Moscow University Physics Bulletin最新文献

This paper presents a catalog of the energy distribution in the spectra of 263 stars in the wavelength range from 0.4 to 100 (mu)m, which are at late stages of evolution and have been observed by the ISO space observatory. For each object in the catalog, estimates of the observed bolometric fluxes were derived from smoothed energy distribution curves. The catalog is available at https://infra.sai.msu.ru/sai_lss_sed both as a table and in machine-readable format. It is shown that for the specified sample of objects, their ISO SWS spectra in the range 2.4–45 (mu)m correspond to the general shape of the continuum in only 60(%) of cases, and can be used without recalibration. A selection of carbon stars, accessible for the infrared observations from the MSU observatories has been made. For some of them the first brightness estimates in the (K,L), and (M) bands were obtained with the new IR camera of the 2.5-m telescope of CMO.

A modified machine learning method is proposed, utilizing an ensemble of artificial neural networks for the extrapolation of energies obtained in variational calculations, specifically in the no-core shell model (NCSM), to the case of the infinite basis. A new neural network topology is employed, and criteria for selecting both the data used for training and the trained neural networks for statistical analysis of the results are formulated. The approach is tested by extrapolating the deutron ground state energy in calculations with the Nijmegen II (NN) interaction and provides statistically significant results. This technique is applied to obtain extrapolated ground state energies of ({}^{6})Li and ({}^{6})He nuclei based on the NCSM calculations with Daejeon16 (NN) interaction.

Within the TANGRA project framework, a new experimental setup has been constructed for the measurement of cross sections of reactions ((n,X,gamma)) in the interaction of 14.1 MeV neutrons with nuclei. The facility has a special feature: the use of the tagged neutron method. This method enables efficient separation of background and useful events, as well as accurate tracking of the neutron flux. Test measurements were performed on ({}^{28})Si, ({}^{12})C, and ({}^{16})O nuclei, and the results showed satisfactory agreement with available experimental data. This paper presents the features of the setup design and the methodology for processing the obtained experimental data.

The subject of this paper is the radiative transfer in media with refractive index gradients. Asymptotic expressions of the intensity distributions in the vicinity of singular directions are derived. Critical conditions for the occurrence of singular intensity distributions in fields of scattered radiation in a medium are formulated. It is shown that singular radiation fields in such media can be generated, among other things, by nonsingular configurations of radiation sources. The obtained results are verified by direct comparison with the results of numerical calculations using the Monte Carlo statistical modelling method.

In the paper, the effect of natural dust deposited from the air on the evaporation rate from the water surface is experimentally investigated. Experiments were conducted for stationary liquid without wind blowing across the surface and with mild wind that does not deform the surface, at a constant rate of particle deposition. It is shown that the evaporation rate is a linear function of the difference in the saturated vapor pressure at the water surface and the partial pressure of the air mixture at the temperature and relative humidity in the laboratory at the beginning of the deposition process, when the proportion of the surface covered with dust is small. With the increase in deposition time, hydrophobic particles gather into conglomerates, reducing the proportion of the exposed surface and the evaporation rate.

The surface treatment of single-crystal germanium with an argon cluster ion beam has been investigated. The original surface of the germanium wafers was bombarded with argon cluster ions with high (105 eV/atom) and low (10 eV/atom) specific energies. Using an atomic force microscope, images were obtained and a comparison of the surface topography before and after cluster ion bombardment was conducted. The smoothing of the surface was demonstrated using the power spectral density function of roughness in the range of spatial frequencies: 1) (nu=1{-}8) (mu)m({}^{-1})—for the high-energy mode; 2) (nu=0.7{-}2.5) (mu)m({}^{-1})—for the low-energy mode.

