10,748 research outputs found
The Structure of Graphene on Graphene/C60/Cu Interfaces: A Molecular Dynamics Study
Two experimental studies reported the spontaneous formation of amorphous and
crystalline structures of C60 intercalated between graphene and a substrate.
They observed interesting phenomena ranging from reaction between C60 molecules
under graphene to graphene sagging between the molecules and control of strain
in graphene. Motivated by these works, we performed fully atomistic reactive
molecular dynamics simulations to study the formation and thermal stability of
graphene wrinkles as well as graphene attachment to and detachment from the
substrate when graphene is laid over a previously distributed array of C60
molecules on a copper substrate at different values of temperature. As graphene
compresses the C60 molecules against the substrate, and graphene attachment to
the substrate between C60s ("C60s" stands for plural of C60) depends on the
height of graphene wrinkles, configurations with both frozen and non-frozen
C60s structures were investigated in order to verify the experimental result of
stable sagged graphene when the distance between C60s is about 4 nm and height
of graphene wrinkles is about 0.8 nm. Below the distance of 4 nm between C60s,
graphene becomes locally suspended and less strained. We show that this happens
when C60s are allowed to deform under the compressive action of graphene. If we
keep the C60s frozen, spontaneous "blanketing" of graphene happens only when
the distance between them are equal or above 7 nm. Both above results for the
existence of stable sagged graphene for C60 distances of 4 or 7 nm are shown to
agree with a mechanical model relating the rigidity of graphene to the energy
of graphene-substrate adhesion. In particular, this study might help the
development of 2D confined nanoreactors that are considered in literature to be
the next advanced step on chemical reactions.Comment: 7 pages, 4 figure
Isospin Constraints on the Parametric Coupling Model for Nuclear Matter
We make use of isospin constraints to study the parametric coupling model and
the properties of asymmetric nuclear matter. Besides the usual constraints for
nuclear matter - effective nucleon mass and the incompressibility at saturation
density - and the neutron star constraints - maximum mass and radius - we have
studied the properties related with the symmetry energy. These properties have
constrained to a small range the parameters of the model. We have applied our
results to study the thermodynamic instabilities in the liquid-gas phase
transition as well as the neutron star configurations.Comment: 11 pages, 10 figure
Analytical Results for the Statistical Distribution Related to Memoryless Deterministic Tourist Walk: Dimensionality Effect and Mean Field Models
Consider a medium characterized by N points whose coordinates are randomly
generated by a uniform distribution along the edges of a unitary d-dimensional
hypercube. A walker leaves from each point of this disordered medium and moves
according to the deterministic rule to go to the nearest point which has not
been visited in the preceding \mu steps (deterministic tourist walk). Each
trajectory generated by this dynamics has an initial non-periodic part of t
steps (transient) and a final periodic part of p steps (attractor). The
neighborhood rank probabilities are parameterized by the normalized incomplete
beta function I_d = I_{1/4}[1/2,(d+1)/2]. The joint distribution
S_{\mu,d}^{(N)}(t,p) is relevant, and the marginal distributions previously
studied are particular cases. We show that, for the memory-less deterministic
tourist walk in the euclidean space, this distribution is:
S_{1,d}^{(\infty)}(t,p) = [\Gamma(1+I_d^{-1})
(t+I_d^{-1})/\Gamma(t+p+I_d^{-1})] \delta_{p,2}, where t=0,1,2,...,\infty,
\Gamma(z) is the gamma function and \delta_{i,j} is the Kronecker's delta. The
mean field models are random link model, which corresponds to d \to \infty, and
random map model which, even for \mu = 0, presents non-trivial cycle
distribution [S_{0,rm}^{(N)}(p) \propto p^{-1}]: S_{0,rm}^{(N)}(t,p) =
\Gamma(N)/\{\Gamma[N+1-(t+p)]N^{t+p}\}. The fundamental quantities are the
number of explored points n_e=t+p and I_d. Although the obtained distributions
are simple, they do not follow straightforwardly and they have been validated
by numerical experiments.Comment: 9 pages and 4 figure
A control on quantum fluctuations in 2+1 dimensions
A functional method is discussed, where the quantum fluctuations of a theory
are controlled by a mass parameter and the evolution of the theory with this
parameter is connected to its renormalization. It is found, in the framework of
the gradient expansion, that the coupling constant of a N=1 Wess-Zumino theory
in 2+1 dimensions does not get quantum corrections.Comment: Comments adde
- …