Experimental assessment of Athabasca river cohesive sediment deposition dynamics.

Polycyclic aromatic hydrocarbons (PAHs) originating from natural sources, and potentially from the Athabasca Oil Sands development, are of concern for the Athabasca River and Lake Athabasca delta ecosystems. In order to model the transport of fine sediments (and associated PAHs), it is important to describe the sediment dynamics within the river system. Flocs possess different settling characteristics compared to individual particles. A key aspect in modelling floc settling behaviour is the mathematical linkage of the floc density to floc size. In this paper, a rotating annular flume is used to determine the settling characteristics of Muskeg River (a tributary of the Athabasca River) sediments under different shear conditions. Simulations of the settling and flocculation behaviour of these sediments were used to calibrate a density vs. floc size model. A relationship of the parameters relating floc size and density with the fractal dimension F shows that as diameter increases flocs become weaker. Recommendations for the practical application of the model are further formulated in this paper. The deposition tests offer a quantitative measure of the relative amount of sediment that is likely to be transported through the river for given flow conditions.Para el rio Athabasca y los ecosistemas deltaicos del lago athabasca, los hidrocarburos Aromaticos policiclicos (HAPs) originados e fuentes naturales y potencialmente por los desarrollos de arenas bituminosas, son una amenaza. Para poder modelar el transporte de sedimentos finos (y HAPs asociados) es importante describir la dinámica de estos dentro del sistema. Los agregados (floculos) que se forman tiene caracteristicas de sedimentación diferentes a las partículas individuales. Un aspoecto importante para modelar la sedimentación de floculos es la relación matemática entre el tamaño de este y su densidad. En este articulo un canal rotatorio circular es usado para determinar las características de sedimentación de sedimentos del río Muskeg(un tributario del Athabasca) para diferentes condiciones de tasa de corte. Un modelo de densidad de los flóculos vs. tamaño de estos fue calibrado con las simulaciones de la sedimentación de esos sedimentos cohesivos. Una relación obtenida entre tamaño de flóculos, densidad y dimensión fractal F muestra que ha medida que su tamaño aumenta se vuelve mas frágil. Recomendaciones para la aplicación práctica del modelo se sugieren en el artículo. Los tests de deposito presentan una medida cuantitativa de la proporción de sedimentos que es posible que sea transportada por el río dada sus condiciones hidrodinámicas.Environment Canada, CONACY

Belted sum decompositions of fully augmented links

Given two orientable, cusped hyperbolic 3-manifolds containing certain thrice-punctured spheres, Adams gave a diagrammatic definition for a third such manifold, their belted sum. Fully augmented links, or FALs, are hyperbolic links constructed by augmenting a link diagram. This work considers belted sum decompositions in which all manifolds involved are FAL complements. To do so, we provide explicit classifications of thrice punctured spheres in FAL complements, making them easily recognizable. These classifications are used to characterize belted sum prime FALs geometrically, combinatorially and diagrammatically. Finally we prove that, in the context of belted sums, every FAL complement canonically decomposes into FALs which are either prime or two-fold covers of the Whitehead link

Pressure and Motion of Dry Sand -- Translation of Hagen's Paper from 1852

In a remarkable paper from 1852, Gotthilf Heinrich Ludwig Hagen measured and explained two fundamental aspects of granular matter: The first effect is the saturation of pressure with depth in a static granular system confined by silo walls -- generally known as the Janssen effect. The second part of his paper describes the dynamics observed during the flow out of the container -- today often called the Beverloo law -- and forms the foundation of the hourglass theory. The following is a translation of the original German paper from 1852.Comment: 4 pages, accepted for publication in Granular Matter, original article (German) can be found under http://www.phy.duke.edu/~msperl/Janssen

Erosion characteristics and floc strenght of Athabasca river cohesive sediments: towards managing sediment-related issues