The observation of waves (sea level oscillations) in the coastal water area of the southeastern coast of Sakhalin Island was carried out from November 2021 to May 2022 using bottom-mounted high-precision ARW 14 K devices with one second discreteness. The analysis of the obtained time series revealed the presence of anomalous waves in the range of tsunami waves in January 2022. It is shown that the waves detected on January 15, 2022 with periods of 15 min–4 h, significantly standing out above the background, are associated with volcanic tsunami waves. Spectral analysis of the time series showed that the maximum in the spectra of sea level oscillations found after the volcanic eruption is close to the period of the first mode of the shelf seiche. This indicates that incoming tsunami waves excite shelf seiches in the coastal zone and contribute to the generation of longshore and transverse seiches into Mordvinov Bay. Time series analysis made it possible to establish that the spectral density of sea level oscillations for the time interval of the beginning of the eruption of the Hunga–Tonga–Hunga–Ha’apai volcano from December 21, 2021 to January 11, 2022 significantly differs from the spectral density for the time of the Plinian volcanic eruption. An analysis of the statistical characteristics of sea level oscillations performed on two-day series in the range of periods 1 min–4 h for background waves and tsunamis showed an increase in the rms by 3.5 times for a time series containing tsunami waves. It has been established that for background time series containing tsunami waves, the coefficients of asymmetry and kurtosis differ little from ‘‘Gaussia’’ values. This indicates that the arrival of tsunami waves from distant sources does not significantly disrupt the stationarity of the wave field in the observation area.

The results of a comparative analysis of various characteristics of the temperature conditions of the planetary atmospheres in the Solar System and their dependence on orbital parameters, in particular on the length and angular frequency of the annual cycle, are presented. A root dependence on the angular frequency of the dry adiabatic lapse rate is noted. The dependence of the planetary equilibrium temperature in the form of the cubic root of the angular frequency of the annual cycle is related to Kepler’s third law. For Venus, Earth, Mars, Jupiter, and Saturn, the root dependence of the scale height and the troposphere height on the annual cycle length is manifested, and the atmospheric features of the most distant planets from the Sun—Uranus and Neptune—are noted.

Using the examples of magic nuclei ({}^{40,48})Ca, ({}^{68,78})Ni, ({}^{132})Sn, and ({}^{208})Pb, the correlation between electric dipole polarizability and the thickness of the neutron ‘‘skin’’ has been studied. The distribution of (E1)-transition strength was calculated within the random phase approximation using the Skyrme energy density functional. Comparison with experimental data made it possible to constrain the value of nuclear symmetry energy within the range (J=30{-}37) MeV.

In positron emission tomography (PET), the scattered photons represent a major image degrading factor. The scatter fraction (SF) of PET scanners is experimentally determined following the National Electrical Manufacturers Association (NEMA) NU 2 protocol, using a polyethylene phantom with a line source inserted at 45 mm radial offset from the phantom’s center. In this work, we aim to investigate the optimal radial offset of the line source, that represents the SF of a uniformly activated phantom, for the lutetium yttrium orthosilicate (LYSO)-based uEXPLORER total body PET scanner. Additionally, we propose to study the impact of several factors (axial field-of-view (AFOV), crystal material and heterogeneities) on this optimal offset, in an effort to provide recommendations for a wide range of PET scanner configurations. We performed Monte Carlo (MC) simulations of the uEXPLORER scanner along with five phantoms of different diameters, using the Geant4 Application for Tomographic Emission (GATE) code. We performed supplemental MC simulations in which we varied the crystal material, the AFOV and we introduced bone and lung heterogeneities in the phantoms to assess their impact on the optimal offset findings. Our results demonstrated that the 45 mm offset overestimates the SF of the uniform 20 cm diameter phantom by 24.3(%). Instead, an offset of 87 mm was reproducing this SF. For the phantoms having diameters in the range of 10–50 cm, an offset of 90.7(%) of the phantom’s radius was shown to be optimal (best fit). No AFOV-related impact has been observed on this optimal offset. The influence of the heterogeneities was also small with less than 1.1(%) absolute deviation in the SF. This offset could then be used for all AFOV lengths PET scanners using LYSO crystal. The impact of the crystal material was shown to be minimal and an offset of 91.5(%) of the phantom’s radius is consequently recommended as an average for other PET scanners.