102 research outputs found
Plasmonic rod dimers as elementary planar chiral meta-atoms
Electromagnetic response of metallic rod dimers is theoretically calculated
for arbitrary planar arrangement of rods in the dimer. It is shown that dimers
without an in-plane symmetry axis exhibit elliptical dichroism and act as
"atoms" in planar chiral metamaterials. Due to a very simple geometry of the
rod dimer, such planar metamaterials are much easier in fabrication than
conventional split-ring or gammadion-type structures, and lend themselves to a
simple analytical treatment based on coupled dipole model. Dependencies of
metamaterial's directional asymmetry on the dimer's geometry are established
analytically and confirmed in numerical simulations.Comment: 3 page
Electro-optical switching by liquid-crystal controlled metasurfaces
We study the optical response of a metamaterial surface created by a lattice
of split-ring resonators covered with a nematic liquid crystal and demonstrate
millisecond timescale switching between electric and magnetic resonances of the
metasurface. This is achieved due to a high sensitivity of liquid-crystal
molecular reorientation to the symmetry of the metasurface as well as to the
presence of a bias electric field. Our experiments are complemented by
numerical simulations of the liquid-crystal reorientation.Comment: 6 pages, 3 figure
Multifocal electroretinographical changes in monkeys with experimental ocular hypertension: a longitudinal study
Purpose To study the time course of changes in the multifocal electroretinograms (mfERG) in monkeys with experimental ocular hypertension (OHT). Methods The mfERGs were recorded in 12 eyes out of 6 monkeys. Two baseline measurements were used to quantify the reproducibility, the inter-ocular and the inter-individual variability of the ERG signals. Thereafter, the trabeculum of one eye of each animal was laser-coagulated in one to three sessions to induce OHT. ERG measurements were repeated regularly in a period of 18months and the changes in ERG waveforms were quantified. Results All animals displayed OHT (between 20 and 50mmHg) in the laser-coagulated eyes. An ERG change was defined as the sum of differences during the first 90ms between the laser-coagulated eye and the same eye before laser coagulation and between the laser-coagulated eye and the non-treated fellow eye. Three animals displayed significant changes for nearly all retinal areas and all stimulus conditions. The three remaining animals displayed significant changes only in one comparison, indicating very mild changes. The data indicate that a high stimulus contrast is more sensitive to detect changes, probably because of a better signal-to-noise ratio. Moreover, the comparisons with the fellow eye are more sensitive to detect changes than comparisons with the measurements before laser-coagulation. Conclusions OHT does not always lead to ERG changes. Comparisons with fellow eyes using high contrast stimuli are more sensitive to detect changes related to OH
Spatial distribution of Cherenkov radiation in periodic dielectric media
The nontrivial dispersion relation of a periodic medium affects both the
spectral and the spatial distribution of Cherenkov radiation. We present a
theory of the spatial distribution of Cherenkov radiation in the far-field zone
inside arbitrary three- and two-dimensional dielectric media. Simple analytical
expressions for the far-field are obtained in terms of the Bloch mode
expansion. Numerical examples of the Cherenkov radiation in a two-dimensional
photonic crystal is presented. The developed analytical theory demonstrates
good agreement with numerically rigorous finite-difference time-domain
calculations.Comment: 14 pages, 5 figures, Journal of Optics A (in press
Smart decentralised energy management
The German–Finnish research project FUture Smart Energy shows, how flexible devices, consuming or producing electricity in electric grids, can be self-organised in a fully decentralised way, using autonomous algorithms integrated with the devices\u27 controllers. By shifting operation time, existing flexible devices are hereby utilised as ‘virtual batteries’, providing high storage capacity and power. To gain sufficient flexibility, a large number of devices like combined heat and power generators, heat pumps (HP), heaters, coolers, charging stations, pumps, household appliances and industrial plants, has to be coordinated. This results in a high system complexity for which the evaluated method provides an easy, resilient, cyber-secure and cost-effective solution. This novel technology uses a new market approach for electric energy systems. A real-time price signal is generated directly out of grid state variables, like frequency, voltage, power or current, and broadcast to the flexible devices. Without a need for central control, the flexible devices react like a natural swarm to the price signal. The system is easily and highly scalable, as adding and removing flexibilities does not imply adapting a central control system. The system can be operated parallel or in addition to existing energy markets
Theory of Cherenkov radiation in periodic dielectric media: Emission spectrum
The Cherenkov radiation is substantially modified in the presence of a medium
with a nontrivial dispersion relation. We consider Cherenkov emission spectra
of a point charge moving in general three- (3D) and two-dimensional (2D)
photonic crystals. Exact analytical expressions for the spectral distribution
of the radiated power are obtained in terms of the Bloch mode expansion. The
resulting expression reduces to a simple contour integral (3D case) or a
one-dimensional sum (2D case) over a small fraction of the reciprocal space,
which is defined by the generalized Cherenkov condition. We apply our method to
a specific case of an electron moving with different velocities in a 2D
square-lattice photonic crystal. Our method demonstrates an excellent agreement
with numerically rigorous finite-difference time-domain calculations while
being less demanding on computational resources.Comment: to appear in Phys. Rev.
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