Slow sedimentation and deformability of charged lipid vesicles

The study of vesicles in suspension is important to understand the complicated dynamics exhibited by cells in vivo and in vitro. We developed a computer simulation based on the boundary-integral method to model the three dimensional gravity-driven sedimentation of charged vesicles towards a flat surface. The membrane mechanical behavior was modeled using the Helfrich Hamiltonian and near incompressibility of the membrane was enforced via a model which accounts for the thermal fluctuations of the membrane. The simulations were verified and compared to experimental data obtained using suspended vesicles labelled with a fluorescent probe, which allows visualization using fluorescence microscopy and confers the membrane with a negative surface charge. The electrostatic interaction between the vesicle and the surface was modeled using the linear Derjaguin approximation for a low ionic concentration solution. The sedimentation rate as a function of the distance of the vesicle to the surface was determined both experimentally and from the computer simulations. The gap between the vesicle and the surface, as well as the shape of the vesicle at equilibrium were also studied. It was determined that inclusion of the electrostatic interaction is fundamental to accurately predict the sedimentation rate as the vesicle approaches the surface and the size of the gap at equilibrium, we also observed that the presence of charge in the membrane increases its rigidity

Ase1/Prc1-dependent spindle elongation corrects merotely during anaphase in fission yeast

The tug of war that ensues when a kinetochore binds microtubules from both spindle poles is resolved by Ase1/Prc1

Vapor emissions from contaminated soils into buildings : comparison between predictions from transport model and field measurements

International audienceSoil vapor migration into house, with subsequent inhalation, is often the main exposure pathway to humans at sites contaminated with Volatile Organic Compounds (VOCs). In the case of VOCs contamination, quantification of indoor gas concentrations is therefore essential while assessing risks for human health. Two approaches are commonly used for quantification of indoor concentrations: indoor gas measurement or transfer modelization from the source (soil, soil vapor phase, groundwater). Model development is relatively well advanced but measurements for model calibration and "validation" hardly exist in the literature. Furthermore, predictions of indoor gas concentrations from different models may vary by several orders of magnitude, depending on the application. Therefore, the validity of the risk calculation obtained through models, and hence of the site management, remains highly uncertain. The research project presented here aims at providing such "validation" data. Long-term goals of the research are improvement of modelization and also development of tools for site-related model-selection. The program consisted in comparing modelization and experimental measurements on a test site. The site was a former factory with a concrete slab, contaminated with chlorinated solvents (trichloroethene and perchloroethylene) in unsaturated soils. Measurements concerned contaminant concentrations and fluxes in different media and at different transfer stages, but also key mode! parameters. The equations of Johnson & Ettinger and VOLASOIL models were used. Air concentrations measured at various times show significant variations, and also differ from model prediction by one or two orders of magnitude. Despite thorough parameter measurements, uncertainty on input values, related to site heterogeneity, induced high uncertainty in the modelization. The preliminary results presented here show intrinsic limitation of some measurements and hence of model validation, but also the need for data on more sites, including very important site instrumentation which would allow to document the impact of site-heterogeneity

Nanocristaux pour les mémoires flash (multicouches, métalliques et organisés)

Les deux principales limitations des mémoires non-volatiles de type Flash à stockage de charges dans des nanocristaux en silicium sont la faible fenêtre mémoire et la dispersion des caractéristiques électriques due à la dispersion en taille des nanocristaux. Dans cette thèse, plusieurs solutions sont étudiées afin de remédier à ces deux défauts. Afin d'augmenter la fenêtre de programmation, une première approche consiste à augmenter la densité de stockage de charges grâce à l'utilisation d'une double couche de nanocristaux en silicium. Le fonctionnement et les performances électriques de ces dispositifs mémoires sont étudiés puis interprétés grâce à un modèle analytique. Une seconde approche, plus amont, consiste à utiliser des nanocristaux métalliques pour augmenter la quantité de charges piégées dans les nanocristaux. Le dépôt, la passivation et l'intégration de nanocristaux à caractère métallique (Pt, TiN, W) en tant que grille flottante dans un dispositif mémoire sont ainsi réalisés. Enfin, l'organisation bottom-up des nanocristaux est proposée comme une solution à la dispersion des caractéristiques électriques des dispositifs mémoires. Un procédé original de transfert et de gravure d'un masque auto-organisé à base de copolymères diblocs est développé.The two main limitations of Flash nonvolatile memories charge storage in silicon nanocrystals are the small memory window and the dispersion of electrical characteristics due to the size dispersion of nanocrystals. In this thesis, several solutions are studied in order to remedy these defects. In order to increase the programming window, a first approach is to increase the density of charges stored in the device through the use of a double layer of silicon nanocrystals. The operation and electrical performance of these memory devices are studied and interpreted through an analytical model. A second approach, more upstream, is the use of metallic nanocrystals to increase the amount of trapped charges in the nanocrystals. Deposition, passivation and integration of metal nanocrystals (Pt, TiN, W) as a floating gate in a memory device have been realized. Finally, the "bottom-up" organisation of nanocrystals is proposed as a solution to the dispersion of electrical characteristics of memory devices. An original process for transferring a self-organized diblock copolymer mask into a hard mask is developed and used to etch nanocrystals with small size dispersion.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Apico-basal forces exerted by apoptotic cells drive epithelium folding

