• Journal of Elementary Mathematics Education in Korea
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• v.21 no.1
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• pp.1-22
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• 2017

The properties of arithmetic are considered as essential to understand the principles of calculation and develop effective strategies for calculation in the elementary school level, thanks to agreement on early algebra. Therefore elementary students' misunderstanding of the properties of arithmetic might cause learning difficulties as well as misconcepts in their following learning processes. This study aims to provide elementary teachers a part of pedagogical content knowledge about the properties of arithmetic and to induce some didactical implications for teaching the properties of arithmetic in the elementary school level. To do this, elementary school mathematics textbooks since the period of the first curriculum were analyzed. These results from analysis show which properties of arithmetic have been taught, when they were taught, and how they were taught. Based on them, some didactical implications were suggested for desirable teaching of the properties of arithmetic.

• Journal of Elementary Mathematics Education in Korea
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• v.21 no.4
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• pp.643-662
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• 2017

The first appearance of the equations in elementary school mathematics is in the expression of the equal sign in the addition sentences without its definition. Most elementary school students have operational understanding of the equal sign in equations. Moreover, students' opportunities to have a clear concept of the properties of operations are limited because they are used implicitly in the textbooks. Based on this fact, it has been argued that it is necessary to introduce the properties of operations explicitly in terms of specific numbers and to deal with various types of equations for understanding a relational meaning of the equal sign. In this study, we use equations to represent the implicit properties of operations and the relational meaning of the equal sign in elementary school mathematics with respect to students' level of understanding. In addition, we give some explicit examples which show how to apply them to make efficient computations.

• Applied Biological Chemistry
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• v.49 no.3
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• pp.196-201
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• 2006

Vitellogenin, which is found in the serum of female and male fishes exposed to environmental endocrine disrupter or estrogen hormone, is used as a biomarker for environmental contamination with an endocrine disrupter. In order to produce antibody against vitellogenin, a synthetic peptide for partial vitellogenin was injected into rabbits. In addition, by using ion exchange chromatography on DE-52, vitellogenin was purified from the serum of carp induced with $17{\beta}$-estradiol. Polyclonal antibody against purified vitellogenin reacted well with vitellogenin in the serum of carp induced with $17{\beta}$-estradiol and the serum of female carp, whereas polyclonal antibody against the vitellogenin peptide did not react with proteins in those samples. This may indicate that vitellogenin proteins, covalently modified largely, could not be detected by Western blotting with the polyclonal antibody against the synthetic vitellogenin peptide.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.6
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• pp.205-212
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• 2004

In this paper the design of a 1-[KVA] fuel cell powered line-interactive UPS system employing modular (fuel cell & DC/DC converter) blocks is proposed. The proposed system employs the two fuel cell modules along with suitable DC/DC converters and these modules share the DC-Link of the DC/AC inverter. A supercapacitor module is also employed to compensate for the instantaneous power fluctuations and to overcome the slow dynamics of the fuel processor. The energy stored in the supercapacitor can also be utilized to handle the overload conditions for a short time period. Due to the absence of batteries, the system satisfies the demand for an environmentally friendly and dean source of the energy. A complete design example illustrating the amount of hydrogen storage required for 1hr power outage, and sizing of supercacpacitor for transient load demand is presented for a 1-[KVA] UPS.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.4
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• pp.791-797
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• 2001

In this paper, high-speed ,large-capacity ATM switching-chip is developed by MCM technology. MCM technology is suited for light-weight portable communications, mobile computing, high-frequency applications. For test of the developed MCM switching-chips, the simulating model is made by VHDL code of previously developed chip and input-output values of modeling pattern are obtained through the simulation. After the pattern values in chip-test machine are inserted , their results are compared with the simulation results. The design in this paper is simulated by synopsys design tool using SUN workstation and functions of chip is measured by TRILLIUM machine. Simulated and measured results have been compared, showing close agreement. Last, the MCM technique presented in this paper will provide useful insight into future designs.

