A morphometric double dissociation: cortical thickness is more related to aging; surface area is more related to cognition

The thickness and surface area of cortex are genetically distinct aspects of brain structure, and may be affected differently by age. However, their potential to differentially predict age and cognitive abilities has been largely overlooked, likely because they are typically aggregated into the commonly used measure of volume. In a large sample of healthy adults (N=647, aged 18-88), we investigated the brain-age and brain-cognition relationships of thickness, surface area, and volume, plus five additional morphological shape metrics. Cortical thickness was the metric most strongly associated with age cross-sectionally, as well as exhibiting the steepest longitudinal change over time (subsample N=261, aged 25-84). In contrast, surface area was the best single predictor of age-residualized cognitive abilities (fluid intelligence), and changes in surface area were most strongly associated with cognitive change over time. These findings were replicated in an independent dataset (N=1345, aged 18-93). Our results suggest that cortical thickness and surface area make complementary contributions the age-brain-cognition triangle, and highlight the importance of considering these volumetric components separately.

Graph Drawing Approaches for Petri Net Visualisation and Representation

Petri net structures can benefit from being modelled using graph drawing approaches. This work presents some advanced graph drawing approaches that can be used for visualising Petri net models. These are i) topological shape metrics, ii) visibility drawing, iii) orthogonalization, iv) hierarchical and v) bi-graph partitioning. The models show that this can be successfully done and the Petri nets that are generated in this work are suitable for visualisation. Graph visualisation is an important topic and the results show that there is a large potential to apply this approach to drawing Petri Nets in novel ways.

The effect of spectral shape on damping modification factors

The main objective of this study is to investigate the effect of spectral shape on damping modification factors η used in equivalent static and response spectrum analyses of structures with damping ratios that are different from 5% critical damping. Record-to-record variability of η is also evaluated through a statistical analysis of 5270 ground motions records from 1137 interface earthquakes recorded in Chile. The effect of spectral shape is studied using recently developed spectral shape metrics SaRatio and epsilon [Formula: see text] and evaluating their use as possible predictors for η. Similarly to previous investigations, this article also examines the effect of oscillator period, earthquake magnitude, and earthquake duration for different levels of damping ratio. Results suggest that SaRatio is an effective predictor of η, particularly for highly damped structures. However, results also indicate that for rock and firm sites, earthquake faulting mechanism and site class do not have a significant influence on η. A simple period-independent regression model for η as a function of SaRatio and damping ratio is proposed. A comparison between median η from this study and those in current Chilean seismic codes shows that code factors are unconservative.

Shape Analysis of the Human Association Pathways

Shape analysis has been widely used in digital image processing and computer vision, but they have not been utilized to compare the structural characteristics of the human association pathways. Here we used shape analysis to derive length, area, volume, and shape metrics from diffusion MRI tractography and utilized them to study the morphology of human association pathways. The reliability analysis showed that shape descriptors achieved moderate to good test-retest reliability. Further analysis on association pathways showed left dominance in the arcuate fasciculus, cingulum, uncinate fasciculus, frontal aslant tract, and right dominance in the inferior fronto-occipital fasciculus and inferior longitudinal fasciculus. The superior longitudinal fasciculus has a mixed lateralization profile with different metrics showing either left or right dominance. The analysis of between-subject variations shows that the overall layout of the association pathways does not variate a lot across subjects, as shown by low between-subject variation in length, span, diameter, and radius. In contrast, the area of the pathway innervation region has a considerable between-subject variation. A follow-up analysis is warranted to thoroughly investigate the nature of population variations and their structure-function correlation.

INVESTIGATION OF CHARACTERISTICS OF SPECIAL POWDERS AND MATERIALS PRODUCED BY MEANS OF SELECTIVE LASER MELTING

The article presents the results of characterization of special powders of metal alloys and materials produced from these powders by selective laser melting (SLM), including comparative analysis of powders produced using VIGA technology. It is noted the importance of a complex study that includes not only a statistical evaluation of particle size distribution of the powders (preferably, by the method of laser diffraction), but also image analysis providing information on the particles’ shape influencing the powders’ flowability. It is shown that the size distribution and shape metrics for nickel refractory alloys and stainless steel powders obtained at the Powder Metallurgy Institute of the National Academy of Sciences of Belarus are at the level of the best foreign analogues. The influence of powder chemical composition on the mechanical properties of SLM samples is considered. The presence of oxygen and undesirable impurities, as a rule, decreases the strength and tensile strain. It is noted that SLM provides extremely wide opportunities for the formation of complex geometric structures with close to full density. Subsequent thermal or thermal and mechanical processing allows reduction of stresses arising during the SLM, densification of products (if necessary) and regulation of their structure and properties. The prospects of applying the backscattered electron diffraction (EBSD) for analysis of the material structure evolution during SLM and subsequent processing are shown. It is noted that products obtained by the SLM from the powders of special alloys exhibit mechanical properties at a level, and in some cases even exceeding the properties of these alloys produced by traditional and other additive technologies.