Search results for "Percolation"

Overlapping community detection versus ground-truth in AMAZON co-purchasing network

2015

International audience; Objective evaluation of community detection algorithms is a strategic issue. Indeed, we need to verify that the communities identified are actually the good ones. Moreover, it is necessary to compare results between two distinct algorithms to determine which is most effective. Classically, validations rely on clustering comparison measures or on quality metrics. Although, various traditional performance measures are used extensively. It appears very clearly that they cannot distinguish community structures with different topological properties. It is therefore necessary to propose an alternative methodology more sensitive to the community structure variations in orde…

Annealed Invariance Principle for Random Walks on Random Graphs Generated by Point Processes in R-d

2016

International audience; We consider simple random walks on random graphs embedded in R-d and generated by point processes such as Delaunay triangulations, Gabriel graphs and the creek-crossing graphs. Under suitable assumptions on the point process, we show an annealed invariance principle for these random walks. These results hold for a large variety of point processes including Poisson point processes, Matern cluster and Matern hardcore processes which have respectively clustering and repulsiveness properties. The proof relies on the use the process of the environment seen from the particle. It allows to reconstruct the original process as an additive functional of a Markovian process und…

Dielectric properties of graphite-based epoxy composites

2014

International audience; Composite materials based on epoxy resin filled with various kinds of graphite particles: exfoliated graphite, natural graphite, and coarse, medium and fine artificial graphites have been prepared. Results of broadband dielectric investigations of such materials in wide temperature (25-450 K) and frequency (20 Hz-3 THz) ranges are presented. The dielectric permittivity strongly increases with graphite particle size. The graphite particle size and shape also have a strong impact on freezing temperature, conductivity activation energy and composite electromagnetic absorption properties at room temperature. The lowest percolation threshold is observed for exfoliated gra…

Percolation model of axon guidance

2013

The role of pH on instability and aggregation of sickle hemoglobin solutions

2004

Understanding the physical basis of protein aggregation covers strong physical and biomedical interests. Sickle hemoglobin (HbS) is a point-mutant form of normal human adult hemoglobin (HbA). It is responsible for the first identified "molecular disease," as its propensity to aggregation is responsible for sickle cell disease. At moderately higher than physiological pH value, this propensity is inhibited: The rate of aggregate nucleation becomes exceedingly small and solubility after polymerization increases. These order-of-magnitude effects on polymer nucleation rates and concurrent relatively modest changes of solubility after polymerization are here shown to be related to both pH-induced…

In-situ synthesis of thiophene-based multifunctional polymeric networks with tunable conductivity and high photolithographic performance

2017

Abstract Design of novel multifunctional polymeric materials combining electrically conducting properties with patterning capability is a significant challenge in materials science. Herein, we report on the synthesis of multifunctional interpenetrating polymer networks (IPN) by the in-situ oxidative polymerization of thiophene-based monomers with Cu(ClO 4 ) 2 inside a novolac-based photoresist. The resulting IPNs show conductivities up to 20 S/cm depending on the monomer properties. Among them, 3,3‴-Dihexyl-2,2’:5′,2’’:5″,2‴-quaterthiophene (DH4T) is chosen because it has the largest conjugation length and excellent solubility in organic solvents. Moreover, it renders a low percolation thre…

Fast proton conduction in hydrogen bonded microheterogeneous systems: Bis(2-ethylhexyl)phosphoric acid/N-methyl formamide liquid mixtures

2009

Structural and dynamical properties of bis(2-ethylhexyl)phosphoric acid (HDEHP)/N-methyl formamide (NMF) liquid mixtures in the whole composition range have been investigated by Fourier Transform Infrared spectroscopy (FT-IR), X-rays Diffraction (XRD), and AC complex impedance spectroscopy. Driven by hydrogen bond interactions among HDEHP PO(4)H group and NMF CO and NH groups, and also by steric effects among the HDEHP alkyl chains, the system microstructure is mainly characterized by the coexistence of spatially separated hydrophilic and hydrophobic nanodomains showing local organization and short-range order. The evolution of this structural feature with system composition has been highli…

Polyisoprene-carbon black nanocomposites as tensile strain and pressure sensor materials

2004

Abstract Electrically conductive polymer composites (ECPC) are shown as prospective large-size flexible pressure and stretch sensors for detecting of dangerous deformations and vibrations of vehicle parts. Reversible change of resistance dependent on stretch and pressure is obtained in electro-conductive polymer nanocomposites. At certain concentrations of carbon nano-particles a change of electrical resistance by more than four orders is observed at 40% relative stretch. The maximum sensitivity of nanocomposites is observed in the vicinity of the transition of electro-conductive percolation. Nanocomposites exhibit a very weak semiconductor-like temperature dependence of resistance. The ten…

Effect of elongational flow on morphology and properties of polymer/CNTs nanocomposite fibers

2010

Carbon nanotubes (CNTs) have been attracting increasing interest for the fabrication of polymer-based nanocomposites because of their excellent properties. Traditional methods for the preparation of polymer/CNTs nanocomposites are in situ polymerization, solution blending, and melt mixing. The achievement of a good CNT dispersion and a percolation network is important in order to obtain better mechanical and electrical properties. However, the rheological behavior of polymer/CNTs systems, in particular regarding the extensional flow, has not been much investigated so far. In this work we present, for the first time, rheological data in non-isothermal extensional flow and an investigation on…

Interaction between a water-in-oil microemulsion and a linear-dendritic poly(propylene oxide)–polyglycerol block copolymer

2011

We present small angle scattering and dielectric spectroscopy results on the influence of an amphiphilic diblock copolymer on the structure and dynamics of a microemulsion. We use a water-in-oil (w/o) droplet microemulsion based on the anionic surfactant AOT (sodium bis(2-ethylhexyl) sulfosuccinate), that forms spherical water droplets coated by a monolayer of AOT dispersed in the continuous oil matrix. The studied polymer consists of a hydrophobic poly(propylene oxide) (PPO) block and a hydrophilic hyperbranched polyglycerol with 74 glycerol units (NG74). Combining small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) we find that the droplet structure is preserved …