Studies on electrostatic interactions of colloidal particles under two-dimensional confinement

We study the effective electrostatic interactions between a pair of charged colloidal particles without salt ions while the system is confined in two dimensions. In particular we use a simplified model to elucidate the effects of rotational fluctuations in counterion distribution. The results exhibit effective colloidal attractions under appropriate conditions. Meanwhile, long-range repulsions persist over most of our studied cases. The repulsive forces arise from the fact that in two dimensions the charged colloids cannot be perfectly screened by counterions, as the residual quadrupole moments contribute to the repulsions at longer range. And by applying multiple expansions we find that the attractive forces observed at short range are mainly contributed from electrostatic interactions among higher-order electric moments. We argue that the scenario for attractive interactions discussed in this work is applicable to systems of charged nanoparticles or colloidal solutions with macroions.Comment: 23 pages, 11 figures, 1 tabl

Cost modelling of floating wind farms with upscaled rotors in Maltese waters

The technical viability of offshore wind projects depends upon a number of factors such as the site-specific wind resource, sea depth, seabed composition, distance to the shore and climatic conditions amongst others. The Mediterranean is characterised by deep seas relatively close to the shore and only a reasonable wind climate if compared to conditions in countries that are forerunners in the offshore wind sector. The development of floating wind turbine support structures will allow wind farms in deeper waters and will be a catalyst for the wider diffusion and larger-scale implementation of offshore wind farms on a global level. This study investigates the prospects for a hypothetical 100 MW floating offshore wind farm well to the west of the island of Malta. The study models three upscaled turbines having rotor diameters of 126, 145 and 170 m. The study shows that the rotor upscaling process can improve the economic viability of offshore wind turbines with the improved energy yield counterbalancing the higher investment costs required for such a project and thus resulting in a lower cost of energy. The levelised cost of electricity is estimated to be in the 21.0 to 23.6 €cent/kWh range which, although still well above the current market prices of electricity generated by conventional means, is expected to drop considerably over the coming years as new international players enter the offshore wind market. Increasing levels of competition, new concepts coming to fruition and wider and larger-scale diffusion of new technologies will help bring down costs of energy for the offshore wind farms of the future.Bajada New Energy, General Membrane, EcoGroup, Econetique, Energy Investment, JMV Vibro Blocks, Solar Engineering, Solar Solutionspeer-reviewe

Comparing the economic feasibility of offshore floating wind and solar photovoltaic technologies in Central Mediterranean deep waters

Malta, being a very small and densely populated island in the central Mediterranean, has little space for large scale onshore wind turbine or photovoltaic projects. Maltese territorial waters are mostly too deep for conventional offshore wind farms to be constructed save for a handful of near-shore reefs and shoals. The quest for offshore wind turbine structure designs capable of being installed in deeper waters will revolutionize prospects for offshore wind projects worldwide; but even more so in the Mediterranean region. This paper presents a preliminary engineering analysis to develop two cost-optimized offshore floating structures to support (1) a single multi-megawatt scale wind turbine and (2) a solar photovoltaic farm with the same energy production as that of the single wind turbine. The primary objective of this work is to determine the most economically feasibility option for harvesting renewable energy at sea: offshore wind or offshore solar photovoltaic energy.peer-reviewe

Analysis of a novel offshore platform with integrated energy storage operating in Central Mediterranean waters

A thermodynamic model of a novel energy storage device is described and simulated in the context of a central Mediterranean climate. The device uses a hydro-pneumatic concept to store energy as compressed air. It is designed to be integrated into an offshore floating platform. The thermodynamic model illustrates the behaviour of the compression process and the heat exchange with the surrounding environment. Different rates of compression are simulated, and it can be observed that faster compression rates lead to higher gas temperatures and pressures. The sensitivity to climatic conditions is also investigated, however this effect was seen to be minimal. A simplified Black-Box Model is also developed, with its parameters obtained through a curve-fitting process. Finally, a stochastic input is fed to both models and a comparison is made. The simplified model results in a minor over-prediction of the efficiency.peer-reviewe

Analysis of a novel offshore platform with integrated energy storage operating in Central Mediterranean waters

A thermodynamic model of a novel energy storage device is described and simulated in the context of a central Mediterranean climate. The device uses a hydro-pneumatic concept to store energy as compressed air. It is designed to be integrated into an offshore floating platform. The thermodynamic model illustrates the behaviour of the compression process and the heat exchange with the surrounding environment. Different rates of compression are simulated, and it can be observed that faster compression rates lead to higher gas temperatures and pressures. The sensitivity to climatic conditions is also investigated, however this effect was seen to be minimal. A simplified Black-Box Model is also developed, with its parameters obtained through a curve-fitting process. Finally, a stochastic input is fed to both models and a comparison is made. The simplified model results in a minor over-prediction of the efficiency.peer-reviewe

Weak Long-Ranged Casimir Attraction in Colloidal Crystals

We investigate the influence of geometric confinement on the free energy of an idealized model for charge-stabilized colloidal suspensions. The mean-field Poisson-Boltzmann formulation for this system predicts pure repulsion among macroionic colloidal spheres. Fluctuations in the simple ions' distribution provide a mechanism for the macroions to attract each other at large separations. Although this Casimir interaction is long-ranged, it is too weak to influence colloidal crystals' dynamics.Comment: 5 pages 2 figures ReVTe

Theoretical Investigation of Local Electron Temperature in Quantum Hall Systems

In this work we solve thermo-hydrodynamical equations considering a two dimensional electron system in the integer quantum Hall regime, to calculate the spatial distribution of the local electron temperature. We start from the self-consistently calculated electrostatic and electrochemical potentials in equilibrium. Next, by imposing an external current, we investigate the variations of the electron temperature in the linear-response regime. Here a local relation between the electron density and conductivity tensor elements is assumed. Following the Ohm's law we obtain local current densities and by implementing the results of the thermo-hydrodynamical theory, calculate the local electron temperature. We observe that the local electron temperature strongly depends on the formation of compressible and incompressible strips.Comment: 10 pages, 4 figure

Electrolytic depletion interactions

We consider the interactions between two uncharged planar macroscopic surfaces immersed in an electrolyte solution which are induced by interfacial selectivity. These forces are taken into account by introducing a depletion free-energy density functional, in addition to the usual mean-field Poisson-Boltzmann functional. The minimization of the total free-energy functional yields the density profiles of the microions and the electrostatic potential. The disjoining pressure is obtained by differentiation of the total free energy with respect to the separation of the surfaces, holding the range and strength of the depletion forces constant. We find that the induced interaction between the two surfaces is always repulsive for sufficiently large separations, and becomes attractive at shorter separations. The nature of the induced interactions changes from attractive to repulsive at a distance corresponding to the range of the depletion forces.Comment: 17 pages, 4 Postscript figures, submitted to Physical Review

Phase behaviour of a model of colloidal particles with a fluctuating internal state

Colloidal particles are not simple rigid particles, in general an isolated particle is a system with many degrees of freedom in its own right, e.g., the counterions around a charged colloidal particle.The behaviour of model colloidal particles, with a simple phenomenological model to account for these degrees of freedom, is studied. It is found that the interaction between the particles is not pairwise additive. It is even possible that the interaction between a triplet of particles is attractive while the pair interaction is repulsive. When this is so the liquid phase is either stable only in a small region of the phase diagram or absent altogether.Comment: 12 pages including 4 figure