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Now showing 1 - 5 of 1811
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    Open Access
    Efficient Bounded Timestamping from Standard Synchronization Primitives
    (2023) Bashari, Benyamin; Jamadi, Ali; Woelfel, Philipp
    Bounded timestamps [9, 19 ] allow a temporal ordering of events in executions of concurrent algorithms. They are a fundamental and well studied building block used in many shared memory algorithms. A concurrent timestamp system keeps track of 𝑚 timestamps, which is usually greater or equal to the number of processes in the system, 𝑛. A process may, at any point, obtain a new timestamp, and later determine a total order of all process’s most recent timestamps. Known timestamp algorithms do not scale well in the number of processes. Getting a new timestamp takes at least a linear number of steps, and a lower bound by Israeli and Li [ 19 ] implies that each timestamp needs to be represented by at least Ω(𝑚) bits. We introduce a slightly different semantics for timestamping, where there is no fixed timestamp value associated with an event. A process can execute operation updateTS() to update its latest timestamp, associating it with the (linearization) point of that operation, and is Earlier (𝑝,𝑞) to determine the temporal order of the latest updateTS() operations executed by processes 𝑝 and 𝑞. Since no static timestamp value is returned by update TS(), the lower bound of Israeli and Li does not apply. We present efficient linearizable and wait-free implementations of these methods using a single bounded fetch-and-add object and 𝑂 (𝑛²) bounded compare-and-swap objects, which are available on standard hardware. The step complexity of each method call is constant, and base objects need only store 𝑂 (log 𝑛) bits.
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    Open Access
    Insects of Alberta - Interactive Identification Guide To Common Orders
    (2023-05-02) Seal, Michaela; Duclos, Kevin; Summers, Mindi; Carson, Arminty
    An interactive guide to insect orders found in Alberta based on and modified from the Entomological Society of Alberta’s “The Insect Collector’s Guide.” This guide was created for undergraduate students and those new to insect identification. Visual images, 3D models, and annotated descriptions are provided for key features and terminology needed to identify insects to order. We welcome recommendations for additions and updates from the entomological community.
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    Open Access
    Influence of saline groundwater discharge on river water chemistry in the Athabasca oil sands region – A chloride stable isotope and mass balance approach
    (Elsevier, 2017-12-01) Gue, Anita; Grasby, Stephen E.; Mayer, Bernhard
    A chloride mass and stable isotope (δ37Cl) balance approach was employed to calculate the effect of saline groundwater discharge into the Athabasca and Clearwater rivers in the Athabasca Oil Sands Region (AOSR) in north-eastern Alberta, Canada. Saline groundwater affected by halite, carbonate, and anhydrite dissolution discharges Na-Cl type water with total dissolved solids (TDS) up to 51,700 mg/L from exposed Devonian and Cretaceous units in the river valleys in this area. In this study, nine springs discharging groundwater with a median Cl concentration of 9800 mg/L were sampled and chloride stable isotope ratios were determined, with δ37Cl values ranging from 0.2 to 1.0‰. In contrast, river waters had historical monthly median Cl concentrations between 5.9 and 49.5 mg/L and δ37Cl values between −2.2 and −1.4‰. The discharge rate of saline groundwater was calculated to be 100 ± 20 L/s into the Clearwater River and 134 ± 68 L/s into the Athabasca River. The chemical composition and discharge rates of saline groundwater were used to estimate its contribution to the mass fluxes of major ions, metals, and PAHs in the Athabasca and Clearwater rivers. Overall, saline groundwater contributed less than 0.2% of river discharge, but 0.04–39% of major ion concentrations in the rivers, with highest contributions under winter low-flow conditions. In the Clearwater River, saline groundwater contributed 23–39% of average monthly Cl flux and 18–32% of average monthly Na flux. For the same major ion fluxes in the Athabasca River, saline groundwater contributed 12–18% and 6–12%, respectively. The influence of saline groundwater discharge on the mass flux of trace elements in the rivers was found to be negligible, contributing less than 1% of river fluxes of Cu, Ni, Pb, and Zn. Similarly, the influence on mass flux of PAHs in the rivers was found to be negligible (<0.03%) but quantifiable. These results provide important insights on the natural contributions of saline groundwater discharge to river chemistry in the AOSR, a necessary factor to consider when monitoring for anthropogenic effects of oil sands development on river water quality.
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    Water-rock interactions and self-remediation: Lessons from a hydraulic fracturing operation in the Vaca Muerta formation, Argentina
    (Elsevier, 2023-02-01) Osselin, F.; Gaucher, E.; Baldony-Andrey, P.; Kloppmann, W.; Mayer, Bernhard
    In order to analyze the effect of a new gelling agent for hydraulic fracturing, fluid samples from different stages of the operation (hydraulic fracturing fluid, coil tubing, flowback and produced waters) were collected from a well in the Vaca Muerta formation in Argentina. Collected samples were analyzed for major and trace elements, first within a few days after sampling, then reanalyzed 6 months later and again 2 years after sampling. Results show that the salinity of samples increased quickly with time, from 2000 mg/L up to 43,000 mg/l a month later, due to the mixing of hydraulic fracturing fluids with formation water. No evidence of water-rock reactions was observed. Results from the later analyses showed that the composition of the samples evolved with time with a sensible decrease of concentration for most trace elements over the course of these two years (e.g. Ba from 137 mg/L to 55 mg/L, Mn from 8 mg/L to 5 mg/L) and heavy metals (e.g. As /L to 1 f/L, Co /L to /L, Cr from /L to /L). Interpretation of the results shows that delayed, post-sampling, precipitation of barite in the preserved samples is the reason for such a decrease. This opens a very interesting option for mitigation and remediation of wastewaters from hydraulic fracturing as natural or even triggered precipitation of barite could involve most of the dissolved heavy metals and decrease strongly their concentrations.