Excited states of beryllium atom from explicitly correlated wave functions

A study of the first excited states of beryllium atom starting from explicitly correlated wave functions is carried out. Several properties are obtained and discussed focusing on the analysis of the Hund's rules in terms of the single--particle and electron pair intracule and extracule densities. A systematic study of the differences on the electronic distributions of the singlet and triplet states is carried out. The trial wave function used to describe the different bound states consists of a generalized Jastrow-type correlation factor times a configuration interaction model wave function. This model wave function has been fixed by using a generalization of the optimized effective potential method to deal with multiconfiguration wave functions. The optimization of the wave function and the calculation of the different quantities is carried out by means of the Variational Monte Carlo method.Comment: 28 pages, 6 figure

Redox capacity of rocks and sediments by high temperature chalcometric titration

We present an analytical method to quantify the absolute redox capacity, ΔO2, of geological materials. The protocol consists in a high temperature chalcometric titration by which a known amount of oxygen gas is exchanged between a solid state oxygen donor, CuO, and an oxygen acceptor, the sample, at elevated temper- ature. Calibration of the method using elemental C, native S and magnetite demonstrates that it effectively oxidizes C, S and Fe to their terminal oxidation state, C4+, S6+ and Fe3+, respectively. Because the metric is independent of processes of internal equilibration within the system, it can be used for quantitative assessments of redox fluxes in open geological systems, in the surface or deep Earth. Preliminary results suggest that the mass specific redox capacity, dO2, of geological materials span many orders of magnitude, ranging from less than 500 μmol O2/g for ultramafic rocks and lower crustal amphibolites, to more than 30000 μmol O2/g for black shales. This highlights a counterintuitive yet fundamental characteristic of our planet. Rocks characterized by elevated dO2 values are ubiquitous in the oxic Earth’s surface, while the upper mantle and lower crust are typically composed of rocks with much lower dO2. This work will contribute to provide a more nuanced and complete perspective on the sedimentary and geodynamic processes that have shaped the redox structure of the Earth

Evidence of a massive planet candidate orbiting the young active K5V star BD+20 1790

Original article can be found at: http://www.aanda.org/ Copyright The European Southern Observatory (ESO). DOI: 10.1051/0004-6361/200811000Context. BD+20 1790 is a young active, metal-rich, late-type K5Ve star. We have undertaken a study of stellar activity and kinematics for this star over the past few years. Previous results show a high level of stellar activity, with the presence of prominence-like structures, spots on the surface, and strong flare events, despite the moderate rotational velocity of the star. In addition, radial velocity variations with a semi-amplitude of up to 1 km s-1 were detected. Aims. We investigate the nature of these radial velocity variations, in order to determine whether they are due to stellar activity or the reflex motion of the star induced by a companion. Methods. We have analysed high-resolution echelle spectra by measuring stellar activity indicators and computing radial velocity (RV) and bisector velocity spans. Two-band photometry was also obtained to produce the light curve and determine the photometric period. Results. Based upon the analysis of the bisector velocity span, as well as spectroscopic indices of chromospheric indicators, Ca ii H & K, Hα, and taking the photometric analysis into account, we report that the best explanation for the RV variation is the presence of a substellar companion. The Keplerian fit of the RV data yields a solution for a close-in massive planet with an orbital period of 7.78 days. The presence of the close-in massive planet could also be an interpretation for the high level of stellar activity detected. Since the RV data are not part of a planet search programme, we can consider our results as a serendipitous evidence of a planetary companion. To date, this is the youngest main sequence star for which a planetary candidate has been reported.Peer reviewe

Dynamical Localization: Hydrogen Atoms in Magnetic and Microwave fields

We show that dynamical localization for excited hydrogen atoms in magnetic and microwave fields takes place at quite low microwave frequency much lower than the Kepler frequency. The estimates of localization length are given for different parameter regimes, showing that the quantum delocalization border drops significantly as compared to the case of zero magnetic field. This opens up broad possibilities for laboratory investigations.Comment: revtex, 11 pages, 3 figures, to appear in Phys. Rev. A, Feb (1997

Pyrite-induced uv-photocatalytic abiotic nitrogen fixation : implications for early atmospheres and Life

Acknowledgements This work has been supported by the MINECO project ESP2017- 89053. Te Instituto Nacional de Técnica Aeroespacial supported the work performed at CAB. Tomas and Celina Huttel Serrano are acknowledged for providing the pyrite samples. This Project has been partially funded by the Spanish State Research Agency (AEI) Project No. MDM-2017-0737 Unidad de Excelencia “María de Maeztu”- Centro de Astrobiología (INTA-CSIC).Peer reviewedPublisher PD

Materials and pathways of the organic carbon cycle through time

The cycle of organic carbon through the atmosphere, oceans, continents and mantle reservoirs is a hallmark of Earth. Over geological time, chemical exchanges between those reservoirs have produced a diversity of reduced carbon materials that differ in their molecular structures and reactivity. This reactive complexity challenges the canonical dichotomy between the surface and deep, short-term and long-term organic carbon cycle. Old and refractory carbon materials are not confined to the lithosphere but are ubiquitous in the surface environment, and the lithosphere hosts various forms of reduced carbon that can be very reactive. The biological and geological pathways that drive the organic carbon cycle have changed through time; from a synthesis of these changes, it emerges that although a biosphere is required to produce organic carbon, mortality is required to ensure its export to the lithosphere, and graphitization is essential for its long-term stabilization in the solid Earth. Among the by-products of the organic carbon cycle are the accumulation of a massive lithospheric reservoir of organic carbon, the accumulation of dioxygen in the atmosphere and the rise of a terrestrial biosphere. Besides driving surface weathering reactions, free dioxygen has allowed the evolution of new metabolic pathways to produce and respire organic carbon. From the evolution of photosynthesis until the expansion of biomineralization in the Phanerozoic, inorganic controls on the organic carbon cycle have diversified, tightening the connection between the biosphere and geosphere

Assessment of GNC Impacts of Chemical Plume Impingement in the Case of Prisma Irides Experiment

This paper presents the preliminary analysis of an in-orbit demonstration opportunity to test plume impingement as a viable means to change the attitude state of a space debris based on the Prisma and Picard missions. This technique has been proposed as part of the COBRA concept studied by ESA in collaboration with GMV, Politecnico di Milano and Thales-Alenia Space, as an active debris removal concept relying on the exhaust plume of a monopropellant chemical propulsion system as a means to impart momentum and ultimately modify the orbit of a space debris object in a contactless manner. The feasibility of the experiment is presented as well as its critical areas, no showstoppers are identified