7,485 research outputs found
Electron induced alpha particle emission
SIGLEAvailable from British Library Document Supply Centre- DSC:D35995/81 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Oscillatory subglacial drainage in the absence of surface melt
The presence of strong diurnal cycling in basal water pressure records
obtained during the melt season is well established for many glaciers. The
behaviour of the drainage system outside the melt season is less well
understood. Here we present borehole observations from a surge-type valley
glacier in the St Elias Mountains, Yukon Territory, Canada. Our data indicate
the onset of strongly correlated multi-day oscillations in water pressure in
multiple boreholes straddling a main drainage axis, starting several weeks
after the disappearance of a dominant diurnal mode in August 2011 and
persisting until at least January 2012, when multiple data loggers suffered
power failure. Jökulhlaups provide a template for understanding spontaneous
water pressure oscillations not driven by external supply variability. Using
a subglacial drainage model, we show that water pressure oscillations can
also be driven on a much smaller scale by the interaction between conduit
growth and distributed water storage in smaller water pockets, basal
crevasses and moulins, and that oscillations can be triggered when water
supply drops below a critical value. We suggest this in combination with a
steady background supply of water from ground water or englacial drainage as a
possible explanation for the observed wintertime pressure oscillations
Elevated CO2 concentration and leaf growth: a biophysical and biochemical analysis of cell expansion
Do specific types of sleep disturbances represent risk factors for poorer health‐related quality of life in inflammatory bowel disease? A longitudinal cohort study
Objectives
Poor global sleep quality is commonly reported in people with inflammatory bowel disease (IBD) and is linked to poorer health‐related quality of life (HRQoL). However, understanding is currently limited by a lack of: (1) longitudinal research and (2) research investigating the impact of specific types of problems sleeping on IBD‐related outcomes, particularly on HRQoL.
Design
Observational longitudinal cohort study.
Methods
N = 276 participants with IBD completed measures at baseline (T1) and 4 weeks later at T2. Four specific sleep disturbances associated with IBD including sleep apnoea, insomnia, restless legs, and nightmares were measured alongside depression, anxiety and stress, and HRQoL.
Results
After controlling for participant demographics and clinical characteristics, T1 depression, anxiety, stress, and T1 HRQoL, more severe symptom severity of sleep apnoea (B = −0.30, p .87) and nightmares (B = −0.14, p > .11) at T1 did not predict HRQoL.
Conclusion
Symptoms synonymous with sleep apnoea and insomnia might represent modifiable risk factors that provide independent contributions to HRQoL over time in those with IBD. These findings suggest that interventions designed to improve sleep apnoea and insomnia could confer benefits to HRQoL in those with IBD. However, more longitudinal research is needed to understand the contribution of sleep disturbances over the longer term, as well as more randomized controlled trials testing the effect of improving sleep on IBD‐related outcomes
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A Symbolic/Connectionist Script Applier Mechanism
We constructed a Modular Connectionist Architecture which consists of meiny different types of 3 layer feed-forward PDP network modules (auto-associative recurrent, hetero-associative recurrent, and heteroassociative) in order to do script-based story understanding. Our system, called DYNASTY (DYNAmic script-based STory understanding sYstem) has the following 3 major functions: (1) DYNASTY can learn distributed representations of concepts and events in everyday scriptal experiences, (2) DYNASTY can do script-based causal chain completion inferences according to the acquired sequential knowledge, and (3) DYNASTY performs script role association and retrieval while performing script application. Our purpose in constructing this system is to show that the learned internal representations, using simple encoder-type networks, can be used in higher-level modules to develop connectionist architectures for fairly complex cognitive tasks, such as script processing. Unlike other neurally inspired script processing models, DYNASTY can learn its own similanty-hased distributed representations from input script data using ARPDP (Autoassociative Recurrent PDP) architectures. Moreover DYNASTY'S role association network handles both script roles and fillers as full-fledged concepts^ so that it can learn the generalized associative knowledge between several script roles and fillers
Spectrum
Spectrum is a multispectral fluorescence imager designed for capturing in vivo genetic expression in a variety of biological organisms, providing a capability that does not currently exist on the International Space Station (ISS). Researching organisms that have been transformed with in vivo reporter genes ligated with fluorescent proteins allows the scientific community to further understand the fundamental biological responses of these organisms when subjected to space environments. Model organisms that may utilize multispectral imaging on the ISS include unicellular organisms (e.g. Saccharomyces cerevisiae), plants (e.g. Arabidopsis thaliana), and invertebrates (e.g. Caenorhabditis elegans)
Contemporary Glacier Processes and Global Change: Recent Observations from Kaskawulsh Glacier and the Donjek Range, St. Elias Mountains
