Experimental non-equilibrium radiation measurements for low-Earth orbit return

This paper reports on absolute radiation measurements performed in synthetic air (20.78% O2, 79.22% N2) shock-heated flows. Experiments were carried out in the Oxford T6 Stalker Tunnel in Aluminium Shock Tube mode. Data is presented for velocities ranging from 5.5-7.2 km/s at a nominal 1 bar post-shock pressure, in both UV/Vis and Vis/NIR spectral ranges. Simulations of the equilibrium radiance using NASA CEA and NEQAIR codes underpredict that obtained from the experimental data. An analysis using the newly developed LASTA code removes shock deceleration from consideration as a cause for this discrepancy. Non-equilibrium data is analysed in the form of spectral and absolute non-equilibrium metrics, and the effects of shock speed and post-shock pressure on the non-equilibrium radiance isolated. Finite-rate one-dimensional two-temperature simulations using POSHAX3 with Park 1993 rates are performed, which significantly underpredict the experimentally acquired data

Radiation measurements of shockwaves in synthetic air and pure nitrogen

Absolute radiance measurements in synthetic air and pure nitrogen have been performed in the Oxford T6 Stalker Tunnel while operating in Aluminium Shock Tube mode. Spatially and spectrally resolved data have been attained for shock speeds from 5.7 to 8 km/s and post-shock pressures from ∼10 to ∼100 kPa. Two independent telecentric optical set ups acquire data from the UV/Vis (200 to 520 nm) and Vis/NIR (585 to 850 nm) regions. The data are presented in multiple formats. An example 2D spectral-spatial map of absolute radiance is provided. Equilibrium spectral radiance comparisons against CEA-NEQAIR demonstrate improved agreement since prior campaigns in both T6 and the Electric Arc Shock Tube at NASA Ames. Spatial radiance profiles demonstrate lower pressure conditions can improve the resolution of non-equilibrium relaxation. Finally, spectral profiles progressing through the relaxation region for a low pressure synthetic air test case are shown. The motivation of this paper is to provide reliable calibrated data that, in future work, can be used to extract thermochemical rates and upon which numerical codes and facility results can be benchmarked against

Anomalous Scaling and Solitary Waves in Systems with Non-Linear Diffusion

We study a non-linear convective-diffusive equation, local in space and time, which has its background in the dynamics of the thickness of a wetting film. The presence of a non-linear diffusion predicts the existence of fronts as well as shock fronts. Despite the absence of memory effects, solutions in the case of pure non-linear diffusion exhibit an anomalous sub-diffusive scaling. Due to a balance between non-linear diffusion and convection we, in particular, show that solitary waves appear. For large times they merge into a single solitary wave exhibiting a topological stability. Even though our results concern a specific equation, numerical simulations supports the view that anomalous diffusion and the solitary waves disclosed will be general features in such non-linear convective-diffusive dynamics.Comment: Corrected typos, added 3 references and 2 figure

Numerical simulations of carbon contaminants in T6 shock tube tests

The influence of carbon contamination on a range of synthetic air and pure nitrogen shock tube experiments conducted in Oxford’s T6 Stalker Tunnel is investigated using a numerical model designed for thermochemically reacting flows. Experimental conditions range from 6 to 7 km/s with fill pressures between 18 and 100 Pa. The addition of carbon was found to significantly improve agreement between the numerical model and experimental data, especially after the non-equilibrium peak and during relaxation towards equilibrium. For the chosen thermochemistry set and test conditions, minimal affect on the chemical kinetics of the original test gas was found especially for the neutral species, with minor changes for ion and electron number densities. The performance of the chosen thermochemistry model in radiance regions corresponding to NO and non-equilibrium atomic oxygen was poor, with improvements also required for the parameters governing translational-vibrational relaxation

