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High-resolution spectra corresponding to the rotational and the ν₂-ν₂ bands of the two most abundant isotopic species of ozone with one heavy ¹⁸O oxygen atom were recorded using SOLEIL synchrotron radiation source in the range 30-200 cm^-1. Additionally, the ν₂ vibrational-rotational bands were recorded between 550 and 880 cm^-1 using a classical glowbar source that made it possible to extend and refine information compared to published data on the observed transitions of these bands. The analyses of recorded spectra permitted us to deduce experimental set of energy levels for the ground (000) and the first bending (010) vibrational states, which significantly exceeds literature data in terms of rotational quantum numbers. For both isotopic species, the weighted fits of all experimental line positions were carried out including previously published microwave data. As a result of this work, the improved values of rotational and centrifugal distortion parameters for the states (000) and (010) were obtained that permitted modelling the experimental line positions with a weighted standard deviation of 1.284 (2235 transitions) and 0.908 (4597 transitions), respectively, for ¹⁶O¹⁶O¹⁸O, and 1.168 (824 transitions) and 1.724 (2381 transitions) for ¹⁶O¹⁸O¹⁶O.

The problem of controlling the parameters of the filamentation region of high-power femtosecond laser pulses for amplitude modulation of radiation by a metal mesh mask is theoretically considered. To this end, the initial laser beam is split into individual lower energy subbeams. This leads to a pronounced regularization of the spatial structure of the filaments, which is formed at the stage of radiation self-focusing due to diffraction interaction between subbeams in a nonlinear medium. Generally, the total length of the filamentation domain of femtosecond laser radiation in air is reduced when using modulation meshes. At the same time, the longitudinal continuity of laser plasma in such filaments can significantly increase. We show that the spatial parameters of filaments (coordinate of the start, length, and continuity) can be controlled over a wide range by changing mesh parameters (crosshair thickness and cell size), as well as the position of the mesh mask relative to the laser beam center. The results are important for predicting the propagation of high-power femtosecond laser radiation in a nonlinear medium, in particular, along atmospheric paths.

Tundra lakes are an important indicator of climate change; therefore, the analysis of the dynamics of their size is of particular interest. This paper presents the results of using the U-Net convolutional neural network for tundra lakes segmentation in satellite optical images using Landsat data as an example. The comparative assessment of segmentation accuracy is performed for the original U-Net design and its modifications: U-Net++, Attention U-Net, and R2 U-Net, including with weights derived from a pre-trained VGG16 network. The segmentation accuracy is assessed based on the results of manual mapping of tundra lakes in northern Siberia. It is shown that more recent U-Net modifications do not provide a practically significant gain in segmentation accuracy, but increase the computational costs. A configuration based on the classic U-Net gives the best result in most cases (the average Soerens coefficient IoU = 0.88). The technique suggested and the resulting estimates can be used in analysis of modern climate trends.

We estimate the long-term variability of the parameters of single-layer cloud fields over the territory of Western Siberia in winter for the period from 2001 to 2019 based on MODIS data. The main idea of the applied method is to use the results of recognition of 11 cloud types from daily winter (December, January, and February) daytime satellite images. Features of single-layer clouds are considered for three latitudinal zones of Western Siberia: southern (< 60° N), transitional (60-65° N), and northern (> 65° N). We found linear trends for the following parameters of different cloud types: the coverage fraction of the target zones, optical thickness, effective particle radius, waterpath, and top height. The paper discusses the results of comparing the data we obtained with information from the annual Roshydromet assessment reports. We propose hypotheses about the reasons for the anomalous parameter values in the time series for different cloud types in the latitudinal zones of Western Siberia under study in winter.

In continuation of the first part of the work, experimental results of Kelvin-Helmholtz wave sounding with an UV BSE-5 lidar (355 nm), with the sensitivity higher than that of BSE-4 lidar (532 nm), are presented. Experiments on atmospheric sounding with the BSE-5 lidar were carried out in the winter-spring period over a built-up area, which is a “heat island". Improved lidar parameters in combination with thermal conditions in the atmospheric boundary layer, which is mainly stable stratified in the cold season, enables us to acquire new data on the shape of Kelvin-Helmholtz waves. It is ascertained that echo signals in both receiving channels of the lidar decrease by 30% after a sounding laser beam passes a turbulence intensity peak at the top of the wave arc. This effect of the atmosphere on echo signals of the turbulent lidar can be explained by beam broadening due to multiple scattering on random inhomogeneities of the medium.

The possibilities of using molecular scattering to determine the wind speed from measurements by a pulsed coherent Doppler lidar (PCDL) from an aircraft at altitudes from 10 to 20 km are numerically studied. The simulation was carried out for probing radiation focused at 500 m at wavelengths of 1 mm and 2 mm, the aperture diameter of the receiving-transmitting telescope was set equal to 10 cm. It is shown that the threshold SNR in measurements from an aircraft is attained at a pulse energy much lower than when sounding from the Earth. Modern PCDLs with probing pulse energies of 1-4 mJ, after adding a molecular scattering recording channel, can be used for airborne wind measurements at altitudes of 10-20 km.

The paper presents the results of a numerical study of flow gas dynamics and integral parameters of the flow at the channel entrance located behind a conical or plane shock wave. The free-stream Mach number range is М = 2 - 4 and the range of the slopes of the compression surfaces of the wedge and cone is δ= 10 - 90°. Data on the flow structure at the channel entrance, mean-mass Mach numbers, total pressure loss, and flow rate coefficients are obtained. A comparative analysis of these parameters is performed, and advantages and drawbacks of the channel entrance positions in various types of the flow are noted.

Rarefied gas flow into a vacuum through short linearly diverging and converging channels has been examined with the direct simulation Monte Carlo method. Solution to the problem has been suggested using complete geometric setup, with quite large areas on inlet and outlet of a model channel in examined geometry. A mass flow rate through the channel and flow field both inside the channel and upstream and downstream have been calculated in a wide range of gas rarefaction. These calculation results are comparable to corresponding data for the channel with constant cross section. A strong impact of channel geometry and gas rarefaction has been proved.

The paper presents the results of experimental study for rising a cluster of monodisperse gas bubbles in viscous liquid with/without surfactant for the Reynolds number in the range Re = 0.01 ÷ 1. The influence of surfactant type on the dynamics the bubble cluster rise has been analyzed. The qualitative pattern of monodisperse bubbles cluster rise was defined as a function of initial volumetric concentration in the range С_V = 0,001 ÷ 0,04. New experimental data were obtained on velocity and drag coefficient for a compact cluster of monosize bubbles rising in a liquid with/without surfactant (both for contact and contactless type of bubble rising.

Using isothermal drop calorimeter, the enthalpy increment of the Na₁₅Pb₄ and Na₅₀Pb₅₀ alloys was measured and the heat capacity was determined in the temperature range of 420-1075 K, including the solid and liquid states. It has been established that the values of the heat capacity of melts significantly exceed the calculations of this value according to the laws for an ideal solution, and this difference decreases with increasing temperature. The obtained results confirm the currently known fact that various complexes with a partially ionic character of the interatomic interaction are formed in melts of alkali metals with lead systems.