• Journal of the Institute of Electronics Engineers of Korea SC
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• v.47 no.6
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• pp.6-11
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• 2010

Amount of power generated from solar photovoltaic can vary according to solar flux of sunlight due to nature of solar cell panel, and an angle that the sun and the surface of cell makes brings difference in amount of power generation. Solar flux is decided by location of surface of the Earth that is classified into longitude and latitude, but on the other hand, an angle that the sung and the surface of cell makes can be changed by changing the angle of a solar power generation device at the fixed location. A method of changing the angle of a solar power generation device as a measure for improving practical power generation efficiency. and studies about a solar tracking device for this are in active. This study conducted a research on a solar tracking system for improvement of solar power generation efficiency. A solar tracking system of this study is composed of a sensor part to confirm a location of the sun with a semiconductor photosensor using the photo conductive effect, and it analyzed output signal of a sensor by using microprocessor and it produced a control signal of driving part for tracking the sun. A solar power generator (25W) was produced to analyze performance of a solar tracking system and usefulness of a solar tracking device that was designed and produced in this study was confirmed through experiments.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.8
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• pp.107-114
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• 2017

In this paper, a novel power factor compensation system based on voltage-controlled method is proposed for 3-phase 4-wire power system. The proposed voltage-controlled power factor compensation system generates a reactive power required for compensation by applying a variable output voltage by a slidac to a capacitor. In conventional power factor compensation system using the capacitor bank method, the power factor compensation error occurs depending on the load condition due to the limited capacity of the capacitors. However, the proposed system compensates the power factor up to 100% without error. In this paper, we have developed a voltage-controlled power factor compensation system and a control algorithm for 3-phase 4-wire power system, and verify its performance through simulation and experiments. If the proposed power factor compensation system is applied to an industrial field, a power factor compensation performance can be maximized. As a result, it is possible to reduce of electricity prices, reduce of line loss, increase of load capacity, ensure the transmission margin capacity, and reduce the amount of power generation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.3 no.1
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• pp.18-25
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• 1978

The 1/f noise spectrum of short-circuited output drain current due to the Shockley-Read-Hal] recombination centers with a single lifetime in homogeneous nondegenerate MOS-field effcte transtors with n-type channel is calculated under the assumptions that the quasi-Fermi level for the carriers in each energy band can not be defined if we include the fluctuation for time varying quantities. and so 1/f noise is a majority carrier effect. Under these assumptions the derived 1/f noise in this paper show some essential features of the 1/f noise in MOS-field effect transistors. That is, it has no lowfrequency plateau and is proportionnal to the channel cross area A and to the driain bias voltage Vd and inversely proportional to the channel length L3 in MOS field effect transistors. This model can explain the discrepancy between the transition frequency of the noise spectrum from 1/f- response to 1/f2 and the frequency corresponding to the relaxation time related to the surface centers in p-n junction diodes. In this paper the results show that the functional form of noise spectrum is greatly influenced by the functional forms of the electron capture probability cn (E) and the relaxation time r (E) for scattering and the case of lattice scattering show to be responsible for the 4 noise in MOS fold effect transistors. So we canconclude that the source of 1/f noise is due to lattice scattering.

• Journal of the Korean Electrochemical Society
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• v.12 no.4
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• pp.342-348
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• 2009

Zn/Air secondary batteries are high energy density type and environment-friendly. Also, they have safer properties than batteries of other type by low manufacturing cost and using the electrolyte solution. But, they have a weak concerning large output discharge. Oxygen evolution reaction(OER) and oxgen reduction reaction(ORR) in aqueous solution make a result of a decrease of cell efficiency and life span. Therefore, to minimize the voltage drop from between OCV and charge/discharge voltage is key point. The problem should be solved through developing catalysts of high efficiency. In this study, we synthesized $Pr_{1-x}(Sr,\;Ca)_x\;CoO_3$ powders by citric method and then measured physical characteristics of each powder by XRD, SEM, TGA etc. We examined its electrochemical properties by the cathodic polarization, anodic polarization and cyclic voltammogram. We achieved results that new catalysts showed better performances than existing $La_{1-x}Sr_xCoO_3$, $La_{1-x}Ca_xCoO_3$, ect. catalysts prepared in our lab.

