1,720,960 research outputs found
The role of primordial atmosphere composition in organic matter delivery to early Earth
No full textA model of the atmospheric entry of sub-mm grains is employed to evaluate the effect of the chemical composition of the primordial Earth’s atmosphere on the grain heating, in the context of organic matter delivery. Calculations are performed with spherical, uniform grains of forsterite/fayalite composition as well with the recently proposed white soft mineral (WSM) grains. Different hypotheses on primordial atmosphere composition affect the scale height and the energy transfer. The present work shows that: the total gas budget of the atmosphere is not highly relevant as far as the determination of the heating associated with slowing to subsonic speed is concerned; accordingly, light components (which are expected to be present in a primordial atmosphere and more abundant in the upper one) may be the primary ones in the evaluation of momentum and heat transfer in such scenarios. Strong reduced heating is obtained in the case of an upper atmosphere rich in light components, showing that the composition of the primordial Earth atmosphere may represent the key issue in the delivery of thermolabile organic matter enclosed in sub-mm extraterrestrial grains
Monte Carlo calculation of the potential energy surface for octahedral confined H 2+
No full textA rich literature has been produced on the quantum states of atoms and molecules confined into infinite potential wells with a specified symmetry. Apart from their interest as basic quantum systems, confined atoms and molecules are useful models for extreme high-pressure states of matter, spectroscopically active defects in solid lattices, and chemical species in molecular cages. A most important case is that of H2+ for which little or no results are available in the case of polyhedral confinement. The authors’ approach makes use of the Diffusion Monte Carlo (DMC) method. The advantage of this method is that previously developed codes are readily adapted to new, even complex, well geometries, and nuclear positions. In this paper, the potential energy surface (PES) of H2+ confined inside an octahedral well is reported for restricted D4h and D3d geometries and different well widths. The results are discussed using the concept of electron compression and the correlation with semi-confined atomic orbitals
Evaluation of CaSO4 micrograins in the context of organic matter delivery: Thermochemistry and atmospheric entry
No full textIn this paper, anhydrous calcium sulphate CaSO4 (anhydrite) is considered as a carrier material for organic matter delivery from Space to Earth. Its capability of incorporating important fractions of water, leading to different species like bassanite and gypsum, as well as organic molecules; its discovery on Mars surface and in meteorites; the capability to dissipate much energy by its chemical decomposition into solid (CaO) and gaseous (SO3) oxide, make anhydrite a very promising material in an astrobiological perspective. Since chemical cooling has been recently considered by some of the present authors for the case of Ca/Mg carbonates, CaSO4 can be placed into a class of 'white soft minerals' (WSM) of astrobiological interest. In this context, CaSO4 is evaluated here by using the atmospheric entry model previously developed for carbonates. The model includes grain dynamics, thermochemistry, stoichiometry, radiation and evaporation heat losses. Results are discussed in comparison with MgCO3 and CaCO3 and show that sub-mm anhydrite grains are potentially effective organic matter carriers. A Monte Carlo simulation is used to provide distributions of the sulphate fraction as a function of altitude. Two-zone model results are presented to support the isothermal grain hypothesis
Computational Astrobiology in Bari University and ISTP-CNR
No full textIn this contribution, we will present some results from our latest studies in the field of computational astrobiology, which are devoted to improving our understanding of the origin and evolution of life in the Universe by means of theoretical and computational models. The phenomena that can be studied by means of numerical modeling range from the micro to the macro scale, from molecules to cosmic grains and communities of primordial organisms. These studies may help to develop a global view of the phenomena involved in the origin of life in the wider context of astrobiology
Plasma Modeling and Prebiotic Chemistry: A Review of the State-of-the-Art and Perspectives
No full textWe review the recent progress in the modeling of plasmas or ionized gases, with compositions compatible with that of primordial atmospheres. The plasma kinetics involves elementary processes by which free electrons ultimately activate weakly reactive molecules, such as carbon dioxide or methane, thereby potentially starting prebiotic reaction chains. These processes include electron-molecule reactions and energy exchanges between molecules. They are basic processes, for example, in the famous Miller-Urey experiment, and become relevant in any prebiotic scenario where the primordial atmosphere is significantly ionized by electrical activity, photoionization or meteor phenomena. The kinetics of plasma displays remarkable complexity due to the non-equilibrium features of the energy distributions involved. In particular, we argue that two concepts developed by the plasma modeling community, the electron velocity distribution function and the vibrational distribution function, may unlock much new information and provide insight into prebiotic processes initiated by electron-molecule collisions
Quantum states of hydrogen cations confined into spherical and nanotube-like potential wells: H2+, H3+(C 2h and C 2v ) and H3+(D 3h )
No full textIn this work, the potential energy surfaces (PESs) of hydrogen-based cations H2+and H3+placed inside infinite potential wells, in the shape of an infinite cylinder and a sphere, are investigated. The calculations are performed using the diffusion Monte Carlo (DMC) technique. Different symmetries are studied, some of them for the first time. The PESs trends are rationalized. The Raman shift of A1' mode of spherically confined H3+ is also calculated
Kinetics of white soft minerals (WSMs) decomposition under conditions of interest for astrobiology: A theoretical and experimental study
No full textIn this paper, the thermal decomposition kinetics of a class of minerals that we call White Soft Minerals (WSMs) is studied by means of theoretical and experimental methods, in connection to the transport of extraterrestrial organic matter to Earth and the possible use of the decomposition reaction in the characterization of these minerals in space. WSMs include, under a single denomination, carbonates and sulphates of Mg, Fe, and Ca. To improve the present knowledge of the properties of such materials, we use the following techniques: kinetic models for chemical decomposition, atmospheric entry models, spectroscopy, and gravimetric analyses. Model results show that the atmospheric entry of WSM grains is strongly affected by their thermal decomposition. The decomposition reaction, being strongly endothermic, tends to significantly lower the grain temperature during the atmospheric entry, especially at high altitudes and for grazing entries. A previously proposed infrared spectroscopic technique to evaluate the degree of advancement of the reaction is found to be in good agreement with gravimetric measurements for calcium carbonate. The numerical model developed for the atmospheric entry scenarios is used to interpret experimental results. These main findings show that an additional contribution to the reaction enthalpy is needed to reproduce the experimental results, suggesting that the present theoretical model needs improvements such as the account of gas diffusion in the materials
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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