With an extensive ice cover and rich display of glacier behaviour, the St. Elias Mountains continue to be an enviable natural laboratory for glaciological research. Recent work has been motivated in part by the magnitude and pace of observed glacier change in this area, which is so ice-rich that ice loss has a measurable impact on global sea level. Both detection and attribution of these changes, as well as investigations into fundamental glacier processes, have been central themes in projects initiated within the last decade and based at the Kluane Lake Research Station. The scientific objectives of these projects are (1) to quantify recent area and volume changes of Kaskawulsh Glacier and place them in historical perspective, (2) to investigate the regional variability of glacier response to climate and the modulating influence of ice dynamics, and (3) to characterize the hydromechanical controls on glacier sliding. A wide range of methods is being used, from ground-based manual measurements to space-based remote sensing. The observations to date show glaciers out of equilibrium, with significant ongoing changes to glacier area, volume, and dynamics. Computer models are being used to generalize these results, and to identify the processes most critical to our understanding of the coupled glacier-climate system.Grâce à leur importante couverture de glace et au riche étalage de comportement des glaciers, les monts St. Elias continuent de servir de laboratoire naturel enviable pour la recherche glaciologique. Des études récentes ont été motivées, en partie, par la magnitude et la vitesse des changements observés dans les glaciers de l’endroit, qui sont riches en glace au point que la perte de glace a une incidence mesurable sur le niveau général de la mer. La détection et l’attribution de ces changements de même que les recherches à l’égard des processus des glaciers ont servi de thème central à des projets qui ont été mis en oeuvre au cours de la dernière décennie à la station de recherche du lac Kluane. Les objectifs scientifiques de ces projets consistent (1) à quantifier les changements récents relativement à l’aire et au volume du glacier Kaskawulsh, puis à les mettre dans une perspective historique, (2) à faire enquête sur la variabilité générale de la réaction du glacier vis-à-vis du climat et de l’influence modulatrice de la dynamique de la glace, et (3) à caractériser le contrôle hydromécanique par rapport au glissement du glacier. Une vaste gamme de méthodes est employée pour parvenir à ces fins, allant des mesures manuelles sur le terrain à la télédétection spatiale. Jusqu’à maintenant, les observations indiquent que les glaciers ne sont pas en équilibre et que d’importants changements se produisent quant à l’aire, au volume et à la dynamique du glacier. Des modèles informatiques sont utilisés pour généraliser ces résultats ainsi que pour cerner les processus les plus critiques à notre compréhension du système couplé glacier-climat
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Integrating Marker Passing and Connectionism for Handling Conceptual and Structureal Ambiguities
This paper discusses the problem of selecting the correct knowledge structures in parsing natural language texts which are conceptually and structurally ambiguous and require dynamic reinterpretation. An approach to this problem is presented which represnets all knowledge structures in a uniform manner and which uses a constrained marker passing mechanism augmented with elements of connectionist models. This approach is shown to have the advantage of completely integrating all parsing processes, while maintatining a simple, domain-independedt processing mechanis
Modeling Sediment Transport in Ice-Walled Subglacial Channels and Its Implications for Esker Formation and Proglacial Sediment Yields
Sediment yields from glacierized basins are used to quantify erosion rates on seasonal to decadal timescales as well as conditions at the glacier bed, and eskers hold valuable information about past subglacial hydraulic conditions in their spatial organization, geometry, and sedimentary structures. Ultimately, eskers are a record of past glacio‐fluvial sediment transport, but there is currently no physical model for this process. We develop a 1‐D model of morphodynamics in semicircular bedrock‐floored subglacial channels. We adapt a sediment conservation law developed for mixed alluvial‐bedrock conditions to subglacial channels. Channel evolution is a function of melt opening by viscous heat dissipation from flowing water and creep closure of the overlying ice, to which we add the closure or enlargement due to sediment deposition or removal, respectively. We apply the model to an idealized land‐terminating glacier and find that temporary sediment accumulation in the vicinity of the terminus, or the formation of an incipient esker, is inherent to the dynamics of the channelized water flow. The alluviation of the bed combined with the pressurized channel flow produces unexpected patterns of sediment evacuation: We show that the direction of hysteresis between sediment and water discharge is not necessarily linked to a supply‐ or transport‐limited system, as has been hypothesized for proglacial sediment yields. We also find that the deposition of an incipient esker is a function of a compromise between water discharge and sediment supply, but perhaps more importantly, ice‐surface slope and the temporal pattern of water delivery to the bed
Bulk viscosity in superfluid neutron star cores. I. Direct Urca processes in npe\mu matter
The bulk viscosity of the neutron star matter due to the direct Urca
processes involving nucleons, electrons and muons is studied taking into
account possible superfluidity of nucleons in the neutron star cores. The cases
of singlet-state pairing or triplet-state pairing (without and with nodes of
the superfluid gap at the Fermi surface) of nucleons are considered. It is
shown that the superfluidity may strongly reduce the bulk viscosity. The
practical expressions for the superfluid reduction factors are obtained. For
illustration, the bulk viscosity is calculated for two models of dense matter
composed of neutrons, protons,electrons and muons. The presence of muons
affects the bulk viscosity due to the direct Urca reactions involving electrons
and produces additional comparable contribution due to the direct Urca
reactions involving muons. The results can be useful for studying damping of
vibrations of neutron stars with superfluid cores.Comment: 14 pages, 7 figures, latex, uses aa.cls, to be published in Astronomy
and Astrophysic
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