Whenever one material moves against another, some energy can be lost due to adhesion hysteris and/or friction. That energy is transferred into unwanted heat, deformation, or wear reducing the material’s lifetime. A number of experimental studies have shown that polymer coatings can be efficiently used to control friction and adhesion between surfaces. Polymer coatings have properties and responsiveness that are contingent on the chemical composition, size and shape of structure, elasticity. However, they are generally suffering from major shortcomings such as lack of responsiveness selectivity and reversibility, poor environmental stability and limited understanding of the structure–function relationship, which are all critical to design reliable rules for building responsive or self-lubricating surfaces. Experimental surface forces studies of different classes of solvated polymer-bearing surfaces carried out using the surface forces apparatus and similar molecular techniques will be presented in order to elucidate the responsiveness mechanism and the structure–property relationship between polymer-coated surfaces in aqueous media. Eventhough conclusive understanding is still hampered by the difficulty of systematically controlling the grafting density, the studies suggest that the effective lubrication mechanisms involve the facility with which macromolecules under compression remain hydrated and hold a significant amount of water at the surfaces to be lubricated.

The binary Kob-Andersen (KA) Lennard-Jones mixture is the standard model for computational studies of viscous liquids and the glass transition. For very long runs the viscous KA system crystallizes, however, by phase separating into a pure A particle phase forming an FCC crystal. We present the phase diagram for KA-type mixtures showing, in particular, that the freezing temperature of the standard KA system at liquid density 1.2 is 1.028(3). At large B particle concentrations the system crystallizes into the CsCl crystal structure. The eutectic corresponding to the FCC and CsCl structures is cut-off in a narrow interval of B particle concentrations around 25% at which the PuBr 3 structure is the thermodynamically stable phase. The melting temperature’s variation with B particle concentration at two other pressures, as well as at the constant density 1.2, are predicted from the simulations using isomorph theory; interface-pinning simulations confirm these predictions. Our data demonstrate approximate identity between the melting temperature and the
onset temperature below which viscous dynamics appears.

Introduction to semimagnetic semiconductors (diluted magnetic semiconductors, DMS) is given. Semimagnetic properties of ZnMnTe are described, as obtained by parallel studies of magneto-reflectivity (MR) and magneto-photoluminescence (MPL). Properties of MR resonances are presented and explained. Spin-polarized MPL spectra are shown, exhibiting simultaneous presence of paramagnetic Mn-ions, excitons and donor- acceptor pairs. A coefficient of MPL circular light polarization P(Mn) is introduced and it is demonstrated that it as an important quantity characterizing a semimagnetic material. A relation between the Zeeman shifts of exciton transitions due to exchange interaction with mobile carriers and Mn-ions and P(Mn) due to internal recombination of Mn-ions is revealed. An enhancement of binding energies with increasing magnetic field for excitons localized by potential fluctuations is demonstrated and explained. Simultaneous presence of Mn paramagnetic ions and residual nonmagnetic impurities in ZnMnTe provides for a rich physical picture.

When fluids are forced to flow, instabilities are commonly observed in simple and complex fluids due to inertia or to elasticity. Shear-thickening, the process by which the viscosity of concentrated particulate dispersions dramatically increases above some critical load, is another widespread phenomenon that can be interpreted in terms of an underlying instability. While recent theoretical work has narrowed down the potential instabilities at play, their experimental demonstration is sorely lacking and mechanisms accurately explaining shear-thickening are still a subject of heated debate.

Our experimental work uncovers for the first time the local origin of the unsteady large-scale dynamics characteristic of shear-thickening in a dense suspension of cornstarch grains. We solicit the suspension under a constant shear stress and image its flow using echography. Introducing and adapting statistical tools from turbulence physics, we pin down the origin of fluctuations: macroscopic regions organize as transient localized bands that travel perpendicular to the flow direction and proliferate as the shear stress is increased. These large-scale “coherent structures” are scattered in a random background reminiscent of turbulence. These key observations urge to introduce stress spatiotemporal correlations in models and to simulate dense three-dimensional systems together with the shearing boundaries

Ce séminaire se situe dans le cadre du projet d'intégration à l'équipe CONNECTOME d'Anne Ducros, professeur et responsable de la recherche clinique sur le thème 'migraines et céphalées' au CHU de Montpellier.
Anne Ducros présentera un état de l'art de la recherche clinique associée aux phénomènes de migraines.
François Molino articulera cette problématique au projet de l'équipe CONNECTOME, tant au niveau du recueil de données d'imagerie que de la modélisation.

