A New Interpretation for the Second Peak of T Coronae Borealis Outbursts: A Tilting Disk around a Very Massive White Dwarf

A new interpretation for the second peak of T Coronae Borealis (T CrB) outbursts is proposed based on a thermonuclear runaway (TNR) model. The system consists of a very massive white dwarf (WD) with a tilting accretion disk and a lobe-filling red-giant. The first peak of the visual light curve of T CrB outbursts is well reproduced by the TNR model on a WD close to the Chandrasekhar mass ($M_{\rm WD} \gtrsim 1.35 ~M_\odot$), while the second peak is reproduced by the combination of the irradiated M-giant and the irradiated tilting disk. The derived fitting parameters are the WD mass $M_{\rm WD} \sim 1.35 ~M_\odot$, the M-giant companion mass $M_{\rm RG} \sim 0.7 M_\odot$ ($0.6-1.0 M_\odot$ is acceptable), the inclination angle of the orbit i \sim 70 \arcdeg, and the tilting angle of the disk i_{\rm prec} \sim 35 \arcdeg. These parameters are consistent with the recently derived binary parameters of T CrB.Comment: 6 pages including 2 figures, to be published in ApJ Letter

Meltwater Intrusions Reveal Mechanisms for Rapid Submarine Melt at a Tidewater Glacier

Submarine melting has been implicated as a driver of glacier retreat and sea level rise, but to date melting has been difficult to observe and quantify. As a result, melt rates have been estimated from parameterizations that are largely unconstrained by observations, particularly at the near-vertical termini of tidewater glaciers. With standard coefficients, these melt parameterizations predict that ambient melting (the melt away from subglacial discharge outlets) is negligible compared to discharge-driven melting for typical tidewater glaciers. Here, we present new data from LeConte Glacier, Alaska, that challenges this paradigm. Using autonomous kayaks, we observe ambient meltwater intrusions that are ubiquitous within 400 m of the terminus, and we provide the first characterization of their properties, structure, and distribution. Our results suggest that ambient melt rates are substantially higher (×100) than standard theory predicts and that ambient melting is a significant part of the total submarine melt flux. We explore modifications to the prevalent melt parameterization to provide a path forward for improved modeling of ocean-glacier interactions.This work was funded by NSF OPP Grants 1503910, 1504191, 1504288, and 1504521 and National Geographic Grant CP4-171R-17. Additionally, this research was supported by the NOAA Climate and Global Change Postdoctoral Fellowship Program, administered by UCAR’s Cooperative Programs for the Advancement of Earth System Science (CPAESS) under award #NA18NWS4620043B. These observations would not be possible without the skilled engineering team who developed the autonomous kayaks—including Jasmine Nahorniak, June Marion, Nick McComb, Anthony Grana, and Corwin Perren—and also the Captain and crew of the M/V Amber Anne. We thank Donald Slater and an anonymous reviewer for valuable feedback that improved this manuscript. Data availability: All of the oceanographic data collected by ship and kayak have been archived with the National Centers for Environmental Information (Accession 0189574, https://accession.nodc.noaa.gov/ 0189574). The glacier data have been archived at the Arctic Data Center (https://doi.org/10.18739/A22G44).Ye

Nitrogen fixation by the savanna tree Philenoptera violacea (Klotzsch) Schrire (Apple leaf) of different ages in a semi-arid riparian landscape

AbstractThe acquisition of nitrogen for growth and maintenance is essential for plants, and having multiple strategies for that acquisition is especially important for those colonizing nutrient poor substrates. Philenoptera violacea (Apple leaf) is a prominent tree in nutrient poor savanna and alluvial soils near rivers in southern Africa, where nutrient availabilities are highly variable in space and time. We investigated nitrogen fixation in P. violacea within riparian corridors flanking the Sabie River in Kruger National Park (KNP) in the Lowveld in northeastern South Africa using the natural 15N abundance technique. Results indicated that P. violacea fixes atmospheric nitrogen and this varies with life history stage. We found that foliar δ15N levels were significantly lower in all life stage classes of P. violacea compared with the reference plant D. mespiliformis growing in open riparian forest. In addition δ15N values were significantly different within the different life stages of P. violacea with the leaves of saplings and juvenile plants having significantly lower δ15N levels than mature plants. While δ15N values increased with age, foliar nitrogen concentration values declined, with leaves from sapling P. violacea having significantly higher total nitrogen than adults and juveniles, which were in turn significantly higher than juvenile D. mespiliformis. However, foliar δ15N levels in seedlings of P. violacea growing in a high nutrient environment in flood debris piles did not differ from levels recorded in seedlings of the reference tree. This study confirms that P. violacea is able to fix nitrogen, but it is dependant on soil conditions and the life stage of the trees

