• Journal of the Korean Mathematical Society
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• v.48 no.2
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• pp.223-240
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• 2011

In this paper, the problem on periodic solutions of the bidirectional associative memory neural networks with both periodic coefficients and periodic time-varying delays is discussed. By using degree theory, inequality technique and Lyapunov functional, we establish the existence, uniqueness, and global asymptotic stability of a periodic solution. The obtained results of stability are less restrictive than previously known criteria, and the hypotheses for the boundedness and monotonicity on the activation functions are removed.

• Journal of the Korean Mathematical Society
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• v.41 no.4
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• pp.747-754
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• 2004

In this paper we investigate the existence and uniqueness of almost periodic and pseudo almost periodic solution for nonlinear differential equation with reflection of argument. For the case of almost periodic forced term, we consider the frequency modules of the solutions.

• Journal of the Chungcheong Mathematical Society
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• v.34 no.1
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• pp.55-60
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• 2021

In this paper we deal with the preservation of the periodic shadowing property of induced hyperspatial systems. More precisely, we show that an expansive system has the periodic shadowing property if and only if its induced hyperspatial system has the periodic shadowing property.

• Journal of Institute of Control, Robotics and Systems
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• v.5 no.7
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• pp.800-807
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• 1999

A Periodic disturbance canceller is proposed to compensate for the periodic disturbance due to cutting process in a CNC machining center. The periodic disturbance canceller estimates the Periodic disturbance without phase delay. This is achieved by using linear phase low-pass filter and frequency response reciprocal filter of plant at the frequency of the periodic disturbance. This method is implemented in the position control system of the CNC machining center with general disturbance compensators in order to compensate for both the frictional force and the periodic disturbance. The experimental results are described to show its effectiveness.

• Journal of computational fluids engineering
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• v.16 no.3
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• pp.52-58
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• 2011

This study investigates the bifurcation sequence to chaos in a horizontal annulus with a constant heat flux wall. After the first Hopf bifurcation from a steady to a simple time-periodic flow with a fundamental frequency, quasi-periodic flows with two or three incommensurable frequencies appear. A reverse transition from a quasi-periodic flow to a simple periodic flow is observed with increase of Rayleigh number. And finally, chaotic convection is established after appearance of three incommensurable frequencies at a high Rayleigh number. Simple periodic flows exist between quasi periodic flows. The transition route to chaos of the present simulations follows the Ruelle-Takens route.

• Bulletin of the Korean Mathematical Society
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• v.61 no.1
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• pp.195-205
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• 2024

In this paper, we consider the set of periodic shadowable points for homeomorphisms of a compact metric space, and we prove that this set satisfies some properties such as invariance and being a G_δ set. Then we investigate implication relations related to sets consisting of shadowable points, periodic shadowable points and uniformly expansive points, respectively. Assume that the set of periodic points and the set of periodic shadowable points of a homeomorphism on a compact metric space are dense in X. Then we show that a homeomorphism has the periodic shadowing property if and only if so is the restricted map to the set of periodic shadowable points. We also give some examples related to our results.

• Journal of applied mathematics & informatics
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• v.10 no.1_2
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• pp.277-282
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• 2002

In this paper we shall discuss the relationship between almost periodic fuzzy mappings and the properties of convergence theorems, and some results of almost periodic fuzzy mappings.

• Journal of the Korean Mathematical Society
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• v.38 no.4
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• pp.853-881
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• 2001

Multiplicity for doubly-periodic solutions and Dirichlet-Periodic solutions are treated.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.2
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• pp.196-203
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• 2015

In order to apply cylindrical periodic array to phased array antenna or frequency selective surface, efficient electromagnetic analysis is required. Finite periodic array is applied in real situation. But, generally, assumed that periodic structure is arranged infinitely, approximate electromagnetic characteristics can be obtained efficiently. But, difference of characteristics between real structure and approximate structure occurs because finite periodic array is approximated to infinite periodic array. Therefore, comparison and analysis of cylindrical infinite array and finite array are required. In this paper, cylindrical infinite periodic array are analyzed using cylindrical Floquet harmonics. Also, cylindrical finite periodic array is analyzed using method of moments (MoM) with thin wire approximation because periodic structures which are composed of strip with narrow width are analyzed. Transmission characteristics and surface currents of infinite and finite periodic structures are compared.

• The Korean Journal of Physiology
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• v.29 no.2
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• pp.225-232
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• 1995

The present study was conducted to evaluate the effect of phorbol 12,13-dibutyrate (PDBu) on the contraction of rabbit jugular vein in vitro. PDBu concentrations of greater than 10 nM induced a periodic contraction which was composed of rapid contraction, plateau and slow relaxation. The frequency of periodic contraction increased as PDBu concentration increased. The PDBu-induced contraction was inhibited by staurosporine (100 nM), it was not changed by tetrodotoxin $(1\;{\mu}M).$ In $Ca^{2+}$-free medium, PDBu induced a sustaining contraction, but not periodic contraction. Addition of $Ca^{2+}$ to medium evoked periodic contraction which was inhibited by nifedipine, PDBu concentrations of greater than $0.1\;{\mu}M$ increased ^{45}Ca^{2+}$ uptake without changing $^{45}Ca^{2+}$ efflux. Charybdotoxin and apamin, $Ca^{2+}$-activated K^{+}$ channel blockers, did not affect the PDBu-induced periodic contraction, whereas tetraethylammonium (TEA) abolished the periodicity. Pinacidil $(10\;{\mu}M).$, a potassium channel activator, blocked PDBu induced periodic contraction, which was recovered by glybenclamide $(10\;{\mu}M).$. In high potassium solution, PDBu did not produce the periodic contraction. These results suggest that the PDBu-induced periodicity of contraction is modulated by voltage dependent $Ca^{2+}$ channel and ATP-sensitive $K^{+}$ channel.