156 research outputs found
The Role of CO2 in Aqueous Alteration of Ultra-Mafic Rocks and the Formation of MF-,FE-Rich Aqueous Solutons on Early Mars
An adequate understanding of water on Mars that moves beyond the simplistic "warmwet" vs. "cold-dry" dichotomy must include strong constraints on the variables: water/rock ratio, time, temperature, and chemical composition. By constraining these variables first on local, then regional and global scales we will be capable of precisely targeting landed missions to definitively understand the history of water on Mars and the possible existence of life. Data from remote sensing of Mars, landed missions, and martian meteorites indicate that secondary minerals formed from aqueous fluids on Mars are predominately Fe- and Mg-rich. The unique Mg-, Fe-rich carbonates in the ALH 84001 meteorite provide an excellent opportunity to provide strong constraints on an Fe-, Mg-rich aqueous system on early Mars. This work seeks to use the unusual chemical compositions of the ALH 84001 carbonates as a constraint for the composition of their formation fluid. These constraints can be used to better understand aqueous processes at a critical time in martian history
Predicted Abundances of Carbon Compounds in Volcanic Gases on Io
We use chemical equilibrium calculations to model the speciation of carbon in
volcanic gases on Io. The calculations cover wide temperature (500-2000 K),
pressure (10^-8 to 10^+2 bars), and composition ranges (bulk O/S atomic ratios
\~0 to 3), which overlap the nominal conditions at Pele (1760 K, 0.01 bar, O/S
~ 1.5). Bulk C/S atomic ratios ranging from 10^-6 to 10^-1 in volcanic gases
are used with a nominal value of 10^-3 based upon upper limits from Voyager for
carbon in the Loki plume on Io. Carbon monoxide and CO2 are the two major
carbon gases under all conditions studied. Carbonyl sulfide and CS2 are orders
of magnitude less abundant. Consideration of different loss processes
(photolysis, condensation, kinetic reactions in the plume) indicates that
photolysis is probably the major loss process for all gases. Both CO and CO2
should be observable in volcanic plumes and in Io's atmosphere at abundances of
several hundred parts per million by volume for a bulk C/S ratio of 10^-3.Comment: 21 pages, 4 figures, 4 tables; accepted by Astrophysical Journa
МЕТОДЫ НОРМАЛИЗАЦИИ СТАТИЧЕСКОГО ГЕОМАГНИТНОГО ПОЛЯ В ЖИЛЫХ ДОМАХ
In the paper, we show the necessity of normalization of the static geomagnetic field (GMF) inside high-rise frame-monolithic houses to safe values (90% of the natural rate at least). Massive ferromagnetic construction of these buildings significantly (up to 50 %) weakens the natural GMF. The normalization methods are based on mathematical modeling of GMF in a residential area. Simplified physical models of reinforced concrete building structures are developed and used. The results of experimental studies are also used in the framework of the development of the methods. The following methods of normalization of GMF are presented and justified: 1) the use of special steel with a relative permeability less than 70 in housing construction; 2) restrictions on the use of long steel elements with the elongation coefficient in the critical range of 4<b<28; 3) demagnetization of steel reinforcement before installing; 4) preventing the magnetization of steel reinforcement in the construction process. Practical recommendations for the design of «magnetic clean» houses with comfortable living conditions in connection to the GMF are proposed.Показана необходимость нормализации до безопасных значений индукции статического геомагнитного поля (ГМП) в помещениях высотных каркасно-монолитных жилых домов, массивные ферромагнитные несущие конструкции которых значительно (на 50%) ослабляют естественное ГМП. Теоретически и экспериментально обоснованы методы нормализации ГМП, реализуемые без применения дополнительных экранирующих элементов. Разработаны рекомендации по проектированию и строительству «магниточистых» жилых домов с комфортными условиями проживания по статическому геомагнитному полю.Показана необхідність нормалізації до безпечних значень індукції статичного геомагнітного поля (ГМП) у приміщеннях висотних каркасно-монолітних житлових будинків, масивні феромагнітні несучі конструкції яких значно (на 50%) послаблюють природне ГМП. Теоретично і експериментально обґрунтовані методи нормалізації ГМП, що реалізуються без застосування додаткових екрануючих елементів. Розроблено рекомендації з проектування та будівництва «магніточистих» житлових будинків з комфортними умовами проживання за статичним геомагнітним полем
The long-term evolution of the atmosphere of Venus: processes and feedback mechanisms
In this chapter, we focus on the long-term evolution of the atmosphere of
Venus, and how it has been affected by interior/exterior cycles. The formation
and evolution of Venus's atmosphere, leading to the present-day surface
conditions, remain hotly debated and involve questions that tie into many
disciplines. Here, we explore the mechanisms that shaped the evolution of the
atmosphere, starting with the volatile sources and sinks. Going from the deep
interior to the top of the atmosphere, we describe fundamental processes such
as volcanic outgassing, surface-atmosphere interactions, and atmosphere escape.
