393 research outputs found
Anisotropic thermal expansion and thermomechanic properties of monolayer -Te
Recently, -Te (atomically 2D tellurium) with rectangular crystal
structure has been synthesized successfully on highly oriented pyrolytic
graphite substrates by using molecular beam epitaxy. It has been found
possessing remarkable properties such as ultralow lattice thermal conductivity
and high thermoelectric efficiency. Based on the first-principles calculations,
we study the thermal expansion and thermomechanic properties of the
experimental phase monolayer -Te, using quasiharmonic approach. It is
found -Te shows large positive thermal expansion at elevated
temperature, while the linear thermal expansion coefficient is negative along a
direction at very low temperature. The linear thermal expansion coefficient
along b direction is 4.9*10 K at 500 K, which is considerably
large in 2D materials. -Te exhibits strong in-plane anisotropy,
including thermal expansion, 2D elastic moduli and Poisson's ratios. However,
the elastic moduli, Poisson's ratios and the in-plane anisotropy are weakened
with increasing temperature, and the variations are dominated by the
generalized mode Gr\"{u}neisen parameters.Comment: 25 pages, 7 figures, 14 formula
Two-dimensional Mechanical Metamaterials with Unusual Poisson Ratio Behavior
We design two-dimensional (2D) mechanical metamaterials that may be deformed
substantially at little or no energy cost. Examples of such deformable
structures are assemblies of rigid isosceles triangles hinged in their corners
on the macro-scale, or polymerized phenanthrene molecules forming porous
graphene on the nano-scale. In these and in a large class of related
structures, the Poisson ratio diverges for particular strain values.
also changes its magnitude and sign, and displays a shape memory effect.Comment: Accepted by Phys. Rev. Applied 10 (2018
Unusually low thermal conductivity of atomically thin 2D tellurium
Tellurium is a high-performance thermoelectric material due to its superior
electronic transport and low lattice thermal conductivity (). Here,
we report the ultralow in the monolayer tellurium, i.e., tellurene,
which has been successfully synthesized in recent experiments. We find
tellurene has a compellingly low room temperature of 2.16 and 4.08 W
m K along the armchair and zigzag directions, respectively, which
is lower than any reported values for other 2D materials. We attribute this
unusually low to the soft acoustic modes, extremely low-energy
optical modes and the strong scattering among optical-acoustic phonons, which
place tellurene as a potential novel thermoelectric material. Finally, we
disclose that is proportional to the largest acoustic phonon
frequency () and the lowest optical phonon frequency at
point () in 2D materials, which reflect both
harmonic and anharmonic thermal properties respectively.Comment: 9 pages, 4 figures, submittin
Stretch diffusion and heat conduction in 1D nonlinear lattices
In the study of 1D nonlinear Hamiltonian lattices, the conserved quantities
play an important role in determining the actual behavior of heat conduction.
Besides the total energy, total momentum and total stretch could also be
conserved quantities. In microcanonical Hamiltonian dynamics, the total energy
is always conserved. It was recently argued by Das and Dhar that whenever
stretch (momentum) is not conserved in a 1D model, the momentum (stretch) and
energy fields exhibit normal diffusion. In this work, we will systematically
investigate the stretch diffusions for typical 1D nonlinear lattices. No clear
connection between the conserved quantities and heat conduction can be
established. The actual situation is more complicated than what Das and Dhar
claimed.Comment: 6 pages, 6 figure
Strain Effects on the Mechanical Properties of Group-V Monolayers with Buckled Honeycomb Structures
Based on first-principles calculations, we study systematically the ideal
tensile stress-strain relations of three monoatomic group-V monolayer two
dimensional (2D) materials with buckled honeycomb lattices: blue phosphorene,
arsenene, and antimonene. The ideal strengths and critical strains for these 2D
materials are investigated under uniaxial and equibiaxial strains. It is found
that the ideal strengths decrease significantly as the atomic number increases,
while the critical strains change not so much. In particular, the ideal
strength of antimonene along armchair direction is found to exceed Griffith
strength limit. The distributions of charge density, buckling heights, bond
lengths, and bond angles are also studied under different types of strains. It
can be concluded that the critical strain is determined by the stretch and
rotation of bonds simultaneously. Furthermore, the phonon dispersions, phonon
instabilities, and failure mechanism of these materials under three types of
strains are also calculated and explored.Comment: 24 pages, 8 figure
Heat conduction and energy diffusion in momentum-conserving 1D full lattice ding-a-ling model
The ding-a-ling model is a kind of half lattice and half hard-point-gas (HPG)
model. The original ding-a-ling model proposed by Casati {\it et.al} does not
conserve total momentum and has been found to exhibit normal heat conduction
behavior. Recently, a modified ding-a-ling model which conserves total momentum
has been studied and normal heat conduction has also been claimed. In this
work, we propose a full lattice ding-a-ling model without hard point collisions
where total momentum is also conserved. We investigate the heat conduction and
