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

Effects of thickness on the spin susceptibility of the 2D electron gas

Using available quantum Monte Carlo predictions for a strictly 2D electron gas, we have estimated the spin susceptibility of electrons in actual devices taking into account the effect of the finite transverse thickness and finding a very good agreement with experiments. A weak disorder, as found in very clean devices and/or at densities not too low, just brings about a minor enhancement of the susceptibility.Comment: 4 pages, 3 figure

A stochastic delay differential model of cerebral autoregulation

Mathematical models of the cardiovascular system and of cerebral autoregulation (CAR) have been employed for several years in order to describe the time course of pressures and flows changes subsequent to postural changes. The assessment of the degree of efficiency of cerebral auto regulation has indeed importance in the prognosis of such conditions as cerebro-vascular accidents or Alzheimer. In the quest for a simple but realistic mathematical description of cardiovascular control, which may be fitted onto non-invasive experimental observations after postural changes, the present work proposes a first version of an empirical Stochastic Delay Differential Equations (SDDEs) model. The model consists of a total of four SDDEs and two ancillary algebraic equations, incorporates four distinct delayed controls from the brain onto different components of the circulation, and is able to accurately capture the time course of mean arterial pressure and cerebral blood flow velocity signals, reproducing observed auto-correlated error around the expected drift

Spin Susceptibility of Interacting Two-dimensional Electrons with Anisotropic Effective Mass

We report measurements of the spin susceptibility in dilute (rs up to 10) AlAs two-dimensional (2D) electrons occupying a single conduction-band valley with an anisotropic in-plane Fermi contour, characterized by longitudinal and transverse effective masses, ml and mt. As the density is decreased, the spin susceptibility is significantly enhanced over its band value, reflecting the role of interaction. Yet the enhancement is suppressed compared to the results of quantum Monte Carlo based calculations that take the finite thickness of the electron layer into account but assume an isotropic effective mass equal to sqrt(ml.mt). Proper treatment of an interacting 2D system with an anisotropic effective mass therefore remains a theoretical challenge.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev.

Design and 3D printing of a modular phantom of a uterus for medical device validation

PurposeThe purpose of this study is to describe the design and validation of a three-dimensional (3D)-printed phantom of a uterus to support the development of uterine balloon tamponade devices conceived to stop post-partum haemorrhages (PPHs). Design/methodology/approachThe phantom 3D model is generated by analysing the main requirements for validating uterine balloon tamponade devices. A modular approach is implemented to guarantee that the phantom allows testing these devices under multiple working conditions. Once finalised the design, the phantom effectiveness is validated experimentally. FindingsThe modular phantom allows performing the required measurements for testing the performance of devices designed to stop PPH. Social implicationsPPH is the leading obstetric cause of maternal death worldwide, mainly in low- and middle-income countries. The proposed phantom could speed up and optimise the design and validation of devices for PPH treatment, reducing the maternal mortality ratio. Originality/valueTo the best of the authors' knowledge, the 3D-printed phantom represents the first example of a modular, flexible and transparent uterus model. It can be used to validate and perform usability tests of medical devices

Trapped vortex cell for aeronautical applications: flow analysis through PIV and Wavelet transform tools

Results of the application of a trapped vortex cell to an airfoil with the aim of improving the aerodynamic performances are presented for two complementary experiments arranged at CIRA and at Politecnico di Torino. In the CIRA experiments, PIV measurements on a simplified configuration were carried out to characterize the trapped vortical structure and its effect on the separating flow downstream of the cell. In the experimental investigation at Politecnico di Torino, static pressure distributions were measured around a complete airfoil model, to yield lift and pitching moment coefficients. Wake surveys were also carried out to measure the drag. To study the unsteady phenomena inside the cavity pressure fluctuations signals were also investigated using Kulite sensors. In both experiments, the angle of attack of the airfoil and the Reynolds number were varied. It is shown that the flow inside the cell is highly unsteady with significant shedding of flow structures downstream. This phenomenon results in a large region of separated flow, in higher drag and lower lift. By contrast, the cell flow is considerably stabilized and regularized by applying distributed suction over the cell wall. As a result, the flow downstream of the cell reattaches and lower drag and larger lift are observed