Plutonium carbide, a promising nuclear fuel, undergoes chemical aging associated with oxygen and nitrogen anion substitution. The correlations between anion incorporation and the resulting electronic and optical evolution — particularly regarding nitrogen doping — remain incompletely understood. Systematic first-principles calculations are conducted on pristine PuC, PuC0.75O0.25, and PuC0.75N0.25, covering structural, magnetic, electronic, and optical properties, as well as defect formation energies. Both dopants preserve PuC's antiferromagnetic ground state, inducing slight lattice expansions of 0.2% and 0.14% for O and N, respectively. Nitrogen weakly perturbs Pu 5f states, retaining a three-peak structure near the Fermi level with marginal charge redistribution. Oxygen, in contrast, collapses the triple-peak feature into a single broad band, suppresses the Fermi-level density of states, and drives pronounced Pu→O charge transfer, enhancing 5f localization via strong orbital hybridization. These electronic variations directly manifest in the optical response. Oxygen doping drastically lifts the zero-frequency dielectric constant from 133.0 to 395.3 and amplifies low-energy absorption, while nitrogen induces only subtle spectral changes. Both substitutions are exothermic under carbon-rich conditions, with O (-5.10 eV) being thermodynamically more favorable than N (-4.92 eV), consistent with the trend in dopant electronegativity. This work builds a consistent thermodynamic–electronic–optical correlation, offering distinct optical fingerprints as a sensitive non-destructive probe for PuC aging evaluation.
This paper develops a cross-scale dual-heat-source coupled model to tackle the difficulty of forecasting nonlinear thermal effects in microbubble-enhanced high-intensity focused ultrasound, encompassing both microscopic single-bubble dynamics and macroscopic biological heat transfer. The model utilizes the Keller–Miksis equation, which includes liquid compressibility, to precisely measure the mechanical work produced by microbubble collapse. A novel approach is also developed to employ a dynamic nonlinear negative feedback mechanism that is triggered by tissue coagulative necrosis. This mechanism is called "acoustic attenuation jump" and "hardening-induced cavitation inhibition." The research indicates that the substantial mechanical work generated by extreme inertial collapse (temporary high temperature of around 5000 K) is the catalyst for the "thermal sting effect." The dynamic negative feedback quickly cuts off the cavitation heat source, keeping the peak temperature at about 81°C. This fixes the static model's serious error of overestimating the amount of damage caused by heat diffusion (by about 89.7%). Also, optimizing the parameters showed that the energy efficiency factor follows a nonlinear 'U-shaped' law, which means that the best duty cycle is about 42%. Two-dimensional acoustic field simulation validated that dynamic feedback efficiently mitigated hazardous axial thermal dispersion and target forward displacement. This study establishes a robust theoretical framework for accurate dose planning and the delineation of a safe operational range for microbubble-enhanced high-intensity focused ultrasound.
The ab initio study was performed using the generalized gradient approximations implemented in the CASTEP code to investigate the impact of vanadium doping on the electronic, optical, and magnetic properties of HgTe. The calculated lattice parameters of the compound under ambient conditions showed good agreement with experimental data. The pure HgTe compound is a semimetal, with the higher energy states of the valence band overlapping only the lower energy states of the conduction band. Doping with vanadium (V) induces ferromagnetism in the system, leading to a significant spin polarization of about 90% at the Fermi surface, making HgTe a potential candidate for spintronic applications. The Curie temperature (TC) was estimated using mean field theory for doping concentrations of 12% and 24%. The double exchange is suggested as the most responsible interaction of ferromagnetism in the system. Optical calculations indicate enhanced absorption in the visible and infrared regions, suggesting its viability for optoelectronic device applications. These findings pave the way for the design of transition-metal-doped HgTe for the technological advancement of spintronics and photonics in the future.
Understanding the oxidation state of sulphur in fine atmospheric particulate matter (PM2.5) is essential for constraining secondary aerosol formation, climate forcing, and health impacts. This study utilises comparison of sulphur K-edge X-ray absorption near-edge structure spectra, combined with linear combination fitting of reference spectra, to characterise sulphur speciation in PM2.5 from Kraków (Poland), Qingdao (China), and Atlanta (USA). Across all regions, sulphate species S(+6) dominate, confirming their role as the principal end product of atmospheric sulphur oxidation, but the distribution of intermediate and reduced sulphur forms varies systematically with emission sources and meteorological conditions. In Kraków, wintertime PM2.5 is richer in ammonium bisulphates relative to summer, consistent with enhanced solid-fuel combustion and more acidic aerosol conditions. In Qingdao, coarse particles contain detectable S(+4) species associated with gypsum and calcium sulphite, linked to interactions between anthropogenic sulphur and mineral dust, whereas fine particles are dominated by ammonium sulphate. In the Atlanta region, ammonium sulphate is prevalent at all sites, with additional contributions from gypsum and metal-containing sulphates that vary between urban, rural, and background locations. Based on literature data employing a consistent spectroscopic methodology for a specific region across three contrasting environments, this study identifies region-specific sulphur speciation fingerprints and demonstrates the capability of X-ray absorption near-edge structure to link emission inventories, atmospheric transformation processes, and policy-relevant indicators of aerosol composition.
