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The high-order harmonic generation (HHG) in xenon is studied by using the time-dependent density-functional theory. The dynamics of all electrons on the outer 4th and 5th atomic shells is considered with subsequent separation of contributions of different atomic orbitals to the HHG amplitude. It is shown that giant enhancement of HHG yield in a spectral region near 100 eV is caused by perturbation of the electron–electron interaction potential induced by recolliding photoelectron wavepacket originated from the 5 p 0 orbital. This perturbation leads to the collective oscillations of all orbitals on the 4th shell closely localized in space and strongly interacting with each other. The resulting HHG yield is enhanced by more than an order of magnitude compared with the response of the single 5 p 0 orbital. The high accuracy of the numerical results is confirmed by comparing the calculated HHG spectra and photoionization cross-sections with experimental results and an analytical parameterization of the HHG yield.

The orographic barrier functions of political borders of Eurasia is analyzed using the geoinformation approach. A review of the evolution of concepts of natural borders from ancient times to the present day is presented. A classification of the barrier functions of political borders has been carried out, including natural, infrastructural, institutional, demographic, ethnocultural, and historical types. The research proposes a method for assessing the orographic barrier functions of borders using the geoinformation approach through elevation differences in the zone 2 km from the border, which is calculated using Shuttle Radar Topography Mission (SRTM) digital elevation models. This article shows significant differences in the conditions of political borders in Eurasia and reveals new patterns between the barrier functions and conflict and integration types of borders, such as a high level of barrier functions of borders in Southeast Asia, a fairly high level of barrier functions of borders on the Korean and Arabian peninsulas, a low level of barrier functions in Eastern Europe and on the Indo-Pakistan border, etc. Using statistical analysis methods, it has been revealed that conflict borders in Eurasia paradoxically more often follow orographic barriers, in contrast to integration borders, exhibiting less naturalness; this, on the contrary, is a refutation of the original theory of natural boundaries. The results of the work can be useful for assessing the influence of geographical entities and for understanding the influence of geographical conditions on the formation and functioning of political borders. The neighborhood matrix that has been developed can serve as an alternative method for calculating the neighborhood weight ( wij ) in Moran’s spatial autocorrelation index (Moran’s I).

We investigate the high harmonic generation during the interaction of the femtosecond laser field with oriented asymmetric diatomic molecules in the presence of an external static electric field. Based on the numerical solution of the time-dependent Schrödinger equation for the model one-electron system, we calculate the high harmonic generation spectrum for a wide range of static-field strengths. The possibilities for visualizing low-frequency (terahertz and mid-infrared) radiation using time-delay measurements of even high harmonics intensities are discussed.

We study the generation of low-order harmonics during the interaction of helium atoms with intense elliptically-polarized laser pulses in the presence of a static electric field. Based on the solution of the three-dimensional time-dependent Schrödinger equation, the spectra of generated radiation are calculated for various pulse ellipticities, intensities, and static-field strengths. We show the possibility of using the second harmonic generation in the free-electron current density by laser pulses with arbitrary (even circular) polarization for high-resolved measuring the waveforms of terahertz and mid-infrared radiation.

Based on the numerical solution of the three-dimensional time-dependent Schrödinger equation, we calculate the secondary generated radiation induced by hydrogen atoms in linearly polarized extreme ultraviolet (XUV) and intense infrared (IR) pulses. We show that XUV-induced channels of secondary generated radiation (second harmonic of the XUV pulse and XUV-assisted high-order harmonic generation) can be well separated at the orthogonal geometry of two pulses by polarization measurements. It is demonstrated that at the orthogonal geometry the accuracy of IR-field retrieving based of XUV second harmonic generation can be significantly increased in comparison with the case of collinear geometry, for which the XUV-assisted HHG channel interferes with the XUV second harmonic generation.

Methodological approaches to the identification of hydrologically sensitive landscapes have been developed and implemented in the Selenga River basin. The topographic wetness index (TWI) is calculated to detect accumulative landscapes using the digital relief model of the region under study. Areas with TWI ranges of 12–15 and 15–18 are recognized as areas with the most likely runoff zones. To assess the possibility of their influence on the formation of the river runoff composition, a map of the total runoff is created using the flow accumulation (FA) model. Hydrologically sensitive areas (HSAs) in a watershed are determined by superimposing a spatial distribution map of areas with maximum total runoff values on the TWI differentiation map. Areas with contours located within the territories of maximum values of total runoff are identified as true hydrologically sensitive landscapes. Model polygons are selected to test the methodology for mapping hydrologically sensitive areas and primary pollution sources. Studies are carried out on the model territory of the city of Ulan-Ude, which is one of the main pollutants of the waters of the Selenga River and Lake Baikal. The main condition for the formation of secondary sources of pollution (accumulative landscapes) is the correspondence of the pollution source coverage area with HSA. The resulting map of production facilities is superimposed on the HSA spatial distribution map, fragments of which within industrial zones are identified as possible secondary sources of pollution (critical sources areas (CSAs)). The accuracy of the CSA allocation has been confirmed by the results of assessing the level of soil pollution in the city of Ulan-Ude.

The paper is devoted to further investigation of the generation of tunable mid-infrared radiation during gas ionization by two-color laser pulses. We demonstrate that control of generated mid-infrared frequency can be ensured with the use of linearly chirped laser pulse by changing the group delay between the laser-pulse components.

The high harmonic generation (HHG) in xenon is studied by using the time-dependent density-functional theory for active 4th and 5th atomic shells. The HHG spectra are calculated for different intensities and carrier-envelope phases of a laser pulse. The HHG spectrum shows enhancement at the frequency region near 100 eV, where the HHG yield is by more than an order of magnitude higher than in the single-active electron approximation. The high accuracy of the obtained results is confirmed by comparing the calculated HHG spectra with experimental results.

We study the ionization and high-order harmonic generation by argon atoms subjected into the intense laser pulse based on the numerical solution of the time-dependent Kohn-Sham equations. We demonstrate that atom polarization leads to significant screening of the external electric field and decrease in the atom ionization probability. At high leaser-pulse intensity, the suppression of depletion lead to enhancement of the HHG yield in comparison with the single-active electron approximation, which neglects the polarization effect.

In general, magnetism and superconductivity are antagonistic to each other. However, there are several families of superconductors in which superconductivity coexists with magnetism, and a few examples are known where the superconductivity itself induces spontaneous magnetism. The best known of these compounds are Sr 2 RuO 4 and some non-centrosymmetric superconductors. Here, we report the finding of a narrow dome of an s + i s ′ superconducting phase with apparent broken time-reversal symmetry (BTRS) inside the broad s -wave superconducting region of the centrosymmetric multiband superconductor Ba 1 −  x K x Fe 2 As 2 (0.7 ≲  x  ≲ 0.85). We observe spontaneous magnetic fields inside this dome using the muon spin relaxation (μSR) technique. Furthermore, our detailed specific heat study reveals that the BTRS dome appears very close to a change in the topology of the Fermi surface. With this, we experimentally demonstrate the likely emergence of a novel quantum state due to topological changes of the electronic system. An exotic s  +  is multiband superconducting state manifests in a doped pnictide superconductor when a second band moves below the Fermi surface. This creates an internal magnetic field, breaking time-reversal symmetry.