14,598 research outputs found
Plasmonic nanoantennas as integrated coherent perfect absorbers on SOI waveguides for modulators and all-optical switches
The performance of plasmonic nanoantenna structures on top of SOI wire
waveguides as coherent perfect absorbers for modulators and all-optical
switches is explored. The absorption, scattering, reflection and transmission
spectra of gold and aluminum nanoantenna-loaded waveguides were calculated by
means of 3D finite-difference time-domain simulations for single waves
propagating along the waveguide, as well as for standing wave scenarios
composed from two counterpropagating waves. The investigated configurations
showed losses of roughly 1% and extinction ratios greater than 25 dB for
modulator and switching applications, as well as plasmon effects such as strong
field enhancement and localization in the nanoantenna region. The proposed
plasmonic coherent perfect absorbers can be utilized for ultracompact
all-optical switches in coherent networks as well as modulators and can find
applications in sensing or in increasing nonlinear effects.Comment: 10 pages, 6 figure
Minkowski Vacuum Stress Tensor Fluctuations
We study the fluctuations of the stress tensor for a massless scalar field in
two and four-dimensional Minkowski spacetime in the vacuum state. Covariant
expressions for the stress tensor correlation function are obtained as sums of
derivatives of a scalar function. These expressions allow one to express
spacetime averages of the correlation function as finite integrals. We also
study the correlation between measurements of the energy density along a
worldline. We find that these measurements may be either positively correlated
or anticorrelated. The anticorrelated measurements can be interpreted as
telling us that if one measurement yields one sign for the averaged energy
density, a successive measurement with a suitable time delay is likely to yield
a result with the opposite sign.Comment: 24 pages, 5 figures; Some additional comments added in Sect. IIB and
a more compact argument given in App.
An unusual growth form of Cladonia furcata: The trampling-resistant primary thallus colonizing a paved pathway
Lichens are well known to be susceptible to damage by trampling. Fruticose species, with their
highly branched structure, are particularly sensitive and Bayfield et al. (1981)
described substantial damage to Cladonia uncialis, C. arbuscula, C. rangiferina,
and C. impexa on paths in lichen-rich heath communities in north-east
Scotland. Less visible communities, biotic soil crusts in arid and semi-arid
areas with their cover of crustose lichens, are also easily disturbed by walking,
car driving, or grazing and recovery can take decades.
We report here an interesting situation where a lichen (Cladonia furcata) is apparently being
maintained and even spread in a habitat because trampling prevents it from
completing its monocarpic life cycle
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