15,060 research outputs found
Effect of sampling rate and record length on the determination of stability and control derivatives
Flight data from five aircraft were used to assess the effects of sampling rate and record length reductions on estimates of stability and control derivatives produced by a maximum likelihood estimation method. Derivatives could be extracted from flight data with the maximum likelihood estimation method even if there were considerable reductions in sampling rate and/or record length. Small amplitude pulse maneuvers showed greater degradation of the derivative maneuvers than large amplitude pulse maneuvers when these reductions were made. Reducing the sampling rate was found to be more desirable than reducing the record length as a method of lessening the total computation time required without greatly degrading the quantity of the estimates
Geometrical and electronic structures of the (5, 3) single-walled gold nanotube from first-principles calculations
The geometrical and electronic structures of the 4 {\AA} diameter perfect and
deformed (5, 3) single-walled gold nanotube (SWGT) have been studied based upon
the density-functional theory in the local-density approximation (LDA). The
calculated relaxed geometries show clearly significant deviations from those of
the ideally rolled triangular gold sheet. It is found that the different
strains have different effects on the electronic structures and density of
states of the SWGTs. And the small shear strain can reduce the binding energy
per gold atom of the deformed SWGT, which is consistent with the experimentally
observed result. Finally, we found the finite SWGT can show the
metal-semiconductor transition.Comment: 11 pages, 4 figure
Thermal rectification in asymmetric U-shaped graphene flakes
In this paper, we study the thermal rectification in asymmetric U-shaped
graphene flakes by using nonequilibrium molecular dynamics simulations. The
graphene flakes are composed by a beam and two arms. It is found that the heat
flux runs preferentially from the wide arm to the narrow arm which indicates a
strong rectification effect. The dependence of the rectification ratio upon the
heat flux, the length and the width of the beam, the length and width of the
two arms are studied. The result suggests a possible route to manage heat
dissipation in U-shaped graphene based nanoelectronic devices.Comment: 3 pages, 4 figure
Thermomechanical properties of graphene: valence force field model approach
Using the valence force field model of Perebeinos and Tersoff [Phys. Rev. B
{\bf79}, 241409(R) (2009)], different energy modes of suspended graphene
subjected to tensile or compressive strain are studied. By carrying out Monte
Carlo simulations it is found that: i) only for small strains () the total energy is symmetrical in the strain, while it
behaves completely different beyond this threshold; ii) the important energy
contributions in stretching experiments are stretching, angle bending,
out-of-plane term and a term that provides repulsion against
misalignment; iii) in compressing experiments the two latter terms increase
rapidly and beyond the buckling transition stretching and bending energies are
found to be constant; iv) from stretching-compressing simulations we calculated
the Young modulus at room temperature 350\,N/m, which is in good
agreement with experimental results (340\,N/m) and with ab-initio
results [322-353]\,N/m; v) molar heat capacity is estimated to be
24.64\,J/molK which is comparable with the Dulong-Petit value,
i.e. 24.94\,J/molK and is almost independent of the strain; vi)
non-linear scaling properties are obtained from height-height correlations at
finite temperature; vii) the used valence force field model results in a
temperature independent bending modulus for graphene, and viii) the Gruneisen
parameter is estimated to be 0.64.Comment: 8 pages, 5 figures. To appear in J. Phys.: Condens. Matte
Enhancing the Mass Sensitivity of Graphene Nanoresonators Via Nonlinear Oscillations: The Effective Strain Mechanism
We perform classical molecular dynamics simulations to investigate the
enhancement of the mass sensitivity and resonant frequency of graphene
nanomechanical resonators that is achieved by driving them into the nonlinear
oscillation regime. The mass sensitivity as measured by the resonant frequency
shift is found to triple if the actuation energy is about 2.5 times the initial
kinetic energy of the nanoresonator. The mechanism underlying the enhanced mass
sensitivity is found to be the effective strain that is induced in the
nanoresonator due to the nonlinear oscillations, where we obtain an analytic
relationship between the induced effective strain and the actuation energy that
is applied to the graphene nanoresonator. An important implication of this work
is that there is no need for experimentalists to apply tensile strain to the
resonators before actuation in order to enhance the mass sensitivity. Instead,
enhanced mass sensitivity can be obtained by the far simpler technique of
actuating nonlinear oscillations of an existing graphene nanoresonator.Comment: published versio
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