• Journal of Korean Elementary Science Education
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• v.25 no.spc5
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• pp.485-494
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• 2007

The aims of this study were to investigate the differences of the proportion of misconceptions and the reasons for selecting responses related to questions about small living things between talented and average students. The study subjects were made up of three groups. They were a class of 37 talented elementary students in science attending J National University of Education, a class of 37 talented students in science attending J City Office of Education, and a class of 33 average students attending J City. A questionnaire was composed of 20 test questions for examination of concepts related to small living things. The data obtained in this study was analyzed using a statistical program. The major results were as follows: In general, the level of the scientific concepts possessed by the talented students was much higher than that of the average students, especially in question 14. The reasons for the misconceptions which were revealed through this study were classified into vagueness of the language used, hasty decision and deduction making, using the wrong analogical inference, mass communications (TV or internet) and experimental differences between individuals. In terms of the reasons for the selection of a given response, the talented students had also a higher frequency in the 'science books for children' category than the average students, indicating that various kinds of science books for children have an influence on the formation of concepts on small living things. The misconception proportion of male students was 5.4% higher than that of female students in mean frequencies of all questions, although the difference was not statistically significant except for question 4. Data from this study may help teachers involved in education for gifted students to reconsider their conceptions on small living things.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.10
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• pp.1499-1507
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• 2017

This paper presents an impact-based piezoelectric vibration energy harvester using a freely movable metal sphere and a piezoceramic fiber-based MFC (Macro Fiber Composite) as piezoelectric cantilever. The free motion of the metal sphere, which impacts both ends of the cavity in an aluminum housing, generates power across a cantilever-type MFC beam in response to low frequency vibration such as human-body-induced motion. Impacting force of the spherical proof mass is transformed into the vibration of the piezoelectric cantilever indirectly via the aluminum housing. A proof-of-concept energy harvesting device has been fabricated and tested. Effect of the indirect impact-based system has been tested and compared with the direct impact-based counterpart. Maximum peak-to-peak open circuit voltage of 39.8V and average power of $598.9{\mu}W$ have been obtained at 3g acceleration at 18Hz. Long-term reliability of the fabricated device has been verified by cyclic testing. For the improvement of output performance and reliability, various devices have been tested and compared. Using device fabricated with anodized aluminum housing, maximum peak-to-peak open-circuit voltage of 34.4V and average power of $372.8{\mu}W$ have been obtained at 3g excitation at 20Hz. In terms of reliability, housing with 0.5mm-thick steel plate and anodized aluminum gave improved results with reduced power reduction during initial phase of the cyclic testing.

• Journal of KIISE
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• v.44 no.10
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• pp.1005-1018
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• 2017

Recently, virtualization has become an essential component of cloud computing due to its various strengths, including maximizing server resource utilization, easy-to-maintain software, and enhanced data protection. However, since virtualization allows sharing physical resources among the VMs, the system performance can be deteriorated due to device contentions. In this paper, we first investigate the I/O overhead based on the number of VMs on the same server platform and analyze the block I/O process of the KVM hypervisor. We also propose an in-memory block cache mechanism, called QBic, to overcome I/O virtualization latency. QBic is capable of monitoring the block I/O process of the hypervisor and stores the data with a high access frequency in the cache. As a result, QBic provides a fast response for VMs and reduces the I/O contention to physical devices. Finally, we present a performance measurement of QBic to verify its effectiveness.

• KIISE Transactions on Computing Practices
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• v.23 no.10
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• pp.605-610
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• 2017

In distributed environments, dynamic partitioning is needed to resolve the load on a particular server or the load caused by communication among servers. In heterogeneous environments, existing dynamic partitioning schemes can distribute the same load to a server with a low physical performance, which results in a delayed query response time. In this paper, we propose a dynamic partitioning scheme for large RDF data in heterogeneous environments. The proposed scheme calculates the query loads with its frequency and the number of vertices used in the query for load balancing. In addition, we calculate the server loads by considering the physical performance of the servers to allocate less of a load to the servers with a smaller physical performance in a heterogeneous environment. We perform dynamic partitioning to minimize the number of edge-cuts to reduce the traffic among servers. To show the superiority of the proposed scheme, we compare it with an existing dynamic partitioning scheme through a performance evaluation.

• Korean Journal of Human Ecology
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• v.10 no.1
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• pp.101-111
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• 2001

The purpose of this study was to investigate using and evaluative criteria for purchasing of sleepwear in winter. Subjects were 523 males and females aged from twenties to fifties, living in Chongju and Taejon. For data analysis, frequency, descriptive analysis, t-test, and F-test were used. The results are as follows. First, the ownership of sleepwear was sweat suits with zippered top, pajamas, T-shirts/pants, underwear, and nightgown in order. The mean of using sweat suits was used the highest, and subjects used more home wear than sleepwear in winter. Second, the using or sleepwear had a significant difference in cold-sensitiveness and body types. Cold-sensitive group used sweat suit and T-shirts/pants more than cold-insensitive group. Also, groups who are thin wore sweat suit the most while groups who are corpulent, used underwear the most when they slept. Third, subjects, who are married women and use bed, used nightgown, but pajamas were used by groups who are older, married, and professional. Sweat suits and T-shirts/pants were used the most by single aged twenties. Forth, consumers considered the wearing comfort when they purchased sleepwear for winter, and they evaluated washing/management, fabric, design/style, economic, service, brand, and others' response in order, for judging the quality of sleepwear. Also, the evaluative criteria had a significant difference in demographic variables such as sex, occupation, and marital state. These results implied that sleepwear would be needed for winter in terms of behavioral temperature regulation. Especially, cold-sensitive and thin group would wear knitted and two-piece sleepwear for thermal comfort when they sleep in winter. Also, Using and evaluative criteria of sleepwear would be different in demographic characteristics. For winter, sleepwear should be develop based on physiologic as well as demographic variables.

