326 research outputs found
Topologically Induced Optical Activity in Graphene-Based Meta-Structures
Non-reciprocity and asymmetric transmission in optical and plasmonic systems
is a key element for engineering the one-way propagation structures for light
manipulation. Here we investigate topological nanostructures covered with
graphene-based meta-surfaces, which consist of a periodic pattern of
sub-wavelength stripes of graphene winding around the (meta-) tube or
(meta-)torus. We establish the relation between the topological and plasmonic
properties in these structures, as justified by simple theoretical expressions.
Our results demonstrate how to use strong asymmetric and chiral plasmonic
responses to tailor the electrodynamic properties in topological
meta-structures. Cavity resonances formed by elliptical and hyperbolic plasmons
in meta-structures are sensitive to the one-way propagation regime in a finite
length (Fabry-Perot-like) meta-tube and display the giant mode splitting in a
(Mach-Zehnder-like) meta-torus.Comment: 20 pages, 5 figures + TOC figure, accepted by ACS Photonic
Validation of moment tensor potentials for fcc and bcc metals using EXAFS spectra
Machine-learning potentials for materials, namely the moment tensor
potentials (MTPs), were validated using experimental EXAFS spectra for the
first time. The MTPs for four metals (bcc W and Mo, fcc Cu and Ni) were
obtained by the active learning algorithm of fitting to the results of the
calculations using density functional theory (DFT). The MTP accuracy was
assessed by comparing metal K-edge EXAFS spectra obtained experimentally and
computed from the results of molecular dynamics (MD) simulations. The
sensitivity of the method to various aspects of the MD and DFT models was
demonstrated using Ni as an example. Good agreement was found for W, Mo and Cu
using the recommended PAW pseudopotentials, whereas a more accurate
pseudopotential with 18 valence electrons was required for Ni to achieve a
similar agreement. The use of EXAFS spectra allows one to estimate the MTP
ability in reproducing both average and dynamic atomic structures
Quantum chemistry studies of the O K-edge X-ray absorption in WO3 and AWO3
In this work we present an interpretation of experimental O K-edge x-ray
absorption near edge structure (XANES) in perovskite-type WO3 and AWO3
compounds (A = H and Na) using three different first principles approaches: (i)
full-multiple-scattering (FMS) formalism (the real-space FEFF code), (ii)
hybrid density functional theory (DFT) method with partial incorporation of
exact Hartree-Fock exchange using formalism of the linear combination of atomic
orbitals (LCAO) as implemented in the CRYSTAL code; (iii) plane-wave DFT method
using formalism of the projector-augmented waves (PAW) as implemented in the
VASP code.Comment: 9 page
DEVELOPMENT AND ANALYSIS OF AUTHENTICATION METHOD FOR IOT DEVICES SOFTWARE ON THE NETWORK USING BLOCKCHAIN TECHNOLOGIES
Currently, there is an unsolved problem of IoT device authentication in networks to ensure their security. Due to low performance, work with traditional methods of protection is complicated and therefore a different approach is required. The article proposes a method for authenticating IoT devices (devices and software) by verifying their data and then entering it into the data storage. The implementation of a data storage using blockchain technology and the comparison of its efficiency with a classical database are considered. The aim of research is evelopment of the IoT device authentication method, analysis of the effectiveness and applicability of the developed method and comparison of various technological approaches to solving the problem. Obtained results is evaluation parameters of the resulting system and methods for constructing systems based on this method
Radiation and Propagation of Waves in Magnetic Materials with Helicoidal Magnetic Structure
In this chapter, we are shortly reviewing some problems of electromagnetic and acoustic wave propagation and radiation in the magnets with helicoidal spin structure. We show the band structure of the coupled wave spectrum in the materials. The band gap width depends on the spiral angle (or, equivalently, on external magnetic field value). Interaction of spin and electromagnetic waves leads to opening the gap in spin-electromagnetic dispersion. This gap leads to opacity window in reflection spectrum of spiral magnet plate. The opacity window closes at phase transition into collinear ferromagnetic state and reaches a maximum at simple spiral state. At the frequencies near band gap boundaries, the rotation of polarization plane of propagating electromagnetic wave is observed. Account of interaction of spin and electromagnetic waves with acoustic subsystem leads to opening the gap in spin-acoustic spectrum. This gap leads to some features in electromagnetic reflectance spectrum and to rotation of acoustic wave polarization plane, i.e. to acoustic Faraday effect. We also show the possibility of acoustic and electromagnetic wave radiation by helicoidal magnets at phase transition into collinear ferromagnetic state. Some features of electromagnetic waves generation by spiral magnets placed in homogeneous magnetic field with harmonical time-dependence are also discussed
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