Strong Suppression of Thermal Conductivity in the Presence of Long Terminal Alkyl Chains in Low-Disorder Molecular Semiconductors

While the charge transport properties of organic semiconductors have been extensively studied over the recent years, the field of organics-based thermoelectrics is still limited by a lack of experimental data on thermal transport and of understanding of the associated structure–property relationships. To fill this gap, a comprehensive experimental and theoretical investigation of the lattice thermal conductivity in polycrystalline thin films of dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (Cn-DNTT-Cn with n = 0, 8) semiconductors is reported. Strikingly, thermal conductivity appears to be much more isotropic than charge transport, which is confined to the 2D molecular layers. A direct comparison between experimental measurements (3ω–Völklein method) and theoretical estimations (approach-to-equilibrium molecular dynamics (AEMD) method) indicates that the in-plane thermal conductivity is strongly reduced in the presence of the long terminal alkyl chains. This evolution can be rationalized by the strong localization of the intermolecular vibrational modes in C8-DNTT-C8 in comparison to unsubstituted DNTT cores, as evidenced by a vibrational mode analysis. Combined with the enhanced charge transport properties of alkylated DNTT systems, this opens the possibility to decouple electron and phonon transport in these materials, which provides great potential for enhancing the thermoelectric figure of merit ZT

Plutonium in the environment: key factors related to impact assessment in case of an accidental atmospheric release

International audienceThis paper deals with plutonium and key factors related to impact assessment. It is based on recent work performed by CEA which summarize the main features of plutonium behaviour from sources inside installations to the environment and man, and to report current knowledge on the different parameters used in models for environmental and radiological impact assessment. These key factors are illustrated through a case study based on an accidental atmospheric release of Pu in a nuclear facility

Thermodynamic data provided through the FUNMIG project: Analyses and prospective

In this paper some of the needs for good quality thermodynamic data in radioactive waste management are highlighted. A presentation of the thermodynamic data produced within the 6th EC framework programme integrated project FUNMIG (Fundamental processes of radionuclide migration) and how these have helped in filling relevant thermodynamic data gaps is given. The manuscript does not intend to be a complete review of thermodynamic data, but a short overview of the aqueous complexation of Am(III), lanthanides (III), U(VI), and Th(IV) by sulfates, silicates, carbonates and phosphates. The work presented is based on the latest developments published in the literature and specifically addressed within the IP FUNMIG

Lightweight Trusted Routing for Wireless Sensor Networks

International audienceCommunication in ad hoc network, such as Wireless Sensor Net- works (WSN), needs the use of decentralised routing algorithms requiring that several sensors behave in an expected way. This introduces a vulnera- bility as the global issue of decentralized tasks depends on local behaviors and is compromised in case of failures or malicious intrusions. We propose here an adaptation of a routing protocol for WSN, the MWAC model, that introduces trust decisions to detect and avoid sensors that exhibit an incor- rect behavior. The proposed trusted routing algorithms takes into account the low energy, communication and memory capacity of sensors to provide a realistic improvement of the routing robustness

Détection de claquages produits par laser (LIBD) pour la caractérisation de nanoparticules en suspension

National audienceLa technique LIBD (laser-induced breakdown detection) a été mise au point dans les années 90 dans le but de détecter et caractériser des nanoparticules en suspension dans un liquide. Elle consiste à focaliser un faisceau laser impulsionnel dans le milieu et détecter les claquages sur les particules soit par voie acoustique, soit par voie optique. Dans le premier cas, on détermine la probabilité de claquage en fonction de l'énergie de l'impulsion. Le seuil et la pente de la courbe en S ainsi obtenue permettent d'obtenir la taille et la concentration moyenne des particules. Dans le deuxième cas, on fixe l'énergie de l'impulsion et on image le volume focal en accumulant un certain nombre de tirs laser. La distribution des claquages dans l'axe de propagation du laser permet également de déterminer la taille et la concentration moyenne des particules.La LIBD a plusieurs avantages essentiels par rapport aux techniques conventionnelles de caractérisation de nanoparticules en suspension, notamment celles basées sur la diffusion de lumière ou sur la microscopie électronique elle est rapide, elle permet de détecter des nanoparticules individuelles jusqu'à des tailles inférieures à 10 nm et en très faible teneur, et on peut la mettre en oeuvre in situ. Elle permet donc de caractériser des suspensions de colloïdes environnementaux, de particules manufacturées, ou encore de déterminer précisément l'initiation de mécanismes de précipitation. Ces différents domaines ouvrent la voie a des applications innovantes notamment dans le secteur de la chimie en milieu nucléaire. Un montage de LIBD a été mis en place au laboratoire. Son pilotage a été réalisé sous LabView, en mode de détection acoustique et optique. Les premiers résultats expérimentaux seront présentés, obtenus sur des suspensions de nanoparticules de polystyrène

The Agent reputation and Trust (ART) Testbed

International audienc