High CO/H_2 ratio supports an exocometary origin for a CO-rich debris disc

We study the effects of grain surface reactions on the chemistry of protoplanetary disks where gas, ice surface layers, and icy mantles of dust grains are considered as three distinct phases. Gas-phase and grain surface chemistry is found to be mainly driven by photoreactions and dust temperature gradients. The icy disk interior has three distinct chemical regions: (i) the inner midplane with low far-UV (FUV) fluxes and warm dust (≳15 K) that lead to the formation of complex organic molecules, (ii) the outer midplane with higher FUV from the interstellar medium and cold dust where hydrogenation reactions dominate, and (iii) a molecular layer above the midplane but below the water condensation front where photodissociation of ices affects gas-phase compositions. Some common radicals, e.g., CN and C2H, exhibit a two-layered vertical structure and are abundant near the CO photodissociation front and near the water condensation front. The three-phase approximation in general leads to lower vertical column densities than two-phase models for many gas-phase molecules owing to reduced desorption, e.g., H2O, CO2, HCN, and HCOOH decrease by roughly two orders of magnitude. Finally, we find that many observed gas-phase species originate near the water condensation front; photoprocesses determine their column densities, which do not vary significantly with key disk properties such as mass and dust/gas ratio.

Molecular hydrogen (̋mol) is the most abundant molecule in the interstellar medium. Because of its excited form in irradiated regions, it is a useful tool for studying photodissociation regions (PDRs), where radiative feedback from massive stars on molecular clouds is dominant. The James Webb Space Telescope (JWST), with its high spatial resolution, sensitivity, and wavelength coverage, provides unique access to the detection of most of the ̋mol rotational and rovibrational lines, as well as the analysis of their spatial morphology. Our goal is to use ̋mol line emission detected with JWST in the Horsehead nebula to constrain the physical parameters (e.g., extinction, gas temperature, and thermal pressure) throughout the PDR and its geometry. We used spectro-imaging data acquired using both the NIRSpec and MIRI-MRS instruments on board JWST to study the ̋mol spatial distribution at very small scales (down to 0.1"). From the ̋mol line ratios, we constrained the extinction throughout the PDR. We then studied the excitation of ̋mol levels in detail and used this analysis to derive the physical parameters. We detect hundreds of ̋mol rotational and rovibrational lines in the Horsehead nebula. The ̋mol morphology reveals a spatial separation between ̋mol lines (∼ 0.5") across the PDR interface. Far-ultraviolet (FUV)-pumped lines (v=0 J_u>6, v>0) peak closer to the edge of the PDR than thermalized lines. From ̋mol lines arising from the same upper level, we estimated the value of extinction throughout the PDR. We find that A_V increases from the edge of the PDR to the second and third ̋mol filaments. We find A_V = 0.3 ± 1.3 in the first filament and A_V = 6.1 ± 1.4 in the second and third filaments. We then studied the ̋mol excitation in different regions across the PDR. The excitation diagrams were fit by two excitation temperatures. As the first levels of ̋mol are thermalized, the colder temperature corresponds to the gas temperature. The second, hotter component corresponds to the FUV-pumped levels. In each filament, we derive a gas temperature of T ∼ 500 K. The temperature profile shows that the observed gas temperature remains nearly constant throughout the PDR, with a slight decrease in each of the dissociation fronts. The spatial distribution of ̋mol reveals that most of the ̋mol column density is concentrated in the second and third filaments. The column density in the first filament is approximately N(̋mol) = (3.8 ± 0.8) cm^-2, while in the second and third filaments it is N(̋mol) = (1.9 ± 0.4) cm^-2 , about five times higher. The ortho-to-para ratio (OPR) is far from equilibrium, varying from 2-2.5 at the edge of each dissociation front to 1.3-1.5 deeper into the PDR. We observe a clear spatial separation between the para and ortho rovibrational levels, as well as between 0--0 S(2) and 0--0 S(1), indicating that efficient ortho-para conversion and preferential ortho self-shielding are driving the spatial variations of the OPR. Finally, we derive a thermal pressure in the first filament of about P_ ̊m gas ≥ 6 10^6 K ç, which is approximately ten times higher than that of the ionized gas. We highlight that template stationary 1D PDR models cannot account for the intrinsic 2D structure and the very high temperature observed in the Horsehead nebula. We argue that the highly excited, over-pressurized ̋mol gas at the edge of the PDR interface could originate from mixing between the cold and hot phases induced by photo-evaporation of the cloud. The analysis of ̋mol lines detected with JWST provides unique access to the geometry and physical conditions in the Horsehead nebula at very small scales and reveals, for the first time, the possible importance of dynamical effects at the edge of the PDR. This study nevertheless highlights the need for extended modeling of these dynamical effects.

