Presence Of High CO Research Articles

Rethinking CO Antibiosignatures in the Search for Life Beyond the Solar System

Abstract Some atmospheric gases have been proposed as counter indicators to the presence of life on an exoplanet if remotely detectable at sufficient abundance (i.e., antibiosignatures), informing the search for biosignatures and potentially fingerprinting uninhabited habitats. However, the quantitative extent to which putative antibiosignatures could exist in the atmospheres of inhabited planets is not well understood. The most commonly referenced potential antibiosignature is CO, because it represents a source of free energy and reduced carbon that is readily exploited by life on Earth and is thus often assumed to accumulate only in the absence of life. Yet, biospheres actively produce CO through biomass burning, photooxidation processes, and release of gases that are photochemically converted into CO in the atmosphere. We demonstrate with a 1D ecosphere-atmosphere model that reducing biospheres can maintain CO levels of ∼100 ppmv even at low H2 fluxes due to the impact of hybrid photosynthetic ecosystems. Additionally, we show that photochemistry around M dwarf stars is particularly favorable for the buildup of CO, with plausible concentrations for inhabited, oxygen-rich planets extending from hundreds of ppm to several percent. Since CH4 buildup is also favored on these worlds, and because O2 and O3 are likely not detectable with the James Webb Space Telescope, the presence of high CO (>100 ppmv) may discriminate between oxygen-rich and reducing biospheres with near-future transmission observations. These results suggest that spectroscopic detection of CO can be compatible with the presence of life and that a comprehensive contextual assessment is required to validate the significance of potential antibiosignatures.

HCN oxidation in an O 2/CO 2 atmosphere: An experimental and kinetic modeling study

HCN is one of the most important intermediates in NO x chemistry including formation and removal processes and the knowledge of HCN oxidation is thus very important to minimize NO x emissions. The present work aims to evaluate the oxidation behavior of HCN in an O 2/CO 2 atmosphere, due to the lack of studies at these specific operating conditions and the increasing importance of the oxy-fuel combustion processes, characterized by an O 2/CO 2 combustion atmosphere instead of air. With this purpose, a flow reactor experimental and kinetic modeling study of the oxidation of HCN under CO 2 diluted conditions, in the 900–1450 K temperature range and for different stoichiometries, ranging from very reducing to oxidizing conditions, has been performed. The large experimental differences observed in the O 2/CO 2 atmosphere in comparison to traditional air-fired combustion corroborate the importance of the HCN oxidation study in an O 2/CO 2 environment. The presence of high CO 2 concentration levels clearly inhibits HCN oxidation, since CO 2 competes with O 2 for atomic hydrogen through the CO 2 + H ⇌ CO + OH reaction. The experimental results show the oxidation regime of HCN for different stoichiometries, analyzing the formation of the main products of the process: CO, NO, N 2, N 2O and HNCO. The higher availability of oxygen increases the HCN conversion, even though the onset temperature for reaction is almost similar at any stoichiometry studied. The mechanism used for calculations was that developed by Dagaut et al. [P. Dagaut, P. Glarborg, M.U. Alzueta, Prog. Energy Combust. Sci. 34 (2008) 1–46] for the oxidation of HCN in air combustion, updated in the present work to take into account the presence of an O 2/CO 2 combustion atmosphere. In general, the modified model gives a reasonably good description of the experiments performed.

Rat carotid body chemosensory discharge and glomus cell HIF-1α expression in vitro: regulation by a common oxygen sensor

Addition of Pco ( approximately 350 Torr) to a normoxic medium (Po(2) of approximately 130 Torr) was used to investigate the relationship between carotid body (CB) sensory discharge and expression of hypoxia-inducible factor 1 alpha (HIF-1 alpha) in glomus cells. Afferent electrical activity measured for in vitro-perfused rat CB increased rapidly (1-2 s) with addition of high CO (Pco of approximately 350 Torr; Po(2) of approximately 130 Torr), and this increase was fully reversed by white light. At submaximal light intensities, the extent of reversal was much greater for monochromatic light at 430 and 590 nm than for light at 450, 550, and 610 nm. This wavelength dependence is consistent with the action spectrum of the CO compound of mitochondrial cytochrome a(3). Interestingly, when isolated glomus cells cultured for 45 min in the presence of high CO (Pco of approximately 350 Torr; Po(2) of approximately 130 Torr) in the dark, the levels of HIF-1 alpha, which turn over slowly (many minutes), increased. This increase was not observed if the cells were illuminated with white light during the incubation. Monochromatic light at 430- and 590-nm light was much more effective than that at 450, 550, and 610 nm in blocking the CO-induced increase in HIF-1 alpha, as was the case for chemoreceptor discharge. Although the changes in HIF-1 alpha take minutes and those for CB neural activity occur in 1-2 s, the similar responses to CO and light suggest that the oxygen sensor is the same (mitochondrial cytochrome a(3)).

