• Journal of applied mathematics & informatics
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• v.29 no.1_2
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• pp.475-483
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• 2011

In this paper, we study the oscillatory and asymptotic behavior of a class of second order nonlinear differential inequality with perturbation and establish several theorems by using classification and analysis, which develop and generalize some known results.

• Molecules and Cells
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• v.43 no.3
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• pp.276-285
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• 2020

Circadian rhythm is an endogenous oscillation of about 24-h period in many physiological processes and behaviors. This daily oscillation is maintained by the molecular clock machinery with transcriptional-translational feedback loops mediated by clock genes including Period2 (Per2) and Bmal1. Recently, it was revealed that gut microbiome exerts a significant impact on the circadian physiology and behavior of its host; however, the mechanism through which it regulates the molecular clock has remained elusive. 3-(4-hydroxyphenyl)propionic acid (4-OH-PPA) and 3-phenylpropionic acid (PPA) are major metabolites exclusively produced by Clostridium sporogenes and may function as unique chemical messengers communicating with its host. In the present study, we examined if two C. sporogenes-derived metabolites can modulate the oscillation of mammalian molecular clock. Interestingly, 4-OH-PPA and PPA increased the amplitude of both PER2 and Bmal1 oscillation in a dose-dependent manner following their administration immediately after the nadir or the peak of their rhythm. The phase of PER2 oscillation responded differently depending on the mode of administration of the metabolites. In addition, using an organotypic slice culture ex vivo, treatment with 4-OH-PPA increased the amplitude and lengthened the period of PER2 oscillation in the suprachiasmatic nucleus and other tissues. In summary, two C. sporogenes-derived metabolites are involved in the regulation of circadian oscillation of Per2 and Bmal1 clock genes in the host's peripheral and central clock machineries.

• Journal of applied mathematics & informatics
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• v.3 no.2
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• pp.169-182
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• 1996

This paper presents the numerical experiment of a dis-cretized loaded cable with periodic forcing. There appeared to be var-ious type of nonlinear oscillations over a wide range of fequencies and amplitudes for the periodic forcing term. The same forcing term can give rise to large or small oscillation by solving initial value problem and observing the solutions after a long time.

• Korean Journal of Optics and Photonics
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• v.23 no.2
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• pp.77-86
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• 2012

The connection between the continuousness of Rabi oscillation and the discontinuity of quantum jumps has long remained one of the conceptual difficulties since the discovery of the quantum physical paradigm. In this study, however, we demonstrate that the behavior of the atom-field composite system gradually changes from the continuous Rabi interaction to the discontinuous quantum jumps as the atom-field coupling strength is reduced. The reduction occurs through enlarging the quantization volume of the mode so that the mode approaches one of the infinitely many modes of the thermal background.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.5
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• pp.367-372
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• 2000

The film-type specimen of poly ethylene terephthalate (PET) was stepwise elongated under tension with various speed range of about 0.5~500 mm/min, and then the necking behavior during its plastic deformation was observed. When elongated at the speed range of about 20~100 mm/min, stress oscillation was apparently occurred in the stress-strain curve. When elongated at the speed range of about 200~500 mm/min, stress oscillation was not did. The transparent/opaque zone and cross-section area in the specimen elongated at the speed of about 50 mm/min were examined using the optical microscopy and scanning electron microscopy. The corrosion characteristic of the specimen elongated at the speed of about 50 mm/min in 3.8 M NaOH alkali solution was examined using the optical microscopy.

• Journal of Power Electronics
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• v.19 no.1
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• pp.307-315
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• 2019

Condition monitoring has been recognized as an effective and low-cost method to enhance the reliability and improve the maintainability of power electronic converters. In power electronic converters, high-frequency oscillation occurs during the switching transients of power transistors, which is known as ringing. The ringing frequency mainly depends on the values of the parasitic capacitance and stray inductance in the oscillation loop. Although circuit stray inductance is an important factor that leads to the ringing, it does not change with transistor aging. A shift in either the inside inductance or junction capacitance is an important failure precursor for power transistors. Therefore, ringing frequency can be used to monitor the health of power transistors. However, the switching actions of power transistors usually result in a dynamic behavior that can generate oscillation signals mixed with background noise, which makes it hard to directly extract the ringing frequency. A frequency extraction method based on empirical mode decomposition (EMD) and Fast Fourier transformation (FFT) is proposed in this paper. The proposed method is simple and has a high precision. Simulation results are given to verify the ringing analysis and experimental results are given to verify the effectiveness of the proposed method.

• Nuclear Engineering and Technology
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• v.27 no.6
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• pp.853-858
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• 1995

The initial condition of a core transient should be consistent with real core state for the simulation of the core tansient. The initial xenon distribution, which can not be measured in the core, has a significant effect on the transient with xenon dynamics. In the simulation of the transient starting from non-equilibrium xenon state, the accurate initialization of the non-equilibrium xenon distribution is essential for the prediction of the core transient behavior. In this study, a xenon initialization method to predict the core transient more accurately was developed through the equivalent pre-xenon-oscillation which represents the tenon oscillation before the transient and verified by the application of the simulation for a startup test of Yonggwang Unit 3.

• Polymer(Korea)
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• v.39 no.3
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• pp.359-364
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• 2015

A self-oscillating interpenetrating polymer network (IPN) poly(acrylic acid)/poly(ethylene glycol) (PAA/PEG) hydrogel was prepared by using radical polymerization with a two-step method. The IPN hydrogel was characterized by FTIR spectroscopy and morphological analysis. The results indicated that the chains of PEG and PAA twined to form porous structure which is beneficial to water molecules entering inside of the hydrogel. In addition, the pH-responsive behavior, salt sensitivity, swelling/de-swelling oscillatory behaviors and self-oscillation in a closed pH oscillator were also studied. The results showed that the prepared hydrogel exhibited pH-sensitivity, good swelling/de-swelling reversibility and excellent salt sensitivity. The self-oscillating behavior of swelling/de-swelling for the prepared hydrogel was caused by pH alteration coupled with the external media. This study may create a new possibility as biomaterial including new self-walking actuators and other related devices.

• The Journal of the Korea institute of electronic communication sciences
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• v.7 no.4
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• pp.855-859
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• 2012

This study derives a generalized PSD formula in the LTV phase noise theory for noisy oscillators. The derived formula analytically proves that the LTV phase noise theory can predict the conservation of the power in the noisy oscillation signals. Additionally, the derived formula allows the theory to account for the behavior of the power spectrum over the entire frequency range including the regions around higher harmonics as well as fundamental frequency.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.05a
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• pp.296-303
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• 2002

Tribology, in other words, interacting surfaces in relative motion, is essential in life. The relative motion on surfaces may cause some problems with heat, vibration, noise, and so on. Unwanted vibrations by friction, which may arise during the operation of machines, are costly in terms of reduction of performance and service life. All these phenomena inolve stick-slip. The telescopic boom operations involves stick-slip oscillations like slideways. Unwanted stick-slip oscillations on telescopic boom operations cannot achieve smooth sliding and many developers of that machine makes a lot of effort to remove or reduce it. So this paper presents stick-slip oscillation with pressure of the hydraulic cylinder which drives booms, and attempts a theoretical approach for the numerical analysis for its stick-slip condition.