• Macromolecular Research
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• 제8권2호
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• pp.59-65
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• 2000

We simulated the conformational changes of polymethacrylates which have side chains with different lengths (methyl and butyl) by molecular dynamics simulation technique. Bulk states of atactic amorphous polymers relaxed at a higher temperature were generated. The chain behaviors of polymethacrylates were investigated upon varying temperatures. Molecular structural information was then obtained by characterizing radial distribution function(RDF), mean square displacement, self diffusion constant, and Connolly surfaces, among others. The estimated self diffusion constants and RDF values of PMMA and PBMA were found to be in good agreement with our expectation in view of the chain flexibility.

• 한국수학교육학회지시리즈B:순수및응용수학
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• 제15권3호
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• pp.329-342
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• 2008

There have been many experimental and observational evidences which indicate the predator response to prey density needs not always monotone increasing as in the classical predator-prey models in population dynamics. Holling type functional response depicts situations in which sufficiently large number of the prey species increases their ability to defend or disguise themselves from the predator. In this paper we investigated the stability and instability property for a Holling type predator-prey system of a generalized form. Hopf type bifurcation properties of the non-diffusive system and the diffusion effects on instability and bifurcation values are studied.

• Bulletin of the Korean Chemical Society
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• 제21권6호
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• pp.577-582
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• 2000

Interdiffusion process at interfaces of chemically identical polymers (e.g., deuterated-nondeuterated pairs) with different molecular weights or polymers with similar physical properties, is studied here by varying the diffusion time. Considering the vacancy flux ($J_v$) and adopting the Cahn-Hilliard interracial energy in describing this system, we can see that the variation of the interfacial composition profile with time is asymetric and the interface moves towards the polymer with the lower molecular weight as interdiffusion progresses. Furthermore, interface shift $\Delta\chi$, which characterizes the interdiffusion between polymers, agrees well with the behaviors of the existing experimental data. We can also obtain the interface shift factor C, which can be converted into values of $D_s$ (self-diffusion coefficient of the smaller molecules), from the slopes of the linear fits to the data of the interface shift.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.232-232
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• 2012

The doping of semiconducting elements is essential for the development of silicon quantum dot (QD) solar cells. Especially the doping elements should be activated by substitution at the crystalline sites in the crystalline silicon QDs. However, no analysis technique has been developed for the analysis of the activated dopants in silicon QDs in $SiO_2$ matrix. Secondary ion mass spectrometry (SIMS) is a powerful technique for the in-depth analysis of solid materials and the impurities analysis of boron and phosphorus in semiconductor materials. For the study of diffusion behaviour of B and P by SIMS, Si/$SiO_2$ multilayer films doped by B or P were fabricated and annealed at high temperatures for the activated doping of B and P. The distributions of doping elements were analyzed by SIMS. Boron found to be preferentially distributed in Si layer rather than the $SiO_2$ layer. Especially the B in the Si layers was separated to two components of an interfacial component and a central one. The central component was understood as the activated elements. On the other hand, phosphorus did not show any preferred diffusion.

• 대한기계학회논문집B
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• 제21권4호
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• pp.486-493
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• 1997

Experimental investigations on the comparison of developments between transient jets and evolving jet diffusion flames have been made in initial injection period. To achieve this experiment, an ignition technique using a residual flame as the ignition source is devised. High speed Schlieren visualizations, and measurements including jet tip penetration velocities and jet widths of the primary vortex are employed to examine the developing processes for several flow conditions. It is seen that the developing behaviors in the presence of flame are greatly different from those in transient jet, and thus the flow characteristics in the transient part are also modified. The discernible differences are shown to consist of the delay of the rollup of the primary vortex, the faster spreading after the rollup due to exothermic expansion, and the survival of only a primary vortex. The growth of primary vortex in the transient jet is properly explained through an impulsively started laminar vortex prior to the interaction. It is also found that the jet tip penetration velocity varies with elapsed time and an increase in Res gives rise to a higher tip penetration velocity.

• 한국건설순환자원학회논문집
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• 제5권1호
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• pp.1-7
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• 2017

초기재령에서의 콘크리트 거동은 시간의 증가에 따른 수화반응에 따라 변화하는데, 염해 저항성과 강도 특성은 다르게 변화한다. 본 연구에서는 재령이 28일에서 6개월로 증가하면서 변화하는 강도 및 염해 저항특성을 보통 콘크리트에 대하여 분석하였다. 이를 위해 3개의 물-시멘트비를 가진 일반 콘크리트에 대하여, 재령 28일과 6개월 수중양생을 수행하였으며, 강도, 염화물 확산계수, 통과전하량을 평가하였다. 재령이 28일에서 6개월로 증가하면서 강도변화는 135.3~138.3% 수준으로 증가하였으나, 염화물 확산계수의 경우 41.8%~51.1% 수준으로, 통과전하량의 경우 53.6%~70.0% 수준으로 감소하였다. 염화물 확산계수와 통과전하량의 경우는 비교적 비슷한 수준으로 감소하였는데, 두 결과는 전기장 내에서의 염화물 이동에 지배적이기 때문이다. 또한 강도의 변화비보다 염화물 확산계수 및 통과전하량의 변화비가 크게 증가하였는데, 이는 공극특성의 제곱에 비례하여 물질이동 특성이 변하기 때문이다.

