Numerical modelling of heat transfer during impact of a molten droplet on a surface

SPH-based numerical technique for modelling of impact of molten drops on a surface with heat transfer and phase transitions effects is proposed. Computational algorithm uses SPH with procedure of restoring of particle consistence and variational approach to calculation of acceleration field. Also, boundary algorithm for free and contact surfaces in 3D setting are develope

Characterization of Population III Stars with Stellar Atmosphere and Evolutionary Modeling and Predictions of their Observability with the James Webb Space Telescope

Population III stars were the first stars to form after the Big Bang, and are believed to have made the earliest contribution to the metal content of the universe beyond the products of the Big Bang Nucleosynthesis. These stars are theorized to have had extremely short lifespans, and therefore would only be observable at high redshifts ($z \geq 3-17$) and faint apparent magnitudes ($m_{AB} \gtrsim 40$). The direct detection of Population III stars therefore remains elusive. However, the recently launched James Webb Space Telescope (JWST) may be capable of detecting stars in the relevant magnitude range in the event of favorable gravitational lensing. Theoretical models are required to interpret these future observations. In this study, new evolutionary models and non-equilibrium model atmospheres were used to characterize the observable properties of zero-age main sequence Population III stars. The calculated models cover a wide range of possible Population III stellar masses, from the minimum mass predicted by star formation studies to the maximum mass capable of maintaining hydrostatic equilibrium. Synthetic photometry and theoretical color-magnitude diagrams were calculated for the bands of the Near-Infrared Camera (NIRCam) on JWST. The final results are compared to the scales of known lensing events and JWST magnitude limits. The purpose of this study is to calculate the observable parameters of Population III stars in the most optimal JWST bands in order to provide a theoretical foundation for anticipated future observations of this stellar population

Bjorken Sum Rule and pQCD frontier on the move

The reasonableness of the use of perturbative QCD notions in the region close to the scale of hadronization, i.e., below \lesssim 1 \GeV is under study. First, the interplay between higher orders of pQCD expansion and higher twist contributions in the analysis of recent Jefferson Lab (JLab) data on the Generalized Bjorken Sum Rule function $\Gamma_1^{p-n} (Q^2)$ at $0.1<Q^2< 3 {\rm GeV}^2$ is studied. It is shown that the inclusion of the higher-order pQCD corrections could be absorbed, with good numerical accuracy, by change of the normalization of the higher-twist terms. Second, to avoid the issue of unphysical singularity (Landau pole at Q=\Lambda\sim 400 \MeV ), we deal with the ghost-free Analytic Perturbation Theory (APT) that recently proved to be an intriguing candidate for a quantitative description of light quarkonia spectra within the Bethe-Salpeter approach. The values of the twist coefficients $\mu_{2k}$ extracted from the mentioned data by using the APT approach provide a better convergence of the higher-twist series than with the common pQCD. As the main result, a good quantitative description of the JLab data down to $Q\simeq$ 350 MeV is achieved.Comment: 10 pages, 3 figures, minor change

Simulation of viscous melt drop crystallization by the SPH method

Heat and mass transfer during absorption on a film of lithium bromide water solution flowing by a cooled wall in the steam atmosphere is numerically investigated in this paper. The self-similar solutions are using as the initial conditions for solving the problem beyond the entrance region. The key criteria characterizing heat and mass transfer in the film absorption with uniform velocity profile and with a constant thickness have been determined

On zero-divisors in group rings of groups with torsion

Nontrivial pairs of zero-divisors in group rings are introduced and discussed. A problem on the existence of nontrivial pairs of zero-divisors in group rings of free Burnside groups of odd exponent $n \gg 1$ is solved in the affirmative. Nontrivial pairs of zero-divisors are also found in group rings of free products of groups with torsion.Comment: 8 pages, to appear in Canadian Math. Bul

Intensive systematic surveys of palaeospits in the Narva-Luga klint bay area: Analysis of methodology and results

Non peer reviewe

Exploring the Chemistry and Mass Function of the Globular Cluster 47 Tucanae with New Theoretical Color-Magnitude Diagrams

Despite their shared origin, members of globular clusters display star-to-star variations in composition. The observed pattern of element abundances is unique to these stellar environments, and cannot be fully explained by any proposed mechanism. It remains unclear whether stars form with chemical heterogeneity, or inherit it from interactions with other members. These scenarios may be differentiated by the dependence of chemical spread on stellar mass; however, obtaining a sufficiently large mass baseline requires abundance measurements on the lower main sequence that is too faint for spectroscopy even in the nearest globular clusters. We developed a stellar modelling method to obtain precise chemical abundances for stars near the end of the main sequence from multiband photometry, and applied it to the globular cluster 47 Tucanae. The computational efficiency is attained by matching chemical elements to the model components that are most sensitive to their abundance. We determined [O/Fe] for ~5000 members below the main sequence knee at the level of accuracy, comparable to the spectroscopic measurements of evolved members in literature. The inferred distribution disfavors stellar interactions as the origin of chemical spread; however, an accurate theory of accretion is required to draw a more definitive conclusion. We anticipate that future observations of 47 Tucanae with JWST will extend the mass baseline of our analysis into the substellar regime. Therefore, we present predicted color-magnitude diagrams and mass-magnitude relations for the brown dwarf members of 47 Tucanae