Single walled carbon nanotube channel flow electrode : hydrodynamic voltammetry at the nanomolar level

The use of single walled carbon nanotube (SWNT) band electrodes in a channel flow cell, for low concentration detection, with hydrodynamic voltammetry is reported. A two dimensional SWNT network electrode is combined with a one piece channel flow cell unit, fabricated by microstereolithography. This configuration provides well defined hydrodynamics over a wide range of volume flow rates (0.05–25 mL min− 1). Limiting current measurements, from linear sweep voltammograms, are in good agreement with the channel electrode Levich equation, for the one electron oxidation of ferrocenylmethyl trimethylammonium (FcTMA+), over a wide concentration range, 1 × 10− 8 M to 2.1 × 10− 5 M, with a detection limit of 5 nM. At the highest flow rates, some influence of the slightly recessed electrode geometry arising from the SWNT electrode fabrication is noted. However, this can be accounted for by a full simulation of the hydrodynamics and solution of the resulting convection–diffusion equation. Application of this hydrodynamic configuration to the voltammetric detection of dopamine is also demonstrated

The kaolinitic clay deposits on Beaconsfield, north of Grahamstown

The Grahamstown clay deposits occur below the Grahamstown Formation silcrete, which forms a remnant of an extensive peneplain that developed on the African erosion surface during the Cretaceous–Tertiary period. This paper provides new data on the distribution of the kaolinitic clay deposits in the Beaconsfield area north of Grahamstown. These data include 23 borehole profiles through the deposits, and the chemistry and mineralogy of the clays. Relatively little information is available on this part of the peneplain. It was found that the thickness of the kaolin horizon varies considerably, but reaches 35m in places. It generally occurs under a silcrete cover, which attains a thickness of 8 m in places. Lithological logs enable direct comparison across the Beaconsfield area. The clays are developed in both the Witteberg Group shale and Dwyka Group tillite. The contact between the clay and underlying bedrock is gradational and relatively uneven. Major-element X-ray fluorescence analyses revealed that there is chemical variation, both vertically and laterally. Al2O3 content is generally near 20%, but may reach 29%. SiO2 content varies between 55 and 70+%. SiO2 contents are highest in the silcretes occurring just below soil level. Fe2O3 is high locally in the top part of the profile. K2O and Na2O are generally low, but increase towards the unweathered bedrock as the primary feldspar content increases. These compositional variations are compatible with residual concentrations of kaolinitic clays through deep weathering below the former African erosion surface

Quantitative localized proton-promoted dissolution kinetics of calcite using scanning electrochemical microscopy (SECM)

Scanning electrochemical microscopy (SECM) has been used to determine quantitatively the kinetics of proton-promoted dissolution of the calcite (101̅4) cleavage surface (from natural “Iceland Spar”) at the microscopic scale. By working under conditions where the probe size is much less than the characteristic dislocation spacing (as revealed from etching), it has been possible to measure kinetics mainly in regions of the surface which are free from dislocations, for the first time. To clearly reveal the locations of measurements, studies focused on cleaved “mirror” surfaces, where one of the two faces produced by cleavage was etched freely to reveal defects intersecting the surface, while the other (mirror) face was etched locally (and quantitatively) using SECM to generate high proton fluxes with a 25 μm diameter Pt disk ultramicroelectrode (UME) positioned at a defined (known) distance from a crystal surface. The etch pits formed at various etch times were measured using white light interferometry to ascertain pit dimensions. To determine quantitative dissolution kinetics, a moving boundary finite element model was formulated in which experimental time-dependent pit expansion data formed the input for simulations, from which solution and interfacial concentrations of key chemical species, and interfacial fluxes, could then be determined and visualized. This novel analysis allowed the rate constant for proton attack on calcite, and the order of the reaction with respect to the interfacial proton concentration, to be determined unambiguously. The process was found to be first order in terms of interfacial proton concentration with a rate constant k = 6.3 (± 1.3) × 10–4 m s–1. Significantly, this value is similar to previous macroscopic rate measurements of calcite dissolution which averaged over large areas and many dislocation sites, and where such sites provided a continuous source of steps for dissolution. Since the local measurements reported herein are mainly made in regions without dislocations, this study demonstrates that dislocations and steps that arise from such sites are not needed for fast proton-promoted calcite dissolution. Other sites, such as point defects, which are naturally abundant in calcite, are likely to be key reaction sites

