Low‐temperature primordial gas in merging halos     

E. O. Vasiliev  Yu. A. Shchekinov 《Astronomische Nachrichten》2008,329(6):625-631

The thermal regime of the baryons behind shock waves arising in the process of virialization of dark matter halos is governed at certain conditions by radiation of HD lines. A small fraction of the shocked gas can cool down to the temperature of the cosmic microwave background (CMB). We estimate an upper limit for this fraction: at z = 10 it increases sharply from about q_T ∼ 10^–3 for dark halos of M = 5 × 10⁷ M_⊙ to ∼ 0.1 for halos with M = 10⁸ M_⊙. Further increase of the halo mass does not lead however to a significant growth of q_T – the asymptotic value for M ≫ 10⁸ M_⊙ is 0.3. We estimate the star formation rate associated with such shock waves, and show that they can provide a small but not negligible fraction of the star formation. We argue that extremely metal‐poor low‐mass stars in the Milky Way may have been formed from primordial gas behind such shocks. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Energy Spectra of Cosmic-Ray Protons and Nuclei Measured in the NUCLEON Experiment Using a New Method     

Atkin  E. V.  Bulatov  V.L.  Vasiliev  O. A.  Voronin  A. G.  Gorbunov  N. V.  Grebenyuk  V. M.  Dorokhov  V. A.  Karmanov  D. E.  Kovalev  I.M.  Kudryashov  I. A.  Kurganov  A.A.  Merkin  M. M.  Panov  A.D.  Podorozhny  D. M.  Polkov  D. A.  Porokhovoi  S. Yu.  Sveshnikova  L. G.  Tkachev  L.G.  Tkachenko  A. V.  Turundaevskiy  A. N.  Filippov  S. B.  Shumikhin  V. V. 《Astronomy Reports》2019,63(1):66-78

Astronomy Reports - Some results of studies of cosmic rays obtained during the NUCLEON space experiment in 2015–2017 are presented. This experiment was intended for direct measurements of the...  相似文献   

Laboratory investigations of the thermal strain of frozen soils, using fiber-optic strain gauges based on Bragg gratings     

Aleksey Marchenko  Nicolai Vasiliev  Artem Nesterov  Yuri Kondrashov  Nikolay Belyaev 《寒旱区科学》2017,9(3):192-196

Measurements of the thermal deformations of frozen soil samples were performed in the cold laboratory in temperature range from 0°C to-12°C.Fiber Bragg Gratings strain and temperature sensors were used to measure the deformation and temperature inside the samples.A number of tests with the samples prepared from Kaolin and Cambrian clay saturated with fresh water,and prepared from fine and silt sand saturated with fresh or saline water,are performed.Thermal deformations of the samples are analyzed depending on the cyclic changes of their temperature.  相似文献   

The influence of variations of the elemental composition on the thermal properties of gas behind shock fronts     

E. O. Vasiliev  Yu. A. Shchekinov 《Astronomy Reports》2017,61(4):342-346

The homogenization of inhomogeneities in the elemental composition of the interstellar medium due to stellar evolution and weak mixing are inevitably related to the action of shocks. This paper considers the influence of variations in the elemental composition on the thermal and ionizational evolution of a collisional gas with the solar metallicity that is cooled behind a shock front with a velocity of 50–120 km/s. The intensities of lines of heavy elements in plasma cooling behind a shock front depend not only on variations in the elemental composition, but also on the shock velocity, due to the different values of the critical density for the transition to the equilibrium level populations in atoms and ions of heavy elements. This circumstance can be used to determine the elemental composition of cool and warm gas of the interstellar medium, as well as the thermal history of the gas.  相似文献   

Ice- and cryogel-soil composites in water-retaining elements in embankment dams constructed in cold regions     

N. K. Vasiliev  A. A. Ivanov  I. N. Shatalin  V. V. Sokurov 《寒旱区科学》2013,5(4):0444-0450

There are a number of serious problems connected with building and repairing water-retaining elements in embankment dams in cold regions. One of them is the difficulty in finding inexpensive clay materials with the necessary structural properties and using them in the winter. Another is the cracks that appear in the upper part of a dam when the core freezes to the banks, and leakage along the cracks threatens to destroy the dam. Still another is the process of erosion at the bottom of the core which may occur through fissures in the rock foundation of a dam and in transport constructions. Also, the behaviour of water-retaining elements during earthquakes is unreliable. All of these problems can be solved by using ice- and cryogel-soil composites created by cryotropic gel formation (CGF). Our laboratory investigations demonstrate that the materials proposed for water-retaining elements have the necessary permeable, plastic, thermophysical, and strength properties to solve all of these problems. Certain constructions of water-retaining elements which may prove to be both safe and cost-effective are proposed. However, these ice- and cryogel-soil composites need to be field-validated before they are used in dams and transport structures in cold regions.  相似文献   

Thermodynamic characteristics of water in natural water bodies with a high mineralization     

S. I. Prokopiev  T. E. Ovchinnikova  O. F. Vasiliev 《Izvestiya Atmospheric and Oceanic Physics》2010,46(2):256-260

To adequately describe the hydrophysical processes in water bodies with a high mineralization, it is necessary to take into account the dependence that the thermodynamic characteristics of water have on the amount of salts contained in it. This work investigates some widely known formulas for calculating a number of thermodynamic parameters of mineralized water. The density, freezing temperature, specific heat of evaporation, and relative pressure of saturated vapor over the surface are considered. The possibilities of using these formulas when modeling hydrophysical processes in water bodies with salinity in the range of 0–250 pro mille are analyzed. It is shown that the formulas under consideration should be used when the salinity does not exceed 100 pro mille. If the mineralization is higher, it is necessary to elaborate more suitable formulas on the basis of an approximation of in situ data or data from handbooks.  相似文献   

