University of Saskatchewan

About: University of Saskatchewan is a education organization based out in Saskatoon, Saskatchewan, Canada. It is known for research contribution in the topics: Population & Health care. The organization has 25021 authors who have published 52579 publications receiving 1483049 citations. The organization is also known as: USask.

Increasing wildfires threaten historic carbon sink of boreal forest soils

Abstract: Boreal forest fires emit large amounts of carbon into the atmosphere primarily through the combustion of soil organic matter1–3. During each fire, a portion of this soil beneath the burned layer can escape combustion, leading to a net accumulation of carbon in forests over multiple fire events4. Climate warming and drying has led to more severe and frequent forest fires5–7, which threaten to shift the carbon balance of the boreal ecosystem from net accumulation to net loss1, resulting in a positive climate feedback8. This feedback will occur if organic-soil carbon that escaped burning in previous fires, termed ‘legacy carbon’, combusts. Here we use soil radiocarbon dating to quantitatively assess legacy carbon loss in the 2014 wildfires in the Northwest Territories of Canada2. We found no evidence for the combustion of legacy carbon in forests that were older than the historic fire-return interval of northwestern boreal forests9. In forests that were in dry landscapes and less than 60 years old at the time of the fire, legacy carbon that had escaped burning in the previous fire cycle was combusted. We estimate that 0.34 million hectares of young forests (<60 years) that burned in the 2014 fires could have experienced legacy carbon combustion. This implies a shift to a domain of carbon cycling in which these forests become a net source—instead of a sink—of carbon to the atmosphere over consecutive fires. As boreal wildfires continue to increase in size, frequency and intensity7, the area of young forests that experience legacy carbon combustion will probably increase and have a key role in shifting the boreal carbon balance. Soil radiocarbon dating reveals that combusted ‘legacy carbon’—soil carbon that escaped burning during previous fires—could shift the carbon balance of boreal ecosystems, resulting in a positive climate feedback.

Longitudinal links between childhood peer victimization, internalizing and externalizing problems, and academic functioning: Developmental cascades

Abstract: Developmental cascade models linking childhood peer victimization, internalizing and externalizing problems, and academic functioning were examined in a sample of 695 children assessed in Grade 3 (academic only) and Grades 5, 6, 7, and 8. Results revealed several complex patterns of associations in which poorer functioning in one domain influenced poorer outcomes in other areas. For example, a symptom driven pathway was consistently found with internalizing problems predicting future peer victimization. Support for an academic incompetence model was also found-- lower GPA in Grade 5, 6, and 7 was associated with more externalizing issues in the following year, and poor writing performance in Grade 3 predicted lower grades in Grade 5, which in turn predicted more externalizing problems in Grade 6. Results highlight the need to examine bidirectional influences and multifarious transactions that exist between peer victimization, mental health, and academic functioning over time.

SourcererCC: Scaling Code Clone Detection to Big Code

Abstract: Despite a decade of active research, there is a marked lack in clone detectors that scale to very large repositories of source code, in particular for detecting near-miss clones where significant editing activities may take place in the cloned code. We present SourcererCC, a token-based clone detector that targets three clone types, and exploits an index to achieve scalability to large inter-project repositories using a standard workstation. SourcererCC uses an optimized inverted-index to quickly query the potential clones of a given code block. Filtering heuristics based on token ordering are used to significantly reduce the size of the index, the number of code-block comparisons needed to detect the clones, as well as the number of required token-comparisons needed to judge a potential clone. We evaluate the scalability, execution time, recall and precision of SourcererCC, and compare it to four publicly available and state-of-the-art tools. To measure recall, we use two recent benchmarks, (1) a large benchmark of real clones, BigCloneBench, and (2) a Mutation/Injection-based framework of thousands of fine-grained artificial clones. We find SourcererCC has both high recall and precision, and is able to scale to a large inter-project repository (250MLOC) using a standard workstation.

An Oxygen and Hydrogen Isotope Study of the Skaergaard Intrusion and its Country Rocks: a Description of a 55 M.Y. Old Fossil Hydrothermal System

