• Journal of Mechanical Science and Technology
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• 제18권8호
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• pp.1271-1287
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• 2004

In this article, vapor bubble nucleation in liquid and the evaporation process of a liquid droplet at its superheat limit were discussed from the viewpoint of molecular clustering (molecular cluster model for bubble nucleation). For the vapor bubble formation, the energy barrier against bubble nucleation was estimated by the molecular interaction due to the London dispersion force. Bubble nucleation by quantum tunneling in liquid helium under negative pressure near the absolute zero temperature and bubble nucleation on cavity free micro heaters were also presented as the homogenous nucleation processes.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1885-1890
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• 2008

3-D heterogeneous nucleation was simulated by classical molecular dynamics (MD), where the Lennard-Jones (LJ) gas and solid cluster-seed molecules have argon and aluminum properties, respectively. There are three shapes of cluster-seeds, cube, rod, and sphere, and three classes of masses and the simulation took place under nine supersaturation ratios, making a total of 81 calculations. Results show that the dimension of the cluster-seed highly affects the rates of cluster development. In order to analyze heterogeneous nucleation above and below the critical supersaturation ratio, growth rate and liquefaction rate were separately defined to supplement the investigation. Design of experiments (DOE) was used for analysis which displayed that the shape and mass of the cluster-seed are prominent for the growth rate, while the supersaturation ratio is most significant followed by the mass for liquefaction rate. The significance of the supersaturation ratio for overall liquefaction suggests that thermal diffusion is more dominant than mass interactions for this system.

• 폴리머
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• 제28권1호
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• pp.51-58
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• 2004

탄성체 (가교된 고분자) 가스가 용해된 고분자 또는 유기 용매에 용해된 고분자 용액에서 기포 생성을 예측하기 위하여 균일한 기포 생성은 고전적인 이론에서의 임계 기포의 생성이 아닌 임계 뭉치의 생성을 통하여 이루어진다는 분자 뭉치 이론을 적용하였다. 또한 탄성체나 고분자 내에서 기포가 생성하는 경우 임계 기포가 극복해야 할 탄성 에너지를 고려하였다. 대략 $10^{8}$∼$10^{12}$개에 달하는 분자 뭉치 이론에 의해 계산된 단위 부피당 생성된 기포 수는 실험치와 잘 일치하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.252-257
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• 2001

With the help of newly arrived technology such as PC clustering, molecular dynamics (MD) seems to be promising for large-scale materials simulations. A cost-effective cluster is set up using commodity PCs connected over Ethernet with fast switching devices and free software Linux. Executing MD simulations in the parallel sessions makes it possible to carry out large-scale materials simulations at acceptable computation time and costs. In this study, the MD computer code for fracture simulation is modified to comply with MPI (Message Passing Interface) specification, and runs on the PC cluster in parallel mode flawlessly. It is noted that PC clusters can provide a rather inexpensive high-performance computing environment comparing to supercomputers, if properly arranged.

• Journal of Advanced Marine Engineering and Technology
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• 제20권3호
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• pp.11-18
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• 1996

Liquid droplets of water and argon surrounded by their vapor have been simulated by the milecular dynamics method. To explore the surface phenomena of clusters, each molecule is classified into 'liquid', 'surface', or 'vapor' with respect to the number of neighbor molecules. The contribution of a 'surface' molecule of the water cluster to the far infrared spectrum is almist the same as that of the 'liquid' molecule. Hence, the liquid-vapor interface is viewed as geometrically and temporally varying boundary of 'liquid' molecules with only a single layer of 'surface' molecules that might have different characteristics from the 'liquid' molecules. The time scale of the 'phase change' of each molecule is estimated for the argon cluster by observing the instantancous kinetic and potential energies of each molecule. To compare the feature of clusters with macroscopic droplets, the temperature dependence of the surface tension of the argon cluster is estimated.

