Minimum Energy and Total Dipole Moment

Several magnetic materials consisting of dipoles owe their properties to the specific nature of the dipole–dipole interaction. In the present work, systems of particles possessing a dipole moment arranged on various types of 2D and 3D structures, completely arbitrary and, in some 2D instances, periodic (albeit finite), are studied. Noteworthy, the work is in the regime of strong dipole moments where a classical treatment is possible. The ultimate goal is to quantitatively address the unknown relation existing between the minimum possible energy of a system of dipoles and the concomitant total dipole moment. To such an end, classical numerical methods are used to the previous minimum energy–total dipole moment tandem for various magnetic configurations at zero temperature. An analytic bound for the minimal energy valid for any dimension is also obtained. With this exploration, new light is shed on the connection between the two former physical quantities, establishing an analytic inequality for $N=3$ particles, and describing other instances of physical interest.     

Large Magnetic Anisotropy Energy and Robust Half-Metallic Ferromagnetism in 2D MnXSe4 (X = As,Sb)

In recent years, intrinsic 2D magnetism has aroused great interest because of its potential application in spintronic devices. However, low Curie temperature (T_c) and magnetic anisotropy energy (MAE) limit its application prospects. Here, using first-principles calculations based on density-functional theory, a series of stable MnXSe₄ (X=As, Sb) single-layer is predicted. The MAE of single-layer MnAsSe₄ and MnSbSe₄ is 648.76 and 808.95 $\mu$eV per Mn atom, respectively. Monte Carlo simulations suggest the T_c of single-layer MnAsSe₄ and MnSbSe₄ is 174 and 250 K, respectively. The energy band calculation with hybrid Heyd–Scuseria–Ernzerhof (HSE06) function indicates the MnXSe₄ (X = As, Sb) is ferromagnetic half-metallic. Also, it has 100% spin-polarization ratio at the Fermi level. For MnAsSe₄ and MnSbSe₄, the spin-gaps are 1.59 and 1.48 eV, respectively. These excellent magnetic properties render MnXSe₄ (X = As, Sb) as promising candidate materials for 2D spintronic applications.     

Possible Link between the Distribution of Atomic Spectral Lines and the Radiation–Matter-Equilibrium in the Early Universe

The uncanny resemblance of the global distribution of all experimentally known atomic spectral lines to the Planckian spectral distribution associated with black body radiation at a temperature of $T\approx 9000\mathrm{K}$ is reported. This value coincides with the critical temperature of equilibrium between the respective densities of radiation and matter in the early universe.     

Efficient Ultraviolet Nanosources Based on Third-Harmonic Generation in Dielectric–Metal Composite Nanodisks

Dielectric materials with high indices have recently attracted much attention in the community of nanophotonics. Severe optical losses in visible–ultraviolet (UV) region, however, limit their applications. This article proposes dielectric–metal nanocomposites as alternative high-index materials for Mie-resonance-based applications. Such composite materials have high indices in the range of wavelength longer than plasmon resonance of inclusion metal nanoparticles, while they have much lower losses in the range from blue-violet down to near-UV compared with commonly used high-index materials such as silicon, enabling near-UV generation with high efficiency based on third-harmonic generation (THG). The numerical results show that ZnO nanodisk containing silver nanoparticles can generate near-UV radiation at 351.3 nm via THG with an efficiency about 20 times higher compared with silicon nanodisk under same pumping condition. Significantly high THG efficiency of 0.015% has been predicted with such a composite nanodisk supported by aluminum substrate under pumping with a peak intensity of 20 GW cm⁻², a spot size of 0.8 $\mu \mathrm{m}$, a duration of 50 fs at 1054 nm, respectively.     

An Order Statistics Post-Mortem on LIGO–Virgo GWTC-2 Events Analyzed with Nested Sampling

The data analysis carried out by the LIGO–Virgo collaboration on gravitational-wave events utilizes nested sampling to compute Bayesian evidences and posterior distributions for inferring the source properties of compact binaries. With poor sampling from the constrained prior, nested sampling algorithms may misbehave and fail to sample the posterior distribution faithfully. Fowlie et al. (2020) outlines a method of validating the performance of nested sampling, or identifying pathologies such as plateaus in the parameter space, using likelihood insertion order statistics. Here, this method is applied to nested sampling analyses of all events in the first and second gravitational wave transient catalogs (GWTC-1 and GWTC-2) of the LIGO–Virgo collaboration. The insertion order statistics are tested for uniformity across 45 events in the catalog and it is found that, with a few exceptions that have negligible effect on the final posteriors, the data from the analysis of events in the catalog is consistent with unbiased prior sampling. There is, however, weak evidence against uniformity at the catalog-level meta-test, yielding a Kolmogorov–Smirnov meta-p-value of $$.     

On the Reconstruction of the Scalar Mode of GW170817 in Scalar-Tensor Gravity Theory

In general metric theory of gravity, a gravitational wave is allowed to have up to six polarizations: two scalar and two vector modes in addition to tensor modes. In case the number of laser-interferometric gravitational wave telescopes is larger than the number of polarizations of a gravitational wave, all the polarizations can be individually reconstructed. Since it depends on theories of gravity which polarizations the gravitational waves have, the investigation of polarizations is important for the test of theories of gravity. In order to test the scalar–tensor gravity theory, one of important alternative theories of gravity, the scalar mode of GW170817 observed by LIGO Livingstone, Hanford and Virgo is reconstructed without prior information about any tensor–scalar gravity theories. The upper limit of the scalar mode in term of the band-limited root-sum-square of the amplitude is $$ with the time window of 2 [s] and frequency window of ≈60–120 [Hz]. It is also studied how much the tensor modes are leaked into the reconstructed scalar mode, and it is found that the reconstructed scalar mode contains roughly 30% of energy leaked from the tensor modes.     

Study of the q-Gaussian distribution with the scale index and calculating entropy by normalized inner scalogram

In this paper, we discuss a method based on wavelet analysis for the study of the q-index of the Gaussian distribution. We derive q-index from the scale index, $i_{\mathit{scale}}$, using the expression; $q\equiv 1+2i_{\mathit{scale}}$ where $i_{\mathit{scale}}$ is a wavelet based tool for measuring the degree of aperiodicity of a dynamical system in the range of $0\le i_{\mathit{scale}}\le 1$. We show that this expression gives consistent results with the numerical approach of q-Gaussian distribution which determines the degree of non-extensivity of a dynamical system in the range of $1<q<3$. We also suggest a new entropy calculation method based on the normalized inner scalogram for studying the chaotic characteristics of nonlinear dynamical systems.