A near-field Gaussian plume inversion flux quantification method, applied to unmanned aerial vehicle sampling

The accurate quantification of methane emissions from point sources is required to better quantify emissions for sector-specific reporting and inventory validation. An unmanned aerial vehicle (UAV) serves as a platform to sample plumes near to source. This paper describes a near-field Gaussian plume inversion (NGI) flux technique, adapted for downwind sampling of turbulent plumes, by fitting a plume model to measured flux density in three spatial dimensions. The method was refined and tested using sample data acquired from eight UAV flights, which measured a controlled release of methane gas. Sampling was conducted to a maximum height of 31 m (i.e. above the maximum height of the emission plumes). The method applies a flux inversion to plumes sampled near point sources. To test the method, a series of random walk sampling simulations were used to derive an NGI upper uncertainty bound by quantifying systematic flux bias due to a limited spatial sampling extent typical for short-duration small UAV flights (less than 30 min). The development of the NGI method enables its future use to quantify methane emissions for point sources, facilitating future assessments of emissions from specific source-types and source areas. This allows for atmospheric measurement-based fluxes to be derived using downwind UAV sampling for relatively rapid flux analysis, without the need for access to difficult-to-reach areas

Determination of the disulfide bond arrangement of dengue virus NS1 protein

The 12 half-cystines of NS1 proteins are absolutely conserved among flaviviruses, suggesting their importance to the structure and function of these proteins. In the present study, peptides from recombinant Dengue-2 virus NS1 were produced by tryptic digestion in 100% (H2O)-O-16, peptic digestion in 50% (H2O)-O-18, thermolytic digestion in 50% (H2O)-O-18, or combinations of these digestion conditions. Peptides were separated by size exclusion and/or reverse phase high performance liquid chromatography and examined by matrix-assisted laser desorption ionization-time of flight mass spectrometry, matrix-assisted laser desorption ionization post-source decay, and matrix-assisted laser desorption ionization tandem mass spectrometry. Where digests were performed in 50% (H2O)-O-18, isotope profiles of peptide ions aided in the identification and characterization of disulfide-linked peptides. It was possible to produce two-chain peptides containing C1/C2, C3/C4, C5/C6, and C7/C12 linkages as revealed by comparison of the peptide masses before and after reduction and by post-source decay analysis. However, the remaining four half-cystines (C8, C9, C10, and C11) were located in a three-chain peptide of which one chain contained adjacent half-cystines (C9 and C10). The linkages of C8/C10 and C9/C11 were determined by tandem mass spectrometry of an in-source decay fragment ion containing C9, C10, and C11. This disulfide bond arrangement provides the basis for further refinement of flavivirus NS1 protein structural models

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements