• Journal of Mechanical Science and Technology
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• v.18 no.8
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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.

• Proceedings of the KSME Conference
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• 2008.11a
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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.

• Polymer(Korea)
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• v.28 no.1
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• pp.51-58
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• 2004

The molecular cluster model for the homogeneous bubble nucleation rather than the classical nucleation theory was extended to predict the bubble nucleation events in elastomers(cross-linked polymers), polymers and polymer which are dissolved in the organic solvent. The classical theory assumes the formation of the critical bubble while the molecular cluster model assumes the critical cluster as for the initiation of the bubble nucleation. For the bubble nucleation in elastomers and polymers, the strain energy overcome by a critical bubble was also considered. The calculation results for the number of bubbles nucleated in elastormers and polymer solutions, which are about 10$\^$8/∼10$\^$12/ bubbles/㎤ are in good agreement with observed ones.

• Proceedings of the KSME Conference
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• 2001.11a
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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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• v.20 no.3
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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.

• Journal of the Korean Vacuum Society
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• v.10 no.3
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• pp.283-288
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• 2001

We have investigated aluminum cluster deposition using a classical molecular dynamics simulations. We studied the variations of the cluster momentum and the impulse force during collisions, and found that the close-packed cluster impact has some of properties of the single particle collision and the linear atomic chain collisions. We also simulated the series of energetic cluster deposition with energy Per atom. When energy Per atom in cluster has some eV rather than very low, the intermixing occurred easily in growth film and we can obtain a good film without subsequent annealing process.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.15-23
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• 2002

For molecular dynamics requires high-performance computers or supercomputers to handle huge amount of computation, it is not until recent days that the application of molecular dynamics to materials fracture simulations draw some attention from many researchers. With the recent advent of high-performance computers, computation intensive methods become more tractable than ever. However, carrying out materials simulation on high-performance computers costs too much in general. In this study, a PC cluster consisting of multiple commodity PCs is established and computer simulations of materials with cracks are carried out on it via molecular dynamics technique. The effect of the number of nodes, speedup factors, and communication time between nodes are measured to verify the performance of the PC cluster. Upon using the PC cluster, materials fracture simulations with more than 50,000 molecules are carried out successfully.

• Proceedings of the KSME Conference
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• 2008.11a
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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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• v.19 no.9
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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.

• Journal of the Korean Vacuum Society
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• v.9 no.3
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• pp.273-278
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• 2000

We studied aluminum cluster deposition using molecular dynamics simulation. We investigated the variations of the substrate temperature and disordered atom number during cluster impact, and found that the correlated collisions between aluminum atoms in the cluster play a very important role in the impact on aluminum substrate surface. The correlated collisions effect is proportional to the cluster size.