• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.1
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• pp.34-44
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• 1992

A numerical model using Hybrid Element Method(HEM) is presented for the prediction of wave agitations in a harbor which are induced by the intrusion and transformation of incident short-period waves. A linear mild-slope equation including bottom friction is used as the governing equation and a partial absorbing boundary condition is used on solid boundaries. Functional derived in the present paper is based on the Chen and Mei(1974)'s concept which uses finite element net in the inner region and analytical solution of Helmholtz equation in the outer region. Final simultaneous equations are solved using the Gaussian Elimination Method. The model appears to be reasonably good from the comparison of numerical calculation with hydraulic experimental results of short-wave diffraction through a breakwater gap(Pos and Kilner, 1987). The problem of requring large computational memory could be overcome using 8-noded isoparametric elements.

• Journal of Sensor Science and Technology
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• v.8 no.1
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• pp.1-9
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• 1999

A study has been made on the fabrication of a dual mode(a longitudinal and shear mode) ultrasonic sensor using a single PZT piezoelectric ceramic element. We investigated the mechanism of the dual mode sensor that generated both of the longitudinal and the shear waves simultaneously with the single PZT element. Through the analysis of analytic wave propagation equations, all the possible crystal cuts have been examined to determine appropriate Euler transformation angles for efficient excitations of the dual modes. We studied the performance of a PZT element as a function of its rotation angle so that its efficiency is optimized to excite the two waves of equal strength. Experimental examination of the waveform on a delay line(STS303) setup confirms that the ultrasonic sensor can transmit and detect both longitudinal and shear waves simultaneously.

• Journal of Information Technology Services
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• v.19 no.1
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• pp.145-158
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• 2020

With the development and widespread application of online shopping, the number of online consumers has increased. With one click of a mouse, people can buy anything they want without going out and have it sent right to the doors. As consumers benefit from online shopping, people are becoming more concerned about protecting their privacy. In the group buying scenario described in our paper, online shopping was regarded as intra-group communication. To protect the sensitive information of consumers, the polynomial-based encryption key sharing method (Piao et al., 2013; Piao and Kim, 2018) can be applied to online shopping communication. In this paper, we analyze security problems by using a polynomial-based scheme in the following ways : First, in Kamal's attack, they said it does not provide perfect forward and backward secrecy when the members leave or join the group because the secret key can be broken in polynomial time. Second, for simultaneous equations, the leaving node will compute the new secret key if it can be confirmed that the updated new polynomial is recomputed. Third, using Newton's method, attackers can successively find better approximations to the roots of a function. Fourth, the Berlekamp Algorithm can factor polynomials over finite fields and solve the root of the polynomial. Fifth, for a brute-force attack, if the key size is small, brute force can be used to find the root of the polynomial, we need to make a key with appropriately large size to prevent brute force attacks. According to these analyses, we finally recommend the use of a relatively reasonable hash-based mechanism that solves all of the possible security problems and is the most suitable mechanism for our application. The study of adequate and suitable protective methods of consumer security will have academic significance and provide the practical implications.

• Journal of the Korean School Mathematics Society
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• v.15 no.1
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• pp.53-80
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• 2012

This study was designed to find the characteristics of mathematical errors and discourse in simultaneous equations and inequalities for migrant students from North Korea. 5 sample students participated, who attended in an alternative school for the migrant students from North Korea at the study in Seoul, Korea. A total of 8 lesson units were performed as an extra curriculum activity once a week during the 1st semester, 2011. The results indicated that students showed technical errors, encoding errors, misunderstood symbols, misinterpreted language, and misunderstood Chines characters of Koreans and the discourse levels improved from the zero level to the third level, but the scenes of the third level did not constantly happen. Nevertheless, the components of discourse, explanation & justification, were activated and as a result, evaluation & elaboration increased in ERE pattern on communication.

• Structural Engineering and Mechanics
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• v.27 no.6
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• pp.713-739
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• 2007

Nowadays computers can perform symbolic computations in addition to mere number crunching operations for which they were originally designed. Symbolic computation opens up exciting possibilities in Structural Mechanics and engineering. Classical areas have been increasingly neglected due to the advent of computers as well as general purpose finite element software. But now, classical analysis has reemerged as an attractive computer option due to the capabilities of symbolic computation. The repetitive cycles of simultaneous - equation sets required by the finite element technique can be eliminated by solving a single set in symbolic form, thus generating a truly closed-form solution. This consequently saves in data preparation, storage and execution time. The power of Symbolic computation is demonstrated by six examples by applying symbolic computation 1) to solve coupled shear wall 2) to generate beam element matrices 3) to find the natural frequency of a shear frame using transfer matrix method 4) to find the stresses of a plate subjected to in-plane loading using Levy's approach 5) to draw the influence surface for deflection of an isotropic plate simply supported on all sides 6) to get dynamic equilibrium equations from Lagrange equation. This paper also presents yet another computationally efficient and accurate numerical method which is based on the concept of derivative of a function expressed as a weighted linear sum of the function values at all the mesh points. Again this method is applied to solve the problems of 1) coupled shear wall 2) lateral buckling of thin-walled beams due to moment gradient 3) buckling of a column and 4) static and buckling analysis of circular plates of uniform or non-uniform thickness. The numerical results obtained are compared with those available in existing literature in order to verify their accuracy.

