• 한국전산유체공학회:학술대회논문집
• /
• 2009.11a
• /
• pp.164-169
• /
• 2009

Study on swimming of microorganisms like, sperm motility, cilia beating, bacterial flagellar propulsion has found immense significance in the field of biological fluiddynamics. Because of the complexity involved, it is challenging for the researchers to model such problems. Immersed boundary method has proved its efficacy in the field of biological fluiddynamics, The present work aims at performing a numerical study on the microorganism locomotion using the immersed boundary method proposed by Peskin[1]. A two-dimensional model of the microorganism is modeled as thin elastic filament described as a sine wave. The neutrally buoyant organism undergoing deformations is immersed in a viscous and incompressible fluid. The fluid quantities are described using Eulerian coordinates and the immersed body is represented by Lagrangian coordinates. The Eulerian and Lagrangian variables are connected by the Dirac delta function. The Navier-Stokes equations governing the fluid flow are solved using the fractional step method on a staggered Cartesian grid system. The developed numerical code in FORTRAN will be validated by comparing the numerical results with the available results.

• Journal of the Korean Mathematical Society
• /
• v.41 no.5
• /
• pp.773-793
• /
• 2004

We consider a system of particles with locations { $X_{i}$ $^{n}$ (t):t$\geq$0,i＝1,…,n} in $R^{d}$ , time-varying weights { $A_{i}$ $^{n}$ (t) : t $\geq$0,i ＝ 1,…,n} and weighted empirical measure processes $V^{n}$ (t)＝1/n$\Sigma$$_{i=1}$$^{n}$ $A_{i}$ $^{n}$ (t)$\delta$ $X_{i}$ $^{n}$ (t), where $\delta$$_{x}$ is the Dirac measure. It is known that there exists the limit of { $V_{n}$ } in the week* topology on M( $R^{d}$ ) under suitable conditions. If { $X_{i}$ $^{n}$ , $A_{i}$ $^{n}$ , $V^{n}$ } satisfies some diffusion equations, applying Ito formula, we prove a central limit type theorem for the empirical process { $V^{n}$ }, i.e., we consider the convergence of the processes η$_{t}$ $^{n}$ ≡ n( $V^{n}$ -V). Besides, we study a characterization of its limit.t.

• Journal of Korean Philosophical Society
• /
• v.105
• /
• pp.269-290
• /
• 2008

The purpose of this paper is to explore the possibility of backwards causation. For study, this paper was divided into four views as follows: The first view was sometimes suggested by the people such as M. Dummett who distinguished observers from behaviors. According to observers' view, backwards causation is impossible, whereas behaviors' view possible. However, in a real or genuine sense, it is incorrect for us to argue for impossibility of backwards causation from the observer aspect. The second view was supported by J. H. Schmidt. He analyzed the possibility of backwards causation in terms of macro and micro level analysis about the causal events. According to micro level analysis, backwards causation is possible, but macro level analysis impossible. Usually the latter makes the former something miraculous. Under the macro level analysis, backwards causation, at first, seems to be miraculous phenomena which belongs to the micro level analysis. The third view had to do with physical equation, and the fourth view physical phenomena, respectively. John Earman argued for the backwards causation by the transformation from Lorentz­-Dirac equation to a second-order integro-differential one in the field of electrodynamic acceleration. His argument was criticized because of his misunderstanding about the relationship between two equations. On the other hand, Phil Dowe defended a version of Reichenbach's own theory about the direction of causation founded on the fork asymmetrical causal relation. However his view was different from Reichenbach's because the former defended the backwards causation model of Bell phenomena in quantum mechanics. On the contrary, Reichenbach put stressed on the priority of cause in the causal process. Subjectivism has recently been defended by H. Price, under the label of perspectivism. According to him, in a certain sense causal asymmetry is not in the world, but is rather a product of our own asymmetric perspective on the world. He also suggested causal net, the symmetry of microphysics, and so on. As mentioned above, there are many kind of suggestions of backwards causation. However none of them replaced objectively the main streams of the direction of causal process. The main stream has been usually defended by pragmatical ground. That is, effects do not precede their causes although causes cannot be without their effects.