852 research outputs found
Infrastructure Exposure, Extreme Weather Events & Climate Change - SF Bay - Napoli
Big Data analysis and computer modeling to compare the Mediterranean-type climate coastlands of San Francisco Bay, California (USA), and Naples Bay, southern Italy, prone to extreme weather events, sea storms and tsunami, climate change and sea level rise
Photoelasticity of sodium silicate glass from first principles
Based on density-functional perturbation theory we have computed the
photoelastic tensor of a model of sodium silicate glass of composition
(NaO)(SiO) (NS3). The model (containig 84 atoms) is
obtained by quenching from the melt in combined classical and Car-Parrinello
molecular dynamics simulations. The calculated photoelastic coefficients are in
good agreement with experimental data. In particular, the calculation
reproduces quantitatively the decrease of the photoelastic response induced by
the insertion of Na, as measured experimentally.
The extension to NS3 of a phenomenological model developed in a previous work
for pure a-SiO indicates that the modulation upon strain of other
structural parameters besides the SiOSi angles must be invoked to explain the
change in the photoelstic response induced by Na
Water on Pt(111): the importance of proton disorder
The structure of a water adlayer on Pt(111) surface is investigated by
extensive first principle calculations. Only allowing for proton disorder the
ground state energy can be found. This results from an interplay between
water/metal chemical bonding and the hydrogen bonding of the water network. The
resulting short O-Pt distance accounts for experimental evidences. The novelty
of these results shed a new light on relevant aspects of water-metal
interaction.Comment: 10 pages 4 figures (color
Mn-Intercalated MoSe under pressure: electronic structure and vibrational characterization of a dilute magnetic semiconductor
Intercalation offers a promising way to alter the physical properties of
two-dimensional (2D) layered materials. Here we investigate the electronic and
vibrational properties of 2D layered MoSe intercalated with atomic
manganese at ambient and high pressure up to 7 GPa by Raman scattering and
electronic structure calculations. The behavior of optical phonons is studied
experimentally with a diamond anvil cell and computationally through density
functional theory calculations. Experiment and theory show excellent agreement
in optical phonon behavior. The previously Raman inactive A mode is
activated and enhanced with intercalation and pressure, and a new Raman mode
appears upon decompression, indicating a possible onset of a localized
structural transition, involving the bonding or trapping of intercalant in 2D
layered materials. Density functional theory calculations reveal a shift of
Fermi level into the conduction band and spin polarization in MnMoSe
that increases at low Mn concentration and low pressure. Our results suggest
that intercalation and pressurization of van der Waals materials may allow one
to obtain dilute magnetic semiconductors with controllable properties,
providing a viable route for the development of new materials for spintronic
applications.Comment: 8 pages, 5 figure
Dataset of measured and commented pantograph electric arcs in DC railways
DC railways are characterized by particularly intense arcing caused by pantograph detachment, due to the large current intensity and the general implementation of onboard resonant filters, whose transient response is triggered by electric transients including electric arcs. Electric arc depends on the train speed (the relative speed between the sliding contact over the pantograph and the hot spot on the catenary system), the intensity of the collected pantograph current and the line voltage level. Electric arcs are broadband in nature and can trigger the system transient response dominated by the resonant filter, besides interfering with the operation of onboard equipment (such as for energy conversion and metering)
Optimal thickness of silicon membranes to achieve maximum thermoelectric efficiency: A first principles study
Silicon nanostructures with reduced dimensionality, such as nanowires, membranes, and thin films, are promising thermoelectric materials, as they exhibit considerably reduced thermal conductivity. Here, we utilize density functional theory and Boltzmann transport equation to compute the electronic properties of ultra-thin crystalline silicon membranes with thickness between 1 and 12 nm. We predict that an optimal thickness of ∼7 nm maximizes the thermoelectric figure of merit of membranes with native oxide surface layers. Further thinning of the membranes, although attainable in experiments, reduces the electrical conductivity and worsens the thermoelectric efficiency
Thermal transistor: Heat flux switching and modulating
Thermal transistor is an efficient heat control device which can act as a
heat switch as well as a heat modulator. In this paper, we study systematically
one-dimensional and two-dimensional thermal transistors. In particular, we show
how to improve significantly the efficiency of the one-dimensional thermal
transistor. The study is also extended to the design of two-dimensional thermal
transistor by coupling different anharmonic lattices such as the
Frenkel-Kontorova and the Fermi-Pasta-Ulam lattices. Analogy between anharmonic
lattices and single-walled carbon nanotube is drawn and possible experimental
realization with multi-walled nanotube is suggested.Comment: To appear in J. Phys. Soc. Jp
Energetics and stability of nanostructured amorphous carbon
Monte Carlo simulations, supplemented by ab initio calculations, shed light
into the energetics and thermodynamic stability of nanostructured amorphous
carbon. The interaction of the embedded nanocrystals with the host amorphous
matrix is shown to determine in a large degree the stability and the relative
energy differences among carbon phases. Diamonds are stable structures in
matrices with sp^3 fraction over 60%. Schwarzites are stable in low-coordinated
networks. Other sp^2-bonded structures are metastable.Comment: 11 pages, 7 figure
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