817 research outputs found
Stable dispersions of polymer-coated graphitic nanoplatelets
A method of making a dispersion of reduced graphite oxide nanoplatelets involves providing a dispersion of graphite oxide nanoplatelets and reducing the graphite oxide nanoplatelets in the dispersion in the presence of a reducing agent and a polymer. The reduced graphite oxide nanoplatelets are reduced to an extent to provide a higher C/O ratio than graphite oxide. A stable dispersion having polymer-treated reduced graphite oxide nanoplatelets dispersed in a dispersing medium, such as water or organic liquid is provided. The polymer-treated, reduced graphite oxide nanoplatelets can be distributed in a polymer matrix to provide a composite material
Ceramic Composite Thin Films
A ceramic composite thin film or layer includes individual graphene oxide and/or electrically conductive graphene sheets dispersed in a ceramic (e.g. silica) matrix. The thin film or layer can be electrically conductive film or layer depending the amount of graphene sheets present. The composite films or layers are transparent, chemically inert and compatible with both glass and hydrophilic SiOx/silicon substrates. The composite film or layer can be produced by making a suspension of graphene oxide sheet fragments, introducing a silica-precursor or silica to the suspension to form a sol, depositing the sol on a substrate as thin film or layer, at least partially reducing the graphene oxide sheets to conductive graphene sheets, and thermally consolidating the thin film or layer to form a silica matrix in which the graphene oxide and/or graphene sheets are dispersed
Dipole Interactions and Electrical Polarity in Nanosystems -- the Clausius-Mossotti and Related Models
Point polarizable molecules at fixed spatial positions have solvable
electrostatic properties in classical approximation, the most familiar being
the Clausius-Mossotti (CM) formula. This paper generalizes the model and
imagines various applications to nanosystems. The behavior is worked out for a
sequence of octahedral fragments of simple cubic crystals, and the crossover to
the bulk CM law is found. Some relations to fixed moment systems are discussed
and exploited. The one-dimensional dipole stack is introduced as an important
model system. The energy of interaction of parallel stacks is worked out, and
clarifies the diverse behavior found in different crystal structures. It also
suggests patterns of self-organization which polar molecules in solution might
adopt. A sum rule on the stack interaction is found and tested. Stability of
polarized states under thermal fluctuations is discussed, using the
one-dimensional domain wall as an example. Possible structures for polar hard
ellipsoids are considered. An idea is formulated for enhancing polarity of
nanosystems by intentionally adding metallic coatings.Comment: 18 pages (includes 6 embedded figures and 3 tables). New references,
and other small improvements. Scheduled for publication by J. Chem. Phys.,
Jan. 200
Nanoscale Weibull Statistics
In this paper a modification of the classical Weibull Statistics is developed
for nanoscale applications. It is called Nanoscale Weibull Statistics. A
comparison between Nanoscale and classical Weibull Statistics applied to
experimental results on fracture strength of carbon nanotubes clearly shows the
effectiveness of the proposed modification. A Weibull's modulus around 3 is,
for the first time, deduced for nanotubes. The approach can treat (also) a
small number of structural defects, as required for nearly defect free
structures (e.g., nanotubes) as well as a quantized crack propagation (e.g., as
a consequence of the discrete nature of matter), allowing to remove the
paradoxes caused by the presence of stress-intensifications
Atomistic Simulations of Nanotube Fracture
The fracture of carbon nanotubes is studied by atomistic simulations. The
fracture behavior is found to be almost independent of the separation energy
and to depend primarily on the inflection point in the interatomic potential.
The rangle of fracture strians compares well with experimental results, but
predicted range of fracture stresses is marketly higher than observed. Various
plausible small-scale defects do not suffice to bring the failure stresses into
agreement with available experimental results. As in the experiments, the
fracture of carbon nanotubes is predicted to be brittle. The results show
moderate dependence of fracture strength on chirality.Comment: 12 pages, PDF, submitted to Phy. Rev.
Gravitational signals emitted by a point mass orbiting a neutron star: a perturbative approach
We compute the energy spectra of the gravitational signals emitted when a
pointlike mass moves on a closed orbit around a non rotating neutron star,
inducing a perturbation of its gravitational field and its internal structure.
The Einstein equations and the hydrodynamical equations are perturbed and
numerically integrated in the frequency domain. The results are compared with
the energy spectra computed by the quadrupole formalism which assumes that both
masses are pointlike, and accounts only for the radiation emitted because the
orbital motion produces a time dependent quadrupole moment. The results of our
perturbative approach show that, in general, the quadrupole formalism
overestimates the amount of emitted radiation, especially when the two masses
are close. However, if the pointlike mass is allowed to move on an orbit so
tight that the keplerian orbital frequency resonates with the frequency of the
fundamental quasi-normal mode of the star (2w_K=w_f), this mode can be excited
and the emitted radiation can be considerably larger than that computed by the
quadrupole approach.Comment: 36 pages, 7 figures, submimtted to Phys. Rev.
Accurate strain measurements in highly strained Ge microbridges
Ge under high strain is predicted to become a direct bandgap semiconductor.
Very large deformations can be introduced using microbridge devices. However,
at the microscale, strain values are commonly deduced from Raman spectroscopy
using empirical linear models only established up to 1.2% for uniaxial stress.
In this work, we calibrate the Raman-strain relation at higher strain using
synchrotron based microdiffraction. The Ge microbridges show unprecedented high
tensile strain up to 4.9 % corresponding to an unexpected 9.9 cm-1 Raman shift.
We demonstrate experimentally and theoretically that the Raman strain relation
is not linear and we provide a more accurate expression.Comment: 10 pages, 4 figure
The rotational modes of relativistic stars: Numerical results
We study the inertial modes of slowly rotating, fully relativistic compact
stars. The equations that govern perturbations of both barotropic and
non-barotropic models are discussed, but we present numerical results only for
the barotropic case. For barotropic stars all inertial modes are a hybrid
mixture of axial and polar perturbations. We use a spectral method to solve for
such modes of various polytropic models. Our main attention is on modes that
can be driven unstable by the emission of gravitational waves. Hence, we
calculate the gravitational-wave growth timescale for these unstable modes and
compare the results to previous estimates obtained in Newtonian gravity (i.e.
using post-Newtonian radiation formulas). We find that the inertial modes are
slightly stabilized by relativistic effects, but that previous conclusions
concerning eg. the unstable r-modes remain essentially unaltered when the
problem is studied in full general relativity.Comment: RevTeX, 29 pages, 31 eps figure
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