Furthermore, we address more complex aspects of the history of Venus, including
the role of meteoritic impacts, how magnetic field generation is tied into
long-term evolution, and the implications of feedback cycles for atmospheric
evolution. Finally, we highlight three plausible end-member evolutionary
pathways that Venus might have followed, from the accretion to its present-day
state, based on current modeling and observations. In a first scenario, the
planet was desiccated early-on, during the magma ocean phase, by atmospheric
escape. In a second scenario, Venus could have harbored surface liquid water
for long periods of time, until its temperate climate was destabilized and it
entered a runaway greenhouse phase. In a third scenario, Venus's inefficient
outgassing could have kept water inside the planet, where hydrogen was trapped
in the core and the mantle was oxidized. We discuss existing evidence and
future observations/missions needed to refine our understanding of the planet's
history and of the complex feedback cycles between the interior, surface, and
atmosphere that operate in the past, present or future of Venus
Kinematics in galactic tidal tails - A source for Hypervelocity stars?
[abridged] In this work we study in detail the kinematics of tidal debris
stars to investigate the implications of the new scenario that the observed
sample of Hypervelocity stars could partly originate from a dwarf-host galaxy
collision. We use a suite of N-body simulations following the encounter of a
satellite galaxy with its Milky Way-type host galaxy to gather statistics on
the properties of stripped-off stars. We study especially the orbital energy
distribution of this population.
We quantify the typical pattern in angular and phase space formed by the
debris stars. We further develop a simple stripping model predicting the
kinematics of stripped-off stars. We show that the distribution of orbital
energies in the tidal debris has a typical form which can be described quite
accurately by a simple function. Based on this we develop a method to predict
the energy distribution which allows us to evaluate the significance and the
implications of high velocity stars in satellite tidal debris.
Generally tidal collisions of satellite galaxy produce stars which escape
into the intragalactic space even if the satellite itself is on a bound orbit.
The main parameters determining the maximum energy kick a tidal debris star can
get is the initial mass of the satellite and only to a lower extent its orbit.
Main contributors to an unbound stellar population created in this way are
massive satellites (M_sat > 10^9 M_sun). We thus expect intragalactic stars to
have a metallicity higher than the surviving satellite population of the Milky
Way. However, the probability that the observed HVS population is significantly
contaminated by tidal debris stars appears small in the light of our results.Comment: 13 pages, 13 figures, accepted for publication in A&
Prospects in Analytical Atomic Spectrometry
Tendencies in five main branches of atomic spectrometry (absorption,
emission, mass, fluorescence and ionization spectrometry) are considered. The
first three techniques are the most widespread and universal, with the best
sensitivity attributed to atomic mass spectrometry. In the direct elemental
analysis of solid samples, the leading roles are now conquered by laser-induced
breakdown and laser ablation mass spectrometry, and the related techniques with
transfer of the laser ablation products into inductively-coupled plasma.
Advances in design of diode lasers and optical parametric oscillators promote
developments in fluorescence and ionization spectrometry and also in absorption
techniques where uses of optical cavities for increased effective absorption
pathlength are expected to expand. Prospects for analytical instrumentation are
seen in higher productivity, portability, miniaturization, incorporation of
advanced software, automated sample preparation and transition to the
multifunctional modular architecture. Steady progress and growth in
applications of plasma- and laser-based methods are observed. An interest
towards the absolute (standardless) analysis has revived, particularly in the
emission spectrometry.Comment: Proofread copy with an added full reference list of 279 citations. A
pdf version of the final published review may be requested from Alexander
Bol'shakov <[email protected]
Astrophysics in 2005
We bring you, as usual, the Sun and Moon and stars, plus some galaxies and a new section on astrobiology. Some highlights are short (the newly identified class of gamma-ray bursts, and the Deep Impact on Comet 9P/ Tempel 1), some long (the age of the universe, which will be found to have the Earth at its center), and a few metonymic, for instance the term "down-sizing" to describe the evolution of star formation rates with redshift
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