Lithuanian Journal of Physics

Title

2024-10-03T11:15:32+03:00

2024-10-03T11:17:26+03:00

Second order Rayleigh–Schrödinger perturbation theory for the Grasp2018 package: Core–core correlations

2024-10-03T14:41:15+03:00

GRASP package is based on the relativistic configuration interaction in which accurate calculations, accounting for valence, valence–valence, core–valence, core and core–core electron correlations, often rely on massive CSF expansions. This paper presents a further development of the method based on the second-order perturbation theory for finding the most important CSFs that have the greatest influence on the core–valence, core and core–core correlations. This method is based on a combination of the relativistic configuration interaction method and the stationary second-order Rayleigh–Schrödinger many-body perturbation theory in an irreducible tensorial form [G. Gaigalas, P. Rynkun, and L. Kitovienė, Second-order Rayleigh–Schrödinger perturbation theory for the GRASP2018 package: Core–valence correlations, Lith. J. Phys. 64(1), 20–39 (2024), https://doi.org/10.3952/physics.2024.64.1.3, and G. Gaigalas, P. Rynkun, and L. Kitovienė, Second-order Rayleigh–Schrödinger perturbation theory for the GRASP2018 package: Core correlations, Lith. J. Phys. 64(2), 73–81 (2024), https://doi.org/10.3952/physics.2024.64.2.1]. In this extension, the perturbation theory takes into account electron core–valence, core and core–core correlations, where an atom or ion has any number of valence electrons, for calculation of energy spectra and other properties. Meanwhile, the rest of the correlations are taken into account in a traditional way. This allows a significant reduction of the space of the configuration state function for complex atoms and ions. We also demonstrate how this method works for calculations of the energy structure and E1 transition properties of Fe XV ion.

Application of the frozen-modes approximation to classical harmonic oscillator systems

2024-10-03T14:47:56+03:00

The problems of open classical systems usually correspond to a motion of a test particle that interacts with a large number of bath oscillators. Often, the test particle itself can be considered a harmonic oscillator. For such composite systems, exact numerical solutions are available, but they can become increasingly costly for a large number of bath oscillators. Here we take inspiration from the recent work on open quantum systems and investigate the applicability of the frozen-modes approximation to such classical systems. This approach assumes that some part of the low-frequency bath modes are frozen, thus only their initial values need to be considered. We show that by applying the frozen-modes approximation one can significantly increase the accuracy of the perturbative multiple-scales solution, especially for slow baths. This approach provides a good accuracy even for strong system–bath couplings, a regime that is not accessible to straightforward applications of the perturbation theory. We also suggest a rule for the splitting of spectral density to the fast and slow bath modes. We find that our approach gives excellent results for the ohmic spectral density, but it could be applied for other similar spectral densities as well.

Effect of CaCO3, SrCO3 and BaCO3 additions on the microstructure and electrical characteristics of SnO2-based varistor ceramics

2024-10-03T14:40:44+03:00

The ceramic varistors SnO2–Co3O4–Nb2O5–Cr2O3 with the addition of CaCO3, SrCO3 or BaCO3 were sintered at temperatures 1250 and 1350°C, then their structures and electrical properties were studied. In all samples, the SnO2 cassiterite phase with a rutile-type structure and the Co2SnO4 phase with a spinel-type structure were observed. All materials exhibited a highly nonlinear dependence of the current density on the electric field with the nonlinearity coefficient 24–50. When alkaline earth metal carbonates were added, the grain size of all samples decreased and the electric field E1 increased. The addition of CaCO3 lead to the decrease of the low-field electrical conductivity of varistors. The lowest low-field conductivities 4·10–13 and 6·10–13 Ω–1 cm–1 were found in the samples with CaCO3 addition baked at 1250 and 1350°C, respectively. The observed effect is due to the increase of the potential barrier height at the SnO2 grain boundaries by 7 and 13%, respectively, and the decrease of the grain size by 26 and 28% compared to SnO2-based varistor ceramics without CaCO3 addition.

Variations of black carbon, particulate matter and nitrogen oxides mass concentrations in urban environment with respect to winter heating period and meteorological conditions

2024-10-03T14:40:28+03:00

The atmospheric concentrations of particulate pollution are of great scientific concern due to their impact on both human health and environment. This study aimed to investigate the concentration of black carbon (BC), particulate matter with an aerodynamic diameter of less than 10 micrometres (PM10) and nitrogen oxides (NOx) at an urban background environment throughout the year, and understand the impact of winter heating and meteorology on its concentration level. The campaign covered heating and non-heating periods, from 1 June 2021 to 31 May 2022. During the heating period, the mass concentrations of BC, PM10 and NOx were 1.17, 24.9 and 19.4 µg m–3, respectively. The analysis revealed that the mass concentrations of BC and NOx were 1.9 and 1.4 times greater during the heating period, respectively, compared to the non-heating period. In contrast, PM10 remained almost constant during the heating (19.4 µg m–3) and non-heating periods (20.0 µg m–3). Throughout the year, the BC mass concentration was dominated by BCFF (71.2%) originating from fossil fuel combustion with a maximum (8.43 µg m–3) during the heating period. Moreover, wind speed presented a weak negative correlation with BC (r = –0.40), PM10 (r = –0.19) and NOx (r = –0.40) during the heating period.

Characterization of SLA-printed ceramic composites for dental restorations

2024-10-03T14:40:13+03:00

This study introduces a novel ceramic-composite resin specifically developed for stereolithography (SLA) 3D printing, aimed at enhancing dental restorations. The integration of advanced digital technologies in dentistry has shifted traditional methods towards more precise and efficient techniques such as computer-aided design/computer-aided manufacturing (CAD/CAM). However, these processes typically involve material waste due to their subtractive nature. Additive manufacturing, or 3D printing, particularly SLA, which uses ultraviolet light to cure photosensitive resins, presents a viable alternative with the potential for creating detailed, custom restorations with minimal waste. Our research focuses on formulating and evaluating a ceramic-composite resin that combines the benefits of light-cured materials with the mechanical robustness required for dental applications. We conducted comprehensive tests to assess the printability, mechanical properties and wear resistance of the developed material. The ceramic-composite resin demonstrated a tensile strength of approximately 73 MPa, significantly higher than the 42 MPa observed for traditional photopolymer resins. Additionally, the ceramic-composite resin showed ability to resist incidental friction and wear. This research could significantly impact the dental prosthetics field by providing a method for producing high-performance, patient-specific restorations efficiently and cost-effectively.