Abiotic Input of Fixed Nitrogen by Bolide Impacts to Gale Crater During the Hesperian: Insights From the Mars Science Laboratory

Molecular hydrogen (H2) from volcanic emissions is suggested to warm the Martian surface when carbon dioxide (CO2) levels dropped from the Noachian (4100 to 3700 Myr) to the Hesperian (3700 to 3000 Myr). Its presence is expected to shift the conversion of molecular nitrogen (N2) into different forms of fixed nitrogen (N). Here we present experimental data and theoretical calculations that investigate the efficiency of nitrogen fixation by bolide impacts in CO2‐N2 atmospheres with or without H2. Surprisingly, nitric oxide (NO) was produced more efficiently in 20% H2 in spite of being a reducing agent and not likely to increase the rate of nitrogen oxidation. Nevertheless, its presence led to a faster cooling of the shock wave raising the freeze‐out temperature of NO resulting in an enhanced yield. We estimate that the nitrogen fixation rate by bolide impacts varied from 7 × 10−4 to 2 × 10−3 g N·Myr−1·cm−2 and could imply fluvial concentration to explain the nitrogen (1.4 ± 0.7 g N·Myr−1·cm−2) detected as nitrite (NO2 −) and nitrate (NO3 −) by Curiosity at Yellowknife Bay. One possible explanation is that the nitrogen detected in the lacustrine sediments at Gale was deposited entirely on the crater's surface and was subsequently dissolved and transported by superficial and ground waters to the lake during favorable wet climatic conditions. The nitrogen content sharply decreases in younger sediments of the Murray formation suggesting a decline of H2 in the atmosphere and the rise of oxidizing conditions causing a shortage in the supply to putative microbial life.We acknowledge the NASA Mars Science Laboratory Program, Centre National d'Études Spatiales, the Universidad Nacional Autónoma de México (PAPIIT IN109416, IN111619, and PAPIME PE103216), and the Consejo Nacional de Ciencia y Tecnología de México (CONACyT 220626) for their support

The Role of Hydrogen Cyanide in Chemical Evolution

Two major research areas are investigated: The electrosynthesis of hydrogen cyanide; and the role of cyanocomplexes in the free - radical oligomerization of hydrogen cyanide. The electric discharge production of hydrogen cyanide from a simulated primitive atmosphere composed of methane, nitrogen and water vapor was investigated. The radiation chemical yield (G) of formation of HCN was determined to be 0.26. A free radical mechanism was proposed to account for the observed chemical changes. Computer simulations of the reaction mechanism could effectively model the early stages of electrolysis of the gas mixture, and permitted the estimation of the rate of electrosynthesis of hydrogen cyanide under various atmospheric conditions . The possible role of cyanocomplexes of transition elements on the free- radical oligomerization of hydrogen cyanide was investigated. Aqueous, oxygenfree, dilute solutions of hydrogen cyanide and hexacyanoferrate(II) or (III) were submitted to various doses of gamma irradiation. The presence of either cyanocomplex led to a significant decrease in the rate of decomposition of hydrogen cyanide. The major products were ammonia and carbon dioxide . Computer simulations of these systems permitted the elucidation of the reaction mechanism and the derivation of rates of reactions of free- radicals with the cyanocomplexes. The results obtained provide an insight into the possible role of cyanocomplexes of transition elements in chemical evolution

Effect of pupil size on wavefront refraction during orthokeratology

Purpose. It has been hypothesized that central and peripheral refraction, in eyes treated with myopic overnight orthokeratology, might vary with changes in pupil diameter. The aim of this work was to evaluate the axial and peripheral refraction and optical quality after orthokeratology, using ray tracing software for different pupil sizes. Methods. Zemax-EE was used to generate a series of 29 semi-customized model eyes based on the corneal topography changes from 29 patients who had undergone myopic orthokeratology. Wavefront refraction in the central 80 degrees of the visual field was calculated using three different quality metrics criteria: Paraxial curvature matching, minimum root mean square error (minRMS), and the Through Focus Visual Strehl of the Modulation Transfer Function (VSMTF), for 3- and 6-mm pupil diameters. Results. The three metrics predicted significantly different values for foveal and peripheral refractions. Compared with the Paraxial criteria, the other two metrics predicted more myopic refractions on- and off-axis. Interestingly, the VSMTF predicts only a marginal myopic shift in the axial refraction as the pupil changes from 3 to 6 mm. For peripheral refraction, minRMS and VSMTF metric criteria predicted a higher exposure to peripheral defocus as the pupil increases from 3 to 6 mm. Conclusions. The results suggest that the supposed effect of myopic control produced by ortho-k treatments might be dependent on pupil size. Although the foveal refractive error does not seem to change appreciably with the increase in pupil diameter (VSMTF criteria), the high levels of positive spherical aberration will lead to a degradation of lower spatial frequencies, that is more significant under low illumination levels.This study has been funded by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of projects PTDC/SAU-BEB/098391/2008, PTDC/SAU-BEB/ 098392/2008, and the Strategic Project PEST-C/FIS/UI607/2011. Dr. Navarro acknowledges funding by the Spanish Ministery of Economy and Competivity, grant FIS2014-58303-P. The authors have no proprietary interests in the methods and devices described in this manuscript

Gibrat’s law for countries

A re-assessment of Gibrat's Law in the context of country size is carried out in this paper. In addition, how similarly population is distributed in cities and countries is analyzed from a temporal perspective. Although evidence of Gibrat's Law is found, it is weaker than that previously established in Rose (2006). This is due to the methodology applied and is especially appreciable in very small countries. Nonetheless, we observe that the population growth process in countries is similar to that of cities. As a result, the similarities between how the population is distributed in these two geographical categories have increased over time

