• Korean Journal of Mathematics
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• v.18 no.3
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• pp.323-334
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• 2010

We give a theorem for the existence of at least three solutions for the fourth order elliptic boundary value problem with the square growth variable coefficient nonlinear term. We use the variational reduction method and the critical point theory for the associated functional on the finite dimensional subspace to prove our main result. We investigate the shape of the graph of the associated functional on the finite dimensional subspace, (P.S.) condition and the behavior of the associated functional in the neighborhood of the origin on the finite dimensional reduction subspace.

• Bulletin of the Korean Mathematical Society
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• v.54 no.3
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• pp.895-909
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• 2017

This paper is concerned with the following fourth-order elliptic equations $${\Delta}^2u-{\Delta}u+V(x)u-{\frac{k}{2}}{\Delta}(u^2)u=f(x,u),\text{ in }{\mathbb{R}}^N$$, where $N{\leq}6$, ${\kappa}{\geq}0$. Under some appropriate assumptions on V(x) and f(x, u), we prove the existence of infinitely many negative-energy solutions for the above system via the genus properties in critical point theory. Some recent results from the literature are extended.

• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.4
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• pp.374-378
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• 2014

PID control method usually has problems of overshoot and oscillation in high order control system, therefore, it is important to improve the control method so as to reduce the overshoot and oscillation. Based on MATLAB simulation, a permanent magnet (PM) DC servomotor control system is studied in this paper. The motor is modeled according to the universal motor theory, and with the help of the fourth order Ronge-Kutta method, its speed control is simulated and compared between two different dual closed-loops PWM control methods. This case study helps undergraduate students to better understand theories related to electrical engineering, such as electrical machinery, power electronics and control theory, as well as digital solution of state equations.

• Korean Journal of Mathematics
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• v.20 no.1
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• pp.125-135
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• 2012

We obtain the multiple solutions for the fourth order elliptic problem with a variable coefficient and a jumping semilinear term. We have a result that there exist at least two solutions if the variable coefficient of the semilinear term crosses some number of the eigenvalues of the biharmonic eigenvalue problem. We obtain this multiplicity result by applying the Leray-Schauder degree theory.

• Communications of the Korean Mathematical Society
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• v.37 no.1
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• pp.137-161
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• 2022

In this article, we study the existence and multiplicity of homoclinic solutions for the following fourth-order differential equation (1) u⁽⁴⁾(x) + ωu''(x) + a(x)u(x) = f(x, u(x)), ∀x ∈ ℝ where a(x) is not required to be either positive or coercive, and F(x, u) = ∫^u₀ f(x, v)dv is of subquadratic or superquadratic growth as |u| → ∞, or satisfies only local conditions near the origin (i.e., it can be subquadratic, superquadratic or asymptotically quadratic as |u| → ∞). To the best of our knowledge, there is no result published concerning the existence and multiplicity of homoclinic solutions for (1) with our conditions. The proof is based on variational methods and critical point theory.

• Structural Engineering and Mechanics
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• v.27 no.6
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• pp.773-776
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• 2007

• Earthquakes and Structures
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• v.16 no.3
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• pp.359-368
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• 2019

This paper focuses on the study of dynamic analysis of thick plates resting on Winkler foundation. The governing equation is derived from Mindlin's theory. This study is a parametric analysis of the reflections of the thickness / span ratio, the aspect ratio and the boundary conditions on the earthquake excitations are studied. In the analysis, finite element method is used for spatial integration and the Newmark-${\beta}$ method is used for the time integration. While using finite element method, a new element is used. This element is 17-noded and it's formulation is derived from using higher order displacement shape functions. C++ program is used for the analyses. Graphs are presented to help engineers in the design of thick plates subjected to earthquake excitations. It is concluded that the 17-noded finite element is used in the earthquake analysis of thick plates. It is shown that the changes in the aspect ratio are more effective than the changes in the aspect ratio. The center displacements of the reinforced concrete thick clamped plates for b/a=1, and t/a=0.2, and for b/a=2, and t/a=0.2, reached their absolute maximum values of 0.00244 mm at 3.48 s, and of 0.00444 mm at 3.48 s, respectively.

• Structural Engineering and Mechanics
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• v.68 no.3
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• pp.325-334
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• 2018

The Nonlinear dynamic response of a sandwich plate subjected to the low velocity impact is theoretically and experimentally investigated. The Hertz law between the impactor and the plate is taken into account. Using the Extended High Order Sandwich Panel Theory (EHSAPT) and the Ritz energy method, the governing equations are derived. The skins follow the Third order shear deformation theory (TSDT) that has hitherto not reported in conventional EHSAPT. Besides, the three dimensional elasticity is used for the core. The nonlinear Von Karman relations for strains of skins and the core are adopted. Time domain solution of such equations is extracted by means of the well-known fourth-order Runge-Kutta method. The effects of core-to-skin thickness ratio, initial velocity of the impactor, the impactor mass and position of the impactor are studied in detail. It is found that these parameters play significant role in the impact force and dynamic response of the sandwich plate. Finally, some low velocity impact tests have been carried out by Drop Hammer Testing Machine. The results are compared with experimental data acquired by impact testing on sandwich plates as well as the results of finite element simulation.

• Journal of Korea Multimedia Society
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• v.20 no.2
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• pp.420-428
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• 2017

In recent trends, the first age of digital device usage has been significantly getting low and the using frequencies for younger generation have been gradually increasing. Also, while there were more negative opinions of this trend in the past, the new idea is changing to more needs of training and approaches for children's sound using guidelines for digital device. In fact, people believe the new generation will face more advanced future, called the Fourth Industrial Revolution. The purpose of the paper is first to explain about the Jacques Lacan's concept of desire theory in order to understand the human's unconscious level through His desire theory. Second, the paper identifies how this unconscious level is affected to ethical aspects of new generations whose unconscious level are frequently and early exposed to digital media. Lastly, the paper will present the necessity of digital literacy education as well as future direction. Furthermore, the paper review for what is the ethics and positive guidelines of digital media for children who will become the future citizens in the era of the Fourth Industrial Revolution.

• Journal of Korean Library and Information Science Society
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• v.5
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• pp.1-31
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• 1978

This thesis is to discuss and prove the identity of the acts of the library and the character of the library which regards these as its objects. And this study is analyzed in view of per ceptual problems and scientific problems and scientific problems, in order to make clear the character of the acts of the library. In these processes, some basic propositions are extracted. First, culture can be found in arranged order. Second, human being can create culture by the acquisition of accmulated culture. Third, an individual is purposely related with culture. Fourth, culture is antonomous to mankind. And in this thesis, library science is defined as the systematic formation of mankind's pursuing acts, and to identify this definition, some theoretical models of library science have been offered as follows : Model I 1. Theory of making culture assets informative. 2. Theory of making culture assets empirical; that of imformation treatment. 3. Theory of medial acts of librarians. Model II 4. Theory of organic systems of libraries. Model III 5. Theory of guiding school activities. 6. Theory of extending the inhabitants' interests of communities. 7. Theory of a kind of resources in social improvement. Model IV 8. Theory of a means of principal approach to the succession of culture. In conclusion, this study is to prove that acts of libraries are the universal ones of those human being that are gualified to be the unique means to the creation of culture and, library science is a science that shapes concepts and rules to describe, to make explanation and to foretell these acts.