École normale supérieure de Cachan

About: École normale supérieure de Cachan is a education organization based out in Cachan, Île-de-France, France. It is known for research contribution in the topics: Decidability & Nonlinear system. The organization has 2717 authors who have published 5585 publications receiving 175925 citations.

Fluoroquinolone structure and translocation flux across bacterial membrane.

Abstract: Bacterial multidrug resistance is a worrying health issue. In Gram-negative antibacterial research, the challenge is to define the antibiotic permeation across the membranes. Passing through the membrane barrier to reach the inhibitory concentration inside the bacterium is a pivotal step for antibacterial molecules. A spectrofluorimetric methodology has been developed to detect fluoroquinolones in bacterial population and inside individual Gram-negative bacterial cells. In this work, we studied the antibiotic accumulation in cells expressing various levels of efflux pumps. The assays allow us to determine the intracellular concentration of the fluoroquinolones to study the relationships between the level of efflux activity and the antibiotic accumulation, and finally to evaluate the impact of fluoroquinolone structures in this process. This represents the first protocol to identify some structural parameters involved in antibiotic translocation and accumulation, and to illustrate the recently proposed "Structure Intracellular Concentration Activity Relationship" (SICAR) concept.

Exact Histogram Specification for Digital Images Using a Variational Approach

Abstract: We consider the problem of exact histogram specification for digital (quantized) images. The goal is to transform the input digital image into an output (also digital) image that follows a prescribed histogram. Classical histogram modification methods are designed for real-valued images where all pixels have different values, so exact histogram specification is straightforward. Digital images typically have numerous pixels which share the same value. If one imposes the prescribed histogram to a digital image, usually there are numerous ways of assigning the prescribed values to the quantized values of the image. Therefore, exact histogram specification for digital images is an ill-posed problem. In order to guarantee that any prescribed histogram will be satisfied exactly, all pixels of the input digital image must be rearranged in a strictly ordered way. Further, the obtained strict ordering must faithfully account for the specific features of the input digital image. Such a task can be realized if we are able to extract additional representative information (called auxiliary attributes) from the input digital image. This is a real challenge in exact histogram specification for digital images. We propose a new method that efficiently provides a strict and faithful ordering for all pixel values. It is based on a well designed variational approach. Noticing that the input digital image contains quantization noise, we minimize a specialized objective function whose solution is a real-valued image with slightly reduced quantization noise, which remains very close to the input digital image. We show that all the pixels of this real-valued image can be ordered in a strict way with a very high probability. Then transforming the latter image into another digital image satisfying a specified histogram is an easy task. Numerical results show that our method outperforms by far the existing competing methods.

Three-dimensional deformation and transverse rotation of the human free Achilles tendon in vivo during isometric plantarflexion contraction

Abstract: Freehand three-dimensional ultrasound (3DUS) was used to investigate longitudinal and biaxial transverse deformation and rotation of the free Achilles tendon in vivo during a voluntary submaximal isometric muscle contraction. Participants (n = 8) were scanned at rest and during a 70% maximal voluntary isometric contraction (MVIC) of the plantarflexors. Ultrasound images were manually digitized to render a 3D reconstruction of the free Achilles tendon for the computation of tendon length, volume, cross-sectional area (CSA), mediolateral diameter (MLD), anteroposterior diameter (APD), and transverse rotation. Tendon longitudinal and transverse (CSA, APD, and MLD) deformation and strain at 70% MVIC were calculated relative to the resting condition. There was a significant main effect of contraction on tendon length and mean CSA, MLD, and APD (P < 0.05), but no effect on tendon volume (P = 0.70). Group mean transverse strains for CSA, MLD, and APD averaged over the length of the tendon were -5.5%, -8.7% and 8.7%, respectively. Peak CSA, MLD, and APD transverse strains all occurred between 40% and 60% of tendon length. Transverse rotation of the free tendon was negligible at rest but increased under load, becoming externally rotated relative to the calcaneal insertion. The relationship between longitudinal and transverse strains of the free Achilles tendon during muscle-induced elongation may be indicative of interfascicle reorganization. The finding that transverse rotation and strain peaked in midportion of the free Achilles tendon may have important implications for tendon injury mechanisms and estimation of tendon stress in vivo.

The structure of branched transportation networks

Abstract: The transportation problem can be formalized as the problem of finding the optimal paths to transport a measure μ + onto a measure μ − with the same mass. In contrast with the Monge–Kantorovich formalization, recent approaches model the branched structure of such supply networks by an energy functional whose essential feature is to favor wide roads. Given a flow s in a road or a tube or a wire, the transportation cost per unit length is supposed to be proportional to s α with 0 < α < 1. For the Monge–Kantorovich energy α = 1 so that it is equivalent to have two roads with flow 1/2 or a larger one with flow 1. If instead 0 < α < 1, a road with flow $$s_1+s_2$$ is preferable to two individual roads s 1 and s 2 because $$(s_1+s_2)^\alpha < s_1^\alpha+s_2^\alpha$$ . Thus, this very simple model intuitively leads to branched transportation structures. Such a branched structure is observable in ground transportation networks, in draining and irrigation systems, in electric power supply systems and in natural objects like the blood vessels or the trees. When $$\alpha > 1-\frac 1N$$ such structures can irrigate a whole bounded open set of $${\mathbb{R}}^N$$ . The aim of this paper is to give a mathematical proof of several structure and regularity properties empirically observed in transportation networks. It is first proven that optimal transportation networks have a tree structure and can be monotonically approximated by finite graphs. An interior regularity result is then proven according to which an optimal network is a finite graph away from the irrigated measure. It is also proven that the branching number of optimal networks has everywhere a universal explicit bound. These results answer questions raised in two recent papers by Xia.