• Applied Chemistry for Engineering
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• v.19 no.3
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• pp.304-309
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• 2008

Cryptand series ion exchange resins were synthesized with 1-aza-12-crown-4 macrocyclic ligand attached to styrene (4 series dangerous matter) divinylbenzene (DVB) copolymer with crosslink of 1％, 2％, 4％ and 8％ by a substitution reaction. The synthesis of these resins was confirmed by content of chlorine, element analysis, electron micrograph, and IR-spectrum. The effects of pH, time, dielectric constant of solvent and crosslink on adsorption of uranium (${UO_2}^{2+}$) ion were investigated. The uranium ion showed a fast adsorption on the resins above pH 3. The optimum equilibrium time for adsorption of metallic ions was about two hours. The adsorption selectivity determined in ethanol was in increasing order uranium (${UO_2}^{2+}$) > nickel ($Ni^{2+}$) > gadolinium ($Gd^{3+}$) ion. The adsorption was in order of 1％, 2％, 4％, and 8％ crosslinked resin and adsorption of resin decreased in proportion to order of dielectric constant of solvents.

• The KIPS Transactions:PartD
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• v.16D no.4
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• pp.571-582
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• 2009

This paper provides a way to overcome limitations of general collaborative software development tools that completely restrict co-ownership of resources among individuals in a team oriented developmental environment. It also provides a solution for users to co-own resources and at the same time manage version control and collision problems that may occur due to the co-ownership of resources.The cooperative development support tool of developed software uses the conventional optimistic technique but employs the algorithm which is improved to reduce costs and efforts required for solving collision. The collaborative software development tool presented in this paper is made up of the classical client/server structure with the P2P(peer to peer) method which supports information exchange among individuals. This tool is developed based on open source software CVS(Concurrent Version System). Functional efficiency was confirmed by comparing it to the utility of prior existing collaborative software development tools.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.10
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• pp.1866-1874
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• 2008

Existing web server lowers the whole capacity of system because of the problem on the processing load of server by closing connection increasing code handshake operation, and remarkable decrease of server capacity if it is the state of overload. Also, there occurs disadvantages of increasing connection tine about client's request and response time because handling of client's multi-requests is not smooth because of thread block and it requests a lot of time and resources for revitalization of thread. Therefore, this paper proposes the extended web server which provides the technique for delay handling and improves the overload of server for better system capacity, communication support, and the unification which is the advantage of web service. And it evaluates the existing system(implemented at Tomcat 5.5) and the proposed mobile web server architecture. The extended server architecture provides excellent exchange condition for system capacity and evaluates improved web server architecture which combines multi-thread with thread pool. The proposed web service architecture in this paper got the better result of improved capacity benefit than the evaluation result of original Tomcat 5.5.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.29 no.2
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• pp.417-429
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• 2019

WPA2-PSK uses a 4-way handshake protocol based on a shared secret to establish a secure session between a client and an AP. It has various security problems such as eavesdropping attacks and the secure session establishment process is inefficient because it requires multiple interactions between client and AP. The WPA3 standard has recently been proposed to solve the security problem of WPA2, but it is a small improvement using the same 4-way handshake methodology. OAuth 2.0 token authentication is widely used on the web, which can be used to keep an authenticated state of a client for a long time by using tokens issued to an authenticated client. In this paper, we apply the dual-token based randomized token authentication technology to the Wi-Fi security protocol to achieve an efficient Wi-Fi security protocol by dividing initial authentication and secure session establishment. Once a client is authenticated and equipped with dual tokens issued by AP, it can establish secure session using them quickly with one message exchange over a non-secure channel.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.4
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• pp.300-308
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• 2019

For drones to be used for industrial or agricultural applications, it is necessary to increase the payload and endurance. Currently, the payload and endurance are limited by the battery technology for electric powered drones. In addition, charging or replacing the batteries may not be a practical solution at the field that requires near continuous operation. In this paper, a procedure to optimize the power system of an electric hybrid drone that consists of an internal combustion engine, a generator, a battery, and electric motors is presented. The example drone for crop dusting is sized for easy transportation with a maximum takeoff weight of 200 kg. The two main rotors that are mechanically connected to the internal combustion engine provides most of the lift. The drone is controled by four electric motors that are driven by the generator. By analyzing the flow of the energy, a methodology to select the optimum propeller and motor among the commercially available models is described. Then, a procedure of finding the optimum operational condition along with the proper gear reduction ratios for the internal combustion engine based on the test data is presented.