The room-temperature X-ray and Mössbauer data on the BiFeO
3
, Bi
0.95
Sr
0.05
FeO
3 –
y
, and Bi
0.90
Sr
0.10
FeO
3 –
y
multiferroics obtained by solid-phase synthesis are presented. The samples ...have a rhombohedral crystal structure with the sp. gr.
R
3
c
. The lattice parameter
a
h
is invariable, while the parameter
c
h
decreases with increasing strontium content. The
57
Fe Mössbauer spectra recorded at a temperature of 295 K have been interpreted within the cycloid spatial spin-modulated structure model. It has been established that the easy-axis magnetic anisotropy is implemented in the investigated multiferroics. The anharmonicity parameter
m
of the spin-modulated structure has been measured. Upon replacement of trivalent Bi
3+
ions in small amounts (
x
= 0–0.10) with divalent Sr
2+
ions, the parameter
m
increases by a factor of more than 3: from 0.10(4) at
x
= 0.00 to 0.36(10) at
x
= 0.10.
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A theory of the asymmetry parameters of a weak shock wave in a binary gas mixture, based on the expansion of the solutions of the Burnett equations in series in a small parameter of the shock wave ...intensity, that ensures the asymptotic accuracy of the required data, is given. The dependence of the solution on the characteristics of the mixture is examined. The known results for a polyatomic gas are refined and supplemented.
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One of the modern modifiers, which is not well studied as a sorbent and a modifier in synthetic resins, is shungite fullerenes. The main property of aqueous solutions of shungite fullerenes is a ...powerful antioxidant effect. Free radicals are short-lived, but chemically active substances that arise during oxidation; i.e. an unsaturated bond does not connect two atoms, but “hangs” in space, actively striving to join something. These are unstable, but extremely aggressive substances, the molecules of which last for a fraction of a second and end up oxidizing the surrounding molecules. Fullerenes are catalysts for recombination, mutual destruction of free radicals, however, they are not consumed, but act as free radicals that attack neighboring molecules and combine with each other; i.e., they recombine, forming a harmless product.
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Experiments aimed at studying the mechanisms of cross-polarized microwave radiation scattering by the surface layer of water under conditions of extremely high wind speeds have been conducted in the ...wind–wave flume of Large Thermo-Stratified Wind-Wave Tank of the Institute of Applied Physics, Russian Academy of Sciences (IAP RAS). It is shown that the normalized radar cross section (NRCS) can be represented as a result of incoherent addition of contributions from breaking wave crests and from nonbreaking wind waves. The effect of smoothing of the water surface after passing the breaking crest made it possible to measure the NRCS of the breaking area in cross polarization, while no dependence of the NRCS on wind speed or the sounding angle was revealed. The NRCS of nonbreaking wind waves was calculated within the framework of the small slope model using the experimentally measured spectra of wind waves. It was shown that the NRCS in cross polarization increases monotonically with increasing wind speed, including hurricane conditions. In this case, the contribution of nonbreaking wind waves to NRCS experiences saturation at wind speeds exceeding 25 m/s. The monotonic increase in NRCS at higher wind speeds is associated with an increase in the surface area occupied by breaking. A composite model of microwave radiation scattering on the surface of rough water has been constructed and verified based on comparison with measurement data. The possibility of constructing a geophysical model function for ocean conditions based on the proposed composite model is shown, which can be used for remote measurements of wind speed under sea storm and hurricane conditions, including space-based instruments.
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•Main regularities of the change in MCE value with a change in composition are found.•We find a structural phase transition in Тb0.4Dy0.3Ho0.3Co1.75Fe0.25 at 375 K using XRD.•Mössbauer effect study ...provided data on the hyperfine parameters in the alloys.•Hydrogenation effect on magnetism of alloys is shown.
In this work, the effects of substitutional elements on the magnetism of complex rare-earth-transition metal compounds RT2 with the Laves phase structure are studied with the aim to find new materials with high magnetocaloric effect (MCE) above room temperature. We determine the main regularities in the MCE magnitude variation when varying composition of the Tb-Dy-Ho-Co-Fe alloys and also after hydrogenation. The crystal structure of the compounds is characterized by X-ray diffraction in a wide temperature range while information on the magnetic properties of the 3d-transition metal sublattice is accessed by means of the 57Fe Mössbauer effect studies. We design a series of Tbx(Dy0.5Ho0.5)1-xCo1.75Fe0.25 samples with constant MCE values, suitable for the use as cooling elements of devices operating at elevated temperatures.
