Use of tunable nanopore blockade rates to investigate colloidal dispersions

Tunable nanopores in elastomeric membranes have been used to study the dependence of ionic current blockade rate on the concentration and electrophoretic mobility of particles in aqueous suspensions. A range of nanoparticle sizes, materials and surface functionalities has been tested. Using pressure-driven flow through a pore, the blockade rate for 100 nm carboxylated polystyrene particles was found to be linearly proportional to both transmembrane pressure (controlled between 0 and 1.8 kPa) and particle concentration (between 7 x 10^8 and 4.5 x 10^10 mL^-1). This result can be accurately modelled using Nernst-Planck transport theory. Using only an applied potential across a pore, the blockade rates for carboxylic acid and amine coated 500 nm and 200 nm silica particles were found to correspond to changes in their mobility as a function of the solution pH. Scanning electron microscopy and confocal microscopy have been used to visualise changes in the tunable nanopore geometry in three dimensions as a function of applied mechanical strain. The pores observed were conical in shape, and changes in pore size were consistent with ionic current measurements. A zone of inelastic deformation adjacent to the pore has been identified as critical in the tuning process

On the generation and propagation of Rossby waves in an ocean with a zonally shoaling mixed layer

This paper presents the theory for freely propagating and forced Rossby waves in a continuously stratified ocean where the bouyancy frequency, N, varies with longitude and depth. In this study zonal variations in N occur because the climatological mixed layer depth, h, varies with longitude.With the assumption that changes in h occur on a length scale which is large compared to a horizontal wavelength the free modes on a β-plane are examined. It is found that realistic mixed layer depth changes can cause amplitude modulations, the largest amplitudes occurring where the mixed layer is shallowest. The requirement that h variations occur slowly is removed by employing a numerical model to study the free modes in a continuously stratified meridional channel. A criterion, based on the ratio of a horizontal length scale associated with the wave packet and the internal Rossby radius, is derived for determining when a free mode may be affected by the zonal variations in the stratification. Using climatological mixed layer depth data at 35N in the Atlantic (taken from Lamb, 1984) the basin modes are numerically determined. The major response is now concentrated where the mixed layer is deepest. This apparent contradiction is explained. A general theory is presented for calculating the forced basin mode response in terms of the free modes. As an example, a wind stress curl is applied as a body force over the mixed layer for a finite duration. After the forcing is removed the percentage that each basin mode contributes to the total solution is calculated. It is found that the dominant response to wind stress curl forcing can be significantly affected by the presence of a variable depth mixed layer. The implication of this study for the interaction between baroclinic Rossby waves and mixed layer dynamics is discussed

Structural Examination of Au/Ge(001) by Surface X-Ray Diffraction and Scanning Tunneling Microscopy

The one-dimensional reconstruction of Au/Ge(001) was investigated by means of autocorrelation functions from surface x-ray diffraction (SXRD) and scanning tunneling microscopy (STM). Interatomic distances found in the SXRD-Patterson map are substantiated by results from STM. The Au coverage, recently determined to be 3/4 of a monolayer of gold, together with SXRD leads to three non-equivalent positions for Au within the c(8x2) unit cell. Combined with structural information from STM topography and line profiling, two building blocks are identified: Au-Ge hetero-dimers within the top wire architecture and Au homo-dimers within the trenches. The incorporation of both components is discussed using density functional theory and model based Patterson maps by substituting Germanium atoms of the reconstructed Ge(001) surface.Comment: 5 pages, 3 figure

Evolution of the interfacial structure of LaAlO3 on SrTiO3

The evolution of the atomic structure of LaAlO3 grown on SrTiO3 was investigated using surface x-ray diffraction in conjunction with model-independent, phase-retrieval algorithms between two and five monolayers film thickness. A depolarizing buckling is observed between cation and oxygen positions in response to the electric field of polar LaAlO3, which decreases with increasing film thickness. We explain this in terms of competition between elastic strain energy, electrostatic energy, and electronic reconstructions. The findings are qualitatively reproduced by density-functional theory calculations. Significant cationic intermixing across the interface extends approximately three monolayers for all film thicknesses. The interfaces of films thinner than four monolayers therefore extend to the surface, which might affect conductivity

Kinematics of women's sprint canoeing technique

Little is known about the biomechanics of sprint canoeing, especially for women’s canoeing, and a quantitative kinematic description of the motion would help coaches to develop valid technique coaching models. Five highly-trained female canoeists were filmed at 150 Hz while undertaking a 50 s maximal effort on a canoe ergometer, whose trolley motions were taken to represent those of the boat. Selected boat, body and paddle kinematics were evaluated at three key stroke cycle events (Contact, Paddle Vertical, and End of Drive) and their patterns monitored across the stroke cycle. While no clear trends between the kinematics and power output emerged, a range of strategies were identified and the data represent an initial step in the construction of detailed technique models that can be used to evaluate and monitor individual athletes

Unit cell of graphene on Ru(0001): a 25 x 25 supercell with 1250 carbon atoms

The structure of a single layer of graphene on Ru(0001) has been studied using surface x-ray diffraction. A surprising superstructure has been determined, whereby 25 x 25 graphene unit cells lie on 23 x 23 unit cells of Ru. Each supercell contains 2 x 2 crystallographically inequivalent subcells caused by corrugation. Strong intensity oscillations in the superstructure rods demonstrate that the Ru substrate is also significantly corrugated down to several monolayers, and that the bonding between graphene and Ru is strong and cannot be caused by van der Waals bonds. Charge transfer from the Ru substrate to the graphene expands and weakens the C-C bonds, which helps accommodate the in-plane tensile stress. The elucidation of this superstructure provides important information in the potential application of graphene as a template for nanocluster arrays.Comment: 9 pages, 3 figures, paper submitted to peer reviewed journa

Web Surveys (Version 2.0)

This contribution addresses fundamental methodological problems facing online surveys, especially the coverage problem and sample-selection issues. The use of online panels based on random samples is seen as a possible solution

Profiling the interface electron gas of LaAlO3/SrTiO3 heterostructures by hard X-ray photoelectron spectroscopy

The conducting interface of LaAlO$_3$/SrTiO$_3$ heterostructures has been studied by hard X-ray photoelectron spectroscopy. From the Ti~2$p$ signal and its angle-dependence we derive that the thickness of the electron gas is much smaller than the probing depth of 4 nm and that the carrier densities vary with increasing number of LaAlO$_3$ overlayers. Our results point to an electronic reconstruction in the LaAlO$_3$ overlayer as the driving mechanism for the conducting interface and corroborate the recent interpretation of the superconducting ground state as being of the Berezinskii-Kosterlitz-Thouless type.Comment: 4 pages, 4 figure