Purpose: Most of Canada’s tar sands exploitations are located in the Athabasca river basin. Deposited cohesive sediments in Athabasca river and tributaries are a potential source of PAHs in the basin. Erosional behavior of cohesive sediments depends not only of fluid turbulence but on sediments structure and particularly the influence of organic content. This research tries to describe this behavior in Athabasca river sediments. Methods: An experimental study of cohesive sediments dynamics in one of the tributaries, the Muskeg river, was developed in a rotating annular flume. Variation of the shear stress allowed the determination of erosional strength for beds with different consolidation periods. Particle size measurements were made with a laser diffraction device operated in a continuous flow through mode. Optical analyses of flocs (ESEM and TEM) were performed with samples taken at the end of the experiments. Results: An inverse relationship between suspended sediment concentration (SS) and the consolidation period was found. The differences are related in this research to the increasing organic content of the sediments with consolidation period. The particle size measurements during the experiments showed differences on floc strength that are also related to changing organic content during different consolidation periods. ESEM and TEM observations confirm the structural differences for beds with different consolidation periods. The effects of SFGL on floc structure and in biostabilization of the bed are discussed. Conclusions: It is recommended in this paper that consolidation period should be taken into account for the modeling of erosion of cohesive sediments in the Athabasca river. Relating to transport models of pollutants (PAHs) it is highly recommended to consider flocs organic content, particularly algae, in the resuspension module.Environment Canada, CONACY

Meeting Report: Aging Research and Drug Discovery

Aging is the single largest risk factor for most chronic diseases, and thus possesses large socioeconomic interest to continuously aging societies. Consequently, the field of aging research is expanding alongside a growing focus from the industry and investors in aging research. This year's 8th Annual Aging Research and Drug Discovery ARDD) meeting was organized as a hybrid meeting from August 30th to September 3rd 2021 with more than 130 attendees participating on-site at the Ceremonial Hall at University of Copenhagen, Denmark, and 1800 engaging online. The conference comprised of presentations from 75 speakers focusing on new research in topics including mechanisms of aging and how these can be modulated as well as the use of AI and new standards of practices within aging research. This year, a longevity workshop was included to build stronger connections with the clinical community

Synaptic Defects in the Spinal and Neuromuscular Circuitry in a Mouse Model of Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a major genetic cause of death in childhood characterized by marked muscle weakness. To investigate mechanisms underlying motor impairment in SMA, we examined the spinal and neuromuscular circuitry governing hindlimb ambulatory behavior in SMA model mice (SMNΔ7). In the neuromuscular circuitry, we found that nearly all neuromuscular junctions (NMJs) in hindlimb muscles of SMNΔ7 mice remained fully innervated at the disease end stage and were capable of eliciting muscle contraction, despite a modest reduction in quantal content. In the spinal circuitry, we observed a ∼28% loss of synapses onto spinal motoneurons in the lateral column of lumbar segments 3–5, and a significant reduction in proprioceptive sensory neurons, which may contribute to the 50% reduction in vesicular glutamate transporter 1(VGLUT1)-positive synapses onto SMNΔ7 motoneurons. In addition, there was an increase in the association of activated microglia with SMNΔ7 motoneurons. Together, our results present a novel concept that synaptic defects occur at multiple levels of the spinal and neuromuscular circuitry in SMNΔ7 mice, and that proprioceptive spinal synapses could be a potential target for SMA therapy

Axons regulate the distribution of Schwann cell microtubules

It is well established that axons regulate Schwann cell phenotype. The purpose of the present study was to determine whether axons influence the arrangement of Schwann cell microtubules (MTs). Using double-labeling immunocytochemistry and confocal microscopy, we show that MTs in undifferentiated Schwann cells are nucleated from and attached to a single MT organizing center (MTOC) that is associated with the centrosome. Physical contact with appropriate axons initiates a myelin-forming phenotype that disperses MT minus ends and induces multiple MT-nucleating sites in Schwann cell perinuclear cytoplasm. The axonal signal that initiates myelin breakdown during Wallerian degeneration induces multiple MTOCs and MT bundles in Schwann cell perinuclear cytoplasm and in cytoplasm between degenerating myelin ovoids. These results establish that axons influence Schwann cell MT distribution by regulating the location and number of MT-nucleation sites