31,350 research outputs found
Resonant transparency of materials with negative permittivity
It is shown that the transparency of opaque material with negative
permittivity exhibits resonant behavior. The resonance occurs as a result of
the excitation of the surface waves at slab boundaries. Dramatic field
amplification of the incident evanescent fields at the resonance improves the
resolution of the the sub-wavelength imaging system (superlens). A finite
thickness slab can be totally transparent to a \textit{p}-polarized obliquely
incident electromagnetic wave for certain values of the incidence angle and
wave frequency corresponding to the excitation of the surface modes. At the
resonance, two evanescent waves have a finite phase shift providing non-zero
energy flux through the non-transparent region
Spatial and spatiotemporal variation in metapopulation structure affects population dynamics in a passively dispersing arthropod
The spatial and temporal variation in the availability of suitable habitat within metapopulations determines colonization-extinction events, regulates local population sizes and eventually affects local population and metapopulation stability. Insights into the impact of such a spatiotemporal variation on the local population and metapopulation dynamics are principally derived from classical metapopulation theory and have not been experimentally validated. By manipulating spatial structure in artificial metapopulations of the spider mite Tetranychus urticae, we test to which degree spatial (mainland-island metapopulations) and spatiotemporal variation (classical metapopulations) in habitat availability affects the dynamics of the metapopulations relative to systems where habitat is constantly available in time and space (patchy metapopulations). Our experiment demonstrates that (i) spatial variation in habitat availability decreases variance in metapopulation size and decreases density-dependent dispersal at the metapopulation level, while (ii) spatiotemporal variation in habitat availability increases patch extinction rates, decreases local population and metapopulation sizes and decreases density dependence in population growth rates. We found dispersal to be negatively density dependent and overall low in the spatial variable mainland-island metapopulation. This demographic variation subsequently impacts local and regional population dynamics and determines patterns of metapopulation stability. Both local and metapopulation-level variabilities are minimized in mainland-island metapopulations relative to classical and patchy ones
Function-led design of multifunctional stimuli-responsive superhydrophobic surface based on hierarchical graphene-titania nanocoating
Multifunctional smart superhydrophobic surface with full-spectrum tunable
wettability control is fabricated through the self-assembly of the graphene and
titania nanofilm double-layer coating. Advanced microfluidic manipulative
functions, including directional water transport, adhesion & spreading
controls, droplet storage & transfer, and droplet sensing array, can be readily
realized on this smart surface. An in-depth mechanism study regarding the
underlying secrets of the tunable wettability and the UV-induced
superhydrophilic conversion of anatase titania are also presented
Full light absorption in single arrays of spherical nanoparticles
In this paper we show that arrays of core-shell nanoparticles function as
effective thin absorbers of light. In contrast to known metamaterial absorbers,
the introduced absorbers are formed by single planar arrays of spherical
inclusions and enable full absorption of light incident on either or both sides
of the array. We demonstrate possibilities for realizing different kinds of
symmetric absorbers, including resonant, ultra-broadband, angularly selective,
and all-angle absorbers. The physical principle behind these designs is
explained considering balanced electric and magnetic responses of unit cells.
Photovoltaic devices and thermal emitters are the two most important potential
applications of the proposed designs.Comment: (e.g.: 18 pages, 5 figures
Electrical Control of Linear Dichroism in Black Phosphorus from the Visible to Mid-Infrared
The incorporation of electrically tunable materials into photonic structures
such as waveguides and metasurfaces enables dynamic control of light
propagation by an applied potential. While many materials have been shown to
exhibit electrically tunable permittivity and dispersion, including transparent
conducting oxides (TCOs) and III-V semiconductors and quantum wells, these
materials are all optically isotropic in the propagation plane. In this work,
we report the first known example of electrically tunable linear dichroism,
observed here in few-layer black phosphorus (BP), which is a promising
candidate for multi-functional, broadband, tunable photonic elements. We
measure active modulation of the linear dichroism from the mid-infrared to
visible frequency range, which is driven by anisotropic quantum-confined Stark
and Burstein-Moss effects, and field-induced forbidden-to-allowed optical
transitions. Moreover, we observe high BP absorption modulation strengths,
approaching unity for certain thicknesses and photon energies
Multilayer optical learning networks
A new approach to learning in a multilayer optical neural network based on holographically interconnected nonlinear devices is presented. The proposed network can learn the interconnections that form a distributed representation of a desired pattern transformation operation. The interconnections are formed in an adaptive and self-aligning fashioias volume holographic gratings in photorefractive crystals. Parallel arrays of globally space-integrated inner products diffracted by the interconnecting hologram illuminate arrays of nonlinear Fabry-Perot etalons for fast thresholding of the transformed patterns. A phase conjugated reference wave interferes with a backward propagating error signal to form holographic interference patterns which are time integrated in the volume of a photorefractive crystal to modify slowly and learn the appropriate self-aligning interconnections. This multilayer system performs an approximate implementation of the backpropagation learning procedure in a massively parallel high-speed nonlinear optical network
Resolving Multi-path Interference in Time-of-Flight Imaging via Modulation Frequency Diversity and Sparse Regularization
Time-of-flight (ToF) cameras calculate depth maps by reconstructing phase
shifts of amplitude-modulated signals. For broad illumination or transparent
objects, reflections from multiple scene points can illuminate a given pixel,
giving rise to an erroneous depth map. We report here a sparsity regularized
solution that separates K-interfering components using multiple modulation
frequency measurements. The method maps ToF imaging to the general framework of
spectral estimation theory and has applications in improving depth profiles and
exploiting multiple scattering.Comment: 11 Pages, 4 figures, appeared with minor changes in Optics Letter
A Review on Mechanics and Mechanical Properties of 2D Materials - Graphene and Beyond
Since the first successful synthesis of graphene just over a decade ago, a
variety of two-dimensional (2D) materials (e.g., transition
metal-dichalcogenides, hexagonal boron-nitride, etc.) have been discovered.
Among the many unique and attractive properties of 2D materials, mechanical
properties play important roles in manufacturing, integration and performance
for their potential applications. Mechanics is indispensable in the study of
mechanical properties, both experimentally and theoretically. The coupling
between the mechanical and other physical properties (thermal, electronic,
optical) is also of great interest in exploring novel applications, where
mechanics has to be combined with condensed matter physics to establish a
scalable theoretical framework. Moreover, mechanical interactions between 2D
materials and various substrate materials are essential for integrated device
applications of 2D materials, for which the mechanics of interfaces (adhesion
and friction) has to be developed for the 2D materials. Here we review recent
theoretical and experimental works related to mechanics and mechanical
properties of 2D materials. While graphene is the most studied 2D material to
date, we expect continual growth of interest in the mechanics of other 2D
materials beyond graphene
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