Expulsion of dust from dark-matter halos at high redshifts

The conditions required for the expulsion of dust grains from primordial galaxies (dark-matter halos) are considered. The initial configuration is taken to be a dark-matter halo with the profile of a modified isothermal sphere; the baryons are taken to be in equilibrium with the corresponding virial temperature. The baryon density profile is calculated assuming hydrostatic equilibrium. A star-formation rate corresponding to a star-forming efficiency of 10% is assumed. The dust is transported from the galaxy by the radiation of stars concentrated in the central regions. Due to friction via collisions with gas in central regions, a fairly high luminosity is required in order for the radiation pressure to be strong enough to expel dust from the galaxy—the ratio of the luminosity to the total mass of the galaxy can reach unity.     

Instabilities in the ionization zones around the first stars

We consider the evolution of the ionization zone around Population III stars with M _* ?? 25?C200M _?? in protogalaxies with M ?? 10⁷ M _?? at redshifts z = 12, assuming that the dark-energy profile is a modified isothermal sphere. We study the conditions for the growth of instabilities in the ionization zones. The Rayleigh-Taylor and thermal instabilities develop efficiently in the ionization zones around 25?C40M _?? stars, while this efficiency is lower for stars withM _* ?? 120M _??. For more massive stars (??200M _??), the flux of ionizing photons is strong enough to considerably reduce the gas density in the ionization zone, and the typical lifetimes of stars (??2 Myr) are insufficient for the growth of instabilities. The gas in a protogalaxy with M ?? 10⁷ M _?? with a 200M _?? central star is completely ionized by the end of the star??s lifetime; in the case of a 120M _?? central star, only one-third of the total mass of gas is ionized. Thus, ionizing photons from stars with M _* ? 120M _?? cannot leave protogalaxies with M ? 10⁷ M _??. If the masses of the central stars are 25 and 40M _??, the gas in protogalaxies of this mass remains essentially neutral. We discuss the consequences of the evolution of the ionization zones for the propagation of the envelope after the supernova explosions of the strs and the efficiency of enrichment of the intergalactic medium in heavy elements.     

Impact of the geomagnetic field and solar radiation on climate change

Recent studies have shown that, in addition to the role of solar variability, past climate changes may have been connected with variations in the Earth??s magnetic field elements at various timescales. An analysis of variations in geomagnetic field elements, such as field intensity, reversals, and excursions, allowed us to establish a link between climate changes at various timescales over the last millennia. Of particular interest are sharp changes in the geomagnetic field intensity and short reversals of the magnetic poles (excursions). The beginning and termination of the examined geomagnetic excursions can be attributed to periods of climate change. In this study, we analyzed the possible link between short-term geomagnetic variability (jerks) and climate change, as well as the accelerated drift of the north magnetic pole and surface temperature variations. The results do not rule out the possibility that geomagnetic field variations which modulate the cosmic ray flux could have played a major role in climate change in addition to previously induced by solar radiation.     

Methane Concentration and Emission in Dominant Landscapes of Typical Tundra of Western Yamal

Doklady Earth Sciences - Methane concentration in dominant landscapes of typical tundra of Western Yamal has been measured. The highest methane content in the active layer was measured in tundra...     

Evolution of High-Magnesium Melts During Crystallization of Rocks in Ultramafic Massifs,Siberian Platform

Doklady Earth Sciences - The results of study of primary melt inclusions in accessory Cr–spinelides from dunite have revealed features of the chemical compositions of high-magnesium...     

Permafrost aggradation and methane production in low accumulative laidas (tidal flats) of the Kara Sea

Doklady Earth Sciences - It was established that along with permafrost degradation, the processes of permafrost aggradation occur in the modern low accumulative surfaces of Kara Sea. The cycle of...     

Computation of elliptic Hansen coefficients and their derivatives

The problem of computation of elliptic Hansen coefficients and their derivatives is considered for constructing a motion theory of an artificial Earth satellite with large eccentricity. An algorithm for analytical and numerical computation of these coefficients and their derivatives is described. The recurrence relations for derivatives of the first and second order and initial values for recurrences are obtained. As an example, numerical values of some elliptic Hansen coefficients are given for the orbit with eccentricityk=0.74.     

Coastal dynamics at the Barents and Kara Sea key sites

The results of permafrost and coastal dynamics investigations at four key sites on the shores of the Kara and Barents Seas are discussed. Three ACD key sites, Marre-Sale, Shpindler, and Kolguev, characterize areas with active thermal erosion; key site Cape Bolvansky is found on a relatively stable coast. It is found that the coastal retreat rate has spatial and temporal variability, which is typical of the entire Arctic coast. Coastal deposits on the Kara and Barents Seas have a low organic carbon content. Annual input of material into the Kara Sea resulting from coastal degradation reaches 35–40 million t, including about 7.5 million t of ice, 0.35 million t of organic carbon, and 0.3 million t of soluble salts.This revised version was published online January 2005 with corrections to the title of the article.     

Year-round cooling and thermal stabilization of water-saturated soils under engineering structures

We consider the problem of year-round cooling of water-saturated soil to freezing temperatures in order to convert it into a state of permafrost.A new soil-cooling apparatus is proposed.The apparatus is to be made in modular form and connected to passive-active thermal piles (thermosyphons).The estimated capacity of one apparatus allows simultaneous use of up to 1,000 thermal piles for ground freezing.The apparatus is based on natural sources of energy:solar radiation and wind;and it can be used for soil freezing.This approach can prevent thawing of soft soils under railways and roads,as well as under buildings or structures,in an area of more than tens of hectares.The apparatus has no mechanical moving parts and can operate for a long time in stand-alone mode without staff involvement.