5,640 research outputs found
Phonon Modes in Single-Walled Molybdenum Disulphide (MoS2) Nanotubes: Lattice Dynamics Calculation and Molecular Dynamics Simulation
We study the phonon modes in single-walled MoS nanotubes via the
lattice dynamics calculation and molecular dynamics simulation. The phonon
spectra for tubes of arbitrary chiralities are calculated from the dynamical
matrix constructed by the combination of an empirical potential with the
conserved helical quantum numbers . In particular, we show that
the frequency () of the radial breathing mode is inversely proportional
to the tube diameter () as {cm}. The eigen vectors
of the first twenty lowest-frequency phonon modes are illustrated. Based on
these eigen vectors, we demonstrate that the radial breathing oscillation is
disturbed by phonon modes of three-fold symmetry initially, and the tube is
squashed by the modes of two-fold symmetry eventually. Our study provides
fundamental knowledge for further investigations of the thermal and mechanical
properties of the MoS nanotubes.Comment: Nanotechnology, publishe
Adaptive and Robust Fault-Tolerant Tracking Control of Contact force of Pantograph-Catenary for High-Speed Trains
Abstract This paper presents a modified multi-body dynamic model and a linear time-invariant model with actuator faults (loss of effectiveness faults, bias faults) and matched and unmatched uncertainties. Based on the fault model, a class of adaptive and robust tracking controllers are proposed which are adjusted online to tolerate the time-varying loss of effectiveness faults and bias faults, and compensate matched disturbances without the knowledge of bounds. For unmatched uncertainties, optimal control theory is added to the controller design processes. Simulations on a pantograph are shown to verify the efficiency of the proposed fault-tolerant design approach
First principle study of the thermal conductance in graphene nanoribbon with vacancy and substitutional silicon defect
The thermal conductance in graphene nanoribbon with a vacancy or silicon
point defect (substitution of C by Si atom) is investigated by non-equilibrium
Green's function (NEGF) formalism combined with first-principle calculations
density-functional theory with local density approximation. An efficient
correction to the force constant matrix is presented to solve the conflict
between the long-range character of the {\it ab initio} approach and the
first-nearest-neighboring character of the NEGF scheme. In nanoribbon with a
vacancy defect, the thermal conductance is very sensitive to the position of
the vacancy defect. A vacancy defect situated at the center of the nanoribbon
generates a saddle-like surface, which greatly reduces the thermal conductance
by strong scattering to all phonon modes; while an edge vacancy defect only
results in a further reconstruction of the edge and slightly reduces the
thermal conductance. For the Si defect, the position of the defect plays no
role for the value of the thermal conductance, since the defective region is
limited within a narrow area around the defect center.Comment: accepted by AP
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