The Physical Properties of ThCr2Si2- Type Co-based Compound SrCo2Si2: An ab-initio Study

In this article, we have studied the mechanical, electronic, and optical features of ThCr2Si2- type compound SrCo2Si2. The investigation has been done by using the first-principles method depend on the density functional theory (DFT) and the calculations were completed with the Cambridge Serial Total Energy Package (CASTEP) code. The optimized lattice parameters are well in accord with the existing synthesized values. The investigated elastic constants for this compound are positive which ensured the mechanical stability of this phase. The calculated values of Pugh’s ratio and Poisson’s ratio ensure the brittle character of SrCo2Si2. The universal anisotropic constant AU ensures the anisotropic behavior of SrCo2Si2.The softness nature of SrCo2Si2 is confirmed by the bulk modulus calculations. The overlapping of the valence band and conduction band near the Fermi level indicates the metallic nature of SrCo2Si2. At the Fermi level, the major contribution comes from Co-3d and Si-3p states. The large reflectivity in the high-energy region indicates that this compound might be useful as coating materials for reducing solar heating. The photoconductivity and absorption begins with zero photon energy which also ensures the metallic nature of SrCo2Si2.

Analysis of Shielding Performance of Radiation-Shielding Materials According to Particle Size and Clustering Effects

In the field of medical radiation shielding, there is an extensive body of research on process technologies for ecofriendly shielding materials that could replace lead. In particular, the particle size and arrangement of the shielding material when blended with a polymer material affect shielding performance. In this study, we observed how the particle size of the shielding material affects shielding performance. Performance and particle structure were observed for every shielding sheet, which were fabricated by mixing microparticles and nanoparticles with a polymer material using the same process. We observed that the smaller the particle size was, the higher both the clustering and shielding effects in the high-energy region. Thus, shielding performance can be improved. In the low-dose region, the effect of particle size on shielding performance was insignificant. Moreover, the shielding sheet in which nanoparticles and microsized particles were mixed showed similar performance to that of the shielding sheet containing only microsized particles. Findings indicate that, when fabricating a shielding sheet using a polymer material, the smaller the particles in the high-energy region are, the better the shielding performance is. However, in the low-energy region, the effect of the particles is insignificant.

Quantitative estimation of track segment yields of water radiolysis species under heavy ions around Bragg peak energies using Geant4-DNA

We evaluate the track segment yield G′ of typical water radiolysis products (eaq−, ·OH and H2O2) under heavy ions (He, C and Fe ions) using a Monte Carlo simulation code in the Geant4-DNA. Furthermore, we reproduce experimental results of ·OH of He and C ions around the Bragg peak energies (< 6 MeV/u). In the relatively high energy region (e.g., > 10 MeV/u), the simulation results using Geant4-DNA have agreed with experimental results. However, the G-values of water radiolysis species have not been properly evaluated around the Bragg peak energies, at which high ionizing density can be expected. Around the Bragg peak energy, dense continuous secondary products are generated, so that it is necessary to simulate the radical–radical reaction more accurately. To do so, we added the role of secondary products formed by irradiation. Consequently, our simulation results are in good agreement with experimental results and previous simulations not only in the high-energy region but also around the Bragg peak. Several future issues are also discussed regarding the roles of fragmentation and multi-ionization to realize more realistic simulations.

Особенности фотолюминесценции в кристаллах ниобата лития, легированных цинком в широком диапазоне концентраций

The concentration changes in the photoluminescence spectra of LiNbO3 : Zn crystals (0.004 ÷ 6.5 mol.% ZnO) were studied. It was found that with the increase of zinc concentration from 0.004 to 1.42 mol.% ZnO, the intensity decrease of luminescence bands caused by VLI, NbNb, and NbNb−NbLi defects was observed. As the crystal composition approached the second concentration threshold (≈ 7.0 mol.% ZnO), the luminescent halo shifted by ≈ 0.41 eV to the high-energy region of the spectrum and the intensity of the luminescence centers increased at 2.66 and 2.26 eV. It was caused by the appearance of ZnLi point defects. It was shown that in the LiNbO3 : Zn(4.69 mol.% ZnO) crystal obtained by homogeneous doping technology, there is a greater number of luminescence centers of different origin than in congruent and zinc-doped crystals obtained by direct melt doping technology. In the LiNbO3 : Zn crystal (4.52 mol.% ZnO), the luminescence of the main defects (VLi, NbNb, ZnLi) was quenched by increasing the fraction of nonradiative transitions relative to other LiNbO3 : Zn crystals in the concentration range [ZnO] = 4.46 ÷ 6.50 mol.%.

Gravitational-Wave Implications for the Parity Symmetry of Gravity at GeV Scale

Einstein's general relativity, as the most successful theory of gravity, is one of the cornerstones of modern physics. However, the experimental tests for gravity in the high energy region are limited. The emerging gravitational-wave astronomy has opened an avenue for probing the fundamental properties of gravity in strong and dynamical field, and in particular, high energy regime. In this work, we focus on the parity symmetry of gravity. For broken parity, the left- and right-handed modes of gravitational waves would follow different equations of motion, dubbed as birefringence. We perform the first full Bayesian inference of the parity conservation of gravity by comparing the state-of-the-art waveform with the compact binary coalescence data released by LIGO and Virgo collaboration. We do not find any violations of general relativity, thus obtain the lower bound of the parity-violating energy scale to be $0.09$ GeV through the velocity birefringence of gravitational waves. This provides the most stringent experimental test of gravitational parity symmetry up to date, and for the first time, in the high energy region, which ushers in a new era of using gravitational waves to test the ultraviolet behavior of gravity. We also find third-generation gravitational-wave detectors can enhance this bound to $\mathcal{O}(10^2)$ GeV if there is still no violation, comparable to the current LHC energy scale in particle physics.

Photodissociation dynamics of CH3I probed via multiphoton ionisation photoelectron spectroscopy

Femtosecond photoelectron spectroscopy measurements of dissociation CH3I show complex dynamics in the high energy region of absorption band A.

High-Order Angle and Polarization Resolved Reflection of Artificial Opal Photonic Crystal

We present angle resolved reflection measurements showing the polarization dependence of photonic band gap in artificial opal photonic crystals. The SiO2 opals were prepared using thermal-assisted cell method. The observation of well-defined diffraction pattern indicates the samples with high quality. The reflection measurements were analyzed in the high energy region up to a/l = 1.6. It is shown that the diffraction peaks depend on s- and p-polarized light illumination. The polarization anisotropy effect due to symmetric properties of opal structure. The experiment results agree fairly well with calculated photonic band structure and are also discussed with predictions based on group theory. Angular reflection has implications in polarized light scattering in plasmonic structures and metamaterials and is also useful in applications like nano scale polarization splitters and lasers.