Kinematics of OB-associations in Gaia epoch Mel'nik, A. M; Dambis, A. K
Monthly Notices of the Royal Astronomical Society,
12/2017, Letnik:
472, Številka:
4
Journal Article
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Abstract
We use stellar proper motions from the Tycho-Gaia Astrometric Solution (TGAS) catalogue to study the kinematics of OB-associations. The TGAS proper motions of OB-associations generally agree ...well with the Hipparcos proper motions. The parameters of the Galactic rotation curve obtained with TGAS and Hipparcos proper motions agree within the errors. The average one-dimensional velocity dispersion inside 18 OB-associations with more than 10 TGAS stars is σv = 3.9 km s−1, which is considerably smaller, by a factor of 0.4, than the velocity dispersions derived from Hipparcos data. The effective contribution from orbital motions of binary OB-stars into the velocity dispersion σv inside OB-associations is σb = 1.2 km s−1. The median virial and stellar masses of OB-associations are equal to 7.1 × 105 and 9.0 × 103 M⊙, respectively. Thus, OB-associations must be unbound objects, provided they do not include a lot of dense gas. The median star-formation efficiency is ε = 2.1 per cent. Nearly one-third of stars of OB-associations must lie outside their tidal radius. We found that the Per OB1 and Car OB1 associations are expanding with the expansion started in a small region of 11–27 pc 7–10 Myr ago. The average expansion velocity is 6.3 km s−1.
Abstract
Dissociation of carbon monoxide in shock heated flows is studied with emphasis to the phenomenon of dissociation induction. Different kinetic schemes are implemented, both neglecting and ...including electronic excitation; various vibrational and electronic state-resolved models of dissociation rate coefficients are assessed. Vibrational-electronic relaxation coupled to dissociation behind the shock front is simulated in the frame of the state-to-state approach for several test cases with varying initial pressure, temperature, mixture composition and shock velocity. It is found that dissociation delay may appear regardless taking into account electronic excitation; the incubation time is mainly governed by mixture composition and initial pressure. Electronic excitation noticeably influences the overall dissociation rate. Recommendations for using specific dissociation models are given for different test cases.
The objective of this study is to examine various combinations of vibration-chemical coupling models in high-temperature air and oxygen flows behind shock waves. Simulations are carried out in the ...frame of the state-to-state approach for detailed vibrational and chemical kinetics in the Euler approximation. Great variety of state-resolved models for the rate coefficients of vibrational energy transitions and chemical reactions are assessed and validated against experimental data; among them are first-order perturbation (SSH) and forced harmonic oscillator (FHO) models; well-known Marrone–Treanor dissociation model with parameters either obtained empirically or by fitting quasiclassical trajectory calculations; new models for state-specific Zeldovich reactions. To validate the models, the results of numerical flow simulations are compared with experimental investigations in a wide range of initial mixture compositions and shock wave velocities. Among numerous model variants, a few models providing the best agreement with the experimental data on the vibrational temperature in oxygen flows and measured NO radiation in air flows are recommended for different sets of free stream conditions. The impact of NO excited states produced in Zeldovich reactions is evaluated; it is shown that neglecting the vibrational excitation of NO molecules may lead to significantly underpredicted maximum of NO number density. In the framework of the code performance study, Matlab and Fortran implementations were compared, the most significant bottlenecks procedures were identified by profiling analysis, and remarkable speed-up was achieved by code optimisation.
•Results of shock heated flow simulations are compared with experimental data.•State-resolved models of vibration-chemical coupling for air species are validated.•Code profiling and optimisation are performed, significant speed-up is achieved.
Abstract
Coupled vibrational, chemical and electronic kinetics in oxygen is studied using the detailed state-to-state model. Simulation of zero-dimensional oxygen relaxation in the presence of free ...electrons in the temperature range 300 – 1000 K is carried out; the master equations for the vibrational state populations and densities of excited species are solved together with the Boltzmann equation for the electron density distribution. Different models for heavy-particle interactions are assessed. It is shown that the forced harmonic oscillator model is suitable in the entire temperature range. The effect of the initial conditions and the presence of free electrons is discussed; it is shown that including electrons modifies the main relaxation mechanisms. Recommendations are given for extending the kinetic scheme to high-temperature regimes.
