• 한국소음진동공학회논문집
• /
• 제13권5호
• /
• pp.334-340
• /
• 2003

Exponential window function Is widely used In impact hammer testing to reduce leakage error as well as to get a good S/N ratio. The larger its decaying rate is, the more effectively the leakage errors are reduced. But if the decay rate of the exponential window is too large, the FRF is distorted. And the modal parameters of the system can not be exactly identified by modal analysis technique. Therefore, it is a difficult problem to determine proper decay rate in impact hammer testing. In this paper, amount of the FRF distortion caused by exponential window is theoretically uncovered. A new circle fitting method is also proposed so that the modal parameters are directly extracted from impulse response spectrum distorted by the exponential-windowed impulse response data. The results by the conventional and proposed circle fitting method are compared through a numerical example.

• 한국정보디스플레이학회:학술대회논문집
• /
• 한국정보디스플레이학회 2003년도 International Meeting on Information Display
• /
• pp.710-713
• /
• 2003

The wall charge is major factor to determine the discharge characteristics. The minimum sustain voltage related to the wall charge decay were investigated as a function of aging time in AC plasma display panel. For the long time scale, the wall charge decay time is dependent on the aging time. The inverse time scale of the wall charge decay has the maximum value at around 3 hours aging time and then fell down.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2011년도 춘계학술대회 논문집
• /
• pp.791-796
• /
• 2011

In order to understand long range wave propagation in railway tracks, it is required to identify how far vibrations can travel along a rail. To answer this question, the attenuation characteristics of the main propagating waves are required as a function of distance. In this work, it is identified which wave types predominantly propagate on various regions of the rail cross-section. Then decay rates of propagating waves in railway tracks are investigated for frequencies up to 80 kHz. A numerical method called the Wavenumber Finite Element (WFE) method is utilized to predict dispersion curves and decay rates for a rail on a continuous foundation. In order to validate the simulated results, measurements have been performed on a test track and an operational railway track. The measured results are compared with the output of the simulations and good agreements are found between them.

• Journal of applied mathematics & informatics
• /
• 제42권3호
• /
• pp.695-708
• /
• 2024

In this paper we present a non-standard finite difference method for solving a fractional decay model. The proposed NSFDM is constructed by incorporating a non-standard denominator function, resulting in an explicit numerical scheme as easy as the conventional Euler method, but it provides very accurate solutions and has unconditional stability. Two examples from the literature are presented to demonstrate the performance of the proposed numerical scheme, which is compared to three methods from the literature. It is found that the method's estimated errors are extremely minimal, such as within the machine precision.

• Nuclear Engineering and Technology
• /
• 제26권4호
• /
• pp.453-460
• /
• 1994

암반(Porous Rock Matrix)과 균열(fracture)에서 일차원의 이동 방정식(Migration Equation)을 3-Member Decay Chain까지 화장하고, Laplace Transform을 이용하여 초기조건이 Delta Function과 Bateman Equation인 각각에 대해 해석해를 구한다. 그 해를 이용하여 Actinide Chain 중 4n＋1과 4n＋2 Chain에서 선택된 Np$^{241}$-U$^{233}$ -Th$^{229}$ 와 U$^{234}$ -Th$^{230}$ -Ra$^{226}$ Chain의 각 핵종들의 균열에서의 농도를 상대농도로 나타낸다. 이핵종들의 지연계수(Retardation Coefficient)는 화강암에 대한 것을 사용하여 균열에서의 농도 변화를 볼 수 있다. 본 연구에 의한 결과로는 U$^{233}$ , Th$^{229}$ , Th$^{230}$ Ra$^{226}$ 같은 핵종들은 비록 초기 inventory에는 작은 양일지라도 균열과 암반에서 모핵종의 붕괴(decay)에 의해 생기므로써 처분장으로부터 먼 거리에서는 중요한 핵종이 된다는 것을 알 수 있다.

