Two hundred years ago, Ampère discovered that electric loops in which currents of electrons are generated by a penetrating magnetic field can mutually interact. Here we show that Ampère's observation ...can be transferred to the quantum realm of interactions between triangular plaquettes of spins on a lattice, where the electrical currents at the atomic scale are associated with the orbital motion of electrons in response to the non-coplanarity of neighbouring spins playing the role of a magnetic field. The resulting topological orbital moment underlies the relation of the orbital dynamics with the topology of the spin structure. We demonstrate that the interactions of the topological orbital moments with each other and with the spins form a new class of magnetic interactions Formula: see text topological-chiral interactions Formula: see text which can dominate over the Dzyaloshinskii-Moriya interaction, thus opening a path for realizing new classes of chiral magnetic materials with three-dimensional magnetization textures such as hopfions.
Abstract
Thermokarst lakes accelerate deep permafrost thaw and the mobilization of previously frozen soil organic carbon. This leads to microbial decomposition and large releases of carbon dioxide ...(CO
2
) and methane (CH
4
) that enhance climate warming. However, the time scale of permafrost-carbon emissions following thaw is not well known but is important for understanding how abrupt permafrost thaw impacts climate feedback. We combined field measurements and radiocarbon dating of CH
4
ebullition with (a) an assessment of lake area changes delineated from high-resolution (1–2.5 m) optical imagery and (b) geophysical measurements of thaw bulbs (taliks) to determine the spatiotemporal dynamics of hotspot-seep CH
4
ebullition in interior Alaska thermokarst lakes. Hotspot seeps are characterized as point-sources of high ebullition that release
14
C-depleted CH
4
from deep (up to tens of meters) within lake thaw bulbs year-round. Thermokarst lakes, initiated by a variety of factors, doubled in number and increased 37.5% in area from 1949 to 2009 as climate warmed. Approximately 80% of contemporary CH
4
hotspot seeps were associated with this recent thermokarst activity, occurring where 60 years of abrupt thaw took place as a result of new and expanded lake areas. Hotspot occurrence diminished with distance from thermokarst lake margins. We attribute older
14
C ages of CH
4
released from hotspot seeps in older, expanding thermokarst lakes (
14
C
CH4
20 079 ± 1227 years BP, mean ± standard error (s.e.m.) years) to deeper taliks (thaw bulbs) compared to younger
14
C
CH4
in new lakes (
14
C
CH4
8526 ± 741 years BP) with shallower taliks. We find that smaller, non-hotspot ebullition seeps have younger
14
C ages (expanding lakes 7473 ± 1762 years; new lakes 4742 ± 803 years) and that their emissions span a larger historic range. These observations provide a first-order constraint on the magnitude and decadal-scale duration of CH
4
-hotspot seep emissions following formation of thermokarst lakes as climate warms.
Background We sought to measure frequency of achieving an optimal outcome after stage 1 palliation (S1P) for hypoplastic left heart syndrome and variants, determine factors associated with optimal ...outcomes, and compare outcomes after stage 2 palliation (S2P) using the National Pediatric Cardiology Quality Improvement Collaborative database (2008–2016). Methods and Results This is a retrospective cohort study with optimal outcome defined a priori as meeting all of the following: (1) discharge after S1P in <19 days (top quartile), (2) no red flag or major event readmissions before S2P, and (3) performing S2P between 90 and 240 days of age. Optimal outcome was achieved in 256 of 2182 patients (11.7%). Frequency varied among centers from 0% to 25%. Factors independently associated with an optimal outcome after S1P were higher gestational age (odds ratio OR, 1.1 per week 95% CI, 1.0–1.2; P =0.02); absence of a genetic syndrome (OR, 2.5 95% CI, 1.2–5; P =0.02); not requiring a post‐S1P catheterization (OR, 2.7 95% CI, 1.5–4.8; P =0.01), intervention (OR, 1.5 95% CI, 1.1–2; P =0.006), or a procedure (OR, 4.5 95% CI, 2.8–7.1; P <0.001) before discharge; and not having a post‐S1P complication (OR, 2.7 95% CI, 1.9–3.7; P <0.001). Those with an optimal outcome after S1P had improved S2P outcomes including shorter length of stay, less ventilator days, shorter bypass time, and fewer postoperative complications. Conclusions Identifying patients at lowest risk for poor outcomes during the home interstage period could shift necessary resources to those at higher risk, alter S2P postoperative expectations, and improve quality of life for families at lower risk.
Methane (CH4) emissions from climate‐sensitive ecosystems within the northern permafrost region represent a potentially large but highly uncertain source, with current estimates spanning a factor of ...seven (11–75 Tg CH4 yr−1). Accelerating permafrost thaw threatens significant increases in pan‐Arctic CH4 emissions, amplifying the permafrost carbon feedback. We used airborne imaging spectroscopy with meter‐scale spatial resolution and broad coverage to identify a previously undiscovered CH4 emission hotspot adjacent to a thermokarst lake in interior Alaska. Hotspot emissions were confined to <1% of the 10 ha lake study area. Ground‐based chamber measurements confirmed average daily fluxes from the hotspot of 1,170 mg CH4 m−2 d−1, with extreme daily maxima up to 24,200 mg CH4 m−2 d−1. Ground‐based geophysical measurements revealed thawed permafrost directly beneath the CH4 hotspot, extending to a depth of ∼15 m, indicating that the intense CH4 emissions likely originated from recently thawed permafrost. Hotspot emissions accounted for ∼40% of total diffusive CH4 emissions from the lake study site. Combining study site findings with hotspot statistics from our 70,000 km2 airborne survey across Alaska and northwestern Canada, we estimate that pan‐Arctic terrestrial thermokarst hotspots currently emit 1.1 (0.1–5.2) Tg CH4 yr−1, or roughly 4% of the annual pan‐Arctic wetland budget from just 0.01% of the northern permafrost land area. Our results suggest that significant proportions of pan‐Arctic CH4 emissions originate from disproportionately small areas of previously undetermined thermokarst emissions hotspots, and that pan‐Arctic CH4 emissions may increase non‐linearly as thermokarst processes increase under a warming climate.
