232 research outputs found
On-Site Wireless Power Generation
Conventional wireless power transfer systems consist of a microwave power
generator and a microwave power receiver separated by some distance. To realize
efficient power transfer, the system is typically brought to resonance, and the
coupled-antenna mode is optimized to reduce radiation into the surrounding
space. In this scheme, any modification of the receiver position or of its
electromagnetic properties results in the necessity of dynamically tuning the
whole system to restore the resonant matching condition. It implies poor
robustness to the receiver location and load impedance, as well as additional
energy consumption in the control network. In this study, we introduce a new
paradigm for wireless power delivery based on which the whole system, including
transmitter and receiver and the space in between, forms a unified microwave
power generator. In our proposed scenario the load itself becomes part of the
generator. Microwave oscillations are created directly at the receiver
location, eliminating the need for dynamical tuning of the system within the
range of the self-oscillation regime. The proposed concept has relevant
connections with the recent interest in parity-time symmetric systems, in which
balanced loss and gain distributions enable unusual electromagnetic responses.Comment: 10 pages, 13 figure
Broadband reflectionless metasheets: Frequency-selective transmission and perfect absorption
Energy of propagating electromagnetic waves can be fully absorbed in a thin
lossy layer, but only in a narrow frequency band, as follows from the causality
principle. On the other hand, it appears that there are no fundamental
limitations on broadband matching of thin absorbing layers. However, known thin
absorbers produce significant reflections outside of the resonant absorption
band. In this paper we explore possibilities to realize a thin absorbing layer
which produces no reflected waves in a very wide frequency range, while the
transmission coefficient has a narrow peak of full absorption. Here we show,
both theoretically and experimentally, that a wide-band-matched thin resonant
absorber, invisible in reflection, can be realized if one and the same resonant
mode of the absorbing array unit cells is utilized to create both electric and
magnetic responses. We test this concept using chiral particles in each unit
cells, arranged in a periodic planar racemic array, utilizing chirality
coupling in each unit cell but compensating the field coupling at the
macroscopic level. We prove that the concept and the proposed realization
approach also can be used to create non-reflecting layers for full control of
transmitted fields. Our results can have a broad range of potential
applications over the entire electromagnetic spectrum including, for example,
perfect ultra-compact wave filters and selective multi-frequency sensors.Comment: 9 pages, 10 figure
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
Metamaterials: optical activity without chirality
We report that the classical phenomenon of optical activity, which is traditionally associated with chirality (helicity) of organic molecules, proteins, and inorganic structures, can be observed in artificial planar media which exhibit neither 3D nor 2D chirality. We observe the effect in the microwave and optical parts of the spectrum at oblique incidence to regular arrays of nonchiral subwavelength metamolecules in the form of strong circular dichroism and birefringence indistinguishable from those of chiral three-dimensional media
Communication in networks with hierarchical branching
We present a simple model of communication in networks with hierarchical
branching. We analyze the behavior of the model from the viewpoint of critical
systems under different situations. For certain values of the parameters, a
continuous phase transition between a sparse and a congested regime is observed
and accurately described by an order parameter and the power spectra. At the
critical point the behavior of the model is totally independent of the number
of hierarchical levels. Also scaling properties are observed when the size of
the system varies. The presence of noise in the communication is shown to break
the transition. Despite the simplicity of the model, the analytical results are
a useful guide to forecast the main features of real networks.Comment: 4 pages, 3 figures. Final version accepted in PR
Effect of SLM parameters on the structure and properties of CP-Ti
Selective laser melting (SLM) is an additive manufacturing technique, which allows varying the relative porosity at the micro and macro levels. In this study, the microstructure, including the porous structure, of cp-Ti Grade 1 ELI produced by SLM and the effect of the scanning parameters on mechanical properties are studied. The mechanical properties are analyzed in terms of ISO 5832-2 for metal implants for surgery. The cp-Ti samples processed by SLM are characterized by increased strength due to the low porosity condition and the acicular martensitic structure. The ductility data scattering is explained by the stratified distribution of porosity in the metal after SLM. © 2018 Author(s)
Transfer-matrix DMRG for stochastic models: The Domany-Kinzel cellular automaton
We apply the transfer-matrix DMRG (TMRG) to a stochastic model, the
Domany-Kinzel cellular automaton, which exhibits a non-equilibrium phase
transition in the directed percolation universality class. Estimates for the
stochastic time evolution, phase boundaries and critical exponents can be
obtained with high precision. This is possible using only modest numerical
effort since the thermodynamic limit can be taken analytically in our approach.
We also point out further advantages of the TMRG over other numerical
approaches, such as classical DMRG or Monte-Carlo simulations.Comment: 9 pages, 9 figures, uses IOP styl
Macroscopic invisibility cloaking of visible light
Invisibility cloaks, which used to be confined to the realm of fiction, have now been turned into a scientific reality thanks to the enabling theoretical tools of transformation optics and conformal mapping. Inspired by those theoretical works, the experimental realization of electromagnetic invisibility cloaks has been reported at various electromagnetic frequencies. All the invisibility cloaks demonstrated thus far, however, have relied on nano- or micro-fabricated artificial composite materials with spatially varying electromagnetic properties, which limit the size of the cloaked region to a few wavelengths. Here, we report the first realization of a macroscopic volumetric invisibility cloak constructed from natural birefringent crystals. The cloak operates at visible frequencies and is capable of hiding, for a specific light polarization, three-dimensional objects of the scale of centimetres and millimetres. Our work opens avenues for future applications with macroscopic cloaking devices
Uncertainty of atmospheric microwave absorption model: impact on ground-based radiometer simulations and retrievals
This paper presents a general approach to quantify absorption model
uncertainty due to uncertainty in the underlying spectroscopic parameters. The
approach is applied to a widely used microwave absorption model (Rosenkranz,
2017) and radiative transfer calculations in the 20–60 GHz range, which are
commonly exploited for atmospheric sounding by microwave radiometer (MWR).
The approach, however, is not limited to any frequency range, observing
geometry, or particular instrument. In the considered frequency range,
relevant uncertainties come from water vapor and oxygen spectroscopic
parameters. The uncertainty of the following parameters is found to dominate:
(for water vapor) self- and foreign-continuum absorption coefficients, line
broadening by dry air, line intensity, the temperature-dependence exponent for
foreign-continuum absorption, and the line shift-to-broadening ratio; (for
oxygen) line intensity, line broadening by dry air, line mixing,
the temperature-dependence exponent for broadening, zero-frequency line
broadening in air, and the temperature-dependence coefficient for line mixing. The
full uncertainty covariance matrix is then computed for the set of
spectroscopic parameters with significant impact. The impact of the
spectroscopic parameter uncertainty covariance matrix on simulated
downwelling microwave brightness temperatures (TB) in the 20–60 GHz
range is calculated for six atmospheric climatology conditions. The
uncertainty contribution to simulated TB ranges from 0.30 K (subarctic
winter) to 0.92 K (tropical) at 22.2 GHz and from 2.73 K (tropical) to 3.31 K
(subarctic winter) at 52.28 GHz. The uncertainty contribution is nearly
zero at 55–60 GHz frequencies. Finally, the impact of spectroscopic
parameter uncertainty on ground-based MWR retrievals of temperature and
humidity profiles is discussed.</p
Features of the formation of communities of microorganisms adapting to the existing conditions in different types of agrophytocenoses
The article is devoted to studying the features of the formation of communities of microorganisms, adapting to the conditions of existence in various types of agrophytocenose
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