• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.10
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• pp.590-597
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• 2018

Recently, the installation of PV systems has been increasing due to the worldwide interest in eco-friendly and renewable solar energy. On the other hand, the output power of PV systems is influenced strongly by the surrounding weather conditions. In addition, the entire operation efficiency of PV systems may be decreased considerably even if only some of the PV modules are in the shade. In other words, the existing control method at which strings with modules in series are connected to an inverter may be not operated in the case that the string voltage in partial shade is lower than the operating range of the grid connected inverter. To overcome these problems, this paper proposes an operation efficiency improvement device of a PV system using a Li-ion battery, which can compensate for the voltage of each string in the PV system when it is partially shaded. In addition, this paper presents the modeling of the operation efficiency improvement device, including PV strings, Li-ion battery and a 3-Phase grid inverter based on the PSIM S/W. From the simulation results, it was confirmed that the proposed control method can improve the operating efficiency of PV systems by compensating for the string voltage with partial shade.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.7
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• pp.20-28
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• 2020

According to the 3020 RE (renewable energy) policy of the Korean Government, distributed generators, including PV (photovoltaic) and WP (wind power) systems, have been installed and operated in distribution systems. On the other hand, if large-scale PV systems are interconnected in a distribution system, the spread of PV systems may be postponed due to a reduction of the hosting capacity in PV systems because of the over-voltage phenomena at the customer end by violating the allowable voltage limits. Under these circumstances, this paper proposes an evaluation algorithm of the hosting capacity of a PV system based on the LDC (line drop compensation) method of SVR (step voltage regulator) to improve the hosting capacity when large-scale PV systems are installed in a distribution system. Moreover, this paper presents a modeling of a complex distribution system, which is composed of a large-scale PV system and SVR with the LDC method using PSCAD/EMTDC. The simulation results confirmed that the proposed algorithm and modeling are useful and practical tools for improving the hosting capacity of a PV system because the customer voltages are maintained within the allowable voltage limits even if 6.5[MW] of the PV system is installed in a distribution system with the LDC method of SVR.

• The Journal of Korean Orthopaedic Ultrasound Society
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• v.1 no.1
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• pp.1-5
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• 2008

Purpose: We studied the diagnostic value of dynamic US in the extensor tendon dislocation at the metacarpophalangeal joint. Materials and Methods: From January 2007 to October, we studied 6 cases that had been diagnosed and followed over 5 months (2-10) in average. US examination using a 10-MHz linear transducer were performed in three cases. The causes of dislocations were traumatic in 5 cases and congenital in one case. Results: In only 3 cases which could not be diagnosed clinically, we performed US. In dynamic US, all three cases showed the extensor tendon dislocation evidently. Operative findings were sagittal band rupture in 4 cases, capsular loosening in one case and sagittal band thinning in one case. Sagittal band repair was performed in 4 cases and capsular augmentation in one case. In case of congenital dislocation showing 4 digital extensor tendon dislocations in right hand, we operated only the second extensor by sagittal band repair with augmentation by looping. At last follow-up, no case showed recurrence or limitation of motion. Conclusion: In case of extensor tendon dislocation without apparent clinical finding, US with dynamic study has so great value that it can detect the dislocation in real time, which is superior to MRI.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.11
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• pp.663-669
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• 2016

A terahertz asymmetric split-loop resonator (ASLR) was analyzed for use in high-sensitivity sensing applications. Its structural asymmetricity induces an asymmetric Fano resonance which has a high quality factor compared to the symmetric eigen-resonance. The variations of the resonant frequency, transmission coefficient, and quality factor of the ASLR in the eigen and Fano resonances are analyzed as a function of its structural asymmetricity. Also, the surface current densities on the ASLR in both resonances are calculated to analyze the main cause of the variations of its transmission characteristics. The surface current of the ASLR in the eigen resonance shows a dipole resonance, which increases the radiation loss and reduces the quality factor. On the other hand, the surface current of the ASLR in the Fano resonance shows a trapped or quadrupole mode which has a low radiation loss. Therefore, the ASLR operated in the Fano resonance has a high quality factor. Terahertz, high-performance filters and high sensitivity sensors can be developed based on our analysis results of the ASLR having a high quality factor. These high-performance devices based on terahertz metamaterials could increase the adoption of terahertz industrial applications.

