Intraindividual variability in inhibitory function in adults with ADHD - an ex-Gaussian approach

OBJECTIVE: Attention deficit disorder (ADHD) is commonly associated with inhibitory dysfunction contributing to typical behavioral symptoms like impulsivity or hyperactivity. However, some studies analyzing intraindividual variability (IIV) of reaction times in children with ADHD (cADHD) question a predominance of inhibitory deficits. IIV is a measure of the stability of information processing and provides evidence that longer reaction times (RT) in inhibitory tasks in cADHD are due to only a few prolonged responses which may indicate deficits in sustained attention rather than inhibitory dysfunction. We wanted to find out, whether a slowing in inhibitory functioning in adults with ADHD (aADHD) is due to isolated slow responses. METHODS: Computing classical RT measures (mean RT, SD), ex-Gaussian parameters of IIV (which allow a better separation of reaction time (mu), variability (sigma) and abnormally slow responses (tau) than classical measures) as well as errors of omission and commission, we examined response inhibition in a well-established GoNogo task in a sample of aADHD subjects without medication and healthy controls matched for age, gender and education. RESULTS: We did not find higher numbers of commission errors in aADHD, while the number of omissions was significantly increased compared with controls. In contrast to increased mean RT, the distributional parameter mu did not document a significant slowing in aADHD. However, subjects with aADHD were characterized by increased IIV throughout the entire RT distribution as indicated by the parameters sigma and tau as well as the SD of reaction time. Moreover, we found a significant correlation between tau and the number of omission errors. CONCLUSIONS: Our findings question a primacy of inhibitory deficits in aADHD and provide evidence for attentional dysfunction. The present findings may have theoretical implications for etiological models of ADHD as well as more practical implications for neuropsychological testing in aADHD

Graphene -- Based Nanocomposites as Highly Efficient Thermal Interface Materials

We found that an optimized mixture of graphene and multilayer graphene - produced by the high-yield inexpensive liquid-phase-exfoliation technique - can lead to an extremely strong enhancement of the cross-plane thermal conductivity K of the composite. The "laser flash" measurements revealed a record-high enhancement of K by 2300 % in the graphene-based polymer at the filler loading fraction f =10 vol. %. It was determined that a relatively high concentration of single-layer and bilayer graphene flakes (~10-15%) present simultaneously with thicker multilayers of large lateral size (~ 1 micrometer) were essential for the observed unusual K enhancement. The thermal conductivity of a commercial thermal grease was increased from an initial value of ~5.8 W/mK to K=14 W/mK at the small loading f=2%, which preserved all mechanical properties of the hybrid. Our modeling results suggest that graphene - multilayer graphene nanocomposite used as the thermal interface material outperforms those with carbon nanotubes or metal nanoparticles owing to graphene's aspect ratio and lower Kapitza resistance at the graphene - matrix interface.Comment: 4 figure

Graphite nanoplatelet/rubbery epoxy composites as adhesives and pads for thermal interface applications

Composites of graphite nanoplatelets (GNPs) and rubbery epoxy (RE) resins as adhesives and pads are evaluated as thermal interface materials (TIM). GNP-15 and GNP-5 (15 and 5 µm across, respectively) were loaded in RE by 3-roll milling to produce GNP/RE composites. The role of composite processing techniques on the texture, thermal and electrical conductivities and compression properties of composites was studied and compared. Scanning electron microscopy revealed uniform dispersion of GNPs in RE, regardless of loading and X-ray diffraction texture measurement showed less platelet alignment in the composites at low loadings. Thermal conductivities of 20 wt% GNP-15/RE (3.29 W/m K) and 35 wt% GNP-5/RE composite (2.36 W/m K) were both significantly higher than pure RE (0.17 W/m K). GNP/RE retained good compliance, compressive moduli at 20 wt% loading being comparable to commercial BN/silicone TIM. Although thermal contact resistance of GNP/RE was higher than for commercial paste, its interfacial thermal transport outperformed GNP/silicone (due to RE’s strongly adhesive nature) and, across thick bond lines, outperformed reported GNP-pastes. The 20 wt% GNP-15/RE thermal pad had significantly lower thermal contact resistance than other GNP/RE pads. This decreased with increasing applied pressure, being comparable to commercial BN/silicone pad. GNP/RE composites are thus promising candidates for thermal interface adhesives and pads

Frequency of intraindividual RTs with fitted ex-Gaussian probability functions exemplary for a control (left) and an ADHD (right) subject.

<p>NOTE: Please keep in mind that RTs in ADHD encompass a broader range (200</p

Experimental study on the porous structure and compressibility of tectonized coals

This paper presents experimental investigations on the porous structure and compressibility of six representative tectonized coals, which were geologically formed because of post-formation tectonic deformation of the coal seam, resulting in various brittle and plastic structure development in the seam, such as fissure and fold. The investigations were carried out using microscopy and mercury intrusion porosimetry, providing experimental information about better characterization of the coal structure for coalbed methane recovery from tectonized coal seams. In combination with measurements of vitrinite reflectance and pore size distribution, the mercury intrusion porosimetry data were further analyzed with the fractal theory and used to determine the pore compressibility of the coal samples. The results show that tectonic deformation mainly reformed the bigger pores (pore size above 100 nm). In general, the increased tectonic deformation led to more open pores and, hence, the enhanced connectivity of the pore network. In fractal analysis, a linear relation was used to fit the mercury intrusion data at high pressure instead of the power law that was typically used in previous studies on ordinary coals. The volume-pressure curves obtained by mercury intrusion measurements for all coal samples exhibit a strong dependence relation with the deformation extent. The pore compressibility of these coals obviously decreases as the deformation extent increased, with only one exception for all coal samples studied. This implies that the weak deformation may be corresponding to a high compressibility. Moreover, the results also show that the rank may be responsible for a significant part of the differences in porosity and pore compressibility as well

Distribution of age for both adult controls and adult ADHD.

<p>Distribution of age for both adult controls and adult ADHD.</p