Plato: a localised orbital based density functional theory code

The Plato package allows both orthogonal and non-orthogonal tight-binding as well as density functional theory (DFT) calculations to be performed within a single framework. The package also provides extensive tools for analysing the results of simulations as well as a number of tools for creating input files. The code is based upon the ideas first discussed in Sankey and Niklewski (1989) [1] with extensions to allow high-quality DFT calculations to be performed. DFT calculations can utilise either the local density approximation or the generalised gradient approximation. Basis sets from minimal basis through to ones containing multiple radial functions per angular momenta and polarisation functions can be used. Illustrations of how the package has been employed are given along with instructions for its utilisation

VibraTip® durability in clinical practice:How long does it last?

VibraTip® is a battery-powered, disposable, key fob-sized source of vibration used to assess the integrity of vibration perception. To find out how long the device lasts, the stability of its vibration output was measured in response to two usage patterns:- in the first, VibraTip® was subject to 7000 half second activations separated by 2 second rests. This yielded fairly consistent frequency output for the first 6000 activations but an early reduction in amplitude over the first 1000 activations, steadying between 2000 and 6000 activations. in the second, designed to mimic more closely real life clinical usage, runs of ten, half second activations at 2 second intervals were interspersed by 10 minute rests. The cycle was repeated 350 times in all with additional overnight rests to allow electrochemical recovery. VibraTip® performance under these conditions was highly consistent over at least the first 1500 activations, with very little change in vibration frequency even after 3500 discharges. These results indicate that usage patterns markedly affect VibraTip® durability. Rests between ‘patients’ and overnight, characteristic of normal clinical activity, suggests that VibraTip® is likely to provide very consistent performance in the clinical arena for many months of routine use. </jats:p

Density-functional study of adsorption of Co on Si(100)

We have studied the stable sites for Co both on the surface of Si(100) and subsurface by using ab initio methods. We show that the most stable surface site for Co is situated in the dimer trenches (the low site). The subsurface sites that we study are all found to be more stable than the most stable surface site. The most stable subsurface site is the under-dimer site. The most stable site of all is, however, the dimer vacancy site formed by removing the dimer above the cobalt in the under-dimer site

Power dissipation in nanoscale conductors: classical, semi-classical and quantum dynamics

Modelling Joule heating is a difficult problem because of the need to introduce correct correlations between the motions of the ions and the electrons. In this paper we analyse three different models of current induced heating (a purely classical model, a fully quantum model and a hybrid model in which the electrons are treated quantum mechanically and the atoms are treated classically). We find that all three models allow for both heating and cooling processes in the presence of a current, and furthermore the purely classical and purely quantum models show remarkable agreement in the limit of high biases. However, the hybrid model in the Ehrenfest approximation tends to suppress heating. Analysis of the equations of motion reveals that this is a consequence of two things: the electrons are being treated as a continuous fluid and the atoms cannot undergo quantum fluctuations. A means for correcting this is suggested

On hybrid circuits exploiting thermistive properties of slime mould

Slime mould Physarum polycephalum is a single cell visible by the unaided eye. Let the slime mould span two electrodes with a single protoplasmic tube: if the tube is heated to approximately ≈40 °C, the electrical resistance of the protoplasmic tube increases from ≈3 Mω to ≈10,000 Mω. The organisms resistance is not proportional nor correlated to the temperature of its environment. Slime mould can therefore not be considered as a thermistor but rather as a thermic switch. We employ the P. polycephalum thermic switch to prototype hybrid electrical analog summator, NAND gates, and cascade the gates into Flip-Flop latch. Computing operations performed on this bio-hybrid computing circuitry feature high repeatability, reproducibility and comparably low propagation delays

Autonomous energy harvesting and prevention of cell reversal in MFC stacks

© The Author(s) 2016. This study presents a novel method for avoiding cell reversal whilst optimising energy harvesting from stacked Microbial Fuel Cells (MFCs) by dynamically reconfiguring the electrical connections between them. The sequential changing of in-parallel and in-series electrical connections in an 8-MFC stack resulted in energy being transferred twice as fast into a super-capacitor avoiding cell reversal in MFCs as opposed to a fixed in-series configuration. This approach, allows for a lower internal resistance state within the stack compared to a fixed electrical configuration. This is critical in the initial stages of energy extraction from MFCs connected electrically in-series where the impedance of the capacitor is drawing high levels of current and cell reversals are likely to occur and hinder performance. Automation of electrical connections doubled the extracted power from the stack whilst halving the charging times without any cell reversal occurrence. The electrical reconfiguring of MFCs was performed by a USB-powered switch-box that modulated the stack's connections. This lead to the development of an energy autonomous switch-box circuitry powered solely by the MFC stack with negligible impact on the overall energy harvesting efficiency (i.e. above 90%)

Inelastic quantum transport: the self-consistent Born approximation and correlated electron-ion dynamics

A dynamical method for inelastic transport simulations in nanostructures is compared with a steady-state method based on non-equilibrium Green's functions. A simplified form of the dynamical method produces, in the steady state in the weak-coupling limit, effective self-energies analogous to those in the Born Approximation due to electron-phonon coupling. The two methods are then compared numerically on a resonant system consisting of a linear trimer weakly embedded between metal electrodes. This system exhibits enhanced heating at high biases and long phonon equilibration times. Despite the differences in their formulation, the static and dynamical methods capture local current-induced heating and inelastic corrections to the current with good agreement over a wide range of conditions, except in the limit of very high vibrational excitations, where differences begin to emerge.Comment: 12 pages, 7 figure