• Journal of applied mathematics & informatics
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• 제29권1_2호
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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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• 제43권3호
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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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• 제3권2호
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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.

• 한국광학회지
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• 제23권2호
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• pp.77-86
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• 2012

양자물리학적 패러다임이 발견된 이래, 라비(Rabi) 진동과 같은 전자(electron)의 에너지 준위 간 연속적인 천이(transition)와 보어(Bohr) 모형으로 대표되는 불연속적 양자 도약(quantum jump)의 상충성(incompatibility)은 현재까지도 서로 자연스럽게 연결하기가 어려운 오랜 개념적 어려움으로 남아 있다. 본 연구에서는 그러나, 빛과 물질의 상호작용을 기술하는 현대적 이론 중의 하나인 양자궤적이론(quantum trajectory theory)의 관점에서 단일 모드 공진기 장(single mode cavity field)과 상호작용하는 단일 원자의 행동을 관찰한 바, 원자-장 간 상호작용의 강도(strength)가 줄어듦에 따라서 원자의 행동이 연속적 라비 진동으로부터 불연속적 양자도약의 양상으로 점진적으로 변화하여 가는 과정을 발견하고, 이 단순하면서도 흥미로운 현상에 대하여 보고한다.

• 한국결정성장학회지
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• 제10권5호
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• pp.367-372
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• 2000

필름형 poly ethylene terephthalate(PET)를 0~1000 mm/min의 속도로 단계적으로 연신시켰을 때, 플라스틱 변형이 일어나면서 형성되는 넥킹 거동을 조사하였다. 필름형 시편을 약 20~100 mm/min의 속도로 연신시켰을 때, 얻어진 응력-변형 곡선에서 응력 진동이 뚜렷하게 발생하였지만, 약 200~500 mm/min의 속도로 연신시켰을 때, 응력 진동이 발생하지 않았다. 약 50 mm/min의 속도로 연신된 시편에서 투명/불투명 존 및 단면을 광학 현미경과 주사형 전자 현미경으로 관찰하였다. NaOH 알칼리 용액 내에서 약 50 mm/min의 속도로 연신된 시편의 부식 특성을 광학 현미경으로 관찰하였다.

• Journal of Power Electronics
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• 제19권1호
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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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• 제27권6호
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• pp.853-858
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• 1995

노심 천 이 현상의 모사계산을 위해서는 노심상태 의 초기조건을 실제노심과 일치시켜야 하는데 특히, 제논동특성이 관심의 대상이 되는 천이현상에 있어서는 직접적인 추정이 불가능한 노심내 제논분포의 초기상태가 천이현상의 해석결과에 커다란 영향을 미치게 된다 초기상태의 노심이 정확히 제논 평형상태에 있지 않는 경우 노심의 시간에 따른 변화를 잘 예측하기 위해서는 비평형 제논분포를 모사하는 초기화가 필수적이다. 본 연구에서는 천이현상 이전에 관측된 비평형 제논진동을 등가 제논진동으로 모사하여 천이현상을 보다 정확히 예측할 수 있는 제논 초기화 기법을 개발하였으며 영광 3, 4호기 시운전 시험에서 입수된 실측자료를 통하여 그 적용성을 입증 하였다.

• 폴리머
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• 제39권3호
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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.

• 한국전자통신학회논문지
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• 제7권4호
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• pp.855-859
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• 2012

본 연구에서는 선형시변 발진기 위상잡음 이론에 있어서 전력 스펙트럼 밀도식의 일반화된 형태를 유도한다. 유도된 전력 스펙트럼 밀도식을 바탕으로 선형시변 발진기 위상잡음 이론은 발진 신호의 전력 보존성을 예측할 수 있음을 본 연구에서 증명한다. 게다가, 유도된 전력 스펙트럼 밀도식은 선형시변 발진기 위상잡음 이론이 기본 주파수와 그 하모닉을 포함하는 전 주파수 영역에 걸친 전력 스펙트럼의 특성을 설명 할 수 있게 한다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 제35회 춘계학술대회
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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.