Le néocortex humain est particulièrement plissé. Des variations de plissement cortical ont été associées à certaines maladies neuro-développementales comme l’autisme ou la schizophrénie. Il est cependant difficile de savoir ce qu’impliquent ces différences de motif, au delà d’être des marqueurs de variations de la structure interne du cortex. Au cours du développement, les plis corticaux apparaissent chez l’humain pendant le dernier trimestre de gestation, simultanément avec le développement de sa connectivité. Aujourd’hui la communauté scientifique semble se retrouver sur des théories qui relient l’émergence des plis à l’organisation cytoarchitectonique et fonctionnelle du cortex. Nous avons développé une hypothèse de plissement prenant également en compte le stress mécanique engendré par la croissance des tissus ainsi que son rôle dans une possible rétro-action mécanique des plis sur l’organisation interne du cortex. Grâce à son développement en partie post-natal, le furet apparait comme un modèle animal idéal pour l’étude de l’organisation et du plissement cortical. A partir de données d’IRM structurales, nous avons segmenté et reconstruit en trois dimensions les surfaces piale et interne du cortex de 28 cerveaux de furets, afin de mener des analyses de surface et d’épaisseur corticale. Par une description anatomique précise du plissement du cortex du furet, basée sur l’étude de cartes de courbure, nous montrons la présence inattendue de plis déjà au 4ème jour après la naissance (P4). Par ailleurs, l’analyse longitudinale du plissement du cortex à partir d’algorithmes de recalage, suggère un gradient rostro-caudal dans la croissance de la surface corticale qui pourrait être impliqué dans la gyrification. En effet, les aires corticales les plus rostrales, plus grandes, et plus plissées à l’âge adulte, semblent croitre plus tôt et plus vite au cours du développement, en comparaison avec les régions caudales plus petites, et moins plissées chez l’adulte. L’analyse de l’épaisseur corticale révèle une corrélation entre l’épaisseur du cortex et la localisation des gyri et sulci. Cependant cette corrélation n’apparait qu’à partir du 8ème jour après la naissance, soit après la formation des plis à P4. L’ensemble de nos résultats suggère donc un possible effet mécanique du plissement du cortex sur son épaisseur, et donc potentiellement sur son organisation cytoarchitectonique et sa connectivité. / The human neocortex is highly folded. Its folding pattern has been associated with neurodevelopmental conditions, like autism or schizophrenia. It is still difficult, however, to understand what theses differences may imply, beyond being a marker of underlying variations in cortical organization. During development, folds appear during the last semester of gestation in human, synchronously with connective development. Nowadays, researchers recognize the existence of a relationship between the geometry of neocortical folds, and its cytoarchitectonic and functional organization. We have developed a hypothesis considering the role that mechanical stress can play in the determination of neocortical organization. The ferret appears as an ideal animal model to study the link between folding and cortical organization, as both processes in the ferret take place after birth. We segmented and reconstructed the pial and white matter cortical surfaces from 28 ferret brain structural MR images, and used them for surface and cortical thickness analysis. We highlight an unexpected significant presence of folds at postnatal day 4 (P4), on curvature maps of the pial surface. Besides, longitudinal analyses of the pial folding using meshes registration suggest the presence of a gradient in surface expansion that can be related to gyrification. The larger rostral areas — that turn to be more folded in adult brains — seem to expand earlier and faster than caudal regions with smaller surface area. In cortical thickness analysis, the correlation between pial surface curvature and thickness reveals a variation of cortical thickness in gyri and sulci. However, this correlation appears after postnatal day 8, thus after the emergence of folds around P4.Together, our results suggest a possible mechanical causal effect of folding on the thickening of the cortex and on its cytoarchitectonic and connective development.

Lubricants additives are inseparable component of modern high-tech lubricants. Viscosity index improvers additives play uncoverable role in a branch of boundary lubrication. They are designed to ensure sufficient oil film thickness in low speeds of frictional surfaces motion. This thesis deal with effect of specific viscosity index improvers additives on boundary lubrication film formation in elliptical contact. The purpose of this work is also checking the effect of concentration changing these additives on lubricantion film thickness formation.

