Arithmétique des lois de probabilité définies sur un espace de Hilbert séparable

RésuméUn des problèmes fondamentaux de l'arithmétique des lois de probabilité est l'étude de la classe des probabilités n'ayant pas de facteur indécomposable (qui coïncide d'après un théorème de Kintchine avec la classe des probabilités indéfiniment divisibles qui n'ont que des facteurs indéfiniment divisibles). Dans le cas où les probabilités sont définies sur l'ensemble des réels ce problème a fait l'objet de nombreux travaux dont on peut trouver l'exposé dans les livres de Linnik, Lukacs et Ramachandran. Dans le cas d'un espace de dimension finie ces travaux ont étéétendus par Cuppens, Ostrovskii, Livsic et Cistyakov. Nous nous interessons ici au cas des probabilités définies sur un espace de Hilbert réel séparable

Thermodynamically consistent force field for coarse-grained modeling of aqueous electrolyte solution

International audienceWe propose a thermodynamically consistent methodology to parameterizeinteractions between charged particles inside the dissipative particle dynamics (DPD) formalism.We have used experimental data of osmotic pressure as a function of the salinity in order tooptimize the required interaction parameters. Our results for NaCl aqueous solution show that theuse of mean osmotic coefficient, as well as the activity coefficient of individual ions, allow tounambiguously determine the Na+-water, cr-water and Na+-cr DPD repulsion parameters. Wepropose a simple linear relationship between the hydration free energies· of ions and the ionwaterrepulsion parameters that allows the parameterization of the complete series of halide andalkaline ions. Two different strategies have been used to derive the anion-cation interactionparameters for halide and alkaline but NaCl. In the first one, parameters are obtained for ail pairsof ions based on the numericàl optimization of the anion-cation repulsion parameter with respectto experimental osmotic pressure data. The mean absolute relative deviation between simuJatedand experimental data is then smaller than 4%. Second, we propose a simple, purely predictiveapproach to obtain the anion-cation interaction parameters based on the free energy difference ofhydration energies of anions and cations in the spirit of the law of matching water affinities(LMW A). This approach predict sait properties with a mean absolute relative deviation of theorder of 13 %, and with an accuracy better than 6% if small ions (Lt and F) are removed

DTLS Performance in Duty-Cycled Networks

The Datagram Transport Layer Security (DTLS) protocol is the IETF standard for securing the Internet of Things. The Constrained Application Protocol, ZigBee IP, and Lightweight Machine-to-Machine (LWM2M) mandate its use for securing application traffic. There has been much debate in both the standardization and research communities on the applicability of DTLS to constrained environments. The main concerns are the communication overhead and latency of the DTLS handshake, and the memory footprint of a DTLS implementation. This paper provides a thorough performance evaluation of DTLS in different duty-cycled networks through real-world experimentation, emulation and analysis. In particular, we measure the duration of the DTLS handshake when using three duty cycling link-layer protocols: preamble-sampling, the IEEE 802.15.4 beacon-enabled mode and the IEEE 802.15.4e Time Slotted Channel Hopping mode. The reported results demonstrate surprisingly poor performance of DTLS in radio duty-cycled networks. Because a DTLS client and a server exchange more than 10 signaling packets, the DTLS handshake takes between a handful of seconds and several tens of seconds, with similar results for different duty cycling protocols. Moreover, because of their limited memory, typical constrained nodes can only maintain 3-5 simultaneous DTLS sessions, which highlights the need for using DTLS parsimoniously.Comment: International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC - 2015), IEEE, IEEE, 2015, http://pimrc2015.eee.hku.hk/index.htm

Is employee ownership so senseless ?

