• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.15 no.1
• /
• pp.253-259
• /
• 2015

In this paper, we propose a transformer of alternating voltage source utilizing a semiconductor, operating in bidirectional fashion. Transformer is a device transferring energy by inductive coupling between its winding circuits. Conventional transformer is a device, composed of a primary coil and a secondary coil, transforming an alternating voltage. The system we propose is designed with a single circuit transforming the level of voltage signal in two ways; from the source to the load, and vice versa. For semiconductor switches, the NPN transistor is connected to the alternating voltage source terminal, and emitter terminal is connected to the inductor in the system as an energy storage element. The control signal is applied to the base terminal of the semiconductors. We have shown that the system we propose, by adopting only one circuit, drives an alternating voltage transformer that changes the amplitudes of voltage signal in reciprocal way.

• Korean Journal of Agricultural Science
• /
• v.44 no.4
• /
• pp.477-486
• /
• 2017

This review provides an overview of dietary nucleotides as an alternative to in-feed antibiotics for weaning pigs. Dietary nucleotides are composed of DNA or RNA molecules and are normally contained in protein-rich feed ingredient, brewer's yeast, yeast extract, and milk. Weaning pigs are suffering from several stresses, such as environmental challenges (i.e. crowding, transportation, and feeding). Such stressors can damage the intestinal epithelium and cause an invasion by Escherichia coli, secondary inflammatory responses, and post weaning diarrhea. To overcome weaning disorder, people often use antibiotics which reduce symptoms and boost growth performance. However, since antibiotics were banned due to concerns of antibiotic resistant bacteria, researchers are studying alternative materials to antibiotics. Dietary nucleotides are one of the alternative materials for replacing antibiotics and can be used in abnormal conditions, such as weaning diarrhea, low digestibility, and disease condition. Nucleotides have substances that have important roles in cell division and cell growth, affecting growth performance, intestinal condition, and immunological effect at the weaning stage. However, nucleotides' composition is very different between sources and this aspect makes it difficult to utilize nucleotides at the weaning stage. Therefore, this review paper focuses on i) the characteristics and functions of dietary nucleotides and ii) the effect of dietary nucleotides on the growth performance and immune system of pigs.

• Journal of Korean Library and Information Science Society
• /
• v.50 no.4
• /
• pp.405-428
• /
• 2019

This study discerned interactions that secondary students experience during their studies and information behaviors that explains their interactions. In addition, when young people collaborate with their friends, this study identified their actions, such as collecting, using, sharing, and generating information, and the social and cultural factors that influence the behavior. The research questions consisted of 'Radical Change Theory' focusing on the information behavior of the digital age youth and the type of radical change in the digital age. As a result of the research, the status of collaborative information behavior of middle and high school students was reflected in our educational reality. Students, however, approached and utilized various information sources, diversified their opinion sharing tools, and discovered channels that were different from adults and used them in information activities. Though not as anticipated, they suggested that the experience of collaboration helped the individual's growth.

• Economic and Environmental Geology
• /
• v.37 no.1
• /
• pp.99-106
• /
• 2004

Pollution reduction and/or control technology becomes one of the pressing post-semiconductor research field to lead an advanced industrial structure. Soil/groundwater remediation techniques may act as a core technology which will create many demands on pollution reduction areas. A plenty numbers of abandoned metal mines were left without any remediation action in Korea, and it may be potential sources of heavy metal and As contamination in the ecosystem. In order to bring this soil contamination to a settlement, the emerging soil/groundwater remediation techniques should be introduced. Main research topics in the United States and Europe move towards the clean remediation technology without any secondary impact and the feasible application of developing technique into the field scale study. With these advantages, several soil/groundwater techniques such as electrokinetic soil processing, permeable reactive barrier, stabilization/solidification, biosorption, soil flushing with biosurfactant, bioleaching and phytoremediation will be summarized in this paper.