In order to understand which mechanism is responsible for accretion in protoplanetary discs, a robust knowledge of the observed disc radius using gas tracers such as 12CO and other CO isotopologues is pivotal. Indeed, the two main theories proposed, viscous accretion and wind-driven accretion, predict different time evolution for the disc radii. In this letter, we present an analytical solution for the evolution of the disc radii in viscously evolving protoplanetary discs using 12CO as a tracer, under the assumption that the 12CO radius is the radius where the surface density of the disc is equal to the threshold for CO photodissociation. We discuss the properties of the solution and the limits of its applicability as a simple numerical prescription to evaluate the observed disc radii of populations of discs. Our results suggest that, in addition to photodissociation, also freeze out plays an important role in setting the disc size. We find an effective reduction of the CO abundance by about two orders of magnitude at the location of CO photodissociation, which, however, should not be interpreted as the bulk abundance of CO in the disc. The use of our analytical solution will allow to compute disc sizes for large quantities of models without using expensive computational resources such as radiative transfer calculations.

We present JWST-MIRI Medium Resolution Spectrometer (MRS) spectra of the protoplanetary disk around the low-mass T Tauri star GW Lup from the MIRI mid-INfrared Disk Survey Guaranteed Time Observations program. Emission from 12CO2, 13CO2, H2O, HCN, C2H2, and OH is identified with 13CO2 being detected for the first time in a protoplanetary disk. We characterize the chemical and physical conditions in the inner few astronomical units of the GW Lup disk using these molecules as probes. The spectral resolution of JWST-MIRI MRS paired with high signal-to-noise data is essential to identify these species and determine their column densities and temperatures. The Q branches of these molecules, including those of hot bands, are particularly sensitive to temperature and column density. We find that the 12CO2 emission in the GW Lup disk is coming from optically thick emission at a temperature of ∼400 K. 13CO2 is optically thinner and based on a lower temperature of ∼325 K, and thus may be tracing deeper into the disk and/or a larger emitting radius than 12CO2. The derived / ratio is orders of magnitude higher than previously derived for GW Lup and other targets based on Spitzer-InfraRed-Spectrograph data. This high column density ratio may be due to an inner cavity with a radius in between the H2O and CO2 snowlines and/or an overall lower disk temperature. This paper demonstrates the unique ability of JWST to probe inner disk structures and chemistry through weak, previously unseen molecular features.

It is said that 1 i and Mo have good high temperature corrosion resistarlce against impurities in helium gas.Thus, in order to investigate the possibility that corrosion resistance rif alloys might be improved by coating these metals on them, oxidation behavior of superalloys with spray coating of i and Mo was studied at 1 OOOCfor duration up to 600 h in impure helium gas.The principal results are as follows.(I) Mo-coated alloys show not on!yhigh corrosion resistance but also good long term stability because rif absence of dif/ilsion of alloying elements from matrices to coatings.H owever, it is observed that adequate thin coating should be selected to avoid cracking in coating.(2) Ni-coated alloys show lower corrosion resistance than Mo-coated alloys because considerable diffusion of alloying elements takes place from matrices to coatings, though they have higher resistance against cracking than Mo-coated alloys.(3) The jJossibility that superalloys with large quantity of Co would be used as materials Q[ high tem/Jerature parts except reactor core was shown.

The photooxidation of glyoxylate by envelope-free spinach chloroplasts and its relation to photorespiration

FTIR analysis of storage behavior and sulfur tolerance in barium-based NOx storage and reduction (NSR) catalysts

Evidence at the Cretaceous/Tertiary boundary suggests that the proposed 'extinction' bolide struck a continental or shallow marine terrane. This evidence includes: shocked quartz and feldspar grains found in the boundary layer inherited from a range of rock types; a high ^(87)Sr/^(86)Sr ratio in some planktonic fossils which could reflect continental-derived Sr(ref.5); and evidence that the platinum-group-element-rich clay layer is underlain (at some localities) by a deposit of possible tsunamic origin. These observations and data demonstrate that sea level at the end of the Cretaceous was ~150-200 m higher than at present, suggesting the possibility that the extinction bolide struck a shallow marine carbonate-rich sedimentary section. Here we show that the impact of such a bolide (~5km in radius) onto a carbonate-rich terrane would increase the CO_2 content of the atmosphere by a factor of two to ten. Additional dissolution of CO_2 from the ocean's photic zone could release much larger quantities of CO_2. The impact induced release of CO_2, by itself, would enhance atmospheric greenhouse heating and give rise to a worldwide increase in temperature from 2 K to 10 K for periods of 10^4 to 10^5 years.

