1,918 research outputs found
Subwavelength position sensing using nonlinear feedback and wave chaos
We demonstrate a position-sensing technique that relies on the inherent
sensitivity of chaos, where we illuminate a subwavelength object with a complex
structured radio-frequency field generated using wave chaos and a nonlinear
feedback loop. We operate the system in a quasi-periodic state and analyze
changes in the frequency content of the scalar voltage signal in the feedback
loop. This allows us to extract the object's position with a one-dimensional
resolution of ~\lambda/10,000 and a two-dimensional resolution of ~\lambda/300,
where \lambda\ is the shortest wavelength of the illuminating source.Comment: 4 pages, 4 figure
Logarithmic periodicities in the bifurcations of type-I intermittent chaos
The critical relations for statistical properties on saddle-node bifurcations
are shown to display undulating fine structure, in addition to their known
smooth dependence on the control parameter. A piecewise linear map with the
type-I intermittency is studied and a log-periodic dependence is numerically
obtained for the average time between laminar events, the Lyapunov exponent and
attractor moments. The origin of the oscillations is built in the natural
probabilistic measure of the map and can be traced back to the existence of
logarithmically distributed discrete values of the control parameter giving
Markov partition. Reinjection and noise effect dependences are discussed and
indications are given on how the oscillations are potentially applicable to
complement predictions made with the usual critical exponents, taken from data
in critical phenomena.Comment: 4 pages, 6 figures, accepted for publication in PRL (2004
Electrostatics of electron-hole interactions in van der Waals heterostructures
The role of dielectric screening of electron-hole interaction in van der
Waals heterostructures is theoretically investigated. A comparison between
models available in the literature for describing these interactions is made
and the limitations of these approaches are discussed. A simple numerical
solution of Poissons equation for a stack of dielectric slabs based on a
transfer matrix method is developed, enabling the calculation of the
electron-hole interaction potential at very low computational cost and with
reasonable accuracy. Using different potential models, direct and indirect
exciton binding energies in these systems are calculated within Wannier-Mott
theory, and a comparison of theoretical results with recent experiments on
excitons in two-dimensional materials is discussed.Comment: 10 pages, 8 figure
All-strain based valley filter in graphene nanoribbons using snake states
A pseudo-magnetic field kink can be realized along a graphene nanoribbon
using strain engineering. Electron transport along this kink is governed by
snake states that are characterized by a single propagation direction. Those
pseudo-magnetic fields point towards opposite directions in the K and K'
valleys, leading to valley polarized snake states. In a graphene nanoribbon
with armchair edges this effect results in a valley filter that is based only
on strain engineering. We discuss how to maximize this valley filtering by
adjusting the parameters that define the stress distribution along the graphene
ribbon.Comment: 8 pages, 6 figure
Diffraction and an infrared finite gluon propagator
We discuss some phenomenological applications of an infrared finite gluon
propagator characterized by a dynamically generated gluon mass. In particular
we compute the effect of the dynamical gluon mass on and
diffractive scattering. We also show how the data on photoproduction
and hadronic reactions can be derived from the and
forward scattering amplitudes by assuming vector meson dominance and
the additive quark model.Comment: 4 pages, 7 figures, added references and figures, changed structure.
Contribution to Proceedings of XVIIIth Reuniao de Trabalho sobre Interacoes
Hadronicas, Sao Paulo, Brazil, 22-24 May, 200
Boolean Chaos
We observe deterministic chaos in a simple network of electronic logic gates
that are not regulated by a clocking signal. The resulting power spectrum is
ultra-wide-band, extending from dc to beyond 2 GHz. The observed behavior is
reproduced qualitatively using an autonomously updating Boolean model with
signal propagation times that depend on the recent history of the gates and
filtering of pulses of short duration, whose presence is confirmed
experimentally. Electronic Boolean chaos may find application as an
ultra-wide-band source of radio wavesComment: 10 pages and 4 figur
Manejo de plantas daninhas na cultura da mandioca no Agreste Alagoano.
bitstream/item/145863/1/CT-74.pd
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