Plea for the use of the exact Stirling formula in statistical mechanics

In statistical mechanics, the generally called Stirling approximation is actually an approximation of Stirling's formula. In this article, it is shown that the term that is dropped is in fact the one that takes fluctuations into account. The use of the Stirling's exact formula forces us to reintroduce them into the already proposed solutions of well-know puzzles such as the extensivity paradox or the Gibbs' paradox of joining two volumes of identical gas. This amendment clearly results in a gain in consistency and rigor of these solutions

A short derivation of Boltzmann distribution and Gibbs entropy formula from the fundamental postulate

Introducing the Boltzmann distribution very early in a statistical thermodynamics course (in the spirit of Feynmann) has many didactic advantages, in particular that of easily deriving the Gibbs entropy formula. In this note, a short derivation is proposed from the fundamental postulate of statistical mechanics and basics calculations accessible to undergraduate students

Pink Noise of Ionic Conductance through Single Artificial Nanopore Revisted

International audienceWe report voltage-clamp measurements through single conical nanopore obtained by chemical etching of a single ion track in polyimide film. Special attention is paid to the pink noise of the ionic current (i.e., 1=f noise) measured with different filling liquids. The relative pink-noise amplitude is almost independent of concentration and pH for KCl solutions, but varies strongly using ionic liquids. In particular, we show that depending on the ionic liquid, the transport of charge carriers is strongly facilitated (low noise and higher conductivity than in the bulk) or jammed. These results show that the origin of the pink noise can be ascribed neither to fluctuations of the pore geometry nor to the pore wall charges, but rather to a cooperative effect on ions motion in confined geometry

Nanoporous beta-PVDF membranes with selectively functionalized pores

International audiencePoly (vinylidene fluoride) ( -PVDF) nanoporous membranes are obtained by heavy ion irradiation and track etching leading to cylindrical pores. Pores diameter measured by Scanning Electron Microscopy and Small Angle Neutron Scattering lies in the 20-50nm range. Electron Paramagnetic Resonance study gives evidence that radicals still remains in PVDF membrane after track-etching. These radicals allows acrylic acid polymerization to be initiated onto membrane. So radiografted and functionalized membranes are characterized using Infrared Spectroscopy, weighing measurements and Energy Dispersive Spectroscopy. Finally, radiografted poly(acrylic-acid) (PAA) has been selectively labeled by fluorophores and imaged by Confocal Laser Scanning Microscopy. Images show the localisation of PAA specifically inside nanopores

Takotsubo Cardiomyopathy in a Squash Player

Takotsubo cardiomyopathy is usually described following acute emotional stress. We report here the case of a 48-year-old woman admitted for acute coronary syndrome after an intensive squash match. Diagnosis of Takotsubo cardiomyopathy due to acute physical stress was suspected in presence of normal coronary arteries and transitory left ventricular dysfunction with typical apical ballooning. Cardiac magnetic resonance imaging confirmed regional wall-motion abnormalities and was helpful in excluding myocardial infarction diagnosis. During squash the body is subject to sudden and vigorous demands inducing a prolonged and severe workload on the myocardium

Nanoprobes to interrogate nonspecific interactions in lipid bilayers: from defect-mediated adhesion to membrane disruption

When a lipid membrane approaches a material/nanomaterial, nonspecific adhesion may occur. The interactions responsible for nonspecific adhesions can either preserve the membrane integrity or lead to its disruption. Despite the importance of the phenomenon, there is still a lack of clear understanding of how and why nonspecific adhesions may originate different resulting scenarios and how these interaction scenarios can be interrogated. This work aims at bridging this gap by investigating the interplay between cationic electrostatic and hydrophobic interactions in modulating the membrane stability during nonspecific adhesion phenomena. Here, the stability of the membrane has been studied employing anisotropic nanoprobes in zwitterionic lipid membranes with the support of coarse-grained molecular dynamics simulations to interpret the experimental observations. Lipid membrane electrical measurements and nanoscale visualization in combination with molecular dynamics simulations revealed the phenomena driving nonspecific adhesion. Any interaction with the lipidic bilayer is defect-mediated involving cationic electrostatically-driven lipid extractions and hydrophobicallydriven chains protrusion, whose interplay determines the existence of a thermodynamic optimum for the membrane structural integrity. These findings unlock unexplored routes to exploit nonspecific adhesion in lipid membranes. The proposed platform can act as a straightforward probing tool to locally interrogate interactions between synthetic materials and lipid membranes for the design of antibacterials, antivirals, and scaffolds for tissue engineering

Emerging Two-Dimensional Crystallization of Cucurbit[8]uril Complexes: From Supramolecular Polymers to Nanofibers.

The binding of imidazolium salts to cucurbit[8]uril, CB[8], triggers a stepwise self-assembly process with semiflexible polymer chains and crystalline nanostructures as early- and late-stage species, respectively. In such a process, which involves the crystallization of the host-guest complexes, the guest plays a critical role in directing self-assembly toward desirable morphologies. These include platelet-like aggregates and two-dimensional (2D) fibers, which, moreover, exhibit viscoelastic and lyotropic properties. Our observations provide a deeper understanding of the self-assembly of CB[8] complexes, with fundamental implications in the design of functional 2D systems and crystalline materials.EPSRC (reference no. EP/ G060649/1), ERC Starting Investigator Grant (project no. 240629, ASPiRe) Next Generation Fellowship from the Walters-Kundert Foundation. MINE- CO, the FSE and the FEDER for funding through projects RYC-2015-18471 (Ramoń y Cajal program) and CTQ2017- 84087-R. Royal Society University Research Fellowship UF160152. EPSRC CDT in Nanoscience and Nanotechnology (NanoDTC), grant number EP/L015978/1

Gelification et vitrification de systemes epoxyde-amine: etude ultrasonore, rheologique, dielectrique et par simulation

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 79530 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Transport d'ions et d'objets dans des nanopores

Il existe différentes techniques de manipulation et de détection de molécules uniques. Parmi elles, la mesure du courant ionique traversant un pore nanométrique unique est la plus ancienne. Le travail effectué dans cette thèse utilise cette technique et s'articule autour de deux objectifs. Tout d'abord, l'utilisation d'un nanopore unique obtenu par attaque de trace permet d'imiter les expériences déjà faites dans la littérature avec d'autres types de pores. Certains phénomènes, tels que la rectification par exemple, ont pu être observés, mais d'autres comme la translocation n'ont pu l'être. Ensuite, une étude du bruit de conductance électrique démontre l'existence d'un phénomène qui n'avait jusqu'alors pas été soulevé dans la littérature. En effet, ce bruit ne peut pas être imputé aux fluctuations des caractéristiques de la géométrie du pore ou de sa paroi, mais plutôt à des effets coopératifs sur la mobilité des ions dans un milieu confinéSeveral ways exist to handle and detect single molecules. The oldest one is to measure the ionic current going through a single nanometric pore. This thesis uses this technique. The discussion is built in two main parts. Firstly, the use of a single track-etched nanopore is aimed to reproduce experiments already made in the litterature with other kinds of pores. Some phenomena, like rectification for example, were observed, whereas others, like translocation, were not. Secondly, the investigation of electric conductance noise proves the existence of a phenomenon which has not been pointed out before in the litterature yet. Indeed, this noise can be ascribed neither to fluctuations of the pore geometry nor to the pore wall charges, but rather to a cooperative effect on ions motion in confined geometry.PALAISEAU-Polytechnique (914772301) / SudocSudocFranceF