5,432 research outputs found
Molecular dynamics study of the stability of a carbon nanotube atop a catalytic nanoparticle
The stability of a single-walled carbon nanotube placed on top of a catalytic
nickel nanoparticle is investigated by means of molecular dynamics simulations.
As a case study, we consider the nanotube consisting of 720 carbon
atoms and the icosahedral Ni cluster. An explicit set of
constant-temperature simulations is performed in order to cover a broad
temperature range from 400 to 1200 K, at which a successful growth of carbon
nanotubes has been achieved experimentally by means of chemical vapor
deposition. The stability of the system depending on parameters of the involved
interatomic interactions is analyzed. It is demonstrated that different
scenarios of the nanotube dynamics atop the nanoparticle are possible depending
on the parameters of the Ni-C potential. When the interaction is weak the
nanotube is stable and resembles its highly symmetric structure, while an
increase of the interaction energy leads to the abrupt collapse of the nanotube
in the initial stage of simulation. In order to validate the parameters of the
Ni-C interaction utilized in the simulations, DFT calculations of the potential
energy surface for carbon-nickel compounds are performed. The calculated
dissociation energy of the Ni-C bond is in good agreement with the values,
which correspond to the case of a stable and not deformed nanotube simulated
within the MD approach.Comment: 11 pages, 5 figures; submitted to Eur. Phys. J.
Parity Doublet Model applied to Neutron Stars
The Parity doublet model containing the SU(2) multiplets including the
baryons identified as the chiral partners of the nucleons is applied for
neutron star matter. The chiral restoration is analyzed and the maximum mass of
the star is calculated.Comment: Proceeding to the conference International Symposium on Exotic States
of Nuclear Matte
Modelling Hybrid Stars in Quark-Hadron Approaches
The density in the core of neutron stars can reach values of about 5 to 10
times nuclear matter saturation density. It is, therefore, a natural assumption
that hadrons may have dissolved into quarks under such conditions, forming a
hybrid star. This star will have an outer region of hadronic matter and a core
of quark matter or even a mixed state of hadrons and quarks. In order to
investigate such phases, we discuss different model approaches that can be used
in the study of compact stars as well as being applicable to a wider range of
temperatures and densities. One major model ingredient, the role of quark
interactions in the stability of massive hybrid stars is discussed. In this
context, possible conflicts with lattice QCD simulations are investigated.Comment: Contribution to the EPJA Topical Issue on "Exotic Matter in Neutron
Stars
Modeling Hybrid Stars
We study the so called hybrid stars, which are hadronic stars that contain a
core of deconfined quarks. For this purpose, we make use of an extended version
of the SU(3) chiral model. Within this approach, the degrees of freedom change
naturally from hadrons (baryon octet) to quarks (u, d, s) as the temperature
and/or density increases. At zero temperature we are still able to reproduce
massive stars, even with the inclusion of hyperons.Comment: To appear in the proceedings of Conference C12-08-0
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