Evidence for a common oxygen sensor for chemosensory discharge and HIF1a expression in glomus cells in rat carotid body

Addition of a partial pressure of carbon monoxide (PCO ~ 350 Torr) to a normoxic medium (PO2 ~ 130 Torr), was used to investigate the relationship between carotid body (CB)sensory discharge and expression of hypoxia-inducible factor-1 (HIF-1) in glomus cells. Afferent electrical activity measured for in vitro perfused rat CB increased rapidly (2–3 seconds)with addition of high CO (PCO ~ 350 Torr; Po2 ~ 130 Torr) and this increase was fully reversedby white light. At submaximal light intensities, the extent of reversal was much greater formonochromatic light at 430 nm and 590 nm than for light at 450 nm, 550 nm and 610 nm. This wavelength dependence is consistent with the action spectrum of the CO compound of mitochondrial cytochrome a3. Interestingly, when isolated glomus cells cultured for 45 min inthe presence of high CO (PCO ~ 350 Torr; Po2 ~ 130 Torr) in the dark, the levels of HIF-1, which turns over slowly (many minutes), increased. This increase was not observed if the cells were illuminated with white light during the incubation. Monochromatic light at 430 nm and 590 nm light was much more effective than that at 450, 550, and 610 nm in blocking the CO induced increase in HIF-1, as was observed for the CO induced increase in chemoreceptor discharge. This similarity indicates they are responding to the same oxygen sensor.

Determination of selenium in nickel and cobalt concentrates applying epithermal neutron activation analysis

Se in Ni and Co concentration in concentrates obtained from the nickel industry has to be determined for quality control requirements in their commercialization. Analysis of Se at minor and trace levels is relatively complicated and destructive procedures are frequently required. In this work the determination of Se by epithemal neutron activation analysis (ENAA) in 17 samples from Cuban nickel industry was investigated. Application of ENAA allowed nondestructive determination of Se concentration down to ppm level in spite of the presence of high Co, Fe, Ni and Cr contents in the samples. For attenuation of the thermal neutron flux a Cd filter was utilized.

Near-IR Spectrophotometric Technique for Fast Identification of Carboxycellulose in Linen Fibers—A Preliminary Report

Near-infrared ( NIR ) reflectance spectrophotometry has been successfully used for rapid, efficient identification of carboxylated cellulose in whole (nondisintegrated) linen textile samples subjected to a thermal treatment in the presence of high CO and CO2 concentrations. Mass spectrometric analysis of enzymatic hydrolysates of the treated textiles demonstrates the existence of carboxylated D-glucose residues produced by this procedure. Near-infrared spectrophotometry proves to be an accurate and simple approach to fast identification and characterization of these carboxylated cel lulose derivatives in whole textile samples.

Photoinhibition of Photosynthesis in Lemna gibba: The Effect of O 2, CO 2 and the Selective Inhibition of Photosystem II

This study demonstrates that photoinhibition of Lemna gibba can be induced by exposing the plants in a N(2) atmosphere to a light intensity which exceeds that used for cultivation. The lack of O(2) and CO(2) appeared to be more important than the sudden increase in photon-flux rate for the induction of photoinhibition. Photoinhibition had no effect on the O(2) inhibition of photosynthesis. Moreover, Lemna exhibited a rather fast recovery to photoinhibition, which suggests that Lemna has some mechanism of protection that may be related to the presence of high CO(2) stored in their air sacs. Studies using selected monochromatic light during photoinhibitory treatment show that in vivo photoinhibition maybe due to reactions connected to the excitation of PS II.

Compact sealed TEA CO<inf>2</inf>lasers with corona-discharge preionization

Optimization of the performance of compact sealed TEA CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> lasers employing a novel version of the corona-discharge preionization scheme is reported. Performance with high oxygen concentrations, long-life operation with organic additives, limits of arc-free operation with gas mixtures without helium, and in the presence of high CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> concentrations have been investigated. Our results show that devices whose construction is considerably simplified by employing this preionization technique are capable of producing performance superior to more complex systems.