The soluble ion content of the active layer and near-surface permafrost was determined at 41 sites in the Mackenzie delta region, Northwest Territories, Canada. In delta soils, Ca2+ and Mg2+ are the ...dominant soluble cations, but the quantity and relative abundance of Na+ increase with proximity to the Beaufort Sea coast. Soils beneath frequently flooded surfaces are ion rich in comparison with ground above the level of decadal flooding. Within a terrain type, near-surface permafrost soil solute concentrations are similar between paired cores spaced <1 m apart, but at greater distances (cores spaced 3-13 m apart), solute concentrations are significantly different. Comparatively low soil solute concentrations in old upland surfaces near Inuvik may be a result of progressive removal of soluble materials from the active layer and permafrost during periods of deeper thaw. In sandy silt alluvium, solutes excluded during downward freezing may accumulate at the base of the active layer and be sequestered by a rising permafrost table. At sites with finer grained clayey silts, the correspondence between zones of ice and cation enrichment indicates coupled movement of water and solutes during freeze-back of the active layer and development of aggradational ice. Solute enrichment of near-surface permafrost is greatest at fine-grained ice-rich alluvial sites, where mean concentrations in permafrost are up to 7.5 times greater than those in the active layer.
Air and near-surface ground temperatures, late-winter snow conditions, and characteristics of the vegetation cover and soil were measured across the forest-tundra transition in the uplands east of ...the Mackenzie Delta, Northwest Territories, in 2004-2010. Mean late-winter snow depth decreased northward from 73 cm in the subarctic boreal forest near Inuvik to 22 cm in low-shrub tundra. Annual near-surface ground temperatures decreased northward by 0.1-0.3°C/km near the northern limit of trees, in association with an abrupt change in snow depth. The rate decreased to 0.01-0.06°C/km in the tundra. The freezing season is twice as long as the thawing season in the region, so measured differences in the regional ground thermal regime were dominated by the contrast in winter surface conditions between forest and tundra.
To assess prostate magnetic resonance imaging (MRI) image quality and compliance with technical standards between centres in the South West region of the UK.
Fifteen imaging sites in the region ...submitted seven consecutive anonymised MRI studies. These were assessed by two experienced radiologists in consensus. Overall, subjective image quality for T2-weighted imaging (T2W), diffusion weighted imaging (DWI), and dynamic contrast enhancement (DCE) was scored on a five-point Likert scale. Five additional quality parameters were also assessed visually, including image noise, motion, artefact, and distortion. The degree of compliance by each site with 21 published technical standards was also assessed.
Ninety-four MRI examinations were reviewed from across all sites (mean 6.3 scans per site, range 5–7). Mean compliance with technical standards was 63% (range 38–86%). Forty-seven percent of sites did not perform DCE. One site used a 3 T scanner. The percentage of patients with overall quality scores of ≥3 (diagnostically acceptable) were 68% for T2W, 81% for DWI, and 60% for both T2W and DWI. Ninety-three percent of the 45 patients who underwent DCE had diagnostically acceptable studies. By scanner age, the percentage of patients with diagnostically acceptable T2W scores was 53% for scanners ≥7 years and 80% when <7 years (p=0.006). Comparing individual sites, the mean overall quality scores were 2.9 (range 2.2–4.2) for T2W, 3.2 (1.8–4.7) for DWI, and 3.4 (2.5–4.7) for DCE.
There is wide variation in compliance with recognised technical standards and image quality across sites. If MRI is to replace biopsy in selected low-risk patients, improvements in image quality may be required.
•There was a large variation in image quality and guideline compliance between sites.•40% of patients had non-diagnostic quality scans.•Scanner age inversely correlated with T2W image quality.•DCE scored highest for image quality, but was only used in 53% of sites.•Image quality needs optimization if MRI is used to rule out cancer or avoid biopsy.
The Arctic Circle, an open club founded to bring together friends interested in all aspects of the North, celebrated its 500th meeting on Apr 8, 2014. The Circle, conceived on Oct 30, 1947, was the ...brain-child of Graham and Diana Rowley and Tom and Jackie Manning, who recognized the need in Ottawa for an informal but regular gathering of people interested in the Arctic. At the time, these people were almost all working for departments and agencies of the federal government, but in an institution notorious for its silos, many were unaware of each other's work, interests, plans, and ideas. For each of its subsequent 67 years, the Circle has met regularly between October and early May, and since 1959 there has been a splendid Annual Dinner. The venues have moved around town-at one point the sofas were so comfortable people complained they could not stay awake during the talks and the meetings should therefore be moved.
To evaluate the magnetic resonance (MR) imaging appearances of uterine fibroleiomyoma before and after embolization and to determine whether there are preembolization MR imaging characteristics that ...are predictive of a successful outcome.
MR imaging was performed in 18 patients (32 fibroleiomyomas) before and at 2 and 6 months after embolization of the uterine arteries. On each occasion, fibroleiomyoma signal intensity and gadolinium enhancement characteristics were assessed in comparison with those of myometrium on T1-weighted and gadolinium-enhanced images or with those of skeletal muscle on T2-weighted images. Fibroleiomyoma volume was measured by using the ellipsoid formula.
The mean fibroleiomyoma volume before embolization was 340 cm3 (range, 15-1,383 cm3). The mean reduction in fibroleiomyoma volume was 43% at 2 months and 59% at 6 months. Before embolization, high signal intensity on T1-weighted images was predictive of a poor response (P = .008), and high signal intensity on T2-weighted images was predictive of a good response (P = .007). The degree of gadolinium enhancement was not correlated with fibroleiomyoma volume reduction (P = .46).
