• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.3
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• pp.200-206
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• 2010

In ultrasound-excited thermography, the injected ultrasound to an object is transformed to heat and the appearance of defects can be visualized by thermography camera. The advantage of this technology is selectively sensitive to thermally active defects. Despite the apparent simplicity of the scheme, there are a number of experimental considerations that can complicate the implementation of ultrasound excitation thermography inspection. Factors including acoustic horn location, horn-crack proximity, horn-sample coupling, and effective detection range all significantly affect the detect ability of this technology. As conclusions, the influence of coupling pressures between ultrasound exciter and specimen was analyzed, which was dominant factor in frictional heating model.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1691-1697
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• 2018

Employing the density functional theory, we have investigated the roles of Coulomb and Hund's interactions in the electronic and magnetic properties of newly discovered ${\alpha}-RuCl_3$ having the $R{\overline{3}}$ symmetry, which is in close proximity of the Kitaev system. We show that both the size and the direction of local magnetic moment are highly dependent on Coulomb and Hund's interactions, and the spin and orbital parts show different behaviors. The validity of the so-called $j^{eff}$ picture is accessed upon interaction parameters, and the explicit roles of Hund's interaction in the local electronic structures and magnetic properties are discussed.

• 한국가스학회:학술대회논문집
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• 2006.11a
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• pp.191-195
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• 2006

Because of the continuous growth of energy consumption and also the tendency to site gas pipeline and power line along the same route, the close proximity of power lines and buried metallic pipelines has become more and more frequent. The lightning strokes collected by an electric substation or power line tower might cause arcing through the soil to an adjacent gas pipeline. This paper gives the outline of the resistance coupling and the standards of distance between gas pipeline and tower ground.

• Proceedings of the KIPE Conference
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• 2000.07a
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• pp.717-720
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• 2000

The sensorless scheme for Switched Reluctance Motor(SRM) dives must have the robustness and reliability because the noise and error are sensitive. These elements make electrically noisy environments due to the proximity of high current power circuits with small signal electronic circuits when SRM drives. Also the leakage inductances and finite coupling capacitances these can cause the noise on any low voltage current and voltage measurement. the error can occur because the current and voltage including the noise are used as the input of sensorless algorithm In this paper the high robustness and resistance of input noise are described and the fuzzy logic based rotor estimation algorithm is used to reduce the tolerance of input data.

• Journal of Magnetics
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• v.10 no.1
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• pp.36-39
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• 2005

We report element-resolved and interface-sensitive magnetization reversals investigated from an oppositely exchange-biased NiFe/FeMn/Co structure by employing soft x-ray resonant Kerr rotation measurements. We have found not only switchable uncompensated antiferromagnetic regions with its sizable thicknesses at both interfaces of the FeMn layer but also their strong coupling to the individual ferromagnetic layers. These experimental results provide a better insight into experimentally observed reductions in exchange-bias field on the basis of an interface-proximity model proposed in this work.

• ETRI Journal
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• v.41 no.3
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• pp.289-297
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• 2019

In this paper, a wideband, circularly polarized patch antenna is proposed that leverages the unidirectional resonant modes of a circular patch mounted on top of a grounded dielectric-ferrite substrate. The proposed antenna is fed via the proximity coupling method and several parasitically coupled patches are placed on a dielectric superstrate to enhance the impedance bandwidth of the antenna. The resonant modes of the structure rotate only in the clockwise or counter clockwise directions. In the frequency range where the effective permeability of the ferrite layer is negative, the resonance frequencies of these modes differ significantly, which produces a large axial ratio (AR) bandwidth. For the proposed antenna, the numerical results show the 10 dB impedance bandwidth to be around 44% and the 3 dB axial ratio bandwidth to be higher than 64%.

