162 research outputs found
Thermal transport across grain boundaries in polycrystalline silicene: a multiscale modeling
During the fabrication process of large scale silicene through common
chemical vapor deposition (CVD) technique, polycrystalline films are quite
likely to be produced, and the existence of Kapitza thermal resistance along
grain boundaries could result in substantial changes of their thermal
properties. In the present study, the thermal transport along polycrystalline
silicene was evaluated by performing a multiscale method. Non-equilibrium
molecular dynamics simulations (NEMD) was carried out to assess the interfacial
thermal resistance of various constructed grain boundaries in silicene as well
as to examine the effects of tensile strain and the mean temperature on the
interfacial thermal resistance. In the following stage, the effective thermal
conductivity of polycrystalline silicene was investigated considering the
effects of grain size and tensile strain. Our results indicate that the average
values of Kapitza conductance at grain boundaries at room temperature were
estimated nearly 2.56*10^9 W/m2K and 2.46*10^9 W/m2K through utilizing Tersoff
and Stillinger-Weber interatomic potentials, respectively. Also, in spite of
the mean temperature whose increment does not change Kapitza resistance, the
interfacial thermal resistance can be controlled by applying strain.
Furthermore, it was found that, by tuning the grain size of polycrystalline
silicene, its thermal conductivity can be modulated up to one order of
magnitude.Comment: 24 pages, 11 figure
Nonlinear Optical Susceptibilities and Linear Absorption in Phosphorene Nanoribbons: Ab initio study
Using Density Functional Theory (DFT) method we compute linear optical
absorption spectra and nonlinear optical susceptibilities of hydrogen
passivated armchair and zigzag Phosphorous Nanoribbons (aPNR and zPNR) as well
as \alpha-phase phosphorous monolayer. We observe that: (a) Crystallographic
direction has a strong effect on the band edge absorption which causes optical
anisotropy as well as a red shift of absorption spectra by increasing the
nanoribbon width. (b) The absorption values are in the order of which are similar to the experimentally measured values. (c) There is
two orders of magnitude enhancement of the 2nd order nonlinear optical
susceptibility, , in nanoribbons which emanates from breaking the
centro-symmetric structure of a monolayer phosphorene by hydrogen surface
terminations. (d) Chief among our results is that the 3rd order susceptibility,
, for phosphorene monolayer and nanoribbons are about
esu () which are in close agreement with
experimentally reported values as well as a recently calculated value based on
semi-analytic method. This strongly supports reliability of our method in
calculating nonlinear optical susceptibilities of phosphorene and in general
other nanostructures. Enhanced 2nd order optical nonlinearity in phosphorene
promises better second harmonic and frequency difference (THz) generation for
photonics applications.Comment: 18 pages, 4 figures, 4 tables, 48 reference
Fermionic Tachyons as a Source of Dark Energy
A model for the universe on the basis of a self interacting fermionic tachyon
field is investigated here. It is shown that, devising a self interaction
potential of a proper form, the fermionic tachyon field is capable of producing
an accelerating expansion that at late time tends to a constant value which is
in consistence with the cosmological constant. This way the introduced
fermionic tachyon field can be interpreted as the source of dark energy.Comment: 5 figure
Cosmic Strings Collision in Cosmological Backgrounds
The collisions of cosmic strings loops and the dynamics of junctions
formations in expanding backgrounds are studied. The key parameter controlling
the dynamics of junctions formation, the cosmic strings zipping and unzipping
is the relative size of the loops compared to the Hubble expansion rate at the
time of collision. We study analytically and numerically these processes for
large super-horizon size loops, for small sub-horizon size loops as well as for
loops with the radii comparable to the Hubble expansion rate at the time of
collision.Comment: 24 pages, 13 figure
Cylindrical solutions in braneworld gravity
In this article we investigate exact cylindrically symmetric solutions to the
modified Einstein field equations in the brane world gravity scenarios. It is
shown that for the special choice of the equation of state for the
dark energy and dark pressure, the solutions found could be considered formally
as solutions of the Einstein-Maxwell equations in 4-D general relativity.Comment: 12 pages, RevTex format, typos corrected and references added.
Accepted for publication in PR
Complexity Growth Following Multiple Shocks
In this paper by making use of the "Complexity=Action" proposal, we study the
complexity growth after shock waves in holographic field theories. We consider
both double black hole-Vaidya and AdS-Vaidya with multiple shocks geometries.
We find that the Lloyd's bound is respected during the thermalization process
in each of these geometries and at the late time, the complexity growth
saturates to the value which is proportional to the energy of the final state.
We conclude that the saturation value of complexity growth rate is independent
of the initial temperature and in the case of thermal initial state, the rate
of complexity is always less than the value for the vacuum initial state such
that considering multiple shocks it gets more smaller. Our results indicate
that by increasing the temperature of the initial state, the corresponding rate
of complexity growth starts far from final saturation rate value.Comment: 19 pages, 3 figs, Ref.s adde
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