One of the earliest symptoms of Alzheimer’s disease (AD) and age-related cognitive decline is topographical disorientation or impairment to spatial navigation. Furthermore, aging and AD are associated with cortical gray-matter thinning, particularly in the medial temporal and posterior cingulate regions, which have been associated with spatial navigation. Aerobic exercise has been well-established as a beneficial intervention to curtail the neurodegenerative effects of aging. This study aims to explore the relationship between cardiorespiratory fitness (CRF), and two markers of AD and cognitive aging, virtual navigation ability and cortical thickness of the entorhinal, parahippocampal and retrosplenial regions. Cross-sectional data utilized in this study was collected from 23 healthy older adults (60-80 years). Measures included in our analyses consisted of estimated VO2max, T1-weighted structural MR images, and behavioral performance on a virtual navigation task, measured as numbers of objects located during recall. Cortical thickness of the regions of interest (ROIs) was determined by processing T1-weighted MR images in FreeSurfer. We hypothesized that greater CRF would correlate with improved virtual navigation performance and greater cortical thickness of ROIs. Our analyses did not reveal statistically significant relationships between CRF and navigation performance or CRF and cortical thickness. However, Pearson’s correlations found right retrosplenial cortical (RSC) thickness and navigation performance to be significantly related. Multiple regression models of right RSC thickness and navigation performance were performed controlling for age, sex, education and task version. These analyses revealed that greater right RSC thickness predicted navigation performance. Additionally, this model showed that older age predicts decline in navigation performance. Our findings did not survive multiple comparisons correction; nonetheless, the results provide promising insight to the relationship between cortical thickness and navigation performance in healthy aging. Further cross-sectional and longitudinal investigations with a larger sample size are required to assess the impact of CRF and exercise on cortical thickness and navigation abilities in healthy aging. Understanding these relationships would contribute to the expansive body of literature that has linked CRF and exercise to neuroprotective mechanisms in the aging brain.

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Socioeconomic status (SES) is a key predictor of a multitude of health and functional outcomes, and growing up in low SES contexts is associated with poor neurocognitive outcomes and mental health problems across the lifespan. Recent studies of the links between SES and brain development suggest that associations between low SES and poor neurocognitive and health outcomes are likely accounted for by impacts on neurodevelopment. Low SES is associated with structural brain development, including reduced cortical thickness in frontal regions relevant to higher-level cognitive functions. However, understanding of how the impacts of SES on neurodevelopment contribute to developing psychopathology is limited. The study of how neurodevelopmental processes may contribute to depression is of particular interest given numerous neural correlates of depression, including reduced cortical thickness in frontal regions. Whereas both SES and depression independently have demonstrated associations with grey matter maturation, no studies to date have examined how the associations between SES, depression, and cortical structure interrelate. The current study addresses this gap in the literature by examining associations between SES at both household and neighborhood levels, depression symptoms, and cortical structure in adolescence. Furthermore, exploratory analyses investigated specific pathways of SES effects on depression symptoms and cortical structure through exposure to psychosocial stress. Data were drawn from an ongoing prospective longitudinal study of reward function development. Participants included 232 youth ages 9-13 (57.03% female; 46.59% White, 39.36% African American, 11.24% Multiracial, 2.81% Other; 11.24% Hispanic) and their primary caregivers who completed assessments of depression symptoms and stress at baseline and a 9-month follow-up, as well as an MRI assessment between baseline and follow up. Regression analyses examined associations between 1) SES to cortical structure, 2) SES to depression symptoms, 3) baseline depression symptoms and cortical structure, and 4) cortical structure to depression symptoms at follow-up. Structural equation models examined indirect effects of 1) SES on depression symptoms through cortical structure, 2) SES on cortical structure through depression symptoms, and 3) SES on cortical structure and depression symptoms through experiences of psychosocial stress. Neighborhood SES was positively associated with mean cortical thickness, and household SES was inversely associated with depression symptoms at follow up, controlling for baseline symptoms. No indirect effects were identified. Findings suggest that different aspects of SES may confer unique risks for neural and psychosocial development in early adolescence, such that SES of the neighborhood appears to have global effects on neurodevelopment that are not mediated by mood or proximal stress, whereas SES of the household appears to be associated with increasing mood symptoms and heightened stress experiences in early adolescence. / Psychology

