16,141 research outputs found
Boosting thermoelectric efficiency using time-dependent control
Thermoelectric efficiency is defined as the ratio of power delivered to the
load of a device to the rate of heat flow from the source. Till date, it has
been studied in presence of thermodynamic constraints set by the Onsager
reciprocal relation and the second law of thermodynamics that severely
bottleneck the thermoelectric efficiency. In this study, we propose a pathway
to bypass these constraints using a time-dependent control and present a
theoretical framework to study dynamic thermoelectric transport in the far from
equilibrium regime. The presence of a control yields the sought after
substantial efficiency enhancement and importantly a significant amount of
power supplied by the control is utilised to convert the wasted-heat energy
into useful-electric energy. Our findings are robust against nonlinear
interactions and suggest that external time-dependent forcing, which can be
incorporated with existing devices, provides a beneficial scheme to boost
thermoelectric efficiency.Comment: 8 pages + 3 figures (Accepted in Scientific Reports
FPU physics with nanomechanical graphene resonators: intrinsic relaxation and thermalization from flexural mode coupling
Thermalization in nonlinear systems is a central concept in statistical
mechanics and has been extensively studied theoretically since the seminal work
of Fermi, Pasta and Ulam (FPU). Using molecular dynamics and continuum modeling
of a ring-down setup, we show that thermalization due to nonlinear mode
coupling intrinsically limits the quality factor of nanomechanical graphene
drums and turns them into potential test beds for FPU physics. We find the
thermalization rate to be independent of radius and scaling as
, where and
are effective resonator temperature and prestrain
Minimum-time trajectory generation for quadrotors in constrained environments
In this paper, we present a novel strategy to compute minimum-time
trajectories for quadrotors in constrained environments. In particular, we
consider the motion in a given flying region with obstacles and take into
account the physical limitations of the vehicle. Instead of approaching the
optimization problem in its standard time-parameterized formulation, the
proposed strategy is based on an appealing re-formulation. Transverse
coordinates, expressing the distance from a frame path, are used to
parameterise the vehicle position and a spatial parameter is used as
independent variable. This re-formulation allows us to (i) obtain a fixed
horizon problem and (ii) easily formulate (fairly complex) position
constraints. The effectiveness of the proposed strategy is proven by numerical
computations on two different illustrative scenarios. Moreover, the optimal
trajectory generated in the second scenario is experimentally executed with a
real nano-quadrotor in order to show its feasibility.Comment: arXiv admin note: text overlap with arXiv:1702.0427
Nonlinear optical response in gapped graphene
We present a formulation for the nonlinear optical response in gapped
graphene, where the low-energy single-particle spectrum is modeled by massive
Dirac theory. As a representative example of the formulation presented here, we
obtain closed form formula for the third harmonic generation (THG) in gapped
graphene. It turns out that the covariant form of the low-energy theory gives
rise to a peculiar logarithmic singularities in the nonlinear optical spectra.
The universal functional dependence of the response function on dimension-less
quantities indicates that the optical nonlinearity can be largely enhanced by
tuning the gap to smaller values.Comment: http://iopscience.iop.org/0953-8984/labtalk-article/4938
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