• Applied Science and Convergence Technology
• /
• 제25권4호
• /
• pp.81-84
• /
• 2016

InP/InGaP quantum structures (QSs) grown on GaAs substrates by a migration-enhanced molecular beam epitaxy method were studied as a function of growth temperature (T) using photoluminescence (PL) and emission-wavelength-dependent time-resolved PL (TRPL). The growth T were varied from $440^{\circ}C$ to $520^{\circ}C$ for the formation of InP/InGaP QSs. As growth T increases from $440^{\circ}C$ to $520^{\circ}C$, the PL peak position is blue-shifted, the PL intensity increases except for the sample grown at $520^{\circ}C$, and the PL decay becomes fast at 10 K. Emission-wavelength-dependent TRPL results of all QS samples show that the decay times at 10 K are slightly changed, exhibiting the longest time around at the PL peak, while at high T, the decay times increase rapidly with increasing wavelength, indicating carrier relaxation from smaller QSs to larger QSs via wetting layer/barrier. InP/InGaP QS sample grown at $460^{\circ}C$ shows the strongest PL intensity at 300 K and the longest decay time at 10 K, signifying the optimum growth T of $460^{\circ}C$.

• Bulletin of the Korean Chemical Society
• /
• 제31권4호
• /
• pp.959-964
• /
• 2010

In this work, equilibrium molecular dynamics (MD) simulations in a microcanonical ensemble are performed to evaluate the friction coefficient of a Brownian particle (BP) in a Lennard-Jones (LJ) solvent. The friction coefficients are determined from the time dependent friction coefficients and the momentum autocorrelation functions of the BP with its infinite mass at various ratios of LJ size parameters of the BP and solvent, ${\sigma}_B/{\sigma}_s$. The determination of the friction coefficients from the decay rates of the momentum autocorrelation functions and from the slopes of the time dependent friction coefficients is difficult due to the fast decay rates of the correlation functions in the momentum-conserved MD simulation and due to the scaling of the slope as 1/N (N: the number of the solvent particle), respectively. On the other hand, the friction coefficient can be determined correctly from the time dependent friction coefficient by measuring the extrapolation of its long time decay to t=0 and also from the decay rate of the momentum autocorrelation function, which is obtained by time integration of the time dependent friction coefficient. It is found that while the friction coefficient increases quadratically with the ratio of ${\sigma}_B/{\sigma}_s$ for all ${\sigma}_B$, for a given ${\sigma}_s$ the friction coefficient increases linearly with ${\sigma}_B$.

• 천문학회지
• /
• 제53권2호
• /
• pp.49-57
• /
• 2020

We present numerical simulations of decaying hydrodynamic turbulence initially driven by solenoidal (divergence-free) and compressive (curl-free) drivings. Most previous numerical studies for decaying turbulence assume an isothermal equation of state (EOS). Here we use a polytropic EOS, P ∝ ρ^γ, with polytropic exponent γ ranging from 0.7 to 5/3. We mainly aim at determining the effects of γ and driving schemes on the decay law of turbulence energy, E ∝ t^-α. We additionally study probability density function (PDF) of gas density and skewness of the distribution in polytropic turbulence driven by compressive driving. Our findings are as follows. First of all, we find that even if γ does not strongly change the decay law, the driving schemes weakly change the relation; in our all simulations, turbulence decays with α ≈ 1, but compressive driving yields smaller α than solenoidal driving at the same sonic Mach number. Second, we calculate compressive and solenoidal velocity components separately and compare their decay rates in turbulence initially driven by compressive driving. We find that the former decays much faster so that it ends up having a smaller fraction than the latter. Third, the density PDF of compressively driven turbulence with γ > 1 deviates from log-normal distribution: it has a power-law tail at low density as in the case of solenoidally driven turbulence. However, as it decays, the density PDF becomes approximately log-normal. We discuss why decay rates of compressive and solenoidal velocity components are different in compressively driven turbulence and astrophysical implication of our findings.

• 한국지능시스템학회:학술대회논문집
• /
• 한국퍼지및지능시스템학회 2001년도 추계학술대회 학술발표 논문집
• /
• pp.137-140
• /
• 2001

In this paper, we design 75(Takagi-Sugeno) fuzzy controllers for the systems that can be represented by the 75 fuzzy model. We use inverse optimal approach in which the cost function is determined later than the Lyapunov function and its corresponding control input satisfying the design requirements such as stability and decay rate. The obtained design procedure is in the form of solving LMI(Linear Matrix Inequalities), thus very efficient in practice.

• 대한수학회지
• /
• 제61권2호
• /
• pp.377-393
• /
• 2024

In this paper, we study the positive solutions to a discrete harmonic function for a random walk satisfying finite range and ellipticity conditions, killed at the boundary of an unbounded cylinder in ℤ^d. We first prove the existence and uniqueness of positive solutions, and then establish that all the positive solutions are generated by two special solutions, which are exponential growth at one end and exponential decay at the other. Our method is based on maximum principle and a Harnack type inequality.