• Strategy21
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• s.41
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• pp.261-293
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• 2017

Nuclear power is a way of attaining an enormous amount of energy with relatively small amount of resources and after it has been introduced to the submarine since 1954, there are approximately 150 of nuclear powered submarine currently on a mission around the world. This is due to the maneuverability, mountability and covertness of nuclear submarines. However, there are other tasks, not only the high level of nuclear technology that are needed to be dealt with in order to construct nuclear powered submarine. The biggest task of all is to secure the enriched uranium. Accordingly, this research is about the way of enriching and securing the nuclear fuel that are used in the nuclear submarine with the characteristics, merits and demerits of the nuclear submarine. Due to the fact that the pressurized water reactor in South Korea is the reactor that was originally built for the development of nuclear powered submarine, many parts is designed to be suitable for the submarine propulsion. However, in order to apply this to submarine it is needed to consider additional requests such as the position of reactor, accident-coping system, radioactive covering, reactor output adjustment and ship's pitch and roll in order to apply this to submarine. Nuclear submarines have much higher speed based on the powerful propulsion in comparison with diesel-electric submarine and also have bigger loading area. Besides, there is no need to snorkel and they also have advantages in covertness with the multi-noise proof system. The nuclear technology in South Korea has seen the dramatic development since 1962 and in 1998 reached to the level that we have succeeded in the localization of nuclear plant and exported the world-class one-piece small-sized reactor (SMART) to UAE. To operate these reactors, we import the whole quantity of low-enriched uranium and having our own uranium enrich facility is not probable because of the budget and international regulations. With the ROK/US nuclear agreement revised on 2015 November, the enrichment of uranium that are available without special permission has changed up to 20%. According to the assumption that we use the 20% enrichment of Uranium on U.S. virginia class submarine, it is necessary to change the fuel after 11 years and it will cause additional cost of 1 billion dollars. But the replace period by the uranium's enrichment rate is not fixed so that it is possible to change according to the design of reactor. Therefore, I would like to make a suggestion on two types of design concepts of nuclear submarine that can be operated for 30 years without nuclear fuel change by using the 20% enriched uranium from ONNp.First of all, it is possible by increasing the size of reactor by 3 times and it results in the 1,000t increase of the weight. And secondly, it is by designing the one piece reactor to insert devices such as steam turbine, condenser into the inside of nuclear core like the Rubis class submarines of France.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.3
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• pp.102-112
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• 2013

In this paper, two step processing method of contour extraction and complement which contain hexagonal shape for low contrast and noisy images is proposed. This method is based on the combination of Laplacian-Gaussian filter and an idea of filters which are dependent on the shape. At the first step, an algorithm which has six masks as its extractors to extract the hexagonal edges especially in the corners is used. Here, two tricorn filters are used to detect the tricorn joints of hexagons and other four masks are used to enhance the line segments of hexagonal edges. As a natural image, a corneal endothelial cell image which usually has regular hexagonal form is selected. The edge extraction of hexagonal shapes in corneal endothelial cell is important for clinical diagnosis. The proposed algorithm and other conventional methods are applied to noisy hexagonal images to evaluate each efficiency. As a result, this proposed algorithm shows a robustness against noises and better detection ability in the aspects of the output signal to noise ratio, the edge coincidence ratio and the extraction accuracy factor as compared with other conventional methods. At the second step, the lacking part of the thinned image by an energy minimum algorithm is complemented, and then the area and distribution of cells which give necessary information for medical diagnosis are computed.

