title: Association of arsenic and phosphorus with iron nanoparticles between streams and aquifers: Implications for arsenic mobility

authors: Hartland, Adam

subjects: Science & Technology

abstract: The microbial oxidation of organic matter coupled to reductive iron oxide dissolution is widely recognized as the dominant mechanism driving elevated arsenic (As) concentrations in aquifers. This paper considers the potential of nanoparticles to increase the mobility of As in aquifers, thereby accounting for discrepancies between predicted and observed As transport reported elsewhere. Arsenic, phosphorus, and iron size distributions and natural organic matter association were examined along a flow path from surface water via the hyporheic zone to shallow groundwater. Our analysis demonstrates that the colloidal Fe concentration (>1 kDa) correlates with both colloidal P and colloidal As concentrations. Importantly, increases in the concentration of colloidal P (>1 kDa) were positively correlated with increases in the concentration of nominally dissolved As (<1 kDa), but no correlation was observed between colloidal As and nominally dissolved P. This suggests that P actively competes for adsorption sites on Fe nanoparticles, displacing adsorbed As, thus mirroring their interaction with Fe oxides in the aquifer matrix. Dynamic redox fronts at the interface between streams and aquifers may therefore provide globally widespread conditions for the generation of Fe nanoparticles, a mobile phase for As adsorption currently not a part of reactive transport models.

text: Association of arsenic and phosphorus with iron nanoparticles between streams and aquifers: Implications for arsenic mobility The microbial oxidation of organic matter coupled to reductive iron oxide dissolution is widely recognized as the dominant mechanism driving elevated arsenic (As) concentrations in aquifers. This paper considers the potential of nanoparticles to increase the mobility of As in aquifers, thereby accounting for discrepancies between predicted and observed As transport reported elsewhere. Arsenic, phosphorus, and iron size distributions and natural organic matter association were examined along a flow path from surface water via the hyporheic zone to shallow groundwater. Our analysis demonstrates that the colloidal Fe concentration (>1 kDa) correlates with both colloidal P and colloidal As concentrations. Importantly, increases in the concentration of colloidal P (>1 kDa) were positively correlated with increases in the concentration of nominally dissolved As (<1 kDa), but no correlation was observed between colloidal As and nominally dissolved P. This suggests that P actively competes for adsorption sites on Fe nanoparticles, displacing adsorbed As, thus mirroring their interaction with Fe oxides in the aquifer matrix. Dynamic redox fronts at the interface between streams and aquifers may therefore provide globally widespread conditions for the generation of Fe nanoparticles, a mobile phase for As adsorption currently not a part of reactive transport models.

year: 2015

title: Speed regulation of model railway controllers: A comparison of technologies

authors: Scott, Jonathan B.

abstract: In this manuscript the relative performance of a variety of model railway controllers is tested in real-world conditions. Model railway locomotives use permanent-magnet, brushed, dc motors. Series resistance in armature windings, brushes and the rail, and magnetic losses in the armature all contribute to non-ideal operation. This manifests most annoyingly as moment by moment variation in locomotive speed. The effect is more noticeable in smaller scales. It is more noticeable on vintage models. Speed regulation performance is compared for a number different controllers using different technologies. Some interesting conclusions are drawn.

text: Speed regulation of model railway controllers: A comparison of technologies In this manuscript the relative performance of a variety of model railway controllers is tested in real-world conditions. Model railway locomotives use permanent-magnet, brushed, dc motors. Series resistance in armature windings, brushes and the rail, and magnetic losses in the armature all contribute to non-ideal operation. This manifests most annoyingly as moment by moment variation in locomotive speed. The effect is more noticeable in smaller scales. It is more noticeable on vintage models. Speed regulation performance is compared for a number different controllers using different technologies. Some interesting conclusions are drawn.

year: 2021

title: Analysing A/O possession in Māori-language tweets

authors: Trye, David

subjects: A/O categories

abstract: This article contributes the first corpus-based study of possession in Māori, the indigenous language of Aotearoa New Zealand. Like most Polynesian languages, Māori has a dual possessive system involving a choice between the so-called A and O categories. While Māori grammars describe these categories in terms of the inherent semantic relationship between the possessum and possessor, there have been no large-scale corpus analyses demonstrating their use in natural contexts. Social media provide invaluable opportunities for such linguistic studies, capturing contemporary language use while alleviating the burden of gathering data through traditional means. We operationalise semantic distinctions to investigate possession in Māori-language tweets, focusing on the [possessum a/o possessor] construction (e.g., te tīmatanga o te wiki ‘the beginning of the week’). In our corpus comprising 2500 tweets produced by more than 200 individuals, we find that users leverage a wide array of noun types encompassing many different semantic relationships. We observe not only the expected predominance of the O category, but also a tendency for examples described by Māori grammars as A-marked to instead be O-marked (59%). Although the A category persists in the corpus, our findings suggest that language change could be underway. Our primary dataset can be explored interactively online.

text: Analysing A/O possession in Māori-language tweets This article contributes the first corpus-based study of possession in Māori, the indigenous language of Aotearoa New Zealand. Like most Polynesian languages, Māori has a dual possessive system involving a choice between the so-called A and O categories. While Māori grammars describe these categories in terms of the inherent semantic relationship between the possessum and possessor, there have been no large-scale corpus analyses demonstrating their use in natural contexts. Social media provide invaluable opportunities for such linguistic studies, capturing contemporary language use while alleviating the burden of gathering data through traditional means. We operationalise semantic distinctions to investigate possession in Māori-language tweets, focusing on the [possessum a/o possessor] construction (e.g., te tīmatanga o te wiki ‘the beginning of the week’). In our corpus comprising 2500 tweets produced by more than 200 individuals, we find that users leverage a wide array of noun types encompassing many different semantic relationships. We observe not only the expected predominance of the O category, but also a tendency for examples described by Māori grammars as A-marked to instead be O-marked (59%). Although the A category persists in the corpus, our findings suggest that language change could be underway. Our primary dataset can be explored interactively online.

year: 2024