• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.10 s.181
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• pp.2487-2495
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• 2000

The acoustic characteristics of expansion chamber will be changed with the variation of inlet/outlet location due to the higher order acoustic mode in a high frequency in which the plane wave theory is not available. In this paper, the acoustic performance of reactive type expansion chamber with circular cross-section is analyzed by using the modified mode matching theory. The sensitivity analysis of four-pole parameters with respect to the location of inlet and outlet is also suggested to increase the acoustic performance. The acoustic power transmission coefficient is used as cost function, and the location of inlet and outlet is used as design variables. The steepest descent method and SUMT algorithm are used for optimization technique. Several results showed that the expansion chamber with optimally located inlet/outlet had better acoustic performance than concentric expansion chamber.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.331-334
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• 1997

The electrical and physical charateristics of aluminum oxide and Pt thin films on it, deposited by reactive sputtering and DC magnetron sputtering, respectively, were analysed with increasing annealing temperature(400~80$0^{\circ}C$) by four point probe, SEM and XRD. Under $600^{\circ}C$ of annealing temperature, aluminum oxide had the properties of improving Pt adhesion to SiO$_2$and insulation without chemical reaction to Pt thin films and the resistivity of Pt thin finns was improved. But these properties of aluminum oxide and Pt thin finns on it were degraded over $700^{\circ}C$ of annealing temperature because aluminum oxide was changed into metal aluminum and then reacted to Pt thin films deposited on it. The thermal characteristics of Pt micro heater were analysed with Pt-RTD integrated on the same substrate. In the analysis of properties of Pt micro heater. active area was smaller size, Pt micro heater had better thermal characteristics. Temperature of Pt micro heater fabricated on membrane was up to 34$0^{\circ}C$ with 1.2watts of the heating power due to reduction of the external thermal loss.

• Journal of the Korean Society for Railway
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• v.19 no.6
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• pp.727-735
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• 2016

Smart transformers are effective at reducing the weight and increasing the efficiency of traction systems for railroad applications. A smart transformer generally consists of rectifier modules and the Dual-Active-Bridge (DAB) converter modules. The efficiency of the smart transformer depends on not only the electrical characteristics, but also on the control method of the converter modules. Especially, a DAB converter has a high order degree of freedom of voltage modulation to control the power transferred through the high frequency transformer, and a voltage modulation method, are very critical for the efficiency of the DAB converter. This paper proposes a new voltage modulation method for the DAB converter to increase the efficiency in the low/medium power transfer condition. The proposed modulation method controls the reactive power in the high frequency transformer, making it zero. And, the switching loss is dramatically reduced by using the received converter module as a diode rectifier. The feasibility of the proposed modulation method is verified by computer simulation of the 900Vdc DAB converter power control.

• Asian-Australasian Journal of Animal Sciences
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• v.33 no.9
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• pp.1477-1486
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• 2020

Objective: The objective of this study was to evaluate the effect of different levels of lycopene supplementation on the carcass traits, meat quality, concentration of lipid oxidation products and antioxidant potential in the meat and liver of finishing barrows and gilts. Methods: A total of 40 barrows and 40 gilts were allotted in a completely randomized block design, arranged in a 2×5 factorial scheme, consisting of two sexes (barrows and gilts) and five dietary levels of lycopene (0, 12.5, 25.0, 37.5, and 50.0 mg/kg). In addition, four storage times (0, 24, 48, and 72 h), at 4℃, were added to the model to evaluate the longissimus lumborum muscle. Results: An interaction (p = 0.010) was observed between storage periods and dietary lycopene levels. The unfolding of the interaction (lycopene×period) showed a decreasing concentration of malondialdehyde concentration as the dietary lycopene increased, at all storage periods. No interactions (p>0.050) were observed for the 2,2 diphenyl 1 picrylhydrazyl (DPPH) in the pork. However, the percentage of DPPH radical inhibition reduced (p = 0.001) up to 72 h. Additionally, there was a linear increase (p = 0.001) in the capture of DPPH radicals by antioxidants, as the dietary lycopene increased. No interactions were observed (p>0.05) between the evaluated factors in liver. However, lipid oxidation was reduced by supplementing lycopene in pig diets. The capture of the DPPH radical, resulted increase in the antioxidant power exerted by lycopene in the liver (p = 0.001). The concentrations of the thiobarbituric acid reactive substances and DPPH in the liver were affected by sex (p = 0.001). Conclusion: Dietary supplementation of lycopene reduced the water loss during thawing and was effective in protecting against oxidation of the longissimus lumborum muscle and liver until 72 hours of storage, and the best results were obtained by supplementing with 50.0 mg of lycopene/kg of diet.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.10
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• pp.1542-1547
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• 2012

Asynchronous phenomenon occurs on the synchronous generators under power system when a generator's amplitude of electromagnetic force, phase angle, frequency and waveform etc become different from those of other synchronous generators which can follow instantly varying speed of turbine. Because the amplitude of electromagnetic force, phase frequency and waveform differ from those of other generators with which are to be put into parallel operation due to the change of excitation condition for load sharing and the sharing load change, if reactive current in the internal circuit circulates among generators, the efficiency varies and the stator winding of generators are overheated by resistance loss. When calculation method of protection settings and logic for protection of generator asynchronization will be recommended, a distance relay scheme is commonly used for backup protection. This scheme, called a step distance protection, is comprised of 3 steps for graded zones having different operating time. As for the conventional step distance protection scheme, zone 2 can exceed the ordinary coverage excessively in case of a transformer protection relay especially. In this case, there can be overlapped protection area from a backup protection relay and, therefore, malfunctions can occur when any fault occurs in the overlapped protection area. Distance relays and overcurrent relays are used for backup protection generally, and both relays have normally this problem, the maloperation, caused by a fault in the overlapped protection area. Corresponding to an IEEE standard, this problem can be solved with the modification of the operating time. On the other hand, in Korea, zones are modified to cope with this problem in some specific conditions. These two methods may not be obvious to handle this problem correctly because these methods, modifying the common rules, can cause another coordination problem. To overcome asynchronizing protection, this paper describes an improved backup protection coordination scheme using a new logic that will be suggested.

