58 research outputs found
Gap prediction in hybrid graphene - hexagonal boron nitride nanoflakes using artificial neural networks
The electronic properties graphene nanoflakes (GNFs) with embedded hexagonal
boron nitride (hBN) domains are investigated by combined {\it ab initio}
density functional theory calculations and machine learning techniques. The
energy gaps of the quasi-0D graphene based systems, defined as the differences
between LUMO and HOMO energies, depend on the sizes of the hBN domains relative
to the size of the pristine graphene nanoflake, but also on the position of the
hBN domain. The range of the energy gaps for different configurations is
increasing as the hBN domains get larger. We develop two artificial neural
network (ANN) models able to reproduce the gap energies with high accuracies
and investigate the tunability of the energy gap, by considering a set of GNFs
with embedded rectangular hBN domains. In one ANN model, the input is in
one-to-one correspondence with the atoms in the GNF, while in the second model
the inputs account for basic structures in the GNF, allowing potential use in
up-scaled structures. We perform a statistical analysis over different
configurations of ANNs to optimize the network structure. The trained ANNs
provide a correlation between the atomic system configuration and the magnitude
of the energy gaps, which may be regarded as an efficient tool for optimizing
the design of nanostructured graphene based materials for specific electronic
properties.Comment: 6 pages, 5 figure
A Laboratory Investigation of Supersonic Clumpy Flows: Experimental Design and Theoretical Analysis
We present a design for high energy density laboratory experiments studying
the interaction of hypersonic shocks with a large number of inhomogeneities.
These ``clumpy'' flows are relevant to a wide variety of astrophysical
environments including the evolution of molecular clouds, outflows from young
stars, Planetary Nebulae and Active Galactic Nuclei. The experiment consists of
a strong shock (driven by a pulsed power machine or a high intensity laser)
impinging on a region of randomly placed plastic rods. We discuss the goals of
the specific design and how they are met by specific choices of target
components. An adaptive mesh refinement hydrodynamic code is used to analyze
the design and establish a predictive baseline for the experiments. The
simulations confirm the effectiveness of the design in terms of articulating
the differences between shocks propagating through smooth and clumpy
environments. In particular, we find significant differences between the shock
propagation speeds in a clumpy medium compared to a smooth one with the same
average density. The simulation results are of general interest for foams in
both inertial confinement fusion and laboratory astrophysics studies. Our
results highlight the danger of using average properties of inhomogeneous
astrophysical environments when comparing timescales for critical processes
such as shock crossing and gravitational collapse times.Comment: 7 pages, 6 figures. Submitted to the Astrophysical Journal. For
additional information, including simulation animations and the pdf and ps
files of the paper with embedded high-quality images, see
http://pas.rochester.edu/~wm
Designing Plasmon-Enhanced Thermochromic Films Using a Vanadium Dioxide Nanoparticle Elastomeric Composite
Vanadium dioxide (VO2) is a common material for use in thermochromic windows due to a semiconductor-to-metal transition (SMT) that is coupled with a change in infrared opacity. Commercialization of VO2-based thermochromic technology is hampered by relatively expensive synthesis and film fabrication techniques as well as overall low performance as a window material. Here, simulations that indicate the plasmon resonance of VO2 nanoparticles in a composite film, which can be tuned to achieve record performance values, are reported. These simulations are experimentally verified by fabricating a VO2 nanoparticle composite in an elastomeric matrix using low-temperature and atmospheric processing conditions. The optical properties of the films are analyzed, yielding visible transmittance and infrared modulation values within the range of top-performing thermochromic windows. In addition, an improvement in performance is observed upon stretching the films, an effect that can be attributed to a local refractive index modulation. The results highlight the potential use of elastomeric composites as a low-cost route to higher-performance smart windows
Abstracts of the 33rd International Austrian Winter Symposium : Zell am See, Austria. 24-27 January 2018.
Nitrous oxide, ammonia and methane from Australian meat chicken houses measured under commercial operating conditions and with mitigation strategies applied
Gap Prediction in Hybrid Graphene-Hexagonal Boron Nitride Nanoflakes Using Artificial Neural Networks
The electronic properties of graphene nanoflakes (GNFs) with embedded hexagonal boron nitride (hBN) domains are investigated by combined ab initio density functional theory calculations and machine-learning techniques. The energy gaps of the quasi-0D graphene-based systems, defined as the differences between LUMO and HOMO energies, depend not only on the sizes of the hBN domains relative to the size of the pristine graphene nanoflake but also on the position of the hBN domain. The range of the energy gaps for different configurations increases as the hBN domains get larger. We develop two artificial neural network (ANN) models able to reproduce the gap energies with high accuracies and investigate the tunability of the energy gap, by considering a set of GNFs with embedded rectangular hBN domains. In one ANN model, the input is in one-to-one correspondence with the atoms in the GNF, while in the second model the inputs account for basic structures in the GNF, allowing potential use in upscaled systems. We perform a statistical analysis over different configurations of ANNs to optimize the network structure. The trained ANNs provide a correlation between the atomic system configuration and the magnitude of the energy gaps, which may be regarded as an efficient tool for optimizing the design of nanostructured graphene-based materials for specific electronic properties
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