24 research outputs found
Crystal nucleation and cluster-growth kinetics in a model glass under shear
Crystal nucleation and growth processes induced by an externally applied
shear strain in a model metallic glass are studied by means of nonequilibrium
molecular dynamics simulations, in a range of temperatures. We observe that the
nucleation-growth process takes place after a transient, induction regime. The
critical cluster size and the lag-time associated with this induction period
are determined from a mean first-passage time analysis. The laws that describe
the cluster growth process are studied as a function of temperature and strain
rate. A theoretical model for crystallization kinetics that includes the time
dependence for nucleation and cluster growth is developed within the framework
of the Kolmogorov-Johnson-Mehl-Avrami scenario and is compared with the
molecular dynamics data. Scalings for the cluster growth laws and for the
crystallization kinetics are also proposed and tested. The observed nucleation
rates are found to display a nonmonotonic strain rate dependency
Analysis of the Dynamics of Liquid Aluminium: Recurrent Relation Approach
By use of the recurrent relation approach (RRA) we study the microscopic
dynamics of liquid aluminium at T=973 K and develop a theoretical model which
satisfies all the corresponding sum rules. The investigation covers the
inelastic features as well as the crossover of our theory into the
hydrodynamical and the free-particle regimes. A comparison between our
theoretical results with those following from a generalized hydrodynamical
approach is also presented. In addition to this we report the results of our
molecular dynamics simulations for liquid aluminium, which are also discussed
and compared to experimental data. The received results reveal that (i) the
microscopical dynamics of density fluctuations is defined mainly by the first
four even frequency moments of the dynamic structure factor, and (ii) the
inherent relation of the high-frequency collective excitations observed in
experimental spectra of dynamic structure factor with the two-,
three- and four-particle correlations.Comment: 11 pages, 4 figure
Zwanzig-Mori projection operators and EEG dynamics: deriving a simple equation of motion
We present a macroscopic theory of electroencephalogram (EEG) dynamics based on the laws of motion that govern atomic and molecular motion. The theory is an application of Zwanzig-Mori projection operators. The result is a simple equation of motion that has the form of a generalized Langevin equation (GLE), which requires knowledge only of macroscopic properties. The macroscopic properties can be extracted from experimental data by one of two possible variational principles. These variational principles are our principal contribution to the formalism. Potential applications are discussed, including applications to the theory of critical phenomena in the brain, Granger causality and Kalman filters