• Nuclear Engineering and Technology
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• v.52 no.3
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• pp.597-609
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• 2020

Accident Tolerant Fuels have been widely studied since the Fukushima-Daiichi accident in 2011 as one of the options on how to further enhance the safety of nuclear power plants. Deposition of protective coatings on nuclear fuel claddings has been considered as a near-term concept that will reduce the high-temperature oxidation rate and enhance accidental tolerance of the cladding while providing additional benefits during normal operation and transients. This study focuses on experimental testing of Zr-based alloys coated with Cr-based coatings using Physical Vapour Deposition. The results of long-term corrosion tests, as well as tests simulating postulated accidents, are presented. Zr-1%Nb alloy used as nuclear fuel cladding serves as a substrate and Cr, CrN, Cr_xN_y layers are deposited by unbalanced magnetron sputtering and reactive magnetron sputtering. The deposition procedures are optimized in order to improve coating properties. Coated as well as reference uncoated samples were experimentally tested. The presented results include standard long-term corrosion tests at 360℃ in WWER water chemistry, burst (creep) tests and mainly single and double-sided high-temperature steam oxidation tests between 1000 and 1400℃ related to postulated Loss-of-coolant accident and Design extension conditions. Coated and reference samples were characterized pre- and post-testing using mechanical testing (microhardness, ring compression test), Thermal Evolved Gas Analysis analysis (hydrogen, oxygen concentration), optical microscopy, scanning electron microscopy (EDS, WDS, EBSD) and X-ray diffraction.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.11
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• pp.2000-2006
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• 2011

Asynchronous phenomenon occurs on the synchronous generators under power system when a generator's amplitude of electromagnetic force, phase angle, frequency and waveform etc become different from those of other synchronous generators which can follow instantly varying speed of turbine. Because the amplitude of electromagnetic force, phase frequency and waveform differ from those of other generators with which are to be put into parallel operation due to the change of excitation condition for load sharing and the sharing load change, if reactive current in the internal circuit circulates among generators, the efficiency varies and the stator winding of generators are overheated by resistance loss. Where calculation method of protection settings and Logic for Protection of Generator Asynchronization will be recommended, A distance relay scheme is commonly used for backup protection. This scheme, called a step distance protection, is comprised of 3 steps for graded zones having different operating time. As for the conventional step distance protection scheme, Zone 2 can exceed the ordinary coverage excessively in case of a transformer protection relay especially. In this case, there can be overlapped protection area from a backup protection relay and, therefore, malfunctions can occur when any fault occurs in the overlapped protection area. Distance relays and overcurrent relays are used for backup protection generally, and both relays have normally this problem, the maloperation, caused by a fault in the overlapped protection area. Corresponding to an IEEE standard, this problem can be solved with the modification of the operating time. On the other hand, in Korea, zones are modified to cope with this problem in some specific conditions. These two methods may not be obvious to handle this problem correctly because these methods, modifying the common rules, can cause another coordination problem. To overcome asynchronizing protection this paper describes an improved backup protection coordination scheme using a new Logic that will be suggested.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2018.10a
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• pp.103-103
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• 2018

Oenothera biennis, commonly known as evening primrose, a potential source of natural bioactive substances: flavonoids, steroids, tannins, fatty acids and terpenoids responsible for a diverse range of pharmacological functions. However, whether extract prepared from aerial part of O. biennis (APOB) protects skin against oxidative stress remains unknown. To investigate the protective effects of APOB against oxidative stress-induced cellular damage and elucidated the underlying mechanisms in the HaCaT human skin keratinocytes. Our results revealed that treatment with APOB prior to hydrogen peroxide ($H_2O_2$) exposure significantly increased viability, and the highest DPPH radical-scavenging activities and reducing power of HaCaT cells. APOB also effectively attenuated H2O2-induced comet tail formation and inhibited the $H_2O_2$-induced phosphorylation levels of the histone ${\gamma}H2AX$, as well as the number of apoptotic bodies and Annexin V-positive cells. In addition, APOB exhibited scavenging activity against intracellular reactive oxygen species (ROS) accumulation and restored the mitochondrial membrane potential loss by $H_2O_2$. Moreover, $H_2O_2$ enhanced the cleavage of caspase-3 and degradation of poly (ADP-ribose)-polymerase (PARP), a typical substrate protein of activated caspase-3, as well as DNA fragmentation; however, these events were almost totally reversed by pretreatment with APOB. Furthermore, APOB increased the levels of heme oxygenase-1 (HO-1), which is a potent antioxidant enzyme, associated with the induction of nuclear factor-erythroid 2-related factor 2 (Nrf2). According to our data, APOB is able to protect HaCaT cells from $H_2O_2$-induced DNA damage and cell death through blocking cellular damage related to oxidative stress through a mechanism that would affect ROS elimination and activating the Nri2/HO-1 signaling pathway.