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Dominant Control (dominant + control)
Selected AbstractsCorrelation of Density Pedestal Width and Neutral Penetration LengthCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-3 2004X. Q. Xu Abstract Pedestal studies in DIII-D and MAST find good correlation between the width of the H-mode density barrier and the neutral penetration length [1, 2]. These results suggest that the width may be set by the combined effects of neutrals and plasma transport. This paper is a report on fluid simulations of boundary plasma using the BOUT code[3] with a neutral source added. Thus both neutral and plasma physics are treated. The plasma transport is self-consistently driven by boundary turbulence due to the resistive X-point mode, while neutrals are described by a simple analytic model. The plasma profiles are evolved on the same time scale as the turbulence for the given heat source from the core plasma and particle source from the neutrals. For prescribed neutral profiles, we find the formation of a density pedestal inside the separatrix in the L-mode even though the calculated plasma diffusion coefficients are almost radially constant and without the formation of a temperature pedestal. These results support the hypothesis that particle fueling can provide the dominant control for the size of the H-mode density barrier. The width of the density barrier decreases as the pedestal density increases which is also consistent with experimental data. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dealing with Landscape Heterogeneity in Watershed Hydrology: A Review of Recent Progress toward New Hydrological TheoryGEOGRAPHY COMPASS (ELECTRONIC), Issue 1 2009Peter A. Troch Predictions of hydrologic system response to natural and anthropogenic forcing are highly uncertain due to the heterogeneity of the land surface and subsurface. Landscape heterogeneity results in spatiotemporal variability of hydrological states and fluxes, scale-dependent flow and transport properties, and incomplete process understanding. Recent community activities, such as Prediction in Ungauged Basins of International Association of Hydrological Sciences, have recognized the impasse current catchment hydrology is facing and have called for a focused research agenda toward new hydrological theory at the watershed scale. This new hydrological theory should recognize the dominant control of landscape heterogeneity on hydrological processes, should explore novel ways to account for its effect at the watershed scale, and should build on an interdisciplinary understanding of how feedback mechanisms between hydrology, biogeochemistry, pedology, geomorphology, and ecology affect catchment evolution and functioning. [source] Sequence stratigraphy of the upper Millstone Grit (Yeadonian, Namurian), North WalesGEOLOGICAL JOURNAL, Issue 5 2007Rhodri M. Jerrett Abstract The upper Millstone Grit strata (Yeadonian, Namurian) of North Wales have been studied using sedimentological facies analysis and sequence stratigraphy. These strata comprise two cyclothems, each containing prodelta shales (Holywell Shale) that pass gradationally upwards into delta-front and delta-plain deposits (Gwespyr Sandstone Formation). The deltas formed in shallow water (<100,m), were fluvial-dominated, had elongate and/or sheet geometries and are assigned to highstand systems tracts. Two delta complexes with distinctive sandstone petrographies are identified: (1) a southerly derived, quartzose delta complex sourced locally from the Wales-Brabant Massif, and (2) a feldspathic delta complex fed by a regional source(s) to the north and/or west. The feldspathic delta complex extended further south in the younger cyclothem. A multistorey braided-fluvial complex (Aqueduct Grit, c. 25,m thick) is assigned to a lowstand systems tract, and occupies an incised valley that was eroded into the highstand feldspathic delta complex in the younger cyclothem. A candidate incised valley cut into the highstand feldspathic delta complex in the older cyclothem is also tentatively identified. Transgressive systems tracts are thin (<5,m) and contain condensed fossiliferous shales (marine bands). The high-resolution sequence stratigraphic framework interpreted for North Wales can be readily traced northwards into the Central Province Basin (,Pennine Basin'), supporting the notion that high-frequency, high-magnitude sea-level changes were the dominant control on stratigraphic architecture. Copyright © 2007 John Wiley & Sons, Ltd. [source] Immunologic tolerance maintained by CD25+ CD4+ regulatory T cells: their common role in controlling autoimmunity, tumor immunity, and transplantation toleranceIMMUNOLOGICAL REVIEWS, Issue 1 2001Shimon Sakaguchi Summary: There is accumulating evidence that T-cell-mediated dominant control of