energy diffusion of this full lattice ding-a-ling model with three different
nonlinear inter-particle potential forms. For symmetrical potential lattices,
the thermal conductivities diverges with lattice length and their energy
diffusions are superdiffusive signaturing anomalous heat conduction. For
asymmetrical potential lattices, although the thermal conductivity seems to
converge as the length increases, the energy diffusion is definitely deviating
from normal diffusion behavior indicating anomalous heat conduction as well. No
normal heat conduction behavior can be found for the full lattice ding-a-ling
model.Comment: 7 pages, 8 figure
Degenerately Doped Transition Metal Dichalcogenides as Ohmic Homojunction Contacts to Transition Metal Dichalcogenide Semiconductors
In search of an improved strategy to form low resistance contacts to MoS2 and
related semiconducting transition metal dichalcogenides, we use ab initio
density functional electronic structure calculations in order to determine the
equilibrium geometry and electronic structure of MoO3/MoS2 and MoO2/MoS2
bilayers. Our results indicate that, besides a rigid band shift associated with
charge transfer, the presence of molybdenum oxide modifies the electronic
structure of MoS2 very little. We find that the charge transfer in the bilayer
provides a sufficient degree of hole doping to MoS2, resulting in a highly
transparent contact region.Comment: 14 pages, 9 figure
Directional Design of Materials Based on the Pareto Optimization: Application to Two-Dimensional Thermoelectric SnSe
Increasing the efficiency of directional design of functional materials is a
challenging work in theory, whose performance and stability are determined by
different factors entangled with each other complicatedly. In this work, we
apply the Pareto Optimization based on the Pareto Efficiency and Particle-Swarm
Optimization to design new functional materials directionally. As a
demonstration, we apply the method to the thermoelectric design of 2D SnSe
materials and identify several novel structures with lower free energy and
better thermoelectric performance than the experimental monolayer structure in
theory. We hope the multi-objective Pareto Optimization method can make the
integrative design of multi-objective and multi-functional materials a reality.Comment: 5 pages, 4 figures, under revie
Adaptive Embedding Pattern for Grayscale-Invariance Reversible Data Hiding
In traditional reversible data hiding (RDH) methods, researchers pay
attention to enlarge the embedding capacity (EC) and to reduce the embedding
distortion (ED). Recently, a completely novel RDH algorithm was developed to
embed secret data into color image without changing the corresponding grayscale
[1], which largely expands the applications of RDH. In [1], for color image,
channel R and channel B are exploited to carry secret information, channel G is
adjusted for balancing the modifications of channel R and channel B to keep the
invariance of grayscale. However, we found that the embedding performance (EP)
of that method is still unsatisfied and could be further enhanced. To improve
the EP, an adaptive embedding pattern is introduced to enhance the competence
of algorithm for selectively embedding different bits of secret data into
pixels according to context information. Moreover, a novel two-level predictor
is designed by uniting two normal predictors for reducing the ED for embedding
more bits. Experimental results demonstrate that, compared to the previous
method, our scheme could significantly enhance the image fidelity while keeping
the grayscale invariant
A Computation Offloading Incentive Mechanism with Delay and Cost Constraints under 5G Satellite-ground IoV architecture
The 5G Internet of Vehicles has become a new paradigm alongside the growing
popularity and variety of computation-intensive applications with high
requirements for computational resources and analysis capabilities. Existing
network architectures and resource management mechanisms may not sufficiently
guarantee satisfactory Quality of Experience and network efficiency, mainly
suffering from coverage limitation of Road Side Units, insufficient resources,
and unsatisfactory computational capabilities of onboard equipment, frequently
changing network topology, and ineffective resource management schemes. To meet
the demands of such applications, in this article, we first propose a novel
architecture by integrating the satellite network with 5G cloud-enabled
Internet of Vehicles to efficiently support seamless coverage and global
resource management. A incentive mechanism based joint optimization problem of
opportunistic computation offloading under delay and cost constraints is
established under the aforementioned framework, in which a vehicular user can
either significantly reduce the application completion time by offloading
workloads to several nearby vehicles through opportunistic vehicle-to-vehicle
channels while effectively controlling the cost or protect its own profit by
providing compensated computing service. As the optimization problem is
non-convex and NP-hard, simulated annealing based on the Markov Chain Monte
Carlo as well as the metropolis algorithm is applied to solve the optimization
problem, which can efficaciously obtain both high-quality and cost-effective
approximations of global optimal solutions. The effectiveness of the proposed
mechanism is corroborated through simulation results
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