16,266 research outputs found
Multipolar expansion of the electrostatic interaction between charged colloids at interfaces
The general form of the electrostatic potential around an arbitrarily charged
colloid at an interface between a dielectric and a screening phase (such as air
and water, respectively) is analyzed in terms of a multipole expansion. The
leading term is isotropic in the interfacial plane and varies with
where is the in--plane distance from the colloid. The electrostatic
interaction potential between two arbitrarily charged colloids is likewise
isotropic and , corresponding to the dipole--dipole interaction
first found for point charges at water interfaces. Anisotropic interaction
terms arise only for higher powers with .Comment: 6 pages, mathematical details adde
Transport properties and structures of vortex matter in layered superconductors
In this paper we analyze the structure, phase transitions and some transport
properties of the vortex system when the external magnetic field lies parallel
to the planes in layered superconductors. We show that experimental results for
resistivity are qualitatively consistent with numerical simulations that
describe the melting of a commensurate rotated lattice. However for some
magnetic fields, the structure factor indicates the occurrence of smectic peaks
at an intermediate temperature regime.Comment: 8 pages, 8 eps figure
Nanowires: A route to efficient thermoelectric devices
Miniaturization of electronic devices aims at manufacturing ever smaller
products, from mesoscopic to nanoscopic sizes. This trend is challenging
because the increased levels of dissipated power demands a better understanding
of heat transport in small volumes. A significant amount of the consumed energy
is transformed into heat and dissipated to the environment. Thermoelectric
materials offer the possibility to harness dissipated energy and make devices
less energy-demanding. Heat-to-electricity conversion requires materials with a
strongly suppressed thermal conductivity but still high electronic conduction.
Nanowires can meet nicely these two requirements because enhanced phonon
scattering at the surface and defects reduces the lattice thermal conductivity
while electric conductivity is not deteriorated, leading to an overall
remarkable thermoelectric efficiency. Therefore, nanowires are regarded as a
promising route to achieving valuable thermoelectric materials at the
nanoscale. In this paper, we present an overview of key experimental and
theoretical results concerning the thermoelectric properties of nanowires. The
focus of this review is put on the physical mechanisms by which the efficiency
of nanowires can be improved. Phonon scattering at surfaces and interfaces,
enhancement of the power factor by quantum effects and topological protection
of electron states to prevent the degradation of electrical conductivity in
nanowires are thoroughly discussed
Numerical simulation of a binary communication channel: Comparison between a replica calculation and an exact solution
The mutual information of a single-layer perceptron with Gaussian inputs
and deterministic binary outputs is studied by numerical simulations. The
relevant parameters of the problem are the ratio between the number of output
and input units, , and those describing the two-point
correlations between inputs. The main motivation of this work refers to the
comparison between the replica computation of the mutual information and an
analytical solution valid up to . The most relevant results
are: (1) the simulation supports the validity of the analytical prediction, and
(2) it also verifies a previously proposed conjecture that the replica solution
interpolates well between large and small values of .Comment: 6 pages, 8 figures, LaTeX fil
Lattice thermal conductivity of graphene nanostructures
Non-equilibrium molecular dynamics is used to investigate the heat current
due to the atomic lattice vibrations in graphene nanoribbons and nanorings
under a thermal gradient. We consider a wide range of temperature, nanoribbon
widths up to 6nm and the effect of moderate edge disorder. We find that narrow
graphene nanorings can efficiently suppress the lattice thermal conductivity at
low temperatures (~100K), as compared to nanoribbons of the same width.
Remarkably, rough edges do not appear to have a large impact on lattice energy
transport through graphene nanorings while nanoribbons seem more affected by
imperfections. Furthermore, we demonstrate that the effects of
hydrogen-saturated edges can be neglected in these graphene nanostructures
Controlling chaos in diluted networks with continuous neurons
Diluted neural networks with continuous neurons and nonmonotonic transfer
function are studied, with both fixed and dynamic synapses. A noisy stimulus
with periodic variance results in a mechanism for controlling chaos in neural
systems with fixed synapses: a proper amount of external perturbation forces
the system to behave periodically with the same period as the stimulus.Comment: 11 pages, 8 figure
Deliverable 4.2 Support of joint learing and innovation in grassroots development initiatives: operational quality of arrangements
Model for quantitative tip-enhanced spectroscopy and the extraction of nanoscale-resolved optical constants
Near-field infrared spectroscopy by elastic scattering of light from a probe
tip resolves optical contrasts in materials at dramatically sub-wavelength
scales across a broad energy range, with the demonstrated capacity for chemical
identification at the nanoscale. However, current models of probe-sample
near-field interactions still cannot provide a sufficiently quantitatively
interpretation of measured near-field contrasts, especially in the case of
materials supporting strong surface phonons. We present a model of near-field
spectroscopy derived from basic principles and verified by finite-element
simulations, demonstrating superb predictive agreement both with tunable
quantum cascade laser near-field spectroscopy of SiO thin films and with
newly presented nanoscale Fourier transform infrared (nanoFTIR) spectroscopy of
crystalline SiC. We discuss the role of probe geometry, field retardation, and
surface mode dispersion in shaping the measured near-field response. This
treatment enables a route to quantitatively determine nano-resolved optical
constants, as we demonstrate by inverting newly presented nanoFTIR spectra of
an SiO thin film into the frequency dependent dielectric function of its
mid-infrared optical phonon. Our formalism further enables tip-enhanced
spectroscopy as a potent diagnostic tool for quantitative nano-scale
spectroscopy.Comment: 19 pages, 9 figure
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