Recycling controls membrane domains

We study the coarsening of strongly microphase separated membrane domains in the presence of recycling of material. We study the dynamics of the domain size distribution under both scale-free and size-dependent recycling. Closed form solutions to the steady state distributions and its associated central moments are obtained in both cases. Moreover, for the size-independent case, the~time evolution of the moments is analytically calculated, which provide us with exact results for their corresponding relaxation times. Since these moments and relaxation times are measurable quantities, the biophysically significant free parameters in our model may be determined by comparison with experimental data.Comment: 5 pages, 4 figure

Composition variation and underdamped mechanics near membrane proteins and coats

We study the effect of membrane proteins on the shape, composition and thermodynamic stability of the surrounding membrane. When the coupling between membrane composition and curvature is strong enough the nearby composition and shape both undergo a transition from over-damped to under-damped spatial variation, well before the membrane becomes unstable in the bulk. This transition is associated with a change in the sign of the thermodynamic energy and hence has the unusual features that it can favour the early stages of coat assembly necessary for vesiculation (budding), while suppressing the activity of mechanosensitive membrane channels and transporters. Our results also suggest an approach to obtain physical parameters that are otherwise difficult to measure

Leaf-to-leaf distances and their moments in finite and infinite m-ary tree graphs

We study the leaf-to-leaf distances on full and complete m-ary graphs using a recursive approach. In our formulation, leaves are ordered along a line. We find explicit analytical formulae for the sum of all paths for arbitrary leaf-to-leaf distance r as well as the average path lengths and the moments thereof. We show that the resulting explicit expressions can be recast in terms of Hurwitz-Lerch transcendants. Results for periodic trees are also given. For incomplete random binary trees, we provide first results by numerical techniques; we find a rapid drop of leaf-to-leaf distances for large r.Comment: 10 pages, 7 figure

Crowd-based positioning of UAVs as Access Points

Unmanned Aerial Vehicles (UAVs) can be a cost saving and easy to deploy solution to implement a temporary network infrastructure. They can act as access points in scenarios such as emergency situations, special events, or specific area monitoring. Two main deployment families can be found in the literature. The first one, the location-based family, is based on the fundamental assumption that the network user positions are known. We do believe that this could not suit the most general scenarios. On the other hand, the location-independent family can not be as efficient as the first one. The main idea in this paper is to introduce a new crowd-based family, based on a probabilistic knowledge of user positions. We then propose a self-deployment method built on a Coulomb's law analogy where users and UAVs act as electrical charges. Short range interactions are implemented through network sensing, while long range ones use a crowd-based approach. Some numerical results are depicted, showing the performance of this self-deploying mechanism as well as a comparison with a well-known clustering algorithm

Déploiement temporaire d'une infrastructure de communication à base de drones

Dernièrement, l'utilisation des drones est en pleine expansion dans multiples domaines, par exemple récemment la livraison des colis ou des repas. Parallèlement, les stations de base mobiles sont incapables parfois de satisfaire les exigences des utilisateurs, surtout en cas d'événements imprévus, tels que les catastrophes, les rassemblements ou les rencontres sportives. Une solution prometteuse consiste à profiter de la disponibilité des drones pour pallier les déficiences des réseaux cellulaires en les aidant à satisfaire les demandes par l'extension de la couverture à l'aide des points d'accès installés à bord des drones. Bien que les drones offrent un déploiement rapide, le placement devient l'un des problèmes clés. Dans ce manuscrit nous nous intéressons à ce type de réseaux et au placement des drones en proposant une méthode de déploiement fondée sur une analogie avec la loi de Coulomb, les utilisateurs et les drones agissant comme des charges électriques, les drones étant attirés par les utilisateurs

Physics of biomembranes

The basic building blocks of all biomembranes are lipid molecules, which self-assemble to form a very thin and stable barrier, where a variety of proteins can be incorporated into its structure. These two-dimensional systems exhibit a plethora of physical phenomena, which are an abundant source of inspiration for a physicist. The physical aspects of biomembranes are described within a phenomenological model, the so-called Canhan{Helfrich theory, which relies primarily on the geometrical aspects of the membrane surface at large scales. Using this theory, we study the response of a membrane to the inclusion of a transmembrane protein or a protein coat by coupling the composition to the mean curvature. A transition is found from an overdamped to an underdamped regime for the membrane shape and its compositional variation. This leads to large membrane undulations near the inclusion, resulting in the activity suppression of mechanosensitive channels and a preference for the formation of protein coats. We also re-examine the methodology for inferring the bending modulus of membranes from their observed thermal fluctuations. Particularly, we analyse the effect due to the optical projection of such shape undulations across the focal depth of the microscope. A comparison of this with the literature approaches reveals a systematic decrease in the value of the bending modulus, resolving a previously recognised discrepancy between shape measurements and other known techniques. Lastly, we investigate an non-equilibrium model for the formation of membrane domains that also involves membrane recycling. The dynamics and the steady-state features of the domain size distribution are analytically revealed and the implication to the heterogeneity observed in biomembranes is discussed

Relative entropy under mappings by stochastic matrices

AbstractThe relative g-entropy of two finite, discrete probability distributions x = (x1,…,xn) and y = (y1,…,yn) is defined as Hg(x,y) = Σkxkg (yk/kk - 1), where g:(-1,∞)→R is convex and g(0) = 0. When g(t) = -log(1 + t), then Hg(x,y) = Σkxklog(xk/yk), the usual relative entropy. Let Pn = {x ∈ Rn : σixi = 1, xi > 0 ∀i}. Our major results is that, for any m × n column-stochastic matrix A, the contraction coefficient defined as ηğ(A) = sup{Hg(Ax,Ay)/Hg(x,y) : x,y ∈ Pn, x ≠ y} satisfies ηg(A) ⩽1 - α(A), where α(A) = minj,kΣi min(aij, aik) is Dobrushin's coefficient of ergodicity. Consequently, ηg(A) < 1 if and only if A is scrambling. Upper and lower bounds on αg(A) are established. Analogous results hold for Markov chains in continuous time

A literacia e seus desafios: promover o pensamento crítico em pessoas subletradas

We begin by defining the concept of literacy and illustrate its impact on cognitive abilities, in particular on memory and language comprehension. We then consider the hypothesis that literacy contributes to raising the quality and depth of critical thinking. This, in turn, supports the capacity for intellectual self-defense – in terms of cognitive science, “epistemic vigilance” – in relation to fake news and other maneuvers to distort the facts or of lying propaganda. Finally, we discuss the results of pre-tests of an experimental project in which several groups of subliterate adults will receive training in literacy and critical thinking skills.Definimos o conceito de literacia e ilustramos o impacto desta nas capacidades cognitivas, em particular de memória e de compreensão da linguagem. A seguir, consideramos a hipótese de que a literacia contribui para elevar a qualidade e a profundidade do pensamento crítico. Este, por sua vez, sustenta a capacidade de autodefesa intelectual – em termos de ciência cognitiva, de “vigilância epistémica” – relativamente às fake news e a outras manobras de desvirtuação dos fatos ou de propaganda mentirosa. Finalmente, são discutidos os resultados de pré-testes de um projeto experimental em que diversos grupos de adultos subletrados receberão treinamento das capacidades de literacia e de pensamento crítico