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Density functional theory has been used to elucidate the mechanistic underpinnings of the regeneration of ammonia‐borane (H₃B−NH₃,AB) from polyborazylene (B_xN_xH_x,PBz) in the presence of hydrazine (H₂N−NH₂,Hz). Herein, borazine (B₃N₃H₆,Bz) is used as the simplest relevant model ofPBzfor the regeneration process. Digestion ofBzusingHzwas found to occur by a string of Lewis acid base adduct (between B atoms ofBzandHzmolecule) formation andHzassisted proton transfer processes. Later, B−H bonds of HB(NHNH₂)₂, theBzdigested product, are redistributed to form hydrazine‐borane (H₃B−NH₂NH₂,HzB) and B(NHNH₂)₃. Redistribution of B−H bonds occurs through hydroboration and concerted proton‐hydride transfer. Another B−H redistributed product, B(NHNH₂)₃, producesHzBas a result of proton and hydride transfer from cis‐diazene (Dz), the oxidized product ofHzin presence of O₂.

 

Abstract. Across the Arctic, vast areas of permafrost are being degraded by climatechange, which has the potential to release substantial quantities ofnutrients, including nitrogen into large Arctic rivers. These rivers heavilyinfluence the biogeochemistry of the Arctic Ocean, so it is important tounderstand the potential changes to rivers from permafrost degradation. Thisstudy utilized dissolved nitrogen species (nitrate and dissolved organicnitrogen (DON)) along with nitrogen isotope values (δ15N-NO3- and δ15N-DON) of samples collectedfrom permafrost sites in the Kolyma River and the six largest Arctic rivers.Large inputs of DON and nitrate with a unique isotopically heavy δ15N signature were documented in the Kolyma, suggesting the occurrenceof denitrification and highly invigorated nitrogen cycling in the Yedomapermafrost thaw zones along the Kolyma. We show evidence for permafrost-derived DON being recycled to nitrate as it passes through the river,transferring the high 15N signature to nitrate. However, the potentialto observe these thaw signals at the mouths of rivers depends on the spatialscale of thaw sites, permafrost degradation, and recycling mechanisms. Incontrast with the Kolyma, with near 100 % continuous permafrost extent,the Ob River, draining large areas of discontinuous and sporadicpermafrost, shows large seasonal changes in both nitrate and DON isotopicsignatures. During winter months, water percolating through peat soilsrecords isotopically heavy denitrification signals in contrast with thelighter summer values when surface flow dominates. This early yeardenitrification signal was present to a degree in the Kolyma, but the abilityto relate seasonal nitrogen signals across Arctic Rivers to permafrostdegradation could not be shown with this study. Other large rivers in theArctic show different seasonal nitrogen trends. Based on nitrogen isotopevalues, the vast majority of nitrogen fluxes in the Arctic rivers is fromfresh DON sourced from surface runoff through organic-rich topsoil and notfrom permafrost degradation. However, with future permafrost thaw, otherArctic rivers may begin to show nitrogen trends similar to the Ob. Ourstudy demonstrates that nitrogen inputs from permafrost thaw can beidentified through nitrogen isotopes, but only on small spatial scales.Overall, nitrogen isotopes show potential for revealing integrated catchmentwide nitrogen cycling processes. 

In this experience report, we describe the accessibility challenges that deaf and hard of hearing users face in teleconferences, based on both our first-hand participation in meetings, and as User Interface and Experience experts. Teleconferencing poses new accessibility challenges compared to face-to-face communication because of limited social, emotional, and haptic feedback. Above all, teleconferencing participants and organizers need to be flexible, because deaf or hard of hearing people have diverse communication preferences. We explain what recurring problems users experience, where current teleconferencing software falls short, and how to address these shortcomings. We offer specific recommendations for best practices and the experiential reasons behind them. 

We present Fermi Gamma-ray Burst Monitor (Fermi-GBM) and Swift Burst Alert Telescope (Swift-BAT) searches for gamma-ray/X-ray counterparts to gravitational-wave (GW) candidate events identified during the third observing run of the Advanced LIGO and Advanced Virgo detectors. Using Fermi-GBM onboard triggers and subthreshold gamma-ray burst (GRB) candidates found in the Fermi-GBM ground analyses, the Targeted Search and the Untargeted Search, we investigate whether there are any coincident GRBs associated with the GWs. We also search the Swift-BAT rate data around the GW times to determine whether a GRB counterpart is present. No counterparts are found. Using both the Fermi-GBM Targeted Search and the Swift-BAT search, we calculate flux upper limits and present joint upper limits on the gamma-ray luminosity of each GW. Given these limits, we constrain theoretical models for the emission of gamma rays from binary black hole mergers.