378 research outputs found
A Superlens Based on Metal-Dielectric Composites
Pure noble metals are typically considered to be the materials of choice for
a near-field superlens that allows subwavelength resolution by recovering both
propagating and evanescent waves. However, a superlens based on bulk metal can
operate only at a single frequency for a given dielectric host. In this Letter,
it is shown that a composite metal-dielectric film, with an appropriate metal
filling factor, can operate at practically any desired wavelength in the
visible and near-infrared ranges. Theoretical analysis and simulations verify
the feasibility of the proposed lens.Comment: 15 pages, 4 figure
Occurence of common dolphins (Delphinus delphis) in the Gulf of Trieste and the northern Adriatic Sea
1. The Mediterranean common dolphin (Delphinus delphis), considered to have been very common in the past, had undergone a dramatic decline across most of the basin by the end of 1970s. In the northern Adriatic Sea, one of the regions with most available historical information, the common dolphin is thought to have been the most common and abundant cetacean throughout most of the 20th century. However, by the end of 1970s, it had virtually disappeared from the region and is now considered generally absent from the entire Adriatic Sea. 2. This contribution summarizes the occurrence of common dolphins in the Gulf of Trieste and provides a brief review of published records in other parts of the Adriatic Sea. 3. Systematic boat surveys in the wider area of the Gulf of Trieste between 2002 and 2019 confirmed that the common bottlenose dolphin (Tursiops truncatus) is the only regularly occurring cetacean species in this area. Despite this, several records of common dolphins were documented in the Gulf of Trieste between 2009 and 2012, through sightings of live animals or recovery of dead stranded animals. 4. Dorsal fin markings allowed the photo‐identification of some of these, suggesting that at least four different live individuals (three adults and one calf) occurred here in recent times. Most cases involved single adult individuals, but one included a mother‐calf pair that was temporarily resident in a port for several months, a behaviour atypical for this species. Photo‐identification showed that the presumed mother had previously been sighted in the Ionian Sea in Greece, over 1,000 km from the Gulf of Trieste, making this the longest documented movement for this species worldwide. 5. At present, the common dolphin continues to be rare in the region.Publisher PDFPeer reviewe
Huge local field enhancement in perfect plasmonic absorbers
In this Letter we theoretically study the possibility of total power
absorption of light in a planar grid modelled as an effective sheet with zero
optical thickness. The key prerequisite of this effect is the simultaneous
presence of both resonant electric and magnetic modes in the structure. We show
that the needed level of the magnetic mode is achievable using the effect of
substrate-induced bianisotropy which also allows the huge local field
enhancement at the same wavelength where the maximal absorption holds.Comment: 4 pages, 4 figure
Impedance investigation of BaCe0.85Y0.15O3-delta properties for hydrogen conductor in fuel cells
International audienceThe influence of the sintering conditions on the electrochemical properties of the proton conducting electrolyte BaCe0.85Y0.15O3-delta (BCY15) and Ni - based BCY15 cermet anode for application in high temperature proton conducting fuel cell are investigated by electrochemical impedance spectroscopy. The results show that at lower sintering temperatures due to the formation of parasitic Y2O3 phase an increase of both the electrolyte and electrode resistances is observed. This effect is strongly reduced by enhancement of the sintering temperature. The obtained BCY15 conductivity (sigma = 2.5x10(-2) S/cm at 700 degrees C) is comparable with that of the best proton conducting materials, while the BCY15-Ni cermet (with ASR = 2.5 Omega cm(2) at 700 degrees C) needs further optimization. The results of impedance investigations of BCY15 as proton conducting electrolyte and cermet anode have been applied in development of innovative high temperature dual membrane fuel cell
AIDX: Adaptive Inference Scheme to Mitigate State-Drift in Memristive VMM Accelerators
An adaptive inference method for crossbar (AIDX) is presented based on an
optimization scheme for adjusting the duration and amplitude of input voltage
pulses. AIDX minimizes the long-term effects of memristance drift on artificial
neural network accuracy. The sub-threshold behavior of memristor has been
modeled and verified by comparing with fabricated device data. The proposed
method has been evaluated by testing on different network structures and
applications, e.g., image reconstruction and classification tasks. The results
showed an average of 60% improvement in convolutional neural network (CNN)
performance on CIFAR10 dataset after 10000 inference operations as well as
78.6% error reduction in image reconstruction.Comment: This paper is submitted to IEEE Transactions Circuits and Systems II:
Express Brief
Anomalous spectral scaling of light emission rates in low dimensional metallic nanostructures
The strength of light emission near metallic nanostructures can scale
anomalously with frequency and dimensionality. We find that light-matter
interactions in plasmonic systems confined in two dimensions (e.g., near metal
nanowires) strengthen with decreasing frequency owing to strong mode
confinement away from the surface plasmon frequency. The anomalous scaling also
applies to the modulation speed of plasmonic light sources, including lasers,
with modulation bandwidths growing at lower carrier frequencies. This allows
developing optical devices that exhibit simultaneously femto-second response
times at the nano-meter scale, even at longer wavelengths into the mid IR,
limited only by non-local effects and reversible light-matter coupling
Transformation bending device emulated by graded-index waveguide
We demonstrate that a transformation device can be emulated using a
gradient-index waveguide. The effective index of the waveguide is spatially
varied by tailoring a gradient thickness dielectric waveguide. Based on this
technology, we demonstrate a transformation device guiding visible light around
a sharp corner, with low scattering loss and reflection loss. The experimental
results are in good agreement with the numerical results.Comment: This paper is published at Optics Express 20, 13006 (2012
Dynamical suppression of unwanted transition paths in multistate quantum systems
We introduce a method to suppress unwanted transition channels, even without
knowing their couplings, and achieve perfect population transfer in multistate
quantum systems by the application of composite pulse sequences. Unwanted
transition paths may be present due to imperfect light polarization, stray
electromagnetic fields, misalignment of quantization axis, spatial
inhomogeneity of trapping fields, off-resonant couplings, etc. Compensation of
simultaneous deviations in polarization, pulse area, and detuning is
demonstrated. The accuracy, the flexibility and the robustness of this
technique make it suitable for high-fidelity applications in quantum optics and
quantum information processing.Comment: 5 figure
Near-Field Intensity Correlations in Semicontinuous Metal-Dielectric Films
Spatial intensity correlation functions are obtained from near-field scanning optical microscope measurements of semicontinuous metal-dielectric films. The concentration of metal particles on a dielectric surface is varied over a wide range to control the scattering strength. At low and high metal coverages where scattering is weak, the intensity correlation functions exhibit oscillations in the direction of incident light due to excitation of propagating surface waves. In the intermediate regime of metal concentration, the oscillatory behavior is replaced by a monotonic decay as a result of strong scattering and anomalous absorption. Significant differences in the near-field intensity correlations between metallic and dielectric random systems are demonstrated
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