• Journal of Korean Society of Water and Wastewater
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• v.31 no.6
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• pp.501-510
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• 2017

In this study, it is estimated that ceramic membrane process which can operate stably in harsh conditions replacing existing organic membrane connected with coagulation, sedimentation etc.. Jar-test was conducted by using artificial raw water containing kaolin and humic acid. It was observed that coagulant (A-PAC, 10.6%) 4mg/l is the optimal dose. As a results of evaluation of membrane single filtration process (A), coagulation-membrane filtration process (B) and coagulation-sedimentation-membrane filtration process (C), TMP variation is stable regardless of in Flux $2m^3/m^2{\cdot}day$. But in Flux $5m^3/m^2{\cdot}day$, it show change of 1-89.3 kpa by process. TMP of process (B) and (C) is increased 11.8, 0.6 kpa each. But, the (A) showed the greatest change of TMP. When evaluate (A) and (C) in Flux $10m^3/m^2{\cdot}day$, TMP of (A) stopped operation being exceeded 120 kpa in 20 minutes. On the other hand, TMP of (C) is increased only 3 kpa in 120 minutes. Through this, membrane filtration process can be operated stably by using the linkage between the pretreatment process and the ceramic membrane filtration process. Turbidity of treated water remained under 0.1 NTU regardless of flux condition and DOC and $UV_{254}$ showed a removal rate of 65-85%, 95% more each at process connected with pretreatment. Physical cleaning was carried out using water and air of 500kpa to show the recovery of pollutants formed on membrane surface by filtration. In (A) process, TMP has increased rapidly and decreased the recovery by physical cleaning as the flux rises. This means that contamination on membrane surface is irreversible fouling difficult to recover by using physical cleaning. Process (B) and (C) are observed high recovery rate of 60% more in high flux and especially recovery rate of process (B) is the highest at 95.8%. This can be judged that the coagulation flocs in the raw water formed cake layer with irreversible fouling and are favorable to physical cleaning. As a result of estimation, observe that ceramic membrane filtration connected with pretreatment improves efficiency of filtration and recovery rate of physical cleaning. And ceramic membrane which is possible to operate in the higher flux than organic membrane can be reduce the area of water purification facilities and secure a stable quantity of water by connecting the ceramic membrane with pretreatment process.

• Journal of the Korean earth science society
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• v.36 no.6
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• pp.501-511
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• 2015

This study suggests a method of alleviating global warming by the increase of the Earth surface albedo through Artificial Sea ice Increasing (ASI) over the Available Freezing Areas (AFA). The method is developed based on the fact that the large sea surface area in or near the Arctic and the Antarctic has no ice even though both water and air temperatures are below zero and the artificial sea ice generation is thus available. The mean energy of $0.85Wm^{-2}$, which was suspected of adding to the earth by the global warming effect was calculated to offset at once when the sea ice area about $4.09{\times}10^6km^2$ was additionally increased. In addition, three techniques for producing ice plates on the sea surface (using ships, installation apparatus, and floating matter such as Green Cell Foam) for ASI were proposed. According to the result of simple analysis using the energy balance model, when ASI was maximally operated only for 3 months (September, October, and November) over AFA, it is expected that the annual mean temperature of earth surface would be decreased about $0.11^{\circ}C$ in the following year. On the other hand, in case of generating the artificial sea ice in all four seasons, a risk of triggering snowball earth was detected.

• Culinary science and hospitality research
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• v.20 no.6
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• pp.175-189
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• 2014

This study was intended to provide fundamental data concerning franchising companies' characteristics and performance in foodservice business by employing financial data from the firms' IDS(Information Disclosure Statements). Multiple regression analysis method was used to identify any correlations among franchising size, marketing competency, operational characteristics, and performance according to technique based upon 169 IDS data as of 2013. In terms of franchisor size and performance, the number of company-operated stores had statistically significant corelation with sales, net income, the total number of stores, and the number of franchisees. With respect to marketing competency and performance, advertising expenses showed statistically significant correlation with sales, the total number of stores, promotion expenses with sales, net income, and the total number of stores. On the other hand, there was no statistically significant correlation with current year's net income. At last, present study found significant correlations among business years, sales, current year's net income, and the total number of stores by regarding operational characteristics and performance, but there was no significant correlation between brands and performance. This study is cross-sectional study which is a limitation to be overcome in further studies. In addition, it is required to review the possibility for franchise management style to contribute to expanding the Korean traditional foods.