Evolution of Intergalactic Gas in the Neighborhood of Dwarf Galaxies and Its Manifestations in the HI 21 cm Line     

E. O. Vasiliev  M. V. Ryabova  Yu. A. Shchekinov  S. K. Sethi 《Astrophysical Bulletin》2018,73(4):401-412

Low-mass galaxies are known to have played the crucial role in the hydrogen reionization in the Universe. In this paper we investigate the contribution of soft x-ray radiation (E ~ 0.1–1 keV) from dwarf galaxies to hydrogen ionization during the initial reionization stages. The only possible sources of this radiation in the process of star formation in dwarf galaxies during the epochs preceding the hydrogen reionization epoch are hot intermediate-mass stars (M ~ 5–8 M_⊙) that entered the asymptotic giant branch (AGB) stage and massive x-ray binaries. We analyze the evolution of the intergalactic gas in the neighborhood of a dwarf galaxy with a total mass of 6 × 10⁸M_⊙ formed at the redshift of z ~ 15 and having constant star-formation rate of 0.01–0.1 M_⊙ yr^?1 over a starburst with a duration of up to 100 Myr. We show that the radiation from AGB stars heats intergalactic gas to above 100 K and ensures its ionization x_e ? 0.03 within about 4–10 kpc from the galaxy in the case of a star-formation rate of star formation 0.03–0.1 M_⊙ yr^?1, and that after the end of the starburst this region remains quasi-stationary over the following 200–300 Myr, i.e., until z ~ 7.5. Formation of x-ray binaries form in dwarf galaxies at z ~ 15 results in a 2–3 and 5–6 times greater size of the ionized and heated region compared to the case where ionization is produced by AGB stars exclusively, if computed with the “x-ray luminosity–star-formation rate” dependence (L_X ~ f_XSFR) factor f_X = 0.1 and f_X ~ 1, respectively. For f_X ? 0.03 the effect of x-ray binaries is smaller that that of AGB star population. Lyα emission, heating, and ionization of the intergalactic gas in the neighborhood of dwarf galaxies result in the excitation of the 21 cm HI line. We found that during the period of the starburst end at z ~11.5–12.5 the brightness temperature in the neighborhood of galaxies is 15–25 mK and the region where the brightness temperature remains close to its maximum has a size of about 12–30 kpc. Hence the epoch of the starburst end is most favorable for 21 cm HI line observations of dwarf galaxies, because at that time the size of the region of maximum brightness temperature is the greatest over the entire evolution of the dwarf galaxy. In the case of the sizes corresponding to almost 0.’1 for z ~ 12 regions with maximum emission can be detected with the Square Kilometre Array, which is currently under construction.  相似文献   

Specialized celestial mechanics systems for symbolic manipulation     

V. A. Brumberg  S. V. Tarasevich  N. N. Vasiliev 《Celestial Mechanics and Dynamical Astronomy》1988,45(1-3):149-162

Construction and application of the current high accuracy analytical theories of motion of celestial bodies necessitates the development of specialized software for the implementation of analytical algorithms of celestial mechanics. This paper describes a typical software package of this kind. This package includes a universal Poisson processor for the rational functions of many variables, a tensorial processor for purposes of relativistic celestial mechanics, a Keplerian processor valid for the solutions of the two body problem in the form of a Poisson series, Taylor expansions in powers of time and closed expressions, and an analytical generator of celestial mechanics functions, facilitating the immediate implementation of the present analytical methods of celestial mechanics. The package is completed with a numerical-analytical interface designed, in particular, for the fast evaluation of the long Poisson series.  相似文献   

Particle decay in the early Universe: predictions for 21 cm     

Yu. A. Shchekinov  E. O. Vasiliev 《Monthly notices of the Royal Astronomical Society》2007,379(3):1003-1010

The influence of ultra-high energy cosmic rays (UHECRs) and decaying dark matter particles on the emission and absorption characteristics of neutral hydrogen in 21 cm at redshifts   z = 10–50  is considered. In the presence of UHECRs, 21 cm can be seen in absorption with the brightness temperature   T _b=−(5–10) mK  in the range   z = 10–30  . Decaying particles can stimulate a 21-cm signal in emission with   T _b∼ 50–60 mK  at   z = 50  and   T _b≃ 10 mK  at   z ∼ 20  . Characteristics of the fluctuations of the brightness temperature, in particular its power spectrum, are also calculated. The maps of the power spectrum of the brightness temperature on the plane wavenumber redshift are shown to be sensitive to the parameters of UHECRs and decaying dark matter. Observational possibilities to detect manifestations of UHECRs and/or decaying particles in 21 cm with the future radio telescopes (LOFAR, 21CMA and SKA), and to distinguish contributions from them, are briefly discussed.  相似文献   

Chemical inhomogeneity of the post-reionization universe     

E. O. Vasiliev  S. Yu. Dedikov  Yu. A. Shchekinov 《Astrophysical Bulletin》2009,64(4):317-324

The statistical properties of the spatial distribution of metals in the intergalactic medium are analyzed during the initial stages of its enrichment, when mixing is determined by the Kelvin-Helmholtz and Rayleigh-Taylor instabilities. The saturation of instabilities due to the damping of relative motions of gaseous flows leads to an incomplete mixing, hence on the small scale there appear regions with high (i.e., close to the initial) metallicity. A comparison with observational data shows that in the “post-reionization” Universe (z < 5) the irregularity of the metal distribution exhibits the features, characteristic of mixing with saturation of hydrodynamic instabilities.  相似文献