Dynamics of the melts

On the other hand, for measurements done at constant temperature (850 °C), Dp and Dpi continually decrease monotonously with the addition of CaF2. These results clearly show the effects of the composition and of the temperature on the self-diffusion. Such observations have been already described for fluorine self-diffusion coefficients in other fluoride systems [14,15]. Nevertheless, the fact that lithium is significantly affected by the composition was not seen in LiF-KF melts. Potassium and lithium cations have close ionic radii and have the same valence. Their ionic potentials corresponding to the polarizing strength of the ions 

The self-diffusion coefficients have been measured at the eutectic composition by HT PFG NMR and Li) and calculated by MD (F , Li+, Ca +) from 780 to 850 °C. The activation energies (EJ have been also determined for the different ions. First, a good agreement is obtained between experiments and simulations and activation energies values are around 40 kJ/mol whatever the ions (Table 4.3.1). These values are higher than the ones obtained for the eutectic composition of molten LiF-KF [19] around 30kJ/mol for F , Li  

The authors acknowledge the support of the French Agence Nationale de la Recherche (ANR) under grant MILIFOX (ANR-09-BLAN-0188-01). 

Nuttin, A., Heuer, D., Billebaud, A. et al. (2005) Potential of thorium molten salt reactors detailed calculations and concept evolution with a view to large scale energy production. Prog. Nucl. Energy, 46, 77-79. 

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Once the chains become larger and larger, the dynamics of the melt slows down dramatically, due to the topological constraints imposed by the chains on each other. For the chain diffusion one observes a transition... 

Several informations are obtained by the solution of Eq.l with the appropriate boundary conditions temperature distribution inside the sample and time dependence, melt propagation and penetration, velocity of the resolidification front. As an example the dynamic of the melt penetration and its dependence on the energy density is shown in Fig.2 for 30 nsec ruby laser pulse ir- ... 

The field-heating effect has been observed most clearly in LuFe204 but is supposed to exist in other compounds, too, at least in YbFe204. It is crucially dependent on the process of sample preparation, although no difference has been detected in composition, contamination of other elements or phases, lattice constants, etc., between specimens with and without the field-heating effect. The dynamics of the melting of frozen spins in these compounds are problems to be investigated. 

It is possible to use the quantum states to predict the electronic properties of the melt. A typical procedure is to implement molecular dynamics simulations for the liquid, which pemiit the wavefiinctions to be detemiined at each time step of the simulation. As an example, one can use the eigenpairs for a given atomic configuration to calculate the optical conductivity. The real part of tire conductivity can be expressed as... 

The five time regions are based on the reptation theory proposed by De Gennes [46,47] and Doi and Edwards [48,49] for bulk dynamics of polymer melts and concentrated polymer solutions, and are discussed in detail in Chapter 3 of Ref. [1]. 

Finally, we want to describe two examples of those isolated polymer chains in a sea of solvent molecules. Polymer chains relax considerably faster in a low-molecular-weight solvent than in melts or glasses. Yet it is still almost impossible to study the conformational relaxation of a polymer chain in solvent using atomistic simulations. However, in many cases it is not the polymer dynamics that is of interest but the structure and dynamics of the solvent around the chain. Often, the first and maybe second solvation shells dominate the solvation. Two recent examples of aqueous and non-aqueous polymer solutions should illustrate this poly(ethylene oxide) (PEO) [31]... 

J. G. van Alsten, B. B. Sauer, D. J. Walsh. Polymer dynamics at the melt/solid interface Experimental evidence of reduced center of mass mobility. Macromolecules 25 4046-4048, 1992. 

Toomey DR, Wileoek WSD, Conder JA, Forsyth DW, Blundy JD, Parmentier EM, Hanunond WC () Asynunetrie mantle dynamics in the MELT region of the East Pacific Rise. Earth Planet Sci Lett 200 287-295... 

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