be supplementary in estimating the prediction error of such kind of model and in improving the model by using the different fitting parameters in cases associated with IPS or not associated with IPS rather than single fitting parameter in the current model.

• Journal of Power Electronics
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• v.16 no.6
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• pp.2119-2128
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• 2016

Due to detection and control errors, some high-frequency harmonics with voltage-source characteristics cause circulating currents in modular inverters. Moreover, the circulating currents are usually affected by the output filters (OF) of each module due to their filter and resonance properties. The interaction among the circulating currents in the modules increase the power loss and reduce system stability and control precision. Therefore, this paper reports the results of a study on the SPWM high-frequency harmonics circulating currents for a double-module VSI. In the paper, an analysis of the circulating-current circuits is briefly described. Next, a mathematic model of the single-module output voltage based on the carrier frequency of SPWM is built. On this basis, through mathematic modeling of high-frequency harmonic circulating currents, the formation mechanism and distribution characteristics of circular currents and their influences are studied in detail. Finally, the influences of the OF on the circulating currents are studied by mainly taking an LC-type filter as an example. A theoretical analysis and experimental results demonstrate some important characteristics. First, the carrier phase shifting of the SPWM for each module is the major cause of the SPWM harmonic circulating currents, and the circulating currents are in an odd distribution around n-times the carrier frequency $n{\omega}_s$, where n = 1, 2, 3, ${\ldots}$. Second, the harmonic circular currents do not flow into the parallel system. Third, the OF can effectively suppress the non-circulating part of the high-frequency harmonic currents but is ineffective for the circulation part, and actually reduces system stability.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.1
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• pp.56-63
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• 2008

This paper describes a 12 bit 1GS/s current mode segmented DAC for WCDMA communication. The proposed circuit in this paper employes segmented structure which consists of 4bit binary weighted structure in the LSB and 4bit thermometer decoder structure in the mSB and MSB. The proposed DAC uses delay time compensation circuits in order to suppress performance decline by delay time in segmented structure. The delay time compensation circuit comprises of phase frequency detector, charge pump, and control circuits, so that suppress delay time by binary weighted structure and thermometer decoder structure. The proposed DAC uses CMOS $0.18{\mu}m$ 1-poly 6-metal n-well process, and measured INL/DNL are below ${\pm}0.93LSB/{\pm}0.62LSB$. SFDR is approximately 60dB and SNDR is 51dB at 1MHz input frequency. Single DAC's power consumption is 46.2mW.

• Korean Journal of Social Welfare
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• v.38
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• pp.33-67
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• 1999

This study is the second phase of the author's larger attempt to investigate the factors affecting housewives' caregiving behavior to their elderly parents-in-law. Specifically, it revises and expands the previous model (1998) and develops a new one by rectifying the three major problems inherent in the previous study: (1) misspecification error; (2) non-equivalent comparison of results between the father-in-law model and mother-in-law model that stems from the inclusion of heterogeneous group of caregivers; (3) measurement problems for the two endogenous variables of eldercare attitude and behavior. To do this, the current study proposes a more comprehensive model by additionally incorporating other salient exogenous variables, renders the comparison of results between the father-in-law and mother-in-law models equivalent by including only homogeneous group of caregivers (i. e., only those housewives whose parents-in-law are both alive), and introduces standardized measurement scales for the endogenous variables. Estimation of the model in terms of maximum likelihood procedures in LISREL8 attests to a better overall performance over the previous model when judged from several criteria such as coefficient of determination, model fit statistics, proportion of significant causal paths, and measurement properties of reliability and validity for the variables. Interpretation of the findings suggests several salient theoretical implications that concern such crucial issues as the inconsistency between eldercare attitude and behavior, patterns of association among the subdimensions of eldercare, and the difference in the antecedents explaining attitude as opposed to behavior of eldercare. In particular, the finding that indicates almost no differences in the determinants between the father-in-law and mother-in-law models suggests a strong case to argue that caregiving behavior to fathers-in-law and mothers-in-law, respectively, is likely to be a uniform phenomenon sharing virtual1y the same antecedents, and that a unified single model is sufficient to account for caregiving behavior to both parties.