<div class="htmlview paragraph">Hydrogen is one of the better fuels for use in fuel cells. In the production of hydrogen by reacting hydrocarbons with steam, large quantities of CO must be converted to hydrogen by the classical water-gas shift reaction. Newer catalysts operating at low temperatures offer certain advantages over “conventional” catalysts. Several applications, are discussed, illustrating the advantages of the low-temperature CO conversion catalyst (400 F and higher).</div>

To comply with recent international trends and initiatives, and in order to help achieve sustainable development, Korea has established a greenhouse gas (GHG) emission reduction target of 37% (851 million tons) of the business as usual (BAU) rate by 2030. Regarding environmentally-oriented standards such as the IGCC (International Green Construction Code), there are also rising demands for the assessment on CO2 emissions during the life cycle in accordance with ISO (International Standardization Organization’s Standard) 14040. At present, precast concrete (PC) engineering-related studies primarily cover structural and construction aspects, including improvement of structural performance in the joint, introduction of pre-stressed concrete and development of half PC. In the manufacture of PC, steam curing is mostly used for the early-strength development of concrete. In steam curing, a large amount of CO2 is produced, causing an environmental problem. Therefore, this study proposes a method to assess CO2 emissions (including absorption) throughout the PC life cycle by using a life cycle assessment (LCA) method. Using the proposed assessment method, CO2 emissions during the life cycle of a precast concrete girder (PCG) were assessed. In addition, CO2 absorption was assessed against a PCG using conventional carbonation and CO2 absorption-related models. As a result, the CO2 emissions throughout the life cycle of the PCG were 1365.6 (kg-CO2/1 PCG). The CO2 emissions during the production of raw materials among the CO2 emissions throughout the life cycle of the PCG were 1390 (kg-CO2/1 PCG), accounting for a high portion to total CO2 emissions (nearly 90%). In contrast, the transportation and manufacture stages were 1% and 10%, respectively, having little effect on total CO2 emissions. Among the use of the PCG, CO2 absorption was mostly decided by the CO2 diffusion coefficient and the amount of CO2 absorption by cement paste. The CO2 absorption by carbonation throughout the service life of the PC was about 11% of the total CO2 emissions, which is about 16% of CO2 emissions from ordinary Portland cement (OPC) concrete.

Integrated environmental influences quantification of pilot-scale constructed wetlands based on modified ecological footprint assessment

Evaluating CO2 sources for power-to-gas applications – A case study for Austria

PurposeWe measured how much CO2 gas was used in urologic laparoscopic surgeries and studied whether the amount of gas was associated with postoperative pain.Materials and MethodsFour hundred sixty-three patients underwent urologic laparoscopic surgeries by a single surgeon. All surgeries were performed by a transperitoneal approach under a 15-mm Hg pneumoperitoneum using CO2 gas. The amount of CO2 was measured. Neuromuscular blockade with rocuronium was performed during the surgery and patient-controlled analgesia was also applied. Postoperative pain was assessed four times for 24 hours using a 10-point visual analogue scale.ResultsThe mean laparoscopic time was 75.65±38.19 minutes and the mean amount of CO2 gas used was 415.70±190.68 L. The mean score on the postoperative pain scale was 6.37±1.48 for 12 hours (sum of measurements taken at 6 and 12 hours after the surgery) and 11.72±2.46 for 24 hours (sum of measurements at 6, 12, 18, and 24 hours). In the statistical analysis, there were no correlations between the amount of CO2 used and pain scores for 12 and 24 hours postoperatively. There were no correlations between laparoscopic time and pain scores for 12 or 24 hours postoperatively. There were also no correlations between operative method and pain scores for 12 or 24 hours postoperatively.ConclusionsWe recorded the amount of CO2 gas used for each laparoscopic surgery. There was no correlation between the amount of CO2 used and postoperative pain. The lack of correlation may have been because the surgery was performed under anesthesia with deep neuromuscular blockade.

We report the results of a deep search for submillimetre lines of 12CO around the nearby main-sequence stars Vega (α Lyr), ε Eridanus, Fomalhaut (α PsA), β Leo and β Pictoris. Upper limits on CO masses about 10 to 100 times lower than those previously reported have been obtained. If ‘normal’ interstellar medium CO abundances are assumed, the data suggest that the gas:dust mass ratio is reduced by a factor of ≳ 103 below that found in molecular clouds. These apparently low values can be explained by photodissociation of CO in the stellar or, in the case of ε Eri, the interstellar UV radiation field. The predicted CO column densities are similar to our limits if the CO is not replenished. Although the β Pic disc has the highest dust mass, the large grain size results in a relatively low UV extinction to the central star, and so CO photodissociation can readily occur. It has been suggested by others that the CO could be replenished by the occasional infall of comets, and we place an upper limit on the rate of cometary accretion for ε Eri.

Coke-assisted microwave ignition and combustion behaviors of anthracite in a switching atmosphere