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 transport‐limited erosion model, while other authors suggest that a detachment‐limited 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 end‐member fluvial erosion models to reproduce the well‐documented 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 transport‐limited model is unable to account for the catchments’response to the increase in uplift rate, consistent with the observed low rates of sediment supply to the channels. Instead, a detachment‐limited model with a threshold corresponding to the field‐derived median grain size of the sediment plus a slope‐dependent 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 slope‐ 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

Controlled motion of electrically neutral microparticles by pulsed direct current

A controlled motion of electrically neutral microparticles in a conductive liquid at high temperatures has not yet been realized under the uniform direct electric current field. We propose a simple method, which employs pulsed direct current to a conductive liquid metal containing low-conductivity objects at high temperature. The electric current enables the low-conductivity particles to pass from the centre towards the various surfaces of the high-conductivity liquid metal. Most interestingly, the directionality of microparticles can be controlled and their speed can be easily regulated by adjusting pulsed current density. We find that the movement may arise from the configuration of electrical domains which generates a driving force which exceeds the force of gravity and viscous friction. All of these features are of potential benefit in separating the particles of nearly equal density but distinctly different electrical conductivities, and also offer considerable promise for the precise and selective positioning of micro-objects or the controlled motion of minute quantities of surrounding fluids

Silica nanowire arrays for diffraction-based bioaffinity sensing

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Arrays of electrodeposited silica nanowires (SiO2 NWs) have been fabricated over large areas (cm(2)) on fluoropolymer thin films attached to glass substrates by a combination of photolithography and electrochemically triggered sol-gel nanoscale deposition. Optical and scanning electron microscopy (SEM) measurements revealed that the SiO2 NW arrays had an average spacing of ten micrometers and an average width of 700 nm with a significant grain structure that was a result of the sol-gel deposition process. The optical diffraction properties at 633 nm of the SiO2 NW arrays were characterized when placed in contact with solutions by using a prism-coupled total internal reflection geometry; quantification of changes in these diffraction properties was applied in various sensing applications. Bulk refractive index sensing by using the SiO2 NW grating was demonstrated with a sensitivity of 1.30×10(-5) RIU. Toposelectively chemically modified SiO2 NW arrays were used for diffraction biosensing measurements of surface binding events, such as the electrostatic adsorption of gold nanoparticles and the bioaffinity adsorption of streptavidin onto a biotin monolayer. Finally, the application of the SiO2 NW arrays for practical medical-diagnostic applications was demonstrated by monitoring the diffraction of SiO2 NW arrays functionalized with a single-stranded (ss)DNA aptamer to detect human α-thrombin from solutions at sub-pathologic nanomolar concentrations

H₂ Mapping on Pt-Loaded TiO₂ Nanotube Gradient Arrays

We describe a rapid screening technique for determining the optimal characteristics of nanophotocatalysts for the production of H₂ on a single surface. Arrays of TiO₂ nanotubes (NTs) with a gradient in length and diameter were fabricated by bipolar anodization, and a perpendicular gradient of Pt nanoparticles (NPs) was generated by the toposelective decoration of the TiO₂ NTs. Photocatalytic hydrogen evolution was locally triggered with a UV laser beam, and the arrays were screened in the <i>x</i> and <i>y</i> directions for spatially resolved kinetic measurements and the mapping of the optimal hydrogen production. By using this technique, we demonstrate the time-efficient and straightforward determination of the tube dimensions and Pt loading for optimized H₂ production. The concept holds promise for generally improving the study of many photoreactions as a function of the physicochemical characteristic of nanophotocatalysts, which renders it highly attractive for the optimization of various important chemical processes