• Journal of Microbiology and Biotechnology
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• v.9 no.5
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• pp.624-630
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• 1999

In order to investigate the position of various fatty acids attached to glycerol and the specificity of Lipolase-100T, hydrolysis of fish oil was carried out with Lipolase-100T derived from Aspergillus oryzae. The amounts of free fatty acids produced from triglyceride, 1,2(2,3)-diglyceride, 1,3-diglyceride, and 2-monoglyceride and conversion rates of 1,2(2,3)-diglyceride to 1,3-diglyceride and 2-monoglyceride to 1(3)-monoglyceride were also calculated. The ratio of 1,2-diglyceride content to 1,3-diglyceride was higher than 70 in the early period of hydrolysis. The fatty acid content of the glyceride mixture after 72 h of hydrolysis was compared with that of fish oil, and it was found that polyunsaturated fatty acids such as C16:4, C20:4 n-3, C20:5 n-3, C21:5 n-3, C22:5 n-3 and C22:6 n-3 were located in the 2-position of glycerol. Material balance of each component in the hydrolysis system was written to obtain a set of simultaneous linear equations. The theoretical quantity of free fatty acids produced from triglyceride, 1,2-diglyceride, 1,3-diglyceride, and monoglyceride, respectively, were calculated by solving the linear equation system. The conversion rate of 1,2(2,3)-diglyceride to 1,3-diglyceride and that of 2-monoglyceride to 1(3)-monoglyceride were also obtained. The results showed that the migration rate of 1,2(2,3)-diglyceride to 1,3-diglyceride was higher than the hydrolysis rate of 1,2(2,3)-diglyceride to 2-monoglyceride and the conversion rate of 2-monoglyceride to 1(3)-monoglyceride was extremely low.

• Journal of the Korean School Mathematics Society
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• v.3 no.2
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• pp.69-82
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• 2000

Mathematics is the subject that requires high mental function such as the ability of logically thinking and investigating. Because of the reason there exists much greater difference in students' individual scholastic abilities in mathematics class than in other classes. Recently many schools organize students into two or three level-based mathematics classes according to each student's level to solve the problem. But in spite of its many merits the new system of class organization has some problems. The problem which is pointed out as the most serious thing frequently is that many teachers still use the same textbook and the same teaching method for all students, not considering student's level. Obviously it causes the reduction of students' interest and motivation. In this point of view, I tried to solve such a problem by development and application of level learning materials reconstructed text book according to students' abilities and levels through this research. As the result of the research to examine the changes of students' emotional factors such as the recognition, interest, and attitude which influence on improving self-educability in learning mathematics has occurred, the following conclusion comes out. 1. Through the mathematics class utilizing level learning materials reconstructed textbook, students come to recognize that level learning materials are more effective than uniformed contents of the same textbook and get more active learning attitude. 2 The application of level learning materials in a level-based class has contributed to increasing students' interest in mathematics. Furthermore it was also effective in the positive changes of students' emotional factors such as the recognition, interest, and attitude which influence on improving self-educability in learning mathematics.

• Journal of Technology Innovation
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• v.24 no.3
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• pp.81-105
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• 2016

The purpose of this study is to estimate the cost-saving effect of R&D investment in the ICT industry. As is well known, the R&D investment induces both the product innovation and the process innovation, in turn leads the effect of creating profit and cutting cost. However, it appears that studies concerned with the cost-saving effect of R&D investment have been unproductive, while most existing studies concentrate on the topic involved with the creating profit of R&D investment. Therefore, we extend the effect of R&D investment to a framework of the cost-saving focusing on the ICT industry. To empirically analyze the effect, we built a simultaneous three-equation model comprising a translog cost function and two cost share equations, and employed the SUR analysis. As a result, we found out that the cost-saving effect on the total cost is statistically significant. In addition, we examined relationships between the R&D investment and each cost of production elements. The results show that on the one hand, the R&D investment and the intermediate good cost have the substitution relationship. On the other hand, the complementary relationship is observed between the R&D investment and each labor or capital cost.

• Transactions of the Korean Society of Automotive Engineers
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• v.23 no.2
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• pp.199-207
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• 2015

Solid materials of ammonia sources with SCR have been considered for the application of lean NOx reduction in automobile industry, to overcome complex problems of liquid urea based SCR. These solid materials produce ammonia gas directly with proper heating and can be packaged by compact size, because of high volumetric ammonia density. Among ammonium salts and metal ammine chlorides, calcium ammine chloride was focused on this paper due to low decomposition temperature. In order to make calcium ammine chloride in lab-scale, simple reactor and glove box was designed and built with ammonium gas tank, regulator, and sensors. Basic test conditions of charging ammonia gas to anhydrous calcium chloride are chosen from equilibrium vapor pressure by Van't Hoff plot based on thermodynamic properties of materials. Synthetic method of calcium ammine chloride were studied for different durations, temperatures, and pressures with proper ammonia gas charged, as a respect of ammonia gas adsorption rate(%) from simple weight calculations which were confirmed by IC. Also, lab-made calcium ammine chloride were analyzed by TGA and DSC to clarify decomposition step in the equations of chemical reaction. To understand material characteristics for lab-made calcium ammine chloride, DA, XRD and FT-IR analysis were performed with published data of literature. From analytical results, water content in lab-made calcium ammine chloride can be discovered and new test procedures of water removal were proposed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.2
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• pp.247-256
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• 1999

The leaky wave emanated from the dielectric-coated parallel-plate waveguide with finite periodic thick slot in its upper plate is investigated theoretically for H-polarization case. For this structure, fields in slot regions are expressed as a summation of the parallel-plate waveguide TM modes, and in other regions are expressed in the spectral domain by use of the inverse Fourier transform. Boundary conditions at the interfaces are enforced, and the simultaneous linear equations are derived. The influences of the slot width, slot thickness, thickness of a dielectric coating, and finite slot number on the radiation characteristics (phase constant, leakage constant, radiation pattern) are examined. The results of the finite periodic slot are compared with those of the infinite extent structure and good agreement has been found.