Nonlinear Correction to the Euler Buckling Formula for\ud Compressible Cylinders

Euler’s celebrated buckling formula gives the critical load N for the buckling of a slender cylindrical column with radius B and length L as\ud \ud N/(π 3B2)=(E/4)(B/L)2,\ud \ud where E is Young’s modulus. Its derivation relies on the assumptions that linear elasticity applies to this problem, and that the slenderness (B/L) is an infinitesimal quantity. Here we ask the following question: What is the first nonlinear correction in the right hand-side of this equation when terms up to (B/L)4 are kept? To answer this question, we specialize the exact solution of non-linear elasticity for the homogeneous compression of a thick cylinder with lubricated ends to the theory of third-order elasticity. In particular, we highlight the way second- and third-order constants —including Poisson’s ratio— all appear in the coefficient of (B/L)4

Specialization of neural mechanisms underlying face recognition in human infants

Newborn infants respond preferentially to simple face-like patterns, raising the possibility that the face-specific region, identified in the adult cortex are functioning from birth. We sought to evaluate this hypothesis by characterizing the specificity Of infants' electrocortical responses to faces in two ways: (1) comparing responses to faces of humans with those to faces of nonhuman primates; and 2) comparing responses to upright and inverted faces. Adults' face-responsive N170 event-related potential (ERP) component showed specificity to upright human faces that was not observable at any point in the ERPs Of infants. A putative "infant N170" did show sensitivity to the species of the face, but the orientation of the face did not influence processing until a later stage. These findings suggest a process of gradual specialization of cortical face processing systems during postnatal development

Resting frontal asymmetry and reward sensitivity theory motivational traits

The revised reinforcement sensitivity theory (rRST) of personality has conceptualized three main systems: the behavioural approach system (BAS), behavioural inhibition system (BIS), and fightflight- freeze system (FFFS). Research links greater relative left-frontal activity with BAS-related tendencies and impulsivity and greater relative right-frontal activity with “withdrawal” motivation that included both BIS and FFFS. Although rRST has addressed the separation of FFFS and BIS, much of personality neuroscience research does not indicate which system is related to right frontal activity. We administered the Reinforcement Sensitivity Theory of Personality Questionnaire (RST-PQ) to measure the BAS and its facets (goal-drive persistence, reward interest, reward reactivity, and impulsivity), BIS, and the withdrawal FFFS. We examined the association of RST-PQ traits with resting electroencephalogram (EEG) alpha-asymmetry in female participants (N = 162) by considering the influence of experimenter’s gender. In the total group, that included two subgroups with experimenters of different gender, BAS-impulsivity was related to greater left- than right-frontal activity, and FFFS, but not BIS, was related to greater relative right-frontocentral activity. These associations remained significant for the subgroup with a young same-sex experimenter, but not with opposite-sex experimenter

Nonlinear Correction to the Euler Buckling Formula for Compressed Cylinders with Guided-Guided End Conditions

Euler's celebrated buckling formula gives the critical load $N$ for the buckling of a slender cylindrical column with radius $B$ and length $L$ as $$N / (\pi^3 B^2) = (E/4)(B/L)^2,$$ where $E$ is Young's modulus. Its derivation relies on the assumptions that linear elasticity applies to this problem, and that the slenderness $(B/L)$ is an infinitesimal quantity. Here we ask the following question: What is the first nonlinear correction in the right hand-side of this equation when terms up to $(B/L)^4$ are kept? To answer this question, we specialize the exact solution of incremental non-linear elasticity for the homogeneous compression of a thick compressible cylinder with lubricated ends to the theory of third-order elasticity. In particular, we highlight the way second- and third-order constants ---including Poisson's ratio--- all appear in the coefficient of $(B/L)^4$.Comment: 12 page

Growth-induced blisters in a circular tube

The growth of an elastic film adhered to a confining substrate might lead to the formation of delimitation blisters. Many results have been derived when the substrate is flat. The equilibrium shapes, beyond small deformations, are determined by the interplay between the sheet elastic energy and the adhesive potential due to capillarity. Here, we study a non-trivial generalization to this problem and consider the adhesion of a growing elastic loop to a confining \emph{circular} substrate. The fundamental equations, i.e., the Euler Elastica equation, the boundary conditions and the transversality condition, are derived from a variational procedure. In contrast to the planar case, the curvature of the delimiting wall appears in the transversality condition, thus acting as a further source of adhesion. We provide the analytic solution to the problem under study in terms of elliptic integrals and perform the numerical and the asymptotic analysis of the characteristic lengths of the blister. Finally, and in contrast to previous studies, we also discuss the mechanics and the internal stresses in the case of vanishing adhesion. Specifically, we give a theoretical explanation to the observed divergence of the mean pressure exerted by the strip on the container in the limit of small excess-length

Parametri temporali del passo nei bambini in età prescolare: analisi mediante sensori inerziali indossabili

La tesi di seguito realizzata ha lo scopo di fornire il risultato derivante dall’analisi di dati relativi a bambini aventi dai 2 ai 24 mesi di esperienza di cammino indipendente. Lo studio ha coinvolto 18 bambini di età compresa tra i 14 e i 34 mesi. Sono stati analizzati i parametri temporali relativi al ciclo del cammino per ogni bambino coinvolto nello studio. In particolare, sono state prese in considerazione le seguenti variabili temporali: doppio supporto (percentuale), tempo di stance (percentuale) e tempo di stride. Per ottenere i dati sono state effettuate delle rilevazioni tramite sensori indossabili Opals (APDM). I dati ottenuti dalle rilevazioni sono stati poi analizzati in Matlab. L’ obiettivo di tale tesi è quello di fornire una base di dati quantitativi descriventi il cammino di un gruppo di bambini di età prescolare che, se ampliata, potrà essere usata in altri studi futuri ad esempio come base di paragone per l’analisi del cammino in bambini con o a rischio di disturbi motori (aventi le stesse caratteristiche di quelli coinvolti in questo studio). Un ulteriore scopo è stato quello di analizzare qualitativamente se l’effetto dell’età anagrafica (in mesi) e dei mesi di esperienza di cammino influisse sui risultati

On nonlinear viscoelastic deformations - a reappraisal of Fung's quasilinear viscoelastic model

This article offers a reappraisal of Fung's method for quasilinear viscoelasticity. It is shown that a number of negative features exhibited in other works, commonly attributed to the Fung approach, are merely a consequence of the way it has been applied. The approach outlined herein is shown to yield improved behaviour, and offers a straightforward scheme for solving a wide range of models. Results from the new model are contrasted with those in the literature for the case of uniaxial elongation of a bar: for an imposed stretch of an incompressible bar, and for an imposed load. In the last case, a numerical solution to a Volterra integral equation is required to obtain the results. This is achieved by a high order discretisation scheme. Finally, the stretch of a compressible viscoelastic bar is determined for two distinct materials: Horgan-Murphy and Gent