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1. An Interferometric View of H-MM1. I. Direct Observation of NH ₃ Depletion

   https://doi.org/10.3847/1538-3881/ac6be7  

   Pineda, Jaime E.; Harju, Jorma; Caselli, Paola; Sipilä, Olli; Juvela, Mika; Vastel, Charlotte; Rosolowsky, Erik; Burkert, Andreas; Friesen, Rachel K.; Shirley, Yancy; et al (May 2022, The Astronomical Journal)

   Abstract Spectral lines of ammonia, NH 3 , are useful probes of the physical conditions in dense molecular cloud cores. In addition to advantages in spectroscopy, ammonia has also been suggested to be resistant to freezing onto grain surfaces, which should make it a superior tool for studying the interior parts of cold, dense cores. Here we present high-resolution NH 3 observations with the Very Large Array and Green Bank Telescope toward a prestellar core. These observations show an outer region with a fractional NH 3 abundance of X (NH 3 ) = (1.975 ± 0.005) × 10 −8 (±10% systematic), but it also reveals that, after all, the X (NH 3 ) starts to decrease above a H 2 column density of ≈2.6 × 10 22 cm −2 . We derive a density model for the core and find that the break point in the fractional abundance occurs at the density n (H 2 ) ∼ 2 × 10 5 cm −3 , and beyond this point the fractional abundance decreases with increasing density, following the power law n −1.1 . This power-law behavior is well reproduced by chemical models where adsorption onto grains dominates the removal of ammonia and related species from the gas at high densities. We suggest that the break-point density changes from core to core depending on the temperature and the grain properties, but that the depletion power law is anyway likely to be close to n −1 owing to the dominance of accretion in the central parts of starless cores. 

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2. Earth abundant perovskite oxides for low temperature CO ₂ conversion

   https://doi.org/10.1039/C7EE03383D  

   Maiti, Debtanu; Hare, Bryan J.; Daza, Yolanda A.; Ramos, Adela E.; Kuhn, John N.; Bhethanabotla, Venkat R. (January 2018, Energy & Environmental Science)

   Conversion of CO 2 in a scalable technology has the potential for enormous energy and environmental impact but remains a challenge. We present several stable, earth abundant perovskite oxide materials for the reverse water gas shift chemical looping (RWGS-CL) process as a potential solution for this CO 2 mitigation problem. This material and process combination circumvents issues plaguing other emerging technologies, viz. poor rates of CO 2 conversion, high operation temperatures, use of precious metal catalysts, or combinations thereof. Using DFT-calculated oxygen vacancy formation energy, a key descriptor for the RWGS-CL process, we have successfully predicted several earth abundant perovskite oxides with high CO 2 conversion capability. We simultaneously achieved 100% selective CO generation from CO 2 at the highest known rates (∼160 μmoles per min per gram perovskite oxide) at record low process temperatures of 450–500 °C using lanthanum and calcium based perovskite oxides. These materials are stable over several RWGS-CL cycles, enabling industrial implementation. 

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3. Dust Temperature Uncertainties Hamper the Inference of Dust and Molecular Gas Masses from the Dust Continuum Emission of Quiescent High-redshift Galaxies

   https://doi.org/10.3847/2041-8213/ac951d  

   Cochrane, R. K.; Hayward, C. C.; Anglés-Alcázar, D. (November 2022, The Astrophysical Journal Letters)

   Abstract Single flux density measurements at observed-frame submillimeter and millimeter wavelengths are commonly used to probe dust and gas masses in galaxies. In this Letter, we explore the robustness of this method to infer dust mass, focusing on quiescent galaxies, using a series of controlled experiments on four massive halos from the Feedback in Realistic Environments project. Our starting point is four star-forming central galaxies at seven redshifts betweenz= 1.5 andz= 4.5. We generate modified quiescent galaxies that have been quenched for 100 Myr, 500 Myr, or 1 Gyr prior to each of the studied redshifts by reassigning stellar ages. We derive spectral energy distributions for each fiducial and modified galaxy using radiative transfer. We demonstrate that the dust mass inferred is highly dependent on the assumed dust temperature,T_dust, which is often unconstrained observationally. Motivated by recent work on quiescent galaxies that assumedT_dust∼ 25 K, we show that the ratio between dust mass and 1.3 mm flux density can be higher than inferred by up to an order of magnitude, due to the considerably lower dust temperatures seen in non-star-forming galaxies. This can lead to an underestimation of dust mass (and, when submillimeter flux density is used as a proxy for molecular gas content and gas mass). This underestimation is most severe at higher redshifts, where the observed-frame 1.3 mm flux density probes rest-frame wavelengths far from the Rayleigh–Jeans regime, and hence depends superlinearly on dust temperature. We fit relations between ratios of rest-frame far-infrared flux densities and mass-weighted dust temperature that can be used to constrain dust temperatures from observations and hence derive more reliable dust and molecular gas masses. 

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4. Structures of glasses created by multiple kinetic arrests

   https://doi.org/10.1063/5.0080846  

   Yu, Junguang; Chen, Zhenxuan; Teerakapibal, Rattavut; Benmore, Chris; Richert, Ranko; Yu, Lian (February 2022, The Journal of Chemical Physics)

   X-ray scattering has been used to characterize glassy itraconazole (ITZ) prepared by cooling at different rates. Faster cooling produces ITZ glasses with lower (or zero) smectic order with more sinusoidal density modulation, larger molecular spacing, and shorter lateral correlation between the rod-like molecules. We find that each glass is characterized by not one, but two fictive temperatures T_f(the temperature at which a chosen order parameter is frozen in the equilibrium liquid). The higher T_fis associated with the regularity of smectic layers and lateral packing, while the lower T_fwith the molecular spacings between and within smectic layers. This indicates that different structural features are frozen on different timescales. The two timescales for ITZ correspond to its two relaxation modes observed by dielectric spectroscopy: the slower δ mode (end-over-end rotation) is associated with the freezing of the regularity of molecular packing and the faster α mode (rotation about the long axis) with the freezing of the spacing between molecules. Our finding suggests a way to selectively control the structural features of glasses. 

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5. A Review of Innovative Frost Heave Mitigation Techniques for Road Pavements

   Michael Uduebor, Emmanuel (August 2022, International Conference on Transportation and Development 2022)

   Frost action (heaving and thawing) is a perennial problem encountered in the design, construction, and management of civil engineering structures, particularly road pavements in cold regions and areas that experience seasonal sub-freezing temperatures. This paper reviews the existing methods for frost heave mitigation and proposes an innovative approach through engineered water repellency. Soil was collected from a test plot at the Charlotte Douglas International Airport and treated with a commercially available organosilane. Preliminary results indicate an increase in the maximum dry density from 17.54kN/m3 to 17.66kN/m3 and a decrease in the optimum moisture content from 17.36% to 11.75% after treatment. Data obtained from performance tests carried out under sub-freezing weather conditions indicated that the treatment was effective in limiting the infiltration and migration of water into the soil matrix when compared with the untreated soil. As such, engineered water repellency may be a viable solution for Airports and Departments of Transportation seeking methods to mitigate frost action. 

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