Numerical modeling of the single-phase Stefan problem in a layer with transparent and semitransparent boundaries

Numerical modeling of the single-phase Stefan problem in a semitransparent layer with transparent, nonabsorbing, and partially radiation-absorbing boundaries is performed. It is shown that at low temperatures of the medium, convection is a determining factor on the boundary of the irradiated sample, and at high temperatures, radiation is predominant. The absence of absorption on the boundaries of the layer leads to acceleration of the heating of the plate and considerable deceleration of melting processes. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 3, pp. 84–91, May–June, 2006.     

Radiant-conductive heat transfer in semitransparent medium with phase transition at boundaries with different absorptivity

The one-phase Stefan problem was simulated numerically in a layer of semitransparent medium with different emissivity factors at the right moving boundary. The effect of optic properties of irradiated surface on formation of temperature fields and radiation flux densities was demonstrated.     

Muon content of ultrahigh-energy air showers: Yakutsk data versus simulations

A sample of 33 extensive air showers (EASs) with estimated primary energies above 2 × 10¹⁹ eV and high-quality muon data recorded by the Yakutsk EAS array is analyzed. The observed muon density is compared event-by-event to that expected from CORSIKA simulations for primary protons and iron using SIBYLL and EPOS hadronic interaction models. The study suggests the presence of two distinct hadronic components, “light” and “heavy.” Simulations with EPOS are in good agreement with the expected composition in which the light component corresponds to protons and the heavy component to iron-like nuclei. With SIBYLL, simulated muon densities for iron primaries are a factor of ∼ 1.5 less than those observed for the heavy component for the same electromagnetic signal. Assuming a two-component proton-iron composition and the EPOS model, the fraction of protons with energies E > 10¹⁹ eV is 0.52_−0.20^+0.19 at the 95% C.L. The text was submitted by the authors in English.     

Luminescence spectrum and structure of the rubidium uranyl nitrate single crystal

A photoelectric spectrometer based on a DPS-12 instrument was used to study the luminescence spectrum of single-crystal rubidium uranyl nitrate at T = 77° K. This spectrum is compared to the infrared spectrum of the same specimen. Several of the frequencies of the luminescence spectrum are attributed to vibrations of the coordinate nitrate groups.The authors wish to express their sincere appreciation to Prof. A. N. Sevchenko, Academician of the Academy of Sciences, Belorussian SSR, for his unflagging interest in the present study.     

A one-phase Stefan problem in a layer of semitransparent medium

A numerical investigation of a one-phase Stefan problem with various boundary conditions in a layer of semitransparent medium is conducted. The significant influence of the optical properties of the medium and the illuminated surface on the generation of temperature fields and radiation flow densities has been demonstrated. Superheating of the specimen near the illuminated surface at the instant of the phase transition has been recorded. The article was translated by L. Vertgeim.