Plain Language Summary
We conducted high‐resolution airborne surveys of near‐surface methane (CH4, a powerful greenhouse gas) anomalies in permafrost ecosystems in Alaska and northwestern Canada as part of NASA's Arctic Boreal Vulnerability Experiment (ABoVE). These measurements provided fine‐scale resolution for the remote detection of CH4 emission hotspots from natural Arctic environments. Repeated flights over Big Trail Lake near Fairbanks, AK revealed a previously undiscovered CH4 hotspot at this intensive study site. Ground‐based measurements confirmed extremely high surface‐to‐atmosphere emissions at this location, on the shore of a permafrost‐thaw pond that formed after 1963. Geophysical surveys confirmed the presence of thawed permafrost underneath the hotspot, extending to a depth ∼15 m. We hypothesize that recent permafrost thaw and subsidence made soils with highly decomposable organic carbon available for microbial metabolism, conversion into CH4, and enhanced emission to the atmosphere. Extrapolating our observed hotspot fluxes across the pan‐Arctic, we estimate that thermokarst CH4 hotspots constitute less than 0.01% of the pan‐Arctic land area, but contribute roughly 4% of annual pan‐Arctic wetland emissions. We further hypothesize that Arctic CH4 emissions may grow significantly in the future with anticipated increases in thermokarst across the permafrost landscape.
Key Points
Repeat airborne spectral imaging geolocated a thermokarst methane (CH4) hotspot with ground‐validated emissions >10 g CH4 m−2 d−1
Hotspot CH4 emissions arose from <1% of our 10 ha thermokarst lake study area but comprised ∼40% of the total diffusive emissions
Ground‐based and airborne observations suggest thermokarst hotspots emit roughly 1.1 Tg CH4 yr−1 or 4% of pan‐Arctic wetland CH4 emissions
Reported long-term outcome measures vary greatly between studies in Fontan patients making comprehensive appraisal of mortality hazard challenging. We sought to create a clinical risk score to assist ...monitoring of Fontan patients in the outpatient setting.
A systematic review was conducted to evaluate risk factors for long-term (beyond the first postoperative year) mortality in Fontan patients. Studies were eligible for inclusion if ≥90 patients were included or ≥20 long-term mortalities we reported. Risk factors for long-term mortality were determined. The pooled hazard ratios were used to create components of a clinical score for long-term mortality using meta-analysis techniques.
Twenty-eight studies were included. The total number of patients was 6707 with an average follow-up of 8.23 ± 5.42 years. There were 1000 deaths. Thirty-five risk factors for late mortality were identified and classified into 9 categories and their relative hazards were used to derive the initial components of a weighted, practical and clinically based Fontan risk score (ranging from 0 to 100). The final score included 8 risk factors: anatomic risk factors, elevated preoperative pulmonary artery pressure, atriopulmonary Fontan, heart failure symptoms, arrhythmia, moderate/severe ventricular dysfunction or atrioventricular valve regurgitation, protein losing enteropathy, and end organ disease (cirrhosis or renal insufficiency).
In patients with Fontan circulation, the influence of readily available risk factors can be quantified in an integer score to predict long-term mortality. Prospective validation and refinement of this risk score will be undertaken.
Background The routine use of angiotensin-converting enzyme inhibitors (ACEI) during palliation of hypoplastic left heart syndrome is controversial. We sought to describe ACEI prescription in the ...interstage between stage 1 palliation (stage I Norwood procedure) discharge and stage 2 palliation (stage II superior cavopulmonary anastomosis procedure) admission using the NPC-QIC (National Pediatric Cardiology Quality Improvement Collaborative) registry. Methods and Results Analysis of all patients (n=2180) enrolled in NPC-QIC from 2008 to 2016 included preoperative anatomy, risk factors, and echocardiographic data. ACEI were prescribed at stage I Norwood procedure discharge in 38% of patients. ACEI prescription declined from 2011 to 2016 compared with pre-2010 (36.8% versus 45%;
=0.005) with significant variation across centers (range 7-100%;
<0.001) and decreased prescribing rates associated with increased center volume (
=0.004). There was no difference in interstage mortality (
=0.662), change in atrioventricular valve regurgitation (
=0.101), or change in ventricular dysfunction (
=0.134) between groups. In multivariable analysis of all patients, atrioventricular septal defect (odds ratio OR, 1.84; 95% CI, 1.28-2.65) or double outlet right ventricle (OR, 1.47; CI, 1.02-2.11), and preoperative mechanical ventilation (OR, 1.37; 95% CI, 1.12-1.68) were associated with increased ACEI prescription. In multivariable analysis of patients with complete echocardiographic data (n=812), ACEI prescription was more common with at least moderate atrioventricular valve regurgitation (OR, 1.88; 95% CI, 1.22-2.31). Conclusions ACEI prescription remains common in the interstage despite limited evidence of benefit. ACEI prescription is associated with preoperative mechanical ventilation, double outlet right ventricle, and atrioventricular valve regurgitation with marked inter-center variation. ACEI prescription is not associated with reduction in mortality, ventricular dysfunction, or atrioventricular valve regurgitation during the interstage.
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