self-reactive T-cells contributes to the maintenance of immunologic self-tolerance and its alteration can cause autoimmune disease. Efforts to delineate such a regulatory T-cell population have revealed that CD25+ cells in the CD4+ population in normal naive animals bear the ability to prevent autoimmune disease in vivo and, upon antigenic stimulation, suppress the activation/proliferation of other T cells in vitro. The CD25+ CD4+ regulatory T cells, which are naturally anergic and suppressive, appear to be produced by the normal thymus as a functionally distinct subpopulation of T cells. They play critical roles not only in preventing autoimmunity but also in controlling tumor immunity and transplantation tolerance. [source] Spatial patterns of simulated transpiration response to climate variability in a snow dominated mountain ecosystemHYDROLOGICAL PROCESSES, Issue 18 2008Lindsey Christensen Abstract Transpiration is an important component of soil water storage and stream-flow and is linked with ecosystem productivity, species distribution, and ecosystem health. In mountain environments, complex topography creates heterogeneity in key controls on transpiration as well as logistical challenges for collecting representative measurements. In these settings, ecosystem models can be used to account for variation in space and time of the dominant controls on transpiration and provide estimates of transpiration patterns and their sensitivity to climate variability and change. The Regional Hydro-Ecological Simulation System (RHESSys) model was used to assess elevational differences in sensitivity of transpiration rates to the spatiotemporal variability of climate variables across the Upper Merced River watershed, Yosemite Valley, California, USA. At the basin scale, predicted annual transpiration was lowest in driest and wettest years, and greatest in moderate precipitation years (R2 = 0·32 and 0·29, based on polynomial regression of maximum snow depth and annual precipitation, respectively). At finer spatial scales, responsiveness of transpiration rates to climate differed along an elevational gradient. Low elevations (1200,1800 m) showed little interannual variation in transpiration due to topographically controlled high soil moistures along the river corridor. Annual conifer stand transpiration at intermediate elevations (1800,2150 m) responded more strongly to precipitation, resulting in a unimodal relationship between transpiration and precipitation where highest transpiration occurred during moderate precipitation levels, regardless of annual air temperatures. Higher elevations (2150,2600 m) maintained this trend, but air temperature sensitivities were greater. At these elevations, snowfall provides enough moisture for growth, and increased temperatures influenced transpiration. Transpiration at the highest elevations (2600,4000 m) showed strong sensitivity to air temperature, little sensitivity to precipitation. Model results suggest elevational differences in vegetation water use and sensitivity to climate were significant and will likely play a key role in controlling responses and vulnerability of Sierra Nevada ecosystems to climate change. Copyright © 2008 John Wiley & Sons, Ltd. [source] Hydrogeologic controls on summer stream temperatures in the McKenzie River basin, OregonHYDROLOGICAL PROCESSES, Issue 24 2007Christina Tague Abstract Stream temperature is a complex function of energy inputs including solar radiation and latent and sensible heat transfer. In streams where groundwater inputs are significant, energy input through advection can also be an important control on stream temperature. For an individual stream reach, models of stream temperature can take advantage of direct measurement or estimation of these energy inputs for a given river channel environment. Understanding spatial patterns of stream temperature at a landscape scale requires predicting how this environment varies through space, and under different atmospheric conditions. At the landscape scale, air temperature is often used as a surrogate for the dominant controls on stream temperature. In this study we show that, in regions where groundwater inputs are key controls and the degree of groundwater input varies in space, air temperature alone is unlikely to explain within-landscape stream temperature patterns. We illustrate how a geologic template can offer insight into landscape-scale patterns of stream temperature and its predictability from air temperature relationships. We focus on variation in stream temperature within headwater streams within the McKenzie River basin in western Oregon. In this region, as in other areas of the Pacific Northwest, fish sensitivity to summer stream temperatures continues to be a pressing environmental issue. We show that, within the McKenzie, streams which are