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Ko, W.,Ahn, I. Academic Press 2013 Journal of mathematical analysis and applications Vol.397 No.1
This paper is a continuation of Ko and Ahn (2013) [1], which investigates the stability at all non-negative equilibria and long time behavior of solutions for a ratio-dependent reaction-diffusion system incorporating one prey and two competing predator species under homogeneous Neumann boundary conditions. We examine the nonexistence and the appearance of stationary patterns in the time-independent system. In achieving these, we deal with the system only when the competition state between two competing predators is weak/strong. In particular, the results explain the phenomenon of a stationary pattern being induced by the introduction of a new predator species in the one-prey and one-predator system with no stationary pattern.
Analysis of ratio-dependent food chain model
Ko, W.,Ahn, I. Academic Press 2007 Journal of mathematical analysis and applications Vol.335 No.1
In this paper, a food chain model with ratio-dependent functional response is studied under homogeneous Neumann boundary conditions. The large time behavior of all non-negative equilibria in the time-dependent system is investigated, i.e., conditions for the stability at equilibria are found. Moreover, non-constant positive steady-states are studied in terms of diffusion effects, namely, Turing patterns arising from diffusion-driven instability (Turing instability) are demonstrated. The employed methods are comparison principle for parabolic problems and Leray-Schauder Theorem.
Online Gain Tuning Method of Roll Force AGC in Hot Strip Mills by Using Fuzzy Logic
Kow LEE, Young,Jin JANG, Yu,Woo KIM, Sang Institute of Electronics, Information and Communic 2007 IEICE transactions on fundamentals of electronics, Vol.90 No.6
<P>Gains of a roll force AGC (Automatic Gain Controller) have been calculated at the first locked-on-time by FSU (Finishing-mill Set-Up model) in hot strip mills and usually these values are not adjusted during the operating time. Consequently, this conventional scheme cannot cope with the continuous variation of system parameters and circumstance, though the gains can be changed manually with the aid of experts to prevent a serious situation such as inferior mass production. Hence, partially uncontrolled variation still remains on delivery thickness. This paper discusses an effective online algorithm which can adjust the gains of the existing control system by considering the effect of time varying variables. This algorithm improves the performance of the system without additional cost and guarantees the stability of the conventional system. Specifically, this paper reveals the major factors that cause the variation of strip and explores the relationship between AGC gains and the effects of those factors through the analysis of thickness signal which occupy different frequency bands. The proposed tuning algorithm is based on the above relationship and realized through ANFIS (Adaptive-Neuro-based Fuzzy Interface System) which is a very useful method because its fuzzy logics reflect the experiences of professionals about the uncertainty and the nonlinearity of the system. The effectiveness of the algorithm is shown by several simulations which are carried out by using the field data of POSCO corporation (South Korea).</P>
Mathematical Problem-Solving Heuristics Used by Secondary 2 Students
Kai Kow Joseph Yeo 대한사고개발학회 2006 The International Journal of Creativity & Problem Vol.16 No.2
Heuristics or heuristic strategies refers to specific tactics, such as guess and check or modeling, which are used by students to solve non-routine problems for which they do not have a readily accessible procedure that determines the solution. The aim of this study was to find out the heuristics used by the Secondary 2 students to solve non-routine problems. A total of 621 Secondary 2 students from ten seconda-ry schools in Singapore participated in the study. The study showed that the heu-ristics used by the Secondary 2 students to solve the problems were “guess and check”, “modeling”, “logical reasoning”, “use of algebra”, “use of formula”, “look for a pattern”, and “number manipulation”.