10 research outputs found
Magnetic dipole ordering in resonant dielectric metasurfaces
Artificial magnetism at optical frequencies can be realized in metamaterials
composed of periodic arrays of subwavelength elements, also called
"meta-atoms". Optically-induced magnetic moments can be arranged in both
unstaggered structures, naturally associated with ferromagnetic (FM) order, or
staggered structures, linked correspondingly to antiferromagnetic (AFM) order.
Here we demonstrate that such magnetic dipole orders of the lattices of
meta-atoms can appear in low-symmetry Mie-resonant metasurfaces where each
asymmetric dielectric (non-magnetic) meta-atom supports a localized trapped
mode. We reveal that these all-dielectric resonant metasurfaces possess not
only strong optical magnetic response but also they demonstrate a significant
polarization rotation of the propagating electromagnetic waves at both FM and
AFM resonances. We confirm these findings experimentally by measuring directly
the spectral characteristics of different modes excited in all-dielectric
metasurfaces, and mapping near-field patterns of the electromagnetic fields at
the microwave frequencies.Comment: 9 pages, 6 figure
The neutron and its role in cosmology and particle physics
Experiments with cold and ultracold neutrons have reached a level of
precision such that problems far beyond the scale of the present Standard Model
of particle physics become accessible to experimental investigation. Due to the
close links between particle physics and cosmology, these studies also permit a
deep look into the very first instances of our universe. First addressed in
this article, both in theory and experiment, is the problem of baryogenesis ...
The question how baryogenesis could have happened is open to experimental
tests, and it turns out that this problem can be curbed by the very stringent
limits on an electric dipole moment of the neutron, a quantity that also has
deep implications for particle physics. Then we discuss the recent spectacular
observation of neutron quantization in the earth's gravitational field and of
resonance transitions between such gravitational energy states. These
measurements, together with new evaluations of neutron scattering data, set new
constraints on deviations from Newton's gravitational law at the picometer
scale. Such deviations are predicted in modern theories with extra-dimensions
that propose unification of the Planck scale with the scale of the Standard
Model ... Another main topic is the weak-interaction parameters in various
fields of physics and astrophysics that must all be derived from measured
neutron decay data. Up to now, about 10 different neutron decay observables
have been measured, much more than needed in the electroweak Standard Model.
This allows various precise tests for new physics beyond the Standard Model,
competing with or surpassing similar tests at high-energy. The review ends with
a discussion of neutron and nuclear data required in the synthesis of the
elements during the "first three minutes" and later on in stellar
nucleosynthesis.Comment: 91 pages, 30 figures, accepted by Reviews of Modern Physic
Koopmans' multiconfigurational self-consistent field (MCSCF) Fukui functions and MCSCF perturbation theory
Prediction of chemical reactivity has become one of the highest priority tasks of computational chemistry since the development of the methods of modeling electronic structure. Despite the general simplicity of the physical concept of reactivity and the rapid development of modern density functional theory (DFT) methods, this task remains state-of-the-art for systems with wavefunctions that have a multiconfigurational character. In such cases, for the accurate description of reactivity one needs to use multiconfigurational approaches that are much heavier computationally then ordinary single-determinant DFT methods. Moreover, the complexity of the calculation of reactivity is increased by the necessity to calculate ionic and transition states. These computational challenges can be addressed by employing the concepts of Koopmans' theorem and its extension to a multiconfigurational case. We present a simplified methodology for the calculation of Fukui functions, based on Koopmans' approximation for multiconfigurational Green's functions developed in our previous works. Also, an extension of this methodology based on perturbation theory has been developed to improve accuracy. \ua9 2013 Published by NRC Research Press.Peer reviewed: YesNRC publication: Ye
Stability range for a flat graphene sheet subjected to in-plane deformation
The effects of the elastic deformation on the mechanical and physical properties of graphene are a subject of intensive current studies. Nevertheless, the stability range for a flat graphene sheet subjected to in-plane deformation is still unknown. Here
Velocities of sound and the densities of phonon states in a uniformly strained flat graphene sheet
The effect of elastic strain on the mechanical and physical properties of graphene has been intensively studied in recent years. Using the molecular dynamics method, a surface has been built in the three-dimensional space of components of the plane strain tensor bounds the region of the structural stability of a flat graphene sheet without considering thermal vibrations and the influence of boundary conditions. The velocities of sound and the densities of phonon states in graphene subjected to an elastic strain within the region of the structural stability have been calculated. It has been shown that one of the velocities of sound becomes zero near the stability boundary of a flat graphene sheet. During biaxial tension of graphene, there is no gap in its phonon spectrum; however, it forms under uniaxial tension along the zigzag or armchair directions and also under combined tensile and compressive strains
Laser printing of optically resonant hollow crystalline carbon nanostructures from 1D and 2D metalâorganic frameworks
Open data from the first and second observing runs of Advanced LIGO and Advanced Virgo
Advanced LIGO and Advanced Virgo are monitoring the sky and collecting gravitational-wave strain data with sufficient sensitivity to detect signals routinely. In this paper we describe the data recorded by these instruments during their first and second observing runs. The main data products are gravitational-wave strain time series sampled at 16384 Hz. The datasets that include this strain measurement can be freely accessed through the Gravitational Wave Open Science Center at http://gw-openscience.org, together with data-quality information essential for the analysis of LIGO and Virgo data, documentation, tutorials, and supporting software
Search for intermediate-mass black hole binaries in the third observing run of Advanced LIGO and Advanced Virgo
International audienceIntermediate-mass black holes (IMBHs) span the approximate mass range 100â105âMâ, between black holes (BHs) that formed by stellar collapse and the supermassive BHs at the centers of galaxies. Mergers of IMBH binaries are the most energetic gravitational-wave sources accessible by the terrestrial detector network. Searches of the first two observing runs of Advanced LIGO and Advanced Virgo did not yield any significant IMBH binary signals. In the third observing run (O3), the increased network sensitivity enabled the detection of GW190521, a signal consistent with a binary merger of mass âŒ150âMâ providing direct evidence of IMBH formation. Here, we report on a dedicated search of O3 data for further IMBH binary mergers, combining both modeled (matched filter) and model-independent search methods. We find some marginal candidates, but none are sufficiently significant to indicate detection of further IMBH mergers. We quantify the sensitivity of the individual search methods and of the combined search using a suite of IMBH binary signals obtained via numerical relativity, including the effects of spins misaligned with the binary orbital axis, and present the resulting upper limits on astrophysical merger rates. Our most stringent limit is for equal mass and aligned spin BH binary of total mass 200âMâ and effective aligned spin 0.8 at 0.056 Gpcâ3 yrâ1 (90% confidence), a factor of 3.5 more constraining than previous LIGO-Virgo limits. We also update the estimated rate of mergers similar to GW190521 to 0.08 Gpcâ3 yrâ1.Key words: gravitational waves / stars: black holes / black hole physicsCorresponding author: W. Del Pozzo, e-mail: [email protected]â Deceased, August 2020