Rapid deposition of oxidized biogenic compounds to a temperate forest

We report fluxes and dry deposition velocities for 16 atmospheric compounds above a southeastern United States forest, including: hydrogen peroxide (H_2O_2), nitric acid (HNO_3), hydrogen cyanide (HCN), hydroxymethyl hydroperoxide, peroxyacetic acid, organic hydroxy nitrates, and other multifunctional species derived from the oxidation of isoprene and monoterpenes. The data suggest that dry deposition is the dominant daytime sink for small, saturated oxygenates. Greater than 6 wt %C emitted as isoprene by the forest was returned by dry deposition of its oxidized products. Peroxides account for a large fraction of the oxidant flux, possibly eclipsing ozone in more pristine regions. The measured organic nitrates comprise a sizable portion (15%) of the oxidized nitrogen input into the canopy, with HNO_3 making up the balance. We observe that water-soluble compounds (e.g., strong acids and hydroperoxides) deposit with low surface resistance whereas compounds with moderate solubility (e.g., organic nitrates and hydroxycarbonyls) or poor solubility (e.g., HCN) exhibited reduced uptake at the surface of plants. To first order, the relative deposition velocities of water-soluble compounds are constrained by their molecular diffusivity. From resistance modeling, we infer a substantial emission flux of formic acid at the canopy level (∼1 nmol m^(−2)⋅s^(−1)). GEOS−Chem, a widely used atmospheric chemical transport model, currently underestimates dry deposition for most molecules studied in this work. Reconciling GEOS−Chem deposition velocities with observations resulted in up to a 45% decrease in the simulated surface concentration of trace gases

Decadal changes in summertime reactive oxidized nitrogen and surface ozone over the Southeast United States

Widespread efforts to abate ozone (O3) smog have significantly reduced emissions of nitrogen oxides (NOx) over the past 2 decades in the Southeast US, a place heavily influenced by both anthropogenic and biogenic emissions. How reactive nitrogen speciation responds to the reduction in NOx emissions in this region remains to be elucidated. Here we exploit aircraft measurements from ICARTT (July–August 2004), SENEX (June–July 2013), and SEAC4RS (August–September 2013) and long-term ground measurement networks alongside a global chemistry–climate model to examine decadal changes in summertime reactive oxidized nitrogen (RON) and ozone over the Southeast US. We show that our model can reproduce the mean vertical profiles of major RON species and the total (NOy) in both 2004 and 2013. Among the major RON species, nitric acid (HNO3) is dominant (∼ 42–45%), followed by NOx (31%), total peroxy nitrates (ΣPNs; 14%), and total alkyl nitrates (ΣANs; 9–12%) on a regional scale. We find that most RON species, including NOx, ΣPNs, and HNO3, decline proportionally with decreasing NOx emissions in this region, leading to a similar decline in NOy. This linear response might be in part due to the nearly constant summertime supply of biogenic VOC emissions in this region. Our model captures the observed relative change in RON and surface ozone from 2004 to 2013. Model sensitivity tests indicate that further reductions of NOxemissions will lead to a continued decline in surface ozone and less frequent high-ozone events

Architecture of human Rag GTPase heterodimers and their complex with mTORC1

© 2019 American Association for the Advancement of Science. All rights reserved. The Rag guanosine triphosphatases (GTPases) recruit the master kinase mTORC1 to lysosomes to regulate cell growth and proliferation in response to amino acid availability. The nucleotide state of Rag heterodimers is critical for their association with mTORC1. Our cryo–electron microscopy structure of RagA/RagC in complex with mTORC1 shows the details of RagA/RagC binding to the RAPTOR subunit of mTORC1 and explains why only the RagAGTP/RagCGDPnucleotide state binds mTORC1. Previous kinetic studies suggested that GTP binding to one Rag locks the heterodimer to prevent GTP binding to the other. Our crystal structures and dynamics of RagA/RagC show the mechanism for this locking and explain how oncogenic hotspot mutations disrupt this process. In contrast to allosteric activation by RHEB, Rag heterodimer binding does not change mTORC1 conformation and activates mTORC1 by targeting it to lysosomes