Gibrat’s law for countries

If the population of a given country evolves according to Gibrat'�s Law, its growth rate will be independent of its initial size. This short paper further investigates this empirical regularity by the application of a suitable panel unit root test and non-parametric methods. The evidence regarding its fulfilment is weaker than that previously found

Depth-of-field after orthokeratology: a theoretical study

Trabajo presentado al 8th European Meeting on Visual and Physiological Optics, celebrado en Antwerp (Bélgica) del 22 al 24 de agosto de 2016.We evaluated the possible effect of orthokeratology on accommodative response. Using optical modelling we computed the negative half of the depth-of-field (DoFi) for the range of target vengeances from –1.00 D to –3.00 D, of two eye models designed to mimic the levels of primary and secondary spherical aberration found in 24 patients before and after undergoing orthokeratology (ortho-k). Five trained observers were subjected to a resolution task to identify the negative threshold of the depth-of-field of these model eyes by viewing a set of computed images representative of the model eyes trough focus retinal image quality for five target vengeances (TV), from –1.00 to – 3.00 D. The differences in the DoFi estimated by the five observers were maximum for a –3.00 D TV (0.21 D), with the post ortho-k model presenting a higher DoFi compared to the pre ortho-k model. Differences were consistent for all five observers and all TV’s. In conclusion, the increase in spherical aberration after ortho-k seems to contribute to a small increase in the DoFi. Although small, the benefits might be sufficient to improve retinal image quality in eyes with high accommodative lag.Peer reviewe

Orthogonal basis for the optical transfer function

We propose systems of orthogonal functions qn to represent optical transfer functions (OTF) characterized by including the diffraction-limited OTF as the first basis function q0 OTF perfect. To this end, we apply a powerful and rigorous theoretical framework based on applying the appropriate change of variables to well-known orthogonal systems. Here we depart from Legendre polynomials for the particular case of rotationally symmetric OTF and from spherical harmonics for the general case. Numerical experiments with different examples show that the number of terms necessary to obtain an accurate linear expansion of the OTF mainly depends on the image quality. In the rotationally symmetric case we obtained a reasonable accuracy with approximately 10 basis functions, but in general, for cases of poor image quality, the number of basis functions may increase and hence affect the efficiency of the method. Other potential applications, such as new image quality metrics are also discussed.This research was supported by the Spanish Ministry of Economía y Competitividad and the European Union MTM2014-52859 and FIS2014-58303

Morphology, topography, and optics of the orthokeratology cornea

The goal of this work was to objectively characterize the external morphology, topography, and optics of the cornea after orthokeratology (ortho-k). A number of 24 patients between the ages of 17 and 30 years (median ¼ 24 years) were fitted with Corneal Refractive Therapy® contact lenses to correct myopia between −2.00 and −5.00 diopters (D) (median ¼ −3.41 D). A classification algorithm was applied to conduct an automatic segmentation based on the mean local curvature. As a result, three zones (optical zone, transition zone, and peripheral zone) were delimited. Topographical analysis was provided through global and zonal fit to a general ellipsoid. Ray trace on partially customized eye models provided wave aberrations and retinal image quality. Monozone topographic description of the ortho-k cornea loses accuracy when compared with zonal description. Primary (C0 4) and secondary (C0 6) spherical aberration (SA) coefficients for a 5-mm pupil increased 3.68 and 19 times, respectively, after the treatments. The OZ area showed a strong correlation with C0 4 (r ¼ −0.49, p < 0.05) and a very strong correlation with C0 6 (r ¼ 0.78, p < 0.01). The OZ, as well as the TZ, areas did not correlate with baseline refraction. The increase in the eye’s positive SA after ortho-k is the major factor responsible for the decreased retinal optical quality of the unaccommodated eyeThis work was funded in part by European Fund for Regional Development (FEDER) through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT). FCT provided financial support in the framework of projects PTDC/SAU-BEB/098391/2008, PTDC/SAU-BEB/ 098392/2008 and the Strategic Project PEST-C/FIS/UI607/ 2011. The authors have no proprietary interest in the methods and devices described in this manuscript

Plauciano: la amenaza de la domus severiana.

En el trabajo presentamos una visión sintética del ascenso y caída de un personaje no demasiado tratado por la historiografía moderna, Plauciano. Sin embargo, tuvo un papel esencial en el acceso al poder de Septimio Severo y también durante los años en que fue prefecto del pretorio, desde 197 hasta enero de 205, cuando murió de forma violenta. De él, dicen las fuentes antiguas que era pariente, pero sobre todo, amigo muy próximo del emperador. Su cercanía a este, más que el propio cargo, le permitió obtener un poder político y económico casi omnímodo, por lo que fue considerado en su tiempo como un cuarto césar. Incluso casó a su hija Plautilla con el heredero al trono, Caracalla. Precisamente sus cotas de poder y su proximidad a Septimio suscitaron recelos y envidias principalmente en el entorno imperial que finalmente provocaron su caída y su muerte inmediata, aunque las fuentes antiguas que escriben estos acontecimientos no coinciden en la narración de los hechos.This paper presents a synthetic view of the rise and fall of a little-treated character in modern historiography, Plautian. However, this person played a key role in the accession to power of Septimius Severus and during the years he was Praetorian Prefect, from 197 to January 205, when he died violently. Ancient sources state that he was a patient person, and above all, a very close friend of the Emperor. His proximity to the Emperor, rather than his position proper, enabled him to obtain almost an absolute political and economic power, being considered at the time as a fourth Caesar. He even managed that his daughter Plautilla married the heir of the Caracalla throne. It is precisely his power and his proximity to Septimius that raised suspicions and jealousies among the Imperial community, leading ultimately to his downfall and his immediate death; though the ancient sources that describe these events do not necessary coincide