• Korean Journal of Materials Research
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• v.22 no.9
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• pp.450-453
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• 2012

In crystalline solar cells, the substrate itself constitutes a large portion of the fabrication cost as it is derived from semiconductor ingots grown in costly high temperature processes. Thinner wafer substrates allow some cost saving as more wafers can be sliced from a given ingot, although technological limitations in slicing or sawing of wafers off an ingot, as well as the physical strength of the sliced wafers, put a lower limit on the substrate thickness. Complementary to these economical and techno-physical points of view, a device operation point of view of the substrate thickness would be useful. With this in mind, BC-BJ Si and GaAs solar cells are compared one to one by means of the Medici device simulation, with a particular emphasis on the substrate thickness. Under ideal conditions of 0.6 ${\mu}m$ photons entering the 10 ${\mu}m$-wide BC-BJ solar cells at the normal incident angle (${\theta}=90^{\circ}$), GaAs is about 2.3 times more efficient than Si in terms of peak cell power output: 42.3 $mW{\cdot}cm^{-2}$ vs. 18.2 $mW{\cdot}cm^{-2}$. This strong performance of GaAs, though only under ideal conditions, gives a strong indication that this material could stand competitively against Si, despite its known high material and process costs. Within the limitation of the minority carrier recombination lifetime value of $5{\times}10^{-5}$ sec used in the device simulation, the solar cell power is known to be only weakly dependent on the substrate thickness, particularly under about 100 ${\mu}m$, for both Si and GaAs. Though the optimum substrate thickness is about 100 ${\mu}m$ or less, the reduction in the power output is less than 10% from the peak values even when the substrate thickness is increased to 190 ${\mu}m$. Thus, for crystalline Si and GaAs with a relatively long recombination lifetime, extra efforts to be spent on thinning the substrate should be weighed against the expected actual gain in the solar cell output power.

• The Journal of the Korea Contents Association
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• v.16 no.2
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• pp.106-116
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• 2016

What made stand out among these police procedurals was its focus on the importance of history to understand both the past and contemporary society and culture. Many of the cases involve aspects of history that are not part of mainstream narratives and constitute the unfinished business of America. The flashback sequences throughout the show visually and affectively transport the viewer back to an earlier historical moment. What all the victims have in common is that they refused to be silent or passive in the face of circumstances they believed were wrong, or they refused to conform to dehumanising and destructive social and cultural expectation. Those promoting these lies have the power to establish their version as the power to establish their version as the "truth" of what happened in context, but viewers are positioned to see the truth as the victims experienced it and to identify with them and against the power abusers. The Cold Case detectives pursue the ghosts of American history, restoring to our view stories of lives and experiences rendered invisible and unspeakable by dominant forms of knowledge and power. The series invites viewrs to empathize with the victim and to develop an ethical commitment to social justice in the future.

• Journal of Advanced Navigation Technology
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• v.21 no.6
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• pp.620-625
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• 2017

Recently, the solar module for charging internet devices is installed in crowded areas to offers services so that people can charge their smartphones or tablets. But this charging module can not be linked with the information related to a bus approach so people are subject to let their belongings such as smartphone, tablet pc at the bus stop while they are still charging it. This paper proposes a system to inform the smart phone when the bus is accessed by using the LPWA technology and BLE technology to resolve such under-failures. This experimental result showed that the power usage of LPWA based bus entry systems is an average of X, confirming that the long period usage of low-power can be possible for low power consumption in this results, enabling information on the bus to be transmitted to smart phones using Advertising mode of BLE.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.298-302
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• 2009

Low power Hall thruster is under development as one of the core technologies for STSAT-3. The Hall thruster has several advantages such as its simple structure, high thrust density and specific impulse etc. Development target values deduced by analyzing requirements are consumed electrical power, thrust, thrust efficiency, and specific impulse of < 300 W, > 10 mN, ~ 35%, and > 1000 s, respectively. In order to achieve the target specifications, two prototype Hall thrusters were developed and compared. To date, thrust and efficiency are 11 mN and 37% under the total power of 290 W with 0.97 mg/s Xe propellent supply.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.2
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• pp.28-36
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• 2018

Islands are supplied with power from diesel generation or from photovoltaic power generation, and problems with offshore environmental impacts (age deterioration, salt pollution), environmental pollution (exhaust gas, noise, dust) and power generation costs (installation, maintenance) have increasingly emerged. In 2016, the cost recovery rate was only 27%, and deficits reached 73% on 65 islands managed by KEPCO. In terms of deficits, the costs incurred in the power generation sector accounted for 91%, with the ratio of fixed costs at about 60%. Analysis suggests that operating costs can be reduced with an optimal power supply system that improves power generation efficiency and makes operating systems more efficient. Therefore, it is possible to simplify fuel transportation and facility maintenance, because one island integrates the power plants of remote islands, and offshore cable is used to supply power to the other islands. From the economic evaluations in this paper, an algorithm deciding offshore cable layout validity for an integrated power supply between adjacent islands is presented. Simulation results based on the proposed algorithm confirmed that an integrated power supply is economical for existing stand-alone operations on islands having diesel generation, low peak power, and near distances.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.11
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• pp.9-16
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• 2005

This paper proposes a programmable PLL (phase locked loop) based clock generator supporting a wide-range-frequency input and output for high performance and low power SoC with multiple clock frequencies domains. The propose system reduces the locking time and obtains a wide range operation frequency by using a dual-charge pumps scheme. For low power operation of a chip, the locking processing circuits of the proposed PLL doesn't be working in the standby mode but the locking data are retained by the DAC. Also, a tracking ADC is designed for the fast relocking operation after stand-by mode exit. The programmable output frequency selection's circuit are designed for supporting a optimized DFS operation according to job tasks. The proposed PLL-based clock system has a relock time range of $0.85{\mu}sec{\sim}1.3{\mu}sec$($24\~26$cycle) with 2.3V power supply, which is fabricated on $0.35{\mu}m$ CMOS Process. At power-down mode, PLL power saves more than $95\%$ of locking mode. Also, the PLL using programmable divider has a wide locking range ($81MHz\~556MHz$) for various clock domains on a multiple IPs system.