• 한국시뮬레이션학회논문지
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• 제20권2호
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• pp.29-40
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• 2011

본 연구에서는 에이전트 모형 기반 시뮬레이션 기법을 이용하여 국내 중형 고급승용차 제품시장에서 경쟁 제품들의 확산 다이나믹스를 예측하기 위한 환경조건을 도출하고자 민감도 분석을 실시하였다. 본 연구에서는 소비자의 구매 특성과 행동을 모방한 소비자 에이전트 모형을 이용하며 사회적 네트워크로 연결된 소비자 에이전트들의 집단은 하나의 가상시장을 이룬다. 제품을 구매한 소비자 에이전트가 이웃 에이전트들에게 제품정보를 전달함으로써 실제 시장처럼 구전현상이 나타나고 이는 잠재적 소비자 에이전트들의 제품선택에 영향을 주게 되어 확산 다이나믹스 패턴이 변화하게 된다. 가상시장의 확산 다이나믹스가 실제 시장의 확산다이나믹스를 반영하기 위해서는 초기채택자 비율, 사회적 네트워크의 구조, 소비자 에이전트의 구매시점 결정방법 등의 가상시장 환경설정이 중요하다. 그러나 이러한 환경조건들은 실제시장에서 측정하기가 어렵기 때문에 본 연구에서는 다양한 환경조건하에서의 확산다이나믹스패턴을 실제 데이터와 비교 분석하여 적합한 환경조건을 찾고자 한다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2014년도 제49회 KOSCO SYMPOSIUM 초록집
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• pp.243-244
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• 2014

The opposed flow flame in a mesoscale channel was constructed to observe the flame stabilization behaviors at low strain rate conditions (<$10s^{-1}$). The purpose of this study is to get the overall flame behaviors of partially premixed flames with oxygen enhanced conditions at low strain rates. The oxygen ratio in oxidizer was changed from 18 to 30 %. Conclusively, the flame extinction limit approached to about $1s^{-1}$, and divided into three representative regimes corresponding to self propagating flame, transitional flame, quenching flame regimes.

• 한국세라믹학회지
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• 제35권4호
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• pp.347-354
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• 1998

Densification and grain growth behaviors of ITO ceramics were investigated as a function of TiO2 ad-ditions. TiO2 addition led to inhibition of the grain growth and promotion of the densification of ITO ceram-ics. From the microstructure observation it was found that the crack-like voids which were formed in pure ITO specimens decreased with increase of TiO2 additon. The grain growth exponent(n) was measur-ed to be 4 for pure ITO 3 for TiO2-doped ITO specimens respectively. It was supposed that the grain boun-dary migration of pure ITO ceramics was controlled by the pores which were moved by surface diffusion. On the contrary the grain boundary migration of TiO2-doped ITO specimens was depressed by solute drag effect. The activation energies for grain growth were measured to be 1013 kJ/mol for pure ITO ceramics and 460kJ/mol for TiO2-doped ITO specimens respectively.

• 대한수학회지
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• 제53권4호
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• pp.929-967
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• 2016

Let p(t, x) be the fundamental solution to the problem $${\partial}^{\alpha}_tu=-(-{\Delta})^{\beta}u,\;{\alpha}{\in}(0,2),\;{\beta}{\in}(0,{\infty})$$. If ${\alpha},{\beta}{\in}(0,1)$, then the kernel p(t, x) becomes the transition density of a Levy process delayed by an inverse subordinator. In this paper we provide the asymptotic behaviors and sharp upper bounds of p(t, x) and its space and time fractional derivatives $$D^n_x(-{\Delta}_x)^{\gamma}D^{\sigma}_tI^{\delta}_tp(t,x),\;{\forall}n{\in}{\mathbb{Z}}_+,\;{\gamma}{\in}[0,{\beta}],\;{\sigma},{\delta}{\in}[0,{\infty})$$, where $D^n_x$ x is a partial derivative of order n with respect to x, $(-{\Delta}_x)^{\gamma}$ is a fractional Laplace operator and $D^{\sigma}_t$ and $I^{\delta}_t$ are Riemann-Liouville fractional derivative and integral respectively.