• Title, Summary, Keyword: time dependent coefficients

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Friction of a Brownian Particle in a Lennard-Jones Solvent: A Molecular Dynamics Simulation Study

  • Lee, Song-Hi
    • Bulletin of the Korean Chemical Society
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    • v.31 no.4
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    • pp.959-964
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    • 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 ${\sigma}_B$.

BLOW-UP PHENOMENA FOR A QUASILINEAR PARABOLIC EQUATION WITH TIME-DEPENDENT COEFFICIENTS UNDER NONLINEAR BOUNDARY FLUX

  • Kwon, Tae In;Fang, Zhong Bo
    • Journal of the Chungcheong Mathematical Society
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    • v.31 no.3
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    • pp.287-308
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    • 2018
  • This paper deals with blow-up phenomena for an initial boundary value problem of a quasilinear parabolic equation with time-dependent coefficient in a bounded star-shaped region under nonlinear boundary flux. Using the auxiliary function method and differential inequality technique, we establish some conditions on time-dependent coefficient and nonlinear functions for which the solution u(x, t) exists globally or blows up at some finite time $t^*$. Moreover, some upper and lower bounds for $t^*$ are derived in higher dimensional spaces. Some examples are presented to illustrate applications of our results.

Structure Borne Noise Analysis of a Flexible Body in Multibody System (다물체계내 유연체의 구조기인 소음해석)

  • 김효식
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.130-135
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    • 2003
  • This paper presents the method for structure borne noise analysis of a flexible body in multibody system. The proposed method is the superposition method using flexible muitibody dynamic analysis and finite element one. This method is executed in 3 steps. In the la step, time dependent quantities such as dynamic loads, modal coordinates ana gross body motion of the flexible body are calculated efficiently through flexible multibody dynamic analysis. And frequency response functions are computed using Fourier transforms of those time dependent quantities. In the 2$\^$nd/ step, acoustic pressure coefficients are obtained through structure-acoustic coupling analysis by finite element analysis. In the final step, frequency responses of acoustic pressure at the acoustic nodes are recovered through linear superposition of frequency response functions with acoustic pressure coefficients. The accuracy of the proposed method is verified in the numerical example of a simple car model.

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S-Domain Equivalent System for Electromagnetic Transient Studies PART I : Frequency Dependent Network Equivalent (전자기 과도현상 해석을 위한 S 영역 등가시스템 PART I : 주파수 의존 시스템 등가)

  • 왕용필
    • The Transactions of the Korean Institute of Electrical Engineers A
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    • v.52 no.11
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    • pp.632-638
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    • 2003
  • Modern power systems are very complex and to model them completely is impractical for electromagnetic transient studies. Therefore areas outside the immediate area of interest must be represented by some form of frequency dependent equivalent. The s-domain rational function form of frequency dependent equivalent does not need refitting if the simulation time-step is changed in the electromagnetic transient program. This is because the s-domain rational function coefficients are independent of the simulation time-step, unlike the z-domain rational function coefficients. S-domain rational function fitting techniques for representing frequency dependent equivalents have been developed using Least Squares Fitting(LSF). However it does not suffer the implementation error that exited in this work as it ignored the instantaneous term. This paper Presents the formulation for developing 1 Port Frequency Dependent Network Equivalent(FDNE) with the instantaneous term in S-domain and illustrates its use. This 1 port FDNE have been applied to the CIGRE Benchmark Rectifier test AC system. The electromagnetic transient package PSCAD/EMTDC is used to assess the transient response of the 1 port (FDNE) developed with Thevenin and Norton Equivalent network. The study results have indicated the robustness and accuracy of 1 port FDNE for electromagnetic transient studies.

BLOW-UP AND GLOBAL SOLUTIONS FOR SOME PARABOLIC SYSTEMS UNDER NONLINEAR BOUNDARY CONDITIONS

  • Guo, Limin;Liu, Lishan;Wu, Yonghong;Zou, Yumei
    • Journal of the Korean Mathematical Society
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    • v.56 no.4
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    • pp.1017-1029
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    • 2019
  • In this paper, blows-up and global solutions for a class of nonlinear divergence form parabolic equations with the abstract form of $({\varrho}(u))_t$ and time dependent coefficients are considered. The conditions are established for the existence of a solution globally and also the conditions are established for the blow up of the solution at some finite time. Moreover, the lower bound and upper bound of the blow-up time are derived if blow-up occurs.

LIE SYMMETRY ANALYSIS AND INVARIANT SOLUTIONS OF THE GENERALIZED FIFTH-ORDER KDV EQUATION WITH VARIABLE COEFFICIENTS

  • Wang, Gang-Wei;Liu, Xi-Qiang;Zhang, Ying-Yuan
    • Journal of applied mathematics & informatics
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    • v.31 no.1_2
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    • pp.229-239
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    • 2013
  • This paper studies the generalized fifth-order KdV equation with variable coefficients using Lie symmetry methods.Lie group classification with respect to the time dependent coefficients is performed. Then we get the similarity reductions using the symmetry and give some exact solutions.

