Channel adjustments to a succession of water pulses in gravel bed rivers

Gravel bed rivers commonly exhibit a coarse surface armor resulting from a complex history of interactions between flow and sediment supply. The evolution of the surface texture under single storm events or under steady flow conditions has been studied by a number of researchers. However, the role of successive floods on the surface texture evolution is still poorly understood. An experimental campaign in an 18 m-long 1 m-wide flume has been designed to study these issues. Eight consecutive runs, each one consisting of a low-flow period of variable duration followed by a sudden flood (water pulse) lasting 1.5 h, have been conducted. The total duration of the experiment was 46 h. The initial bed surface was created during a 280 h-long experiment focused on the influence of episodic sediment supply on channel adjustments. Our experiments represent a realistic armored and structured beds found in mountain gravel bed rivers. The armor surface texture persists over the duration of the experiment. The experiment exhibits downstream fining of the bed-surface texture. It was found that sorting processes were affected by the duration of low-flow between flood pulses. Since bed load transport is influenced by sediment sorting, the evolution of bed load transport is impacted by the frequency of the water pulses: short interpulse durations reduce the time over which fine material (transported as bed load) can be winnowed. This, in turn, contributes to declining reduction of the bed load transport over time while the sediment storage increases.Peer ReviewedPostprint (author's final draft

Influence of the sediment supply texture on morphological adjustments in gravel-bed rivers

The role played by the texture of the sediment supply on channel bed adjustments in gravel-bed rivers is poorly understood. To address this issue, an experimental campaign has been designed. Flume experiments lasting 96 h in a 9 m long, 0.60 m wide have been performed with different sand-gravel mixtures as feed textures. The response of the surface texture has been found to be highly dependent on the grain size distribution of the feed. When the feed texture included gravel, the finest fractions of the sediment supply infiltrate beneath the surface. Conversely, sand remains on the surface when the feed texture lacks gravel. This different textural response becomes obscured when water discharge increases. Further, the sediment transport rate approaches the feed rate differently depending on the content of gravel in the feed texture. When a small proportion of gravel is part of the feed texture, bed load transport rate asymptotically approaches the feed rate. However, when a significant fraction of gravel is part of the feed grain size distribution, bed load transport rate approaches the feed rate by following an oscillatory path. These findings have been verified in terms of a one-dimensional numerical model. This modeling reveals that the higher the differences in mobility among the grain sizes contained in the feed texture, the more evident is the nonasymptotic transient trend toward equilibrium.Peer ReviewedPostprint (published version

Coupling between downstream variations of channel width and local pool–riffle bed topography

A potential control of downstream channel width variations on the structure and planform of pool–riffle sequence local bed topography is a key to the dynamics of gravel bed rivers. How established pool–riffle sequences respond to time-varying changes in channel width at specific locations, however, is largely unexplored and challenging to address with field-based study. Here, we report results of a flume experiment aimed at building understanding of how statistically steady pool–riffle sequence profiles adjust to spatially prescribed channel width changes. We find that local bed slopes near steady-state conditions inversely correlate with local downstream width gradients when the upstream sediment supply approximates the estimated transport capacity. This result constrains conditions prior to and following the imposed local width changes. Furthermore, this relationship between local channel bed slope and downstream width gradient is consistent with expectations from scaling theory and a broad set of field-based, numerical, and experimental studies (n=88). However, upstream disruptions to coarse sediment supply through actions such as dam removal can result in a transient flipping of the expected inverse correlation between bed slope and width gradient, collectively highlighting that understanding local conditions is critical before typically implemented spatial averaging schemes can be reliably applied.Postprint (published version

A model based on Hirano-Exner equations for two-dimensional transient flows over heterogeneous erodible beds

