Multifocal Transcranial Direct Current Stimulation Modulates Resting-State Functional Connectivity in Older Adults Depending on the Induced Current Density

Combining non-invasive brain stimulation (NIBS) with resting-state functional magnetic resonance imaging (rs-fMRI) is a promising approach to characterize and potentially optimize the brain networks subtending cognition that changes as a function of age. However, whether multifocal NIBS approaches are able to modulate rs-fMRI brain dynamics in aged populations, and if these NIBS-induced changes are consistent with the simulated electric current distribution on the brain remains largely unknown. In the present investigation, thirty-one cognitively healthy older adults underwent two different multifocal real transcranial direct current stimulation (tDCS) conditions (C1 and C2) and a sham condition in a crossover design during a rs-fMRI acquisition. The real tDCS conditions were designed to electrically induce two distinct complex neural patterns, either targeting generalized frontoparietal cortical overactivity (C1) or a detachment between the frontal areas and the posteromedial cortex (C2). Data revealed that the two tDCS conditions modulated rs-fMRI differently. C1 increased the coactivation of multiple functional couplings as compared to sham, while a smaller number of connections increased in C1 as compared to C2. At the group level, C1-induced changes were topographically consistent with the calculated electric current density distribution. At the individual level, the extent of tDCS-induced rs-fMRI modulation in C1 was related with the magnitude of the simulated electric current density estimates. These results highlight that multifocal tDCS procedures can effectively change rs-fMRI neural functioning in advancing age, being the induced modulation consistent with the spatial distribution of the simulated electric current on the brain. Moreover, our data supports that individually tailoring NIBS-based interventions grounded on subject-specific structural data might be crucial to increase tDCS potential in future studies amongst older adults.

Optimization of Electric Field Assisted Mining Process Applied to Rare Earths in Soils

The extraction of rare earths has been studied worldwide, however some of these processes have a high cost and can cause negative environmental impacts. In order to mine these species from the soil, Electric Field Assisted Mining arises as an alternative to conventional mining processes. Therefore, the experimental parameters can be improved to obtain better results in the extraction of these species. The aim of this paper is to propose the optimization of the Electric Field Assisted Mining process of yttrium, to obtain the optimal experimental configuration to be applied in real soils. An optimization problem was defined to obtain the maximum extraction mass of yttrium ion (Y3+), considering the limitation for the quantity of electric current density. A hybrid optimization technique was used, based on the sequential application of genetic algorithms and non-linear programming. Different optimal process configurations were obtained, considering distinct limits for the electric current density. The best experimental configuration resulted in 0.5386 V cm−1 electric field strength and 0.10 mol L−1 electrolyte concentration. This condition was reproduced in real soil, which obtained a Y3+ electromining efficiency of 41.48%. The results showed that this technique is promising for the extraction of rare earth in real soils.

Ohmic and Diamagnetic Currents Contribution on the Electromagnetic Penetration Depth of a Conducting Surface

Due to its conducting electron, metal is a good reflector for electromagnetic wave. An electromagnetic wave penetrating a metallic surface has a finite penetrating depth. There are two limit that are well studied in the physics textbooks. They are high frequency electromagnetic wave penetrating a metal with small conductivity and a static (low frequency) field penetrating a superconductor (metal with infinitely large conductivity). In this article we study the intermediate regime between these two limits. By setting the electric current density as the total sum of both Ohmic and Diamagnetic currents, we derive the penetration depth in the intermediate regime., we show the transition between these two limits.

Improving Performance of Laser and Shaped Tube Electrochemical Machining by Using Retracted Hybrid Tubular Tool Electrode

The coaxial laser has been introduced to shaped tube electrochemical machining (STEM), referred to as Laser-STEM, to enhance the materials removal rate and precision. To address the issue of central residual formation during the Laser-STEM process, which limited the machining stability and feeding rate, the retracted hybrid tubular electrode was applied. The formation mechanisms and effects of the W-shaped central residual were analyzed. Simulation and experiments were conducted to study the impact of the retracted length of the tubular electrode. Simulation results showed that a retracted length of 1-1.5 mm of the inner low-refractive layer could improve the electric current density distribution homogeneity to remove the W-shaped central residual in the machining area. The electric current density distribution homogeneity in the machining zone has been decreased by 38% by utilizing the hybrid tubular electrode with a retracted length of 2.0 mm. With a proper retracted length, the laser coupling efficiency exceeded 74.5%. Hence, the retracted hybrid tubular electrode could act as both the tool electrode and optical waveguide in the Laser-STEM process. Experimental results proved that the machining efficiency and precision of Laser-STEM could be enhanced by utilizing the retracted hybrid tubular electrode. With the retracted length deg rising from 0 mm to 1.5 mm, the maximum feeding speed increased by 373%, and the machining precision was improved by 42.2%. The maximum feeding rate of 4.1 mm/min has been achieved using the retracted hybrid tubular electrode in the Laser-STEM process, which has been improved by 105%, compared with the available maximum feeding rate of the tubular electrode in the STEM process. Finally, the small holes with a diameter of 1.4 mm and an aspect ratio of 15 have been processed by Laser-STEM with the retracted hybrid tubular electrode.

Hydrodynamically enhanced electrochemical mass transfer on the surface of an electrically conductive droplet

A fully coupled model is proposed to investigate the influence of flow on electrochemical mass transfer at the interface between the electrolyte and an electrically conductive droplet. The electric current flows through the droplet, and consequently the droplet acts as both anode and cathode. Computations of flow, concentration of reactant, and electric current density fields were carried out. Various droplet sizes (0.5, 2, 4 mm) under different flow regimes considering Reynolds number (Re = 0.2, 2, 20, 40 and 80) were investigated. An iterative numerical method is proposed to determine the concentration of reactant and electric current density at droplet-electrolyte interface considering the reaction kinetics (Butler-Volmer) formula and the diffusion-advection of the reactant through the hydrodynamic boundary layer around the droplet. With the increase of Reynolds number, the amount of electric current density which flows through the droplet increases. It is found that the mass transfer at droplet-electrolyte interface is controlled by reaction kinetics for the small droplet (0.5 mm). However, the diffusion of the reactant governs the efficiency of mass transfer with the increase of the droplet size (2 and 4 mm). With the increase of Reynolds number, the anodic area on the surface of droplet is enlarged.

Mineral Prospect Identification Using Inducedpolarization And Very Low Frequency-EM Methods At Sangon, Kalirejo Village, Kokap Sub-District, Kulonprogo Regency, Special Region Of Yogyakarta, Indonesia

A research of induced polarization and very low frequency method was carried out at Sangon Village, Kulonprogo to identify mineralization zone. The result of these methods were able to be used to support each other. Mineralization zone is shown by high resistivity and high hargeability area of induced polarization method, and is also shown by high electric current density area of very low frequency method. Interpretation of resistivity and chargeability model shows that mineralization zone is mostly located at the depth below 10 m from surface. On the other hand, interpretation of electric current density models at depth 10 m and 20 m show that mineralization zone is not well distributed respect to alteration zone, which is the character of low sulfidation epithermal type, mostly at north-south direction.