To date, numerous studies have examined the range of cranial thickness variation in modern humans. The purpose of this investigation is to present a new method that would be easier to replicate, and to examine sex and age variation in cranial thickness in a white sample. The method consists of excising four cranial segments from the frontal and parietal regions. The sample consists of 165 specimens collected at autopsy and 15 calvarial specimens. An increase in cranial thickness with age was observed. The results suggest that cranial thickness is not sexually dimorphic outside the onset of hyperostosis frontalis interna (HFI).

Black liquor is an intermediate product of pulp production. Recovery boilers process black liquor to recover the inorganic material for recycling in the mill and to generate electricity and steam for the paper mill. Black liquor droplet combustion rates and mechanisms dictate many aspects of recovery boiler performance. This investigation documents new experimental data on single droplet pyrolysis and combustion in a laboratory furnace that mimics many of the essential features of commercial boilers (temperature, composition, droplet size, etc.). These experiments monitored single droplets placed on a thermocouple wire and suspended from a mass balance. Simultaneous video images and pyrometry data provide mass loss and internal temperature data. These investigations provide an extensive data set from which to validate a model and insight into the mechanisms of combustion. Particles burning in air expelled ejecta from the particle during the entire combustion process, though ejection rates during the late stages of char combustion were observed to be higher than during other stages. In addition, char burning began almost the instant the particle entered the reactor; showing significant overlap in the combustion processes. A transient, 1-dimensional, single-droplet model describes droplet combustion. This model solves the momentum, energy, species continuity, and overall continuity equations using the control volume method. The model uses the power-law scheme for combined advection diffusion, and the fully-implicit scheme for the time step. It predicts internal velocities, gas and solid temperatures (assumed equal), pressure, and composition. Pressure and velocity equations use Darcy's Law for flow through a porous medium. Modeling results show the large effect of swelling on all particle properties. This model describes the flame region by extending the control volume into the gas phase.

Background and Purpose—There is controversy in the literature regarding the relationship between intima-media thickness (IMT) and body composition among adolescents. This study investigated the relationship between body fat percentage and IMT, while controlling for height, weight, age, blood pressure, cholesterol, glucose, triglycerides and VO2max in 12 to 17-year-old children. Methods—111 children (mean age = 14.33 years) participated in this study. Body fat percentage was assessed using dual energy x-ray absorptiometry (DXA). A B-mode, high-resolution ultrasonograph was used to measure the IMT of the right and left common carotid arteries (CCA). Fasting blood tests were performed to obtain blood lipid and glucose profiles. Blood pressure was measured using an automatic blood pressure cuff.Results—Data were divided into body fat tertiles to compare differences between the upper and lower tertile. Contrary to what might be expected, the mean IMT of the group with the lowest body fat percent was 0.516 mm and the mean IMT for the upper tertile of body fat percent was 0.483 mm (F(2,103) = 5.883, p = 0.004). Post hoc analysis indicated that the two leanest groups had significantly thicker IMT than the group with the highest percent body fat (p = 0.005 and p = 0.027, respectively). The two leanest groups were not significantly different from each other. When controlling for gender, no significant relationship existed between CCA-IMT and body fat percentage (F(2,103) = 2.267, p = 0.109). Conclusions—This study found that there were significant differences in IMT between body fat percentage and CCA-IMT in children and adolescents 12 to 17-years of age. This study did indicate that as body fat increases, risk factors such as cholesterol and triglycerides also increase. Overall, the direct relationship between CCA-IMT and body fat percentage is poorly understood in children and adolescents. Further research is necessary to determine a standardized protocol for assessing atherosclerotic risk in adolescents.