• Geosystem Engineering
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• v.21 no.6
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• pp.297-308
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• 2018

In this paper, we investigate the differences between LNG price of South Korea and Japan. Although S. Korean and Japanese LNG markets have similar structures, there are some differences in the price formation. From DCC-MGARCH, we confirm that Japan LNG price have less persistence of disturbance on time than S. Korean LNG price. The conditional correlation also shows linkage effects between LNG prices and impacts of S-curve and DS-curve. Moreover, ARDL estimation result shows that there is co-integration in all models and that impacts of Fukushima accident and LNG volumes are responsible for the increase in Japanese LNG price. Also, adjustment speed of error correction term shows that Japan's deviation from long-run equilibrium disappears faster than S. Korea does, indicating relatively strong Japanese linkage between LNG price and oil price.

• Electronics and Telecommunications Trends
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• v.36 no.3
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• pp.23-33
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• 2021

Two main technologies of III-V/Si laser diode for optical communication, direct epitaxial growth, and wafer bonding were studied. Until now, the wafer bonding has been vigorously studied and seems promising for the ideal III-V/Si laser. However, the wafer bonding process is still complicated and has a limit of mass production. The development of a concise and innovative integration method for silicon photonics is urgent. In the future, the demand for high-speed data processing and energy saving, as well as ultra-high density integration, will increase. Therefore, the study for the hetero-junction, which is that the III-V compound semiconductor is directly grown on Si semiconductor can overcome the current limitations and may be the goal for the ideal III-V/Si laser diode.

• Journal of Ocean Engineering and Technology
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• v.36 no.2
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• pp.108-114
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• 2022

Most studies on the shape of the steady vortex ring have been based on the Stokes stream function approach. In this study, the velocity approach is introduced as a trial approach. A contour dynamics method for fluid velocity is used to analyze the Norbury-Fraenkel family of vortex rings. Analytic integration is performed over the logarithmic-singular segment. A system of nonlinear equations for the discretized shape of the vortex core is formulated using the material boundary condition of the core. An additional condition for the velocities of the vortical and impulse centers is introduced to complete the system of equations. Numerical solutions are successfully obtained for the system of nonlinear equations using the iterative scheme. Specifically, the evaluation of the kinetic energy in terms of line integrals is examined closely. The results of the proposed method are compared with those of the stream function approaches. The results show good agreement, and thereby, confirm the validity of the proposed method.

• International Journal of Computer Science & Network Security
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• v.22 no.5
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• pp.5-10
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• 2022

Photovoltaic systems provide a reliable green energy solution. The sustainability and low-maintenance of Photovoltaic systems motivate the integration of Photovoltaic systems into the electrical grid and further contribute to a greener environment, as the system does not cause any pollution or emissions. Developing methodologies based on machine learning techniques to assist in reducing the burden of studies related to integrating Photovoltaic systems into the electric grid are of interest. This research aims to develop a methodology based on a unsupervised machine learning algorithm that can reduce the burden of extensive studies and simulations related to the integration of Photovoltaic systems into the electrical grid.

• Journal of Sensor Science and Technology
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• v.31 no.2
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• pp.71-78
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• 2022

Wearable devices have the potential to revolutionize future medical diagnostics and personal healthcare. The integration of biosensors into scalable form factors allow continuous and noninvasive monitoring of key biomarkers and various physiological indicators. However, conventional wearable devices have critical limitations owing to their rigid and obtrusive interfaces. Recent developments in functional biocompatible materials, micro/nanofabrication methods, multimodal sensor mechanisms, and device integration technologies have provided the foundation for novel skin-interfaced bioelectronics for advanced and user-friendly wearable devices. Nonetheless, it is a great challenge to satisfy a wide range of design parameters in fabricating an authentic skin-interfaced device while maintaining its edge over conventional devices. This review highlights recent advances in skin-compatible materials, biosensor performance, and energy-harvesting methods that shed light on the future of wearable devices for digital health and personalized medicine.

