• Title/Summary/Keyword: diffusion motion

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Numerical Simulation of Buoyant Diffusion Flame (부력을 받는 확산화염에 대한 수치 시뮬레이션)

  • Oh, Chang-Bo;Lee, Eui-Ju
    • Proceedings of the Korea Institute of Fire Science and Engineering Conference
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    • 2008.04a
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    • pp.234-237
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    • 2008
  • A direct numerical simulation (DNS) code suitable for the prediction of buoyant jet diffusion flames was developed in this study. The thermodynamic and transport properties were evaluated using CHEMKIN package to enhance the prediction performance of the developed DNS code. A two dimensional simulations were performed for the jet diffusion flames in normal and zero-gravity conditions where the Froude numbers are 5 and infinity, respectively. The simulated buoyant jet diffusion flame in normal gravity showed that the unsteady and dynamic motion although the reynolds number is low (400). It was identified that the flame in normal gravity flickered periodically. The periodic motion of the flame disappeared in zero-gravity condition. The dynamic motion of the buoyant jet diffusion flame could be well understood by comparing the flame structures obtained by the simulations of normal and zero-gravity conditions.

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Development of the intermittency turbulence model for a plane jet flow (자유 평면 제트유동 해석을 위한 간혈도 난류모델의 개발)

  • 조지룡;정명균
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.3
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    • pp.528-536
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    • 1987
  • In a turbulent free shear flow, the large scale motion is characterized by the intermittent flow which arises from the interaction between the turbulent fluid and the irrotational fluid of the environment through the mean velocity gradient. This large scale motion causes a bulk convection whose effect is similar to the spatial diffusion process. In this paper, the total diffusion process is proposed to be approximated by weighted sum of the bulk convection due to the large scale motion and the usual gradient diffusion due to small scale motion. The diffusion term in conventional .kappa.-.epsilon. model requires on more equation of the intermittency transport equation. A production term of this equation means mass entrainment from the irrotational fluid to the turbulent one. In order to test the validity of the proposed model, a plane jet is predicted by this method. Numerical results of this model is found to yield better agreement with experiment than the standard .kappa.-.epsilon. model and Byggstoyl & Kollmann's model(1986). Present hybrid diffusion model requires further tests for the check of universality of model and for the model constant fix.

THE LOCAL TIME OF THE LINEAR SELF-ATTRACTING DIFFUSION DRIVEN BY WEIGHTED FRACTIONAL BROWNIAN MOTION

  • Chen, Qin;Shen, Guangjun;Wang, Qingbo
    • Bulletin of the Korean Mathematical Society
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    • v.57 no.3
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    • pp.547-568
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    • 2020
  • In this paper, we introduce the linear self-attracting diffusion driven by a weighted fractional Brownian motion with weighting exponent a > -1 and Hurst index |b| < a + 1, 0 < b < 1, which is analogous to the linear fractional self-attracting diffusion. For the 1-dimensional process we study its convergence and the corresponding weighted local time. As a related problem, we also obtain the renormalized intersection local time exists in L2 if max{a1 + b1, a2 + b2} < 0.

Identifying the Diffusion Patterns of Movies by Opening Strength and Profitability (개봉 규모와 수익성에 따른 영화의 분류와 확산 패턴 분석)

  • Kim, Taegu;Hong, Jungsik
    • Journal of Korean Institute of Industrial Engineers
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    • v.39 no.5
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    • pp.412-421
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    • 2013
  • Motion picture industry is one of the most representative fields in the cultural industry and has experienced constant growth both worldwide and within domestic markets. However, little research has been undertaken for diffusion patterns of motion pictures, whereas various issues such as demand forecasting and success factor analysis have been widely explored. To analyze diffusion patterns, we adopted extended Bass model to reflect the potential demand of movies. Four clusters of selected movies were derived by k-means clustering method with criteria of opening strength and profitability and then compared by their diffusion patterns. Results indicated that movies with high profitability and medium opening strength are most significantly influenced by word of mouth effect, while low profitability movies display nearly monotonic decreasing diffusion patterns with noticeable initial adoption rates and relatively early peak points in their runs.

GLOBAL COUPLING EFFECTS ON A FREE BOUNDARY PROBLEM FOR THREE-COMPONENT REACTION-DIFFUSION SYSTEM

  • Ham, Yoon-Mee
    • Journal of the Korean Mathematical Society
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    • v.43 no.3
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    • pp.659-676
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    • 2006
  • In this paper, we consider three-component reaction-diffusion system. With an integral condition and a global coupling, this system gives us an interesting free boundary problem. We shall examine the occurrence of a Hopf bifurcation and the stability of solutions as the global coupling constant varies. The main result is that a Hopf bifurcation occurs for global coupling and this motion is transferred to the stable motion for strong global coupling.