Abstract: Oxygen isotope analyses have been obtained on rocks and coexisting minerals, principally plagioclase and clinopyroxene, from about 400 samples of the Skaergaard layered gabbro intrusion and its country rocks. The δ^(18)O values of plagioclase decrease upward in the intrusion, from ‘normal’ values of about +6.0 to +6.4 in the Lower Zone and parts of the Middle Zone, to values as low as −2.4 in the Upper Border Group. The ^(18)O depletions of the plagioclase all took place under subsolidus conditions, and were produced by the Eocene meteoric-hydrothermal system established by this pluton. Clinopyroxene, which is more resistant to ^(18)O exchange than is plagioclase, also underwent depletion in ^(18)O, but to a lesser degree (δ^(18)O = +5.2 to +3.5). The ^(18)O-depleted rocks typically show reversed Δ^(18)Oplag−px fractionations, except at the top of the Upper Zone, where the pyroxenes are very fine-grained aggregates pseudomorphous after ferrowollastonite; these inverted pyroxenes were much more susceptible to subsolidus ^(18)O exchange (δ^(18)O = +3–9 to +0.7). D/H analyses of the chloritized basalt country rocks and of the minor quantities of alteration minerals in the pluton (δD = −116 to −149) confirm these interpretations, indicating that the rocks interacted with meteoric groundwaters having an original δD ≈ −100. and δ^(18)O ≈ −14. Low δD values (≈ −125) were also found throughout the biotites of the Precambrian basement gneiss, requiring that small amounts of water penetrated downward to depths of at least 6 to 10 km. These values, together with the lack of ^(18)O depletion of the gneiss, imply that the overall water/rock ratios were very small in that unit (<0.01), and thus that convective circulation of these waters was much more vigorous in the overlying highly jointed plateau basalts (δ^(18)O ≈ −4.0 to +4–0) than in the relatively impermeable gneiss (δ^(18)O ≈ +7–3 to +7–7). This contrast in permeabilities of the country rocks is also reflected in the distribution of δ^(18)O values in the pluton; the plagioclases with ‘normal’ δ^(18)O values all lie stratigraphically beneath the projection of the basalt-gneiss unconformity through the pluton. Elsewhere, the ^(18)O depletions are correlated with abundance of fractures and faults, particularly in the NE portion of the intrusion, where the Layered Series is very shallow-dipping and permeable basalts underlie the gabbro. The transgressive granophyres in the lower part of the intrusive have δ^(18)O values identical to those of the basement gneiss, indicating they were probably formed by partial melting of stoped blocks of gneiss. In the upper part of the intrusion these granophyre dikes have δ^(18)O values similar to the adjacent host gabbro; this suggests that much of the hydrothermal alteration occurred after their emplacement. However, because of the rarity of low-temperature hydrous alteration minerals, it is also clear that most of the influx of H_2O into the layered gabbro occurred at very high temperatures (>400–500 °C). Prior to flowing into the gabbro, these fluids had exchanged with similar mineral assemblages in the basaltic country rocks, explaining the lack of chemical alteration of the gabbro. Xenoliths of roof rock basalt and of Upper Border Group leucogabbro were strongly depleted in ^(18)O by the hydrothermal system prior to their falling to the bottom of the magma chamber and being incorporated in the layered series. This proves that the hydrothermal system was established very early, at the time of emplacement of the Skaergaard intrusion. However, no measurable ^(18)O depletion of the gabbro magma could be detected, indicating that very little H_2O penetrated directly into the liquid magma, in spite of the fact that a hydrothermal circulation system totally enveloped the magma chamber for at least 100,000 years during its entire period of crystallization. Only as crystallization proceeded was the hydrothermal system able to collapse inward and interact with the solidified and fractured portions of the gabbro. Nevertheless some H_2O was clearly added directly to the magma by dehydration of the stoped blocks of altered roof rock. It is also plausible that small amounts of meteoric water diffused directly into the magma, most logically in the vicinity of major fracture zones that penetrated close to, or were underneath, the late-stage sheet of differentiated ferrodiorite magma. It is suggested that such influx of meteoric waters was responsible for many of the gabbro pegmatite bodies that are common in the Marginal Border Group; also, such H_2O might have produced local increases in Fe^(+3)/Fe^(+2) in the magma that in turn could explain some of the asymmetric crystallization effects in the magma chamber. Local lowering of the liquidus temperature would also occur, perhaps leading to topographic irregularities on the floor of the magma chamber (e.g. the trough bands?).

Microclimate of tree cavity nests: is it important for reproductive success in northern flickers?

Abstract: I measured structural characteristics of 160 Northern Flicker (Colaptes auratus) nests at Riske Creek, British Columbia, and placed electronic data-loggers in a subsample of 86 nests to record internal temperatures after the flickers completed nesting. Using multiple regression, I found that the best predictors of a variety of nest-cavity temperature variables were tree health, diameter of the tree at cavity height, and orientation of the cavity. Small and dead trees showed the most extreme (maximum and minimum) temperatures during the day, but, on average, were the coldest nests from the perspective of incubation. South-facing cavities reached the highest temperatures during the day, and the orientation of natural cavities was also biased towards the south. I predicted that cold nests would be energetically expensive for adults and nestlings, and found that clutch size was positively correlated with mean cavity temperature. However, there did not appear to be any relationship among nest temperat...