Modeling subcortical white matter stimulation

ObjectiveIntracranial electrical stimulation of subcortical axonal tracts is particularly useful during brain surgery, where mapping helps identify and excise dysfunctional tissue while avoiding damage to functional structures. Stimulation parameters are generally set empirically and consequences for the spatial recruitment of axons within subcortical tracts are not well identified.ApproachComputational modeling is employed to study the effects of stimulation parameters on the recruitment of axons: monophasic versus biphasic stimuli induced with monopolar versus bipolar electrodes, oriented orthogonal or parallel to the tract, for isotropic and anisotropic tracts.Main resultsThe area and depth of axonal activation strongly depend on tissue conductivity and electrode parameters. The largest activation area results from biphasic stimulation with bipolar electrodes oriented orthogonal to axonal fasciculi, for anisotropic and especially isotropic tracts. For anisotropic tracts, the maximal activation depth is similar regardless of whether a monopolar or bipolar electrode is employed. For isotropic tracts, bipolar parallel and monopolar stimulation activate axons deeper than orthogonal bipolar stimulation. Attention is warranted during monophasic stimulation: a blockade of action potentials immediately under cathodes and a propagation of action potentials under anodes are found.SignificanceConsidering the spatial patterns of blockade and activation present during monophasic stimulation with both monopolar and bipolar electrodes, biphasic stimulation is recommended to explore subcortical axon responses during intraoperative mapping. Finally, the precise effect of electrical stimulation depends on conductivity profiles of tracts, and as such, should be explicitly considered for each individual subject and tract undergoing intracranial mapping.

Pre-Decommissioning Radiological Characterization of Concrete

The decommissioning of the BR3 (Belgian Reactor 3) approaches its final phase, in which the building structures are being decontaminated and either denuclearized for possible reuse or demolished. Apart from the presence of naturally occurring radionuclides in building materials, other radionuclides might be present due to contamination or activation. The overall process of the BR3 building structure D&D (Decontamination & Decommissioning) consists of the following steps: • make a complete inventory and preliminary categorize all elements based on historical data; • characterize and determine the contamination or activation depth; • determine the decontamination method; • perform the decontamination and clean up; • a possible intermediate characterization followed by an additional decontamination step; and • characterize for clearance. A good knowledge of the contamination and activation depth (second step) is fundamental in view of cost minimization. Currently, the method commonly used for the determination of the depth is based on core drilling and destructive analysis. Recently, we have introduced a complementary non destructive assay based on in-situ gamma spectroscopy. Field tests at BR3, both for contamination and activation, showed promising results.

The Management of Radioactive Concrete Arising From the Dismantling of a Pressurised Water Reactor: The R&D Project on the Recycling of Radioactive Concrete

Activated concrete represents the greatest volume of radioactive materials produced during the dismantling operations of a PWR reactor. For heavy barytes concrete, 133Ba is the dominating γ nuclide whereas in the rebars, it is the 60Co isotope. During the dismantling of the BR3 PWR reactor, we studied various aspects of the radioactive concrete issue: • the characterization of the activation depth and its modelization; • the efficiency of various demolition techniques and their application on real scale mock-ups; • the active testing and use of various dismantling and demolition techniques among which the remote controlled jack hammer and the diamond cutting techniques were the most extensively used. As alternative to the conditioning of the radioactive concrete as radioactive waste using the classical cement embedding strategy, we started an extensive R&D programme on the the recycling of the radioactive concrete. The basic idea is to perform a pretreatment of the radioactive concrete so that it can be re-used as aggregates for the fabrication of “radioactive grout”. This grout is then used for the conditioning of metallic radioactive waste. We demonstrated that it is technically feasible to prepare a good quality grout using heavy radioactive concrete as raw material mixed with fresh cement.

A Buoyancy and Stability Mechanism for Underwater Vehicles

This paper describes the design of a simple, inexpensive but effective ‘detach weight’ device that can aid in the stability as well as the recovery of underwater vehicles and unpropelled consoles. If the vehicle attempts to cross the maximum specified sea depth due to water seepage, poor stability, failure of normal recovery schedule, or inherent negative buoyancy as that of a console, then the proposed mechanism gets activated to achieve terminal buoyancy. Non-reliance on electrical, pneumatic or hydraulic power and sensors distinguish the device from conventional ballasting methods. Insitu assembly and adjustments of activation depth and weight can add flexibility to the vehicle design parameters such as overall CG, weight, trim, list etc.

Phenomenological and Operational Characterization of Factor-Analytically Derived Dimensions of Emotion

Based on ratings of 30 emotions on 50 adjective scales, secured from 117 university students, factor analysis yielded 3 dimensions of emotion, phenomenologically characterized as pleasantness vs unpleasantness, activation, depth. Operational characterization resulted from the correlations of the dimensions with personality measures: pleasantness vs unpleasantness converged with extraversion vs introversion, ego strength vs ego weakness, field independence vs field embeddedness, activation converged with impulsivity and cognitive simplicity. Depth was associated with enhanced self-evaluation.