The proper motions of OB-associations computed using the old and new reductions of the Hipparcos data are in good agreement with each other. The Galactic rotation curve derived from an analysis of ...the line-of-sight velocities and proper motions of OB-associations is almost flat in the 3-kpc neighbourhood of the Sun. The angular rotation velocity at the solar distance is Ω0= 31 ± 1 km s−1 kpc−1. The standard deviation of the velocities of OB-associations from the rotation curve is σ= 7.2 km s−1. The distance scale for OB-associations should be shortened by 10–20 per cent. The residual velocities of OB-associations calculated for the new and old reductions differ, on average, by 3.5 km s−1. The mean residual velocities of OB-associations in the stellar-gas complexes depend only slightly on the data reduction employed.
A new complex of composition Cu(2-NO
2bz)
2(nia)
2(H
2O)
2 (
1) (nia
=
nicotinamide, 2-NO
2bz
=
2-nitrobenzoate) has been prepared and studied.
The complex
1 exhibits magnetic moment
μ
eff
=
1.86
...B.M. at 300
K which decreases to
μ
eff
=
1.83
B.M. at 1.8
K. EPR spectra at room temperature as well as at 77
K are of axial type with
g
⊥
=
2.065 and
g
∥
=
2.280 with parallel hyperfine splitting of
A
II
=
160
G. The dataset of 72 structures similar to that of
1 extracted from CCD confirmed a significant correlation between the average Cu–O
ax bond length and tetragonality parameter
τ.
A new complex of composition Cu(2-NO
2bz)
2(nia)
2(H
2O)
2 (
1) (nia
=
nicotinamide, 2-NO
2bz
=
2-nitrobenzoate) has been prepared and its composition and stereochemistry as well as coordination mode have been determined by elemental analysis, electronic, infrared and EPR spectroscopy, magnetization measurements over the temperature range 1.8–300
K, and its structure has been solved, as well. The complex structure consists of the centrosymmetric molecules with Cu(II) atom monodentately coordinated by the pair of 2-nitrobenzoato anions and by the pair of nicotinamide molecules, forming nearly tetragonal basal plane, and by a pair of water molecules that complete tetragonal–bipyramidal coordination polyhedron about the copper atom. The complex
1 exhibits magnetic moment
μ
eff
=
1.86
B.M. at 300
K which decreases to
μ
eff
=
1.83
B.M. at 1.8
K. The magnetic susceptibility temperature dependence obeys Curie–Weiss law with Curie constant of 0.442
cm
3
K
mol
−1 and with Weiss constant of −1.0
K. EPR spectra at room temperature as well as at 77
K are of axial type with
g
⊥
=
2.065 and
g
∥
=
2.280 and exhibit clearly, but partially resolved parallel hyperfine splitting with
A
II
=
160
G, that is consistent with the determined molecular structure of
1. In order to analyze the factors influencing the degree of tetragonal distortion of coordination polyhedron, the dataset of 72 structures similar to that of
1 was extracted from CCD and analyzed. A significant correlation between the average Cu–O
ax bond length and tetragonality parameter
τ which was found as a consequence of the Jahn–Teller effect.
RATIONAL NATURE UTILIZATION FACTORS Melnik, M
International Multidisciplinary Scientific GeoConference : SGEM,
01/2018, Letnik:
18, Številka:
5.3
Conference Proceeding
Relevance of results. One of the main factors of the accelerated transition to innovative development of the economy on the basis of the formation of high-tech industries is rational nature ...management, which makes it possible to use the country's natural resources with the greatest impact and, on the basis of their deep processing, create new types of structural materials and promote the introduction of advanced technologies and industries. The implementation of these tasks determines the need for a well-founded priority and conditions for the extraction of natural resources, timely enrichment and full utilization, the transition to non-waste technologies and the useful processing of unavoidable wastes, and control over compliance with environmental safety. Purpose of the study. To organize an end-to-end system for monitoring the use of natural resources along the value chain of the final consumption product, including determining priority areas for their use, the full use of resources, minimizing waste through the development of wasteless technologies and subsequent processing of unavoidable wastes, which will increase the efficiency of the extractive and processing industries . Description of the methodology. Orientation to the reproductive approach, taking into account a single chain of value creation, the choice of methods for optimizing indicators of effectiveness and efficiency of natural resources, while meeting the requirements of environmental safety. Main results. The principles of the territorial organization of production based on vertical integration with the expansion of the variability of processing business processes are substantiated, and the greatest benefits are obtained, the intensification of the use of natural resources due to new production technologies and the formation of knowledge-intensive enterprises in processing industries.
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