• Korean Journal of Human Ecology
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• v.20 no.1
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• pp.257-271
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• 2011

The purpose of this study is to provide basic data that is necessary for planning an adequate environment for various child-care activities and programs by recognizing the environmental characteristics of a group room, where children's activities take place. A survey was conducted of 257 childcare centers and 544 teachers all over the country, including only those of which that have opened after year 2000 with more than 20 children capacities. The survey period was from January 18th to 28th of 2010. The data was analyzed using SPSS WIN 15 software, calculating the data's frequency, percentage, $x^2$, multiple response analysis, F-test, and factor analysis. The results of this study led us to the following conclusions. 1) We would like to propose a group room space design varying by the room size, so that interesting and diverse activities can take place after taking account of the child's development and childcare centers program. 2) Group room space and facilities should be made of proper finishing materials, various materials with differing textures, and lighting for the kinds of childcare activities that gives various sensational experiences and comfortable feelings to the children. 3) Teachers with higher age and education tend to believe that child's competence and a homelike atmosphere are important factors in a group room environment.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.6
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• pp.105-112
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• 2003

Diode rectifier which can't be controlled output voltage and phase control converter as AC/DC converter have low power factor and harmonics of lower order in the line current. In this paper, three phase PWM(Pulse Width Modulation) AC/DC boost converter is studied to solve these problems. The characteristics of a proposed converter are to control the phase of current without current sensor as a very simple control algorithm using circuit parameters only and to apply sinusoidal PWM method with fixed switching frequency due to a difficult design of input filter and switching device. We simulate for the proposed algorithm that high power factor is achieved and DC link voltage has fast dynamic response without ripple in rectifying and regenerating operation. As a result of experiment with circuit parameter(inductor, capacitor) decided in simulation, the proposed converter had high power factor and reduction of low order harmonics as against diode rectifier.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.3C
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• pp.59-63
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• 2005

We propose non-DC-free generalized PRML (GPRML) that are suppressed DC contents for matching to the response of perpendicular magnetic recording channel with a ring-head. In addition, DC-free encoding is considered to prevent low-frequency disturbances. The SNR performance is obtained by combining the various PRML channels with DC-free and non-DC-free codes during the normalized recording density increases from 2.5 to 3.5. The GPRML detections without using DC-free code get SNR gains more than 1dB compared to the conventional PRML systems at 10/sup -5/BER. We confirmed that the rate 127/136 DC-free coded GPRML systems show good performances compared with the 16/17 non-DC-free coded GPRML systems. In results, DC-free coded GPRML detections get gains about 1.4dB and 2.0dB at the density of 3.3 and 3.5, respectively.

• Journal of Power Electronics
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• v.18 no.5
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• pp.1315-1324
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• 2018

A novel three-phase four-wire inverter topology is presented in this paper. This topology is equipped with a special capacitor balance grid without magnetic saturation. In response to unbalanced load and unequal split DC-link capacitors problems, a qusi-full-bridge DC/DC topology is applied in the balance grid. By using a high-frequency transformer, the energy transfer within the two split dc-link capacitors is realized. The novel topology makes the voltage across two split dc-link capacitors balanced so that the neutral point voltage ripple is inhibited. Under the condition of a stable neutral point voltage, the three-phase four-wire inverter can be equivalent to three independent single phase inverters. As a result, the three-phase inverter can produce symmetrical voltage waves with an unbalanced load. To avoid forward transformer magnetic saturation, the voltages of the primary and secondary windings are controlled to reverse once during each switching period. Furthermore, an improved mode chosen operating principle for this novel topology is designed and analyzed in detail. The simulated results verified the feasibility of this topology and an experimental inverter has been built to test the power quality produced by this topology. Finally, simulation results verify that the novel topology can effectively improve the inhibition of an inverter with a three-phase unbalanced load while decreasing the value of the split capacitor.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.3
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• pp.218-223
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• 2016

This study examined the order of the Butterworth filter for the correlation on the sensitivity of the receiver in the receiver of an optical system. In the general case, the sensitivity of the receiver is increased if the order of the filter was increased more. This is because increasing the order of the filter response of the normalized frequency of the filter is similar to the rectangular wave. For that reason, the method used to increase the order of the filter increases the sensitivity of the receiver. On the other hand, a method of increasing the order of the filter and makes the system complicated increases the cost of the system. This study examined the correlation between the order of the sensitivity of the receiver filter and to configure the system by simply looking for ways to reduce the cost of the system. The simulation results showed that increasing the order of the filter resulted in a receiver that can determine if the sensitivity is raised. In addition, the order of the Butterworth filter range that does not reduce the sensitivity of the receiver was 2. Therefore, it will be possible to implement an inexpensive optical system of the receiver using the data from this study.