Gas diffusivity and permeability through the firn column at Summit, Greenland: measurements and comparison to microstructural properties

The physical structure of polar firn plays a key role in the mechanisms by which glaciers and ice sheets preserve a natural archive of past atmospheric composition. This study presents the first measurements of gas diffusivity and permeability along with microstructural information measured from the near-surface firn through the firn column to pore close-off. Both fine- and coarse-grained firn from Summit, Greenland are included in this study to investigate the variability in firn caused by seasonal and storm-event layering. Our measurements reveal that the porosity of firn (derived from density) is insufficient to describe the full profiles of diffusivity and permeability, particularly at porosity values above 0.5. Thus, even a model that could perfectly predict the density profile would be insufficient for application to issues involving gas transport. The measured diffusivity profile presented here is compared to two diffusivity profiles modeled from firn air measurements from Summit. Because of differences in scale and in firn processes between the true field situation, firn modeling, and laboratory measurements, the results follow a similar overall pattern but do not align; our results constitute a lower bound on diffusive transport. In comparing our measurements of both diffusivity and permeability to previous parameterizations from numerical 3-D lattice-Boltzmann modeling, it is evident that the previous relationships to porosity are likely site-specific. We present parameterizations relating diffusivity and permeability to porosity as a possible tool, though use of direct measurements would be far more accurate when feasible. The relationships between gas transport properties and microstructural properties are characterized and compared to existing relationships for general porous media, specifically the Katz–Thompson (KT), Kozeny–Carman (KC), and Archie's law approximations. While those approximations can capture the general trend of gas transport relationships, they result in high errors for individual samples and fail to fully describe firn variability, particularly the differences between coarse- and fine-grained firn. We present a direct power law relationship between permeability and gas diffusivity based on our co-located measurements; further research will indicate if this type of relationship is site-specific. This set of measurements and relationships contributes a unique starting point for future investigations in developing more physically based models of firn gas transport

Botanical Dermatology JohnMitchellAruthurRookBotanical Dermatology1979VancouverGreengrass787

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Dominance of grain size impacts on seasonal snow albedo at deforested sites in New Hampshire

Snow cover serves as a major control on the surface energy budget in temperate regions due to its high reflectivity compared to underlying surfaces. Winter in the northeastern United States has changed over the last several decades, resulting in shallower snowpacks, fewer days of snow cover, and increasing precipitation falling as rain in the winter. As these climatic changes occur, it is imperative that we understand current controls on the evolution of seasonal snow albedo in the region. Over three winter seasons between 2013 and 2015, snow characterization measurements were made at three open sites across New Hampshire. These near-daily measurements include spectral albedo, snow optical grain size determined through contact spectroscopy, snow depth, snow density, black carbon content, local meteorological parameters, and analysis of storm trajectories using the Hybrid Single-Particle Lagrangian Integrated Trajectory model. Using analysis of variance, we determine that land-based winter storms result in marginally higher albedo than coastal storms or storms from the Atlantic Ocean. Through multiple regression analysis, we determine that snow grain size is significantly more important in albedo reduction than black carbon content or snow density. And finally, we present a parameterization of albedo based on days since snowfall and temperature that accounts for 52% of variance in albedo over all three sites and years. Our improved understanding of current controls on snow albedo in the region will allow for better assessment of potential response of seasonal snow albedo and snow cover to changing climate

Learning by doing: Action performance facilitates affordance perception

AbstractWe investigated the effect of action performance on perceptual judgments by evaluating accuracy in judging whether doorways allowed passage. Participants made judgments either before or after walking through doorways of varying widths. Participants in the action-first group benefited from action feedback and made more accurate judgments compared to a perception-first group that judged doorways before walking through them. Action feedback aided perceptual judgments by facilitating scaling to body dimensions: Judgments in the action-first group were strongly related to height, weight, and torso size, whereas judgments in the perception-first group were not

Oral health in relation to all-cause mortality: the IPC cohort study

We evaluated the association between oral health and mortality. The study population comprised 76,188 subjects aged 16–89 years at recruitment. The mean follow-up time was 3.4 ± 2.4 years. Subjects with a personal medical history of cancer or cardiovascular disease and death by casualty were excluded from the analysis. A full-mouth clinical examination was performed in order to assess dental plaque, dental calculus and gingival inflammation. The number of teeth and functional masticatory units 10 missing teeth and functional masticatory units 10 missing teeth (HR = 2.31, [95% CI: 1.40–3.82]) and functional masticatory units <5 (HR = 2.40 [95% CI 1.55–3.73]). Moreover, when ≥3 oral diseases were cumulated in the model, the risk increased for all-cause mortality (HR = 3.39, [95% CI: 2.51–5.42]), all-cancer mortality (HR = 3.59, [95% CI: 1.23–10.05]) and non-cardiovascular and non-cancer mortality (HR = 4.71, [95% CI: 1.74–12.7]). The present study indicates a postive linear association between oral health and mortality