We report the revised crystal structure, static and dynamic magnetic properties of quasi-two dimensional honeycomb-lattice silver delafossite Ag3Co2SbO6. The magnetic susceptibility and specific heat ...data are consistent with the onset of antiferromagnetic long range order at low temperatures with Néel temperature TN ∼ 21.2 K. In addition, the magnetization curves revealed a field-induced (spin-flop type) transition below TN in moderate magnetic fields. The GGA+U calculations show the importance of the orbital degrees of freedom, which maintain a hierarchy of exchange interaction in the system. The strongest antiferromagnetic exchange coupling was found in the shortest Co-Co pairs and is due to direct and superexchange interaction between the half-filled xz + yz orbitals pointing directly to each other. The other four out of six nearest neighbor exchanges within the cobalt hexagon are suppressed, since for these bonds the active half-filled orbitals turned out to be parallel and do not overlap. The electron spin resonance (ESR) spectra reveal a broad absorption line attributed to the Co(2+) ion in an octahedral coordination with an average effective g-factor g = 2.40 ± 0.05 at room temperature and show strong divergence of the ESR parameters below ∼150 K, which implies an extended region of short-range correlations. Based on the results of magnetic and thermodynamic studies in applied fields, we propose a magnetic phase diagram for the new honeycomb-lattice delafossite.
The range of applications for distributed fiber-optic sensors is constantly expanding due to both the growing needs of industry and the development of the measurement capabilities of the sensors ...themselves. In connection with the need to develop methods for interpreting sensor signals, it is extremely important to form sets of test signals for distributed fiber-optic sensors obtained under known conditions and effects on the fiber. In the presence of reliable analytical models of signals from distributed fiber-optic sensors, it is extremely convenient to obtain test signals in the course of numerical experiments. The paper will consider the processes of formation of backscattering signals in Rayleigh reflectometric systems and describe physical and mathematical models that allow calculations of signals under different operating conditions. Two approaches for calculating the resulting backscatter signal are proposed: (1) based on the temporal representation of the probing signal and the impulse response of the sensitive fiber and (2) an alternative approach based on the spectral representation of the probing signal and the transfer function of the fiber. The presented results can be used both for direct simulation of the operation of reflectometric systems using Rayleigh scattering and for the analysis of existing limitations and the specifics of their operation.
Abstract
The paper presents the study results of the stress state at the contour points of an underground horizontal working carried out by the methods of the complex variable theory. This study is ...the basis for solving the problem of determining an allowable value of the uniform pressure transmitted to the contour of the working, with predetermined values of the depth of its laying. The condition proposed by the authors of the paper is used as a criterion of strength (stability), according to which the working’s contour strength is ensured if at any point the amount of the tangential normal stress does not exceed the tensile and compressive strength of the host soil (rock), i.e.
σ
t
≤
σ
e
≤
σ
c
. As a result of the solution, an assessment of the stress distribution on the contour of an underground horizontal working has been made. The working has a cross-section in the form of a curved trapezoid, which is under the action of uniform all-round stretching of a given intensity with a varying depth and various values of the host mass lateral expansion coefficient. The allowable values of the tensile internal pressure on the contour of an underground horizontal working of a trapezoidal cross-section have been determined at the given values of its depth and a constant coefficient value of the lateral expansion of the host mass
μ
= 0.25. The materials presented in the paper can be used when choosing the maximum or minimum allowable depth of the working used as a storage facility for liquid or gaseous hydrocarbons.
A quantum spectral-domain optical coherence tomography technique based on the control of the joint spectral amplitude of a biphoton has been developed. An analytical expression for a quantum ...spectral-domain optical coherence tomography signal has been obtained in the case of a Gaussian joint spectral amplitude. The effect of the shape of the joint spectral amplitude of the biphoton on the resulting interference signal has been analyzed. The possibility of improving the quality of the interference signal by controlling the parameters of the joint spectral amplitude has been considered. It has been shown theoretically that the proposed approach provides a higher longitudinal spatial resolution than other optical coherence tomography techniques.