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Oil in an oilfield of the Perm region is situated in porous layers, which are similar to a sponge. Reservoir pressure is not enough to raise it to the surface, and therefore the following method of ...oil production is used: spaced apart rigs are mounted in two rows (one row is forcing, the other one is extracting); rigs of a forcing row pump some liquid (usually water) underground, this liquid forces oil out of the porous layer, which allows extracting rigs to bring it to the surface. Simulation of this process is a rather difficult problem; part of it is to model the behavior of the porous medium itself. In this paper we consider the method of modeling a porous medium by its representation as a bundle of parallel capillaries, based on a method of statistical experiments. The goal of modeling is to derive dependence of such characteristics of medium as porosity and permeability on redundant pressure in the layer.
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A potassium salt of the N2S2O2-coordination Fe(III) anion KFe(5Cl-thsa)2 (1) (5Cl-thsa − 5-chlorosalicylaldehyde thiosemicarbazone) is synthesized and characterized structurally and magnetically ...over a wide temperature range. Two polymorphs of salt 1 characterized by the common 2D polymer nature and assigned to the same orthorhombic Pbcn space group have been identified. The molecular structure of the minor polymorph of 1 was solved and refined at 100, 250, and 300 K is shown to correspond to the LS configuration. The dominant polymorph of 1 features K+ cations disordered over a few crystallographic sites, while the minor polymorph includes fully ordered K+ cations. The major polymorph exhibits a complete three-step cooperative spin-crossover transition both in the heating and cooling modes: The first step occurs in a temperature range from 2 to 50 K; the second abrupt hysteretic step occurs from 200 to 250 K with T 1/2 = 230 K and a 6 K hysteresis loop. The third gradual step occurs from 250 to 440 K. According to 57Fe Mössbauer, XRPD, and EXAFS data, the spin-crossover transition for the dominant polymorph is quite peculiar. Indeed, the increase in the HS concentration by 57% at the second step does not result in the expected significant increase in the iron(III)–ligand bond lengths. In addition, the final step of the spin conversion (ΔγHS = 26%) is associated with a structural phase transition with a symmetry lowering from the orthorhombic (Pbcn) to the monoclinic (P21/n) space group. This nontrivial phenomenon was investigated in detail by applying magnetization measurements, electron spin resonance, 57Fe Mössbauer spectroscopy, and DFT calculations. These results provide a new platform for understanding the multistep spin-crossover character in the Fe(III) thsa-complexes and related compounds.
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Glued wooden structures are promising products for use in different fields of industrial and civil construction. The main factor that affects the durability of glued wooden structures consists in the ...internal stresses acting within the structure. A novel method for estimating the magnitude of internal stresses acting in a glued wooden structure (based on melamine–formaldehyde binders) has been proposed and experimentally tested. The method is based on use of basic benchmarks, which allow measuring deformations resulting from gouging of the samples followed by subsequent deforming thereof under load by the amount of free strain. The stress value has been calculated as a ratio between the load value and the cross-sectional area of the sample. The testing has shown that the stresses in the samples are unevenly distributed and not balanced throughout the length. The distribution of total stresses throughout the width and height of the section turned out to be close to the equilibrium distribution. However, the absolute values of the stresses are much lower than the stresses in the samples.
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Three particular cases from the class of exact moment solutions of the Boltzmann–Maxwell kinetic equation for homoenergetic affine flows of a monatomic gas of Maxwellian molecules are considered. ...Conditions are formulated under which local expressions for the viscous stresses closing the gas-dynamic problem (here this is the energy equation) follow from exact relations.
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Some effects in gases are completely or partially determined by the Burnett terms of the stress tensor and the heat flux vector. Usually, approximate values of the Burnett transport coefficients for ...a monatomic gas are used to calculate the above-mentioned quantities. “Exact” expressions for these coefficients correct to values less than one percent are obtained for elastic-sphere molecules. The results of calculations of certain such effects are compared with one another using the approximate and exact Burnett transport coefficients for a monatomic gas consisting of elastic-sphere molecules.
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