Université Nantes Angers Le Mans

About: Université Nantes Angers Le Mans is a education organization based out in Nantes, France. It is known for research contribution in the topics: Geology & Finite element method. The organization has 434 authors who have published 249 publications receiving 7208 citations. The organization is also known as: PRES Universite Nantes Angers Le Mans.

Brain Activity during Mental Imagery of Gait Versus Gait-Like Plantar Stimulation: A Novel Combined Functional MRI Paradigm to Better Understand Cerebral Gait Control.

Abstract: Human locomotion is a complex sensorimotor behavior whose central control remains difficult to explore using neuroimaging method due to technical constraints, notably the impossibility to walk with a scanner on the head and/or to walk for real inside current scanners. The aim of this functional MRI (fMRI) study was to analyze interactions between two paradigms to investigate the brain gait control network: 1) mental imagery of gait, and 2) passive mechanical stimulation of the plantar surface of the foot with the Korvit boots. The Korvit stimulator was used through two different modes, namely an organized (“gait like”) sequence and a destructured (chaotic) pattern. Eighteen right-handed young healthy volunteers were recruited (mean age, 27±4.7 years). Mental imagery activated a broad neuronal network including the supplementary motor area-proper (SMA-proper), pre-SMA, the dorsal premotor cortex, ventrolateral prefrontal cortex, anterior insula, and precuneus/superior parietal areas. The mechanical plantar stimulation activated the primary sensorimotor cortex and secondary somatosensory cortex bilaterally. The paradigms generated statistically common areas of activity, notably bilateral SMA-proper and right pre-SMA, highlighting the potential key role of SMA in gait control. There was no difference between the organized and chaotic Korvit sequences, highlighting the difficulty of developing a walking-specific plantar stimulation paradigm. In conclusion, this combined-fMRI paradigm combining mental imagery and gait-like plantar stimulation provides complementary information regarding gait-related brain activity and appears useful for the assessment of high-level gait control.

Influence of angularity of coarse fraction grains on internal erosion process

Abstract: In earth structures and their foundations, two types of erosion can be distinguished: interface erosion and suffusion. This paper deals with suffusion process also named internal instability, which takes place inside the soil matrix. In this process, finer particles of a soil migrate within its own pore spaces. These fine particles can be cohesionless particles or clay particles. With the objective to study the effect of angularity of coarse fraction grains on suffusion a series of tests was performed on different clayey sand. Three sand type samples were tested which are different by the grain size distribution and also by the angularity of grains. A specific triaxial device was used in order to force fluid through the samples in downward direction under constant hydraulic gradients. It is shown that the angularity of coarse fraction grains may contribute to increase the erosion resistance of the tested soils by a factor of 5. Moreover for the tested soils, the grain shape has an effect on hydraulic conductivity decrease. The angularity of coarse fraction grains may intensify the geometric blocking of eroded clay particles. Finally a study is conducted to compare the different ways to characterize the angularity of grains: by an analysis of grain pictures, by using an angulometer or by measuring the internal friction angle.

Influence of layer roughness for road survey by Ground Penetrating Radar at nadir : theoretical study

Abstract: In civil engineering, conventional methods used to estimate the thickness of pavements assume flat interfaces. In contrast, this study uses a rigorous electromagnetic method called propagation-inside-layer-expansion (PILE) to simulate the radar backscattered signal at nadir from a rough pavement made up of two rough interfaces separating homogeneous media. The statistical distribution of the first two echoes is studied by comparison with the default flat case, together with their frequency behaviour. Within the scope of road pavement survey by ground penetrating radar, the scattering model is finally used to assess the performance of the estimation of signal parameters via rotational invariance techniques (ESPRIT) algorithm, one of the well-known high-resolution time-delay estimation techniques.