570 research outputs found
\u3cem\u3eRhizobium leguminosarum\u3c/em\u3e CFN42 Genetic Regions Encoding Lipopolysaccharide Structures Essential for Complete Nodule Development on Bean Plants
Eight symbiotic mutants defective in lipopolysaccharide (LPS) synthesis were isolated from Rhizobium leguminosarum biovar phaseoli CFN42. These eight strains elicited small white nodules lacking infected cells when inoculated onto bean plants. The mutants had undetectable or greatly diminished amounts of the complete LPS (LPS I), whereas amounts of an LPS lacking the O antigen (LPS II) greatly increased. Apparent LPS bands that migrated between LPS I and LPS II on sodium dodecyl sulfate-polyacrylamide gels were detected in extracts of some of the mutants. The mutant strains were complemented to wild-type LPS I content and antigenicity by DNA from a cosmid library of the wild-type genome. Most of the mutations were clustered in two genetic regions; one mutation was located in a third region. Strains complemented by DNA from two of these regions produced healthy nitrogen-fixing nodules. Strains complemented to wild-type LPS content by the other genetic region induced nodules that exhibited little or no nitrogenase activity, although nodule development was obviously enhanced by the presence of this DNA. The results support the idea that complete LPS structures, in normal amounts, are necessary for infection thread development in bean plants
A probabilistic framework for the cover effect in bedrock erosion
The cover effect in fluvial bedrock erosion is a major control on bedrock channel morphology and long-term channel dynamics. Here, we suggest a probabilistic framework for the description of the cover effect that can be applied to field, laboratory, and modelling data and thus allows the comparison of results from different sources. The framework describes the formation of sediment cover as a function of the probability of sediment being deposited on already alluviated areas of the bed. We define benchmark cases and suggest physical interpretations of deviations from these benchmarks. Furthermore, we develop a reach-scale model for sediment transfer in a bedrock channel and use it to clarify the relations between the sediment mass residing on the bed, the exposed bedrock fraction, and the transport stage. We derive system timescales and investigate cover response to cyclic perturbations. The model predicts that bedrock channels can achieve grade in steady state by adjusting bed cover. Thus, bedrock channels have at least two characteristic timescales of response. Over short timescales, the degree of bed cover is adjusted such that the supplied sediment load can just be transported, while over long timescales, channel morphology evolves such that the bedrock incision rate matches the tectonic uplift or base-level lowering rate
Bedload transport controls bedrock erosion under sediment-starved conditions
Fluvial bedrock incision constrains the pace of mountainous landscape
evolution. Bedrock erosion processes have been described with incision models
that are widely applied in river-reach and catchment-scale studies. However,
so far no linked field data set at the process scale had been published that
permits the assessment of model plausibility and accuracy. Here, we evaluate
the predictive power of various incision models using independent data on
hydraulics, bedload transport and erosion recorded on an artificial bedrock
slab installed in a steep bedrock stream section for a single bedload
transport event. The influence of transported bedload on the erosion rate
(the "tools effect") is shown to be dominant, while other sediment effects
are of minor importance. Hence, a simple temporally distributed incision
model, in which erosion rate is proportional to bedload transport rate, is
proposed for transient local studies under detachment-limited conditions.
