We
report the femtomolar detection of silver (Ag) nanoparticles
by direct-impact voltammetry. This is achieved through the use of
a random array of microelectrodes (RAM) integrated into a purpose-built
flow cell, allowing combined diffusion and convection to the electrode
surface. A coupled RAM-flow cell system is implemented and is shown
to give reproducible wall-jet type flow characteristics, using potassium
ferrocyanide as a molecular redox species. The calibrated flow system
is then used to detect and quantitatively size Ag nanoparticles at
femtomolar concentrations. Under flow conditions, it is found the
nanoparticle impact frequency increases linearly with the volumetric
flow rate. The resulting limit of detection is more than 2 orders
of magnitude smaller than the previous detection limit for direct-impact voltammetry (900 fM) [J. Ellison et al. Sens. Actuators, B2014, 200, 47], and is more than 30 times smaller than the previous detection
limit for mediated-impact voltammetry (83 fM) [T.
M. Alligrant et al. Langmuir2014, 30, 13462].
The search for an improved mechanised method of maintaining railway track to the correct level and alignment led to the development of the Stoneblower, a machine that lifts the rail and attached sleepers and pneumatically injects the required amount of 20 mm stone into the void created. This minimises disturbance to the existing well-compacted ballast. By 1999 a fleet of Stoneblowers was fully operational across the UK rail network and achieving target rates of track maintenance. This paper compares the track-quality data recorded before, during and after Stoneblower maintenance and confirms the potential of the Stoneblower. Detailed analysis of the data has given a better understanding of the performance, and has provided guidance for optimising the deployment of the Stoneblowers and the stoneblowing procedures.
The design and construction of a new automatic volume change unit, which is capable of measuring large volume changes without the need for reversing flow direction, is described. It works on the principle of a floating magnet at an air-water interface activating a magnetorestrictive sensor. Its performance is assessed against the criteria listed by Lade (1988) as desirable for any automatic volume change measuring device, and is shown to satisfy these criteria.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.