© 2015 Macmillan Publishers Limited. All rights reserved. Epithelium folding is a basic morphogenetic event that is essential in transforming simple two-dimensional epithelial sheets into three-dimensional structures in both vertebrates and invertebrates. Folding has been shown to rely on apical constriction. The resulting cell-shape changes depend either on adherens junction basal shift or on a redistribution of myosin II, which could be driven by mechanical signals. Yet the initial cellular mechanisms that trigger and coordinate cell remodelling remain largely unknown. Here we unravel the active role of apoptotic cells in initiating morphogenesis, thus revealing a novel mechanism of epithelium folding. We show that, in a live developing tissue, apoptotic cells exert a transient pulling force upon the apical surface of the epithelium through a highly dynamic apico-basal myosin II cable. The apoptotic cells then induce a non-autonomous increase in tissue tension together with cortical myosin II apical stabilization in the surrounding tissue, eventually resulting in epithelium folding. Together our results, supported by a theoretical biophysical three-dimensional model, identify an apoptotic myosin-II-dependent signal as the initial signal leading to cell reorganization and tissue folding. This work further reveals that, far from being passively eliminated as generally assumed (for example, during digit individualization), apoptotic cells actively influence their surroundings and trigger tissue remodelling through regulation of tissue tension.Agence Nationale de la Recherche (ANR), Fondation de la Recherche et de l’Innovation The´rapeutique en Cance´rologie (RITC) and the University of Toulouse.Peer Reviewe

Tip1/CLIP-170 Protein Is Required for Correct Chromosome Poleward Movement in Fission Yeast

The plus-end microtubule binding proteins (+TIPs) play an important role in the regulation of microtubule stability and cell polarity during interphase. In S. pombe, the CLIP-170 like protein Tip1, together with the kinesin Tea2, moves along the microtubules towards their plus ends. Tip1 also requires the EB1 homolog Mal3 to localize to the microtubule tips. Given the requirement for Tip1 for microtubule stability, we have investigated its role during spindle morphogenesis and chromosome movement. Loss of Tip1 affects metaphase plate formation and leads to the activation of the spindle assembly checkpoint. In the absence of Tip1 we also observed the appearance of lagging chromosomes, which do not influence the normal rate of spindle elongation. Our results suggest that S. pombe Tip1/CLIP170 is directly or indirectly required for correct chromosome poleward movement independently of Mal3/EB1

Live cell division dynamics monitoring in 3D large spheroid tumor models using light sheet microscopy

<p>Abstract</p> <p>Background</p> <p>Multicellular tumor spheroids are models of increasing interest for cancer and cell biology studies. They allow considering cellular interactions in exploring cell cycle and cell division mechanisms. However, 3D imaging of cell division in living spheroids is technically challenging and has never been reported.</p> <p>Results</p> <p>Here, we report a major breakthrough based on the engineering of multicellular tumor spheroids expressing an histone H2B fluorescent nuclear reporter protein, and specifically designed sample holders to monitor live cell division dynamics in 3D large spheroids using an home-made selective-plane illumination microscope.</p> <p>Conclusions</p> <p>As illustrated using the antimitotic drug, paclitaxel, this technological advance paves the way for studies of the dynamics of cell divion processes in 3D and more generally for the investigation of tumor cell population biology in integrated system as the spheroid model.</p

A Dependently-Typed Linear &#960; -Calculus in Agda

Session types have consolidated as a formalism for the specification and static enforcement of communication protocols. Many different theories of dependent session types have been proposed, some enabling refined specifications on the content of messages, others allowing the structure of the protocols to depend on data exchanged in the protocol itself. In this work we continue a line of research studying the foundations of binary session types. In particular, we propose a variant of the linear π-calculus whose type structure encompasses virtually all dependent session types using just two type constructors: linear channel types and linear dependent pairs. We use Agda not only to formalize the metatheory of the calculus and obtain machine-checked proofs of type soundness, but also as host language in which we implement data-dependent protocols

Type Inference for Deadlock Detection in a Multithreaded Polymorphic Typed Assembly Language

We previously developed a polymorphic type system and a type checker for a multithreaded lock-based polymorphic typed assembly language (MIL) that ensures that well-typed programs do not encounter race conditions. This paper extends such work by taking into consideration deadlocks. The extended type system verifies that locks are acquired in the proper order. Towards this end we require a language with annotations that specify the locking order. Rather than asking the programmer (or the compiler's backend) to specifically annotate each newly introduced lock, we present an algorithm to infer the annotations. The result is a type checker whose input language is non-decorated as before, but that further checks that programs are exempt from deadlocks