Modeling and experimental measurements of a tunable microstrip resonator using plasma discharges.

In this paper, we suggest the use of a cold plasma as tunable material inside a microstrip resonant cavity. Plasma dielectric constant can indeed be moved to values below 1 to tune its resonant frequency. DC plasma analysis were conducted and integrated into classic electromagnetic solvers to investigate tuning abilities. Numerical simulations are consistent with experimental results and make this original tuning techniques viable for high power applications

Analytical Model to Study the Electrostatic Resonance of Sub-Wavelength Radially Inhomogeneous Negative Permittivity Spheres

This letter presents an analytical model to study the electrostatic scattering of subwavelength radially inhomogeneous spheres whose permittivity can be expressed as a general polynomial function of the radial distance r. This technique is particularly well suited to characterize the electrostatic resonance, also known as surface plasmon resonance, of radially inhomogeneous negative permittivity spheres

Modélisation et caractérisation expérimentale d’un résonateur microruban reconfigurable en fréquence par décharge plasma

Dans ce papier, la reconfigurabilité en fréquence d’un résonateur microruban par décharge plasma est démontrée. Des simulations plasma (prenant en compte la dynamique des fluides, l’électrostatique, etc.) sont considérées afin d’intégrer un modèle de plasma réaliste dans les simulations électromagnétiques du résonateur. Les résultats de simulation sont cohérents avec la mesure et rendent prometteur cette technique d’intégration de plasma volumique dans des circuits microondes

Antenne VHF miniature reconfigurable en fréquence par décharge plasma : modélisation et résultats expérimentaux

Dans ce papier, nous proposons l’utilisation d’un plasma froid hors équilibre thermodynamique comme matériau à permittivité négative dans la réalisation d’une antenne sphérique miniature à résonance quasi-statique. Cette résonance est étudiée analytiquement puis numériquement et un prototype expérimental est présenté

Frequency-agile microstrip resonator using DC plasma discharge

An original and integrated solution to provide frequency agility to microstrip circuits using plasma is proposed. A volume DC plasma discharge is implemented inside a microstrip circular resonator to change its dielectric permittivity in order to tune its frequency. Plasma relative permittivity indeed exhibits positive values lower than 1. Experimental measurements confirm the tuning abilities and performances of such a solution for different pressures and types of gas

Modélisation et caractérisation expérimentale d’un résonateur microruban reconfigurable en fréquence par décharge plasma

Dans ce papier, la reconfigurabilité en fréquence d’un résonateur microruban par décharge plasma est démontrée. Des simulations plasma (prenant en compte la dynamique des fluides, l’électrostatique, etc.) sont considérées afin d’intégrer un modèle de plasma réaliste dans les simulations électromagnétiques du résonateur. Les résultats de simulation sont cohérents avec la mesure et rendent prometteur cette technique d’intégration de plasma volumique dans des circuits microondes

Jump then Climb: can rearrangements predict the occurrence of mutational bursts?

International audienc

Testing evolution predictability using the aevol software

International audienceMotivated by RNA virus’ genome biology, we used the aevol software to simulate the evolution of compacted genomes under high mutation rates. 30 independent digital wild-type (WT) genomes were generated after 200,000 generations of evolution under similar conditions. Then, each of these WTs was cloned 30 times and we let evolution to continue for 30,000 extra generations. By comparing these clones, we aimed to reveal the extent of evolutionary predictability for such compacted genomes. Results show that: (i) WTs are not equivalent in terms of evolutionary potential: some WTs are more prone than the others to increase their fitness during the last 30,000 generations. (ii) Evolution frequently occurs in bursts which implies that the probability to fix a mutation is increased after fixation of another mutation. Moreover these bursts are often initiated by chromosomal rearrangements (mainly duplications) because these rearrangements open new evolutionary pathways in the fitness landscape. Indeed, we quantified the "evolvability potential" of every clone after each mutation and found that the bursts are triggered by a strong increase of evolvability that quickly leads to point substitutions and indels fixation

Aevol-4b: Toward a new simulation platform to benchmark phylogenetic tools

National audienceAevol (www.aevol.fr) is a computational platform that allows for the study and manipulation of populations of digital organisms evolving under different conditions. Using Aevol simulations, one can better understand evolutionary forces and mechanisms leading to specific genome and transcriptome structures, as well as indirect selection pressures involved in the evolution of cooperation and genetic information transfer. Recently, we used aevol as a benchmarking tool. Indeed, Molecular evolutionary methods and tools are difficult to validate, as we have almost no direct access to ancient molecules. Inference methods may be tested with simulated data but this requires that the inference methods and the simulation be design independently (Biller et al., Computation in Europe 2016; Biller et al., Jobim 2016). Using aevol we can simulate perfectly characterized phylogenies and obtain a final population that evolved accordingly. Then we can use this final population to try to recover the initial phylogeny using various tools and assess their efficiency in doing so. This approach has recently been applied to test various estimators of inversion distance, revealing their limits and suggesting important improvement directions (Biller et al., Genome Biology and Evolution 2016). However, current aevol structure – more specifically the use of a binary representation for the genomic sequence – strongly limits its usability as a benchmarking tool. That is why we recently started the development of a new version of the software in which the genome sequence will use a four-nucleotides code and the translation from genetic sequence to polypeptide sequences will use the extant genetic code to map the 4-bases alphabet to the 20-amino-acids one. Although the development of this new version is in its infancy a first prototype has been developed and we would like to discuss the main modelling choices with the Alphy community that will be the potential users of the generated benchmarks. In particular, in this prototype the genotype-to-phenotype map is be based a mathematical description of traits under selection and on A.D. Solis (Proteins, 2015) classification of amino-acids, two crucial modelling choices that deserve discussion before we start final software implementation

The complexity ratchet: Stronger than selection, stronger than evolvability, weaker than robustness

International audienceUsing the in silico experimental evolution platform Aevol, we have tested the existence of a "complexity ratchet" by evolving populations of digital organisms under environmental conditions in which simple organisms can very well thrive and reproduce. We observed that in most simulations, organisms become complex although such organisms are a lot less fit than simple ones and have no robustness or evolvability advantage. This excludes selection from the set of possible explanations for the evolution of complexity. However, complementary experiments showed that selection is nevertheless necessary for complexity to evolve, also excluding non-selective effects. Analyzing the long-term fate of complex organisms, we showed that complex organisms almost never switch back to simplicity despite the potential fitness benefit. On the contrary, they consistently accumulate complexity on the long term, meanwhile slowly increasing their fitness but never overtaking that of simple organisms. This suggests the existence of a complexity ratchet powered by negative epistasis: mutations leading to simple solutions, that are favourable at the beginning of the simulation, become deleterious after other mutations-leading to complex solutionshave been fixed. This also suggests that this complexity ratchet cannot be beaten by selection, but that it can be overthrown by robustness because of the constraints it imposes on the coding capacity of the genome