MR imaging was useful for evaluation of changes in fibroleiomyoma volume after uterine arterial embolization. MR imaging characteristics of fibroleiomyomas before embolization can help predict subsequent response to treatment.
Context.
Previous theoretical works on planet formation around low-mass stars have often been limited to large planets and individual systems. As current surveys routinely detect planets down to ...terrestrial size in these systems, models have shifted toward a more holistic approach that reflects their diverse architectures.
Aims.
Here, we investigate planet formation around low-mass stars and identify differences in the statistical distribution of modeled planets. We compare the synthetic planet populations to observed exoplanets and we discuss the identified trends.
Methods.
We used the Generation III Bern global model of planet formation and evolution to calculate synthetic populations, while varying the central star from Solar-like stars to ultra-late M dwarfs. This model includes planetary migration,
N
-body interactions between embryos, accretion of planetesimals and gas, and the long-term contraction and loss of the gaseous atmospheres.
Results.
We find that temperate, Earth-sized planets are most frequent around early M dwarfs (0.3
M
⊙
–0.5
M
⊙
) and that they are more rare for Solar-type stars and late M dwarfs. The planetary mass distribution does not linearly scale with the disk mass. The reason behind this is attributed to the emergence of giant planets for
M
⋆
≥ 0.5
M
⊙
, which leads to the ejection of smaller planets. Given a linear scaling of the disk mass with stellar mass, the formation of Earth-like planets is limited by the available amount of solids for ultra-late M dwarfs. For
M
⋆
≥ 0.3
M
⊙
, however, there is sufficient mass in the majority of systems, leading to a similar amount of Exo-Earths going from M to G dwarfs. In contrast, the number of super-Earths and larger planets increases monotonically with stellar mass. We further identify a regime of disk parameters that reproduces observed M-dwarf systems such as TRAPPIST-1. However, giant planets around late M dwarfs, such as GJ 3512b, only form when type I migration is substantially reduced.
Conclusions.
We are able to quantify the stellar mass dependence of multi-planet systems using global simulations of planet formation and evolution. The results fare well in comparison to current observational data and predict trends that can be tested with future observations.
Remote sensing, regional ground temperature and ground ice observations, and numerical simulation were used to investigate the size, distribution, and activity of ice wedges in fine‐grained mineral ...and organic soils across the forest‐tundra transition in uplands east of the Mackenzie Delta. In the northernmost dwarf‐shrub tundra, ice wedge polygons cover up to 40% of the ground surface, with the wedges commonly exceeding 3 m in width. The largest ice wedges are in peatlands where thermal contraction cracking occurs more frequently than in nearby hummocky terrain with fine‐grained soils. There are fewer ice wedges, rarely exceeding 2 m in width, in uplands to the south and none have been found in mineral soils of the tall‐shrub tundra, although active ice wedges are found there throughout peatlands. In the spruce forest zone, small, relict ice wedges are restricted to peatlands. At tundra sites, winter temperatures at the top of permafrost are lower in organic than mineral soils because of the shallow permafrost table, occurrence of phase change at 0°C, and the relatively high thermal conductivity of icy peat. Due to these factors and the high coefficient of thermal contraction of frozen saturated peat, ice wedge cracking and growth is more common in peatlands than in mineral soil. However, the high latent heat content of saturated organic active layer soils may inhibit freezeback, particularly where thick snow accumulates, making the permafrost and the ice wedges in spruce forest polygonal peatlands susceptible to degradation following alteration of drainage or climate warming.
Key Points
Density and size of ice wedges increase northward across tree lineProperties of organic soils favor ice wedge developmentMoisture has contrasting effect on thermal regime of peat across tree line
Burn presents an obituary for Diana Mary Rustat Rowley, founder of the Arctic Circle Club, who died on September 2018 at the age of 100. Rowley edited the journal Arctic for the Arctic Institute of ...North America from 1949 to 1955, at a time when Arctic research was evolving from its pre-war expeditionary modus operandi to more consistent programs facilitated by post-war logistics.
Low‐centered ice wedge polygons in the Big Lake Delta Plain of the outer Mackenzie Delta are unusual because their bounding ramparts appear to have a single ridge. Twenty‐two ice wedges in the area ...were examined between 2006 and 2009 to describe their morphology and diagnose their growth processes. The ground above ice wedges had a subtle microtopography, with ridges of 0.12 m relief and 4.0 m total width, bisected by troughs only 0.05 m wide and 0.09 m deep. The troughs, initially obscured by vegetation growth and organic matter, were underlain by ice wedges with average widths that increased downward in the uppermost 1 m of permafrost from 0.03 to 0.95 m. “Shoulders” on the ice wedges indicated vertical growth stages. Temperatures near the top of permafrost were favorable to thermal‐contraction cracking, and ice veins connected to the top of wedge ice were observed in the active layer at five sites. These observations indicate the ice wedges are syngenetic and active, although without dating control, we cannot unequivocally dismiss the possibility that the wedges are epigenetic features that were truncated by a recent thaw unconformity. Muted relief above the ice wedges, which is uncommon above epigenetic ice wedges, was largely due to aggradation of the surface. Secondary ice wedges have not developed within the polygons, suggesting that climate variability has not led to polygon network development in this area. Wedge ice occupied only about 1.5% of the uppermost 1 m of permafrost, a much smaller volumetric proportion than in epigenetic settings.
Key Points
Syngenetic ice wedges are well developed in the outer Mackenzie Delta
Surficial relief above ice wedges is muted in this sedimentary environment
The environmental setting has prevented the evolution of secondary ice wedges
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