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Comment on "Interaction of two solitary waves in quantum electron-positron-ion plasma" [Phys. Plasmas \textbf{18}, 052301 (2011)]
Recently, Yan-Xia Xu, et al. in the article Ref. [Phys. Plasmas \textbf{18},
052301 (2011)] have studied the effects of various plasma parameters on
interaction of two ion-acoustic solitary waves in an unmagnetized
three-dimensional electron-positron-ion quantum plasma. They have used the
extended reductive perturbation technique, the so-called, extended
Poincare'-Lighthill-Kuo (PLK) technique, to deduce from the model governing the
quantum hydrodynamics (QHD) differential equations leading to the soliton
dynamical properties, namely, Korteweg-de Vries evolution equations (one for
each wave) and coupled differential equations describing the phase-shift in
trajectories of solitons due to the two dimensional collision. The variation of
the calculated collision phase-shifts are then numerically inspected in terms
of numerous plasma fractional parameters. In this comment we give some notes
specific to the validity of the results of above-mentioned article and refer to
important misconceptions about the use of the Fermi-temperature in quantum
plasmas, appearing in this article and many other recently published ones.Comment: Accepted Journal Physics of Plasma
Computational investigation of structure, dynamics and nucleation kinetics of a family of modified Stillinger-Weber model fluids in bulk and free-standing thin films
In recent decades, computer simulations have found increasingly widespread
use as powerful tools of studying phase transitions in wide variety of systems.
In the particular and very important case of aqueous systems, the commonly used
force-fields tend to offer quite different predictions with respect to a wide
range of thermodynamic and kinetic properties, including the ease of ice
nucleation, the propensity to freeze at a vapor-liquid interface, and the
existence of a liquid-liquid phase transition. It is thus of fundamental and
practical interest to understand how different features of a given water model
affect its thermodynamic and kinetic properties. In this work, we use the
forward-flux sampling technique to study the crystallization kinetics of a
family of modified Stillinger-Weber (SW) potentials with energy ()
and length () scales taken from the monoatomic water (mW) model, but
with different tetrahedrality parameters (). By increasing
from 21 to 24, we observe the nucleation rate increases by 48 orders of
magnitude at a supercooling of . Using classical
nucleation theory, we are able to demonstrate that this change can largely be
accounted for by the increase in , the thermodynamic driving
force. We also perform rate calculations in freestanding thin films of the
supercooled liquid, and observe a crossover from a surface-enhanced
crystallization at to a bulk-dominated crystallization for
.Comment: 10 pages, 9 figures, five table
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