Steric effects in adsorption of ions from mixed electrolytes into microporous carbon

With the goal to improve the capacitance in electrochemical double-layer capacitors (EDLCs) many studies on pore size/ion size relationship have been undertaken to achieve a better understanding of the charge storage mechanism in the electrochemical double-layer in confinement. A significant capacitance increase was achieved by using carbon electrodes with micropores (b1 nm), when the carbon pore size was close to the ion size. In this paper, the accessibility of narrow pores is investigated by selecting a carbon with a small pore size (b0.7 nm) and electrolyte mixtures with different ion sizes. It has been shown that the adsorption capacitance limitation observed for large cations and anions could be overcome by adding ions with a smaller effective size. This result demonstrates that the pores are accessible when their size matches the effective ion size and contradicts the surface saturation assumption; effective ion size which exceeds the pore size leads to current limitation. This work confirms that the steric effect is involved when ions are adsorbed into pores and highlights the importance of controlling ion size/pore size relationship for optimisation of the capacitive performance of EDLC devices

Outer layer turbulence intensities in smooth- and rough-wall boundary layers

Clear differences in turbulence intensity profiles in smooth, transitional and fully rough zero-pressure-gradient boundary layers are demonstrated, using the diagnostic plot introduced by Alfredsson, Segalini & Örlü (Phys. Fluids, vol. 23, 2011, p. 041702) – u?/U versus U/Ue, where u? and U are the local (root mean square) fluctuating and mean velocities and Ue is the free stream velocity. A wide range of published data are considered and all zero-pressure-gradient boundary layers yield outer flow u?/U values that are roughly linearly related to U/Ue, just as for smooth walls, but with a significantly higher slope which is completely independent of the roughness morphology. The difference in slope is due largely to the influence of the roughness parameter (?U+ in the usual notation) and all the data can be fitted empirically by using a modified form of the scaling, dependent only on ?U/Ue. The turbulence intensity, at a location in the outer layer where U/Ue is fixed, rises monotonically with increasing ?U/Ue which, however, remains of O(1) for all possible zero-pressure-gradient rough-wall boundary layers even at the highest Reynolds numbers. A measurement of intensity at a point in the outer region of the boundary layer can provide an indication of whether the surface is aerodynamically fully rough, without having to determine the surface stress or effective roughness height. Discussion of the implication for smooth/rough flow universality of differences in outer-layer mean velocity wake strength is include

Solvent effect on the ion adsorption from ionic liquid electrolyte into sub-nanometer carbon pores

This paper presents the results from the investigation of the influence of ion size on the capacitance behaviour of TiC-derived carbon (CDC) powders in the ethyl-methylimmidazolium-bis(trifluoromethane-sulfonyl)imide ionic liquid (EMI, TFSI) used as neat electrolyte at 60°C or as salt dissolved in acetonitrile and tested at room temperature. These studies were carried out with the assembly of conventional 3-electrode electrochemical cells as well as using the Cavity-MicroElectrode (CME) technique. The issues regarding the extents of desolvation of the electrolyte ions when adsorbed in the pores of the CDCs under applied potential were studied, the CME technique was found to be particularly efficient in the deduction of the effective ion size under solvated conditions

A local and integrable lattice regularization of the massive Thirring model

The light--cone lattice approach to the massive Thirring model is reformulated using a local and integrable lattice Hamiltonian written in terms of discrete fermi fields. Several subtle points concerning boundary conditions, normal--ordering, continuum limit, finite renormalizations and decoupling of fermion doublers are elucidated. The relations connecting the six--vertex anisotropy and the various coupling constants of the continuum are analyzed in detail.Comment: Latex, 24 pages, some corrected misprints and minor changes, 2 Postscript figures unchange

Application of Low Potential Electric Fields for Improving Slope Stability

AbstractThe aim of this research is the application of low potential direct currents in order to improve slope stability by inducing the reduction of potential swelling and water content, and the precipitation of carbonates in cohesive soil pertaining to a possible sliding surface. Two different types of tests were performed: the first one on small samples and the other one on a physical model reproducing a slope. Main results showing the effectiveness of this application are described

Preparation of the measurement system for the spatial characterization of SPIDER negative-ion plasma source

Neutral beam injectors are fundamental auxiliary heating systems for nuclear fusion machines. The formation of the negative-ion beam, precursor of the neutral beam, occurs by extracting the ions from a plasma through a multi-aperture, multi-electrode electrostatic accelerator. In the case of the ITER neutral beam injector, to obtain sufficient current, the extraction takes place through 1280 openings distributed over a very large area, which must be illuminated by a sufficiently uniform plasma. The plasma, formed in 8 radio-frequency drivers, passes through an expansion chamber before reaching the extractor. The experimental study of the plasma parameters at the location of the ion extraction, and of its expansion from the driver region, is possible using Langmuir probes on mobile supports. In this dissertation, a preparatory study is conducted for characterizing negative ion plasma in SPIDER negative-ion plasma source. A bibliographic research is performed in order to understand how similar measures were taken in the past in similar devices, at the end of which three different kind of probes are designed and tested: a Mach probe, a double Langmuir probe and a planar Langmuir probe. The Mach probe is composed of 4 cylindrical pins and is designed in order to measure plasma flux and velocity drift. It was tested by assembling it on a rotating system inside an Argon plasma, in order to verify its symmetry and if it is suitable for an RF source like SPIDER. Next, the double probe (named ADEL, i.e. A Double Electrode Langmuir probe) consists of two parallel cylindrical electrodes, and it should give a completely floating measures of the plasma parameters. It was tested inside the CRISPy experiment (Compact RF Ion Source Prototype for emittance scanner testing) in order to give an estimate of electron temperature and plasma density. Regarding the planar Langmuir probe, it is composed of two electrodes: a main electrode and a compensation one. A model in LTSpice is used to simulate its behaviour in an RF plasma, so as to find the optimum capacity to be put in parallel between the two electrodes. Finally, a plan for probes installation and measurements in SPIDER is established in light of the results obtained.ope