ABSTRACT
Statistical analysis of samples of the orbits of celestial bodies is complicated by the fact that the Keplerian orbit is a multidimensional object, the coordinate representation of which ...non-linearly depends on the choice of orbital elements. In this work, using the construction of the Fréchet mean, concepts of mean orbit and dispersion of the orbit family are introduced, consistent with the distance function on the orbit set. The introduced statistical characteristics serve as analogues of sample mean and variance of a one-dimensional random variable. Exact formulas for calculating the elements of mean orbits and dispersion quantities with respect to two metrics on the orbit space are derived. For a large sample of meteoroid orbits from the Geminid stream, numerical simulations of orbit evolution over 20 000 yr in the past were conducted. By analysing the dependency of statistical characteristics on time, estimates for the age of the stream and the gas outflow velocity are obtained under the assumption of the birth of the Geminids due to the rapid destruction of the cometary nucleus. The estimate of the age of the stream lies in the interval from 1200 to 2400 yr, and the speed of gas outflow at perihelion should have been more than 1.2 km s−1.
Results of an experimental study and numerical simulation of the curing kinetics of an epoxy binder under the conditions of violation of the stoichiometric equilibrium of its components are ...presented. The object of research is a two-component composition of an L epoxy resin and an EPH 161 hardener, certified as a binder for composite materials of aerospace purpose. As the basic model, we used a system of two ordinary differential equations describing the behavior of the resin and hardener during the curing process. The values of material parameters necessary for calculations were obtained by a rheological method, where the viscosity of binder was analyzed as a function of polymerization time and hardener concentration. The estimates of model parameters obtained by processing data of full-scale experiments are presented. The effective values of kinetic parameters at which the calculated time of yield loss is in good agreement with the experimental one are determined. The adequacy of the model was confirmed by direct measurements using the IR spectroscopy.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this paper, we describe a method for creating new custom models of partial Mössbauer spectra based on the existing ones built into the SpectrRelax program without changing the program itself by ...writing code fragments in the built-in Lua programming language. The extension of the capabilities of the SpectrRelax program is demonstrated using the example of studying hyperfine interactions of
57
Fe nuclei in quasibinary Tb(Fe
0.8
Al
0.2
)
2
and Ho(Fe
0.8
Mn
0.2
)
2
alloys with the C15 Laves phase structure. A model for processing the spectra, which simultaneously takes the composite and magnetic nonequivalence of the positions of Fe atoms in these alloys, has been created and used, which makes it possible to obtain new data about the orientation of the axis of the easiest magnetization, the anisotropy of the hyperfine magnetic field, and the effect of substitution of Al and Mn atoms for Fe atoms on hyperfine parameters of Mössbauer spectra.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The results of numerical study of relaxation processes in oxygen at high temperatures are presented. Collisions of particles (atoms and molecules) are described by the molecular dynamics methods ...based on trajectory calculations within the framework of classical mechanics. A complex of programs for calculating the relaxation processes in mixtures of high-temperature gases involving internal modes that describe rotational and vibrational motions in molecules and molecular dissociation and atomic recombination in the presence of a third body is described. The relaxation process is described with reference to variation in the parameters in a mixture of atomic and molecular oxygen with various initial temperatures of the translational and internal modes. The results of calculations of the structure of shock wave in oxygen with the maximum translational temperature on the front higher than 5000–11 000 K are given. The results obtained are compared with experimental data.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•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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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The existing ideas on the status of the Navier–Stokes equations are changed in taking into account the following facts: generally speaking, the terms of these equations neglected in the boundary ...layer equations are of the order of certain Burnett terms in the conservation equations; the Navier–Stokes equations cannot be used to describe slow nonisothermal gas flows since in this case it is necessary to take the Burnett temperature stresses into account; and in the transport relations the Burnett terms determine certain effects (for example, the mechanocaloric effect).
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The influence of the modification of α-Fe
2
O
3
nanoparticles by electron irradiation on their stability to natural aging processes during a long-term (three years) storage has been studied. ...Nanoparticles of this type (obtained by chemical vapor deposition with subsequent thermal annealing) were chosen due to the wide range of their practical applications. The changes in the properties of α-Fe
2
O
3
nanoparticles during natural aging, depending on the irradiation dose, were investigated by X-ray diffraction and Mössbauer spectroscopy. It is found that modification by electron irradiation provides stability of α-Fe
2
O
3
nanoparticles to hydration processes and phase transformations during a long-term storage; an increase in the irradiation dose increases the resistance to structural disordering during aging, thus retaining the nanoparticle properties for a long time.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We investigate the curing of large shell construction made of epoxy resin/carbon fibers prepreg under free space conditions in solar synchronous Low Earth Orbit. The curing kinetics is described by ...first order kinetic equation with auto-acceleration and deceleration parameters based on the experimental data. Heating of the shell is provided by solar radiation. The heat distribution in the shell is modelled based on partial absorbance of the solar radiation, the prepreg thermal conductivity and thermal capacity, radiation heat transfer between inner surfaces of the shell and the gas thermal conductivity. The iterated algorithm of curing was developed. Three flight regimes based on the circular motion of a construction have been considered: 1 – the axis of a shell lies in the tangent plane to the orbit and makes a constant angle with the tangent; 2 – under conditions (1), a shell rotates around its axis with a constant angular velocity; 3 – under conditions (2), the axis of the shell precesses around the tangent to the orbit. It was found, that the parameters of the motion (i.e. angular velocity of the rotation around the axis, precession angular velocity and precession angle) could be optimised in such way, that the whole shell can be completely cured under the solar radiation.
•Curing of epoxy composite in space is proposed for large space construction.•Solar synchronous Low Earth Orbit is considered for a curing orbit.•Orbital motion with the axis of the shell precesses around the tangent is optimised.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