Since Enron and the ruin of thousands of its employees, employee ownership is harshly criticized. Investing savings in employer's stock would be equivalent to bet on only one asset. Moreover, employee ownership's debated efficiency would not justify employers to grant company stock to their employees. Still, employee ownership is put in place by thousands of companies and withhold by millions of employees throughout the world. This paper considers a moral hazard setting where a risk neutral entrepreneur grants company stock to its risk averse employee as an incentive. We show that there is an optimal transfer of employee ownership that satisfies employee's risk preference and has an incentive effect. We thus bring about rational argument in favor of employee ownership.Depuis Enron et la ruine de milliers de ses employés, l'actionnariat salarié est critiqué. Investir son épargne en actions de son entreprise équivaudrait à parier sur un seul actif. De plus, l'efficacité contestée de l'actionnariat salarié ne justifierait pas que les entreprises distribuent des actions à leurs salariés. Pourtant, l'actionnariat salarié est adopté par des milliers d'entreprises et des millions de salariés à travers le monde. Cet article propose un modèle d'aléa moral où un entrepreneur neutre envers le risque utilise l'actionnariat salarié pour inciter son salarié averse au risque. Nous montrons l'existence d'un transfert optimal d'actionnariat salarié qui satisfait les préférences du salarié et s'accompagne d'un effet incitatif. Nous apportons ainsi un argument rationnel en faveur de l'actionnariat salarié

Synchrotron x-ray μ-tomography to model the thermal radiative properties of an opaque ceramic coating at T: 1000 K

Synchrotron x-ray μ-tomography has been used to reconstruct the three-dimensional view of a rough surface extracted from a heterogeneous ceramic coating composed of Pr2NiO4+δ. Radiographs with a resolution of 0.7 μm have been recorded at T = 300, 600, and 900 K. The analysis of surface geometry makes use of the geometrical optic approximation up to T = 900 K possible. Subsequently, a large number of rays (105) are impinged onto the numerical surface, as revealed by x-ray tomography, to reproduce the normal emissivity of the coating. This normal emissivity was obtained beforehand by infrared emittance spectroscopy at T = 1000 K. Comparison of the two approaches suggests that the optical contribution of the coating micropores can be integrated into the ray tracing code. The effective medium approximation is used for this purpose. Finally, the applicability of this hybrid approach is discusse

Lipids behaviour in aqueous solution of disrupted microalgae cultivated under nitrogen starving conditions: molecular simulation compared to experimental study of representative synthetic mixtures

International audienceThis work deals with the microalgae culture and biorefinery for biofuel production. Microalgae transform CO 2 into biomass and valuable molecules, including lipids. The downstream processing to valorise intracellular compounds necessitates innovative, efficient and clean processes for biomass harvesting, concentration, cell disruption and fractionation. Membrane filtration is a promising process for the concentration and the purification of lipids in a wet pathway to produce biofuel. The behaviour of the biomolecules and particles during the filtration processes is unknown. Yet it drives their performances. For example, strong interactions between lipids and polar molecules released during the cell disruption may prevent an efficient separation and valorisation of both compounds because of the water-oil interface stabilisation. Consequently, to achieve oil droplets coalescence, the interface must be disturbed during filtration. The understanding of the local organisation on the target molecules is a necessary step to develop innovative fractionation strategies and optimize the coupling of different processes. To bring understanding, a multiscale approach is proposed. The use of synthetic mixtures drives the link between the different scales. These synthetic mixtures are simplified emulsions that mimic a supernatant of a real grinded biomass, centrifugated to get rid of cell fragments. The composition is based on the characterisation of disrupted cells samples, from a P. kessleri culture, under nitrogen starving conditions. The synthetic mixtures contain water, triglycerides and polar lipids. On the one hand, coarse-grained molecular simulations were carried out, to study the behaviour of lipids in the solution. Interfacial tension of the water-lipids interface was calculated for several compositions and validated with experiments. On the other hand, the interfacial properties of complex mixtures were related to molecular organisation deduced from molecular simulation. The perspective of this project is at first the characterization of water-lipid interfaces with real products, to compare to the results with synthetic solutions. This necessitates a large-scale culture in starving conditions to recover enough lipids in the supernatant. The acquired knowledge on the behaviour and organisation of lipids at the interfaces will help the optimization of membrane processes for the concentration and coalescence of lipids before valorisation into biofuels