• 한국항공우주학회지
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• 제30권5호
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• pp.15-23
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• 2002

분자 동역학 기법을 사용한 재료 파괴 시뮬레이션은 계산량의 방대함으로 인하여 극히 최근까지 활발한 연구가 진행되지 못하였으나 최근 컴퓨터의 성능향상으로 인하여 새로운 연구분야로 떠오르고 있다. 분자 동역학은 그 특성상 계산 집약적인 환경을 요구함으로 대규모의 연산을 위해서는 슈퍼컴퓨터나 클러스터(cluster)의 사용이 필수적이나 고가의 장비와 사용료로 인하여 많은 제한을 받아왔다. 본 연구에서는 PC를 사용하여 클러스터를 제작하고, 균열이 있는 시편을 사용하여 파괴현상에 대한 분자 수준의 거동을 시뮬레이션 하였으며, 클러스터의 노드(node) 수, 효율, 분자 수, 노드간의 통신시간 등의 상호관계를 파악하여 최적의 성능을 가진 클러스터를 구성하는 데 필요한 요소들을 분석하였다. 제작된 PC 클러스터를 사용하여 약 50,000개의 분자를 사용한 재료 파괴 시뮬레이션을 수행하였다.

• 한국진공학회지
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• 제10권3호
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• pp.283-288
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• 2001

본 연구에서는 분자동력학 방법을 사용하여 알루미늄 덩어리 충돌에 관하여 연구하였다. 충돌에 따른 운동량 및 충격력 변화를 통하여, 덩어리 충돌은 단일입자충돌(single particle collision) 특성 일부와 선형사슬충돌(linear chain collisions) 특성 일부를 가지는 것을 살펴보았다. 또한 연속적인 덩어리 증착을 통하여 성장된 박막의 특성을 살펴보았다 원자당 에너지가 너무 낮은 경우보다는 일정 에너지 이상에서 혼합(intermixing) 발생이 잘 이루어지며 짝은 어닐링 공정으로 좋은 박막을 얻을 수 있다는 것을 살펴보았다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1788-1793
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• 2008

Classical molecular dynamics simulations (MDS) were conducted to simulate nano-sized cluster collisions with a weakly attractive static surface. Energy exchanges associated with the cluster collision and the adhesion probability are discussed. Routes of the energy exchanges and the kinetic energy loss are vastly altered in their mode according to the cluster incident velocity. In the elastic collision regime ($V_0$<0.1), most incident kinetic energy is recovered into the rebounding kinetic energy, but a little loss in the incident kinetic energy causes the cluster adhesion. Dissipated kinetic energy is converted into the rotational energy. In the weakly plastic collision regime (0.1<$V_0$<0.3), the transition from elastic to plastic collision occurs, and a large part of the released potential energy is converted into rebounding translational energy. For strongly plastic collisions ($V_0$>0.3), permanent cluster deformation occurs with extensive collapse of the lattice structure inducing a solid-to-solid phase transition; moreover, most of the cluster kinetic energy is converted into cluster potential and thermal energy.

• Journal of Microbiology and Biotechnology
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• 제19권9호
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• pp.881-887
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• 2009

Forty-four eicosapentaenoic acid (EPA)-producing microbial strains were isolated from the intestines of marine fishes. Among them, one strain showing a maximum level of EPA (4.78% of total fatty acids) was identified as Shewanella sp. BR-2 on the basis of its 168 rRNA sequence. The EPA content reached a maximum level during the mid-exponential phase of cell growth, and gradually decreased with further growth of the cells. A cosmid DNA including the EPA biosynthesis gene cluster consisting of pfaA-E was isolated from a cosmid library of genomic DNA of Shewanella sp. BR-2, named pCosEPA-BR2. An E. coli clone harboring pCosEPA-BR2 produced EPA at a maximum level of 7.5% of total fatty acids, confirming the EPA biosynthesis activity of the cloned gene cluster.

• 한국진공학회지
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• 제9권3호
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• pp.273-278
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• 2000

본 연구에서는 분자동력학 방법을 사용하여 알루미늄 덩어리 증착에 관하여 연구하였다. 다양한 크기의 덩어리 충돌에서 기판의 온도와 비정렬 원자수 변화를 관찰하여 알루미늄 덩어리 증착시 덩어리내의 원자들 상호간의 상관충돌이 기판으로의 에너지전달과 원자 재배열과정에 큰 영향을 미치는 것을 발견하였다. 덩어리 크기가 클수록 상관충돌 효과는 커지는 것을 알 수 있었다.