The relevance of the work is related to the need to develop methods for determining individual opportunities to minimize the harmful effects of ionizing radiation. Experiments were conducted to ...search for informative indicators of the structure of mast cells to predict the individual effectiveness of the radioprotective effect of hypoxia. A study was performed on white male rats. In 81 animals, before the main experiment, a hypoxic sample was carried out once, by placing the rats in a gas mixture containing 8% oxygen and 92% nitrogen (GGS-8). In each of these rats, a biopsy of the skin of the auricle was performed immediately before the test and at the time of its completion. In the biopsies, the content of various forms of mast cells detected by the method of metachromasia with toluidine blue was determined. After a week, all animals of the main group (81 rats) were exposed to total γ-irradiation at a dose of 11 Gy under the protection of GGS-8. Rats in the control group (63 rats) were irradiated in the same dose in the air. The life expectancy after the exposure was assessed. The radioprotective effect of the gas hypoxic mixture was confirmed, which is expressed in an increase in the average life expectancy of irradiated rats by 2.2 times. A weak relationship between individual quantitative characteristics of mast cells and the life expectancy of irradiated animals is shown. A formal expression of the equation of regression of the number of mast cells on the life expectancy of animals irradiated under the protection of hypoxia has been created. On the basis of regression analysis, groups of animals in which the highest radioprotective effect of hypoxia was manifested were revealed. The minimum life expectancy after irradiation is characteristic of rats with extreme values of the mast cell reactivity index, and all surviving cases are noted in rats with average values of the indicator. Among them there was not a single animal with an intestinal form of death. This indicates the possibility of predicting the radioprotective effect of hypoxia based on an assessment of the functional activity of mast cells.
Addition of NH-pyrroles acting as electrophiles to zwitterionic adducts of Δ
1
-pyrrolines and electron-deficient acetylenes (20–25 °C, 4–30 h) gave 2-(pyrrol-1-yl)pyrrolidin-1-ylacrylonitriles and ...2-(pyrrol-1-yl)pyrrolidin-1-ylenones in 18–48% yields.
We study angular and frequency-angular distributions of the terahertz (THz) emission of the low-frequency region (0.3-3 THz) from a two-color femtosecond plasma spark experimentally and in ...three-dimensional numerical simulations. We investigate the dependence of the angular shapes of the THz radiation on focusing conditions and pulse durations by using two laser facilities (pulse durations 35 and 150 fs) for different focusing geometries. Our experiments and simulations show that decrease in the numerical aperture from NA ≈0.2 to NA ≈0.02 results simultaneously in (I) squeezing of the THz angular distribution and (II) formation of the bright conical emission in the THz range. The moderate focusing NA ≈0.05, which forms the relatively narrow unimodal THz angular distribution, is identified as optimal in terms of angular divergence. Numerical simulations with carrier wave resolved show that bright THz ring structures appear at the frequencies ≥2 THz for longer focuses (NA ≈0.02), while for optimal focusing conditions NA ≈0.05 the conical emission develops at THz frequencies higher than 10 THz.
The results of constructing an underground horizontal mine working of the given size and the specified shape of the cross section are presented based on the method proposed by the authors. The stress ...state is investigated at the points of the work-out contour of a non-circular shape with a vertical axis of symmetry cross-section. The safe laying depth of the mine working under the given uniform pressure applied at the points of its contour is determined.
The article reports on the current status of the Baksan Large Neutrino Telescope project and describes some selective results of the first stage of the project, a detector prototype with a liquid ...scintillator mass of 0.5 tons. The results of the second stage of the project, a prototype with liquid scintillator mass of 5 tons, and project prospects also presented.
Complexation between (18-crown-6)stilbene and alkanediammonium ions
+
H
3
N(CH
2
)
n
NH
3
+
(
n
= 2−4) resulting in the pseudo-sandwich 2:1 stilbene—dication complexes and 1:1 stilbene—dication ...complexes was studied by NMR spectroscopy. The stability of the complexes decreases as the methylene chain length in the alkanediammonium ion increases. UV photolysis of the bis-ligand complexes produces two major products,
viz.
, the
rctt
isomer of a biscrown-containing cyclobutane derivative formed as a result of intra-supramolecular 2+2 photocycloaddition and a crown-containing phenanthrene derivative (product of electrocyclization reaction). The effective quantum yields of both cyclization reactions occurring in the pseudo-sandwich complexes increase as the number of methylene units in the dication decreases.
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