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Optimal Policy Derivation for Transmission Duty-Cycle Constrained LPWAN
Low-power wide-area network (LPWAN) technologies enable Internet of Things (IoT) devices to efficiently and robustly communicate over long distances, thus making them especially suited for industrial environments. However, the stringent regulations on the usage of certain industrial, scientific, and medical bands in many countries in which LPWAN operate limit the amount of time IoT motes can occupy the shared bands. This is particularly challenging in industrial scenarios, where not being able to report some detected events might result in the failure of critical assets. To alleviate this, and by mathematically modeling LPWAN-based IoT motes, we have derived optimal transmission policies that maximize the number of reported events (prioritized by their importance) while still complying with current regulations. The proposed solution has been customized for two widely known LPWAN technologies: 1) LoRa and 2) Sigfox. Analytical results reveal that our solution is feasible and performs remarkably close to the theoretical limit for a wide range of network activity patterns
Optical absorption and energy-loss spectra of aligned carbon nanotubes
Optical-absorption cross-sections and energy-loss spectra of aligned
multishell carbon nanotubes are investigated, on the basis of photonic
band-structure calculations. A local graphite-like dielectric tensor is
assigned to every point of the tubules, and the effective transverse dielectric
function of the composite is computed by solving Maxwell's equations in media
with tensor-like dielectric functions. A Maxwell-Garnett-like approach
appropriate to the case of infinitely long anisotropic tubules is also
developed. Our full calculations indicate that the experimentally measured
macroscopic dielectric function of carbon nanotube materials is the result of a
strong electromagnetic coupling between the tubes. An analysis of the
electric-field pattern associated with this coupling is presented, showing that
in the close-packed regime the incident radiation excites a very localized
tangential surface plasmon.Comment: 7 pages, 12 figures, to appear in Eur. Phys. J.
Bosonic versus fermionic pairs of topological spin defects in monolayered high-T_c superconductors
The energy associated with bosonic and fermionic pairs of topological spin
defects in doped antiferromagnetic quantum spin-1/2 square lattice is estimated
within a resonating valence bond scenario, as described by a t-t'-J-like model
Hamiltonian, plus a t-perpendicular, responsible of a three-dimensional
screening of the electrostatic repulsion within the bosonic pairs. For
parameters appropriate for monolayered high-T_c superconductors, both fermionic
and bosonic pairs show x^2-y^2 symmetry. We find a critical value of doping
such that the energy of the bosonic pairs goes below twice the energy of two
fermionic pairs at their Fermi level. This finding could be related to the
onset of high-T_c superconductivity.Comment: 10 pages, 6 figures. To be published in Phys. Rev.
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