This model can be site-calibrated with temporally lumped bedload and erosion
data and its applicability can be assessed by visual inspection of the study
site. For the event at hand, basic discharge-based models, such as
derivatives of the stream power model family, are adequate to reproduce the
overall trend of the observed erosion rate. This may be relevant for
long-term studies of landscape evolution without specific interest in
transient local behavior. However, it remains to be seen whether the same
model calibration can reliably predict erosion in future events
Additive decomposition applied to the semiconductor drift-diffusion model
A new numerical method for semiconductor device simulation is presented. The additive decomposition method has been successfully applied to Burgers' and Navier-Stokes equations governing turbulent fluid flow by decomposing the equations into large-scale and small-scale parts without averaging. The additive decomposition (AD) technique is well suited to problems with a large range of time and/or space scales, for example, thermal-electrical simulation of power semiconductor devices with large physical size. Furthermore, AD adds a level of parallelization for improved computational efficiency. The new numerical technique has been tested on the 1-D drift-diffusion model of a p-i-n diode for reverse and forward biases. Distributions of , n and p have been calculated using the AD method on a coarse large-scale grid and then in parallel small-scale grid sections. The AD results agreed well with the results obtained with a traditional one-grid approach, while potentially reducing memory requirements with the new method
sedFlow â a tool for simulating fractional bedload transport and longitudinal profile evolution in mountain streams
Especially in
mountainous environments, the prediction of sediment
dynamics is important for managing natural hazards, assessing
in-stream habitats and understanding geomorphic evolution. We
present the new modelling tool {sedFlow} for simulating
fractional bedload transport dynamics in mountain streams. sedFlow is a one-dimensional model that aims
to realistically reproduce the total transport volumes and overall
morphodynamic changes resulting from sediment transport events such as major
floods. The model is intended for temporal scales from the individual event (several hours to few days)
up to longer-term evolution of stream channels (several years). The envisaged spatial scale covers complete
catchments at a spatial discretisation of several tens of metres to a few hundreds of metres. sedFlow
can deal with the effects of streambeds that slope uphill in a downstream direction and uses recently proposed and
tested approaches for quantifying macro-roughness effects in steep
channels. sedFlow offers different options for bedload transport equations, flow-resistance
relationships
and other elements which can be selected to fit the current application in a particular catchment. Local grain-size distributions are dynamically adjusted
according to the transport dynamics of each grain-size fraction. sedFlow features fast calculations and straightforward
pre- and postprocessing of simulation data. The high simulation speed allows for simulations of several
years, which can be used, e.g., to assess the long-term impact of river engineering works or climate change
effects. In combination with the straightforward pre- and postprocessing, the fast calculations facilitate
efficient workflows for the simulation of individual flood events, because the modeller gets the immediate
results as direct feedback to the selected parameter inputs.
The model is provided
together with its complete source code free of charge under the
terms of the GNU General Public License (GPL)
(www.wsl.ch/sedFlow). Examples of the application of
sedFlow are given in a companion article by
Heimann et al. (2015)
AnsĂ€tze fĂŒr die Verbesserung von PPS-Systemen durch Fuzzy-Logik
Ziel dieses Arbeitsberichts ist es, die Teilbereiche von Produktionsplanungs- und -steuerungssystemen (PPS-Systemen) zu identifizieren, die unter Beachtung der Interdependenzen zu anderen Teilbereichen mit einem Fuzzy-Ansatz modelliert und dadurch in ihrer Effizienz gesteigert werden können. Nach einer kurzen EinfĂŒhrung in die Fuzzy-Logik werden zunĂ€chst AnsĂ€tze fĂŒr den Einsatz der Fuzzy-Logik innerhalb der Datenstrukturen der Produktionsplanung und -steuerung dargestellt. Danach werden die Funktionen von PPS-Systemen systematisch auf diesbezĂŒgliche Potentiale untersucht, wobei zwischen originĂ€rer und derivativer Verwendung der Fuzzy-Logik unterschieden wird, und Nutzeffekte sinnvoller 'VerunschĂ€rfungen' aufgezeigt werden. Der Arbeitsbericht schlieĂt mit einem Ausblick
Studying sediment transport in mountain rivers by mobile and stationary RFID antennas
River engineeringInnovative field and laboratory instrumentatio
Measuring streambed morphology using range imaging
River engineeringInnovative field and laboratory instrumentatio
Testing fluvial erosion models using the transient response of bedrock rivers to tectonic forcing in the Apennines, Italy
The transient response of bedrock rivers to a drop in base level can be used to
discriminate between competing fluvial erosion models. However, some recent studies of
bedrock erosion conclude that transient river long profiles can be approximately
characterized by a transportâlimited erosion model, while other authors suggest that a
detachmentâlimited model best explains their field data. The difference is thought to be
due to the relative volume of sediment being fluxed through the fluvial system. Using a
pragmatic approach, we address this debate by testing the ability of endâmember fluvial
erosion models to reproduce the wellâdocumented evolution of three catchments in the
central Apennines (Italy) which have been perturbed to various extents by an
independently constrained increase in relative uplift rate. The transportâlimited model is
unable to account for the catchmentsâresponse to the increase in uplift rate, consistent with
the observed low rates of sediment supply to the channels. Instead, a detachmentâlimited
model with a threshold corresponding to the fieldâderived median grain size of the
sediment plus a slopeâdependent channel width satisfactorily reproduces the overall
convex long profiles along the studied rivers. Importantly, we find that the prefactor in the
hydraulic scaling relationship is uplift dependent, leading to landscapes responding faster
the higher the uplift rate, consistent with field observations. We conclude that a slopeâ
dependent channel width and an entrainment/erosion threshold are necessary ingredients
when modeling landscape evolution or mapping the distribution of fluvial erosion rates in
areas where the rate of sediment supply to channels is low
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