Multi-level analysis of an interaction network between individuals in a mailing-list

It is well known now that most real-world complex networks have some properties which make them very different from random networks. In the case of interactions between authors of messages in a mailing-list, however, a multi-level structure may be responsible for some of these properties. We propose here a rigorous but simple formalism to investigate this question, and we apply it to an archive of the Debian user mailing-list. This leads to the identification of some properties which may indeed be explained this way, and of some properties which need deeper analysis.     

Modification of emission wavelength in organic random lasers based on photonic glass

Control of the emission wavelength of a random laser (RL) system over a 7-nm waveband is demonstrated using a green-emitting π-conjugated polymer infiltrated into a photonic glass formed by nano/micro-size monodisperse silica spheres. The use of a solution-based conjugated polymer enables the complete filling of the voids within the photonic glass without suffering from quenching and the gain can therefore be maximized. The emission wavelength of these structures is set by a combination of the material system spectral gain and of the transport mean free path, the latter being controlled by the mean diameter of the spheres in the nano-scale range. Transport mean free paths of photons in the RL’s active region are calculated using Mie scattering theory and corroborated with coherent backscattering measurements. Further wavelength modification is also possible by changing the pump spot size and the pump fluence.     

Impact of Freezing Process on Salt Diffusivity of Seafood: Application to Salmon (Salmo salar) Using Conventional and Pressure Shift Freezing

The depression of the melting temperature of ice under pressure permits to obtain a rapid freezing of foods. The expected benefit lies in reduced water diffusion from the intra- toward the extracellular media, resulting in a reduced drip loss during thawing. Beside, the modification of the cellular structure induced by ice formation may affect the mass diffusivity of the flesh. In the present study, salmon was used as a model food. Slabs of salmon (1-cm thick) were frozen using blast air and pressure shift freezing at 200 MPa. The impact of the freezing process on the mass diffusivity of salt was evaluated using an aqueous solution (NaCl, 3% w/w). Results indicate that the effective mass diffusivity was slightly increased in comparison to non-frozen flesh when a rapid freezing process was used. This may be attributed to a change in the permeability of cell membranes caused by freezing and high pressure.     

Methane hydrates bearing synthetic sediments—Experimental and numerical approaches of the dissociation

The production of methane gas from methane hydrate bearing sediments may reach an industrial scale in the next decades owing to the huge energy reserve it represents.However the dissociation of methane hydrate in a porous medium is still poorly understood and controlled: the melting of methane hydrate involves fluids flows and heat transfer through a porous medium whose properties evolve as the hydrate phase disappears, and is replaced (or not) by an ice phase. Mass and heat transfers can be coupled in a complex way, firstly because of the permeability changes, and secondly due to material conduction changes. In our work, mass and heat transfers have been studied both experimentally and numerically.A 2D numerical model is proposed where heat and mass transfers govern the dissociation of methane hydrate. This model has been used to design an experimental device. Experiments have been obtained and finally the model has been validated.The experimental set-up consists of five cylindrical sand packs having the same diameter but different lengths. Each experiment starts by crystallizing a hydrate phase in a porous medium. Then the hydrate is dissociated by controlling the pressure at one boundary. The kinetic of dissociation is monitored by collecting gases in ballast. Simulations and experiments demonstrate that the dissociation limiting step switches from thermal transfer to mass transfer depending on the initial permeability and conductivity of the porous medium.     

Influence of the suspension flocculated state on the microstructure of alumina spheres elaborated by colloidal granulation

A process of granulation by a colloidal method based on ceramic powder agglomeration makes it possible to produce millimetric spheres with a very homogeneous distribution in terms of shape and size. The starting suspension consists of a mixture of alumina submicrometer particles and silica nanoparticles such as mSiO₂/mAl₂O₃ = 1.1%. Heterocoagulation between the two oxides occurs forming a flocculated network the structure of which can be modified by a shear application. The outer appearance of the spheres is nearly perfect whereas the inner structure exhibits some defects (cracks and porosity). It has been shown that the green spheres are more porous as well as the grains of the starting suspension are less flocculated. During the drying step, the high mobility of these agglomerates increases the overall density on the surface and leads to the formation of a spherical empty cavity in the sphere centre.     

A new chemically defined medium for wine lactic acid bacteria

Growth and activity of lactic acid bacteria is crucial for the production and quality of grape wines but studying their metabolism is difficult in wines or complex laboratory media because of the undefined substrate pools. This work presents a new chemically defined medium that meets the fastidious nutritional requirements of wine lactic acid bacteria and yields rapid and strong growth. The new medium is composed of 44 constituents and a precise protocol is provided for its preparation. Maximum specific growth rates and growth yields of the wine strains studied were comparable to those obtained in common laboratory media, and the new medium allows for various modifications, such as changing the medium pH to the wine range, addition of L-malic acid or utilization of different carbon sources while maintaining growth of wine lactic acid bacteria. The medium was successfully tested with 22 wine strains of the genera Oenococcus, Lactobacillus and Pediococcus. It is suggested that this chemically defined medium be considered for the investigation of the nutritional requirements and metabolism of wine lactic acid bacteria.     

Influence of emulsion composition on lubrication capacity and texture perception

The role of fat content and type of surfactant for oral friction processes and texture perception of oil-in-water emulsions was assessed. Emulsions at 22% and 33% fat content containing either sodium caseinate or a sucrose ester as emulsifier were compared with viscosity-adapted aqueous solutions of dextran using both sensory evaluation and friction coefficient measurements on a tongue-palate contact model. The impact of saliva on the emulsion droplet size distribution was studied using tribology, differential interference contrast microscopy and light diffraction measurements. Emulsions at 33% and the corresponding iso-viscous aqueous solutions were discriminated in the sensory experiment whereas emulsions at 22% were not. Friction was significantly different for emulsions at 33% and the corresponding iso-viscous aqueous solutions. The difference was not significant for emulsions with 22% fat level when compared with the iso-viscous aqueous solutions. Saliva significantly decreased the friction coefficient of emulsions depending on the surfactant and amount of fat used.     

RNA Relics and Origin of Life

A number of small RNA sequences, located in different non-coding sequences and highly preserved across the tree of life, have been suggested to be molecular fossils, of ancient (and possibly primordial) origin. On the other hand, recent years have revealed the existence of ubiquitous roles for small RNA sequences in modern organisms, in functions ranging from cell regulation to antiviral activity. We propose that a single thread can be followed from the beginning of life in RNA structures selected only for stability reasons through the RNA relics and up to the current coevolution of RNA sequences; such an understanding would shed light both on the history and on the present development of the RNA machinery and interactions. After presenting the evidence (by comparing their sequences) that points toward a common thread, we discuss a scenario of genome coevolution (with emphasis on viral infectious processes) and finally propose a plan for the reevaluation of the stereochemical theory of the genetic code; we claim that it may still be relevant, and not only for understanding the origin of life, but also for a comprehensive picture of regulation in present-day cells.