Generalization of the mathematical model of lungs for describing the intensity of the tracheal sounds during forced expiration

The possibility to relate the nature of the forced expiration tracheal sounds with the sound radiation by a separated flow that arises in the region of dynamic trachea constriction during forced expiration is investigated. A mathematical model of forced expiration is used for estimating. The calculated form of the time dependence of the sound intensity during forced expiration qualitatively corresponds to the experimental dependence obtained experimentally for normal subjects. The results should be taken into account in the physical explanation of tracheal sound generation mechanisms and in the justification of using the tracheal sound characteristics in the diagnostics of human lung pathologies.     

Synthesis of new 7-alkylmethylene derivatives of 2-(thio)oxo-2,5,6,7-tetrahydro-1<Emphasis Type="Italic">H</Emphasis>-pyridine-3-carbonitriles

Alkylmethyleneamines of cyclic ketones were used for the synthesis of earlier unknown 7-alkylmethylene-2-(thio)oxo-2,5,6,7-tetrahydro-1H-pyridine-3-carbonitriles.     

On the Shapiro–Lopatinkii condition for elliptic problems

This paper considers elliptic problems with high-order derivatives multiplied by a small parameter. We found the algebraic conditions for an operator and the boundary conditions that guarantee the Fredholm property. An a priori estimate for the solution with a constant independent of the small parameter is proved. These results are known for elliptic boundary-value problems with small parameter in the half-space R _n ⁺. We extend them to the case of bounded domains with smooth boundary. The small-parameter coercive conditions are formulated, and a two-sided estimate is proved.     

Phase transitions in FeBO<Subscript>3</Subscript> under pressure: DFT + DMFT study

We present a theoretical study of spectral, magnetic, and structural properties of the iron borate FeBO₃. Within the DFT + DMFT method combining density functional theory with dynamical mean-field theory FeBO₃ was investigated under pressures up to 70 GPa at 300 K. We found that FeBO₃ is an insulator with a gap of 2.0 eV with antiferromagnetic ordering at ambient pressure in agreement with experiments. In our calculations, we showed that Fe ions in FeBO₃ undergo a high-spin to low-spin transition under pressure with change from antiferromagnetic to paramagnetic state, and demonstrate that the spin and magnetic transitions occur simultaneously with an isostructural transition at 50.4 GPa with the volume collapse of 13%.     

Erratum to: Monitoring of Fast Variations in the Content of Endogenous CO in Exhaled Air by Methods of Diode Laser Spectroscopy

Optics and Spectroscopy - An Erratum to this paper has been published: https://doi.org/10.1134/S0030400X21010197     

Superharmonic instability of stokes waves

A stability of nearly limiting Stokes waves to superharmonic perturbations is considered numerically in approximation of an infinite depth. Investigation of the stability properties can give one an insight into the evolution of the Stokes wave. The new, previously inaccessible branches of superharmonic instability were investigated. Our numerical simulations suggest that eigenvalues of linearized dynamical equations, corresponding to the unstable modes, appear as a result of a collision of a pair of purely imaginary eigenvalues at the origin, and a subsequent appearance of a pair of purely real eigenvalues: a positive and a negative one that are symmetric with respect to zero. Complex conjugate pairs of purely imaginary eigenvalues correspond to stable modes, and as the steepness of the underlying Stokes wave grows, the pairs move toward the origin along the imaginary axis. Moreover, when studying the eigenvalues of linearized dynamical equations we find that as the steepness of the Stokes wave grows, the real eigenvalues follow a universal scaling law, that can be approximated by a power law. The asymptotic power law behavior of this dependence for instability of Stokes waves close to the limiting one is proposed. Surface elevation profiles for several unstable eigenmodes are made available through  http://stokeswave.org website.     

Cycloalka[<Emphasis Type="Italic">c</Emphasis>]pyridine derivatives. Methods of synthesis and chemical properties

The review generalizes and systemizes data published over the past 15 years on the synthesis and chemical properties of cycloalka[c]pyridine derivatives that are important intermediate products used in the synthesis of alkaloids, enzyme inhibitors, and drugs for the treatment of cardiovascular diseases and bronchial asthma.