• Journal of the Korea Society of Computer and Information
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• v.19 no.12
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• pp.143-152
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• 2014

This paper introduces Database security to prevent the rapidly increasing issue of private information leakage. The Database security examined in the paper separates into DB access control area and DB encryption area which further leads the paper to analyze the factors of the two areas and suggest necessary elements for creating stable Database security. In addition, the paper examines previous DB security programs by areas and analyzes pros and cons from the tested result. The experiment indicated that while DB access control presents less degradation and reduced the need to modify the existing DBMS since the access control operates at the end point of the network, DB encryption presented strength in protecting the data from unauthorized access. On the other hand, DB access control is less useful in preventing the attack in advance which leaves the log to enable tracking afterward while DB encryption can only be operated by limited types of Database and causes degradation due to system load and shows higher percentage of failure when creating the system. This paper examines characteristics of Database security areas in order to be used as a reference for institutions or companies seeking stable Database security.

• Korean Journal of Ecology and Environment
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• v.41 no.3
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• pp.367-373
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• 2008

A freshwater bivalve (Unio douglasiae) was examined to assess the filtering rate (FR) on the cyanobacterial assemblage in a hypertrophic lake. Animal U. douglasiae used in the present study was collected using a hand-operated dredge from the North Han River (Gapyeong, Korea). The FR was measured at different feeding conditions such as feeding interval (1, 4, 7, and 24 h), mussel size (4.2$\sim$8.1 cm, n=23), prey concentration (506.7, 409.8, 327.5, 199.7 and 88.6 ${\mu}g\;L^{-1}$), and mussel density (0.5, 1.0 and 1.5 indiv. $L^{-1}$). On the applied feeding interval, the maximum FR (0.21 L $g^{-1}h^{-1}$) and minimum feces production (FP, 0.12 mg $g^{-1}h^{-1}$) were observed at 1 and 24 hr, respectively. Both weight-based FR and FP were not correlated with the mussel size, and the values lied in a limited range with some degree of variation. Likewise, no significant relations between FR and FP were observed in the mussel size. The FR values were negatively correlated with food concentration, but positively with FP. For the food concentrations, the maximum FR (0.41 L $g^{-1}h^{-1}$) and FP (0.16 mg $g^{-1}h^{-1}$) were 88.6 ${\mu}gL^{-1}$ and 327.5 ${\mu}gL^{-1}$, respectively. These results indicate that U. douglasiae collected from the North Han River, although the filtering rate were slightly less than Keum River mussel, may be applied as a strategic bio-filter to mitigate cyanobacterial bloom in eutrophic lake.

• The Korean Journal of Food And Nutrition
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• v.19 no.2
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• pp.193-200
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• 2006

The objective of this study was to identify factors affecting the job satisfaction of cooks employed in school foodservice and to propose a plan to improve school foodservice quality. Therefore, in this paper, we examined the job satisfaction of 119 elementary school foodservice employees in the Northern Gyeonggi Province using a 5-point scale method. The results were analyzed by the SPSS Package Program(Ver 12.0) to determine percentages and frequency. Among the employees, 99.2% were women, and 75.9% were employed by contract. All of the subjects worked in elementary schools with self operated foodservice system and 57.6% of them served food in the classroom. The total number of diners served by these foodservice programs was $1,391.6{\pm}307.6$ an average of $135.0{\pm}18.2$ diners per cook. Among the foodservice employees, 82.2% had completed high school academic courses, and 98.4% had never changed jobs. Their overall degree of job satisfaction degree was relatively high at $3.05{\pm}0.85$, but the wage and welfare system($2.45{\pm}0.86$), and the merit rating methods($2.25{\pm}0.87$) ranked among the lowest in the job satisfaction survey. On the other hand, the relationships between the managers and the coworkers marked relatively higher at $3.02{\pm}1.03$, compared with other aspects of job satisfaction. As for the work environment, the scaled score was $2.38{\pm}0.85$. Finally the ranking of achieving job improvement through education($3.28{\pm}0.93$), and the effectiveness of education($3.58{\pm}0.78$) showed us the importance and necessity of education.