• Progress in Superconductivity
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• v.5 no.1
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• pp.1-4
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• 2003

A five-year project for Nb-based single flux quantum (SFQ) circuits supported by Japan's Ministry of Economy Trade and Industry (METI) in Japan was started in September 2002. Since April 2003, the New Energy and Industrial Technology Development Organization (NEDO) has supported this Superconductor Network Device Project. The aim of the project is to improve the integration level of Nb-based SFQ circuits to several ten thousand Josephson junctions, in comparison with their starting integration level of only a few thousand junctions. Actual targets are a 20 GHz dual processor module for the servers and a 0.96 Tbps switch module for the routers. Starting in April 2003, the Nb project was merged with SFQ circuit research using a high-T$_{c}$ superconductor (HTS). The HTS research targets are a wide-band AD converter for mobile-phone base stations and a sampling oscilloscope for wide-band waveform measurements.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.345-346
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• 2016

The grid-connected energy storage systems, which could increase the reliability, efficiency, and cleanliness of the grid is presently restricted by the high cost of batteries. This problems could be solved by batteries retired from automotive services. These batteries can provide a low-cost system for energy storage and other applications such as residential applications and renewable energy integration. This paper gives an overview of technical requirements for the re-use of the electric vehicle batteries in energy storage systems.Firstly, the motivation of research is introduced. Secondly, the technologies needed for the re-use of the battery are introduced such asidentification of the battery characteristics, grading of the aged batteries, identification of the state-of-charge and state-of-health of the battery and suitable power electronic converter topologies. In addition the control strategy to maximize the battery lifespan and bypass the faulty batteries is presented and one-stop solution to implement the above mentioned technologies are also given.

• Journal of the Korean Solar Energy Society
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• v.26 no.3
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• pp.63-69
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• 2006

In order to positively cope with the international environmental regulations like UNFCCC (UN Framework Convention on Climate Change) and to overcome energy crisis Korea, who depends on import for more than 97% of required energy, needs to continuously proceed to development, spread and expansion of alternativeenergy and then, to cultivate the capacity to keep the balance of demand and supply of energy by itself. In this aspect, the technology of BIPV (Building Integrated Photovoltaic) is the field that the world is most interested in. However, at present, this technology is centered on increasing the efficiency of the module itself so it has lots of problems to be applied to buildings. Application of the integrated PV system in building external curtain wall can obtain much more generation of electric power than in roof-types whose area for installation is restricted, so it is excellent in terms of its possibility of application. Therefore, this paper intends to advance its practical use by proposing how to get integrated PV system which can be applied to building external curtain wall, and how to apply it.

• Journal of Power Electronics
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• v.18 no.5
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• pp.1479-1488
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• 2018

Power packet (PP) distribution system distributes power to different loads that share the same distribution cable in a packetized form. When compared with conventional power systems, a PP distribution system (PPDS) can reduce standby power, eliminate Point-of-Load (PoL) power conversion, and intelligently control the load demand from the source side. Due to the absence of PoL conversion, when multiple power sources at different voltage levels and conditioning requirements jointly send power to various loads at different voltage ratings, the generated voltage has an irregular shape. A large filter at each of the load sides is required to reduce such a large voltage ripple. In this paper, a single-inductor, multiple-input-single-output converter structure based multiple-energy-source mixer is proposed. It combines PP generation, maximum power point tracking (MPPT) of renewable energy sources (RESs) and filtering at the source side. To demonstrate the possible renewable energy integration, a PV panel is used as a power source together with other constant voltage sources. The PV power is approximately tracked using the constant voltage method and it is used for each of the PP generations. The proposed PP distribution system is experimentally verified and it is shown that a conventional PI controller is sufficient for stable system operation.

• Journal of Biomedical Engineering Research
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• v.39 no.5
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• pp.208-212
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• 2018

Microbial fuel cell (MFC) technology has been attractive since it can not only treat organic waste in an eco-friendly way by digesting it but also generate electricity by the unique metabolic process of microbes. However, it hasn't been employed in practical use until now because it is hard to integrate a small electricity up to an adequate amount of electric power and difficult to keep its bio-electric activity consistent. In this study, we combined an energy harvester with MFC (MFC-EH) to make the power-integration convenient and developed an energy self-sustainable wireless sensor system driven by a stable electric power produced by MFC-EH. Additionally, we build the low power application measuring data to be cast by the web in real-time so that it can be quickly and easily accessed through the internet. The proposed system could contribute to improvement of waste treatment and up-cycling technologies in near future.