838 research outputs found
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Lifespan map creation enhances stream restoration design.
Research and engineering efforts are establishing a vast number of stream restoration planning approaches, design testing frameworks, construction techniques, and performance evaluation methods. A primary question arises as to the lifespan of stream restoration features. This study develops a framework to identify relevant parameters, design criteria and survival thresholds for ten multidisciplinary restoration techniques: âąParameterize relevant features, notably, (1) bar and floodplain grading; (2) berm setback; (3) vegetation plantings; (4) riprap placement; (5) sediment replenishment; (6) side cavities; (7) side channel and anabranches; (8) streambed reshaping; (9) structure removal; and (10) placement of wood in the shape of engineered logjams and rootstocks.âąIdentify survival thresholds for parameters, where the feature life ends when the threshold value is exceeded.âąCompare parameter thresholds with spatial data of topographic change and hydrodynamic forces as a result of hydrodynamic modelling of multiple discharges. The discharge or topographic change rate that is related to the lowest (flood) return period spatially determines the feature's lifespan in years
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How alternative urban stream channel designs influence ecohydraulic conditions.
Streams draining urban catchments ubiquitously undergo negative physical and ecosystem changes, recognized to be primarily driven by frequent stormwater runoff input. The common management intervention is rehabilitation of channel morphology. Despite engineering design intentions, ecohydraulic benefits of urban channel rehabilitation are largely unknown and likely limited. This investigation uses an ecohydraulic modeling approach to investigate the performance of alternative channel design configurations intended to restore key ecosystem functioning in urban streams. Channel reconfiguration design scenarios, specified to emulate the range of channel topographic complexity often used in rehabilitation are compared against a reference 'natural' scenario using ecologically relevant hydraulic metrics. The results showed that the ecohydraulic conditions were incremental improved with the addition of natural oscillations to an increasing number of individual topographic variables in a degraded channel. Results showed that reconfiguration reduced excessive frequency of bed mobility, loss of habitat and hydraulic diversity particularly as more topographic variables were added. However, the results also showed that none of the design scenarios returned the ecohydraulics to their reference conditions. This indicate that channel-based restoration can offer some potential changes to hydraulic habitat conditions but are unlikely to completely mitigate the effects of hydrologic change. We suggest that while reach-scale channel modification may be beneficial to restore urban stream, addressing altered hydrology is critical to fully recover natural ecosystem processes
Recurrence relation for relativistic atomic matrix elements
Recurrence formulae for arbitrary hydrogenic radial matrix elements are
obtained in the Dirac form of relativistic quantum mechanics. Our approach is
inspired on the relativistic extension of the second hypervirial method that
has been succesfully employed to deduce an analogous relationship in non
relativistic quantum mechanics. We obtain first the relativistic extension of
the second hypervirial and then the relativistic recurrence relation.
Furthermore, we use such relation to deduce relativistic versions of the
Pasternack-Sternheimer rule and of the virial theorem.Comment: 10 pages, no figure
Minimizing efforts in validating crowd answers
In recent years, crowdsourcing has become essential in a wide range of Web applications. One of the biggest challenges of crowdsourcing is the quality of crowd answers as workers have wide-ranging levels of expertise and the worker community may contain faulty workers. Although various techniques for quality control have been proposed, a post-processing phase in which crowd answers are validated is still required. Validation is typically conducted by experts, whose availability is limited and who incur high costs. Therefore, we develop a probabilistic model that helps to identify the most beneficial validation questions in terms of both, improvement of result correctness and detection of faulty workers. Our approach allows us to guide the experts work by collecting input on the most problematic cases, thereby achieving a set of high quality answers even if the expert does not validate the complete answer set. Our comprehensive evaluation using both real-world and synthetic datasets demonstrates that our techniques save up to 50% of expert efforts compared to baseline methods when striving for perfect result correctness. In absolute terms, for most cases, we achieve close to perfect correctness after expert input has been sought for only 20% of the questions
Relativistically extended Blanchard recurrence relation for hydrogenic matrix elements
General recurrence relations for arbitrary non-diagonal, radial hydrogenic
matrix elements are derived in Dirac relativistic quantum mechanics. Our
approach is based on a generalization of the second hypervirial method
previously employed in the non-relativistic Schr\"odinger case. A relativistic
version of the Pasternack-Sternheimer relation is thence obtained in the
diagonal (i.e. total angular momentum and parity the same) case, from such
relation an expression for the relativistic virial theorem is deduced. To
contribute to the utility of the relations, explicit expressions for the radial
matrix elements of functions of the form and
---where is a Dirac matrix--- are presented.Comment: 21 pages, to be published in J. Phys. B: At. Mol. Opt. Phys. in Apri
Relativistic Kramers-Pasternack Recurrence Relations
Recently we have evaluated the matrix elements ,O={1,\beta, i\mathbf{\alpha n}\beta} _{3}F_{2}(1) $ for all suitable powers and established two sets of
Pasternack-type matrix identities for these integrals. The corresponding
Kramers--Pasternack three-term vector recurrence relations are derived here.Comment: 12 pages, no figures Will appear as it is in Journal of Physics B:
Atomic, Molecular and Optical Physics, Special Issue on Hight Presicion
Atomic Physic
Requirement of Osteopontin in the migration and protection against Taxol-induced apoptosis via the ATX-LPA axis in SGC7901 cells
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