Gauge-gravity duality allows for the reformulation of certain strongly coupled quantum field theories in terms of higher-dimensional gravity. In these lectures, aimed at the graduate level, we will introduce the general set-up of the correspondence, and describe the dictionary that maps between the observables on the field theory and gravity sides of the duality. We will cover topics such as how, by making use of the gravity dual description, one can compute correlation functions in strongly coupled theories, how to extract the spectrum of composite states, the relation between renormalization group flow and the geometry of the gravity dual, as well as how linear confinement can be modelled on the gravity side. Once the general framework has been introduced, we will discuss some applications to scenarios for strongly coupled physics beyond the Standard Model.

Nano-force spectroscopy: insight into intercellular de-adhesion dynamics

Attila-Gergely Végh PhD

Institute of Biophysics, Biological Research Centre, Temesvári Krt. 62, H-6726 Szeged, Hungary

Proper homeostasis of the central nervous system relies on the structural and functional integrity of the neurovascular unit (NVU). The most important physiological function of the NVU is formation and maintenance of the blood-brain barrier (BBB). Anatomically the cerebral microvascular endothelium together with pericytes, astrocytes, neurons and the extracellular matrix builds up the NVU. From a mechanical point of view, the endothelium is the most exposed to mechanical stress they represent the first defense and signaling line of the BBB. Unfortunately, most of the neoplasms found in the CNS are of metastatic origin. The first and crucial step of brain metastasis formation is the establishment of firm adhesion between the blood travelling tumor cells and the tightly connected layer of the endothelium. Amongst all tumors, the melanoma exhibits elevated frequency to metastasise to the brain.
Intercellular dynamics might present crucial nanomechanical aspects, therefore direct investigation with high accuracy provides important information. Using single-cell force spectroscopy, de-adhesion dynamics of melanoma cells with different level of malignancy (WM35, A2058 and A375) from a confluent layer of brain micro-capillary endothelial cells (hCMEC/D3) was investigated. Based on simple mechanical assumptions, hereby is presented our latest data on comparing the de-adhesion dynamics between the studied cell types. Apparent mechanical properties showed altered characteristics pointing towards cell type dependent aspects. Our results show that nanomechanical properties can be associated to higher metastatic potential and invasive characteristics may rely on stronger adhesive properties mediated by altered tether formation dynamics.

Gauge-gravity duality allows for the reformulation of certain strongly coupled quantum field theories in terms of higher-dimensional gravity. In these lectures, aimed at the graduate level, we will introduce the general set-up of the correspondence, and describe the dictionary that maps between the observables on the field theory and gravity sides of the duality. We will cover topics such as how, by making use of the gravity dual description, one can compute correlation functions in strongly coupled theories, how to extract the spectrum of composite states, the relation between renormalization group flow and the geometry of the gravity dual, as well as how linear confinement can be modelled on the gravity side. Once the general framework has been introduced, we will discuss some applications to scenarios for strongly coupled physics beyond the Standard Model.

Heavy neutrinos that couple appreciably to Standard Model particles are a common prediction of low-scale neutrino mass models. If kinematically accessible, such hypothetical particles can be produced copiously at the Large Hadron Collider, and its potential successors, and shed light on the mysterious origin of tiny neutrino masses [1]. In this seminar, the results of a newly proposed search methodology for heavy neutrinos at hadron colliders are presented. The analysis proposal focuses on an unusual (but "safe" [2]) implementation of jet vetoes to separate signal from background. Nontrivial increases in sensitivity at the High-Luminosity LHC and potential successor hadron colliders are discussed.

[1] https://arxiv.org/abs/1711.02180
[2] https://arxiv.org/abs/1805.09335