• Journal of the Korean Magnetics Society
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• v.12 no.3
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• pp.109-116
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• 2002

We designed the flyback planar transformer, which had 8 W capacity, with 70 V input voltage and 8.2 V output voltage for the establishment of design method and the confirmation of application possibility. The numerical value of inductance measured under the switching frequency of 120 kHz was 1650 $\mu$H, which was the inductance efficiency of'85∼87% against theoretical value. The A.C. resistance of primary and secondary coil was 4.2 Ω and 0.25 Ω respectively, On the other hand, the quality factor for each wound numbers showed quite a high value of 158 and 75 respectively. And the Coupling Factor was 0.96∼0.97 under 120 kHz switching frequency. The inductance rapidly increased as the thickness of the core plane increased until it became 1.4 mm but under the thickness more than 1.4 mm, there was no substantial change. Therefore, the critical value of the plane thickness of core was 1.4 mm. And the shape of the output wave of the planar transformer at 70V input voltage was a stable square wave.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.1
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• pp.74-81
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• 2001

The sensorless scheme for Switched Reluctance Motor(SRM) drives must have the robustness and reliability because the noise and error are sensitive. These elements make electrically noisy environments due to the proximity of high current power circuits with small signal electronic circuits when SRM drives. Also, due to the leakage inductances and finite coupling capacitances, these can cause the noise on any low voltage current and voltage measurement circuit. The position estimate error occurs because the current and voltage including the noise are sued as the inputs of sensorless algorithm. In this paper the high robustness and resistance of input noise re described. The fuzzy logic based rotor estimation algorithm and the observer model are used to reduce the tolerance of input data.

• Nuclear Engineering and Technology
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• v.50 no.5
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• pp.788-793
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• 2018

High-density spent fuel (SF) storage racks have been installed to increase SF pool capacity. In these SF racks, neutron absorber materials were placed between fuel assemblies allowing the storage of fuel assemblies in close proximity to one another. The purpose of the neutron absorber materials is to preclude neutronic coupling between adjacent fuel assemblies and to maintain the fuel in a subcritical storage condition. METAMIC neutron absorber has been used in high-density storage racks. But, neutron absorber materials can be subject to severe conditions including long-term exposure to gamma radiation and neutron radiation. Recently, some of them have experienced degradation, such as white spots on the surface. Under these conditions, the material must continue to serve its intended function of absorbing neutrons. For the first time in Korea, this article uses a neutron attenuation test to examine the performance of METAMIC surveillance coupons. Also, scanning electron microscope analysis was carried out to verify the white spots that were detected on the surface of METAMIC. In the neutron attenuation test, there was no significant sign of boron loss in most of the METAMIC coupons, but the coupon with white spots had relatively less B-10 content than the others. In the scanning electron microscope analysis, corrosion material was detected in all METAMIC coupons. Especially, it was confirmed that the coupon with white spots contains much more corrosion material than the others.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.206-206
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• 2021

The necessity for appropriate management of water resources infrastructures such as reservoirs, levees, and dikes is increasing due to unexpected hydro-climate irregularities and rising water demands. To meet this need, past studies have focused on advancing theoretical optimization algorithms such as nonlinear programming, dynamic programming (DP), and genetic programming. Yet, the optimally derived theoretical solutions are limited to be directly implemented in making release decisions in the real-world systems for a variety of reasons. This study first aims to comparatively analyze the two prominent optimization methods, DP and evolutionary multi-objective direct policy search (EMODPS), under historical inflow series using K-fold cross validation. A total of six optimization models are formed each with a specific formulation. Then, one of the optimization models was coupled with the actual zone-based hedging rule that has been adopted in practice. The proposed methodology was applied to Boryeong Dam located in South Korea with conflicting objectives between supply and demand. As a result, the EMODPS models demonstrated a better performance than the DP models in terms of proximity to the ideal. Moreover, the incorporation of the real-world policy with the optimal solutions improved in all indices in terms of the supply side, while widening the range of the trade-off between frequency and magnitude measured in the sides of demand. The results from this study once again highlight the necessity of closing the gap between the theoretical solutions with the real-world implementable policies.