In order to study the morphological evolution of river beds composed of heterogeneous material, the interaction among the different grain sizes must be taken into account. In this paper, these equations are combined with the two-dimensional shallow water equations to describe the flow field. The resulting system of equations can be solved in two ways: (i) in a coupled way, solving flow and sediment equations simultaneously at a given time-step or (ii) in an uncoupled manner by first solving the flow field and using the magnitudes obtained at each time-step to update the channel morphology (bed and surface composition). The coupled strategy is preferable when dealing with strong and quick interactions between the flow field, the bed evolution and the different particle sizes present on the bed surface. A number of numerical difficulties arise from solving the fully coupled system of equations. These problems are reduced by means of a weakly-coupled strategy to numerically estimate the wave celerities containing the information of the bed and the grain sizes present on the bed. Hence, a two-dimensional numerical scheme able to simulate in a self-stable way the unsteady morphological evolution of channels formed by cohesionless grain size mixtures is presented. The coupling technique is simplified without decreasing the number of waves involved in the numerical scheme but by simplifying their definitions. The numerical results are satisfactorily tested with synthetic cases and against experimental data

Interplay between optical emission and magnetism in the van der Waals magnetic semiconductor CrSBr in the two-dimensional limit

The Van der Waals semiconductor metamagnet CrSBr offers an ideal platform for studying the interplay between optical and magnetic properties in the two-dimensional limit. Here, we carried out an exhaustive optical characterization of this material by means of temperature and magnetic field dependent photoluminescence (PL) on flakes of different thicknesses down to the monolayer. We found a characteristic emission peak that is quenched upon switching the ferromagnetic layers from an antiparallel to a parallel configuration and exhibits a different temperature dependence from that of the peaks commonly ascribed to excitons. The contribution of this peak to the PL is boosted around 30-40 K, coinciding with the hidden order magnetic transition temperature. Our findings reveal the connection between the optical and magnetic properties via the ionization of magnetic donor vacancies. This behavior enables a useful tool for the optical reading of the magnetic states in atomically thin layers of CrSBr and shows the potential of the design of two-dimensional heterostructures with magnetic and excitonic properties.Comment: 20 pages, 5 figure

Incision and width changes caused by dam removal. Experiments and data analysis

River morphodynamics and sediment transportRiver morphology and morphodynamic

Interplay between optical emission and magnetism in the van der Waals magnetic semiconductor CrSBr in the two-dimensional limit

The van der Waals semiconductor metamagnet CrSBr offers an ideal platform for studying the interplay between optical and magnetic properties in the two-dimensional limit. Here, we carried out an exhaustive optical characterization of this material by means of temperature- and magnetic-field-dependent photoluminescence (PL) on flakes of different thicknesses down to the monolayer. We found a characteristic emission peak that is quenched upon switching the ferromagnetic layers from an antiparallel to a parallel configuration and exhibits a temperature dependence different from that of the peaks commonly ascribed to excitons. The contribution of this peak to the PL is boosted around 30-40 K, coinciding with the hidden order magnetic transition temperature. Our findings reveal the connection between the optical and magnetic properties via the ionization of magnetic donor vacancies. This behavior enables a useful tool for the optical reading of the magnetic states in atomically thin layers of CrSBr and shows the potential of the design of 2D heterostructures with magnetic and excitonic properties

Variable hillslope-channel coupling and channel characteristics of forested mountain streams in glaciated landscapes