• International Journal of Aeronautical and Space Sciences
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• v.8 no.1
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• pp.10-20
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• 2007

For spacecraft attitude control, reaction wheel (RW) steering laws with more than three wheels for three-axis attitude control can be derived by using a control allocation (CA) approach.1-2 The CA technique deals with a problem of distributing a given control demand to available sets of actuators.3-4 There are many references for CA with applications to aerospace systems. For spacecraft, the control torque command for three body-fixed reference frames can be constructed by a combination of multiple wheels, usually four-wheel pyramid sets. Multi-wheel configurations can be exploited to satisfy a body-axis control torque requirement while satisfying objectives such as minimum control energy.1-2 In general, the reaction wheel steering laws determine required torque command for each wheel in the form of matrix pseudo-inverse. In general, the attitude control command is generated in the form of a feedback control. The spacecraft body angular rate measured by gyros is used to estimate angular displacement also.⁵ Combination of the body angular rate and attitude parameters such as quaternion and MRPs(Modified Rodrigues Parameters) is typically used in synthesizing the control command which should be produced by RWs.¹ The attitude sensor signals are usually corrupted by noise; gyros tend to contain errors such as drift and random noise. The attitude determination system can estimate such errors, and provide best true signals for feedback control.⁶ Even if the attitude determination system, for instance, sophisticated algorithm such as the EKF(Extended Kalman Filter) algorithm⁶, can eliminate the errors efficiently, it is quite probable that the control command still contains noise sources. The noise and/or other high frequency components in the control command would cause the wheel speed to change in an undesirable manner. The closed-loop system, governed by the feedback control law, is also directly affected by the noise due to imperfect sensor characteristics. The noise components in the sensor signal should be mitigated so that the control command is isolated from the noise effect. This can be done by adding a filter to the sensor output or preventing rapid change in the control command. Dynamic control allocation(DCA), recently studied by Härkegård, is to distribute the control command in the sense of dynamics⁴: the allocation is made over a certain time interval, not a fixed time instant. The dynamic behavior of the control command is taken into account in the course of distributing the control command. Not only the control command requirement, but also variation of the control command over a sampling interval is included in the performance criterion to be optimized. The result is a control command in the form of a finite difference equation over the given time interval.⁴ It results in a filter dynamics by taking the previous control command into account for the synthesis of current control command. Stability of the proposed dynamic control allocation (CA) approach was proved to ensure the control command is bounded at the steady-state. In this study, we extended the results presented in Ref. 4 by adding a two-step dynamic CA term in deriving the control allocation law. Also, the strict equality constraint, between the virtual and actual control inputs, is relaxed in order to construct control command with a smooth profile. The proposed DCA technique is applied to a spacecraft attitude control problem. The sensor noise and/or irregular signals, which are existent in most of spacecraft attitude sensors, can be handled effectively by the proposed approach.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.9
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• pp.1045-1050
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• 2014

$N_2O$(Nitrous Oxide) is known as the third major GHG(Green House Gas) following $CO_2$(Carbon Oxide) and $CH_4$(Methane). The GWP(Global Warming Potential) factor of $N_2O$ is 310 times as large as that of $CO_2$ because $N_2O$ in the atmosphere is very stable, and it becomes a source of secondary contamination after photo-degradation in the stratosphere. Investigation on the cause of the $N_2O$ formation have been continuously reported by several researchers on power sources with continuous combustion form, such as a boiler. However, in the diesel engine, research on $N_2O$ generation which has effected from fuel components has not been conducted. Therefore, in this research, author has investigated about $N_2O$ emission rates which was changed by nitrogen and sulfur concentration in fuel on the diesel engine. The test engine was a 4-stroke direct injection diesel engine with maximum output of 12 kW at 2600rpm, and operating condition of that was set up at a 75% load. Nitrogen and sulfur concentrations in fuel were raised by using six additives : nitrogen additives were Pyridine, Indole, Quinoline, Pyrrol and Propionitrile and sulfur additive was Di-tert-butyl-disulfide. In conclusion, diesel fuels containing nitrogen elements less than 0.5% did not affect $N_2O$ emissions in the all concentrations and kinds of the additive agent in the fuel. However, increasing of the sulfur additive in fuel increased $N_2O$ emission in exhaust gas.