• Journal of the Korean Magnetics Society
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• v.18 no.6
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• pp.227-231
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• 2008

Magnetic and structural properties of CoFeZr alloy films as a function of Zr concentration and magnetoresistive properties of spin valves incorporated with amorphous CoFeZr alloy films have been studied. Magnetization and coercivity of CoFeZr alloy films decreased as the Zr content increased. A single amorphous CoFeZr phase was formed when the Zr content is about above 18 at%. Magnetoresistance ratio and exchange coupling field of spin valves with amorphous CoFeZr were reduced slightly as compared with spin valves with CoFe because the resistance of amophous CoFeZr is higher than that of crystalline CoFe. However, the ${\Delta}{\rho}$ of spin valves with amorphous CoFeZr was improved due to reduction of current shunting.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.171-174
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• 2006

A large number of service providers in countries all over the world have established GNSS reference station networks in the last years and are using network software today to provide a correction stream to the user as a routine service. In current GNSS network processing, all the geometric related information such as ionospheric free carrier phase ambiguities from all stations and satellites, tropospheric effects, orbit errors, receiver and satellite clock errors are estimated in one centralized Kalman filter. Although this approach provides an optimal solution to the estimation problem, however, the processing time increases cubically with the number of reference stations in the network. Until now one single Personal Computer with Pentium 3.06 GHz CPU can only process data from a network consisting of no more than 50 stations in real time. In order to process data for larger networks in real time and to lower the computational load, a federated filter approach can be considered. The main benefit of this approach is that each local filter runs with reduced number of states and the computation time for the whole system increases only linearly with the number of local sensors, thus significantly reduces the computational load compared to the centralized filter approach. This paper presents the technical aspect and performance analysis of the federated filter approach. Test results show that for a network of 100 reference stations, with the centralized approach, the network processing including ionospheric modeling and network ambiguity fixing needs approximately 60 hours to process 24 hours network data in a 3.06 GHz computer, which means it is impossible to run this network in real time. With the federated filter approach, only less than 1 hour is needed, 66 times faster than the centralized filter approach. The availability and reliability of network processing remain at the same high level.

• The Transactions of the Korea Information Processing Society
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• v.4 no.10
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• pp.2485-2492
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• 1997

Nowadays the traffic conditions have been getting worse due to continuous increase in the number of vehicles. So it has become more important to manage traffic signal lights efficiently. Recently fuzzy logic is introduced to control the cycle time of traffic lights adaptively. Conventional fuzzy logic controller adjusts the extension time of current green phase by using the fuzzy input variables such as the number of entering vehicles at the green light and the number of waiting vehicle during the red light. However this scheme is inadequate for an intersection with variable traffic densities. In this paper, a new FLC with asymmetric membership functions that reflects more exactly traffic flows than other FLCs with symmetric ones regardless of few control rules is propsed. The effectiveness of the proposed method was shown through simulation of a single intersection. The experimental results yielded the superior performance of the proposed FLC in terms of the average delay time, the number of passed vehicles, and the degree of saturation.

• Korean Journal of Construction Engineering and Management
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• v.20 no.6
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• pp.11-22
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• 2019

Current construction project processes pose difficulties for construction management as inefficient communication between project participants seldom accurately reflects the needs of the owner. To solve this problem, lean construction-based Integrated Project Delivery (IPD), which facilitates cooperation and builds trust through the formation of horizontal relationships among participants, is becoming increasingly popular. However, although lean construction-based IPD improves productivity in the construction industry, few studies have focused specifically on developing effective methods that maximize the benefits gained from lean construction-based IPD. This study therefore analyzed success factors for lean construction-based IPD projects by analyzing prior studies to identify factors that support IPD success. Application methods were analyzed and an example of how they are actually used in the field was examined through an in-depth single case analysis. The findings of this research can be applied to support lean construction-based IPD projects in Korea, improving their efficiency and boosting owner satisfaction.

• Journal of Powder Materials
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• v.26 no.1
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• pp.34-39
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• 2019

Current synthesis processes for titanium dioxide ($TiO_2$) nanoparticles require expensive precursors or templates as well as complex steps and long reaction times. In addition, these processes produce highly agglomerated nanoparticles. In this study, we demonstrate a simple and continuous approach to synthesize $TiO_2$ nanoparticles by a salt-assisted ultrasonic spray pyrolysis method. We also investigate the effect of salt content in a precursor solution on the morphology and size of synthesized products. The synthesized $TiO_2$ nanoparticles are systematically characterized by X-ray diffraction, transmission electron micrograph, and UV-Vis spectroscopy. These nanoparticles appear to have a single anatase phase and a uniform particle-size distribution with an average particle size of approximately 10 nm. By extrapolating the plots of the transformed Kubelka-Munk function versus the absorbed light energy, we determine that the energy band gap of the synthesized $TiO_2$ nanoparticles is 3.25 eV.