sourced from deeper groundwater reservoirs versus shallow subsurface flow systems have distinct summer temperature regimes. Groundwater streams are colder, less variable and less sensitive to air temperature variation. We use these results from the western Oregon Cascade hydroclimatic regime to illustrate a conceptual framework for developing regional-scale indicators of stream temperature variation that considers the underlying geologic controls on spatial variation, and the relative roles played by energy and water inputs. Copyright © 2007 John Wiley & Sons, Ltd. [source] A classification of drainage and macropore flow in an agricultural catchmentHYDROLOGICAL PROCESSES, Issue 1 2002Dr C. M. Heppell Abstract This paper uses a variety of multivariate statistical techniques in order to improve current understanding of the antecedent and rainfall controls on drainage characteristics for an agricultural underdrained clay site. Using the dataset obtained from a two-year hillslope study at Wytham (Oxfordshire, UK) a number of patterns in the nature and style of drainage events were explored. First, using principal components analysis, a distinction was drawn between drainflow controlled by antecedent conditions and drainflow controlled by rainfall characteristics. Dimensional analysis then distinguished between two further types of drainflow event: antecedent limited events (ALE) and non-antecedent limited events (NALE). These were drainflow events requiring a minimum antecedent hydraulic head to occur (ALE) and events that occurred in response to rainfall irrespective of the antecedent conditions, because the rainfall was either of high enough intensity or duration to prompt a response in drainflow (NALE). 2. The dataset also made possible a preliminary investigation into the controls on and types of macropore flow at the site. Principal components analysis identified that rainfall characteristics were more important than antecedent conditions in generating high proportions of macropore flow in drainflow. Of the rainfall characteristics studied, rainfall amount and intensity were the dominant controls on the amount of macropore flow, with duration as a secondary control. Two styles of macropore flow were identified: intensity-driven and duration-driven. Intensity-driven events are characterized by rainfall of high intensity and short duration. During such events the amount of macropore flow is proportional to the rainfall intensity and the interaction between macropore and matrix flow is kinetically limited. The second style of macropore flow is characterized by long-duration events. For these events the amount of macropore flow approaches a maximum value whatever the rainfall duration. This suggests that these events are characterized by an equilibrium interaction between macropores and matrix flow. Copyright © 2002 John Wiley & Sons, Ltd. [source] Landscape metrics indicate differences in patterns and dominant controls of ribbon forests in the Rocky Mountains, USAAPPLIED VEGETATION SCIENCE, Issue 2 2009Matthew F. Bekker Abstract Question: Do landscape metrics reflect differences in dominant factors controlling ribbon forest patterns among sites? Location: West Flattop Mountain, Glacier National Park, Montana (Flattop); Medicine Bow Mountains, Wyoming (Medicine Bow); Park Range, Colorado (Park Range). Methods: High-resolution aerial photography was used to delineate ribbon forest patches, and to calculate landscape metrics to distinguish between long, narrow, regular patterns expected from strong microtopographic control, and smaller, more compact, and variable patterns expected from wind-snowdrift interactions. Results: All but two metrics were significantly different (P<0.05) among the three sites. The rank and magnitude of differences indicated that ribbons at Flattop and Park Range are more similar to each other than to those at Medicine Bow. Flattop ribbons were also more elongated, narrower and less variable than those at Park Range, suggesting differences in the type and strength of structural control. Previous research showed that Flattop ribbons occupy regular lithologic ridges, while our observations of ribbons and analysis of geologic maps suggests weaker and less consistent microtopographic control at Park Range, and dominant wind-snowdrift interactions with little to no microtopographic influence at Medicine Bow. Conclusions: Landscape metrics indicate differences in pattern among sites that reflect differences in dominant factors influencing ribbon forest development and maintenance. Explanations of ribbon forest dynamics are site-specific and are more complex than is currently recognized. The sites vary in the level of endogenous versus exogenous control of ribbon patterns, and consequently in the sensitivity of this phenomenon to climate. [source] | ||||||||||