• The Journal of Korean Medicine Ophthalmology and Otolaryngology and Dermatology
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• v.29 no.4
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• pp.14-23
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• 2016

Objectives : One of major complications of diabetes, diabetic ulcer is also one of the main reasons for amputation, and the prevalence rate is 4-10%. Laser therapy is widely used for leg ulcer and diabetic ulcer, and it is known to improve wound epithelialization, cellular content, and collagen deposition. The purpose of this study is to investigate the properties of the laser and the spectrum of laser instruments for diabetic ulcer. Methods : We performed literature search using the PubMed, Cochrane, CINAHL and Web of science for the data in English. In addition, other databases were checked for different languages such as OASIS and NDSL for the literature in Korean, CNKI in Chinese, and CiNii and J-STAGE written in Japanese. We excluded all review article and experimental studies, and only clinical studies using laser or light emitting diode (LED) for diabetic ulcer were selected. Results : A total twenty papers were selected. Different light sources were used as follows: LED, HeNe, InGaAlP, GaAlAs, GaAs, CO2, and KTP. The number of LED studies was 9, and HeNe laser was 7, and InGaAlP and GaAlAs laser was 2, GaAs, CO2, and KTP laser was 1 for each. Various energy density of the clinical study were reported. Conclusions : It is suggested that to select appropriate laser type and give the adequate output power to treat diabetic ulcer. Further evaluation and research for the condition of laser therapy to treat diabetic ulcers are warranted.

• Proceedings of the Korean Society of Crop Science Conference
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• 2017.06a
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• pp.3-3
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• 2017

The question of how to establish sustainable agricultural systems has become as prominent as questions related to water, energy and climate change. High input/high output agriculture has brought with it many adverse effects; the massive deterioration of soil and water in both quantity and quality, increased greenhouse gas emissions and an increased prevalence of unsafe foods. Additionally, urbanization and climate change has worsened the shortage of farmland and reduced the supply of agricultural water. Given these challenges, maintaining, conserving and efficiently using agri-environmental resources, through fostering of sustainable agriculture, have emerged as key tasks in solving these problems. What is needed therefore is research, based on systematic and comprehensive empirical analyses, that can propose plans and methods for establishing an appropriate sustainable agricultural system. The empirical analysis of sustainable agricultural system is approached separately from economic, environmental and social aspects. An analysis of environment effect reveals that the available phosphate level is 1.3~2.1 times greater than the optimal amount in rice paddies, upland fields and orchards. Further examination has revealed that the excess nutrient is polluting both ground water and surface water. Analytical results for economic feasibility show that factors of production have been invested heavily in the rice crop. Under these conditions, sustainable agriculture, including low-input agriculture, appears to be a possible alternative that will facilitate simultaneous improvements in both economic feasibility and environment effects. Analysis results for sociality reveal that social factors include the value of producer, association and interior networks. Social conditions are comprised of leadership, consumers' awareness, education and conflict solutions. In addition, analysis as to the degree investments contribute to improving agricultural value added has revealed that the direct payment program is the most effective instrument. Experts confirm that economic feasibility can be improved by scientific and well-reasoned nutrient management on the basis of soil testing. Farmers pointed to 'economic factors' as being the largest obstacle to switching to the practice of sustainable agriculture. They also indicate 'uncertainty with regards to sustainable agriculture technology' as an impediment to practicing sustainable agriculture. Even so, farmers who believe environmental and regional issues to be the most pressing problems have expanded their practice of sustainable agriculture. The keys to establishing sustainable agriculture system are classified into the following four aspects. Firstly, from an economic aspect, the research indicates that agricultural policy needs to be integrated with environmental policy and that the function of market making based on the value chain needs to be revitalized. Secondly, from an environmental aspect, there is a need for an optimal resource management system to be established in the agricultural sector. In addition, sustainable agriculture practice will need to be extended with attendant environmentally-friendly and sustainable intensive technology also requiring further development. Thirdly, from a social aspect, green agriculture management needs to be fostered, technology and education extended, and social conflict mediated. Lastly, from a governance aspect, it will be necessary to strengthen good governance, assign and share suitable roles and responsibilities, build a cooperation system and utilize community supported agriculture.