• Journal of Electrical Engineering and Technology
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• v.1 no.3
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• pp.359-365
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• 2006

Since the start of the KSTAR (Korea Superconducting Tokamak Advanced Research) project, Instrumentation and Control (I&C) of the Neutral Beam Test Facility (NB-TF) has been striving to answer diverse requests arising from various facets during the project's development and construction phases. Hard-wired electrical circuits have been designed, tested, fabricated, and finally installed to the relevant parts of the system. In relation to the vacuum system I&C, controlling functions for the rotary pumps, a Roots pump, two turbomolecular pumps, and four cryosorption pumps have been constructed. I&C for the ion source operation are the temperature and flow rate signal monitoring, Langmuir probe signal measurements, gradient grid current measurements, and arc detector circuit. For the huge power system to be monitored or safely operated, many temperature measurement functions have also been implemented for the beam line components like the neutralizer, bending magnet, ion dump, and calorimeter. Nearly all of the control and probe signals between the NB test stand and the control room were made to be transmitted through the optical cables. Failures of coolant flow or beam line vacuum pressure were made to be safely blocked from influencing the system by an appropriate interlock circuit that will shut down the extraction voltage application to the system or prevent damages to the vacuum components. Preliminary estimation of the beam power through the calorimetric measurement shows that 87.9% of the total power of the 60kV/18A beam with 200 seconds duration is absorbed by the calorimeter surface. Most of these I&C results would be highly appropriate for the construction of the main NBI facility for the KSTAR national fusion research project.

• 한국태양에너지학회:학술대회논문집
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• 2008.04a
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• pp.227-232
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• 2008

Stirling engine for solar thermal power is an essential part of Dish-Stirling system which generates electricity by using direct normal irradiation and will go into commercialization in near future. For the Stirling engine used in this study is Solo 161 model the capacity of which is 10 kWe and was already used for the Dish-Stirling system of KIER in Jinhae. The receiver of Stirling engine absorbes concentrated solar radiation and transfer it to working fluid of Hydrogen. The working condition of striling engine is high temperature and high pressure to make high efficiency. Therefore the receiver should stand against high temperature of above 800 $^{\circ}C$ and high pressure of max. 150 bar with good performance of heat transfer. The receiver is composed of 78 Inconel tubes of 1/8" with thickness of 0.71 mm and two reserviors which is connected with two cylinders. In order to know the charaterristics of heat transfer of Stirling engine receiver, simulation on the heat transfer of the receiver of Solo 161 is conducted by using CFD code of Fluent. The heat flux on the receiver surface has a shape of Gaussian distribution so, it is necessary to simulate a whole receiver. However, It is difficult and time consuming to simulate the whole receiver that one tube with different heat flux conditions are considered in this study. From the simulation results, heat transfer charateristics of receiver are observed and tube wall and fluid temperature and heat transfer coefficient are obtained and compared with the calculated results from Dittus-Boelter's correlation.

• Proceedings of the KIEE Conference
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• 1995.07b
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• pp.871-873
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• 1995

The purpose of this paper is to design and construct the compact type joint driver and controller of the biped robot. This biped robot will be designed to be suitable for the practical usages and applications in the work environment, which is not plat floor, like a stairs by taking the stand-alone style that equipped all the parts except power sources. Generally, highly nonlinear motion dynamics of the biped robot is realized to linear approximations by installing a high-ratio speed reducer at each joint and dividing motions into a several piecewise linear motions, which is realized by the digital controller design techniques. This biped robot has symmetrical structure to get the stable walking ability and also the hierachical structure to control each joint as well. That is, all of the joint controllers are connected to the main controller in the composition of overall controllers. The driver and controller of each joint uses PI controller that compensate the velocity and position errors by the data of the encoder. And the signal characteristics of each joint controller forms a trapezoid speed profile which is predefined by the values of direction, maximum velocity and position.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.8
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• pp.1-7
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• 2018

A folding solar power system is a stand-alone system and is a structure with solar panels attached. It consists of supporting parts and folding parts for ease of movement. While the efficiency of solar panels is also important to produce electricity by maximizing the power efficiency of solar panels, the most important thing is structure stability. The folding solar power structure intended to be developed in this study is a collapsible structure that is easy to move and install into systems that can produce electricity from grid to independent. Since these structures are installed outdoors, wind loads, snow cover, etc. In this paper, the wind loads most affected by the folding solar power generation structure were obtained using the MeshFree Finite Element Method. MeshFree is a program that makes it easier for users to interpret by simplifying the mesh tasks required by an existing analysis. The analysis showed that the greater the angle of inclination of the wind to the ground, the greater the wind load. In addition, reliability was ensured by wind load testing.