Channel morphology of forested, mountain streams in glaciated landscapes is regulated by a complex suite of processes, and remains difficult to predict. Here, we analyze models of channel geometry against a comprehensive field dataset collected in two previously glaciated basins in Haida Gwaii, B.C., to explore the influence of variable hillslope\u2013channel coupling imposed by the glacial legacy on channel form. Our objective is to better understand the relation between hillslope\u2013channel coupling and stream character within glaciated basins. We find that the glacial legacy on landscape structure is characterized by relatively large spatial variation in hillslope\u2013channel coupling. Spatial differences in coupling influence the frequency and magnitude of coarse sediment and woody material delivery to the channel network. Analyses using a model for channel gradient and multiple models for width and depth show that hillslope\u2013channel coupling and high wood loading induce deviations from standard downstream predictions for all three variables in the study basins. Examination of model residuals using Boosted Regression Trees and nine additional channel variables indicates that ~10 to ~40% of residual variance can be explained by logjam variables, ~15\u201340% by the degree of hillslope\u2013channel coupling, and 10\u201320% by proximity to slope failures. These results indicate that channel classification systems incorporating hillslope\u2013channel coupling, and, indirectly, the catchment glacial legacy, may present a more complete understanding of mountain channels. From these results, we propose a conceptual framework which describes the linkages between landscape history, hillslope\u2013channel coupling, and channel form. \ua9 2018 John Wiley & Sons, Ltd

Efecto de la aplicación de un campo electromagnético sobre el contenido de proteínas solubles y carbohidratos de embriones cigóticos de Coffea arabica L. cultivados in vitro

Electromagnetic fields have been applied to increase plant growth and in vitro germination of coffee. Even though it is not clear yet the mechanisms developed during the interaction of electromagnetic fields and plant tissue. This study aimed to determine the effect of applying an electromagnetic field on the concentration of soluble proteins and carbohydrates of coffee zygotic embryos during in vitro establishment stage. After three days of embryos establishment the treatment was applied with 2ì T magnetic induction level and 60 Hz frequency for an exposure time of 3 minutes. An electromagnetic stimulator for in vitro cultures BioNaK-03 was used. Embryos free of electromagnetic treatment were used as controls. The content of protein and carbohydrates was determined after 6 weeks of culture. Results showed a significant increase in the concentrations of these compounds in treated embryos. The application of electromagnetic fields at this stage of culture could improved the quality of plants obtained from coffee zygotic embryos by changing the way of some physiological and biochemical processes. This leads to increase the vigour and ensure a better plant development at later stages.Key words: Caturra rojo, coffee, in vitro plantsLos campos electromagnéticos han sido aplicados para acelerar el crecimiento y germinación de plantas in vitro de cafeto, sin embargo aún no queda claro cuáles son los mecanismos que se desarrollan durante la interacción de los campos electromagnéticos y el tejido vegetal. Este trabajo tuvo como objetivo determinar el efecto de la aplicación de un campo electromagnético sobre la concentración de proteínas solubles y carbohidratos de embriones cigóticos de cafeto durante la fase de establecimiento in vitro. A los tres días de establecidos los embriones se aplicó el tratamiento magnético con nivel de inducción de 2μT y frecuencia de 60 Hz durante un tiempo de exposición de 3 minutos. Para ello se empleó un estimulador electromagnético para cultivos in vitro BioNaK-03. Como control se emplearon embriones que no recibieron tratamiento electromagnético. A las 6 semanas de cultivo se determinó el contenido de proteínas y carbohidratos. Los resultados mostraron un incremento significativo de las concentraciones de estos compuestos para los embriones tratados. La aplicación de campos electromagnéticos en esta fase de cultivo puede contribuir a mejorar la calidad de las plantas obtenidas de embriones cigóticos de cafeto al modificar el curso de algunos procesos fisiológicos y bioquímicos. Esto conllevaría a un aumento del vigor y aseguraría un mejor desarrollo de la planta en fases posteriores.Palabras clave: Caturra rojo, café, plantas in vitr

Accurate characterization of multi-resonant reflectarray cells by artificial neural networks

This paper describes the accurate characterization of the reflection coefficients of a multilayered reflectarray element by means of artificial neural networks. The procedure has been tested with different RA elements related to actual specifications. Up to 9 parameters were considered and the complete reflection coefficient matrix was accurately obtained, including cross polar reflection coefficients. Results show a good agreement between simulations carried out by the Method of Moments and the ANN model outputs at RA element level, as well as with performances of the complete RA antenna designed