3,720 research outputs found
Performance analysis of an interacting quantum dot thermoelectric system
We analyze the nanocaloritronic performance of an interacting quantum dot
that is subject to an applied bias and an applied temperature gradient. It is
now well known that, in the absence of phonon contribution, a weakly coupled
non-interacting quantum dot can operate at thermoelectric efficiencies
approaching the Carnot limit. However, it has also been recently pointed out
that such peak efficiencies can only be achieved when operated in the
reversible limit, with a vanishing current and hence a vanishing power output.
In this paper, we point out three fundamental results affecting the
thermoelectric performance due to the inclusion of Coulomb interactions: a) The
reversible operating point carries zero efficiency, b) operation at finite
power output is possible even at peak efficiencies approaching the Carnot
value, and c) the evaluated trends of the the maximum efficiency deviate
considerably from the conventional {\it{figure of merit}} based result.
Finally, we also analyze our system for thermoelectric operation at maximum
power output.Comment: 10 pages, 6 figures, Resubmission- to be published in Phys. Rev.
Phonon-assisted tunneling in interacting suspended single wall carbon nanotubes
Transport in suspended metallic single wall carbon nanotubes in the presence
of strong electron-electron interaction is investigated. We consider a tube of
finite length and discuss the effects of the coupling of the electrons to the
deformation potential associated to the acoustic stretching and breathing
modes. Treating the interacting electrons within the framework of the Luttinger
liquid model, the low-energy spectrum of the coupled electron-phonon system is
evaluated. The discreteness of the spectrum is reflected in the differential
conductance which, as a function of the applied bias voltage, exhibits three
distinct families of peaks. The height of the phonon-assisted peaks is very
sensitive to the parameters. The phonon peaks are best observed when the system
is close to the Wentzel-Bardeen singularity.Comment: 14 pages, 3 figure
Theory of STM junctions for \pi-conjugated molecules on thin insulating films
A microscopic theory of the transport in a scanning tunnelling microscope
(STM) set-up is introduced for \pi-conjugated molecules on insulating films,
based on the density matrix formalism. A key role is played in the theory by
the energy dependent tunnelling rates which account for the coupling of the
molecule to the tip and to the substrate. In particular, we analyze how the
geometrical differences between the localized tip and extended substrate are
encoded in the tunnelling rate and influence the transport characteristics.
Finally, using benzene as an example of a planar, rotationally symmetric
molecule, we calculate the STM current voltage characteristics and current maps
and analyze them in terms of few relevant angular momentum channels.Comment: 19 pages, 12 figures, minor changes to conform to published versio
Localized Faraday patterns under heterogeneous parametric excitation
Faraday waves are a classic example of a system in which an extended pattern
emerges under spatially uniform forcing. Motivated by systems in which uniform
excitation is not plausible, we study both experimentally and theoretically the
effect of heterogeneous forcing on Faraday waves. Our experiments show that
vibrations restricted to finite regions lead to the formation of localized
subharmonic wave patterns and change the onset of the instability. The
prototype model used for the theoretical calculations is the parametrically
driven and damped nonlinear Schr\"odinger equation, which is known to describe
well Faraday-instability regimes. For an energy injection with a Gaussian
spatial profile, we show that the evolution of the envelope of the wave pattern
can be reduced to a Weber-equation eigenvalue problem. Our theoretical results
provide very good predictions of our experimental observations provided that
the decay length scale of the Gaussian profile is much larger than the pattern
wavelength.Comment: 10 pages, 9 figures, Accepte
Threats to and viability of the giant anteater, Myrmecophaga tridactyla (Pilosa: Myrmecophagidae), in a protected Cerrado remnant encroached by urban expansion in central Brazil
Simulation and evaluation of deep learning autoencoders for image compression in multi-UAV network systems
Mobile multi-robot systems are versatile alternatives
for improving single-robot capacities in many applications, such
as logistics, environmental monitoring, search and rescue, photogrammetry,
etc. In this sense, this kind of system must have a
reliable communication network between the vehicles, ensuring
that information exchanged within the nodes has little losses. This
work simulates and evaluates the use of autoencoders for image
compression in a multi-UAV simulation with ROS and Gazebo
for a generic surveillance application. The autoencoder model
was developed with the Keras library, presenting good training
and validation results, with training and validation accuracy
of 70%, and a Peak Signal Noise Ratio (PSNR) of 40dB. The
use of the CPU for the simulated UAVs for processing and
sending compressed images through the network is 25% faster.
The results showed that this compression methodology is a good
choice for improving the system’s performance without losing too
much information.The authors thank CEFET/RJ, UFF, UFRJ, and the Brazilian
research agencies CAPES, CNPq, and FAPERJ. Besides, the authors are grateful to the Foundation for Science and Technology
(FCT, Portugal) for financial support through national
funds FCT/MCTES (PIDDAC) to CeDRI (UIDB/05757/2020
and UIDP/05757/2020) and SusTEC (LA/P/0007/2021).info:eu-repo/semantics/publishedVersio
Spatially Controlled Membrane Depositions for Silicon-Based Sensors
The membrane deposition technology on silicon-based transducers constitutes the most delicate part of the miniaturized (bio)chemical sensor fabrication. Membrane adhesion to the transducer, reproducibility of the deposition process and its spatial control are the three most important parameters which determine the sensor performance and lifetime.The fabrication of two sensors is described: 1) a combined pO2, pCO2, pH sensor for which a polyacrylamide gel and a polysiloxane gas-permeable membrane were deposited and patterned at the on-wafer level and 2) a glucose amperometric enzyme electrode where the glucose oxidase was immobilized electrochemically either in a polypyrrole matrix or co-deposited with bovine serum albumin by electrochemically aided adsorption. The optimization of the deposition procedures allowed reproducible devices with reasonable lifetimes to be obtained
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