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11.
This paper examines the effect of HD molecules on the thermochemical evolution of the primordial gas behind the fronts of
shock waves that may develop during the epoch of galaxy formation. A critical shock velocity is found at which deuterium efficiently
converts to HD molecules and the contribution of HD molecules to cooling is dominant. Above this value of the shock velocity
the gas can cool to temperatures close to that of the cosmic background radiation. In this case the Jeans mass will depend
only on the red shift and the initial density, with MJ ∝ δ
c
−0.5
(1 + z)0.5. For z≳45, HD molecules heat the gas and for large red shifts they generally cease to play a significant role in the thermal
evolution of the gas.
__________
Translated from Astrofizika, Vol. 48, No. 4, pp. 585–601 (November 2005). 相似文献
12.
A. I. Neishtadt D. J. Scheeres V. V. Sidorenko P. J. Stooke A. A. Vasiliev 《Celestial Mechanics and Dynamical Astronomy》2003,86(3):249-275
Reactive torques, due to anisotropic sublimation on a comet nucleus surface, produce slow variations of its rotation. In this paper the secular effects of this sublimation are studied. The general rotational equations of motion are averaged over unperturbed fast rotation around the mass center (Euler-Poinsot motion) and over the orbital comet motion. We discuss the parameters that define typical properties of the rotational evolution and discover different classifications of the rotational evolution. As an example we discuss some possible scenarios of rotational evolution for the nuclei of the comets Halley and Borrelly. 相似文献
13.
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 qT ∼ 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 qT – 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
14.
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
15.
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
16.
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
17.
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
18.
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
19.
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
20.
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