• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.30 no.1
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• pp.55-65
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• 2016

This paper proposed a new control method which is capable of controlling circulating current considering current capacity of switching device. In the unbalanced voltage conditions, active power and reactive power have double line frequency. Thus, in order to provide active power without ripple, it is necessary to inject the negative sequence current components. However, when the negative current components is injected, it increases the total current flowing in the Arm, and in the Sub-module(SM) the current more than rated is impressed, which leads to destroy the system. Also, in impressing the circulating current reference of each arm, conventional control method impressed applicable $i_{dck}/3$ in the case of balanced voltage conditions. In the case of unbalanced conditions, as arm circulating current of three phase show difference due to the power impressed to each arm, reference of each arm is not identical. In this study, in the case of unbalanced voltage, within permitted current, the control method to decrease the ripple of active power is proposed, through circulating current control and current limitations. This control method has the advantage that calculates the maximum active power possible to generate capacity and impressed the current reference for that much. Also, in impressing circulating current reference, a new control method proposes to impress the reference from calculating active power of each phase. The proposed control method is verified through the simulation results, using the PSCAD/EMTDC.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.4
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• pp.653-660
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• 2021

Renewable energy resources are rapidly becoming an integral part of electricity generation portfolios around the world due to declining costs, government subsidies, and corporate sustainability goal. Interacting wind, solar, and load forecast errors can create significant unpredictable impacts on the distribution system, feeder congestion, voltage standard and reactive power stability margins. These impacts will be increasing with the increasing penetration levels of variable renewable generation in the power systems. There is a limit to the maximum amount of renewable energy sources that can be connected in a distribution feeder by the connection rule of transmission & distribution facility in Korea. This study represents the decision plans of hosting capacity for distribution feeders without the need for significant upgrades to the existing transmission infrastructure. Especially, the paper suggests and discusses the hosting capacity standard of feeder cables and minimum load calculation of distribution feeders.

• Molecules and Cells
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• v.45 no.12
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• pp.935-949
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• 2022

Liver cancer has a high prevalence, with majority of the cases presenting as hepatocellular carcinoma (HCC). The prognosis of metastatic HCC has hardly improved over the past decade, highlighting the necessity for liver cancer research. Studies have reported the ability of the KiSS1 gene to inhibit the growth or metastasis of liver cancer, but contradictory research results are also emerging. We, therefore, sought to investigate the effects of KiSS1 on growth and migration in human HCC cells. HepG2 human HCC cells were infected with lentivirus particles containing KiSS1. The overexpression of KiSS1 resulted in an increased proliferation rate of HCC cells. Quantitative polymerase chain reaction and immunoblotting revealed increased Akt activity, and downregulation of the G1/S phase cell cycle inhibitors. A significant increase in tumor spheroid formation with upregulation of β-catenin and CD133 was also observed. KiSS1 overexpression promoted the migratory, invasive ability, and metastatic capacity of the hepatocarcinoma cell line, and these effects were associated with changes in the expressions of epithelial mesenchymal transition (EMT)- related genes such as E-cadherin, N-cadherin, and slug. KiSS1 overexpression also resulted in dramatically increased tumor growth in the xenograft mouse model, and upregulation of proliferating cell nuclear antigen (PCNA) and Ki-67 in the HCC tumors. Furthermore, KiSS1 increased the angiogenic capacity by upregulation of the vascular endothelial growth factor A (VEGF-A) and CD31. Based on these observations, we infer that KiSS1 not only induces HCC proliferation, but also increases the metastatic potential by increasing the migratory ability and angiogenic capacity.

• Transactions of the Korean hydrogen and new energy society
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• v.34 no.4
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• pp.350-357
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• 2023

In this study, the experimental investigation and theoretical analysis were conducted to verify the cooling capacity of the cryocooler used for pre-cooling of hydrogen gas. The effect of the flow rate on a copper pipe attached to the bottom of the cryocooler, which has a coil shape in a hydrogen line, was investigated. Temperature sensors were strategically placed at various positions on the cryocooler to analyze the temperature variations with respect to the flow rate. In this study, the thermal properties of hydrogen for the pressure and temperature were utilized using REFPROP to analyze the cooling capacity of the cryocooler. Based on the experimental results derived from this study, the cooling capacity of the cryocooler for pre-cooling hydrogen gas was considered by calculating the cooling temperature according to the flow rate through theoretical analysis.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.8
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• pp.1144-1151
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• 2009

Refrigeration systems can be incorporated with non-adiabatic capillary tubes to improve their efficiency. The non-adiabatic capillary tube is constructed by joining the capillary tube with suction pipe to allow heat transfer between them, which is called capillary tube-suction line heat exchanger(SLHX). There are various joining methods and they may influence the characteristics of the refrigeration cycle. The present work aims to analyze the effect of widely-used two joining methods on the refrigeration cycle. The results show that soldered SLHX has much less thermal resistance than tapered SLHX but slightly outperforms in terms of coefficient of performance(COP) and cooling capacity. The soldered SLHX increased COP and cooling capacity of a refrigerator by 5.09% and 14.77% while the tapered SLHX did by 5.05% and 14.75%, respectively.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.427-432
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• 2005