Edge Enhancement due to Diffusion Effect in Magnetic Resonance Imaging (MR 영상에서 확산현상에 의한 경계강조)

  • Hong, I.K.;Ro, Y.M.;Cho, Z.H.
    • Proceedings of the KOSOMBE Conference
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    • v.1995 no.11
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    • pp.124-127
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    • 1995
  • Due to the self-diffusion of nuclear spins, the edge of phantoms is enhanced in the magnetic resonance imaging (MRI), especially in the case of microscopy [1]. According to several published works, theory has been established that the edge enhancement is caused by the motion narrowing around bounded regions due to diffusions of nuclear spins during data acquisition. It is found, however, that the signal decreases due to the diffusion attenuation and image is distorted as edge of the image is sharpened. In this paper, we wilt investigate this signal loss during data acquisition and its effects on image, i.e., image edge enhancement due to the diffusion phenomenon. This result is new and different from the previously discussed edge enhancement due to the diffusion, namely, by motion narrowing effect or spin bouncing effect at the boundary.

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Development of Web-Based Simulation Program Using the Randomwalk Theory (Randomwalk 이론을 이용한 Web 기반 동영상 프로그램의 개발)

  • Kim, Sung Geun;Kim, Ju Rae;Woo, Kyu Whan
    • Journal of the Korean Chemical Society
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    • v.43 no.4
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    • pp.469-474
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    • 1999
  • In this study, the simulation program using the randomwalk model is developed. Generally, students in the chemistry class have some difficulties to understand the motion of atomic particles or molecules. And then, they have many mis-conceptions about the motion of molecules. This program expressed by the computer simulations using the randomwalk theory may help students to understand visually the process of molecular motion. This program can be used easily, because it is based on Web by application of JAVA languages. The program consists of two parts. One is 'Diffusion' program, expressing the process of molecular diffusion as a computer simulation. Another is 'Randomwalk' program, expressing the trajectory of molecular motion to help the students to follow the random motion virtually.

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A Study on Particle Diffusion to Develop Faraday Cup Array of Particle Beam Mass Spectrometer System (Faraday cup array 개발을 위한 Particle Beam Mass Spectrometer 시스템 내에서의 입자 확산 연구)

  • Mun, Ji-Hun;Shin, Yong-Hyun;Kim, Tae-Sung;Kang, Sang-Woo
    • Particle and aerosol research
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    • v.8 no.1
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    • pp.29-35
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    • 2012
  • The Faraday cup electrode of different size has been developed and evaluated to investigate the diffusion effect of particles by Brownian motion in a particle beam mass spectrometer(PBMS). Particles which focused and accelerated by aerodynamic lens are charged to saturation in an electron beam, and then deflected electrostatically into a Faraday cup detector for measurement of the particle current. The concentration of particles is converted from currents detected by Faraday cup. Measurements of particle current as a function of deflection voltage are combined with measured relationships between particle velocity and diameter, charge and diameter, and mass and diameter, to determine the particle size distribution. The particle currents were measured using 5, 10, 20, 40 mm sized Faraday cup that can be move to one direction by motion shaft. The current difference for each sizes as a function of position was compared to figure out diffusion effect during transport. Polystyrene latex(PSL) 100, 200 nm sized standard particles were used for evaluation. The measurement using 5 mm sized Faraday cup has the highest resolution in a diffusion distance and the smaller particles had widely diffused.

Minimum Density Power Divergence Estimator for Diffusion Parameter in Discretely Observed Diffusion Processes

  • Song, Jun-Mo;Lee, Sang-Yeol;Na, Ok-Young;Kim, Hyo-Jung
    • Communications for Statistical Applications and Methods
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    • v.14 no.2
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    • pp.267-280
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    • 2007
  • In this paper, we consider the robust estimation for diffusion processes when the sample is observed discretely. As a robust estimator, we consider the minimizing density power divergence estimator (MDPDE) proposed by Basu et al. (1998). It is shown that the MDPDE for diffusion process is weakly consistent. A simulation study demonstrates the robustness of the MDPDE.

A mathematical model of blood flow and convective diffusion processes in constricted bifurcated arteries

  • Chakravarty S.;Sen S.
    • Korea-Australia Rheology Journal
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    • v.18 no.2
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    • pp.51-65
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    • 2006
  • Of concern in the present theoretical investigation is the study of blood flow and convection-dominated diffusion processes in a model bifurcated artery under stenotic conditions. The geometry of the bifurcated arterial segment having constrictions in both the parent and its daughter arterial lumen frequently appearing in the diseased arteries causing malfunction of the cardiovascular system, is constructed mathematically with the introduction of suitable curvatures at the lateral junction and the flow divider. The streaming blood contained in the bifurcated artery is treated to be Newtonian. The flow dynamical analysis applies the two-dimensional unsteady incompressible nonlinear Wavier-Stokes equations for Newtonian fluid while the mass transport phenomenon is governed by the convection diffusion equation. The motion of the arterial wall and its effect on local fluid mechanics is, however, not ruled out from the present model. The main objective of this study is to demonstrate the effects of constricted flow characteristics and the wall motion on the wall shear stress, the concentration profile and on the mass transfer. The ultimate numerical solutions of the coupled flow and diffusion processes following a radial coordinate transformation are based on an appropriate finite difference technique which attain appreciable stability in both the flow phenomena and the convection-dominated diffusion processes.