Statistical Topology of Cellular Networks in Two and Three Dimensions

Cellular networks may be found in a variety of natural contexts, from soap foams to biological tissues to grain boundaries in a polycrystal, and the characterization of these structures is therefore a subject of interest to a range of disciplines. An approach to describe the topology of a cellular network in two and three dimensions is presented. This allows for the quantification of a variety of features of the cellular network, including a quantification of topological disorder and a robust measure of the statistical similarity or difference of a set of structures. The results of this analysis are presented for numerous simulated systems including the Poisson-Voronoi and the steady-state grain growth structures in two and three dimensions

The relationship between social cognitive processes and behavior changes in people with amnestic Mild Cognitive Impairment or dementia using the Edinburgh Social Cognition Test (ESCoT)

Objectives: People with amnestic Mild Cognitive Impairment (aMCI) or dementia often exhibit a decline in their social abilities, but few tests of social cognition exist that are suitable for clinical use. Moreover, the relationship between changes in behaviour and impairments in social cognition is poorly understood. We examined the utility of the Edinburgh Social Cognition Test (ESCoT) in people with aMCI/dementia and explored associations between social cognition performance and behaviour changes. Methods: We administered the ESCoT and two established social cognition tests (Reading the Mind in the Eyes; RME and the Social Norms Questionnaire; SNQ) to 28 people with aMCI or dementia and 28 age and sex matched cognitively healthy controls. Behaviour change was measured using a semi-structured interview which assesses behavioural abnormalities found in frontotemporal dementia. Results: People with aMCI/dementia were impaired on the ESCoT affective ToM, ESCoT total score and the RME. Behaviour changes in the domains of apathy, loss of sympathy/empathy, perseveration, and psychotic symptoms were associated with poorer affective ToM scores. Disinhibition, loss of sympathy/empathy and hyperorality or altered food preferences were associated with cognitive ToM. All behaviours were significantly associated with poorer performance on ESCoT total score, but not the RME or SNQ.Conclusion: The ESCoT was sensitive to social cognition impairments in people with aMCI/dementia and it relates to behaviour change in aMCI/dementia unlike established tests. Different subtests of the ESCoT were related to different behaviour changes. These findings suggest that the ESCoT may be a clinically valuable tool when examining social cognition

An investigation of the validity of the Edinburgh Social Cognition Test (ESCoT) in acquired brain injury (ABI)

Objectives: Social cognition is frequently impaired following an acquired brain injury (ABI) but often overlooked in clinical assessments. There are few validated and appropriate measures of social cognitive abilities for ABI patients. The current study examined the validity of the Edinburgh Social Cognition Test (ESCoT, Baksh et al., 2018) in measuring social cognition following an ABI. Methods: Forty-one patients with ABI were recruited from a rehabilitation service and completed measures of general ability, executive functions and social cognition (Faux Pas; FP, Reading the Mind in the Eyes; RME, Social Norms Questionnaire; SNQ and the ESCoT). Forty-one controls matched on age, sex and years of education also performed the RME, SNQ and ESCoT. Results: A diagnosis of ABI was significantly associated with poorer performance on all ESCoT measures and RME while adjusting for age, sex and years of education. In ABI patients, the ESCoT showed good internal consistency with its subcomponents and performance correlated with the other measures of social cognition demonstrating convergent validity. Better Trail Making Test performance predicted better ESCoT total, RME and SNQ scores. Higher TOPF IQ was associated with higher RME scores, while higher WAIS-IV working memory predicted better FP performance. Conclusions: The ESCoT is a brief, valid and internally consistent assessment tool able to detect social cognition deficits in neurological patients. Given the prevalence of social cognition deficits in ABI and the marked impact these can have on an individual’s recovery, this assessment can be a helpful addition to a comprehensive neuropsychological assessment