This study treats the advantage of in situ line source method measuring the heat transfer capacity of a borehole, using mobile equipment, to determine the thermal properties of the entire borehole system such as thermal conductivity, diffusiveity. volumetric heat capacity, and borehole thermal resistance. The results from the response test include not only the thermal properties of the ground and the borehole, but also conditions that are difficult to estimate, e,g. natural convection in the boreholes, asymmetry in the construction, etc. In this study, 1) theoretical in situ methods for assessing working fluid temperature variation in V-type PE tube have been introduced, and 2) TRTE(Thermal Response Test Equipment) has been built based on these kinds of theoretical in situ methods. Basically TRTE consists of a pump, a heater and temperature sensors for measuring the inlet and outlet temperatures of the borehole. In order to make equipment easily transportable it is set up on a small trailer. Since the response test takes above two days to execute, the test was fully automatic in recording measured data using Labview DAS(Data acquisition system) program. The test was demonstrated in the course of intensive research in this field through the one site at Ulsan city in Korea. From this kind of thermal properties test of borehole systems in situ, the design of the borehole system can be optimized regarding the total geological, hydro-geological and technical conditions at the location.

• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.95-104
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• 2016

Flexural strength of concrete ground slab reinforced with steel fiber is evaluated using the equivalent flexural strength ratio of steel fiber reinforced concrete based on the yield line theory. Recently, the European standard specifies that the tensile performance of the steel fiber reinforced concrete be evaluated directly from the residual flexural strength after the cracking of concrete. Thus, in the study, an experiment was carried out to evaluate the conventional equivalent flexural strength ratio and the residual flexural strength of the steel fiber reinforced concrete. Then the design flexural strength was investigated according to the location of a point load, based on the ratio of the radius of contact area of the load to the radius of relative stiffness. Design flexural capacity obtained from ACI 360R-10 was smaller than that from TR 34 (2003 & 2013). In addition, TR 34 (2013), which evaluates the design flexural capacity based on the residual flexural strength, showed slightly smaller value than TR 34 (2003).

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.18
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• pp.7611-7615
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• 2014

Aims: To prepare 5-fluorouracil (5-Fu) nanoparticles with higher encapsulation efficiency and drug loading, and then investigate interaction with the SGC-7901 gastric cancer cell line. Materials and Methods: Prescription was optimized by orthogonal experiments, the encapsulation efficiency and loading capacity were tested by high-performance liquid chromatography, and inhibition of proliferation by 5-Fu nanoparticles and 5-Fu given to cells for 24, 48 and 72 hours was investigated by methyl thiazolyl tetrazolium assay (MTT). In addition, 5-Fu nanoparticles were labeled by fluorescein isothiocyanate (FITC), and absorption into cells was tested by flow cytometry. Results: The optimal conditions for preparation were concentrations of 5-Fu of 5mg/ml, of $CaCl_2$ of 60 mg/ml and of chitosan of 2 mg/ml. With a stirring speed of 1200rpm, encapsulation efficiency of 5-Fu nanoparticles was $55.4{\pm}1.10%$ and loading capacity was $4.22{\pm}0.14%$; gastric cancer cells were significantly inhibited by 5-Fu nanoparticles in a time and concentration dependent manner, and compared to 5-Fu with slower drug release, in a certain concentration range, inhibition with 5-Fu nanoparticles was stronger. 5-Fu nanoparticles were absorbed by the cells in line with the concentration. Conclusions: 5-Fu nanoparticles can inhibit growth of gastric cancer cells in vitro to a greater extent than with 5-Fu with good adsorption characteristics, supporting feasibility as a carrier.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.2
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• pp.131-139
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• 1992

Based on the equi-flooding line theory, this study suggests method of evaluating safety of detent tion reservoirs with drainage pumping facilities in Seoul metropolitan area, and derives equi-flooding lines according to destruction frequency for each detention reservoir. In most part of detention reservoirs, its flood prevention are so much dependent upon drainage capacity that inland flooding prevention can be serious problems in case of its malfunction. In this study, the detention reservoirs which are below 5 year destruction frequency estimated as 29.3%, and below 10 year as 39.6% of the total. To improve reservoir safety, the detention reservoir capacities (including drainage and pumping capacity) should be upgraded above 20 year in its destruction frequency, and its reinforcement capacities are calculated.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.10
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• pp.1916-1922
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• 2009

Introducing distributed generators(DGs) to utility distribution system can cause malfunction of relay on the grid when ground faults or severe load unbalances are occurred on the system. Because DGs interconnected to the grid can contribute fault currents and make bidirectional power flows on the system, fault currents from DGs can cause an interference of relay operation. A directional over current relay(DOCR) can determine the direction of power flow whether a fault occurs at the source side or load side through detecting the phases of voltage and current simultaneously. However, it is identified in this paper that the contributed fault current(Ifdg) from the ground source when was occurred to contribute single-line-to-ground(SLG) fault current, has various phases according to the distances from the ground source. It means that the directionality of Ifdg may not be determined by simply detecting the phases of voltage and current in some fault conditions. The magnitude of Ifdg can be estimated approximately as high as 3 times of a phase current and its maximum is up to 2,000 A depending on the capacity of generation facilities. In order to prevent malfunction of relay and damage of DG facilities from the contribution of ground fault currents, Ifdg should be limited within a proper range. Installation of neutral ground reactor (NGR) at a primary neutral of interconnection transformer was suggested in the paper. Capacity of the proposed NGR can be adjusted easily by controlling taps of the NGR. An algorithm for unidirectional relay was also proposed to prevent the malfunction of relay due to the fault current, Ifdg. By the algorithm, it is possible to determine the directionality of fault from measuring only the magnitude of fault current. It also implies that the directionality of fault can be detected by unidirectional relay without replacement of relay with the bidirectional relay.