Analysis Technique for Chloride Penetration in High Performance Concrete Behavior Considering Time-Dependent Accelerated Chloride Diffusivity (촉진염화물 확산계수의 시간의존성을 고려한 고성능 콘크리트의 염화물 침투 해석기법)

  • Kwon, Seung-Jun;Park, Sun-Gyu
    • Journal of the Korea Concrete Institute
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    • v.25 no.2
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    • pp.145-153
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    • 2013
  • Recently, accelerated chloride diffusion coefficients are used for an evaluation of chloride behavior. Similar as apparent diffusion coefficients, accelerated diffusion coefficients decrease with time. In this study, decrease in diffusion coefficient with time is simulated with porosity. Utilizing DUCOM-program, porosities from 15 mix proportions are obtained and diffusion coefficients are modelled with regression analysis of porosity for 270 days. Considering non-linear binding capacity which means the relation between free and bound chloride ion, chloride behavior in high performance concrete is evaluated. Through utilizing the previous test results for concrete under chlorides for 180 days, the applicability of the proposed technique is verified. The proposed technique is evaluated to reasonably predict the chloride behavior in concrete with various w/c (water to cement) ratios and mineral admixtures (GGBFS and FA). It is also shown that decrease in chloride diffusion should be considered for chloride prediction in concrete with mineral admixture since it has very clear decrease in diffusivity with time.

A Direct Integration Approach for the Estimation of Time-Dependent Boundary Heat Flux

  • Kim, Sin;Kim, Min-Chan;Kim, Kyung-Youn
    • Journal of Mechanical Science and Technology
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    • v.16 no.10
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    • pp.1320-1326
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    • 2002
  • In a one-dimensional heat conduction domain with heated and insulated walls, an integral approach is proposed to estimate time-dependent boundary heat flux without internal measurements. It is assumed that the expression of the heat flux is not known a priori. Hence, the present inverse heat conduction problem is classified as a function estimation problem. The spatial temperature distribution is approximated as a third-order polynomial of position, whose four coefficients are determined from the heat fluxes and the temperatures at both ends at each measurement. After integrating the heat conduction equation over spatial and time domain, respectively, a simple and non-iterative recursive equation to estimate the time-dependent boundary heat flux is derived. Several examples are introduced to show the effectiveness of the present approach.

A Study on the Temperature- and Field-Dependent Impact ionization for GaAs (GaAs임팩트이온화의 온도와 전계의존특성에 대한 연구)

  • 고석웅;유창관;김재홍;정학기;이종인
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • pp.460-464
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    • 2000
  • As device dimensions are lastly scaled down, impact ionization(I.I.) events are very important to analyze hot carrier transport in high energy region, and the exact model of impact ionization is demanded on device simulation. We calculate full band model by empirical pseudopotential method and the impact ionization rate is derived from modified Keldysh formula. We calculate impact ionization coefficients by full band Monte Carlo simulator to investigate temperature-and field-dependent characteristics of impact ionization for GaAs. Resultly impact ionization coefficients are In good agreement with experimental values at 300k. We know energy is increasing along increasing the field. while energy is decreasing along increasing the temperature since the phonon scattering rates for omission mode are very high at high temperature. The logarithmic fitting function of impact ionization coefficients is described as a second orders function for temperature and field. The residuals of the logarithmic fitting function are mostly within 5%. We know, therefore, logarithm of impact ionization coefficients has quadratic dependence on temperature and field, and we can save time of calculating the temperature- and field-dependent impact ionization coefficients.

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Speaker-Dependent Emotion Recognition For Audio Document Indexing

  • Hung LE Xuan;QUENOT Georges;CASTELLI Eric
    • Proceedings of the IEEK Conference
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    • pp.92-96
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    • 2004
  • The researches of the emotions are currently great interest in speech processing as well as in human-machine interaction domain. In the recent years, more and more of researches relating to emotion synthesis or emotion recognition are developed for the different purposes. Each approach uses its methods and its various parameters measured on the speech signal. In this paper, we proposed using a short-time parameter: MFCC coefficients (Mel­Frequency Cepstrum Coefficients) and a simple but efficient classifying method: Vector Quantification (VQ) for speaker-dependent emotion recognition. Many other features: energy, pitch, zero crossing, phonetic rate, LPC... and their derivatives are also tested and combined with MFCC coefficients in order to find the best combination. The other models: GMM and HMM (Discrete and Continuous Hidden Markov Model) are studied as well in the hope that the usage of continuous distribution and the temporal behaviour of this set of features will improve the quality of emotion recognition. The maximum accuracy recognizing five different emotions exceeds $88\%$ by using only MFCC coefficients with VQ model. This is a simple but efficient approach, the result is even much better than those obtained with the same database in human evaluation by listening and judging without returning permission nor comparison between sentences [8]; And this result is positively comparable with the other approaches.

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