• Journal of applied mathematics & informatics
• /
• v.28 no.1_2
• /
• pp.193-207
• /
• 2010

In this paper, a predator-prey model with stage structure and distributed delay is investigated. Mathematical analyses of the model equation with regard to boundedness of solutions, nature of equilibria, permanence, extinction and stability are performed. By the comparison theorem, a set of easily verifiable sufficient conditions are obtained for the global asymptotic stability of nonnegative equilibria of the model. Taking the product of the per-capita rate of predation and the rate of conversing prey into predator as the bifurcating parameter, we prove that there exists a threshold value beyond which the positive equilibrium bifurcates towards a periodic solution.

• Journal of Mechanical Science and Technology
• /
• v.17 no.11
• /
• pp.1775-1783
• /
• 2003

The method of flame hole dynamics is demonstrated as a mean to simulate turbulent flame extinction. The core of the flame hole dynamics involves derivation of a random walk mapping for the flame holes, created by local quenching, between burning and quenched states provided that the dynamic characteristics of flame edges is known. Then, the random walk mapping is projected to a background turbulent field. The numerical simulations are carried out with further simplifications of flame string and unconditioned scalar dissipation rate. The simulation results show how the chance of partial quenching is influenced by the crossover scalar dissipation rate. Finally, a list of improvements, necessary to achieve more realistic turbulent flame quenching simulation, are discussed.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.1
• /
• pp.29-35
• /
• 2001

Radiation-induced oscillatory instability in CH$_4$/Air diffusion flames is numerically investigated by adopting detailed chemistry. Counterflow diffusion flame is employed as a model flamelet and optically thin gas-phase radiation is assumed. Attention is focused on the extinction regime induced by radiative heat loss, which occurs at low strain rate. Once a steady flame structure is obtained for a prescribed value of initial strain rate, transient solution of the flame is calculated after a finite amount of strain-rate perturbation is imposed on the steady flame. Depending on the initial strain rate and the amount of perturbed strain rate, transient evolution of the flame exhibits various types of flame-evolution behaviors. Basically, the dynamic behaviors can be classified into two types, namely oscillatory decaying solution and diverging solution leading to extinction.

• Journal of The Korean Astronomical Society
• /
• v.21 no.2
• /
• pp.155-171
• /
• 1988

We have examined how sensitively the extinction value determined by the method of star-count depends on such factors as the plate limit, the size of counting reseau, the non-linearity in the number distribution of stars with magnitude, and the angular resolution demanded by the given problem. We let the Poisson distribution portray the statistical nature of the countings, and chose the region containing the globule Barnard 361 as an example field. Uncertainties due to various combinations of the factors are presented in graphic forms: (1) Dynamic range in the extinction measurements is evaluated as a function of reseau size for varying plate limits. (2) Statistical errors involved in the star-count are analized in terms of the signal-to-noise ratio, the plate limit and the reseau size. (3) Systematic error due to the non-linearity in the number distribution are thoroughly analized. (4) Finally, a methodology is presented for correcting the systematic error in the observed radial density gradient. These graphs are meant to be used in selecting proper size of the reseau and in estimating errors inherent to the star-count analysis.

• Bulletin of the Korean Mathematical Society
• /
• v.53 no.1
• /
• pp.103-117
• /
• 2016

Abstract. In this paper, we study a modified stochastic predator-prey system with general ratio-dependent functional response. We prove that the system has a unique positive solution for given positive initial value. Then we investigate the persistence and extinction of this stochastic system. At the end, we give some numerical simulations, which support our theoretical conclusions well.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2006.05a
• /
• pp.275-278
• /
• 2006

Systematic experiments in $CH_4/Air$ counterflow diffusion flames diluted with He have been undertaken to study the oscillatory instability in which lateral heat loss could be remarkable at low global strain rate. The oscillatory instability arises for Lewis numbers greater than unity and occurs near extinction condition. The dynamic behaviors of extinction in this configuration can be classified into three modes; growing, harmonic and decaying oscillation mode near extinction. As the global strain rate decreases, the amplitude of the oscillation becomes larger. This is caused by the increase of lateral heat loss which ran be confirmed by the reduction of lateral flame size. Oscillatory edge flame instabilities at low global strain rate are shown to be closely associated with not only Lewis number but also heat loss (radiation and lateral heat loss).

• Fire Science and Engineering
• /
• v.27 no.6
• /
• pp.64-69
• /
• 2013

The Numerical simulation was performed on the flow field around the two-dimensional rectangular bluff body in order to simulate an engine nacelle fire and to complement the previous experimental results of the bluff body stabilized flames. Fire Dynamic Simulator (FDS) based on the Direct Numerical Simulation (DNS) was employed to clarify the characteristics of reacting flow around bluff body. The overall reaction was considered and the constant for reaction was determined from flame extinction limits of experimental results. The air used atmosphere and the fuel used methane. For both fuel ejection configurations against an oxidizer stream, the flame stability and flame mode were affected mainly by vortex structure near bluff body. In the coflow configuration, air velocity at the flame extinction limit are increased with fuel velocity, which is comparable to the experiment results. Comparing with the isothermal flow field, the reacting flow produces a weak and small recirculation zone, which is result in the reductions of density and momentum due to temperature increase by reaction in the wake zone.

• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.35D no.8
• /
• pp.53-61
• /
• 1998

Dynamic characteristics of widely tunable SGDBR/SSGDBR laser diodes integrated with an electroabsorption modulator is inestigated using an improved large-signal timef-domain model. First, wide tunning properties of a SGDBR laser diode and a SSGDBR laser diode are analyzed respectively and compared with each other. And, intensity-modulation characteristics of a SGDBR laser diode incorprating an electroabsorption modulator are investigated. It is shown that an external modulation has the lower frequency chirp by 1/20 for almost same extinction ratios than a direct modulation, and a nearly transform-limited pulse train can be generated using the optical gating of an electroabsorption modulator.

• Korean System Dynamics Review
• /
• v.14 no.4
• /
• pp.5-35
• /
• 2013

The study examines the play theory based internet rumor process by using simulating tools, Vensim, which offer a new theoretical basis from which to explore complex adaptive social system. Internet rumor is not a simple linear diffusion process, but a complex interaction behavior between the actors of production and diffusion. Rumor actors consist of two type of diffusion, which is rumor mongers and playful mongers. These two type of mongers make the internet rumor as collective system. Playful mongers play strategically to maximize playfulness. Internet rumor as play is consequence of collective framing constituted by dynamic interaction and playfulness. The networking space spreading internet rumor function as a playground which mobilize play rule, ignoring fact based framing. Rumor as paly, even though it turns out to be a false and loses the public attentions rumor sustains the game play function which makes the rumor without natural extinction. The study proves that playful mongers is a main actors in rumor play ground.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.1A
• /
• pp.11-15
• /
• 2006

A pre-amplified semiconductor optical amplifier-Mach-Zehnder interferometer(SOA-MZI) wavelength converter (WC) using a continuous wave-holding beam(CW-HB) is proposed and experimentally demonstrated at 10Gb/s. The proposed scheme achieves not only enhancement of input power dynamic range(IPDR) to over 20dB but also higher Q parameter of about 2 to 3 by no output signal distortion and higher extinction ratio(ER) of about 2dB to 5dB by low noise figure (NF), compared with the bias current control method.