• Health Policy and Management
• /
• v.7 no.1
• /
• pp.73-99
• /
• 1997

This study was carried out by using questionnaires with 126 insurance societies from Sept. 30, 1995 to Oct. 18, 1995. The primary data collected bythe survey have been significantly supplemented by secondary data obtained from sources such as health insurance statistical year books and internal data in the Ministry of Health and Wolfare. Major findings were summarized as follows: Two financial coordinating programs have significantly improved financial status of regional health insurance societies: the catastrophic program for high cost medical care that was initiated in 1991 and the program for hospitalization cost of the aged in 1995. Another finding is that there existed ambiguity and inconsistency of equity index that had been used by stabilization programs and its side effects could not be ignored. Regression analyses were made to identify factors that affect financial transfers. Inde pendent variables in the regression include utilization frequency, dependancy ration, insurance contribution per insured and medical expense per insured. All these variables were statistically significant in the equations of applying distribution rate (distribution/contribution) and transfer rate (transfer/contribution) as dependent variables. Policy suggestions for the catastrophic program for high cost medical care are modifying the definition of catastrophic case and setting the maximum amount of subsidies for each society based on distribution rates. To solve the problems of the financial coordinating program for the aged, we could consider reimbursing more than 50% of the copayment incurred by the aged 65 or more and determining the maximum amount of outpatient copayment at 10,000 Won per day or per visit for the elderly. More fundamental improvement could be made by amending the Welfare Benefit Act to establish and expand medical and welfare facilities for the elderly.

• Journal of Korean Society for Atmospheric Environment
• /
• v.31 no.1
• /
• pp.15-27
• /
• 2015

The collection of fine particulate matter samples was made at Gosan site of Jeju Island, one of the background sites of Korea, during a year of 2013, and their water-soluble ionic species were analyzed in order to examine the chemical compositions and pollution characteristics. The concentrations of $nss-SO_4{^{2-}}$, $NH_4{^{+}}$, $NO_3{^{-}}$, and $K^+$ had occupied 66.0% of water-soluble ionic species in $PM_{10}$, especially 94.3% in $PM_{2.5}$ fine mode, however the $nss-Ca^{2+}$ and $Na^+$ showed high concentrations in $PM_{10-2.5}$ coarse mode. $NO_3{^-}/nss-SO_4{^{2-}}$ concentration ratios in $PM_{10}$ and $PM_{10-2.5}$ were 0.30 and 0.13, showing less significant effect from automobile and local pollution sources. The sulfate and nitrate compounds were presumed to be long-range transported to Gosan area by the relatively high SOR and NOR values. The trajectory cluster analysis showed the higher concentrations of the major secondary pollutants ($nss-SO_4{^{2-}}$, $NO_3{^{-}}$, $NH_4{^{+}}$) and $nss-Ca^{2+}$ when the air masses had moved from China continent and Korean peninsula into Gosan area.

• Journal of Environmental Health Sciences
• /
• v.4 no.1
• /
• pp.47-50
• /
• 1977

This report is intended to describe as brief as possible the result of study on purity of the Korean Bee Honey. Purity of bee honey was measured by scaling the enzyme activities of two different honey groups: such as, the standard group and control group each including the samples of honey originated from the resource of acarcia, chestnut or miscellaneous origin. The samples of honey were collected from different sources: to wit, honey belonging to the standard group were collected from the township of Seoboo, Yangju county, Kyunggido province, Korea, while honey belonging to the control group were collected from the street side shops, market or the companies producing the secondary food from honey. The results of this study were summarized as follow: 1. It was found that honey belonging to the standard group contained less moisture than those belonging to the control group. Republic of Korea Ministry of Health and Social Affairs Food Control Regulation stipulates that honey must contain moisture less than 20%. The samples of' both groups contained moisture more than 20%, although honey belonging to the control group were relatively more so than honey belonging to the standard group. 2. Honey belonging to the standard group were found stronger in sugar reduction activities than those belonging to the control group. It was also noted that honey of acracia origin was strongest in reduction activities of the three different origin in the same group. 3. $\alpha$-Amylase and $\beta$-amylase were discovered to have activated more strongly in honey belonging to the standard group than those belonging to the control group. The enzyme activitie, varied depending on the origin of plant where honey comes from. For instance, honey of miscellaneous origin indicated the strongest activities in $\alpha$-amylase while honey of chestnut origirt indicated strongest in $\beta$-amylase.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.22 no.11
• /
• pp.918-924
• /
• 2009

