190 research outputs found
Thermal conductivity of monolayer MoS2, MoSe2, and WS2: Interplay of mass effect, interatomic bonding and anharmonicity
Phonons are essential for understanding the thermal properties in monolayer
transition metal dichalcogenides, which limit their thermal performance for
potential applications. We investigate the lattice dynamics and thermodynamic
properties of MoS2, MoSe2, and WS2 by first principles calculations. The
obtained phonon frequencies and thermal conductivities agree well with the
measurements. Our results show that the thermal conductivity of MoS2 is highest
among the three materials due to its much lower average atomic mass. We also
discuss the competition between mass effect, interatomic bonding and anharmonic
vibrations in determining the thermal conductivity of WS2. Strong covalent W-S
bonding and low anharmonicity in WS2 are found to be crucial in understanding
its much higher thermal conductivity compared to MoSe2.Comment: 19 pages, 7 figure
Fast Algorithms for Surface Reconstruction from Point Cloud
We consider constructing a surface from a given set of point cloud data. We
explore two fast algorithms to minimize the weighted minimum surface energy in
[Zhao, Osher, Merriman and Kang, Comp.Vision and Image Under., 80(3):295-319,
2000]. An approach using Semi-Implicit Method (SIM) improves the computational
efficiency through relaxation on the time-step constraint. An approach based on
Augmented Lagrangian Method (ALM) reduces the run-time via an Alternating
Direction Method of Multipliers-type algorithm, where each sub-problem is
solved efficiently. We analyze the effects of the parameters on the level-set
evolution and explore the connection between these two approaches. We present
numerical examples to validate our algorithms in terms of their accuracy and
efficiency
Triggering Boundary Phase Transitions through Bulk Measurements in 2D Cluster States
We investigate the phase diagram at the boundary of an infinite
two-dimensional cluster state subject to bulk measurements using tensor network
methods. The state is subjected to uniform measurements on the lower boundary qubits and in all bulk
qubits. Our results show that the boundary of the system exhibits volume-law
entanglement at the measurement angle and area-law
entanglement for any . Within the area-law phase, a phase
transition occurs at . The phase with is characterized by a noninjective matrix product state,
which cannot be realized as the unique ground state of a one-dimensional local,
gapped Hamiltonian. Instead, it resembles a cat state with spontaneous symmetry
breaking. These findings demonstrate that the phase diagram of the boundary of
a two-dimensional system can be more intricate than that of a standard
one-dimensional system.Comment: 7 pages, 6 figure
Commercial Janus Fabrics as Reusable Facemask Materials: A Balance of Water Repellency, Filtration Efficiency, Breathability, and Reusability
Facemasks as personal protective equipment play a significant role in helping prevent the spread of viruses during the COVID-19 pandemic. A desired reusable fabric facemask should strike a balance of water repellency, good filtration efficiency (FE), breathability, and mechanical robustness against washing cycles. Despite significant efforts in testing various commercial fabric materials for filtration efficiency, few have investigated fabric performance as a function of the fiber/yarn morphology and wettability of the fabric itself. In this study, we examine commercial fabrics with Janus-like behaviors to determine the best reusable fabric facemask materials by understanding the roles of morphology, porosity, and wettability of the fabric on its overall performance. We find that the outer layer of the diaper fabric consisted of laminated polyurethane, which is hydrophobic, has low porosity (∼5%) and tightly woven yarn structures, and shows the highest overall FE (up to 54%) in the submicron particle size range (0.03-0.6 μm) among the fabrics tested. Fabric layers with higher porosity lead to lower-pressure drops, indicating higher breathability but lower FE. Tightly woven waterproof rainwear fabrics perform the best after 10 washing cycles, remaining intact morphologically with only a 2-5% drop in the overall FE in the submicron particle size range, whereas other knitted fabric layers become loosened and the laminated polyurethane thin film on the diaper fabric is wrinkled. In comparison, the surgical masks and N95 respirators made from nonwoven polypropylene (PP) fibers see over a 30% decline in the overall FE after 10 washing cycles. Overall, we find that tightly woven Janus fabrics consisting of a low porosity, a hydrophobic outer layer, and a high porosity and hydrophilic inner layer offer the best performance among the fabrics tested as they can generate a high overall FE, achieve good breathability, and maintain fabric morphology and performance over multiple washing cycles
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