Temperature dependence of spatially heterogeneous dynamics in a model of viscous silica

Molecular dynamics simulations are performed to study spatially heterogeneous dynamics in a model of viscous silica above and below the critical temperature of the mode coupling theory, $T_{MCT}$. Specifically, we follow the evolution of the dynamic heterogeneity as the temperature dependence of the transport coefficients shows a crossover from non-Arrhenius to Arrhenius behavior when the melt is cooled. It is demonstrated that, on intermediate time scales, a small fraction of oxygen and silicon atoms are more mobile than expected from a Gaussian approximation. These highly mobile particles form transient clusters larger than that resulting from random statistics, indicating that dynamics are spatially heterogeneous. An analysis of the clusters reveals that the mean cluster size is maximum at times intermediate between ballistic and diffusive motion, and the maximum size increases with decreasing temperature. In particular, the growth of the clusters continues when the transport coefficients follow an Arrhenius law. These findings imply that the structural relaxation in silica cannot be understood as a statistical bond breaking process. Though the mean cluster sizes for silica are at the lower end of the spectrum of values reported in the literature, we find that spatially heterogeneous dynamics in strong and fragile glass formers are similar on a qualitative level. However, different from results for fragile liquids, we show that correlated particle motion along quasi one-dimensional, string-like paths is of little importance for the structural relaxation in this model of silica, suggesting that string-like motion is suppressed by the presence of covalent bonds.Comment: 13 pages, 11 figure

Conceptual Design of a Fast-Ignition Laser Fusion Reactor FALCON-D

A new conceptual design of the laser fusion power plant FALCON-D (Fast ignition Advanced Laser fusion reactor CONcept with a Dry wall chamber) has been proposed. The fast ignition method can achieve the sufficient fusion gain for a commercial operation (~100) with about 10 times smaller fusion yield than the conventional central ignition method. FALCON-D makes full use of this property and aims at designing with a compact dry wall chamber (5~6m radius). 1-D/2-D hydrodynamic simulations showed the possibility of the sufficient gain achievement with a 40 MJ target yield. The design feasibility of the compact dry wall chamber and solid breeder blanket system was shown through the thermomecanical analysis of the dry wall and neutronics analysis of the blanket system. A moderate electric output (~400MWe) can be achieved with a high repetition (30Hz) laser. This dry wall concept not only reduces some difficulties accompanied with a liquid wall but also enables a simple cask maintenance method for the replacement of the blanket system, which can shorten the maintenance time. The basic idea of the maintenance method for the final optics system has also been proposed. Some critical R&D issues required for this design are also discussed

Monte Carlo and molecular dynamics studies for the colour rewritable films

The structure of the developers plays an important role in the colouring/decolouring process for the colour rewritable films. We study the chain-like polymers structure of the developer through both the Monte Carlo and molecular dynamics simulations. In these simulations we focus our attention on the thermal (temperature) effects as well as the effective interaction between developers (chain-like polymers), and with these how the lamellar structure can be constructed when the system is quenched from high temperature (low density) to low temperature (high density). We found the transition of the states from a disordered state to an aggregated state at a temperature (282 K). We obtained the lamellar structure in a preferable condition of the potential parameter, while in either smaller or larger interactions, it is rather difficult for the developer chains to form lamellar structures.Структура проявників відіграє важливу роль в процесі забарвлення/знебарвлення для кольорових записуючих плівок. Ми вивчаємо ланцюжковоподібну полімерну структуру проявника методом Монте Карло і молекулярної динаміки. В цих моделюваннях ми зосереджуємо увагу як на термічних (температурних) ефектах так і на ефективній взаємодії між проявниками (ланцюжково подібними полімерами) і на тому як шарувата структура може бути сконструйована, коли система є різко охолоджена від високої температури (низької густини) до низької температури (високої густини). Ми знайшли перехід станів з невпорядкованого стану до агрегатного стану при температурі (282 К). Ми отримали шарувату структуру при певній умові потенціального параметра, тоді як при слабких і сильних взаємодіях шарувата структура проявника формується важко