In this paper, we designed micro-structured electromagnetic transducers for energy harvesting and verified the performance of proposed transducers using finite element analysis software, COMSOL Multiphysics. To achieve higher energy transduce efficiency, around the magnetic core material, three-dimensional micro-coil structures with high number of turns are fabricated using semiconductor fabrication process technologies. To find relations between device size and energy transduce efficiency, generated electrical power values of seven different sizes of transducers ($3{\times}3\;mm^2$, $6{\times}6\;mm^2$, $9{\times}9\;mm^2$, $12{\times}12\;mm^2$, $15{\times}15\;mm^2$, $18{\times}18\;mm^2$, and $21{\times}21\;mm^2$) are analyzed on various magnetic flux density environment ranging from 0.84 T to 1.54 T and it showed that size of $15{\times}15\;mm^2$ device can generate $991.5\;{\mu}W$ at the 8 Hz of environmental kinetic energy. Compare to other electromagnetic energy harvesters, proposed system showed competitive performance in terms of power generation, operation bandwidth and size. Since proposed system can generate electric power at very low frequency of kinetic energy from typical life environment including walking and body movement, it is expected that proposed system can be effectively applied to various pervasive computing applications including power source of embodied medical equipment, power source of RFID sensors and etc. as an secondary power sources.

• Journal of Power Electronics
• /
• v.18 no.5
• /
• pp.1595-1607
• /
• 2018

In this paper, a hierarchical control strategy is introduced to control a new three-port multidirectional DC-DC converter for integrating an energy storage system (ESS) to a bipolar DC microgrid (BPDCMG). The proposed converter provides a voltage-balancing function for the BPDCMG and adjusts the states of charge (SoC) of the ESS. Previous studies tend to balance the voltage of the BPDCMG buses with active sources or by transferring power from one bus to another. Furthermore, the batteries available in BPDCMGs were charged equally by both buses. However, this power sharing method does not guarantee efficient operation of the whole system. In order to achieve a higher efficiency and lower energy losses, a triple-layer hierarchical control strategy, including a primary droop controller, a secondary voltage restoration controller and a tertiary optimization controller are proposed. Thanks to the multi-functional operation of the proposed converter, its conversion stages are reduced. Furthermore, the efficiency and weight of the system are both improved. Therefore, this converter has a significant capability to be used in portable BPDCMGs such as electric DC ships. The converter modes are analyzed and small-signal models of the converter are extracted. Comprehensive simulation studies are carried out and a BPDCMG laboratory setup is implemented in order to validate the effectiveness of the proposed converter and its hierarchical control strategy. Simulation and experimental results show that using the proposed converter mitigates voltage imbalances. As a result, the system efficiency is improved by using the hierarchical optimal power flow control.

• Journal of Soil and Groundwater Environment
• /
• v.22 no.3
• /
• pp.10-17
• /
• 2017

In this study, the evolution and origin of major dissolved constituents of crystalline bedrock groundwater in a coastal area were evaluated using multivariate statistical and groundwater quality analyses. The groundwater types mostly belonged to the $Na(Ca)-HCO_3$ and $Ca-HCO_3$ types, indicating the effect of cation exchange. Stable isotopes of water showed two areas divided by first and secondary evaporative effects, indicating a pattern of rapid hydrological cycling. Saturation indices of minerals showed undersaturation states. Thus, the degree of evolution of groundwater is suggested as in the low to intermediate stage, based on field and laboratory analytical conditions. According to the principal component analysis (PCA) results, the chemical components of EC, $Ca^{2+}$, $Mg^{2+}$, $K^+$, $HCO_3{^-}$, $SO{_4}^{2-}$ (PCA 1), $F^-$ (PCA 3), $SiO_2$ (PCA 4), and $Fe^{2+}$ (PCA 5) are derived from various water-rock interactions. However, $NO_3{^-}$, $Na^+$, and $Cl^-$ (PCA 2) represented the chemical characteristics of both anthropogenic sources and natural sea spray.