Phosphorus sorption characteristics and interactions with leaf litter‑derived dissolved organic matter leachate in iron‑rich sediments of a sub‑tropical ephemeral stream

This study investigated the infuence of dissolved organic matter (DOM) additions on phosphate sorption kinetics of iron-rich sediments (39–50% hematite and goethite) from an ephemeral stream in the arid Pilbara region of sub-tropical northwest Australia. While phosphate sorption in stream sediments is known to be strongly infuenced by sediment mineralogy as well as interactions with DOM, the mechanisms and signifcance of DOM on P-release from sediments with high sorption capacities, are largely undescribed. We assessed phosphorus (P) sorption behaviours by adding a range of solutions of known inorganic P concentrations that were amended with variable loadings of DOM derived from leachates of leaf litter to sediments from stream pools during the non-fowing phase. We compared the sorption capacity of the sediments and concurrent changes in DOM composition measured using fuorescence spectroscopy. We show that the low-dose DOM addition (~ 4 mg L−1 DOC) had the efect of reducing sediment P adsorption capacity, while for the high-dose DOM addition (~ 45 mg L−1 DOC), it was increased. The high-dose DOM was similar to pore water DOC and likely saturated sediment surface adsorption sites and produced P–OM–Fe complexes. This resulted in increased removal of P from solution. Sediment P sorption characteristics were well ftted to both Freundlich and Langmuir isotherm models regardless of DOC concentration. Langmuir P sorption maxima ranged from 0.106 to 0.152 mg g−1. General P sorption characteristics of these iron-rich sediments did not difer among pools of contrasting hydrological connectivity. Our results show how humic-rich DOM can modulate the sediment P availability in dryland streams. Unravelling the complexities of P availability is of particular significance to further our understanding of biogeochemical processes in aquatic ecosystems where P often acts as a limiting nutrient

Success in horizontal barrier developments

A successful proof of concept demonstration has been conducted of operational methods and tooling for the in situ construction of underground horizontal barriers for the control and containment of groundwater and contamination. The method involves jet grouting with specially adapted tools guided between twin, parallel wells for the placement of a grout beneath a waste site. The objective of the work is to develop reliable methods of constructing extensive, competent horizontal barriers underneath waste sites without excavating or penetrating the waste during the process

Medical student use of communication elements and association with patient satisfaction: a prospective observational pilot study

BACKGROUND: Effective communication with patients impacts clinical outcome and patient satisfaction. We measure the rate at which medical students use six targeted communication elements with patients and association of element use with patient satisfaction. METHODS: Participants included fourth year medical students enrolled in an emergency medicine clerkship. A trained observer measured use of six communication elements: acknowledging the patient by name, introducing themselves by name, identifying their role, explaining the care plan, explaining that multiple providers would see the patient, and providing an estimated duration of time in the emergency department. The observer then conducted a survey of patient satisfaction with the medical student encounter. RESULTS: A total of 246 encounters were documented among forty medical student participants. For the six communication elements evaluated, in 61% of encounters medical students acknowledged the patient, in 91% they introduced themselves, in 58 % they identified their role as a student, in 64% they explained the care plan, in 80% they explained that another provider would see the patient, and in only 6% they provided an estimated duration of care. Only 1 encounter (0.4%) contained all six elements. Patients' likelihood to refer a loved one to that ED was increased when students acknowledged the patient and described that other providers would be involved in patient care (P = 0.016 and 0.015 respectively, Chi Square). Likewise, patients' likelihood to return to the ED was increased when students described their role in patient care (P = 0.035, Chi Square). CONCLUSIONS: This pilot study demonstrates that medical students infrequently use all targeted communication elements. When they did use certain elements, patient satisfaction increased. These data imply potential benefit to additional training for students in patient communication